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  • Articles  (30,873)
  • Inorganic Chemistry  (20,565)
  • Cell & Developmental Biology  (10,038)
  • Bone
  • 1990-1994  (10,110)
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  • Articles  (30,873)
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  • 1
    Electronic Resource
    Electronic Resource
    The biochemistry of ancient DNA in bone (1994)
    Springer
    Cellular and molecular life sciences 50 (1994), S. 530-535 
    Details
    ISSN: 1420-9071
    Keywords: Bone ; collagen ; fulvic acids ; DNA ; ancient DNA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The amount of DNA in ancient bone was determined by ethidium bromide staining after the removal of the potent Taq inhibitor, fulvic acid. A complete decalcification and a perfusion protocol were used to recover DNA from bone. A variety of purification techniques including molecular sieve, hydroxyapatite binding and ‘Magic’ preparations yielded DNA that spanned from 3.4μg/g of bone to below detectable limits. Fulvic acid was shown to interfere with the quantification of DNA derived from ancient human skeletal material one hundred to over seven thousand years old. Scanning UV in the 300 to 230 nm range is a simple and sensitive technique for documenting fulvic acid contamination in ancient bone extracts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01921721
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  • 2
    Electronic Resource
    Electronic Resource
    Purification of mineralized tissue-associated osteopontin (1994)
    Springer
    Methods in cell science 16 (1994), S. 211-215 
    Details
    ISSN: 1573-0603
    Keywords: Bone ; Bone sialoprotein ; Osteopontin ; Protein purification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A protocol to extract and purify osteopontin, a protein with cell adhesion and mineral-crystal binding properties, from mineral-associated tissues is described. This procedure provides for the complete separation of osteopontin from bone sialoprotein, a mineralized tissue-specific protein with similar properties to that of osteopontin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01540653
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  • 3
    Electronic Resource
    Electronic Resource
    Effects of magnesium deficiency on strength, mass, and composition of rat femur (1994)
    Springer
    Calcified tissue international 54 (1994), S. 44-49 
    Details
    ISSN: 1432-0827
    Keywords: Bone ; Stress ; Elasticity ; Mechanical properties ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract Magnesium (Mg) participates in the normal formation and remodeling of bone. However, little is known about effects of Mg status on the biomechanical function of bone. We examined gross morphometry and composition as well as biomechanical properties of the femurs of male rats fed diets adequate or deficient in Mg. Comparison of deficient animals and controls yielded a number of differences (all significant at P〈0.05). Mg-depleted animals exhibited slow growth, inefficient food utilization, and greatly reduced concentrations of Mg in both serum and femur ash. Compared with controls, femurs from depleted animals were shorter, but wet weights, diameters, and midfemoral cross-sectional areas showed no differences. Bone length was reduced to a greater degree than could be accounted for by differences in body weights between the groups. Bones of Mg-deficient rats contained less dry matter and less ash (which contained more Ca/g) than those of controls, along with a higher percentage of moisture. Significantly reduced bone strength in depleted animals was evident from the lighter loads supported at the elastic limit (yield point) and at fracture and from decreased stresses accompanying those loads. Modulus of elasticity, however, was not affected by Mg depletion. Different yield and breaking loads were related to different body weights of groups, but stresses were reduced for deficient bones even after adjusting for body size. Our data establish abnormal biomechanical behavior of cortical bone in Mg-deficient animals and emphasize the importance of measuring such functional properties of bone in the assessment of responses to altered metabolic conditions under experimental conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00316289
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  • 4
    Electronic Resource
    Electronic Resource
    Broadband ultrasonic attenuation imaging: A new imaging technique of the os calcis (1994)
    Springer
    Calcified tissue international 54 (1994), S. 83-86 
    Details
    ISSN: 1432-0827
    Keywords: Ultrasound attenuation ; Bone ; Osteoporosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract Ultrasound transmission measurement through the os calcis is an emerging technique and a promising clinical tool for early assessment of osteoporosis. However, several previous studies showed that broadband ultrasonic attenuation (BUA) is sensitive to small variations in bone mass or structure. The os calcis is an inhomogeneous bone and therefore, the attenuation depends on the location in the os calcis. BUA distribution within the os calcis can be measured by rectilinear scanning over the entire bone. We used a mechanical scanning device with both unfocused and focused transducers. The spatial resolution of these was about 25 mm and 4 mm, respectively. There was good agreement (r=0.97) between the results with unfocused and focused transducers. In addition, imaging the variations of BUA is possible with the focused transducers, and high quality images are obtained. These images permit the selection of optimal regions of interest for ultrasound attenuation measurement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00296055
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  • 5
    Electronic Resource
    Electronic Resource
    Age-dependence of bone material quality shown by the measurement of frequency of resonance in the ulna (1994)
    Springer
    Calcified tissue international 54 (1994), S. 96-100 
    Details
    ISSN: 1432-0827
    Keywords: Bone ; Material quality ; Sound transmission ; Frequency of resonance ; Age ; Bone width
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract In women before and after the age of peak bone mass, identical values of bone mineral density (BMD) can be obtained. However, there is a much higher incidence of osteoporotic fractures in older women. We investigated whether a deterioration of bone material quality with increasing age might contribute to this phenomenon. Material properties of bone tissue can be characterized by the modulus of elasticity, which is correlated to the square of sound transmission velocity. In this study, sound transmission velocity was determined in cortical bone by measuring the frequency of resonance in the ulna in the direction of the bone's longitudinal axis and correcting the values by multiplying by ulna length. Validation of this method indicated acceptable reproducibility: interobserver variability determined as the mean coefficient of variation was 1.82%. In a clinical study, 21 young women (22.5±1.2 years old) were compared with 21 middle-aged women (52.9±2.7 years old). Pairs were matched that had identical values of BMD in the nondominant forearm at a location representing mainly cortical bone (SPA). The product of ulna length and frequency of resonance in the ulna in the younger women was found to be 61.4±5.8 m/second, and in the middle-aged women 55.7±4.5 m/second. The difference was highly significant with P〈0.005. Our results confirm recent findings indicating a deterioration of bone material quality independent of BMD with increasing age. As shown by comparing ulna width at the site of measurement of bone mineral density between both groups of women, the deterioration of bone material quality in ulnar cortical bone with increasing age might at least in part be functionally compensated by an increase of the moment of inertia due to greater bone width [8, 10].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00296058
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  • 6
    Electronic Resource
    Electronic Resource
    Helodermin, helospectin, and PACAP stimulate cyclic AMP formation in intact bone, isolated osteoblasts, and osteoblastic cell lines (1994)
    Springer
    Calcified tissue international 54 (1994), S. 284-289 
    Details
    ISSN: 1432-0827
    Keywords: Helodermin ; Bone ; Cyclic AMP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract Helodermin and helospectin are peptides structurally similar to vasoactive intestinal polypeptide (VIP) which were recently isolated from the salivary gland venom of the lizard Heloderma suspectum. Pituitary adenylate cyclaseactivating polypeptide (PACAP) has been isolated from ovine hypothalamus and also shows sequence homology to VIP. A helodermin-like peptide has been detected by combined immunohistochemical and immunochemical techniques in the thyroid C-cells. In the present study, lizard helodermin was found to cause a time- and dose-dependent stimulation of cyclic AMP (cAMP) formation in neonatal mouse calvarial bones. Also, helospectin I, PACAP 27, and the C-terminally extended PACAP 38 stimulated cAMP accumulation in the mouse calvariae. The cAMP rise in response to helodermin was comparable to that induced by VIP, both in terms of potency and magnitude of the response. Helodermin, helospectin I, PACAP 27, and PACAP 38, at concentrations of 1 μmol/liter, stimulated cAMP accumulation in enzymatically isolated mouse calvarial bone cells. A significant response to all peptides was observed in both early and late released bone cells isolated from the calvariae, with low and high alkaline phosphatase activity, respectively. Helodermin and VIP stimulated cAMP accumulation in the cloned mouse calvarial osteoblastic cell line MC3T3-E1, in rat (UMR 106-01), and human (Saos-2) osteoblastic osteosarcoma cell lines, but not in the rat osteosarcoma cell line ROS 17/2.8. The effect of helodermin was synergistically and dose-dependently enhanced by forskolin (0.1 and 1 μmol/liter). These data show that bone cells, including osteoblasts, respond to several peptides of the VIP family, including helodermin, helospectin I, PACAP 27, and PACAP 38. Whether the responses are mediated via one or several receptor populations remains to be established. The finding that VIP and helodermin, at maximally effective concentrations, did not cause additive effect on cAMP formation in intact mouse calvariae suggests that these two agonists may use a common receptor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00295952
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  • 7
    Electronic Resource
    Electronic Resource
    Human recombinant interleukin-1 receptor antagonist blocks bone resorption induced by interleukin-1β but not interleukin-1α (1994)
    Springer
    Calcified tissue international 55 (1994), S. 12-15 
    Details
    ISSN: 1432-0827
    Keywords: IL-1α ; IL-1β ; IL-1 receptor antagonist ; Bone ; Calcium ; Parathyroid hormone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract Both interleukin-1α (IL-1α) and interleukin-1β (IL-1β) are powerful stimulators of bone resorption in vivo and in vitro. Interleukin-1 receptor antagonist (IL-1ra) binds to many interleukin-1 receptors. It does not activate the receptor and effectively blocks the action of IL-1α and IL-1β. In this study, human recombinant IL-1ra, at 100-fold excess, was found to block bone resorption in cultured mouse calvaria due to IL-1β but not IL-1α. These observations may be explained by differential affinities of receptors for IL-1α, IL-1β and rhIL-1ra on target bone cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00310162
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  • 8
    Electronic Resource
    Electronic Resource
    Combined magnetic fields increased net calcium flux in bone cells (1994)
    Springer
    Calcified tissue international 55 (1994), S. 376-380 
    Details
    ISSN: 1432-0827
    Keywords: Electromagnetic ; Bone ; Calcium ; Osteoblast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract Low energy electromagnetic fields (EMF) exhibit a large number of biological effects. A major issue to be determined is “What is the lowest threshold of detection in which cells can respond to an EMF?” In these studies we demonstrate that a low-amplitude combined magnetic field (CMF) which induces a maximum potential gradient of 10-5 V/m is capable of increasing net calcium flux in human osteoblast-like cells. The increase in net calcium flux was frequency dependent, with a peak in the 15.3–16.3 Hz range with an apparent bandwidth of approximately 1 Hz. A model that characterizes the thermal noise limit indicates that nonspherical cell shape, resonant type dynamics, and signal averaging may all play a role in the transduction of lowamplitude EMF effects in biological systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00299318
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  • 9
    Electronic Resource
    Electronic Resource
    Contribution of collagen and mineral to the elastic anisotropy of bone (1994)
    Springer
    Calcified tissue international 55 (1994), S. 381-386 
    Details
    ISSN: 1432-0827
    Keywords: Acoustic microscopy ; Bone ; Collagen fiber ; Elastic anisotropy ; Mineral crystal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract It has long been thought that collagen fibers within the bone matrix are deposited in an aligned pattern that channels mineral growth. If this model of bone structure is correct, both organic and inorganic phases of bone should have similar elastic anisotropy. Using an acoustic microscope, we measured longitudinal and transverse acoustic velocities of cortical specimens taken from 10 dog femurs before and after removal of either the mineral (using 10% EDTA) or collagen phases (using 7% sodium hypochlorite) and calculated longitudinal (CL) and transverse (CT) elastic coefficients. The anisotropy ratio (CL/CT) decreased significantly after demineralization (1.61 before versus 1.06 after, P〈0.0001, paired t-test). However, there was no significant change after decollagenization (1.51 before versus 1.48 after, P=0.617, paired t-test). We conclude that the orientation of mineral crystals is the primary determinant of bone anisotropy, and the collagen matrix within osteonal bone has little directional orientation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00299319
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  • 10
    Electronic Resource
    Electronic Resource
    Magnesium distribution in human bone (1994)
    Springer
    Calcified tissue international 54 (1994), S. 34-37 
    Details
    ISSN: 1432-0827
    Keywords: Magnesium ; Bone ; Aging ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract The present study was undertaken to reveal the magnesium distribution in human bone. Sixty human ribs, obtained from subjects aged 10–80 years of age, were used. Transverse sections were prepared from the middle region of the human ribs. Adjacent sections were ground to a thickness of about 1000 μm. One section was used for magnesium determination by atomic absorption spectrophotometry, and the other was used for analysis with X-ray microanalysis. Thirty micron thick samples were abraded continuously from the periosteal and the endosteal surfaces by abrasive microsampling, as previously described by Weatherell et al. [3]. Results showed that magnesium concentrations were higher in both the periosteal and endosteal surfaces and did not change with age in general, although it tended to be higher among teenagers and lower over 80 years old.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00316287
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  • 11
    Electronic Resource
    Electronic Resource
    Antiresorptive drugs and trabecular bone turnover: Validation and testing of a computer model (1994)
    Springer
    Calcified tissue international 54 (1994), S. 179-185 
    Details
    ISSN: 1432-0827
    Keywords: Bone ; Drugs ; Trabecular ; Turnover ; Computer ; Model ; Sensitivity ; Activation frequency
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract A computer model of trabecular bone turnover has been developed, based on concepts of Jonathan Reeve [1]. This model predicts changes in bone volume by summing bone resorption and formation over a large number of remodeling sites. Clinical data [histomorphometry and bone mineral content (BMC)] from two clinical studies using an antiresorptive drug (etidronate disodium, EHDP) in post-menopausal osteoporosis were used to test the model. The results for BMC obtained from the EHDP and placebo groups in each study at 60 and 120 weeks were correctly predicted by the model from the histomorphometric data obtained from baseline and week 60 biopsies. The parameter in this model having the greatest influence on predicted changes in bone volume was found by sensitivity analysis to be activation frequency. These results suggest that the contribution of bone turnover to BMC can be predicted solely by considering the cell kinetics of the basic multicellular unit (BMU), and that, in the case of antiresorptive drugs, maximal effects on bone volume may be achieved by pharmacological reduction of activation frequency. The results also suggest that the present model may be useful in predicting in clinical studies the effects of EHDP and similar drugs on bone turnover.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00301675
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  • 12
    Electronic Resource
    Electronic Resource
    Intact serum parathyroid hormone levels increase during running exercise in well-trained men (1994)
    Springer
    Calcified tissue international 54 (1994), S. 256-261 
    Details
    ISSN: 1432-0827
    Keywords: Calcium ; Lactate ; Acidosis ; Treadmill ; Bone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract The purpose of this study was to examine the influence of exercise on the serum concentrations of intact parathyroid hormone (PTH). Serum PTH and plasma lactate were measured in 15 well-trained men, 9 long-distance runners and 6 fire-fighters, during two running exercises. Test one consisted of 40-minute treadmill running with a stepwise increased load and test two consisted of 50-minute treadmill running with a constant velocity. When the load was step-wise increased, the PTH concentrations increased moderately at the slower running paces but reached a final value that was about 50% higher than the starting value. This rise occurred despite a concomitant increase of total serum calcium from 2.38±0.06 to 2.49±0.05 mmol/liter (P〈0.01). During the constant running exercise, the long-distance runners, but not the fire-fighters, displayed a significant increase in PTH concentrations although the rise in total serum calcium was similar in both groups. There was a weak correlation between the changes in PTH and lactate in both exercises. The findings demonstrate that both high and low intensity exercise enhance release of PTH in long-distance runners through a mechanism that does not involve serum calcium. This relationship might be of importance for bone mass in men performing long-distance training.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00295947
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  • 13
    Electronic Resource
    Electronic Resource
    Lower extremity stress fractures during intermittent cyclical etidronate treatment for osteoporosis (1994)
    Springer
    Calcified tissue international 54 (1994), S. 431-434 
    Details
    ISSN: 1432-0827
    Keywords: Bone ; Diphosphonate ; Osteoporosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract During intermittent cyclical etidronate treatment, a lower extremity pain syndrome associated with stress fractures was observed in three osteoporotic patients. This report describes the development of stress fractures during initial cycles of treatment, with recurrence of symptoms in two patients when etidronate therapy was resumed. Further studies are needed to confirm whether stress fractures are associated with cyclic etidronate treatment and if so, the incidence and pathophysiology need to be determined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00305532
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  • 14
    Electronic Resource
    Electronic Resource
    The modulatory effect of endogenous parathyroid hormone on the action of hydrochlorothiazide in pseudohypoparathyroidism type I (1994)
    Springer
    Calcified tissue international 54 (1994), S. 473-476 
    Details
    ISSN: 1432-0827
    Keywords: Pseudohypoparathyroidism ; Thiazide ; Kidney ; Bone ; Parathyroid hormone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract We compared the effect of orally administered 100 mg of hydrochlorothiazide (HCTZ) among eight patients with pseudohypoparathyroidism (PHP) type I, 11 patients with idiopathic hypoparathyroidism (IHP), and 12 patients with primary hyperparathyroidism (1oHPT). Patients with PHP type I or with IHP were studied during the treatment with 1α-hydroxylated metabolites of vitamin D3. HCTZ raised serum levels of calcium (Ca) in 1oHPT (P〈0.001) and PHP type I (P〈0.01) but did not increase urinary excretion of Ca. Serum parathyroid hormone (PTH) in PHP type I decreased (P〈0.02) after HCTZ administration in response to the increase in serum Ca. HCTZ did not raise serum levels of Ca in IHP but increased urinary excretion of Ca in this group (P〈0.01). HCTZ suppressed tubular reabsorption of phosphate (P) in IHP (P〈0.01) and 1oHPT (P〈0.05) but not in PHP type I. Urinary excretion of cAMP did not change after HCTZ administration in PHP type I, IHP, or 1oHPT. Endogenous PTH modulated the effects of HCTZ on Ca mobilization from bone and renal reabsorption of Ca in PHP type I with normal or high serum levels of PTH and in 1oHPT with high serum levels of PTH. The inhibitory effect of HCTZ on renal tubular reabsorption of P (probably from proximal tubules) was independent of PTH. The resistance to this inhibitory effect of HCTZ on P reabsorption in PHP type I suggested a proximal tubular dysfunction in this disorder.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00334326
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  • 15
    Electronic Resource
    Electronic Resource
    Selective extractability of noncollagenous proteins from chicken bone (1994)
    Springer
    Calcified tissue international 55 (1994), S. 230-235 
    Details
    ISSN: 1432-0827
    Keywords: Noncollagenous ; Proteins ; Bone ; Sialo-protein ; Osteopontin ; Osteocalcin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract Quantitative analyses of a wide variety of different solvents used for the extraction of several of the noncollagenous proteins of fully mineralized chicken bone powder were carried out to compare both the effectiveness of various procedures and the distribution of specific proteins which were solubilized. Extraction procedures included solutions of 6 M guanidine-HCl, pH 7.0, 0.5 M EDTA, pH 7.4, 0.3 N citric acid, 0.3 N HCl, 0.3 N formic acid, and 0.3 N acetic acid. Chelation of calcium ions by EDTA and dissolution of the mineral phase by acid extraction released 95% or more of the total calcium content of the bone powder by 48 hours, guanidine-HCl released less than 20% or less of the total calcium content even when extraction was carried out by 168 hours. Moreover, although guanidine-HCl solubilized a significant amount of collagen as gelatin, essentially none of the phosphoproteins, osteocalcin, or the proteoglycan decorin were solubilized, as detected by immunological techniques. In contrast, extraction of the mineralized bone powder by HCl and formic acid was very efficient in selectively solubilizing osteocalcin and osteopontin, while bone sialoprotein was selectively released by EDTA, and solubilized to a lesser extent by formic acid. Similarly, EDTA selectively removed decorin compared with HCl, formic, acetic, or citric acids. Only small amounts of osteopontin and osteocalcin were detected in the acetic acid extracts. These results provide methods for the selective solubilization of several different major, noncollagenous proteins from mineralized bone which should significantly aid in maximizing the amount of the specific protein recovered, and the ease with which the various proteins can be purified. The data also provide some insight into the intrinsic solubility characteristics of collaten, the specific noncollagenous proteins, and their potential association with each other and the mineral phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00425880
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  • 16
    Electronic Resource
    Electronic Resource
    Effects of infusion of parathyroid hormone and primary hyperparathyroidism on formation and breakdown of type I collagen (1994)
    Springer
    Calcified tissue international 55 (1994), S. 412-416 
    Details
    ISSN: 1432-0827
    Keywords: Bone ; Biochemical markers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract The influence of chronic and acute exposure to parathyroid hormone (PTH) on formation and breakdown of type I collagen, using two recently developed radioimmunoassays for serum PICP (the carboxyterminal propeptide of type I procollagen) and serum ICTP (the carboxyterminal telopeptide of type I collagen), have been evaluated. Fasting morning values were obtained from 18 women with primary hyperparathyroidism (HPT) and an equal number of age-matched, healthy controls. A 24-hour infusion of synthetic human parathyroid hormone (PTH 1-38) was performed in 14 healthy females. The patients with HPT had higher values for serum ICTP than the controls (6.0±3.0 and 4.1±2.1 μg/liter; P〈0.05), whereas the serum PICP concentrations were not different (170±72 and 151±65 μg/liter; n.s.). During infusion of PTH in healthy subjects, there was an increase of the serum ICTP concentrations (from 3.6±1.3 to 4.4±1.8 μg/liter; P〈0.001) whereas those of serum PICP decreased (from 185±78 to 118±42 μg/liter; P≤0.0001). The increase of serum ICTP during infusion of PTH was positively related to the increase of serum calcium and other indices of bone resorption, i.e., fasting urinary excretions of hydroxyproline and calcium. The decrease of serum PICP was also related to the changes of serum ICTP and hydroxyproline in urine, serum calcium, and alkaline phosphatase but not to osteocalcin, an established marker of osteoblastic activity. The findings support the fact that serum ICTP is a valuable method for evaluating bone resorption and is also easy to perform. Furthermore, the discordant results for the different markers of osteoblastic activity indicat that they reflect different functions of the cell.
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    URL: http://dx.doi.org/10.1007/BF00298553
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  • 17
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    Dietary variation in arctic foxes (Alopex lagopus)-an analysis of stable carbon isotopes (1994)
    Springer
    Oecologia 99 (1994), S. 226-232 
    Details
    ISSN: 1432-1939
    Keywords: Carbon isotopes ; Arctic fox ; Diet ; Bone ; Collagen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We used stable carbon isotopes to analyse individual variation in arctic fox diet. We extracted collagen from bones (the lower jaw), and measured stable carbon isotopes. The foxes came from three different localities: Iceland, where both microtines and reindeer are rare; west Greenland, where microtines are absent; and Sweden, where scat analyses showed the primary food to be microtine rodents and reindeer. The Icelandic samples included foxes from both coastal and inland habitats, the Swedish sample came from an inland area, and the Greenland sample from coastal sites. The spatial variation in the isotopic pattern followed a basic division between marine and terrestrial sources of protein. Arctic foxes from inland sites had δ13C values of −21.4 (Iceland) and −20.4‰ (Sweden), showing typical terrestrial values. Coastal foxes from Greenland had typical marine values of −14.9‰, whereas coastal foxes from Iceland had intermediate values of −17.7‰. However, there was individual variation within each sample, probably caused by habitat heterogeneity and territoriality among foxes. The variation on a larger scale was related to the availability of different food items. These results were in accordance with other dietary analyses based on scat analyses. This is the first time that stable isotopes have been used to reveal individual dietary patterns. Our study also indicated that isotopic values can be used on a global scale.
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    URL: http://dx.doi.org/10.1007/BF00627734
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  • 18
    Electronic Resource
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    Immunologicalization of complement C1s and matrix metalloproteinase 9 (92kDa gelatinase/type IV collagenase) in the primary ossification center of the human femur (1994)
    Springer
    Cell & tissue research 277 (1994), S. 239-245 
    Details
    ISSN: 1432-0878
    Keywords: Bone ; Ossification ; Cartilage ; Matrix ; Chondrocytes ; Complement ; Matrix metalloproteinase ; Immunocytochemistry ; Man
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The first component of complement $$C\bar 1s$$ has been shown to degrade type I and type II collagens (Yamaguchi et al. 1990), the latter of which is a major constituent of the cartilage matrix. In order to understand the physiological roles of $$C\bar 1s$$ in cartilage resorption, the expression of C1s was examined by immunohistochemistry in the primary ossification center where the matrix is removed and replaced by bone marrow. Hypertrophic chondrocytes, endothelium and hematogenous elements in the capillary buds were intensely stained by a monoclonal antibody against C1s. Matrix metalloproteinase 9 (MMP-9, 92kDa gelatinase/type IV collagenase) was also immunolocalized in hypertrophic chondrocytes, mesenchymal cells in the primitive bone marrow and the cartilage matrix adjacent to the marrow. In addition, $$C\bar 1s$$ was found to activate the zymogen of MMP-9. These observations suggest that $$C\bar 1s$$ and MMP-9 coordinately participate in matrix degradation in cartilage.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00327771
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  • 19
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    The effect ofin vitro fluoride ion treatment on the ultrasonic properties of cortical bone (1994)
    Springer
    Annals of biomedical engineering 22 (1994), S. 404-415 
    Details
    ISSN: 1573-9686
    Keywords: Bone ; Ultrasound ; Interfacial bonding ; Anisotropy ; Fluoride
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The mechanical properties of composites are influenced, in part, by the volume fraction, orientation, constituent mechanical properties, and interfacial bonding. Cortical bone tissue represents a short-fibered biological composite where the hydroxyapatite phase is embedded in an organic matrix composed of type I collagen and other noncollagenous proteins. Destructive mechanical testing has revealed that fluoride ion treatment significantly lowers theZ-axis tensile and compressive properties of cortical bone through a constituent interfacial debonding mechanism. The present ultrasonic data indicates that fluoride ion treatment significantly alters the longitudinal velocity in theZ-axis as well as the circumferential and radial axes of cortical bone. This suggests that the distribution of constituents and interfacial bonding amongst them may contribute to the anisotropic nature of bone tissue.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02368247
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  • 20
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    Statistical model of the habit and arrangement of mineral crystals in the collagen of bone (1994)
    Springer
    Journal of statistical physics 77 (1994), S. 125-143 
    Details
    ISSN: 1572-9613
    Keywords: Bone ; collagen ; Voronoi tesselations ; small-angle scattering ; structure function ; calcified tissue
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Randomly colored space tesselations are considered as models for the mineral/organic structure of bone. First, it is shown that the structure function for such models is always proportional to the average form factor of the individual tiles and hence independent of the mineral density in the sample. Then the structure function is calculated for three such models: for model I, based on a hexagonal, and model 2, on a Poisson-Voronoi tesselation of the plane and for model 3, based on a random tesselation of the line. These results are compared to experimental structure functions measured by small-angle scattering and excellent agreement is obtained between model 2 and the bone from mice and rats, as well as between model 3 and calcified turkey leg tendon. Divergent conclusions following recent experiments by small-angle x-ray scattering and by electron microscopy are discussed in the light of these structural models and an explanation is proposed which might remove the discrepancy.
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    URL: http://dx.doi.org/10.1007/BF02186835
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  • 21
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    Elektrophile Additionen an das Bicyclo[1.1.0]butan-System von Tricyclo[4.1.0.02,7]heptan-Derivaten: Halogen-ElektrophileHerrn Professor Helmut Werner zum 60. Geburtstag gewidmet. (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 381-391 
    Details
    ISSN: 0009-2940
    Keywords: Norpinanes, preparation ; Carbocations, classical and nonclassical ; Neighbouring group participation ; Halonium ions ; Migratory aptitudes in carbocations ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Electrophilic Additions to the Bicyclo[1.1.0]butane System of Tricyclo[4.1.0.02,7]heptane Derivatives: Halogen ElectrophilesThe known reactions of 8,8-dibromotetracyclo[5.1.0.02,4.03,5]octane (3a) and homobenzvalene (7) with pyridinium bromide perbromide and iodine, respectively, were carried out in the presence of tetra-n-butylammonium chloride. The formation of the chloro-substituted norpinane derivatives 6a and 9 is evidence for cationic intermediates. The same mechanism is operative in the reaction of pyridinium bromide perbromide with the dichlorotetracyclooctane 3b, which was prepared from 7 and dichlorocarbene. On exposure of tricyclo[4.1.0.02,7]heptane (1) to N-bromosuccinimide in acetone/water/triethylamine, the bromonorpinanol 22, the bromonorcaranols 23, and cyclohex-1-ene-1-carboxaldehyde (24) were obtained. On the basis of the steric course and thermodynamic considerations, the cationic intermediates generated in the above reactions by attack of the electrophiles at the bicyclobutane systems are assigned the halonium ion structure 38 and the nonclassical structures 34 and 35, respectively. Elemental bromine and iodine converted the phenyltricycloheptane 10 into the respective diastereomeric norpinanes 11 and 12, which were transformed smoothly into the diastereomeric methyl ethers 13 and 14 by treatment with sodium methoxide in methanol. The reactions of 10 with pyridinium bromide perbromide in pyridine, cyanogen bromide in the presence of aluminium trichloride, and N-bromosuccinimide in acetone/water gave rise to norpinane derivatives, i.e. the pyridinium salt 15, the nitrile 16, and the alcohol 18, respectively. In the case of cyanogen iodide in acetonitrile, the solvent participated in the process to yield the 2-(norpinylimino)propionitriles 17. Corresponding to the configurations of the products, the attack of a halogen electrophile at 10 leads to classical 6-phenyl-6-norpinyl cations 41, which may be approached by nucleophiles from the two possible faces. As origin for the low tendency of the cations 33-35 and 41 to rearrange to norcaryl cations, the electronegativity of the halogen atoms is suggested. The reduced migratory aptitude of a CHHal relative to a CH2 group results from its electron deficiency and from the decreased stability of 7-halo-2-norcaryl relative to the parent 2-norcaryl cations. The chlorophenyltricycloheptane 25 was prepared from 10 and treated with aqueous sulfuric acid to give the norpinanol 27. Formed by protonation of the bicyclobutane system of 25, the cationic precursor of 27 shows a behaviour similar to that of cations 41.
    Additional Material: 2 Tab.
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  • 22
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    Thermal and Photochemical Rearrangement of 3-Substituted 2-Methylbenzofuran Epoxides and Their Valence-Isomeric Quinone Methides (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 433-436 
    Details
    ISSN: 0009-2940
    Keywords: Epoxidation ; Dioxirane, dimethyl- ; Benzofurans, 2-methyl- ; Benzofuran epoxides ; Quinone methides ; Photoisomerization ; Chromenes ; 3-Benzofuranones ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dimethyldioxirane oxidation of the 3-substituted 2-methylbenzofurans 1 [1a: 3(E)-styryl, 1b: 3-acetoxy, 1c: 3-(tert-butyldimethylsilyloxy)] is reported. Only quinone methide 3a, none of the benzofuran epoxides 2a-c, could be detected by 1H- and 13C-NMR spectroscopy at low temperature (-30°C), which on photoisomerization led to chromene 7a. The benzofuran-3-ones 5b, c and the α-diketone 6c are presumably formed by thermal isomerization of the transient benzofuran epoxides 2b, c and quinone methide 3c.
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    URL: http://dx.doi.org/10.1002/cber.19941270220
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  • 23
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    Funktionalisierung von C60 mit Nitriloxiden zu 4,5-Dihydroisoxazolen und deren Strukturbestimmung (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 581-584 
    Details
    ISSN: 0009-2940
    Keywords: Fullerenes ; [3 + 2] Cycloadditions ; Nitrile oxides ; Isoxazoles ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Functionalization of C60 with Nitrile Oxides to 4,5-Dihydroisoxazoles and Their Structure DeterminationCycloadducts 3 of nitrile oxides 2 with C60 (1) are synthesized and isolated. The cycloadducts are characterized by 13C-NMR spectroscopy and high-resolution FAB mass spectrometry. X-ray structure determination of the 3-(9-anthryl)-4,5-dihydroisoxazole derivative 3a of C60 with CS2 included in the crystals is achieved at 173 K without disorder problems.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/cber.19941270318
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  • 24
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    In 2- und 3-Stellung verzweigte, enantiomerenreine 4,4,4-Trifluor-3-hydroxy-buttersäure-Derivate aus 6-Trifluormethyl-1,3-dioxan-und -dioxin-4-onen (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 565-579 
    Details
    ISSN: 0009-2940
    Keywords: Li enolates, of 6-trifluoromethyl-1,3-dioxan-4-one ; Alkylation, of Li enolates ; Michael additions, to 1,3-dioxin-4-ones, to nitroolefins ; Benzylation, abnormal products ; Methyl 3-hydroxy-3-trifluoromethyl propionates ; 1,3-Dioxanones, 2,5,6-trisubstituted ; Conformation, of 1,3-dioxan-4-ones ; Twist-boat conformation, of cis,cis- and trans,trans-2.5,6-trisubstituted 1,3-dioxan-4-ones ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Preparation of Enantiomerically Pure 4,4,4-Trifluoro-3-hydroxy-butanoic Acid Derivatives, Branched in the 2- or 3-Position, from 6-Trifluoromethyl-1,3-dioxan- and -dioxin-4-onesEnantiomerically pure 3-hydroxy-3-trifluoromethyl-propionic acid and esters, substituted in the 2- or 3-position, are prepared (13 examples) from (R)- or (S)-4,4,4-trifluoro-3-hydroxy-butanoic acid. Key intermediates are the 2-t-butyl-6-trifluoromethyl-1,3-dioxan- and -dioxin-4-ones. The Li enolate of the cis-dioxanone is generated with t-BuLi and reacts with electrophiles (alkyl halides, aldehydes, imines, nitroolefins, Br2, I2) with predominant formation of trans,trans-2,5,6-trisubstituted dioxanones (9 examples). Elimination of HBr from the 5-Br-substituted dioxanone gives the (R)- or (S)-dioxinone, a chiral derivative of 4,4,4-trifluoro-3-oxo-butanoic acid (trifluoro-acetoacetate). Michael additions of cuprates or of CuCl-doped Grignard reagents to the dioxinone produce 6,6-disubstituted dioxanones (10 examples) bearing a CF3 group in the 6-position. In most cases this addition is highly diastereoselective, with the new substituent winding up in the trans position. There are, however, surprising exceptions, such as the product formed with benzylmagnesium chloride which is an abnormal adduct with a p-quinoid structure (26) and with the newly introduced group in the cis position with respect to the t-Bu group. The structures of four trisubstituted dioxanones bearing CF3 groups are determined by X-ray crystal structure analysis (Figure 1, Table 1), one of them including the absolute configuration (by anomalous diffraction). Besides the well-known sofa, a twist-boat conformation of dioxanones appears to be favorable. The solution conformations of the different types of CF3-substituted dioxanones are derived from Nuclear Overhauser NMR measurements and compared with the crystal structures (Figure 3).
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/cber.19941270317
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  • 25
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    Koordinationschemie mit den komplexen Chelatliganden [{Fe2Cp2(CO)3}2{CN[CH2]nNC}] (n = 2, 3). Heteropentanukleare „Superkomplexe“ mit μ5Diisocyanid-BrückenHerrn Professor Dr. O. J. Scherer zum 60. Geburtstag gewidmet. (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 621-629 
    Details
    ISSN: 0009-2940
    Keywords: Isocyanide-bridged metal complexes ; Metal complexes as ligands ; N-Protonation (alkylation, metalation) ; Heteropentanuclear metal complexes ; Diisocyanide bridges ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Coordination Chemistry with the Complex Chelating Ligands [{Fe2Cp2(CO)3)2{CN[CH2]n NC}] (n = 2, 3). Heteropentanuclear “Supercomplexes” with μ5-Diisocyanide BridgesHerrn Professor Dr. O. J. Scherer zum 60. Geburtstag gewidmet.The tetranuclear complexes [(Fe2Cp2(CO)2(μ-CO)}2(μ4-CN[CH2]nNC}] [n = 2 (2), 3 (3)] act as bidentate chelating ligands towards the Lewis-acidic metal halides MnCl2, MnBr2, FeCl2, CoCl2, NiCl2, NiBr2, CuCl2, CuBr2, ZnCl2, ZnI2, CdCl2, CdI2, HgCl2, the chloro complexes [MCl2-(NCPh)2] (M = Pd, Pt), Zn(OAc)2 · H2O, and [Mo(CO)4(η-NBD)] (NBD = 2,5-norbornadiene) to give a total of 22 pentanuclear “supercomplexes” ,6-21, which have been characterized by elemental analyses and IR and NMR (1H, 13C) spectra. Reaction of 2 with [Ni(COD)2] in CH2Cl2 gave only rise to the dichloronickel(II) species 9a. Very remarkably, the pentairon complex [(Fe2Cp2(CO)2(μ-CO)2(μ5-CN(CH2)2-NC)}]FeCl2 (7) also formed spontaneously (!) when 2 was refluxed in chloroform for several hours. The X-ray structure analysis of [{Fe2Cp2(CO)2(μ-CO))2{μ5-CN(CH2)2NC}]CdI2 (14b) confirms the twofold μ3-(C,C,N) bridging mode of a diisocyanide ligand in a cis/cis-anti-configurated [Fe2]2Cd pentanuclear system of crystallographic C2 symmetry.
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  • 26
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    Synthese von ( - )-(Acetoxymethyl)(hydroxymethyl)methyl(phenyl)german [( - )-MePhGe(CH2OAc)(CH2OH)] durch eine Esterase-katalysierte Umesterung: Die erste enzymatische Synthese eines optisch aktiven Germans (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 639-642 
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    ISSN: 0009-2940
    Keywords: Germane, optically active ; Biotransformation, stereoselective ; Transesterification, enzymatic ; Porcine liver esterase ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of ( - )-(Acetoxymethyl)(hydroxymethyl)methyl(phenyl)germane [( - )-MePhGe(CH2OAc)(CH2OH)] by an Esterase-Catalyzed Transesterification: the First Enzymatic Synthesis of an Optically Active GermaneThe prochiral germane MePhGe(CH2OH)2 (1) was synthesized by a six-step synthesis starting from GeCl4 (3) [3 → Cl2Ge(CH2Cl)2 (4) → Ph2Ge(CH2Cl)2 (5) → (CF3S(O)2O)PhGe(CH2Cl)2 (6) → MePhGe(CH2Cl)2 (7) → MePhGe(CH2OAc)2 (8) → 1]. Reaction of 1 with Ac2O/NEt3 (molar ratio 1: Ac2O = 1:1) gave the racemic germane rac-MePhGe(CH2OAc)(CH2OH) (rac-2). Stereoselective transesterification of 1 with vinyl acetate (acetate source and solvent), catalyzed by immobilized porcine liver esterase (PLE; E.C.-3.1.1.1), yielded the optically active germane ( - )-MePhGe(CH2OAc)(CH2OH) [( - )-2] (yield 57%, enantiomeric purity 50% ee).
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    URL: http://dx.doi.org/10.1002/cber.19941270409
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  • 27
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    Synthesis and Structural Characterization of the Bent Nitrosyl Organometallic Complex [NBu4][Pt(C6Cl5)2Cl2(NO)]Throughout this Paper, the convention of Enermark and Feltham to classify metal-nitrosyl complexes {M—N—O}n according to the number of electrons with an important d character has been used (see ref.[2b]). (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 651-652 
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    ISSN: 0009-2940
    Keywords: Platinum complexes, five-coordinate ; Nitrosyl complexes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The title complex has been prepared in 36% yield by reaction of [NBu4]2[trans-Pt(C6Cl5)2Cl2] with NOClO4 (1:1) in CH2Cl2. The anion exhibits an almost tetragonal-pyramidal geometry (X-ray analysis), the platinum atom being virtually located in the basal plane and the NO ligand occupying the apical position. The Pt—N—O unit is bent [119.5(8)°].
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    URL: http://dx.doi.org/10.1002/cber.19941270412
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  • 28
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    Enantioselective Oxidation of Chiral Titanium Enolates Derived from Propiophenone by Dimethyldioxirane or 3-Phenyl-2-phenylsulfonyloxazirdineDedicated to Professor Helmut Werner on the occasion of his 60th birthday. (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 667-671 
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    ISSN: 0009-2940
    Keywords: Dimethyldioxirane ; 3-Phenyl-2-phenylsulfonyloxaziridine ; Titanium enolates ; Enantioselective hydroxylation ; α-Hydroxy carbonyl compounds ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stereoselective oxidation of the optically active titanium enolate complexes 2 of propiophenone by dimethyldioxirane (3) (as acetone solution) and 3-Phenyl-2-phenylsulfonyloxaziridine (4) has been investigated. The chiral titanium enolates 2 were synthesized by the reaction of the lithium enolate of propiophenone and the respective optically active chlorotitanate complexes 1. For 3 as oxidant, the stereoselectivity of the α hydroxylation strongly depends on the substitution pattern at the central titanium atom and reached for the best case, namely 2e, an enantiomeric excess (ee) of 63%. Solvent and temperature exhibited only small effects on the stereoselectivity. Compound 4 as oxidant gave lower enantiomeric excesses than 3.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/cber.19941270415
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  • 29
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    Substituenteneffekte auf die C—C-Bindungsstärke, 14. Kinetische und thermodynamische Stabilität von 2,3-Bis(dialkylamino)-1,4-diketonen  -  Stabilisierungsenergie capto-dativ substituierter a-Dialkylamino-a-Carbonylalkyl-RadikaleProf. Dr. H.-G. Viehe zum 65. Geburtstag gewidmet. (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 697-710 
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    ISSN: 0009-2940
    Keywords: C—C Bond cleavage, kinetics of ; Heats of formation ; Radicals, stability of ; Capto-dative effect ; Geminal substituents, energetic interaction of ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Substituent Effects on the Strength of C—C Bonds, 14[1].  -  Kinetic and Thermodynamic Stability of 2,3-Bis(dialkylamino)-1,4-diketones  -  Energy of Stabilization of α-Dialkylamino α-Carbonylalkyl Radicals with Capto-dative SubstituentsProf. Dr. H.-G. Viehe zum 65. Geburtstag gewidmet.The equilibrium constants and rate constants for the dissociation of the 2,3-bis(dialkylamino)-1,4-diketone diastereomers meso- and DL-7a and 7b were measured over a temperature range of 40°C. From the enthalpies of dissociation ΔHDiss and enthalpies of activation ΔH≠ and the strain enthalpies of 7 the bond dissociation enthalpies BDE(C—C) of 7 were determined. By comparison with the dissociation enthalpies of Ct-Ct alkanes[21] the change of these BDEs(C—C) by the cap-to-dative substitution was determined to be 85.4 kJ mol-1 (20.4 kcal mol-1). The heats of formation ΔHof (g) of a series of amino ketones 8 were determined from their heats of combustion and their heats of evaporation. From the ΔHof(g) values in combination with MM2 calculations of their strain enthalpies strain-free increments CHn[N, CO, C2 - n] with n With n = 0, 1, 2 were derived and geminal interaction enthalpies in the ground states were obtained thereof. The radical stabilization enthalpy RSE of 6 was deduced from the ΔBDE(C—C) values and the ground state effect to be 73.6 kJ mol-1 (17.6 kcal mol-1). From these data and the radical stabilization enthalpies RSE of α-aminoalkyl radicals (4.2 kJ mol-1) and α-carbonyl radicals (28.9 kJ mol-1) a synergetic radical stabilization enthalpy of 40.5 kJ mol-1 (9.7 kcal mol-1) is deduced. This number combines “extra” resonance stabilization and general inductive or anomeric geminal substituent interaction in the radicals. The crystal structure of meso-7a has been determined by X-ray diffraction methods.
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    Transition Metal-Catalyzed Annulation Reactions, VII. Palladium-Catalyzed C—H Activation at Methoxy Groups: Regiochemistry of the Domino Coupling Process (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 739-742 
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    ISSN: 0009-2940
    Keywords: C—H Activation ; Palladium catalysis ; Domino coupling processes ; Palladium(IV) intermediates ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By palladium catalysis substituted ortho-iodoanisoles (5, 8, 10, 13) are transformed either to annulated pyran (6) or furan derivatives (7, 9, 11, 14, 15), depending on the reactivity of additional substituents. The regiochemistry of the domino coupling processes is analyzed and a mechanistic rationale developed. Key step is the C—H activation at methoxy groups.
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    URL: http://dx.doi.org/10.1002/cber.19941270425
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  • 31
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    Photoreaktionen mit Fulleren-C60 [3 + 2]-Photocycloaddition von 2,3-Diphenyl-2H-azirin (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 787-789 
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    ISSN: 0009-2940
    Keywords: Fullerenes ; Azirines ; Photochemistry ; [3 + 2] Cycloadditions ; Electron transfer reactions ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Photoreactions with C60-Fullerene. [3 + 2] Photocycloaddition of 2,3-Diphenyl-2H-azirineUpon irradiation 2,3-Diphenyl-2H-azirine (2) is added to C60 1 with formation of mono and oligo adducts. 1,9-(3,4-Dihydro-2,5-diphenyl-2H-pyrrolo)fulleren-60 (3) has been isolated and identified by standard spectroscopic methods. Mechanistic studies revealed two reaction paths leading to 3, i.e. the classic 1,3-dipolar cycloaddition via the nitrile ylide 4 (direct irradiation) or a route via 2-azaallenyl radical cations 5 (sensitization by photoinduced electron transfer).
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  • 32
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    Seven-Membered Heterodimetallic Ring Systems from (Conjugated Diene) Group 4 Metallocene Complexes and Organoaluminium Reagents (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 805-811 
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    ISSN: 0009-2940
    Keywords: Bent metallocene complexes ; Heterodimetallic zirconium-aluminium compounds ; Hydrocarbyl-bridging ligands ; “π-Agostic” interaction ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The (s-trans/s-cis-η4-butadiene)zirconocene reagent adds dimethylaluminium chloride to yield the heterodimetallacyclic main group/transition-metal system 2b, containing a seven-membered metallacyclic framework that exhibits a “π-agostic” s̰-allyl zirconium interaction. Similar compounds (2c-f, 5a, 6) are obtained upon reaction of (butadiene)zirconocene with Et2All and (butadiene)hafnocene with Me2AlCl or Et2AlI. Addition of Me2AlCl or Et2AlI to (isoprene)zirconocene proceeds regioselectively to yield the corresponding heterodimetallacycles bearing the methyl substituent at C-3 (i.e. near to the attached aluminium center). The iodide-bridged heterodimetallacycles exhibit dynamic NMR spectra that indicate a rapid enantiomerization process on the NMR time scale (ΔG±ent ≈ 11-12 kcal mol-1). It is assumed that this automerization reaction proceeds by rate-limiting aluminium-halogen bond cleavage leading to an acyclic mixed metal heterodimetallic intermediate. This process is markedly inhibited by the presence of excess diethylaluminium iodide.
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    URL: http://dx.doi.org/10.1002/cber.19941270503
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  • 33
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    Metallkomplexe funktioneller Isocyanide, XXIV. Reaktionen von N-Isocyandialkylamin-Metallkomplexen mit sekundären Aminen (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 829-833 
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    ISSN: 0009-2940
    Keywords: N-Isocyandialkylamine complexes ; Cyanamide complexes ; Guanidine complexes ; Reactions at the coordinated ligand ; N—N bond breakage ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Metal Complexes of Functional Isocyanides, XXIV.  -  Reactions of N-Isocyanodialkylamine Complexes with Secondary AminesReactions of pentacarbonyl(N-isocyanodialkylamine) group 6-metal complexes [M(CO)5CNNR2] [M = Cr, W; R = Et, iPr; 2R = -{MeCH(CH2)3CHMe}-] with secondary amines proceed with cleavage of the N—N bond and C→N migration of the metal to give the corresponding N-cyanamide complexes [M(CO)5NCNR′2] (1a-2g) [R′ = Me, Et, nPr, nBu; 2R′ = —(CH2)4—, —(CH2)5—, —(CH2)2O(CH2)2—]. However, when diiodobis(N-isocyanodialkylamine)platinum(II) was allowed to react with an excess of the amine amine(guanidine)platinum(II) complexes [PtI2(HNR′2){HN=C(NR′2)2}] (3a-c) [R′ = Et; 2R′ = —(CH2)5—, —(CH2)2O(CH2)2—] were obtained. Structural assignments are made on the basis of IR, NMR (1H, 13C), and mass spectroscopy as well as of an X-ray structure analysis of trans-[PtI2(HNEt2){HN=C(NEt2)2}] (3a).
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    Derivate des Imidazols, IX. Stabilisierung von Selendiiodid durch KomplexbildungHerrn Professor Helmut Werner zum 60. Geburtstag gewidmet. (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 849-851 
    Details
    ISSN: 0009-2940
    Keywords: Selenium iodides ; Imidazoles ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Imidazole Derivatives, IX.  -  Stabilisation of Selenium Diiodide by ComplexationHerrn Professor Helmut Werner zum 60. Geburtstag gewidmet.Stable selenium diiodide complexes 2 are obtained by the reaction of the 2-selenoxoimidazolines 1 with iodine. An X-ray structure analysis of 2c reveals its monomeric nature. In the trigonal bipyramid, the iodo substituents are situated in axial positions forming elongated iodine bonds [Se-I(1) 2.854(1), Se—I(2) 2.768(1) Å; I(1)—Se—I(2) 175.4(0)°].
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    Synthese und Reaktionen der ersten zweifach überbrückten Fiscellane (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 881-885 
    Details
    ISSN: 0009-2940
    Keywords: Fiscellanes, doubly-bridged ; Semibullvalenes, doubly-bridged ; Cyclopropanes ; SEM-protective groups ; Annulenes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis and Reactions of the First Doubly-Bridged FiscellanesThe synthesis of the novel hexacycle 2 containing a fiscellane framework is described. Starting from Weiss' tetraester 6, the fiscellane 2 is build up in six steps by successive chemical transformation of the methoxycarbonyl functions using SEM protecting groups. The behaviour of the novel diol 2 towards introduction of several leaving groups is examined. Upon treatment with methanesulfonyl chloride the highly strained hexacycle 2 undergoes a skeletal rearrangement with formation of the triene 4. Instead of reacting to a doubly-bridged semibullvalene 3, the diol 2 gives rise to a new heterocyclic π perimeter 5 when the trifluoroacetyl derivative 12 is treated with sodium iodide in acetone.
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    URL: http://dx.doi.org/10.1002/cber.19941270515
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    Chelat-kontrollierte diastereoselektive Addition an α,ß-Epoxy-Aldehyde (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 905-909 
    Details
    ISSN: 0009-2940
    Keywords: Allyltributylstannane ; Trimethylsilyl cyanide ; α,β-Epoxy aldehydes ; Chelation-controlled addition ; Diastereoselectivity ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chelate-Controlled Diastereoselective Addition to α,β-Epoxy AldehydesLiClO4-mediated reaction of trans-substituted α,β-epoxy aldehydes 1 with allyltributyltin (2) or trimethylsilyl cyanide provides a general method for the synthesis of the corresponding syn-alcohols 3 with high selectivity. In the case of cis-substituted α,β-epoxy aldehydes the selectivity depends on the size of the substituents.
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    URL: http://dx.doi.org/10.1002/cber.19941270519
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    On the Reaction of 1-Aza-2-azoniaallene Salts with Isocyanates (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 947-953 
    Details
    ISSN: 0009-2940
    Keywords: 1-Aza-2-azoniaallene cations ; Isocyanates ; 4,5-Dihydro-5-oxo-1,2,4-triazolium salts ; Cinnolinium salts ; Cycloadditions ; Calculations, AM1 ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1-Aza-2-azoniaallene salts 3, prepared in situ from geminal chloroalkylazo compounds 2 with Lewis acids, react with isocyanates 4 to give 4,5-dihydro-5-oxo-3H-1,2,4-triazolium salts 6 and 4,5-dihydro-5-oxo-1H-1,2,4-triazolium salts 7, respectively. The intramolecular cyclization of 3u opens a new route to cinnolinium salts 11. Allenes 3 react with isobutene to give pyrazolium salts 8. According to AM1 calculations the cycloadditions of 3 to isocyanates proceed in two steps via acylium salts 5 as intermediates. Mechanistically, the rearrangements 6 → 7 resemble Wagner-Meerwein rearrangements rather than pericyclic [1,5]-sigmatropic shifts.
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  • 38
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    Photoenolization of 4-Naphthoyl[2.2]paracyclophanes (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 965-966 
    Details
    ISSN: 0009-2940
    Keywords: Cyclophanes ; Photochemistry ; Triplet states ; Enolization ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: When ethanolic solutions of 4-(1-naphthoyl)[2.2]paracyclophane (3) and 4-(2-naphthoyl)[2.2]paracyclophane (4) are subjected to UV irradiation at low temperature, 1,5-hydrogen migration of the 2-H bridge proton to the carbonyl group takes place, leading to the enol of type 2. In the context of mechanistic considerations the triplet spectroscopic properties of 3 and 4 are discussed.
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    Transition Metal Chemistry of Main Group Hydrazides, VI. New Directed Synthetic Strategies to Functionalized Heterocyclic Phosphorus(III) Hydrazides. First Examples of Crystal and Molecular Structures of [RPN(Me)N(H)]2 (R = Et, Ph, and tBu) (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 979-984 
    Details
    ISSN: 0009-2940
    Keywords: Cyclophosphahydrazides ; Dinitrogen-bridged ; Conformation ; Chair and Boat forms ; Dinuclear Mo(0) complexes ; 1,2,4,5,3,6-Tetrazadiphosphorinanes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactions of methylhydrazine with RPC12 (R = Et, tBu, and Ph) produced the cyclic phosphorus (III) hydrazides (1,2,4,5,3,6-tetrazadiphosphorinanes) [RPN(Me)N(H)2 (R = Et, 1; (Ph, 2; tBu, 3) in good yields. The 1H-and 31P-NMR spectroscopic analysis indicated that 1 exists in chair and boat conformations. However, it crystallizes in the chair conformation exclusively. The X-ray crystallographic investigation of all the three cyclo-phosphorus hydrazides 1-3 confirms the existence of these compounds in the chair conformations in the solid state. The reaction of Mo(CO)4-(NHC5H10)2 with 1 and 2 gives the dinuclear Mo(0) complexes [{Mo(CO)4(NHC5H10)}2(μ-[RPN(Me)N(H)]2}] (R = Et, 5; Ph, 6). Based on 1H- and 31P-NMR spectroscopic data, a bridging dinuclear dimetallic formulation is proposed for 5 and 6. The IR spectra indicate that the carbonyls are disposed in cis-geometry around the Mo(0) center.
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    Substituierte N,N-Chelat-Liganden - Anwendungen in der Molybdän-katalysierten Olefin-EpoxidationHerrn Prof. Dr. H. Schmidbaur zum 60. Geburtstag gewidmet. (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 2373-2379 
    Details
    ISSN: 0009-2940
    Keywords: Chelating ligands ; Molybdenum complexes ; Peroxo complexes ; Catalysis ; Olefine epoxidation ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Substituted N,N-Chelate Ligands - Applications in Molybdenum-Catalyzed Epoxidation of Olefins*Oxodiperoxomolybdenum complexes 4 of substituted 2-[3(5)-pyrazolyl]pyridines (2a-g) were synthesized in order to control the solubility of these complexes in organic solvents. Alkyl side chains (butyl, octyl, octadecyl) increase the solubility of the complexes and enable spectroscopic investigations in solution. Due to the symmetry of the ligands the peroxo complexes 4 appear in two isomeric forms, with the terminal oxo ligand in the trans position either to pyridine or to pyrazole. The latter isomer of (C5H4NC3H2N2CH2COOEt)MoO(O2)2 (4f) was characterized by an X-ray structure analysis. The alkyl-substituted peroxo complexes are active catalysts for the epoxidation of olefins with tert-butyl hydroperoxide.
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    URL: http://dx.doi.org/10.1002/cber.19941271206
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  • 41
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    1,3-Diaza-2λ2-phosphonia-4λ4-gallatacyclobutane (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 2397-2401 
    Details
    ISSN: 0009-2940
    Keywords: [Amino(imino)phosphane]gallium trichloride adduct ; 1,3-Diaza-2λ2-phosphonia-4λ4-gallatacyclobutanes ; Nickel tricarbonyl complexes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,3-Diaza-2λ2-phosphonia-4λ4-gallatacyclobutanesReaction of amino(imino)phosphanes 1a-c with gallium trichloride results in the formation of 1,3-diaza-2λ2-phosphonia-4λ4-gallatacyclobutanes 3a, b with elimination of chlorotrimethylsilane (1a) or tert-butyl chloride (1b, c). The intermediately formed amino(imino)phosphane/Lewis acid adducts R(Me3Si)NPN(GaCl3)R′ (2, R,R′ = tBu, Me3Si) can be isolated in the case of compound 2a (R = R′ = SiMe3). A diazaphosphasilacyclobutane - gallium trichloride adduct 4 is formed in a side reaction by isomerization of 2a. Reaction of compound 3b with Ni(CO)4 gives the corresponding transition metal complex 5. The NMR data and X-ray structures of compounds 2a, 4, and 5 are reported.
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    Komplexierung von 1,4-Dihydro-1,4-diborafulvenen mit Ni(cod)- und Pt(cod)-FragmentenHerrn Professor Hubert Schmidbaur zum 60. Geburtstag gewidmet. (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 2393-2396 
    Details
    ISSN: 0009-2940
    Keywords: 1,4-Diborafulvenes, 1,4-dihydro- ; Slipped triple-decker ; Nickel complexes ; platinum complexes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Complexation of 1,4-Dihydro-1,4-diborafulvenes with Ni(cod) and Pt(cod) Fragments*Reactions of the 1,4-diborapentafulvene derivatives 1 and 2a, b with M(cod)2 (M = Ni, Pt) yield the complexes [(η5-1)Ni-(cod)] (8), [(μ,η2η5-2a){Ni(cod)}2] (9a), [(μ,η2,η5-2b){Ni(cod)}2] (9b), and [(μ,η2,η5-2a){Pt(cod)}2] (10). Compounds 9 and 10 are the first examples of complexes with 2a, b as a μ,η2,η5-ligand. The X-ray structure analyses of 9b and 10 are described.
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    URL: http://dx.doi.org/10.1002/cber.19941271209
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    Stereoselective Synthesis of Alcohols, XLVII[1] Application of Chiral Z-Pentenylboronates to the Synthesis of Erythronolide Building Blocks (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 2511-2518 
    Details
    ISSN: 0009-2940
    Keywords: Allylboration, stereoselective ; Erythronolide building blocks ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chiral pentenylboronate 3 was the key reagent in the stereoselective construction of two erythronolide building blocks 6 and 7. Addition of 3 to achiral aldehydes furnished homoallylic alcohols 21 and 26 with 〉98% e.e. Addition of 3 to chiral aldehydes 8 or 11 generated homoallylic alcohols with 〉95% d.e. In the mismatched case of addition to the aldehyde 29 diastereoselectivity reached merely 80%.
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    (η3-Allyl)(η5-pentamethylcyclopentadienyl)cobalt - ein selektiver Katalysator für die Pyridinsynthese (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 2535-2537 
    Details
    ISSN: 0009-2940
    Keywords: Cobalt complexes, (η3-allyl)(η5-pentamethylcyclopentadienyl)- ; Pyridine synthesis ; Catalytic activity ; Chemoselectivity ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (η3-Allyl)(η5-pentamethylcyclopentadienyl)cobalt - a Selective Catalyst for the Pyridine Synthesis(η3-Allyl)(η5-pentamethylcyclopentadienyl)cobalt (1) catalyses the synthesis of various pyridines from alkynes and nitriles under mild conditions. Only small amounts of benzenes are formed in this selective reaction.
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    Stereoselective Synthesis of Alcohols, XLVI. Synthesis of a Hydroxytrioxaadamantane, a Model for the Trioxaadamantane Moiety of Muamvatin (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1317-1322 
    Details
    ISSN: 0009-2940
    Keywords: Cyclization of a hydroxy triketone ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A protected hydroxy triketone 22 has been generated by direct Swern oxidation of a δ-trimethylsilyloxy alcohol 11, avoiding the formation of a δ-hydroxy ketone as an intermediate. Conditions have been worked out, which allow the deprotection of a tert-butyldimethylsilyl group and the spontaneous tricyclization of the resulting hydroxy triketone 4 to an acid-sensitive hydroxytrioxaadamantane 5.
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    URL: http://dx.doi.org/10.1002/cber.19941270722
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    Synthesis and X-Ray Structures of New Macrocyclic Thioethers (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1327-1329 
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    ISSN: 0009-2940
    Keywords: Macrocyclic thioethers ; Adamantane as a building block ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 4,6:12,14-Di(1,3-adamantano)-1,9-dithiacyclohexadecane (1), 4,6:12,14:20,22-tri(1,3-adamantano)-1,9,17-trithiacyclotetracosane (2), and 5,7:14,16-di(1,3-adamantano)-1,2,10,11-tetrathiacyclooctadecane (3) have been obtained by intermolecular cyclization of 1,3-bis(2-bromoethyl)adamantane (4) with thioacetamide using a high-dilution technique. The reaction is concentration-dependent. The crystal structures of 1, 2, and 3 have been determined by single-crystal X-ray diffraction.
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    Masthead (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994) 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    URL: http://dx.doi.org/10.1002/cber.19941270801
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    (5aS,10aS)-Octahydro-1H,5H-dipyrrolo[1,2-a:1′,2Prime;-d]pyrazin «DPP» als Hilfsreagenz bei der enantioselektiven 1,2-Addition von Grignard-Reagenzien an prochirale Carbonylverbindungen (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1323-1326 
    Details
    ISSN: 0009-2940
    Keywords: Dipyrrolo[1,2a:1′,2′-d]pyrazine, (5aS,10aS)-octahydro-1H,5H- ; 1,2-Addition, enantioselective ; Grignard reagents ; Chiral solvent ; Cryoscopic measurements ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (5aS,10aS)-Octahydro-1H,5H-dipyrrolo[1,2-a:1′,2′-d]pyrazine «DPP» as Auxiliary Reagent for Enantioselective Alkylations of Prochiral Carbonyl CompoundsIn the presence of one equivalent of the title compound «DPP» (1) prochiral carbonyl compounds 2 react with Grignard reagents 3 in THF to form enantioselectively alcohols 4 with up to 98% ee, whereas the addition of one equivalent of triethylamine yields the opposite enantiomers with up to 97% ee. The optimal molar ratio of 1 and magnesium reagent 3 was determined by cryoscopic measurements. Asymmetric induction is supposed to arise from transition states involving monomeric octahedral complexes of Grignard reagent, chiral solvent, and carbonyl compound. DPP (1) also catalyses Grignard alkylations, because a tenth of its stochiometric amount gives an enantiomeric eccess four times more than as expected. Prepared from (S)-proline, only the boat conformation of 1 induces the observed selectivity as detected by 13C-NMR spectroscopy.
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    Borylation of a Stable Primary Enamine (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1331-1332 
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    ISSN: 0009-2940
    Keywords: Primary enamines ; Borylation ; 9-BBN ; Amino-polyene ; Enamines, borylation of ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stable conjugated primary enamine 1,6-diamino-1,6-diphenyl-1,3,5-hexatriene (2a) was treated with 9-borabicyclo-[3.3.1]nonane. At 40°C in dichloromethane solution (18 h) only borylation at nitrogen was observed. With loss of dihydrogen a 9-BBN substituent became attached to each enamine nitrogen. The N,N′-diborylated diaminohexatriene product 3 was characterized by X-ray diffraction.
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    URL: http://dx.doi.org/10.1002/cber.19941270725
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    Übergangsmetallsubstituierte Acylphosphane und Phosphaalkene, XXI. Isophosphaalkine als μ3-Liganden in Übergangsmetallkomplexen (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1349-1353 
    Details
    ISSN: 0009-2940
    Keywords: Isophosphaalkynes ; Transition metal complexes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Transition-Metal-Substituted Acylphosphanes and Phosphaalkenes, XXI.  -  Isophosphaalkynes as μ3-Ligands in Transition Metal ComplexesReaction of the μ-isophosphaalkyne complex (η5-C5H5)2 (CO)2(μ-CO)Fe2(μ-CPMes) (Mes = 2,4,6-Me3C6H2) (2a) with [(Z)-Cyclooctene]Cr(CO)5 or Fe2(CO)9 gives rise to the μ3-isophosphaalkyne complexes (η5-C5H5)2(CO)2(μ-CO)Fe2{μ-CP[M(CO)n]Mes} 3a [M(CO)n = Cr(CO)5] and 4a [M(CO)n = Fe(CO)4]. Similarly (η5-C5H5)2(CO)2(μ-CO)Fe2{μ-CP[Cr (CO)5]C6H2(CF3)3-2,4,6} (3d) is obtained. The metal carbonyl fragments are attached to 2 in a η1-fashion by the lone-pair at the phosphorus. In contrast to this the treatment of 2a with (Ph3P)2Pt(η2-C2H4) affords complex 5a in which 2a serves as an η3-3e ligand towards the PtPPh3 moiety. The molecular structures of 3a and 5a are determined by single-crystal X-ray analysis.
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    Preparation, Properties, and Reactions of Metal-Containing Hetercycles, XC. Reactivity of Differently Activated Alkynes toward Ruthenium and Osmium Complexes of the Type (η2-C2H4)M(CO)4Dedicated to Professor Reinhard Schmutzler on the occasion of his 60th birthday. (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1343-1347 
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    ISSN: 0009-2940
    Keywords: Ruthenium compounds ; Osmium compounds ; Alkynes, activated ; Cyclotrimerization ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Depending on the substituents, the reaction of the activated alkynes ZC≡CZ (2a-g) [Z = CO2R: R = Me (a), Et (b); Z = R1: R1 = CF3 (c), CH2Cl (d), CH2Br (e); Z = CH2OC(O)R2: R2 = Me (f), CCl3 (g)] with the labile ruthenium complex (η2-C2H4)Ru(CO)4 (1) results in the formation of three different types of heterocycles. While the reactions of the dialkyl acet-ylenedicarboxylates 2a, b lead to the dimeric tricarbonylru-thenacyclopentadienes 3a, b, being catalytically active in the cyclotrimerization of alkynes like 2a, b, the application of the 1,4-halogeno-2-butynes 2c-e yields the bicyclic heterocycles 4c-e. The esters of 2-butyne-1,4-diol 2f, g are converted into the tetracarbonylruthenacyclopentadienes 5f, g. Investigation of the primary attack of the alkynes 2a-g at complex 1 leads to the conclusion, that an ionic mechanism is preferred in the ruthenium-catalyzed cyclotrimerization of electron-poor alkynes. If, instead of 1, (η2-C2H4)Os(CO)4 (6) is allowed to react with the acetylenes 2a, b the osmium complexes (η4-C6Z6)Os(CO)3 (7a, b) are isolated. In the presence of CO at 2 bar 7a, b release the benzene derivatives C6Z6 (8a, b) with the formation of Os3(CO)12.
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    Wismutverbindungen mit voluminösen, mehrfach alkylierten Cyclopentadienyl-LigandenHerrn Professor Helmut Werner zum 60. Geburtstag gewidmet. (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1335-1342 
    Details
    ISSN: 0009-2940
    Keywords: Fulvalenes ; Bismuth complexes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bismuth Compounds with Crowded Multiply Alkylated Cyclopentadienyl LigandsHerrn Professor Helmut Werner zum 60. Geburtstag gewidmet.Bismuth complexes of alkylated cyclopentadienyl ligands are obtained in good yield on treating bismuth(III) halides with tetraisopropylcyclopentadienylsodium or 1,2,4-tri-tert-butyl-cyclopentadienyllithium. A 1:1 stoichiometric ratio gives the complexes [Cp4iBiCl2] (1), [Cp3tBiCl2] (2), and [Cp4iBiI2] (3) (Cp4i = C5iPr4H, Cp3t = C5H2tBu3-1,2,4). According to X-ray crystal structure analyses, 1 and 3 display dimeric structures with two bridging and two terminal halogeno ligands and η3-coordination of the cyclopentadienyl rings. With half an equivalent of tetraisopropylcyclopentadienylsodium BiCl3 forms [Cp4iBi2Cl5] (4). An X-ray crystal structure analysis of 3 reveals a central Bi2Cl10 core of two edge-sharing BiCl6 octahedra coordinated to two Bi(η5-Cp4i) fragments generating a framework of two face-sharing cubes. Reaction of two equivalents of 1,2,4-tri-tert-butylcyclopentadienyllithium with BiCl3 yields deep purple [Cp3t2BiCl] (5), a bent sandwich complex with an η3,η2-bonding mode of the cyclopentadienyl ligands. Attempted formation of the octaisopropyl analogue of 5 from BiCl3 and two equivalents of tetraisopropylcyclo-pentadienylsodium with elimination of propene gives [Cp4iCp3iBiCl] (6) (Cp3i = C5H2iPr3). Use of monodeuterated tetraisopropylcyclopentadienylsodium in the second substitution step gave pure [Cp4i([D1]Cp3i)BiCl] ([D1]6) proving the absence of ring exchange reactions under the reaction conditions employed and elimination of propene from the second incoming sterically crowded tetraisopropylcyclopentadienyl ring system. The importance of proper choice of solvent and reaction conditions on the formation of alkylated cyclopentadienyl bismuth derivatives is demonstrated by extensive formation of 1,1′,3,3′,5,5′-hexa-tert-butyldihydrofulvalene (7) from 1,2,4-tri-tert-butylcyclopentadienylsodium and BiCl3.
    Additional Material: 8 Ill.
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    Transition Metal Chemistry of Main Group Hydrazides, 9. Platinum Complexes of Diphosphanylhydrazides R2PN(Me)N(Me)PR2 · PtCl2 (R = OPh, o-OC6H4CH2CHCH2) (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1355-1357 
    Details
    ISSN: 0009-2940
    Keywords: Diphosphanylhydrazides ; Diphosphanes, dinitrogen-bridged ; Cycloplatinaphosphahydrazides ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: While the transition metal complexes of bis(phosphanyl)amines (PII-N-PIII) have been known for over three decades, the ligating properties of the next homologue PIII-N-N-PIII have been unprecedented so far. The X-ray structures of cycloplatinaphosphanehydrazides, [(OR)2PN(Me)N(Me)P(OR)2-PtCl2], reveal short distances for the P-N [1.639(5) Å] bonds.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/cber.19941270805
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    A Synthetic Pathway to 1,3-Bis(trisilylmethyl)disiloxane [(H3Si)3CSiH2]2O  -  the Octasila Analogue of Dineopentyl Ether [(H3C)3CCH2]2O (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1359-1362 
    Details
    ISSN: 0009-2940
    Keywords: Silanes ; Siloxanes ; Si - C bond, selective cleavage ; Arylsilylmethanes ; Si,C,O single-source CVD precursor ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A synthetic route to partly silylated tetra(silyl)methanes (ArH2Si)nC(SiH3)4  -  n′ to their precursors (TfH2Si)nC-(SiH2Ar)4  -  n (Ar = p-tolyl, phenyl; Tf = CF3SO3; n = 3, 2, 1), and to 1,3-bis(trisilylmethyl)disiloxane [(H3Si)3CSiH2]2O (9) is reported. Starting from symmetrical tetrakis(arylsilyl)-methanes (aryl = p-tolyl, phenyl), we have obtained the selectively dearylated (arylsilyl)silylmethanes (ArH2Si)nC(SiH3)4  -  n (Ar = p-tolyl, phenyl; n = 3, 2, 1) by Si - Ar cleavage with equivalent quantities of trifluoromethanesulfonic acid (triflic acid) and hydrogenation of the corresponding silyl triflates (TfH2Si)nC(SiH2Ar)4  -  n (n = 3, 2, 1) with LiAlH4. The synthesis of 9 has been accomplished by treating trisilyl(p-tolylsilyl)methane p-TolH2SiC(SiH3)3 (7) with stoichiometric amounts of triflic acid to give (trisilylmethyl)silyl triflate TfH2SiC(SiH3)3 (8) and hydrolysing the latter with water.
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    URL: http://dx.doi.org/10.1002/cber.19941270806
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    Ein neuer Zugang zu 1,2- und 1,3-DiborolHerrn Prof. Dr. Joachim Knappe zum 65. Geburtstag gewidmet. (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1363-1368 
    Details
    ISSN: 0009-2940
    Keywords: 1,2-Diboroles, 2,5-dihydro- ; 1,3-Diboroles, 2,3-dihydro- ; Cobalt complexes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A New Approach to 1,2- and 1,3-DiboroleHerrn Prof. Dr. Joachim Knappe zum 65. Geburtstag gewidmet.Diaminoborylation of 1,3-dilithiopropenes leads to the (Z)-1,3-bis(diaminoboryl)propenes 4a, b, which are transformed by an amine/chlorine exchange to the (Z)-1,3-bis(aminochloroboryl)propenes 5a, b. These react with sodium to yield the 2,5-dihydro-1H-1,2-diboroles 2c, d, whereas the reaction with potassium leads to the 2,3-dihydro-1H-1,3-diboroles 6a, b by rearrangement of the C3B2 skeleton. The constitutions of the heterocycles 2c, d and 6a, b are established by X-ray structure analyses. Reaction of the 1,2-diboroles 2c, d with (C5H5)Co(C2H4)2 leads to the red (1-borabutadiene)cobalt complexes 3c, d. In 3c a sigmatropic rearrangement is studied by NMR spectroscopy.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/cber.19941270807
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    Kohlenwasserstoffverbrückte Komplexe, XXX. Nucleophile Addition von Carbonylmetallaten an kationische Vinyl-, Dien-, Dienyl- und Trien-Komplexe von Eisen, Ruthenium und Cobalt: Zwei-, drei-, vier- und fünfkernige Komplexe mit σ,σ- und σ,π-KohlenwasserstoffbrückenHerrn Professor Ekkehard Lindner zum 60. Geburtstag gewidmet. (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1369-1377 
    Details
    ISSN: 0009-2940
    Keywords: Tungsten complexes ; Rhenium complexes ; Iron complexes ; Ruthenium complexes ; Osmium complexes ; Cobalt complexes ; Vinyl ; Cyclohexadienyl ; Cycloheptadienyl ; Cyclooctatrienyl ; Hydrocarbon-bridged complexes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydrocarbon-Bridged Complexes, XXX.  -  Nucleophilic Addition of Carbonylmetallates to Cationic Vinyl, Diene, Dienyl and Triene Complexes of Iron, Ruthenium and Cobalt: Di-, Tri-, Tetra- and Pentametallic Complexes with σ,σ- and σ,π-Hydrocarbon BridgesHerrn Professor Ekkehard Lindner zum 60. Geburtstag gewidmet.The reactions of [Re(CO)5]-, [Ru(CO)2Cp]-, and [Os(CO)4]2- with [Cp2(OC)2Fe2(μ-CO)(μ-η1:η2-CH=CH2)]+, [Cp*Ru(η2:η4-1,3,7-octatriene)]+, [(OC)Fe(η4-diene)(η5-cycloheptadienyl)]+, and [CpCo(η5-cyclodienyl)]+ give the nucleophilic adducts whereas with [Mn(CO)5]-, [W(CO)3Cp]-, and [Fe(CO)2Cp]- formation of the corresponding C-C coupling products and of the metal-metal-bonded dimers is observed. The structures of Cp*Ru(μ-η1:η2:η3-1,5-octadienyl)Re(CO)5 (4), [Cp* Ru(μ-η1:η2:η3-1,5-octadienyl)]2Os(CO)4 (6), and of (OC)-Fe(η4-1,3-cyclohexadiene) (μ-η1:η4-1,3-cycloheptadiene)Re(CO)5 (9) have been determined by X-ray diffraction.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/cber.19941270808
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    Binary [Hydrotris(1,2,4-triazolyl)borate]metal Complexes [M{HB(C2H2N3)3}2] with M = Fe, Co, Cu, Zn: Synthesis, Characterization, Magnetochemistry, and X-ray Structure of [Cu{HB(C2H2N3)3}2·4CH3 (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1379-1385 
    Details
    ISSN: 0009-2940
    Keywords: Hydrotris(triazolyl)borate ; metal complexes ; Chelate ligands ; Clathrates ; Magnetochemistry ; Spin crossover ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The bis[hydrotris(1,2,4-triazolyl)borate]metal complexes [M{HB(C2H2N3)3}2] with M = Fe (5), Co (6), Cu (7), Zn (8) are obtained from MX2 and K[HB(C2H2N3)3] (9). The complexes are characterized by IR, UV/Vis, and MS. Temperature-variable magnetic measurements show a Curie-Weiss behavior for the paramagnetic complexes 6 and 7 with a temperature-dependent magnetic moment for 6. The iron complex 5 exhibits a spin crossover from diamagnetic to paramagnetic, starting at around 270 K. Single-crystal X-ray structures of the solvates 7 · 4 CH3OH and 9 · 2 H2O have been determined. The structure of 7 · 4 CH3OH shows the Jahn-Teller distorted copper complex 7 surrounded by methanol molecules through hydrogen bonding to exocyclic nitrogen atoms of the tris(1,2,4-triazolyl)borate ligand. The crystal system for 7 · 4 CH3OH is monoclinic, space group P21/n. Compound 9 · 2 H2O is a one-dimensional coordination polymer with the potassium atom bridged by the water molecules and the tris(1,2,4-triazolyl)borate ligand and crystallizes in the orthorhombic space group Ccm21.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/cber.19941270809
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    2,6-Disubstituted 4-Aminopyridines from 1,3-Dialkoxy-2-azapropenylium Salts and N-Methyl-4-piperidone EnaminesDedicated to Prof. D. Dr. Ernst Würthwein on the occasion of his 85th birthday. (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1437-1440 
    Details
    ISSN: 0009-2940
    Keywords: 2-Azapropenylium salts, 1,3-dialkoxy- and 1,1,3,3-tetraalkoxy- ; Enamines of N-methyl-4-piperidone ; 4-Aminopyridines ; 3,7-Diazabicyclo[3.3.1]non-2-en-9-ones ; Retro-Mannich reaction ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,3-Dialkoxy-2-azapropenylium salts 1 react with enamines 2 of N-methyl-4-piperidone at room temperature to give 2,6-disubstituted 4-aminopyridines 4, 5 in low to moderate yield after hydrolysis. Intermediates of the reaction of 1a with 2 are the bicyclic iminium salts 6 and 7, which may be detected 1H-NMR spectroscopically prior to hydrolysis. Hydrolysis of the mixture obtained from the reaction of 1a with 2a under basic conditions furnishes the bicyclic ketone 3 as the major product. A “retro-Mannich”-type reaction is suggested to explain the degradation of the bicyclic intermediates 6, 7 with the formation of the pyridines 4, 5.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/cber.19941270817
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    Regio- and Diastereoselective Synthesis of Stannyl Epoxy Alcohols by Direct Hydroxy Epoxidation of Vinylstannanes (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1441-1445 
    Details
    ISSN: 0009-2940
    Keywords: Vinylstannanes ; Photooxygenation ; Schenck reaction ; Hydroxy epoxidation ; Stannyl epoxy alcohols ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The direct synthesis of stannyl epoxy alcohols 3 from vinylstannanes 1 is described. The procedure involves the photooxygenation of Vinylstannanes 1, which proceeds in a highly regioselective manner with predominant hydrogen abstraction geminal to the stannyl group. Subsequent reaction of the resulting hydroperoxides 2 with Ti(OiPr)4 afforded in a one-pot procedure the epoxy alcohols 3 in high diastereomeric excess, which ranged from 81:19 to greater than 95:5. This convenient and effective method was applied to acyclic and cyclic vinylstannanes as well as to γ-trydroxyvinylstannane 1e, which was converted into the stannyl epoxy diol 3e. In this novel hydroxy epoxidation of vinylstannanes the regioselectivity of the singlet oxygen ene reaction (Schenck reaction) is controlled by the stannyl group.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/cber.19941270818
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    Stereoselective Additions of Chiral, Functionalized Organozinc Reagents to Achiral and Chiral Aldehydes: a Matched-Mismatched Case in Organozinc Chemistry (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1447-1457 
    Details
    ISSN: 0009-2940
    Keywords: Addition Stereoselective, nonchelation-controlled ; Reagent, organozinc ; Stereodifferentiation, double ; Oligo(tetrahydrofuran) ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The additions of the enantiomerically pure organozinc reagents 17 and 33 to the THF-aldehyde 1 in the presence of the monodentate Lewis acid boron trifluoride - ether give the nonchelation-controlled addition products 7 and 36, respectively (stereoselectivity 95:5, 86:14). These results provide a route to oligo(tetrahydrofuran)s with the relative stereochemistry trans-syn-cis. A stereodirecting effect of the chiral center in the organozinc reagent 17 is found, leading to simple diastereoselectivies in the reaction with achiral aldehydes and to a matched-mismatched case in the reaction with the chiral aldehyde 1.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/cber.19941270819
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    New Cyclopropyl Building Blocks for Organic Synthesis, 28. Pd(0)-Catalysed Coupling of Cyclopropenylzinc Chlorides and Cyclopropenylstannanes  -  A New Efficient Synthesis of 1-Phenyl-, 1-Ethenyl-, and 1-Ethynyl-1-cyclopropenesDedicated to Professor Christoph Rüchardt on the occasion of his 65th birthday. (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1511-1515 
    Details
    ISSN: 0009-2940
    Keywords: Cyclopropenes, 3,3-dimethyl, 1-substituted ; Cyclopropenylzinc chlorides, coupling reactions of ; Palladium catalysis ; Cyclopropenylstannanes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: [3,3-Dimethyl-2-(trimethylsilyl)-1-cyclopropen-1-yl]zinc chloride (4) reacts with haloarenes and -alkenes as well as 1-bromo-acetylenes under Pd(0) catalysis to give the corresponding 1-phenyl-, 1-ethenyl-, and 1-ethynyl-1-cyclopropenes 6 in isolated yields ranging from 47 to 99%. The corresponding 1-cyclopropen-1-ylstannane 5 reacts with haloarenes only at higher temperatures, and the yields range from 10 to 98%, depending on the substrate and reaction conditions.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/cber.19941270826
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    Das Thermogramm einer C6H6-Chemie im Temperaturbereich von 450 bis 730°C (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1747-1753 
    Details
    ISSN: 0009-2940
    Keywords: Isomerization, thermal ; Radicals ; D-Labeling ; 1,5-Hexadiyne ; Pentafulvene ; Rearrangement, homoallyl ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Thermal Rearrangements, XXIII[1].  -  The Thermogram of a C6H6 Chemistry in the Temperature Range from 450 to 730°CThe thermal isomerization of 1,5-hexadiyne (1) and its [1,6-D2]-labeled derivative (1a) was studied in the temperature range 450-730°C and in the presence of different carrier gases (N2, H2, D2, N2/toluene). By detailed analysis (GC, GC MS, NMR) all volatile reaction products were identified and determined quantitatively by using hexafluorobenzene as an internal standard. The experimental data show clearly that the reaction products are formed by two different routes: (i) electrocyclization leading to dimethylene cyclobutene (3) at temperatures up to about 600°C and (ii) radical reaction leading to benzene (4) and pentafulvene (5) at temperatures above 550°C. Cyclopentadienylmethyl radicals are supposed to be the essential radical intermediates.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/cber.19941270926
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    1,3,5-Cyclohexatrien-1,4-diyl und 2,4-Cyclohexadien-1,4-diyl (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1765-1779 
    Details
    ISSN: 0009-2940
    Keywords: Diradicals ; NO and O2 trapping ; Heat of formation ; Energy well ; Rearrangments ; Bergman cyclisation ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Energy Well of Diradicals, V[1].  -  1,3,5-Cyclohexatriene-1,4-diyl and 2,4-Cyclohexadiene-1,4-diylThe energy profile of the Bergman rearrangement of (Z)-3-hexene-1,5-diyne (4) has been established from the NO and oxygen dependance of the trapping rate of the intermediate diradical 1 which leads to a heat of formation for 1,4-didehy-drobenzene (1) of δHOf= 138.0 ± 1.0 kcal . morl-1. By the same technique the heat of formation of 1,2,4-cyclohexatriene (2), generated by thermolysis of (Z)-1,3-hexadien-5-yne (10), gives δHOf = 105.1 ± 1.0 kcal . mol-1 which indicates a high diradical character for 2.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/cber.19941270929
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    Zur Reaktion von Bis(trimethylphosphan)titanocen mit Ketonen (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1797-1798 
    Details
    ISSN: 0009-2940
    Keywords: Titanocenes ; Fulvenes ; Solvent effect ; Ketyls ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: On the Reaction of Bis(trimethylphosphane)titanocene with KetonesFulvenes are the products of the reaction of aliphatic and aromatic ketones with bis(trimethylphosphane)titanocene in nonpolar solvents, but no formation of pinacols is observed. The mechanism is discussed.
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    URL: http://dx.doi.org/10.1002/cber.19941270931
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    Propargyl-Stabilisierungsenergie (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1781-1795 
    Details
    ISSN: 0009-2940
    Keywords: Resonance energy ; Stabilisation energy ; Propargyl resonance ; Force field calculation ; Intrinsic rotational barrier ; Single pulse shock tube ; Gasphase kinetics ; Heats of hydrogenation ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Propargyl Stabilisation EnergyFor the alkynyl-substituted olefines 1-14 activation parameters for the geometrical isomerisation have been determined in the gasphase by the single-pulse shoke-tube technique. By comparison of these barriers with the corresponding one of the isolated double bonds, each corrected by the steric energy contribution of the ground and transition state, a value of 7.8 ± 1.3 kcal · mol-1 for the propargyl stabilisation energy (PrSE) has been derived.
    Additional Material: 11 Tab.
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    URL: http://dx.doi.org/10.1002/cber.19941270930
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    Synthesis of Novel Heteroaromatic Polyfused as-Triazines by Ring Transformation[1] (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1799-1802 
    Details
    ISSN: 0009-2940
    Keywords: as-Triazinium salt, fused ; Ring opening ; Ring transformation Heteroaromaticity ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ring transformation of the tricyclic furo-fused as-triazinium salt 1 in the presence of nucleophilic reagents (e.g. sodium hydrogensulfide, sodium salts of malonic ester, ethyl cyanoacetate, acetylacetone, dimedone, or malononitrile) leads to the two new heteroaromatic ring systems thieno[2,3-e]pyrido[1,2-b]-as-triazinium salt (5) and differently substituted cyclopenta[e]pyrido[1,2-b]-as-triazine compounds (8, 9, 10, 11, and 13).
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    URL: http://dx.doi.org/10.1002/cber.19941270932
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    Wanzlick-Carbene in der [4 + 1]-Cycloaddition mit Bis(methylthio)- und Bis(trifluormethyl)-1,2,4,5-tetrazin (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1803-1806 
    Details
    ISSN: 0009-2940
    Keywords: Singlet carbenes ; [4 + 1] Cycloadditions ; 1,2,4,5-Tetrazines ; SEAr reactions, intramolecular ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Wanzlick Carbenes in the [4 + 1] Cycloaddition Reaction with Bis(methylthio)- and Bis(trifluoromethyl)-1,2,4,5-tetrazineThe 3,6-disubstituted 1,2,4,5-tetrazines 3 and 4 have been submitted to a [4 + 1] cycloaddition reaction with the nucleophilic singlet carbenes (Wanzlick carbenes) 2a-d, which are generated from the precursors 1a-d. With 3 as diazadiene the expected spiro compounds 6a-d are formed. In contrast to this presumed two-step reaction sequence of 3, with the tetrazine 4 the cascade cycloaddition/cycloelimination is surprisingly followed by an intramolecular electrophilic aromatic substitution to yield the chiral tetracyclic compounds of type 8 with high diastereoselectivity. The crystal structure of 8d has been determined by X-ray diffraction methods.
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    [2,3]-Thia-Wittig Rearrangements of α-Lithiated Sulfides Via De-aromatized Cyclohexadiene Intermediates Proceed with Inversion of Configuration at the Carbanionic Center (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1949-1957 
    Details
    ISSN: 0009-2940
    Keywords: Stannanes, α-(alkylthio) ; Wittig rearrangement ; Configurational stability ; α-Lithio sulfides ; [2,3] Rearrangement ; Stereoselectivity ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The nBuLi-induced tin/lithium exchange reactions of the di-astereomeric γ-[(methoxyethoxy)methoxy]-]α-(tributylstannyl) sulfides anti- and syn-8 delivered the α-(lithioalkyl) benzyl sulfides anti- and syn-11, respectively. Within 1 h at -78°C, these species underwent [2,3]-thia-Wittig rearrangements in THF via the de-aromatized cyclohexadiene intermediates syn- and anti-12. Tautomerization and protonation yielded 81:19 (85%) and 19:81 mixtures (96%) of the ortho-functionalized toluenes syn- and anti-13. Probably, both Wittig rearrangements proceeded with 100% inversion of configuration at the carbanionic stereocenter, and the overall loss of stereoselectivity is due to an epimerization anti-11 ⇌ syn-11 of the lithio sulfide intermediates at a rate which is 3.3 times slower than the rearrangement.
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/cber.19941271019
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    (R)-1,2,2-Triphenyl-2-(trimethylsiloxy)ethyl Propionate: anti-Selective and Diastereofacially Selective Aldol Addition; Diastereoselective Silylation and Alkylation (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1959-1968 
    Details
    ISSN: 0009-2940
    Keywords: Aldol reaction ; Chiral etiolate ; Mandelic acid ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The propionates (R)-5 and (R)-6 which are derived from the readily available chiral auxiliary reagent (R)-triphenylglycol (4) have been applied in stereoselective aldol reactions. Whereas the enolate 7 and the silyl ketene acetal 12, both generated from the ester (R)-6, display only moderate diastereoselectivity when treated with benzaldehyde, ß-hydroxyesters 8b and 16a, b are formed in diastereomeric ratios up to 95:5 (ratio of the main product to the sum of all other stereoisomers) when the propionate (R)-5 is subsequently deprotonated, transmetalated into the zirconium enolate and allowed to react with aldehydes. Alkaline hydrolysis or reduction with LiAlH4 enables the conversion of the adducts 8a and 16a
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    URL: http://dx.doi.org/10.1002/cber.19941271020
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    Synthesis and Reactions of 7-Oxonorbornane-2,3-dicarboximides (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1933-1947 
    Details
    ISSN: 0009-2940
    Keywords: 7-Oxonorbornane-2,3-dicarboximides ; Reductive amination ; 4,7-Methanoisoindoles ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ozonizations of several 7-isopropylidenenorbornane-2,3-dicarboximides (2, 10) yield 7,7-dihydroxynorbornane-2,3-dicarboximides (3, 11) and/or 7-oxonorbornane-2,3-dicarboxi-mides (4, 12). Dehydration of the dihydroxy derivatives to the corresponding carbonyl compounds can be carried out by reaction with P2O5 in an aprotic solvent. Reaction of hydrates 3 with methanol gives mixtures of the stereoisomeric hemiacetals 13 and 14, whereas reaction with other nucleophiles give only the stereoisomer derived from attack by the less hindered carbonyl face. Thus NaBH4 or Al(iPRO)3 reduction of 3 or 4 yields alcohols 15 and LiAlH4 reduction of 3 or 4 amino alcohols 16. Reaction of 4b with phenylmagnesium bromide gives alcohol 22 and a direaction product (rac-26) that easily dehydrates to a tetracyclic compound (rac-30). Reductive aminations of 3 or 4 lead to amines 19 directly or via imines rac-20 and amines 23. LiAIH4 reduction of amine 23b affords tricyclic compounds (rac-27) and (rac-28). The last one was converted to diamine 24 by reduction with NaBH3CN. Similarly, amine 21 was converted into diamine 25, partially via aminal 29 as intermediate. The structures of compounds 3b, 19a, rac-27, and rac-30 have been established by X-ray diffraction analysis.
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    Enantioselektive Protonierung von Lacton-EnolatenHerrn Professor Helmut Werner zum 60. Geburtstag gewidmet. (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1969-1980 
    Details
    ISSN: 0009-2940
    Keywords: Protonation ; Enantioselectivity ; Lactone enolates ; Chiral proton sources ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stereoselective Protonation of Carbanions, 4[1].  -  Enantioselective Protonation of Lactone Enolates[2]The prochiral lithium enolates derived from the five-membered lactones rac-1 and rac-2 were protonated by 37 OH-and 21 NH-chiral proton sources in THF at  -  78°C. The enantioselectivities, determined directly from the reaction mixture by chiral HPLC, are always higher for system 1, probably due to restricted rotation of the phenyl group in 1Li at low temperature (NMR) and range from 0-54% ee. The strongest stereodifferentiation is observed if the OH or NH acids carry an adjacent O- or N-containing group (structures G-J) which allows complexation with the lithium ion. A plausible transition state involving the dimeric lithium enolate is proposed.
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    Hexakis(alkylthio)-Substituted Unsymmetrical Phthalocyanines (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 2009-2012 
    Details
    ISSN: 0009-2940
    Keywords: Phthalocyanines, unsymmetrical, soluble ; Boron complex ; Phthalonitrile derivatives ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cyclotrimerization of 4,5-bis(hexylthio)phthalodinitrile (1) in 1-chloronaphthalene in the presence of BCl3 leads to the subphthalocyanine 4. Unsymmetrical phthalocyanines (5, 6) with six alkylthio substituents on three of the benzenoid units are synthesized by the reaction of 4 with an diiminoisoindoline derivative (R′ = H or NO2). These extremely soluble compounds are characterized by IR, 1H- and 13C-NMR as well as UV/Vis spectra.
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    URL: http://dx.doi.org/10.1002/cber.19941271025
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    Enantioselektive Protonierung von γ-Butyrolacton-EnolatenHerrn Professor Wolfgang Lüttke zum 75. Geburtstag gewidmet. (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1989-1992 
    Details
    ISSN: 0009-2940
    Keywords: Enantioselectivity ; Protonation ; Ester enolates ; Lactones ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stereoselective Protonation of Carbanions, 6[1].  -  Enantioselective Protonation of γ-Butyrolactone Enolates*The lithium enolates 3Li-7Li, produced from 3-7 by LDA or LiHMDS in THF, are protonated with eleven chiral proton sources at -78°C in THF which produced high enantioselectivities with 1Li and 2Li[5]. Although the enolates (3Li, 6Li, 7Li) are not deuterated quantitatively[1], 1H- and 13C-NMR spectra in THF at -78°C reveal not only quantitative deprotonation (3Li, 6Li) but also aggregation (dimerisation) and hindered rotation of the phenyl group in 3Li. From comparison of the enantioselectivities produced by five chiral proton sources with 1Li-6Li (Tab. 4) definite structure/selectivity correlations can not be derived both for the enolates and the proton sources.
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    URL: http://dx.doi.org/10.1002/cber.19941271023
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    Einfluß der Reaktionsbedingungen auf die enantioselektive Protonierung von Lacton-EnolatenProfessor Helmut Quast zum 60. Geburtstag gewidmet. (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1981-1988 
    Details
    ISSN: 0009-2940
    Keywords: Enantioselectivity ; Protonation ; Solvent effects ; Lewis acids ; Lithium salts ; Deuteration ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stereoselective Protonation of Carbanions, 5[1].  -  Effects of Reaction Conditions on the Enantioselective Protonation of Lactone Enolates[2]Protonation of the enolates 1Li and 2Li by using standard conditions yields enantioselectivities up to 54 and 50% ee, respectively, depending on the chiral proton source[1]. These values may change dramatically by the following variations (standard ee's in parenthesis): (i) In Et2O/THF (90:10) (S)-2 with 72% ee (44%) is formed with (R)-pantolactone (3) but only 48% ee (39%) with (R,R)-tartaric ester 4 (Figure 1). (ii) Lewis acids may produce rac-2 (SnCl2, MgBr2) or definitely increase the enantioselectivity: With lactone 3: 46% ee (44%); with esters 4: 48% ee (39%); with bissulfonamide 7: 67% ee (47%) (Table 1, 2). (iii) Lithium chloride (2-4 equiv.) in THF yields (S)-1 with 68% ee (47%) and (S)-2 with 77% ee (39%) but only if ester 4 ist employed as chiral proton source (Figure 2). (iv) Chiral Lewis bases create (S)-2 with up to 30% ee on protonation with achiral acids (Table 3, 4). (v) Deuteration of 2Li ranges from 16 to 95% depending on the nature of the base as well as the deuteron source. The degrees of deuteration and enantioselectivity are not correlated. All results demonstrate the complexity of enantioselective protonation of enolates which still needs empirical optimization.
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    Oligooxa[3n.3]paracyclophane Quinhydrones  -  Cation-Induced Charge-Transfer Absorptions and Structures of the Metal Complexes (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1993-2008 
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    ISSN: 0009-2940
    Keywords: Electron donor-acceptor cyclophanes ; Charge-transfer compounds ; Crown ethers ; Oligooxaparacyclophane metal complexes, charge-transfer absorption of, crystal structures of ; Cyclophanes, electron donor-acceptor ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The intramolecular oligooxa[3n.3]paracyclophane quinhy-drones 2-5 (with n = 3 to 6) were synthesized and their interactions with alkali and alkaline earth metal and mercury(II) ions were studied by electron absorption and NMR spectroscopy. Remarkable enhancements of the CT absorptions were observed by complexation with metal ions of the pentaoxa[15.3]paracyclophane quinhydrone 4 and the hexaoxa[18.3]paracyclophane quinhydrone 5 to the corresponding complexes 6a-e and 7, respectively. The various donor-acceptor orientations and the crown ether-like complexation in the calcium complex 6d, the mercury complex 6e and the barium complex 7 were determined by X-ray analysis. Moreover, the X-ray structures of the tetramethoxy-2,5,8-trioxa[9.3]paracyclophane 8a, a precursor of the quinhydrone 2, and of the pentaoxa[15.3](2,5)-p-benzoquinonophane 20, the product of oxidative demethylation of the quinhydrone 4, are given. For comparison with the cyclic quinhydrones acyclic analogs are also described.
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    Neue Synthesen von Methyleniminium-Salzen aus Carbonylverbindungen und aus α-Chlorethern; ein Zugang zu vinylogen Viehe-Salzen* (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 2013-2022 
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    ISSN: 0009-2940
    Keywords: Methyleniminium salts, preparation, mechanisms of formation ; (Dialkylamino)trimethylsilanes ; Ethers, α-chloro ; Viehe salts, vinylogous ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New Syntheses of Methyleniminium Salts from Carbonyl Compounds and from α-Chloro Ethers; an Access to Vinylogous Viehe Salts*Two methods for the synthesis of isolable methyleniminium salts and amidinium salts are presented. In the first case carbonyl compounds A are treated with a mixture of (dialkyl-amino)trimethylsilane (12) and chlorotrimethylsilane (13) or 12 and trimethylsilyl triflate (14) leading to the iminium chlorides F or iminium triflates G, respectively. With 12/13 the preparation of F is limited to non-enolizable aldehydes and dimethylformamide (10), while 12/14 enables the preparation of G, e.g. 23a-25a, 27a, also with ketones and with substituted amides. The second procedure is based on the treatment of α-chloro ethers L with 12. Both methods afford the Mannich reagent 16a in high yields. By reaction of the α-chloro ether 35 with 12 in diethyl ether the vinylogous Viehe salts 36a-c, e become available for the first time. The reaction pathways are discussed.
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    Dithiacyclooctine (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 2035-2041 
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    ISSN: 0009-2940
    Keywords: Alkynes ; Cycloalkynes ; Strain, steric ; Cycloaddition reactions ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enthalpies of formation ΔHf and the ring strain energies Eg were calculated for the nine isomeric dithiacyclooctynes 1--9 by applying the MNDO method. Reaction Scheme 2 shows the synthesis of 1,4-dithia-2-cyclooctyne (1), which was the highest Eg value in this series. It dimerizes to 13 in the absence of reaction partners. Scheme 4 summarizes the preparation of 1,5-dithia-2-cyclooctyne (2) and its homologue 1,5-dithia-2-cyclononyne (23) and Scheme 6 the preparation of 1,4-dithia-6-cyclooctyne (6) and its homologue 1,5-dithia-7-cyclononyne (29). Depending on the position of the sulfur atoms, all three reaction sequences contain different steps for the introduction of the triple bonds.
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    URL: http://dx.doi.org/10.1002/cber.19941271028
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    Diastereoselective Synthesis of α-Hydroxy- and α-Aminoindolizidines and -quinolizidines. Evidence for a Novel Cyclization/Hydride Migration Mechanism in the TiCl4-Induced Reaction of Prolinal Benzylimines by Deuterium Labeling Studies (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 2023-2034 
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    ISSN: 0009-2940
    Keywords: Imines ; Indolizidines ; Quinolizidines ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Lewis acid-catalyzed cyclization of prolinal and 2-piperidine-carbaldehyde benzylimines 11, 12 results in the diastereoselective formation of α-amino-β-alkyl-substituted indolizidines 15, 17, 19, 21 and -quinolizidines 16, 18, 20, respectively. Both diastereoselectivity and constitution depend on the Lewis acid. FeCl3 yields α,β-trans-α-(benzylamino)-β-isopropenyl derivatives 15 and 16, probably by a cationic cyclization via carbenium ions 32a, b. In contrast, TiCl4 yields α,β-cis-α-(benzylideneamino)-β-isopropyl derivatives 19 and 20 by a novel cyclization/intermolecular hydride transfer mechanism, which was supported by deuterium labeling studies. Compounds 15, 16, 19, and 20 were converted to the diastereomeric acetamides 24, 25 and 28, 29. By an analogous cyclization of the aldehydes 8 and 9 only α,β-cis-α-hydroxy-β-isopropenylindolizidines 51 and -quinolizidines 52 were obtained irrespective of the Lewis acid used. The structures of 30 and 52 were elucidated by X-ray analysis.
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    Thianthren-Radikalkation-Tetrachloroaluminat (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 2043-2049 
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    ISSN: 0009-2940
    Keywords: Thianthrene radical cation salt ; Crystallization ; Calculations ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Structures and Molecular Properties of Charge-Perturbed Molecules, 53[1,2].  -  Thianthrene Radical Cation TetrachloroaluminateOne-electron oxidation of thianthrene, which exhibits a reversible half-wave potential at + 1.3 V and an irreversible one at + 1.65 V, under aprotic conditions with AlCl3/H2CCl2 yields the violet radical cation salt [H4C6S2C6H4⊕][AlCl4⊖]. Its single-crystal structure analysis at 90 K reveals an interplanar angle between the phenyl rings of 174° and demonstrates that the neutral sulfur heterocyclic molecule, bent by 128°, is considerably flattened upon one-electron removal. Semiempirical enthalpy of formation hypersurfaces allow to rationalize the experimental results by a double-minimum potential for the bent neutral molecule with a rather low inversion barrier and a single minimum one for a planar radical cation. Other radical cation properties such as the spin distribution deduced from its ESR spectrum or the visible absorption maxima near \documentclass{article}\pagestyle{empty}\begin{document}$ \tilde \nu $\end{document} = 11000 and at 18250 cm-1 corresponding to π → π* and π → σ* transitions are also satisfactorily reproduced by PM3 calculations partly including configuration interaction based on the experimental structure.
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    Synthesis, Separation and Characterization of Unsymmetrically Substituted PhthalocyaninesDedicated to Professor E. Lindner on the occasion of his 60th birthday. (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 2051-2057 
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    ISSN: 0009-2940
    Keywords: Phthalocyanines, unsymmetrically substituted, chromatographic separation ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Unsymmetrically substituted (phthalocyaninato)nickel(II) complexes -7 were synthesized by statistical condensation of 4,5-dipentoxy- (2a), 4,5-diheptyl- (2b), 3,6-dihexoxy- (2c), and 3,6-diheptylphthalonitrile (2d) with 3,4,5,6-tetraphenylphthalonitrile (1) and separated by column chromatography. The obtained phthalocyanines 3-7 were characterized by UV-, IR-, and 1H-NMR spectroscopy.
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    X-Ray Crystal Structures of the Enolate of tert-Butyl α-Cyanoacetate with Li+ or Protonated 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU-H+) as Gegenion. N - H Hydrogen Bridge from DBU-H+ to the Enolate Oxygen Atom (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 2059-2064 
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    ISSN: 0009-2940
    Keywords: Enolate of tert-butyl cyanoacetate with Li+ or DBU-H+ as gegenions ; Hydrogen bridge from DBU-H+ to the enolate oxygen atom ; Enolates of cyanoacetates, reaction with electrophiles ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: For the first time a solid-state structure with protonated 1,8-diazobicyclo[5.4.0]undec-7-ene (DBU-H+) as the gegenion of an “organic” anion, namely tert-butyl α-cyanoacetate (2-), is determined. The DBU-H+ N - H bond forms a hydrogen bridge to the enolate oxygen atom of 2-, the first N-H bridge to an enolate oxygen atom ever characterized. The structure of 2- DBU-H+ is compared with that of the corresponding lithium compound [2- Li+ · TMEDA]2 in which the cations are bound to the N atoms of the cyano groups and the enolate O atoms forming a twelve-membered ring. Literature reports on the rather different chemistry of anions like 2- having alkali metal ions or DBU-H+, respectively, as the gegenions can be understood by means of the two new solid-state structures disclosed in this publication.
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    Metalloragnische Verbindungen der Lanthanoide, 90[1] [(tert-Butylcyclopentadienyl)dimethyl(tetramethylcyclopentadienyl)silan]-Komplexe von Lanthan, Neodym und Lutetium (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 2363-2367 
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    ISSN: 0009-2940
    Keywords: Cyclopentadienyl complexes ; Lanthanum compounds ; Neodymium compounds ; Lutetium compounds ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Organometallic Compounds of the Lanthanides, 90[1]. - [(tert-Butylcyclopentadienyl)dimethyl-(tetramethylcyclopentadienyl)silane] Complexes of Lanthanum, Neodymium, and Lutetium[(tBuC5H3)SiMe2(C5Me4)]Li2 (1) reacts with LnCl3 (Ln = La, Lu) in THF to yield [(tBuC5H3)SiMe2(C5Me4)]Ln(μ-Cl)2Li-(OEt2)2 [Ln = La (3a), Lu (3c)]. The reactions of LnCl3 (Ln = La, Nd) with [(tBuC5H3)SiMe2(C5Me4)]Na2 (2) and (C5Me4H)Na in THF result in the formation of the chiral tris(cyclopentadienyl) complexes [(tBuC5H3)SiMe2(C5Me4)]Ln-(C5Me4H)(THF) [Ln = La (4a), Nd (4b)]. The 1H- and 13CNMR and mass spectra of the new compounds as well as the X-ray crystal structure of 4a are discussed.
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    URL: http://dx.doi.org/10.1002/cber.19941271204
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    Titan-, Zirconium- und Hafniumkomplexe mit 1,2,4-Tri-tert-butylcyclopentadienyl-LigandenHerrn Professor Otto J. Scherer zum 60. Geburtstag gewidmet. (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 3-9 
    Details
    ISSN: 0009-2940
    Keywords: 1,2,4-Tri-tert-butylcyclopentadienyl complexes ; Group IV metallocene derivatives ; Titanocene dichloride, alkylated ; Zirconocene dichloride, alkylated ; (Cyclopentadienyl)hafnium trichloride ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Titanium-, Zirconium- and Hafnium Complexes with 1,2,4-Tri-tert-butylcyclopentadienyl LigandsLithium salts of easily available 1,3,5-tri-tert-butylcyclopentadiene and 1,2,3,4,5-pentaethylcyclopentadiene are used to synthesize the trichlorides [Cp‴MCl3] [Cp‴ = C5H2tBu3-1,2,4; M = Zr (1), Hf (2), Ti (3)] and [(Et5C5)ZrCl3] (4). Complex 1 is converted into the mixed zirconocene dichlorides [Cp‴CpZrCl2] (5), [Cp‴Cp-ZrCl2] (6), [Cp‴Cp″ZrCl2] (7), [Cp‴Cp4ZrCl2] (9) (Cp = C5H5, Cp* = C5Me5, Cp″ = C5H3tBu2-1,3, Cp4 = C5iPr4H) and into the benzyl complexes [Cp‴Zr(PhCH2)2Cl] (10) and [Cp‴Zr(PhCH2)3] (11). Variable-temperature 1H-NMR spectra of 6-9 (8 is the Ti analogue of 7) indicated hindered oscillation of the Cp‴ ligand with ΔG≠ values between ≤8 kcal/mol (7, 9) and 13.2 kcal/mol (6). X-ray structural analyses of complexes 7 and 9 reveal strong distortions owing to extreme steric congestion.
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    Functionalized, 1,1-Ethenedithiolates as Ligands, III. Palladium(II) and Platinum(II) Complexes with Ferrocenyl-Substituted 1,1-Ethenedithiolate Ligands. Crystal Structure Analyses of cis-(Ph3P)2M[S2C=CH—C(O)-(η5-C5H4)Fe(η5-C5H5)] (M = Pd, Pt)Dedicated to Professor Dr. Dr. h. c. mult. E. O. Fischer on the occasion of his 75th birthday. (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 23-26 
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    ISSN: 0009-2940
    Keywords: Ferrocene derivatives ; 1,1-Ethenedithiolate complexes ; Group 10 metal complexes ; Heterodimetallic compounds ; Heterotrimetallic compounds ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ferrocenyl-substituted mono- (3) and 1,1′-bis-dithiocarboxylic acids (4) have been prepared. These acids react with L2MCl2 (M = Pd, Pt; L = PEt3, PPh3, and 1/2 dppe) in the presence of sodium acetate to give the cis heterodi- and heterotrimetallic complexes cis-L2M[S2C=CH—C(O)-(η5-C5H4)Fe(η5-C5H5)] (5a: M = Pd, L = PPh3; 5b: M = Pt, L = PPh3; 5c: M = Pt, L = 1/2 dppe) and [cis-L2MS2C = CH—C(O)-(η5—C5H4)]2Fe (6a: M = Pd, L = PPh3; 6b: M = Pt, L = PEt3; 6c: M = Pt, L = PPh3; 6d: M = Pt, L = 1/2 dppe). The structures of 5a and 5b have been determined by single-crystal X-ray diffraction.
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    URL: http://dx.doi.org/10.1002/cber.19941270105
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    η3-Allyl- und η3-Benzyl-Rhodiumkomplexe: Synthese, Strukturdynamik und Reaktionen mit Carbonsäuren (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 27-38 
    Details
    ISSN: 0009-2940
    Keywords: η3-Allylrhodium complexes, preparation with Grignard reagents ; η3-Benzylrhodium complexes, antara- and suprafacial rearrangements in solution ; Unsymmetrical η3-benzyl-to-metal bonding in the solid state ; Rhodium, η1-benzyl(carbonyl) compound ; Rhodium, monomeric square-planar η2-carboxylato complexes ; η3-Allyl(η1-carboxylato)hydridometal intermediates, formation by oxidative addition ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: η3-Allyl and η3-Benzyl Rhodium Complexes: Synthesis, Structure Dynamic, and Reactions with Carboxylic AcidsThe (η3-allyl)rhodium complexes [Rh(η3-2-RC3H4)(PiPr3)2] (3-5) have been prepared in 70-90% yield from the in situ generated chlororhodium precursor [RhCl(PiPr3)2] (2) and 2-RC3H4MgX. On a similar route, the corresponding ethene(phosphane) derivative [Rh(η3-2-MeC3H4)(PiPr3)] (9) has been obtained. Compound 9 smoothly reacts with PiPr3 and PMe3 to give 4 (R = Me) and [Rh(η3-2-MeC3H4)(PMe3)-(PiPr3)] (10), respectively. In contrast to the η3-allyl complexes which are configurationally stable, the η3-benzyl analogues [Rh(η3-CH2C6H4R) (PiPr3)2] (11, 12), prepared from 2 and 4-RC6H4CH2MgCl, are highly fluctional in solution. At room temperature, an antarafacial (π-δ-π) as well as a suprafacial rearrangement occurs, the first one of which is frozen out at 263 K. On cooling to 193 K, the faster process (equally designated as a metallotropic shift) is also slowed down, and the rigid structure of 11 and 12 is observed. The ΔG* values for the antara and suprafacial rearrangements of 11 and 12 which have been determined from the 1H- and 31P-NMR spectra at variable temperature are 60.0 ± 1.5 and 39.5 ± 1.0 kJ/mol, respectively. The η3-benzyl compound 11 reacts even at -78°C with CO to give the monocarbonylrhodium(I) complex trans-[Rh(η1-CH2C6H5)(CO)(PiPr3)2] (13). Treatment of 3,4, or 11 with RCO2H (R = CF3, CH3, C6H5, C6H4-4-OMe, C6H4-4-NO2) affords the monomeric η2-carboxylatorhodium(I) compounds [Rh(η2-O2CR) (PiPr3)2] (14-18) almost quantitatively. If the reaction of 3 or 4 with CF3CO2H is performed at -20°C in pentane, the octahedral (η3-allyl)hydrido complexes [Rh(η3-2-RC3H4)(H)(η1-O2CCF3)(PiPr3)2] (19, 20) are isolated. The crystal structures of 12 (at 223 K) and of 15 (at 298 K) have been determined by X-ray diffraction studies. They confirm that the η3-benzyl ligand is highly unsymmetrically and the acetato ligand completely symmetrically bound to the [Rh(PiPr3)2] unit.
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    (2,4,6-iPr3C6H2)(tBu)Si(AsH2)2: Das erste Diarsanylsilan und seine Umwandlung in ein 1,3-Diarsa-2-sila-4-germacyclobutan und ein 1,3-Diarsa-2-sila-4-germabicyclo[1.1.O]butan-DerivatHerrn Prof. Dr. Otto J. Scherer zum 60. Geburtstag gewidmet. (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 477-480 
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    ISSN: 0009-2940
    Keywords: Diarsinosilane ; 1,3-Diarsa-2-sila-4-germacyclobutane ; 1,3-Diarsa-2-sila-4-germabicyclo[1.1.0]butane ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (2,4,6-iPr3C6H2)(tBu)Si(AsH2)2: The First Diarsanylsilane and Its Transformation into a 1,3-Diarsa-2-sila-4-germabicyclobutane and a 1,3-Diarsa-2-sila-4-germabicyclo[1.1.0]butane Derivative*The crowded diarsanylsilane (2,4,6-iPr3C6H2)(tBu)Si(AsH2)2 (1) is synthesized by the reaction of (2,4,6-iPr3C6H2)(tBu)-SiCl2 with two equivalents of [LiAsH2(dme)] in 80% yield. Treatment of 1 with two equivalents of nBuLi yields the dilithio compound 7, which reacts with Mes(tBu)GeF2 to give the corresponding 1,3-diarsa-2-sila-4-germacyclobutane 8. The X-ray crystal structures of 1 and 8 were determined. The bond angles at silicon of 1 lie between 113.0(4) and 96.1(4)° indicating a distorted tetrahedral geometry. The four-membered SiGeAs2 ring in 8 is puckered (As1-Si1-As2/As1-Ge1-As2 23.5°) with the two tBu groups being transoriented. Dilithiation of the AsH positions in 8 with nBuLi and subsequent reaction with tBuHgCl leads to the 1,3-bis-(tert-butylmercurio) compound 9. The light-induced elimination of the tBu groups in 9 gives the tBu/tBu-exo,endo-SiGeAs2-bicyclo[1.1.0]butane 10 in 91% yield. 10 does not rearrange to the exo,exo isomer 11.
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    Transanulare Wechselwirkungen in difunktionellen mittleren Ringen, 4. Spektroskopische und theoretische Untersuchungen an bicyclischen Boraalkenen (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 509-518 
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    ISSN: 0009-2940
    Keywords: 3-Borabicyclo[3.3.1]nonanes ; 7-methylene ; 3-Borabicyclo[3.3.1]non-6-enes ; Photoelectron spectroscopy ; Electronic structure ; Conformational analysis ; Transanular interaction ; Calculations, MMX, AM1 ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Transanular Interactions in Difunctional Medium Rings, 4[1].  -  Spectroscopic and Theoretical Investigations on Bicyclic BoraalkenesThe 3-borabicyclo[3.3.1]nonene and -nonane derivatives 3 and 5 with an endo- or exocyclic CC double bond, respectively, have been synthesized as well as the corresponding monofunctional compounds bicyclo[3.3.1]non-2-ene (1), 3-methylenebicyclo[3.3.1]nonane (2), and the 3-borabicyclo[3.3.1]nonanes 4. The compounds were investigated by PE, 13C- and 11B-NMR spectroscopy. In addition, molecular mechanics and semi-empirical quantum-chemical calculations have been performed. Although the transanular distances in both groups of compounds vary little, the difunctional compounds with an exocyclic double bond (5) show distinct transanular interactions whereas in the compounds with an endocyclic double bond (3) such effects are virtually absent. While the theoretical methods proved to be insufficient for the investigation of transanular interactions, PE and 11B-NMR spectroscopy were well suited for this study.
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    Zur Bildung eines Fe2(CO)6-Komplexes mit (Boryloxy)allyl-Brücke (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 91-92 
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    ISSN: 0009-2940
    Keywords: Boranes, amino(imino) ; Iron, tricarbonyl(butanone) ; Diiron, [(boryloxy)allyl]hexacarbonyl ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: On the Formation of a Fe2(CO)6 Complex with a (Boryloxy)allyl BridgeThe amino(imino)borane Me3Si(tBu)N=B=NtBu (1) reacts with (benzylideneacetone)tricarbonyliron (2) in 1:2 molar ratio to give a 50% yield of the hexacarbonyldiiron complex 3 with a fly-over (boryloxy)allyl bridge, which crystallizes in the space group P21/c. The structure of 3 can be described as a pyramid with Fe(CO)3 at the apex and a non-planar pentagon [-Fe(CO)3-O(BXX′)-C(Me)-CH-C(Ph)-] [X = NHtBu, X′ = N(SiMe3)tBu] as the basis, but there is no bond between the apex and the O atom.
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    Bis(pentamethylcyclopentadienyl)methanol: Synthese, Struktur und Derivatisierung (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 107-112 
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    ISSN: 0009-2940
    Keywords: Bis(pentamethylcyclopentadienyl)methanol ; Diels-Alder reaction, intramolecular ; Chloroformate, bis(pentamethylcyclopentadienyl)methanol ; Tosylate, bis(pentamethylcyclopentadienyl)methanol ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bis(pentamethylcyclopentadienyl)methanol: Synthesis, Structure, and DerivatizationBis(pentamethylcyclopentadienyl) ketone (1) reacts at low temperatures with LiAlH4 to form in good yields (pentamethylcyclopentadienyl)methanol (2) and its corresponding intramolecular Diels-Alder product 3 in a ca. 2:1 ratio. The alcohol 2 is separated from the tetracyclic compound 3 by crystallisation at -70°C from hexane/pyridine as pyridine adduct. The pyridine-free alcohol 2 is available by repeated dissolving of the adduct in hexane and removal of the volatile components in vacuo. The alcohol tends to intramolecular [4 + 2] cycloaddition even at room temperature with formation of 3. A derivatization of 2 is possible by deprotonation with alkyllithium compounds, which leads to the alcoholate 4, and subsequent treatment with phosgen and tosyl chloride, thus affording the chloroformate 6 and the tosylate 7, respectively, in good yields. The thermolabile tosylate 7 decomposes to pentamethylbenzene or, under basic conditions, to the pentacyclic compound 7.
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    Kleine Ringe, 79. Synthese und Eigenschaften neuer Silyl-substituierter Cyclobutadiene und Tetrahedrane (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 191-200 
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    ISSN: 0009-2940
    Keywords: Diazo compounds ; Valence isomerization ; „Corset effect“ ; limits of ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Small Rings, 79[1].  -  Synthesis and Properties of Novel Silyl-Substituted Cyclobutadienes and TetrahedranesThe cyclobutadienes 2b, d as well as the corresponding tetrahedranes 3b, d have been prepared according to the “Masamune route” by starting from the diazo compounds 1b, d. Low-temperature 13C—NMR measurements of the cyclobutadienes 2a, b, d lead to the first exact values of the barrier heights in the interconversion of the two rectangular forms of the cyclobutadienes. Fluorodesilylation of 3d probably proceeds via tri-tert-butyltetrahedrane (3h) and cyclobutadiene 2h and finally yields diketone 18. Reaction of tetrahedrane 3d with LiAlH4 in boiling THF leads to tetrahedrane 3e, which is much less stable than all previously known tetrahedrane derivatives.
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    Relative Reactivities of Acetals and Ethers under Friedel-Crafts Conditions (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 213-217 
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    ISSN: 0009-2940
    Keywords: Alkylation ; Alkoxyalkylation ; Carboxonium ions ; Acetals ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Competition experiments have been performed to determine the relative reactivities of acetals and ethers toward allyltrimethylsilane in the presence of catalytic amounts of BF3 OEt2. It is found that acetals R-CH(OMe)2 and their phenylogous p-anisyl ethers R-CH(p-MeOC6H4)(OMe) show very little differences in reactivity. The reactivity scales are employed to rationalize the results of Lewis acid-catalyzed additions of acetals and ethers to CC double bonds.
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    Gas-Phase Kinetics of the Pyrolysis of Some 3,3-Dimethyl-1-(trimethylsilyl)-cyclopropenes  -  Unexpected Product Distribution in the Cyclopropene Rearrangement (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 237-245 
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    ISSN: 0009-2940
    Keywords: Cyclopropenes, 3,3-dimethyl-1-trimethylsilyl-substituted ; Cyclopropene, isomerisation ; Gas-phase kinetics ; Ring opening ; Diradical intermediates ; Cyclopropylidene intermediates ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The gas-phase pyrolyses of 1,3,3-trimethyl-2-(trimethylsilyl)-cyclopropene (9), 3,3-dimethyl-1,2-bis(trimethylsilyl)cyclopropeneTextReactantlog (A/s-1)Ea/kj mol-1(kcal mol-1)913.41 ± 0.22192.1 ± 2.5(45.9 ± 0.6)1013.54 ± 0.19184.4 ± 2.1(44.1 ± 0.5)1112.17 ± 0.38124.6 ± 3.1(29.8 ± 0.7)(10), and 3,3-dimethyl-1-(methylthio)-2-(trimethylsilyl)cyclopropene (11) have been studied, and the pressure-independent Arrhenius parameters listed in the table were obtained. All three rearrangements are homogeneous, first-order and unimolecular reactions. Rather surprisingly all reactions give the corresponding isomeric allenes as the main products. Amongst possible mechanisms discussed, 10 is proposed to react via a cyclopropylidene intermediate, whilst the results for 9 and 11 throw light on the relative importance of the diradical- and vinylcarbene-type intermediates produced by cyclopropene ring opening.
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    Graphical Abstract (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. A5 
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    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    URL: http://dx.doi.org/10.1002/cber.19941270139
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    Masthead (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994) 
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    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19941270101
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    Thermal Rearrangements, XXII. The Propargyl-Cope Rearrangement of meso- and d,l-3,4-Dimethyl-1,5-hexadiyne-3,4-diol (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 959-963 
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    ISSN: 0009-2940
    Keywords: Rearrangements, thermal ; Propargyl-Cope reaction ; 1,5-Hexadiyne-3,4-diol ; Cyclobutene ; 3,4-diacetyl ; Fragmentations, retro-ene ; Tandem reactions ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal behavior of meso- and d,1-3,4-dimethyl-1,5-hexadiyne-3,4-diol (meso- and d,1-4) has been studied at 400°C in the gas phase. In a tandem reaction the diols isomerize via the bisallenes 5 first to cis- and trans-3,4-diacetylcyclobutene (cis- and trans-8) which have been detected as intermediates by 13C-NMR spectroscopy as well as catalytic hydrogenation to 1,2-diacetylcyclobutane (9). Subsequently, 8 stabilizes itself by ring opening to (E,Z)- and (E,E)-3,5-octa-dien-2,7-dione (E,Z) and [(E,Z)-6]. As a side reaction retroene cleavage of 4 to 2-butynone (10) and methyl vinyl ketone (12) is observed. By pyrolysis of the pure diastereomers 4 it is shown that the retro-ene process is more pronounced in the d,l than in the meso series.
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    URL: http://dx.doi.org/10.1002/cber.19941270526
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    The supramolecular structures of complex tri[gold(I)]sulfonium cations (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 2387-2391 
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    ISSN: 0009-2940
    Keywords: Gold(I) complexes ; Sulfonium salts ; Trigoldsulfonium salts ; Au-Au interactions ; Supramolecular aggregation ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tris[(trimethylphosphane)gold(I)]sulfonium tetrafluoroborate (1) has been prepared from the corresponding oxonium salt [(Me3P)Au]3O+ BF-4 and bis(trimethylsilyl) sulfide, (Me3Si)2S. The analogous triisopropylphosphane and methyldiphenylphosphane complexes (2, 3) have been obtained in a similar way. The products are stable crystalline solids, the structure of which has been determined by X-ray methods. They are composed of independent tetrafluoroborate anions and pyramidal tri(gold)sulfonium cations, which are aggregated to form dimeric units (as in 3) or even strings of dimers (as in 1). It is only in complex 2 that steric effects, originating from the bulky phosphane ligands, prevent the building of supra-molecular (supracationic) aggregates. In the independent pyramidal cations of 2 only short intracationic Au…Au contacts have been detected. These are complemented by intercationic gold-gold contacts of similar length in the structures of 1 and 3. - In the preparation of complex 1, the species [(Me3P)Au]4S2+ (BF-4)2 (4) with hypercoordinate sulfur atoms has also been detected by mass spectroscopy.
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    URL: http://dx.doi.org/10.1002/cber.19941271208
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    A Comparative Study of the Reactivity of Mn(no)2L2H and Mn(CO)3L2H Complexes (L = Phosphorus Donor)Dedicated to Prof. E. Lindner, Universität Tübingen, on the occasion of his 60th birthday. (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 2403-2415 
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    ISSN: 0009-2940
    Keywords: Manganese complexes ; Insertion processes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Mn(NO)2L2H complexes [L = PMe3 1a, PEt3 1b, P(OMe)3 1c, P(OEt)3 1d, P(OiPr)3 1e] have been prepared by the reaction of the corresponding Mn(NO)2L2Br compounds with NaBH4 in ethanol. The reactivity of 1a and 1b is compared to that of Mn(CO)3L2H species (L = PMe3 2a, L = PEt3 2b). Compound 1b reacts with weak acids like PhOH, (CF3)2CHOH and CH3COOH to yield Mn(NO)2(PEt3)2X complexes [X = OPh 3a, OCH(CF3)2 3b, OC(O)CH3 3c] and H2. Compound 2b does not undergo reaction with these acids. At room temperature in toluene 1a, b undergo facile CO2 insertion processes, while 2a, b do not show this reactivity even under more rigorous reaction conditions. From 1a, b and CO2 formato complexes Mn(NO)2L2[OC(O)H] (L = PMe3 4a, L = PEt3 4c) are obtained. The reaction of 1b with salicylaldehyde in toluene proceeds with the formation of a [2-(hydroxymethyl)-phenoxy]dinitrosylbis(triethylphosphane) manganese complex 5b, which exchanges the phenoxy ligand in the presence of excess of salicylaldehyde to give (2-formylphenoxy)-dinitrosylbis(triethylphosphane)manganese (6b) and α,2-dihydroxytoluene. p-Hydroxybenzaldehyde, vanilline, and 4-hydroxy-3,5-dimethoxybenzaldehyde and 1b also afford phenoxy derivatives Mn(NO)2(PEt3)2(OAr) [Ar = p-OC6H4-CHO 7a; OC6H3-2-OCH3-4-CHO 7b; OC6H2-2,6-(OCH3)2-4-CHO 7c] and H2. Compounds 2a, b do not react with any of these hydroxybenzaldehydes. Compounds 1a, b have been converted into Mn(NO)2L2 [(Z)-C(COOR′)≡C(R)H] species (L = PMe3, R = H, R′ = Me 8a; L = PEt3, R = H, R′ = Me 8b; L = PMe3 R, R′ = Me 9a; L = PMe3, R = Ph, R′ = Et 10a; L = PMe3, R = COOMe, R′ = Me 11a; L = PEt3, R = COOMe, R′ = Me 11b) in the presence of alkyl propiolates RC≡CCOOMe (R = H, Me, Ph, COOMe; R′ = Me, Et). Similarly, but under more rigorous conditions, insertion of RC≡CCOOMe (R = H, COOMe) into 2a, b occurs and α metalation products Mn(CO)3(PMe3)2[(Z)-C(COOMe) = CHR] (L = PMe3, R = H 12a; L = PEt3, R = H 12b; L = PMe3, R = COOMe 13a; L = PEt3, R = COOMe 13b) are formed. In the case of the methyl propiolate insertion into 2a, 10% of an additional β-metalation compound Mn(CO)3(PMe3)2[(Z)-CH = CH(COOMe)] (12c) have been detected spectroscopically. Compounds 11b and 13a, b have been transformed into manganacyclic complexes MN[C(COOMe)=CH(COOMe)]-(NO)2(PEt3)2 (14b) and MN[C(COOMe)=CH(COOMe)]-(CO)2L2 (L = PMe3 15a; L = PEt3, CO 15b; L = PEt3 15c). Compound 15c has been identified spectroscopically, and 1a, 8a, and 9a have been characterized by X-ray structure determinations.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19941271211
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  • 98
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    Synthesis and Complexation of a New 14-Membered N2O2 Macrocycle with vic-Dioxime Moieties (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 2483-2488 
    Details
    ISSN: 0009-2940
    Keywords: vic-Dioximes ; N2O2 macrocycles ; Trinuclear complexes ; Pentanuclear complexation ; Tribenzo[b.h.l][1,10,4,7]dioxadiazacyclotetradecine derivatives ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The new vic-dioxime ligand 2 (LH4) carrying a 14-membered N2O2 macrocycle has been prepared. Mononuclear complex (LH3)2Ni, trinuclear complexes (LH)2Cu3, (LH)2Co3, (LH)2-Pd3, and (LH)2Co3(py)3Cl3, dinuclear complex (LH3)2-(UO2)2(OH)2, and pentanuclear complex [L2Cu5(phen)2]-(NO3)2 have been synthesized from LH4. The electrochemical properties of tri- and pentanuclear complexes were investigated by cyclic voltammetry. For (LH)2Cu3 two reduction waves appeared at 0.215 and -0.870 V. [L2Cu5(phen)2](NO3)2 exhibited four reduction waves at 0.200, -0.025, -0.670, and -1.170 V.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19941271219
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  • 99
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    Face-Selective and endo-Selective Cycloadditions with Enantiomerically Pure Cyclopentadienes (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 2505-2509 
    Details
    ISSN: 0009-2940
    Keywords: Cyclopentadienes, bicyclic ; Face selectivity ; endo selectivity ; Chiral discrimination ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A general synthetic route to the enantiopure bicyclic cyclopentadienes (S)-3 and (R)-3 of the hydrindane series, starting from the Hajos-Wiechert ketone 4 or its enantiomer is described. Reasons for the excellent face and endo selectivity of cycloadditions and the resulting consequences for chiral recognition are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19941271223
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  • 100
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    Stereoselective Synthesis of Alcohols, XLVIII[1] Linear Synthesis of (9S)-Dihydro-Erythronolide A (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 2519-2526 
    Details
    ISSN: 0009-2940
    Keywords: Erythronolide A ; Allylboration, stereoselective ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Starting from building block 3 comprising the C-7 to C-15 segment of erythronolide A, a linear synthesis of erythronolide A has been achieved. Key steps were a Sharpless-epoxidation to set up the sterocenter at C-6, and two stereoselective allylboration reactions to generate the stereocenters at C-2, C-3, C-4, and C-5.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19941271225
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