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  • General Chemistry  (10,264)
  • AERODYNAMICS
  • 1995-1999  (6,949)
  • 1920-1924  (3,414)
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Year
  • 101
    Electronic Resource
    Electronic Resource
    A Variation of Titanium-Induced Carbonyl Coupling - Synthesis and Conformations of Terfluorenyl (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1979-1984 
    Details
    ISSN: 1434-193X
    Keywords: McMurry reaction ; C-C coupling ; Low-valent titanium ; Reductive “trimerization” ; Semiempirical calculations ; Overcrowding ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of fluorenone (4) with a low-valent titanium reagent generated from TiCl4 and Zn in THF in the presence of pyridine gave terfluorenyl (6) in 71% yield, bifluorenylidene (2), the conventional McMurry reaction product, in 2% yield, and additional reduction products. The reductive “trimerization” was rationalized in terms of an attack of the intermediate fluorenone dianion on bifluorenylidene. The molecular structure of a single crystal of 6 indicated an approximately C2 conformation, with a slightly twisted central ring, and two equally folded side moieties with dihedral angles of 58.1° and 58.0° between the central and side five-membered rings. The AM1 and PM3 calculations showed C2 global minima, similar to the conformation in the crystal. The calculated Cs transition state conformations were found to be 21.3 (AM1) and 19.9 (PM3) kcal/mol higher in energy than the global C2 minima. A 2D-NMR NOESY experiment on 6 supported the C2 (+sc,+sc) or C2 (-sc,-sc) conformation in solution.
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  • 102
    Electronic Resource
    Electronic Resource
    Asymmetric Synthesis Employing a Chiral 5-Methoxy-1,4-oxazin-2-one Derivative: Preparation of Enantiomerically Pure α-Quaternary α-Amino Acids (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1967-1978 
    Details
    ISSN: 1434-193X
    Keywords: 1,4-Oxazines ; Asymmetric synthesis ; Amino acids ; Glycine derivatives ; Aminocyclopropanecarboxylic acid derivatives ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new asymmetric synthesis of disubstituted α-amino acids is presented. This synthesis is based on the chiral 5-methoxy-1,4-oxazin-2-one derivative 5 relying on the α-hydroxy acid 1 as a chiral auxiliary. Alkylation reactions of the glycine equivalent 5 are performed by deprotonation with sec-butyllithium and subsequent reaction with alkyl halides, yielding the monoalkylated compounds 13 and 14. A second alkylation step of the lithium enolates of 13 and 14 leads to the α,α-disubstituted compounds 17. Both steps proceed with good yields and excellent stereoselectivities (up to 99% de). From the major diastereomers 17c-d the corresponding α-amino acids 19c-d are obtained enantiomerically pure upon hydrolytic cleavage with aqueous sodium hydroxide. Alkylation of the enolate ion of 5 with epichlorohydrines as bifunctional electrophiles provides the cyclopropyl derivatives 20a-b. Direct hydrolysis or oxidation of 20a-b, followed by reductive amination and hydrolysis leads to the substituted 1-aminocyclopropanecarboxylic acids 21a-b and 24a-b.
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  • 103
    Electronic Resource
    Electronic Resource
    An Efficient Synthesis of Bicyclo[3.3.0]oct-2-en-4-ones and 2-Azabicyclo[3.3.0]oct-7-en-6-ones via β-Amino-Substituted α,β-Unsaturated Fischer Carbene Complexes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2025-2031 
    Details
    ISSN: 1434-193X
    Keywords: Fischer carbene complexes, β-amino-substituted, α,β-unsaturated ; Alkoxycyclopentadienes ; Aldol reaction, diastereoselective ; Bicyclo[3.3.0]octenones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The formal [3+2] cycloaddition of β-amino-substituted α,β-unsaturated Fischer carbenechromium complexes 2, which are easily prepared in a one-pot procedure from terminal alkynes 1 via an initially formed alkynylidene complex by a Michael-type addition of a secondary amine, with a variety of alkynes 3 afford the 1,2,5-trisubstituted 3-alkoxy-5-dialkylamino-1,3-cyclopentadienes 4 with an acetal-protected aldehyde or ketone carbonyl group in either the 5-substituent R1 or the N-substituent R2. Under acidic conditions, both the enol ether moiety in the 5-membered ring as well as the acetals in the side chains are hydrolyzed, and the resulting cyclopentenones 6 with carbonyl-group containing side-chains undergo facile intramolecular aldol reactions to give bicyclo[3.3.0]oct-2-en-4-ones 8 and 8-azabicyclo[3.3.0]oct-2-en-4-ones 12, respectively, in good to very good yields for most cases.Supporting information for this article is available on the WWW under //http://www.wiley-vch.de/contents/jc_2046/1999/99100_s.pdf or from the author.
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  • 104
    Electronic Resource
    Electronic Resource
    A New Diastereodivergent Synthesis of 1,2-Disubstituted Homopropargylic Alcohols (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2067-2078 
    Details
    ISSN: 1434-193X
    Keywords: Propargylic oxiranes ; Homopropargylic alcohols ; Bromoallenes ; Allenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,2-Disubstituted homopropargylic alcohols can be prepared in a diastereodivergent fashion starting from propargylic epoxides by BF3-catalysed direct ring-opening or by double inversion through the intermediate formation of a bromoallenol moiety.
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  • 105
    Electronic Resource
    Electronic Resource
    The Preparation of 2,3,5-Tri- and 2,3-Disubstituted Furans by Regioselective Palladium(0)-Catalyzed Coupling Reactions: Application to the Syntheses of Rosefuran and the F5 Furan Fatty Acid (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2045-2057 
    Details
    ISSN: 1434-193X
    Keywords: Homogenous catalysis ; Palladium ; Cross-coupling ; Heterocycles ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 5-acceptor-substituted 2,3-dibromofurans 1 and 2 underwent a regioselective Pd0-catalyzed coupling reaction at the C-2 carbon atom. With alkynes the corresponding 2-alkynylfurans 4 and 5 were accessible (49-97% yield). Alkyl-, aryl-, and alkenylzinc reagents gave the 2-substituted furans 8 starting from compound 2 (66-84% yield). The 2-allylfurans 8e and 8f were obtained by a regioselective Stille coupling in 79% and 73% yield. The latter reaction was also applied to the parent 2,3-dibromofuran (27) and yielded the substitution product 28 (60% yield). Subsequent Pd0-catalyzed reactions to introduce a methyl group in 3-position by a methyldebromination were successfully conducted for 2-alkynyl-3-bromofurans with MeZnCl and PdCl2(PPh3)2 as the catalyst in THF (reflux) to yield compounds 13-16 and 24 (67-76%) and with SnMe4 and PdCl2[P(o-Tol)3]2 as the catalyst in DMA (90 °C) for the 2-allyl-3-bromofuran 8e to yield 18 (70%). The more facile reaction of the 2-alkynylfurans relative to those of furans bearing an sp3-carbon atom at C-2 appears to be due to steric reasons. Studies on the 2-alkyl-3-bromofuran 20 supported this notion. With the regioselective coupling methodology the terpene rosefuran (22) was prepared in four steps starting from furan 2 (35% yield overall). The F5 furan fatty acid (26) was synthesized from furan 1 in five steps (29% yield overall).
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  • 106
    Electronic Resource
    Electronic Resource
    Synthesis of Germacrene-B and Its Extension to the Synthesis of (±)-9-Methylgermacrene-B, the Racemate of the Male-Produced Sex Pheromone of the Sandfly Lutzomyia longipalpis from Lapinha, Brazil (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2159-2165 
    Details
    ISSN: 1434-193X
    Keywords: Leishmaniasis ; Lutzomyia longipalpis ; Pheromones ; Sandfly ; Terpenoids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Both germacrene-B (2) and 9-methylgermacrene-B [(±)-1] were synthesized by employing cyclization reactions [8 → 9 and (±)-20 → (±)-21] as the key steps. The latter [(±)-1] was shown to be the racemate of the male-produced sex pheromone of the sandfly Lutzomyia longipalpis from Lapinha, Brazil.
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  • 107
    Electronic Resource
    Electronic Resource
    Synthetic Disproof of the Structure Proposed for Alectrol, the Germination Stimulant from Vigna unguiculata (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2195-2199 
    Details
    ISSN: 1434-193X
    Keywords: Alectrol ; Ecology ; Lactones ; Phytochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several compounds [(±)-3a, (±)-3b, (±)-10, (±)-11, and (±)-12] with structures related to that proposed for alectrol (3), the germination stimulant for seeds of parasitic weeds, have been synthesized. Structure (±)-3a has been solved by X-ray-crystallographic analysis. Comparison of the 1H-NMR data of the synthetic compounds with those reported for alectrol showed the proposed structure 3 to be incorrect. The synthetic products (±)-3a and (±)-3b showed significant germination stimulating activity on clover broomrape (Orobanche minor) seeds.
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  • 108
    Electronic Resource
    Electronic Resource
    The Formal Total Synthesis of Epothilone A (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2817-2823 
    Details
    ISSN: 1434-193X
    Keywords: Epothilone A ; Ring-closing metathesis ; Aldol reactions ; Lactones ; Diastereoselective alkylation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The formal total synthesis of epothilone A is described. The key steps in the synthesis of the northern hemisphere are a Z-selective ten-membered ring-closing metathesis reaction (RCM) and the diastereoselective alkylation at C8. Aldehyde 3 is formed by introduction of the thiazole moiety by a Wittig reaction and subsequent functional group transformation. An efficient route to keto acid 5 is described.
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  • 109
    Electronic Resource
    Electronic Resource
    Origin of the Slow-Binding Inhibition of Aldolase by D-glycero-Tetrulose 1-Phosphate (D-Erythrulose 1-Phosphate) from the Comparison with the Isosteric Phosphonate Analog (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2853-2857 
    Details
    ISSN: 1434-193X
    Keywords: Bioorganic chemistry ; Enzyme inhibitors ; Aldolase ; Structure-activity relationship ; Enzyme mechanism ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mechanistic reaction pathway for the slow-binding inhibition of rabbit muscle aldolase by D-glycero-tetrulose 1-phosphate (D-erythrulose 1-phosphate) was investigated through the use of its phosphonomethyl isoster 4 which was synthezised for this study. The latter is not a substrate nor a slow-binding inhibitor but interferes in the enzyme-catalyzed reaction with the substrate fructose 1,6-diphosphate in a competitive manner. It was found that phosphonate 4 forms an iminium ion with aldolase and undergoes subsequent α-proton abstraction to form an enamine intermediate. We show from these results that enzyme slow-binding inhibition by D-erythrulose 1-phosphate is consistent with a phosphate β-elimination reaction through the enamine intermediate. This mechanism takes into account the stereochemical features known for aldolase, the parallel between enzyme activity recovery and phosphate release after action of D-erythrulose 1-phosphate, and also the same reaction from dihydroxyacetone phosphate.
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  • 110
    Electronic Resource
    Electronic Resource
    Phenanthro[1.10]-Annelated [3.3.3]Propellanes by Cyclodehydrogenation Reactions of Mono-, Di-, and Tribenzylidenetriptindanes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2867-2878 
    Details
    ISSN: 1434-193X
    Keywords: Propellanes ; Phenanthrenes ; Polycyclic hydrocarbons ; Aromatic hydrocarbons ; Cyclization ; Cyclodehydrogenation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of [3.3.3]propellanes 18, 19, and 3 bearing one, two, or three [1,10]-fused phenanthrene units instead of a simple benzene ring has been performed. Starting from tryptindan-9-one 4, the hitherto unknown tryptindane-9,10-dione 5 and tryptindane-9,10,11-trione 10, the corresponding mono-, di-, and tribenzylidenetriptindanes 7, 9, and 13 have been prepared. In all three cases, the stereoisomers bearing cis-oriented benzylidene groups, i.e., (Z)-stilbene units, are formed predominantly. The monostilbene (Z)-7 and the tristilbene (Z,Z,Z)-13 were obtained in pure form and their stereochemistry was fully characterized. Photoicyclodehydrogenation of 7 under Mallory-Katz conditions gave dibenzo(phenanthro-[1,10])[3.3.3]propellane 18 in an almost quantitative yield, irrespective of the stereoisomeric composition of 7. In contrast, photocyclodehydrogenation of distilbene 9 gave the unusual propellane-fused elassovalene 20 in a moderate yield, and the expected benzodi(phenanthro-[1,10])[3.3.3]propellane 19 was only obtained in a low yield. As an extreme case, tristilbene (Z,Z,Z)-13 eluded the desired threefold photolytic cyclodehydrogenation; however, catalytic cyclodehydrogenation by Pt/Al2O3/Ti at 310 °C furnished the threefold acephenanthrylene 3 in a yield of 18%.
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  • 111
    Electronic Resource
    Electronic Resource
    Specific Isotope Enrichment of Methyl Methacrylate (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2909-2914 
    Details
    ISSN: 1434-193X
    Keywords: Methyl methacrylate ; 13C label ; Mass spectrometry ; 1H NMR ; 13C NMR ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A synthetic scheme has been developed to prepare methyl methacrylate specifically 13C-labelled at all different positions and in any combination of positions, from simple, commercially available starting materials. According to this scheme methyl (1-13C)- and methyl (2-13C)methacrylate (1a and 1b) have been prepared with high label incorporation (99%).
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  • 112
    Electronic Resource
    Electronic Resource
    Conformer Equilibria in 2,4-Disubstituted Pentane Derivatives (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2915-2927 
    Details
    ISSN: 1434-193X
    Keywords: Conformational analysis ; Conformational isomerism ; Isotopic labeling ; 2,4-Disubstituted pentanes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2,4-Disubstituted pentanes are molecules which adopt essentially only two conformations. Substituents have been varied in order to find those which lead to a strong preference of the conformer equilibrium. Studying 2-substituted 4-methylpentanes 3 and 4-benzyloxypentanes 12, it has been shown that substituent effects on the conformer equilibria are not additive, as would be expected on the grounds of steric effects alone. Rather, interactions between polar groups reinforce the bias of the conformer equilibria. When applied to 2,4-disubstituted pentanes, substituents such as chloro or phthalimido shift the conformer equilibrium to the side of the gg conformer with preferences exceeding 90%.
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  • 113
    Electronic Resource
    Electronic Resource
    Synthesis of (-)-Cytoxazone, a Novel Cytokine Modulator Isolated from Streptomyces sp. (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2965-2967 
    Details
    ISSN: 1434-193X
    Keywords: Amino alcohol ; Asymmetric synthesis ; Cell signaling ; Dihydroxylations ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cytoxazone [(4R,5R)-(-)-5-hydroxymethyl-4-(4-methoxyphenyl)-2-oxazolidinone, 1], a new immunosuppressant, was synthesized by starting from p-methoxycinnamyl alcohol (2) employing the Sharpless asymmetric dihydroxylation as the key reaction in 26% overall yield (7 steps).
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  • 114
    Electronic Resource
    Electronic Resource
    Synthesis and Cycloaddition Reactions of Ethyl 3-Aryl-2-(perfluoroalkanesulfonyl)propenoates - A Revised Stereochemistry of the Cyclopentadiene Adducts (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2969-2976 
    Details
    ISSN: 1434-193X
    Keywords: Vinyl triflones ; Vinyl nonaflones ; Knoevenagel reaction ; Diels-Alder reaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ethyl 3-aryl-2-(perfluoroalkanesulfonyl)propenoates were prepared by the Knoevenagel reaction from various aldehydes and ethyl (trifluoromethanesulfonyl)acetate or ethyl (nonafluorobutanesulfonyl)acetate. These deactivated olefins were used in Diels-Alder cycloaddition reactions with cyclopentadiene. The reactions occurred at room temperature to give [4+2] cycloadducts as racemates. The endo stereochemistry of the carboxylic ester and aryl groups was unambiguously assigned by NOE experiments and X-ray analysis.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2046/1999/99164_s.pdf or from the author.
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  • 115
    Electronic Resource
    Electronic Resource
    Iodocyclisation of 1,4-Dihydropyridines; Synthesis and Reactivity of 1-Iodoindolo[2,3-a]quinolizidines (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2997-3003 
    Details
    ISSN: 1434-193X
    Keywords: Alkaloids ; Cyclizations ; Iodine ; Nitrogen heterocycles ; Oxidations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The addition of iodine (or related species) to β-acyl-N-alkyl-1,4-dihydropyridines 1, which possess an N-substituent with an appropriate nucleophile moiety, leads to the corresponding 3-iododihydropyridinium ions, which undergo an internal nucleophilic attack to give, regio- and stereoselectively, the iodobi(poly)heterocyclic ring systems 2a-f in good yields. Reactivity studies on the iodoindoloquinolizidines 2e,f lead to the pentacyclic cyclopropane systems 4a,b, azides 5 and 6, norderivative 9 and, by a base-induced elimination, dihydropyridine 10, a precursor of the zwitterionic alkaloids flavopereirine and 6,7-dihydroflavopereirine.
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  • 116
    Electronic Resource
    Electronic Resource
    A Chiral β,δ-Dioxo-ε-sulfinyl Ester in a Convergent Enantioselective Synthesis towards the C1-C13 Polyol Fragment of Amphotericin B (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3021-3026 
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    ISSN: 1434-193X
    Keywords: Natural products ; Antibiotics ; Macrolides ; Asymmetric synthesis ; Chiral sulfoxide ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This paper describes an efficient stereocontrolled and convergent approach towards the C1-C13 polyol fragment of amphotericin B. The strategy is based on the stereoselective reduction of a chiral β,γ-dioxo-ε-sulfinyl ester to obtain anti- or syn-1,3-diols.
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  • 117
    Electronic Resource
    Electronic Resource
    Synthesis of Axially Chiral Biaryls by Atropo-Diastereoselective Cleavage of Configurationally Unstable Biaryl Lactones with Menthol-Derived O-Nucleophiles (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3047-3055 
    Details
    ISSN: 1434-193X
    Keywords: Axial chirality ; Biaryls ; Atropisomerism ; Dynamic kinetic resolution ; Asymmetric synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Configurationally unstable lactone-bridged biaryls 4 are cleaved atropo-diastereoselectively using chiral menthol-derived alkali metal alkoxides, to give axially chiral biaryl esters of type 5 in high yields and excellent diastereomeric ratios of up to 〉 99:1. The method permits the optional preparation of each of the two atropisomers from the same lactone precursor (“atropo-divergence”), simply according to the choice of the appropiate mentholate or its enantiomer as the O-nucleophile - or by the use of the mentholate in solution or in suspension. Undesired minor atropisomers of 5 possibly formed (if at all) can be recycled (“axially chiral economy”) by cyclization back to the lactone 4. For the preparation of larger amounts of enantiopure biaryl alcohols 9, an efficient reaction sequence was developed: alcoholysis of 4 → in situ reduction → crystallization. The synthetic value of these alcoholysis reactions for asymmetric biaryl synthesis is illustrated by the transformation of 5 into a broad series of enantiopure biaryls of type 6 with various functional groups ortho to the axis.
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  • 118
    Electronic Resource
    Electronic Resource
    Kinetic Resolution of Racemic Cyclic Sulfoxides Using Hydrolytic Enzymes (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2573-2578 
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    ISSN: 1434-193X
    Keywords: Enzymes ; Kinetic resolution ; Sulfoxides ; Chiral resolution ; Hydrolyses ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Selected racemic trans-2-alkoxycarbonyl-3,6-dihydro-2H-thiopyran S-oxides 2a-h have been subjected to enzyme-assisted hydrolysis under conditions of kinetic resolution to give the corresponding acids and recovered esters with moderate to high enantiomeric purities (up to 95%). The enantioselectivity of the reaction was found to be strongly dependent on the structures of the substrates used.
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  • 119
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    Approach Toward a Generic Treatment of Gram-Negative Infections: Synthesis of Haptens for Catalytic Antibody Mediated Cleavage of the Interglycosidic Bond in Lipid A (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2593-2600 
    Details
    ISSN: 1434-193X
    Keywords: Endotoxin ; Immunotherapy ; Catalytic antibodies ; Glycosidases ; Azasugars ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to develop a generic treatment for infections with Gram-negative bacteria, we developed a synthesis of 2-acylamino-deoxynojirimycin derivatives (17, 18, 19 and 20), which will be used as haptens for raising catalytic antibodies capable of hydrolyzing the interglycosidic bond in the lipid A moiety of endotoxins. A key intermediate in the preparation of compounds 17, 18, 19 and 20 is 3,4,6-tri-O-benzyl-2-[(benzyloxycarbonyl)amino]-2-deoxy-D-glucono-δ-lactam (6), which was prepared from known 3,4,6-tri-O-benzyl-2-[(benzyloxycarbonyl)amino]-2-deoxy-D-glucosamine (1) in four steps in 47% overall yield. Antibodies were generated against 2-[(6-aminohexanoyl)amino]-2-deoxy-D-glucono-δ-lactam (17) coupled to the carrier protein bovine serum albumin.
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  • 120
    Electronic Resource
    Electronic Resource
    Synthesis of Isotopically Labelled L-Phenylalanine and L-Tyrosine (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2609-2621 
    Details
    ISSN: 1434-193X
    Keywords: Amino acids ; Isotopic labelling ; Ethyl benzoate ; Benzonitrile ; Sodium phenylpyruvate ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A synthetic route to stable-isotope-substituted L-phenylalanine is presented, which allows the introduction of 13C, 15N, and deuterium labels at any position or combination of positions. For labelling of the aromatic ring, a synthetic route to ethyl benzoate (or benzonitrile) has been developed, based on the electrocyclic ring-closure of a 1,6-disubstituted hexatriene system, with in situ aromatization by elimination of one (amino) substituent. Several important (highly isotopically enriched) synthons have been prepared, namely benzonitrile, benzaldehyde, ethyl benzoate, and ethyl diphenyloxyacetate. Labelled L-phenylalanines have been synthesized from both aromatic precursors by initial conversion into sodium phenylpyruvate and subsequent transformation of this intermediate into the L-α-amino acid by an enzymatic reductive amination reaction. In this manner, highly enriched phenylalanines are obtained on the 10-gram scale and with high enantiomeric purities (≥ 99% ee). The method has been validated by the synthesis of [1′-13C]-L-Phe and [2-D]-L-Phe. In addition, two methods are described for the introduction of isotopes into L-tyrosine starting from the isotopically enriched precursors benzonitrile and ethyl benzoate.
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    An Efficient Asymmetric Synthesis of Prostaglandin E1 (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2655-2662 
    Details
    ISSN: 1434-193X
    Keywords: Prostaglandins ; Asymmetric synthesis ; In situ inversion ; CBS reduction ; Cuprates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An asymmetric total synthesis of Prostaglandin E1 (5) has been achieved in a two-component coupling process. The chiral hydroxycyclopentenone 6 was readily available from furan with 96% ee. The key reaction step was a kinetic enzymatic resolution followed by an in situ inversion. A catalytic asymmetric reduction of the γ-iodo vinyl ketone 19 with the Corey CBS catalyst gave the ω-side chain 7 with 〉96% ee. Conjugate addition using the reaction with dilithiocyanocuprate followed by mild cleavage of the silyl protective groups and enzymatic hydrolysis of the methyl ester 22 gave (-)-PGE15in high yield.
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    Palladium(0)-Catalyzed Synthesis of 2-Vinyl-2,3-dihydro-benzo[1,4]dioxins (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2665-2673 
    Details
    ISSN: 1434-193X
    Keywords: 2-Vinyl-2,3-dihydro-benzo[1,4]dioxins ; Cyclizations ; Palladium ; Chirality ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of 1,4-bis(methoxycarbonyloxy)but-2-ene (2a-3a) or 3,4-bis(methoxycarbonyloxy)but-1-ene (4a) with various substituted benzene-1,2-diols was catalyzed by a palladium(0) complex to give substituted 2-vinyl-2,3-dihydro-benzo[1,4]dioxins in good yields via a tandem allylic substitution reaction. In the case of 4-substituted benzene-1,2-diols, the ratio of regioisomers is determined by the relative acidity of the two phenolic protons. For 3-substituted benzene-1,2-diols, this ratio is determined only by steric effects in the case of alkyl substituents, although it is determined mainly by the relative stabilities of the corresponding phenates for other substituents; however, for 3-nitrobenzene-1,2-diol, this ratio is determined by the relative leaving-group ability of 2-nitro- or 3-nitrophenate. When the cyclisation was performed in the presence of an optically active phosphane, chiral 2-vinyl-2,3-dihydro-benzo[1,4]dioxin (5) was obtained with enantioselectivity of up to 45% using BINAP as the chiral phosphane.
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    Synthesis of a Constitutional Isomer of Nerol by Consecutive Ireland-Claisen and Cope Rearrangements (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2781-2785 
    Details
    ISSN: 1434-193X
    Keywords: Rearrangements ; Ireland-Claisen reaction ; Nerol ; Odoriferous substances ; Terpenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (2Z,6E)-3,6-Dimethylocta-2,6-dien-1-ol (6) was synthesized by Steglich esterification of (2E)-2-methylbut-2-en-1-ol (tiglic alcohol, 7) with 3-methylbut-2-en-1-oic acid (senecioic acid, 8), followed by selective Ireland-Claisen rearrangement of the resulting ester 9 at 0°C and subsequent Cope rearrangement of the product at 140°C. A standard LAH reduction in the last step of the synthetic sequence transformed the α,β-unsaturated acid 12 into the target molecule 6, a constitutional isomer of nerol (5) with interesting olfactory properties.
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    Structure Determination of Tigridial, an Iridopentaene from Tigridia pavonia (Iridaceae) (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2793-2797 
    Details
    ISSN: 1434-193X
    Keywords: Iridaceae ; Tigridia pavonia ; Iridals ; Spiro compounds ; Triterpenoids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Besides numerous known iridals, which are unusual mono- or bicyclic triterpenoids of Iridaceae, lipid extracts of Tigridia pavonia bulbs contain tigridial (17), a new spirobicyclic hemiacetal with a conjugated pentaene moiety in the terpenoid side chain. The isolated natural product decomposes rapidly despite exclusion of light and oxygen. In contrast, derivatives of 17 formed by Diels-Alder reaction with 4-phenyl-3H-1,2,4-triazole-3,5-(4H)-dione (13) are stable, as are the products of a subsequent reduction with NaBH4. The products 15a,b and 16a,b of this reaction sequence were isolated and their structures elucidated by spectroscopic techniques. From these results structure 17 was inferred for the new natural product, which was confirmed by 1D and 2D NMR spectroscopy of a mixture of 11 and 17, in which the latter had been stabilized by addition of hydroquinone. The stereochemistry of 17 was deduced from 2D NOE experiments and comparison with known compounds.
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    Diastereoselective Formation of Dithioacetal Oxides from Aliphatic Sulfines under Thermodynamic Control (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2859-2865 
    Details
    ISSN: 1434-193X
    Keywords: Aliphatic sulfine ; Organolithium, thiophilic addition of ; Carbanions ; Protonation ; Stereoselectivity ; Sulfur ; Lithium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Protonation of α-sulfinyl carbanions 3, resulting from the selective thiophilic addition of organolithium compounds to aliphatic sulfines 2, provided dithioacetal oxides 4 (63-94% yield). The diastereomeric ratio ranged from 52:48 up to 100:0 with sterically hindered substituents. Thus, (1S*,SS*)-2,2-dimethyl-1-methylsulfanyl-1-methylsulfinylpropane (4ca) was obtained as a single isomer. The origin of the stereoselectivity is rationalized in terms of a thermodynamic equilibrium between the two diastereomers of α-sulfinyl carbanions 3, at which protonation occurs under kinetic control and with retention of configuration with the assistance of the lithium cation. Moreover, the stereochemistry could be totally reversed by converting the lithiated anion intermediate into an aluminium “ate” complex. Thus, (1R*,SS*)-2,2-dimethyl-1-methylsulfanyl-1-methylsulfinylpropane (4ca) was selectively obtained by this method (dr = 0:100).
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    Solvent Effect on the Protonation of Acetylene and Ethylene - Continuum Solvent Quantum Chemical Calculations (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 2893-2897 
    Details
    ISSN: 1434-193X
    Keywords: Acetylene ; Ethylene ; Carbocations ; Vinyl cation ; Ethyl cation ; Basicity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The protonation of acetylene and ethylene (yielding the vinyl and ethyl cation, respectively) was investigated computationally by ab initio calculations [B3LYP/6-31G(d,p)], in the gas phase and in water, as modeled by the IPCM and SCIPCM continuum methods. The structures and NBO atomic charges were thus determined for the neutral bases and their protonated forms, while the comparison of gas-phase and aqueous basicities afforded the hydration energies of the protonated bases. It was found that the aqueous protonation of acetylene is more endothermic than that of ethylene by 5 kcal/mol, owing to the lower intrinsic basicity of the former (by 7.4 kcal/mol), which is only partly compensated for by the more exothermic hydration (by 3.8 kcal/mol) of the vinyl cation.
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    Water-Soluble Tripodal Phosphane Ligands and Their Rhodium Complexes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 37-41 
    Details
    ISSN: 1434-1948
    Keywords: Tripodal P ligands ; Rhodium ; Water-soluble complexes ; Immobilization ; Biphasic hydroformylation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the water-soluble tripodal phosphane ligand cis,cis-1,3,5-(PPh2)3-1,3,5-[CH2(OCH2CH2)xOCH3]C6H6 (x = 30-160) (5) has been achieved in a four-step reaction sequence. The alcohol Mo(CO)3[cis,cis-1,3,5-(PPh2)3-1,3,5-(CH2OH)3C6H6] (1) is converted to the corresponding alcoholate 2, which forms the polyethylene glycol derivative 3 in a polyaddition reaction with oxirane. After methylation of the end groups of 3, the ligand 5 is obtained by a combined photochemical/oxidative demolybdenation reaction. The water-soluble tripodal phosphane 5 and the methoxymethyl functionalized tripodal ligand 6 react with Rh(PPh3)3(CO)H to form the water-soluble and water-insoluble rhodium carbonyl hydrido complexes 5a and 6a, respectively. The catalytic activity of the rhodium complex 5a in the hydroformylation of 1-hexene was found to be comparable in a single-phase system (1-hexene/methanol) with that in the biphasic system (1-hexene/water). Only traces of alcohol were found, which demonstrates that the catalyst 5a displays higher selectivity in hydroformylation than in hydrogenation.
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    Metalloarsaalkene [(η5-C5Me5)(CO)2FeAs=C(NMe2)2] as a Ligand in Carbonylchromium, -iron, and -nickel Complexes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 55-59 
    Details
    ISSN: 1434-1948
    Keywords: Arsaalkenes ; Arsenic ligands ; Carbonyl complexes ; Chromium ; Iron ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of equimolar amounts of the metalloarsaalkene [(η5-C5Me5)(CO)2FeAs=C(NMe2)2] (1) with the carbonyl complexes [Ni(CO)4], [Fe2(CO)9], and [{(Z)-cyclooctene}Cr(CO)5], respectively, affords the adducts [(η5-C5Me5)(CO)2FeAs{M(CO)n}=C(NMe2)2] with [M(CO)n] = [Ni(CO)3] (2); [Fe(CO)4] (3), and [Cr(CO)5] (4). These feature η1 coordination of the arsaalkene ligand via the arsenic atom. The molecular structures of the complexes 3 and 4 have been determined by X-ray diffraction analyses.
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    Synthesis of Novel Steroid Alkaloids by Cyclization of Arylimines from Estrone (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3013-3020 
    Details
    ISSN: 1434-193X
    Keywords: Cycloadditions ; Domino reactions ; Iminium ions ; Lewis acids ; Quinolines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Intramolecular Lewis or Brønsted acid-catalyzed cyclization reactions of steroid arylimines 6 yielded either tetrahydroquinolines condensed to the estrane skeleton 9 or N-arylamino-D-homosteroids 12-16, depending on the substituent of the arylimino group.
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    The Addition Patterns of C60 Trisadducts Involving the Positional Relationships e and trans-n (n = 2-4): Isolation, Properties, and Determination of the Absolute Configuration of Tris(malonates) and Tris[bis(oxazolines)] (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3027-3039 
    Details
    ISSN: 1434-193X
    Keywords: Chirality ; Circular dichroism ; Cycloadditions ; Fullerenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of regioisomeric trisadducts of C60 (5-11, 14-18) having the positional relationships e and trans-n (n = 2-4) resulting from successive additions of malonates or bis(oxazolines) to [6,6]-double bonds of the fullerene framework has been isolated and characterized. The new adducts 8-11 and 15-17 represent examples of unprecedented addition patterns. The addition patterns of the new trisadducts with C2, Cs or C1 symmetry have been assigned on the basis of the known positional relationships of the addends in their precursor bisadducts, and those of the C2- or Cs-symmetric representatives have been verified by analysis of their NMR spectra. The absolute configurations of the adducts with inherently chiral addition patterns could be determined either by comparison of the calculated and experimental CD spectra of the bis(oxazoline) adducts or with knowledge of the absolute configurations of the chiral bisadduct precursors containing bis(oxazoline) addends. The CD spectra of the pairs of diastereomers with an enantiomeric addition pattern fA -15/fC -15, fA -16/fC -16, and fA -18/fC -18 show mirror image behavior and pronounced Cotton effects.
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    Characterisation of the Intermediate C2H4…Cl2 in a Gaseous Mixture of Ethene and Chlorine by Rotational Spectroscopy: A Weak π-Type Complex (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 17-25 
    Details
    ISSN: 0947-6539
    Keywords: chlorine complexes ; ethene complexes ; intermediates ; rotational spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A complex of ethene and Cl2 has been characterised in the gas phase. Rotational spectra of the isotopomers C2H4…35Cl2, C2H4…35Cl37Cl and C2H4…37Cl35Cl were recorded by using a fast-mixing nozzle in an FT microwave spectrometer. Rotational constants, centrifugal distortion constants and Cl nuclear quadrupole coupling constants. χgg (Cl) are reported in each case. The complex is of the π-donor-acceptor type and has a C2v geometry in which Cl2 lies along the C2 axis perpendicular to the plane of the C2H4 nuclei. The binding is weak, and only small changes in the χgg (Cl) attend complex formation. A simple model attributes these changes to a transfer of around 0.02e from the inner to the outer Cl nucleus, thus confirming that the complex is of the Mulliken outer type. Similarities in the properties of C2H4… Cl2 and C2H4… HCl indicate that the angular geometry is in both cases determined mainly by the electrostatic part of the interaction. The distance from the π-bond midpoint to Cl decreases from C2H4… HCl to C2H4… Cl2; this suggests that Cl2 is “snub-nosed”.
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    5,10,15,20-Tetraphenylsapphyrin-Identification of a Pentapyrrolic Expanded Porphyrin in the Rothemund Synthesis (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 68-73 
    Details
    ISSN: 0947-6539
    Keywords: porphyrinoids ; Rothemund synthesis ; sapphyrin ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Rothemund-type condensation of pyrrole and benzaldehyde yields, apart from 5,10,15,20-tetraphenylporphyrin (TPPH2) and inverted tetraphenylporphyrin 2-aza-21-carba-5,10,15,20-tetraphenylporphyrin (CTPPH2), a unique pentapyrrolic macrocyclic molecule with the aromatic nucleus of sapphyrin, namely, 5,10,15,20-tetraphenylsapphyrin (TPSH3). Its unorthodox structural skeleton with an inverted pyrrole ring lying opposite to the bipyrrole unit accounts for the spectroscopic properties of the novel sapphyrin. The diprotonation of TPSH3 acts as a trigger for a structural transformation involving a flip of the pyrrole units, which relocates the 27-NH pyrrolic nitrogen from the periphery into the center of the macrocycle. The formation of 5,10,15,20-tetraphenylsapphyrin proves that the pentapyrrolic product is accessible by the mechanism of the Rothemund synthesis.
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    A Tale of Two Complexes, [PtMen(RN=CH—CH=NR)] (n = 2 and n = 4, R = Cyclohexyl): Why do PtII and PtIV Complexes Exhibit Virtually Identical Redox Behavior and Colors? (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 95-99 
    Details
    ISSN: 0947-6539
    Keywords: charge transfer ; EPR spectroscopy ; organometallic compounds ; platinum compounds ; spectroelectrochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In spite of their very similar cyclic voltammograms, absorption spectra, and solvatochromic behavior, the two 1,4-diazabutadiene title complexes exhibit markedly different photoreactivities and underlying electronic structures, as evident from absorption and EPR spectra of the persistent anion radical forms. The lowest excited state of the nonphotoreactive PtII system [(CyN=CH—CH=NCy)-PtMe2] has MLCT (metal-to-ligand charge-transfer, 5d → π*) character, and the EPR spectrum of the corresponding anion radical at 〈g〉 = 2.016 exhibits sizable metal/ligand orbital mixing. On the other hand, the structurally characterized PtIV complex [(CyN=CH—CH=NCy)-PtMe4] (C2/c; a = 2021.6(2), b = 805.3(1), c = 1254.2(1) pm; β = 111.05(1)°; V = 1905.7(4) × 106 pm3; Z = 4) has a lowlying photoreactive LLCT (ligand-to-ligand charge-transfer, σPt—C → π*) excited state in which the axial Pt—C bonds are activated, as already suggested by the longer Pt—C(ax) bonds (214.0(8) pm) relative to Pt—C(eq) in the ground state (204.5(5) pm). The anion radical of the PtIV complex has lost the long-wavelength absorption band in the visible; it shows a well-resolved EPR spectrum at 〈g〉 = 1.9945 with π-ligand and 195Pt hyperfine structure and a small g anisotropy. A qualitative MO scheme is presented to account for the similar frontier-orbital energy differences despite dissimilar underlying electronic structures.
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    Linear and Cyclic Platinum σ-Acetylide Complexes of Tetraethynylethene (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 111-117 
    Details
    ISSN: 0947-6539
    Keywords: alkyne complexes ; carbon networks ; macrocycles ; platinum compounds ; tetraethynylethene ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The syntheses of the first organometallic mono- and dinuclear platinum complexes bearing the tetraethynylethene unit as an η1-ligand are reported. Structural characterization of two of the trans σ-bis(acetylide) derivatives by X-ray crystallography reveals coplanarity of the acetylenic π-ligands and indicates possible electronic delocalization across the metal center. This notion is further supported by comparing the electronic absorption spectra of the platinum-containing compounds with those of related tetraethynylethene derivatives without metals. The solidstate structure of a dinuclear complex with two iodoplatinum fragments attached to one set of geminal acetylenes of tetraethynylethene was also investigated by X-ray diffraction. Hay coupling of a mononuclear species leads to the incorporation of the σ-bis(acetylide) moiety into a diplatinated metallacycle. This macrocyclic compound represents a novel structural motif in the design of a transition metal linked carbon network based on tetraethynylethene.
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    Asymmetric Control of 1,3-Dipolar Cycloaddition Reactions with Azomethine Ylides by Means of Proline Esters as Chiral Auxiliary Groups (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 150-154 
    Details
    ISSN: 0947-6539
    Keywords: asymmetric syntheses ; azomethine ylides ; chiral auxiliaries ; cycloadditions ; pyrrolidines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Upon treatment with triethylamine or DBU in the presence of LiBr, aromatic and aliphatic imines of amino acid esters are converted to N-metalated azomethine ylides. These 1,3-dipoles undergo highly stereoselective cycloadditions with N-acryloyl-(S)-proline esters in THF at -78 to -40°C to afford highly substituted pyrrolidines with complete regiocontrol and good to excellent diastereomeric ratios. The chiral auxiliary groups can readily be removed from the cycloadducts by simple acid hydrolysis. To rationalize the observed stereoselectivity a transition-state model is proposed in which the lithium cation is coordinated to both the 1,3-dipole and the dipolarophile.
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    Synthesis of a Methyl Heptaglucoside with Phytoalexin Elicitor Activity Based on Oxidative Coupling of Glucals (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 161-164 
    Details
    ISSN: 0947-6539
    Keywords: block synthesis ; epoxidations ; glycosylations ; oligosaccharides ; selenoglycosides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several suitable building blocks for the construction of the phytoalexin elicitor α-methyl-32, 34-di-β-D-glucopyranosylgentiopentaoside (2) were readily accessible by oxidative coupling of glucals. Block coupling of trimeric phenylseleno- and ethylthioglucosyl donors 17 and 18 with tetrasaccharide 16 in the presence of the thiophilic promoter N-iodosuccinimide and catalytic trifluoromethanesulfonic acid furnished the desired heptaglucan 2 in high overall yield.
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    Cover Page (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. cpi 
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    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010401
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    Graphical Abstract (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. i 
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    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010403
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    Asymmetric syn-Selective Michael Addition of Enolates to Chiral 8-Phenylmenthyloxy Vinyl Chromium Carbene Complexes (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 236-242 
    Details
    ISSN: 0947-6539
    Keywords: asymmetric syntheses ; enol ethers ; Fischer carbenes ; Michael additions ; syn diastereoselectivity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Michael addition reactions of ketone and ester lithium enolates to optically active Fischer vinylcarbene complexes derived from (-)-8-phenylmenthol take place with high syn selectivity and high levels of asymmetric induction. The initial Michael adducts can be further elaborated through diastereoselective addition of organometallic reagents to ketones and aldol reactions. Removal of the metal fragment and chiral auxiliary group leads to cyclic enol ethers with three or five contiguous stereogenic centers and of high enantiomeric purity.
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    Synthesis of a Fullerene[60] Cryptate and Systematic Langmuir-Blodgett and Thin-Film Investigations of Amphiphilic Fullerene Derivatives (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 243-251 
    Details
    ISSN: 0947-6539
    Keywords: amphiphiles ; C-glycosides ; cryptates ; fullerenes ; ionophores ; Langmuir-Blodgett films ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the first fullerene cryptate 7 with a sodium ion bound to a benzo[2.2.2]cryptand covalently attached to a methanofullerene[60] is described. The amphiphilic properties of 7 as well as of a variety of other covalent fullerene derivatives with polar functional groups and the ability of these compounds to form Langmuir monolayers at the air-water interface were investigated in a systematic study. Among these derivatives are Diels-Alder adducts of C60 and methanofullerenes, four of which are fullerene C-glycosides. The films at the water surface were characterized by their surface pressure versus molecular area isotherms, compression and expansion cycles, and optical light microscopy. UV/Vis spectroscopy and small-angle X-ray diffraction (SAXS) were employed for LB film characterization on solid substrates. Parameters influencing the spreading and monolayer character include (a) polarity, (b) balance of hydrophobicity to hydrophilicity, (c) size and bulkiness of the polar groups attached to the fullerene, and (d) presence of aromatic residues in these groups.
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    Light-Triggered Molecular Devices: Photochemical Switching Of optical and Electrochemical Properties in Molecular Wire Type Diarylethene Species (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 275-284 
    Details
    ISSN: 0947-6539
    Keywords: diarylethenes ; molecular devices ; nonlinear optics ; photochromes ; redox switches ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Organic photochromic systems represent a starting point for the elaboration of light-triggered molecular switching devices. The novel bispyridinium and bispyridine compounds 12+ and 6 were synthesized as their uncyclized isomers from 3,5-dibromo-2-methylthiophene in overall yields of 43 and 44%, respectively. The diarylethene photochromes 2 and 10-13, substituted with electron donors and acceptors, were prepared from 5-methylthiophene-2-carboxaldehyde in 21-32% overall yield. All of the compounds were found to exhibit pronounced photochromic properties. Irradiation with UV light resulted in essentially complete photocyclization of the open forms to the intensely coloured closed isomers which could, in turn, be reconverted back to the open state with visible light of γ〉600 nm. The absorption maxima of the described compounds in their closed forms are shifted far towards, and even into, the near-IR region. Whereas no thermochromic properties were observed for the open isomers, the rates of thermal decolouration of the cyclized forms was found to be highly dependent on the nature of the substituents on the thiophene rings. It was demonstrated that reversible photochemical interconversion between the two photochromic states could be used to effectively switch a number of physical properties. Thus, the molecules 12+ and 12 represent two kinds of redox switches, the former in reduction and the latter in oxidation, in which electron conduction is switched on in the closed state and off in the open state. Compound 12 may also be considered to be a photoswitchable analogue of tetrathiafulvalene type substances. On the other hand, compound 2 displays a marked increase in nonlinear optical activity on conversion from the open to the closed form. Such systems are prototypes of photoswitchable molecular wires where electron conduction and push-pull interaction can be reversibly modulated by an external stimulus, namely, irradiation by light.
    Additional Material: 10 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19950010504
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    A Dual-Mode Molecular Switching Device: Bisphenolic Diarylethenes with Integrated Photochromic and Electrochromic PropertiesDedicated to Professor George Just on the occasion of his 65th birthday. (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 285-293 
    Details
    ISSN: 0947-6539
    Keywords: diarylethenes ; electrochromes ; molecular devices ; optical memory ; photochromes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The bisphenolic dithienylethene molecules 1a and 1b were synthesized in overall yields of 45% from 4-bromoanisole and 44% from 2.6-di-tert-butyl-4-iodophenol, respectively. The corresponding extended quinones 3a and 3b were also prepared. Photochemical studies showed that compounds 1 are photochromic; the open forms 1 could be converted with UV light of 312nm to the closed coloured forms 2 with photostationary states lying at essentially complete conversion (〉 98%). The 1a-2a system was found to exhibit good resistance to photofatigue and thermal stability for both photoisomers. Cyclic voltammetry studies involving the 2/3 couples showed that whereas 2b undergoes irreversible oxidation at + 0.85 V (vs. SCE in THF), the hydroquinone 2a is reversibly oxidized at an E1/2 of + 0.72V (in MeCN, quasi-reversibly in THF at + 0.81 V); this reflects the differences in deprotonation behaviour of the generated QH2/2+ species. The large difference in oxidation potential between 1a and 2a allows the photochemical switching of redox properties. In a complementary fashion, redox switching of the photochromic properties within the 2a-3a pair is possible since 3a is stable to visible light. Owing to this unique behaviour, the triad consisting of 1-3a represents a novel molecular device with mutually regulating photo- and electrochromic behaviour. In addition, the ability to interconvert between the three stable states makes the system well-suited as the basis for an optical memory system with multiple storage and nondestructive readout capacity through a write-lock-read-unlock-erase cycle.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19950010505
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    Graphical Abstract (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. i 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010603
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  • 144
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    Diastereo- and Enantioselective Synthesis of L-threo- and D-erythro-SphingosineDedicated to Professor Peter Paetzold on the occasion of his 60th birthday (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 382-388 
    Details
    ISSN: 0947-6539
    Keywords: asymmetric syntheses ; alkenylations ; SAMP/RAMP hydrazones ; selenyl aldehydes ; sphingosine ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: L-threo-sphingosine and its D-erythro isomer (1) are subunits of many glycosphingolipids, gangliosides and ceramides. This paper describes the highly diastereo- and enantioselective synthesis of both isomers (de, ee 〉 98%). The key steps in the synthesis are the aldol reaction of the SAMP hydrazone (S)-2 with racemic α-phenylselenylpentadecanal 3, the diastereoselective triacetoxyborohydride reduction of ketone 5 and exclusive (E) C—C double bond formation in the elimination of hydroxyl and selenyl moieties promoted by methanesulfonyl chloride. Mesylate 8 was then readily converted via the 1,3-O-acetonide-protected azidosphingosine 9 to L-threo-sphingosine. Conversion to the known 1-O,2-N-diacetyl-protected sphingosine 13 with subsequent Mitsunobu inversion of the C3—OH centre afforded the D-erythro-sphingosine epimer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010609
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    Potential Linear-Chain Organic Ferromagnets (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 403-413 
    Details
    ISSN: 0947-6539
    Keywords: conjugation ; ferromagnetism ; helices ; magnetic properties ; polymers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electronic structures of conjugated polymers containing methyl radicals, carbenes, and nitrogen-based radicals coupled in various ways through benzene rings are examined, employing band-structure calculations in the extended Hückel approximation. The structural and electronic properties of polymers with a para-phenylene or meta-phenylene coupling unit are compared. In the polymer with methyl radicals coupled through a para-phenylene unit, a pairing or Peierls distortion occurs to remove the degeneracy at the Fermi level. The resulting bandgap is nevertheless relatively small; we conclude that such polymers are likely to exhibit high electrical conductivity upon doping, very much like polyacetylene. On the other hand, in the polymers with a meta-phenylene coupling unit, striking symmetry-determined, halfoccupied narrow bands appear at the Fermi level and contribute to the stability of the ferromagnetic state. The relation of a potential ferromagnetic state to metallic, CDW, and SDW states is discussed from the viewpoint of orbital interactions in extended systems. We suggest novel 3- and 4-fold helical structures for the meta-phenylene-coupled polymers.
    Additional Material: 12 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19950010704
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    Reversibility in the Reaction of Cyclohexadienyl Radicals with Oxygen in Aqueous Solution (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 423-429 
    Details
    ISSN: 0947-6539
    Keywords: kinetics ; peroxyl radicals ; pulse radiolysis ; radicals ; superoxide radicals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydroxyl radicals were generated radiolytically and reacted with a number of benzene derivatives (PhH). In the presence of oxygen, the hydroxycyclohexadienyl radicals thus formed were converted into their corresponding peroxyl radicals. Pulse radiolysis has shown the oxygen addition (forward reaction, f) to be reversible (reverse reaction, r) [Eq. (1)]. The peroxyl radicals can eliminate HO2· to yield phenols, alongside some ring-fragmentation products (product-forming reaction, p). The rate constants for the forward and reverse reactions (kf and kr) and the corresponding stability constants K (= kf/kr) were determined for the hydroxy-cyclohexadienyl radicals derived from anisole, toluene, fluorobenzene, benzene, chlorobenzene, benzyl chloride, benzoate ion, phenylalanine, and terephthalate ion. The constants kf lie between 8 × 108 (anisole) and 1.6 × 107 dm3 mol-1 s-1 (terephthalate ion), and kr between 7.5 × 104 (toluene) and 3.4 × 103 s-1 (terephthalate ion). The stability constants lie between 2.6 × 104 (benzene) and 3.3 × 103 dm3 mol-1 (phenylalanine). The rate constants for the product-forming reactions kp are between 5.5 × 103 (anisole) and 3.4 × 102 s-1 (benzoate). For the peroxyl radical derived from phenylalanine, a bond dissociation energy of 5.5 kcal mol-1 has been derived. A number of hydroxy-cyclohexadienyl radicals (e.g., those derived from benzoic acid, ethylbenzoate, benzonitrile, and nitrobenzene) react too slowly to allow the equilibrium constant to be determined by means of pulse radiolysis. These reactions have rate constants kf in the order of 5 × 106 dm3 mol-1 s-1, except for nitrobenzene where the reaction is too slow for measurement. The rate constants kr are below 500 s-1, and the product-forming reaction is too slow to be detected by pulse radiolysis. γ-Radiolysis of N2O/O2(4:1)-saturated aqueous solutions of benzonitrile gave dimeric compounds (e.g., dicyanobiphenyls) in low yield, alongside the three isomeric phenols; this again proves the low reactivity of its hydroxycyclohexadienyl radical toward oxygen.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19950010706
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    Semiconductor-Catalysed Photoaddition of Olefins and Enol Ethers to 1,2-Diazenes: A New Route to AllylhydrazinesHeterogeneous Photocatalysis XIII. Part XII: H. Kisch. J. Prakt. Chem. 1994, 336, 635Dedicated to Professor Hans-Dieter Scharf on the occasion of his 65th birthday (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 441-448 
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    ISSN: 0947-6539
    Keywords: allylhydrazines ; cadmium compounds ; catalysis ; photochemistry ; zinc compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Suspensions of zinc or cadmium sulfide powders in a protic solvent catalyse the linear addition of enol ethers and olefins to 1,2-diaryl- and 1-aryl-2-alkyl-1,2-diazenes, producing allylhydrazine derivatives. Relative quantum yields decrease sharply when the 1,2-diazene is more difficult to reduce, while their relationship to the oxidation potential of the enol ether/olefin is complicated. Reduction to 1,2-diarylhydrazine and concomitant dehydrodimerization of the enol ether occurs as a side reaction. It is favoured by increasing light intensity and becomes the major reaction path when platinized (5 mol%) photocatalysts are employed. It is proposed that the photogenerated electron-hole pair in a proton-coupled electron transfer reduces the diazene to a hydrazyl radical and oxidizes the olefin/enol ether to a radical cation. The allylic radical obtained from the latter by deprotonation then undergoes C—N coupling with the hydrazyl radical to afford the allylhydrazine. Diarylhydrazine formation occurs by disproportionation of the hydrazyl radical or by a successive proton-coupled reduction. Thus photoaddition can be classified as a 1 e-/1 h+ process while 2e-/2h+ are necessary for the reduction.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19950010709
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    Masthead (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995) 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010802
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    Stereoselective Homologation-Amination of Aldehydes by Addition of Their Nitrones to C-2 Metalated Thiazoles - A General Entry to α-Amino Aldehydes and Amino Sugars (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 505-520 
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    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A general method for the homologation of aldehydes to α-amino aldehydes (aminohomologation) has been developed, which employs nitrones as iminium derivatives of the aldehydes. Key operations include a) the addition of a thiazole metalated at C-2 to the N-benzylnitrone derived from the aldehyde, b) the reductive dehydroxylation of the resultant thiazolyl N-benzylhydroxylamine, and c) the unmasking of the formyl group from the thiazole ring. The homologation sequence was studied by employing nitrones derived from various chiral polyalkoxy aldehydes and dialdoses. The addition of 2-lithiothiazole to these nitrones was syn-selective, whereas the reaction with the same nitrones precomplexed with Lewis acids was anti-selective. Hence, from each nitrone a pair of diastereoisomeric hydroxylamines was obtained. These compounds were then converted by the above sequence into α-epimeric α-amino aldehydes. Model elaborations of some of these products afforded the amino sugars D-glucosamine, D-mannosamine, D-nojirimycin, and advanced intermediates for the synthesis of destomic acid and lincosamine.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19950010804
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    The Alkenyl Mechanism for Fischer-Tropsch Surface Methylene Polymerisation; the Reactions of Vinylic Probes with CO/H2 over Rhodium Catalyst (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 549-556 
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    ISSN: 0947-6539
    Keywords: alkenyl ; Fischer-Tropsch synthesis ; labelling studies ; rhodium compounds ; vinyl ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Results consistent with the participation of vinyls in the initiation and of alkenyl species in the propagation steps of the Fischer-Tropsch reaction are reported. Substantial incorporation of 13C2 into the alkene and alkane (C3-C7) hydrocarbon products occurred when doubly labelled vinyls (13C2H3Br. (13C2H3)4Si, or 13C2H4) were added as molecular probes to the hydrogenation of carbon monoxide over rhodium/ceria/silica catalysts (1 atm, 220°C). There was, by contrast, no significant incorporation of 13C1 into any of the organic products; thus cleavage of the C2 probe did not occur. The degree of 13C2 incorporation decreased with increasing molecular mass of the hydrocarbon; this indicates that the probe molecule initiated but did not propagate. A mathematical model based on polymerisation of surface methylenes initiated by a vinyl, propagated by alkenyls and terminated by reaction with a surface hydrogen or by coupling has been developed to explain the 13C2 incorporation data. Under the conditions of the experiments, the relative ability of the probes to initiate is: vinyl bromide (60%)〉tetravinylsilane (30%)〉ethene (15%). Substantial formation of 13C4 products also occurred when vinyl bromide or tetravinylsilane were used as probes; this arises from a dimerisation of the vinyl on the surface, a process which has been modelled in homogeneous systems and also by other workers in studies on single crystal surfaces. There was no significant 13C incorporation into the oxygenates (methanol, ethanol, acetaldehyde); these products are formed by a different path.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19950010809
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    Masthead (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995) 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010902
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    A Novel Low Molecular Weight Chiral Gelator for Apolar Organic Solvents (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 594-597 
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    ISSN: 0947-6539
    Keywords: electron microscopy ; gels ; helices ; self-assembly ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis, molecular structure, and properties of a new chiral gelforming agent 1 are described. Key structural features in 1 are a γ-alkoxybutyro-lactone tetralin moiety and an angular phenylsulphone unit. The new low molecular weight gelator 1 can reversibly form stable gels in low concentrations (e.g., 1:800 for n-hexane) with isopropanol and a variety of apolar organic solvents. The gels were studied with differential scanning calorimetry and a combination of electron microscopy techniques, which revealed a highly ordered three-dimensional network of entangled fibers. X-ray analysis showed that the aggregation of 1 leads to a helical structure in the solid state. Nonchiral analogues 2 and 3 were unable to initiate gel formation.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19950010905
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    Alkenyl Fischer Carbene Complexes and α,β-Unsaturated Imine Derivatives: Synthesis of Azepines and Mechanistic NMR StudiesDedicated to Professor Heinz Hoberg on the occasion of his 70th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 88-97 
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    ISSN: 0947-6539
    Keywords: azadienes ; azepines ; cycloadditions ; Fischer carbenes complexes ; reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 4-Amino-1-azadienes 1 react with α,β-unsaturated Fischer carbene complexes at -40°C to give stereoselectively a variety of substituted 3H-4,5-dihydroazepines 3; similarly, 1-hydroxy-1-azadienes (α,β-unsaturated oximes) 6 afforded the corresponding azepine derivatives 7. Chiral, nonracemic carbene complexes 11 gave azepines 12-13 (d.e. = 40-44%) upon reaction with oxime 6a; the major isomers were obtained in a diastereomerically and enantiomerically pure form (45-50% overall yield) after crystallization. An X-ray structure of 12a allowed assignment of the absolute stereochemistry. The acid hydrolysis of azepines synthesized provided racemic and enantiomerically pure 1,6-dicarbonyl compounds (±)-5, (±)-9, and (-)-14, as well as diol (-)-15. The mechanism of the reaction of 1 and 2 was investigated by multinuclear (1H, 13C, 15N, and 183W) NMR characterization of four intermediates (A, B, C, and D) at low temperature. The experimental sequence of events involves: i) 1,2-nucleophilic addition of the unsubstituted imine nitrogen of 1 to the metal carbene function (zwitterion A, -60°C), ii) cyclization to the seven-membered ring with 1,2-migration of the pentacarbonyl metal (zwitterion B, -40°C), iii) reductive elimination and coordination of the metal to the amine nitrogen (intermediate C, -40°C), and iv) thermal decomplexation and tautomerization (intermediate D and compound 3, above -20°C).
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19960020116
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    Cover page (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. cpi 
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    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020201
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    Masthead (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996) 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020202
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    Mechanism of an Alkyl-Dependent Photochemical Homolysis of the Re-Alkyl Bond in [Re(R)(CO)3(α-diimine)] Complexes via a Reactive σπ* Excited State (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 228-237 
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    ISSN: 0947-6539
    Keywords: homolytic cleavage ; organometallic compounds ; photochemistry ; rhenium complexes ; time-resolved spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: MLCT excitation of the complexes [Re(R)(CO)3(α-diimine)] (R = Me, Et, benzyl (Bz); α-diimine = iPr-PyCa, R′-DAB) results in the homolysis of the Re-R bond leading to the formation of radicals R. and [Re(CO)3(α-diimine)]. as primary photoproducts. The quantum yield of this photoprocess is dependent on the alkyl group used. For R = Me, the quantum yield is low (10-2) and depends on the temperature and excitation wave-length, whereas for R = Et and Bz the quantum yield is near unity and independent of T and λexc. The reaction is shown to proceed via a σ(Re-R)π* excited state that is rapidly (〈 20 ps) populated by a nonradiative transition from the optically excited MLCT state. Time-resolved IR and UV/Vis absorption spectra studied in the ns-μs and ps-μs time domains, respectively, show that the σπ* excited state is rather long-lived (τ ≈ 250 ns) in noncoordinating solvents; the dissociation of the Re-R bond from this state is strongly accelerated by polar or coordinating solvents (τσπ*〈 20 ps). The σπ* excited state is spectroscopically characterized by a (presumably σπ* → MLCT) transition at approximately 500 nm and by CO stretching frequencies closely resembling their ground-state values. The relative energies of the MLCT and reactive σπ* states, controlled by the nature of the alkyl lig-and, determine the photoreactivity of the complexes.
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    Design and Synthesis of a “Starburst”-Type Nonadiazo Compound and Magnetic Characterization of Its Photoproduct (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 259-264 
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    ISSN: 0947-6539
    Keywords: dendrimers ; high-spin molecules ; photochemistry ; polycarbenes ; solid solutions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A “starburst”-type nonadiazo compound was designed and synthesized by using the cyclotrimerization of 3,5-dibenzylphenyl ethynyl ketone as a key step. The diazo compound was photolyzed in methyltetrahydrofuran solid solution at cryogenic temperatures and analyzed by means of Faraday magnetometry and EPR spectroscopy. While the m-phenylene-connected nonacarbene was predicted to have a nonadecet (S = 9) ground state, the magnetic data of the photoproduct was more consistent with a pentadecet (S = 7) species. The result was interpreted in terms of the intramolecular cross-linking between the carbene centers by the determination of both the amount and the multiplicity of the spin. In the “starburst”-type polycarbenes with extended branching, the reactive carbene centers are able to approach one another and thus appear to readily recombine. This study highlights one of the limitations of the extension of the carbene network by way of flexible “starburst”-type structures.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19960020305
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    Synthesis, Structure, and Stereoselective Reaction of a Chiral Hydroxy-Stabilized Metal-Free Enolate (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 382-384 
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    ISSN: 0947-6539
    Keywords: asymmetric synthesis ; chirality ; enolates ; hydrogen bonds ; structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of acetophenone with tetrabutylammonium hydroxide affords the tetrabutylammonium enolate of phenyl (2-hydroxy-2-phenyl)propyl ketone. The crystal structure of this chiral enolate shows intramolecular hydrogen bonding between the hydroxyl group and the enolate oxygen atom. Furthermore, the α-methylene units of the ammonium counterion form hydrogen bonds to the basic enolate C and O atoms and to the O atom of the hydroxy group. This three-point bonding occurs selectively on the Re,Re side, a phenomenon which may be responsible for the direction of diastereo-selectivity in the epoxide-forming reaction of the enolate with N-bromosuccinimide.
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    URL: http://dx.doi.org/10.1002/chem.19960020405
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    A 2,3-Connected Tellurium Net and the Cs3 Te22 Phase (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 390-397 
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    ISSN: 0947-6539
    Keywords: band structures ; hypervalent bonding ; semiempirical calculations ; tellurium compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The bonding in the recently reported Cs3 Te22 phase, which contains both Te8 rings and remarkable Te6 sheets, is studied by approximate molecular orbital theory. Our focus is on the geometric and electronic features of the unique 2,3-connected Te net found as a substructure in this phase. The calculations show that both the linear and T-shaped Te geometries in the 2,3-connected Te net of Cs3 Te22 are determined by their particular electron count. Both types of tellurium atoms are hypervalent; we make connections to other well known hypervalent molecules, such as XeF2, I3-, and BrF3. Several possible variations and distortions of this net are discussed, all of which are found to be less stable. The discrete crown-shaped Te8 units that appear in the phase show normal covalent bonding and should occur in smaller molecular entities, too. According to our computations, Cs3 Te22 should be metallic. Two structurally related phases, CsTe7 and Cs2 Te15, are suggested.
    Additional Material: 10 Ill.
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    Zirconium(II)- and Hafnium(II)-Assisted Reductive Coupling of Coordinated Carbonyl Groups Leading to Ketenylidene Complexes of Zirconium(IV) and Hafnium(IV) (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 412-419 
    Details
    ISSN: 0947-6539
    Keywords: carbon-carbon coupling ; carbonyl complexes ; hafnium complexes ; ketenylidene complexes ; zirconium complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The biscyclopentadienyldicarbonyl derivatives of zirconium(II) and hafnium(II) ([MCp2(CO)2]; M=Zr, Hf) promote the reductive coupling of coordinated carbon monoxide to give, in the presence of N,N-dialkylcarbamtes of the tetravalent metals [M(O2CNR2)4], the ketenylidene complexes [M3Cp2(μ2-CCO)-(μ3-O)(O2CNR2)6] (1 a: M=Zr, R=Et; 1 b: M=Zr, R=iPr; 2: M=Hf, R=iPr). The yields of the isolated zirconium complexes are as high as 60%, while that of the hafnium derivative is 40%. The X-ray crystal structure analysis of 1 b shows that it consists of trinuclear molecules, with the three zirconium atoms held together by the bidentate C2O ligand, by the tridentate bridging oxide and by the bidentate carbamato groups. Labelling experiments with [ZrCp2(13CO)2] show that the ketenylidene ligand originates from the coordinated CO groups. These ketenylidene complexes, which are rare examples of compounds containing a CCO but no CO ligand, are characterized by an intense IR band at about 2015 cm-1, associated with the bridging C2O ligand. The ketenylidene group of 1 b was readily removed and replaced by a bidentate μ-oxo ligand of the same hapticity by reaction with carbon dioxide or acetone or by thermal decomposition. The resulting product [Zr3Cp2(μ-O)(μ3-O)-(O2CNiPr2)6] (3) crystallizes in the same space group as 1 b and with similar cell constants and bond parameters.
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    9-Borabarbaralanes (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 458-461 
    Details
    ISSN: 0947-6539
    Keywords: ab initio calculations ; barbaralanes ; borabarbaralanes ; Cope rearrangement ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of MgCOT(thf)x with tBuBF2 or PhBCl2 affords the first 9-borabarbaralanes 2 (C8H8BR, a: R = tBu; b: R=Ph). With the aminoboron dihalides BCl2NiPr2 and BCl2N(SiMe3)tBu 9-borabicyclo[4.2.1]-nona-2,4,7-trienes 3 (a: R=NiPr2, b: R=N(SiMe3)tBu) and the trans-9-borabicyclo[4.3.0]nona-2,4,7-triene 4 are obtained. The bicyclic compounds 3a and 3 b are converted into 9-borabarbaralanes 2c and 2 d, respectively, by irradiation in solution as well as by heating. All 9-borabarbaralanes 2 are fluxional in solution. In the crystalline state, the B-phenyl derivative 2b displays a well-ordered van der Waals crystal structure. The theoretical prediction that the degenerate Cope rearrangement in barbaralanes will be retarded by π-acceptor groups in the 9 position has been verified. Quantum chemical calculations employing density functional theory support and help interpret the experimental findings. The isoelectronic 9-barbaralyl cations, in contrast, have such high Cope barriers that other rearrangement pathways are followed instead.
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    Solvent Effect on the NMR Chemical Shieldings in Water Calculated by a Combination of Molecular Dynamics and Density Functional Theory (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 452-457 
    Details
    ISSN: 0947-6539
    Keywords: density-functional theory ; liquid water ; molecular dynamics simulations ; NMR chemical shifts ; solvent effects ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The solvent effect on the NMR chemical shielding in liquid water is calculated from a combination of molecular dynamics simulations and quantum chemical calculations for protons and 17O. The simulations are performed with three different potentials, ab initio as well as empirical ones, to study the influence of the force field. From the liquid configurations obtained in these simulations, molecules are randomly chosen together with neighbouring molecules to give clusters of water typical for the liquid at the selected temperature and density. Different cluster sizes are studied. The clusters are treated as supermolecules in quantum chemical calculations of chemical shifts by sum-over-states density functional perturbation theory with individual gauge for localised orbitals. The influence of the quantum chemical method is studied with an ab initio coupled Hartree-Fock gauge including atomic orbitals calculations with different basis sets for a selected cluster. An average over clusters yields the chemical shielding in the liquid at the selected temperature and density. The calculated values for the gas-liquid shift, which are in best agreement with experiment, are -3.2 ppm (exp. -4.26 ppm) for the proton and -37.6 ppm (exp. -36.1 ppm) for 17O, but the results depend strongly on the chosen interatomic potential.
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    Editorial (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 3-3 
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    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    URL: http://dx.doi.org/10.1002/chem.19950010104
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    Hexaalkyl Terpyrrole: A New Building Block for the Preparation of Expanded Porphyrins (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 56-67 
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    ISSN: 0947-6539
    Keywords: amethyrin ; orangarin ; porphyrinoids ; terpyrroles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new, general synthesis of the first β-substituted tetra- and hexaalkyl terpyrroles is described. Also described are two new classes of expanded porphyrins derived from the hexaalkyl terpyrrole. The key step in the terpyrrole formation is the copper(II)-mediated oxidative coupling of the LDA-derived enolates of α-keto pyrroles. The first new expanded porphyrin reported here, the so-called “orangarin”, contains five pyrrolic subunits and two bridging carbon atoms, and is formally a 20π-electron nonaromatic macrocycle. The second new class of expanded porphyrins, the “amethyrins”, are 24π-electron nonaromatic macrocycles containing six pyrrole units. Both of these new macrocycles, as well as one of the new terpyrrolic precursors have been structurally characterized by single crystal X-ray diffraction analysis.
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    Ninth European Symposium on Organic Chemistry. Warsaw, Poland. June 18-23, 1995 (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 100-100 
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    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    URL: http://dx.doi.org/10.1002/chem.19950010115
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    Cover Page (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. cpi 
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    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    URL: http://dx.doi.org/10.1002/chem.19950010201
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    In3Ti2Br9: Jahn-Teller Unstable Indium(I) and Antiferromagnetically Coupled Titanium(III) Atoms (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 118-123 
    Details
    ISSN: 0947-6539
    Keywords: antiferromagnetic exchange ; crystal structure ; indium compounds ; Jahn-Teller distortion ; titanium compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dark green crystals of In3Ti2Br9 have been synthesized from elemental Ti and molten InBr3 at 450°C. The X-ray diffractional characterization by means of single-crystal and powder Rietveld refinement reveals a hexagonal crystal structure (a = 738.2(2), c = 1813.9(3) pm; P63/mmc, Z = 2) of Cs3Cr2Cl9 type, containing Ti2Br3-9 dimers and univalent indium cations. Self-consistent, semiempirical band structure calculations show the structural distortions of the two monovalent indium cations to arise from a second-order Jahn-Teller instability. The new compound's magnetic susceptibility and microscopic antiferromagnetic exchange are analyzed by using a Bleaney-Bowers ansatz.
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    Anion-cation redox competition and the formtion of new compounds in highly covalent systems (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1053-1059 
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    ISSN: 0947-6539
    Keywords: chalcogenides ; periodic trends ; redox reactions ; soft chemistry ; transition metals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The increase in energy of the sp anionic band on going from oxides to the less electronegative sulfides, selenides, or tellurides (with a similar trend in neighboring columns) facilitates anion-cation redox interactions involving the d levels of transition metal cations and the sp levels of anionic species. The interactions can induce phase transitions or gradual change within a given structural model. When a cation is reduced by electron transfer to its d levels from the sp band, holes appear at the top of the latter. Interesting soft chemistry can be carried out based on redox processes that neutralize the holes with electrons. This approach also allows particular structural types to be stabilized. Three structural domains can be recognized amongst the transition elements: 1) on the left-hand side of the periodic table layered structures are observed involving M4+ and (chalcogen)2- ions; 2) formation of sets of metal-metal bonds is then observed, the geometry of which depends on both the initial electron population and the electron transfer to the metal; 3) on the right-hand side the metals in their highest oxidation state are no longer active, and the holes at the top of the sp band are taken up by a catenation of the anions, which can lead to full polymerization of the anionic sublattice.
    Additional Material: 8 Ill.
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    Dendritic models of redox proteins: X-ray photoelectron spectroscopy and cyclic voltammetry studies of dendritic bis(terpyridine) iron(II) complexes (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1085-1091 
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    ISSN: 0947-6539
    Keywords: cyclic voltammetry ; dendrimers ; metallodendrimers ; terpyridine ; X-ray photoelectron spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of iron-containing metallodendrimers from the zeroth to the third generation was synthesized and characterized. The iron(II) ion of these metal complexes is encapsulated within a hydrophobic polyether dendritic envelope. X-ray photoelectron spectroscopy analysis revealed that the bonding environment of the iron atom was essentially ronment of the iron atom was essentially the same in dendrimers of different generations. However, cyclic voltammetry studies indicated that the reversibility of the metal redox process decreased in the higher-generation dendrimers. These observations were similar to those of a related electrochemical study conducted on the redox protein cytochrome C, in which the decrease in electron transfer reversibility was explained as a result of the increasing remoteness of the metal ion of the higher-generation dendrimers from the electrode surface.
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    URL: http://dx.doi.org/10.1002/chem.1460020906
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    An unexpected structural principle for crystalline MgBr2·OEt2: Chains of trigonal bipyramids (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1112-1114 
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    ISSN: 0947-6539
    Keywords: coordination ; crystal structure ; halogen compounds ; magnesium compounds ; structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: MgBr2·OEt2 (1), which is commercially available and has been examined by different methods in the past, was obtained in crystalline form as a by-product of the reaction of amine-stabilised A1C1 solution with mesitylene magnesium bromide. The following unexpected structure was obtained by X-ray techniques: five-coordinate magnesium centres form trigonal bipyramids, which are connected by two common bromine atoms into chains. Structural details and especially the relationship with solid MgBr2, MgBr2·(OEt2)2 and MgI2·(OEt2)2 (2) are discussed in order to illuminate the unusual bonding in 1.
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    High-spin → low-spin relaxation in [Fe(bpp)2](CF3SO3)2 H2O after LIESST and thermal spin-state trapping - dynamics of spin transition versus dynamics of phase transitionDedicated to Professor Gerhard Herberich on the occasion of his 60th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1134-1138 
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    ISSN: 0947-6539
    Keywords: iron complexes ; magnetic susceptibility ; Mössbauer spectroscopy ; phasetransitions ; spin crossover ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The iron(II) complex [Fe(bpp)2]-(CF3SO3)2 H2O (bpp = 2,6-bis(pyrazolyl-3-yl)pyridine) shows a thermal spin transition associated with a hysteresis of approximately 140 K width. The transition temperatures T1/2 (where the fraction of HS species γHS = 0.5) are 147 K and ≍285 K in the cooling and heating directions, respectively. The compound shows the LIESST and reverse-LIESST effects at low temperatures. The relaxation of the metastable HS states generated by LIESST was observed quantitatively at temperatures between 77.5 and 85 K by Mössbauer spectroscopy. Metastable HS states can also be generated by rapid cooling of the sample. The relaxation of the metastable HS states formed by thermal spin-state trapping was monitored at temperatures between 104 and 118 K by magnetic susceptibility measurements. The relaxation mechanisms of the HS states generated by LIESST and thermal spinstate trapping are completely different. We suggest that the HS → LS relaxation after thermal spin-state trapping is triggered by an additional structural phase transition of the system.
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    Synthesis of enantiopure homoallylic alcohols and ethers by diastereoselective allylation of aldehydes (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1164-1172 
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    ISSN: 0947-6539
    Keywords: allylations ; allylsilanes ; double stereodifferentiation ; ephedrine ; homoallylic alcohols ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantiopure homoallylic alcohols 5, which are important building blocks in organic synthesis, are obtained with an ee of greater than 99% and a yield of 75-95% by cleavage of the secondary homoallylic ethers 4 using sodium in liquid ammonia. The ethers 4 are formed with excellent diastereoselectivity and in 52-89% yield by treatment of the aldehydes 1 with the trimethylsilyl ether of N-trifluoroacetylnorpseudoephedrine (2) in the presence of a catalytic amount of TMS triflate or TMS borontriflate, followed by addition of allylsilane 3. Nearly all achiral aliphatic aldehydes employed gave a diastereoselectivity of over 99:1. With the chiral aldehydes 24, the difference between matched and mismatched pairs was low; this reveals that there is strong reagent control.
    Additional Material: 2 Tab.
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    Masthead (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996) 
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    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    URL: http://dx.doi.org/10.1002/chem.19960021002
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    Hydrogen, the First Alkali Metal (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1201-1203 
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    ISSN: 0947-6539
    Keywords: alkali metals ; hydrogen ; metallic hydrogen ; metallization densities ; periodicity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We examine the density-dependent metal-nonmetal transition (MNMT) for the Group 1 elements hydrogen, rubidium and caesium. Remarkably, the experimentally observed metallization densities agree closely with those predicted from the 1927 classical theory of K. F. Herzfeld, which outlines the critical conditions necessary for the metallization of any element of the periodic system. The metallization densities of the alkali metal elements are also consistent with the quantum mechanical theory of the MNMT, as first set out by Sir Nevill Mott.
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    Synthesis, Structure, and Reactivity of Chiral Rhenium N-Pyrrolyl Complexes Regiochemistry of Electrophilic Addition and Unprecedented Rearrangements to Carbon-Ligated Species (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 294-303 
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    ISSN: 0947-6539
    Keywords: electrophilic additions ; N-pyrrolyl complexes ; rearrangements ; rhenium compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of [{Re}(OTf)] (1; {Re}  -  (η5-C5H5)Re(NO)(PPh3) and potassium pyrrolide gives the N-pyrrolyl complex 2, 88%). Reactions of 2 with (CF3CO)2O/N(C2H5)3 and CH3O2CC=CCO2CH3 give 3- and 2-substituted pyrrolyl complexes respectively (3, R/R′ = H/COCF3, 77%; 5, R/R′ = C(CO2CH3)=CHCO2CH3/H, 69-87%). Free pyrrole is much less reactive towards these reagents. Reactions of 2 and TfOH or HBF4·OEt2 give the 2H-pyrrole adducts +X- (7+X-; 89-83%). At 0-25°C in CH2Cl2, these rearrange to the carbon-ligated tautomers +X-(8+X-) and then +X-; (9+X-; 72-96 h, 90-96%). Reaction of 1 and pyrrole in refluxing toluene gives 8+TfO- and then 9-TfO- (92%). However, 1 and pyrrole react too slowly in CH2Cl2 to be intermediates in the conversion of 7+TfO- to 9+TfO-. Reaction of 9+ TfO- and KH gives the C-pyrrolyl complex (68%), which adds TfOH to give 9+TfO-. Mechanistic aspects of the preceding reactions are discussed. The crystal structures of 2 and 9+TfO- are determined, and the NC4Hx ligand conformations analyzed with extended Hückel MO calculations.
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    Cover Page (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. cpi 
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    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    URL: http://dx.doi.org/10.1002/chem.19950010601
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    Total Synthesis of RapamycinA list of abbreviations used in this article is given in ref. [49]. (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 318-333 
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    ISSN: 0947-6539
    Keywords: rapamycin ; stannylethenes ; Stille coupling ; vinyl iodides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Details of the total synthesis of rapamycin (1) are reported. The synthesis required the preparation of intermediates 4 - 9 in nonracemic form; key coupling reactions included a chromium-mediated addition of vinyl iodide 8 to aldehyde 7 and an Evans aldol reaction to couple fragments 62 and 9. Intermediates 4 and 6 were joined through an amide bond formation to afford advanced intermediate 71. Swern oxidation of the diol in 71 was followed by a selective removal of the TES groups and a second Swern oxidation. Finally, removal of the remaining silyl protecting groups provided fully deprotected, penultimate intermediate 2 in which all carbons were in their proper oxidation state. Macrocyclization was achieved through a tandem inter/intramolecular palladium-mediated Stille coupling reaction between distannylethene 3 and bis(vinyl iodide) 2. This latter process accomplished in one step the installation of the remaining two carbons of the natural product and the completion of its total synthesis.
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    New Coordinatively Unsaturated Lutetium Mono- and Bis(alkyl) Complexes with a Bis(ortho)-Chelating Aryldiamine Ligand - Crystal Structures of [LuCl2{2,6-(Me2NCH2)2C6H3}(μ-Cl)(μ-Li(thf)2)]2 and [Lu(μ-Cl){2,6-(Me2NCH2)2C6H3}(CH2SiMe3)]2 (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 343-350 
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    ISSN: 0947-6539
    Keywords: ate complexes ; intramolecular coordination ; lutetium complexes ; organometallic compounds ; yttrium complexes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New complexes of lutetium and yttrium containing the monoanionic, terdentate ligand [2,6-(Me2NCH2)2C6H3]- (NCN) have been synthesized by substitution reactions starting from MCl3 (M = Lu, Y). Reaction of MCl3 (M = Y, Lu) with one equivalent of (NCN)Li affords the ate complexes [(NCN)MCl2(μ-Cl)(μ-Li(thf)2)]2) (M = Lu (1a), Y (1b)) in which the terdentate ligand is bound in mer fashion and all three chloride atoms are retained in the product. Crystals of 1a are monoclinic (space group P21/n, a =10.4559(4), b = 21.6150(9), c=12.1700(7) Å, β = 105.294(4)°, Z = 2, final R = 0.039 for 3695 observed reflections [I〉2.50σ(I)]). Attempted substitution of chloride in the yttrium complex 1b by Me3SiCH2- leads to decomposition. However, reaction of 1a with Me3SiCH2Li gives the monoalkyl complex [(NCN)Lu-(μ-Cl)(CH2SiMe3)]2 2, 30% yield), in which the terdentate ligand is bound in a pseudo-facial manner. Crystals of 2 are triclinic (space group P1, a = 9.8575(7), b = 10.0171(7), c = 11.1460(14) Å, α = 75.096(8). β = 78.092(8), γ =77.474(6)°, Z = 1, final R1 = 0.11 for 1361 reflections [I 2σ(I)]). Substitution of the chloride ions in 2 by Me3SiCH2- is possible and affords quantitatively the bisalkyl complex [(NCN)Lu(CH2SiMe3)2] (3). The lutetium complexes 2 and 3 are formally coordinatively unsaturated complexes, which are moisture-sensitive and thermally stable for several weeks when dissolved in aromatic solvents. However, they decompose rapidly in aliphatic solvents such as hexane, and a decomposition route involving the formation of carbene species is proposed.
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    Masthead (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995) 
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    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010702
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  • 180
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    Biologically Induced Reduction in Symmetry: A Study of Crystal Texture of Calcitic Sponge Spicules (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 414-422 
    Details
    ISSN: 0947-6539
    Keywords: biomineralization ; calcite ; crystal morphology ; mosaic structure ; symmetry reduction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Organisms can exert a remarkable degree of control over crystal growth. One way of achieving this is by the adsorption of specialized macromolecules on specific planes of the growing crystals. With continued growth of the crystal, the macromolecules are incorporated inside the crystal bulk. Their presence does not change the crystal structure, but creates discontinuities in the perfect lattice. Here we study in detail three unusual cases of reduction in symmetry at the level of crystal domain shapes, induced by this controlled intercalation. We examined sponge spicules, which are single crystals of Mg-bearing calcite. They were specifically chosen for this study, because their morphologies do not reflect the hexagonal symmetry of calcite. Their crystal textures (coherence lengths and angular spreads) were characterized by high-resolution X-ray diffraction with well-collimated synchrotron radiation. The results are compared to analogous studies of synthetic calcite and Mg-bearing calcite. In all the selected spicules reduction in symmetry is observed in the coherence lengths among symmetry-related crystallographic directions. The reconstructed shapes of the domains of perfect structure closely match the specific spicule morphologies. The synthetic crystals show no such reduction in symmetry. Although the manner by which such exquisite control is achieved is not known, we envisage it involving a combination of oriented nucleation with either physical or stereochemically driven adsorption.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/chem.19950010705
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  • 181
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    Asymmetric Synthesis of Carboranyl Amino Acids with Potential use in BNCT (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 430-435 
    Details
    ISSN: 0947-6539
    Keywords: amino acids ; asymmetric synthesis ; BNCT ; carboranes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two α-amino acids containing the 1,2-dicarba-closo-dodecaborane (12) cage, namely, 5-(1,2-dicarba-closo-dodecaboran (12)-1-yl)-2-aminopentanoic acid (1) and 5-(2-methyl-1,2-dicarba-closo-dodecaboran (12)-1-yl)-2-aminopentanoic acid (2), were prepared by asymmetric synthesis (e.p. 〉 98%) by using the chiral glycine equivalent, imidazolidinone 3, introduced by Seebach, and Oppolzer's camphor-derived sultam derivative 4. The dextrorotatory enantiomers (sodium D line in methanol) of the amino acids 1 and 2 were both shown to have (S) configuration.
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  • 182
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    Ab initio Study of the Coordination Modes of the Tetrahydroborato Ligand: Structure of the [Cu(BH4)(PH3)n] (n = 1, 2, 3) Complexes (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 436-440 
    Details
    ISSN: 0947-6539
    Keywords: ab initio calculations ; copper compounds ; organometallic compounds ; tetrahydroborato ligand ; theoretical chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: All-electron ab initio calculations (MP4/MP2 level) have been performed on [Cu(BH4)(PH3)n] (n = 1, 2, 3) complexes. Full-geometry optimizations were carried out in each case, and the stationary points were characterized by the diagonalization of the analytically calculated Hessian matrix. The η2 coordination mode, with a tetrahedral arrangement around the copper atom, is the most stable structure for n = 2, while for n = 3 a strongly nonlinear η1 coordination mode is preferred. These results are in agreement with the experimental data available on related complexes. For n = 1, for which there is no experimental data, the η3 structure turns out to be the most stable. The energy differences associated with some changes in the coordination mode (η1 → η2 for n = 3 and η3 → η2 for n = 1) are small. Finally, a mechanism for the exchange between terminal and bridging hydrogen atoms is proposed for each complex under study.
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    Total Synthesis of Balanol and Designed Analogues (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 454-466 
    Details
    ISSN: 0947-6539
    Keywords: antitumour agents ; balanol ; enzyme inhibitor ; natural product ; total synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The total synthesis of balanol, a potent protein kinase C inhibitor isolated from the fungus Verticillium balanoides, is described. The hexahydroazepine fragment was prepared from D-serine through a sequence of reactions including the diastereoselective allylboration of a derived amino aldehyde and a base-induced 7-exo-tet ring closure as key steps. The benzophenone fragment was secured through the initial coupling of the two functionalised aromatic components through an ester linkage, followed by intramolecular nucleophilic attack of an aryl lithium derivative to form the desired ketone bridge. After coupling of the two balanol domains, the adoption of benzylderived protecting groups for the latent functionalities then allowed the liberation of balanol in a single step by catalytic hydrogenolysis. Finally, the newly developed synthetic strategy was applied to the synthesis of a variety of designed balanol analogues for biological evaluation.
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    Graphical Abstract (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. i 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010803
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  • 185
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    New PF3 and Carbonyl Chemistry of TantalumHighly Reduced Organometallics, Part 37. Part 36: M. Jang, J. E. Ellis, Angew. Chem. 1994, 106, 2036; Angew. Chem. Int. Ed. Engl. 1994, 33, 1973.Dedicated to Professor Fausto Calderazzo on the occasion of his 65th birthday (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 521-527 
    Details
    ISSN: 0947-6539
    Keywords: carbonyl ligands ; organometallic compounds ; phosphorus ligands ; tantalum compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reduction of [TaCl5] by six equivalents of alkali metal naphthalenide in 1,2-dimethoxyethane at -60°C followed by treatment with gaseous PF3 provides the first homoleptic phosphane complex containing tantalum in the -1 oxidation state, [Ta(PF3)6]-. This can be protonated by concentrated sulfuric acid to yield the previously unknown highly acidic and volatile hydride [HTa(PF3)6]. An improved normal-pressure synthesis of [Ta(CO)6]- is described. Reduction of the latter species by sodium in liquid ammonia gives the carbonyl trianion [Ta(CO)5]3- which undergoes monoprotonation and stannylation to form [HTa(CO)5]2- and [Ph3SnTa(CO)5]2-, respectively. The hydride is a useful precursor to [(Ph3PAu)3Ta(CO)5], the only known gold cluster of tantalum.
    Additional Material: 3 Ill.
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    The Reduction of [Fe(CO)2L2X2] (L = P(OMe)3, P(OiPr)3, PEt3; X = Br, I) - From Iron(II) to Iron(0) via Stable Iron(I) Intermediates (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 541-548 
    Details
    ISSN: 0947-6539
    Keywords: dinitrogen complexes ; EPR spectroscopy ; iron compounds ; reductions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reduction of [Fe(CO)2-L2X2] (L = P(OMe)3 X = Br (1a), I (1b); L = P(OiPr)3, X = Br (2a), I (2b); L = PEt3, X = Br (3a), I (3b)) with Zn in dioxane (1a,b-2a,b) or PhLi in ether (3a,b) led to formation of the corresponding dicarbonyl(halo)bis(phosphorus donor)iron(I) complexes (L = P(OMe)3, X = Br (4a), I (4b); L = P(OiPr)3, X = Br (5a), I (5b); L = PEt3, X = Br (6a), I (6b)). Slightly contaminated 5a,b and pure 6a,b were isolated as stable crystalline blue or blue-green complexes. Complexes 4a,b were obtained, with only minor impurities, by comproportionation of 1a,b and the dicarbonyl(halo)bis-(trimethylphosphite)ferrate anions 7a,b and characterized in THF solution. The comproportionation products 5a,b-6a,b were obtained in high yields by reaction of 2a,b-3a,b with the dinitrogen complexes 13-15. Further reduction of 4a,b-6a,b or exhaustive reduction of 1a,b-3a,b with sodium amalgam or iBuLi in THF afforded the nonisolable dicarbonyl-(halo)bis(phosphorus donor)ferrate(o) anions (7a,b-9a,b). The latter were characterized by acidification with trifluoroacetic acid or acetic acid yielding stable dicarbonyl (halo) hydridobis (phosphorus donor)iron(II) complexes (L = P(OMe)3, X = Br (10a), I (10b); L = P(OiPr)3, X = Br (11a), I (11b);L = PEt3, X = Br (12a), I (12b)). In the presence of N2, 8a was transformed into dinitrogen complex [Fe(CO)2{P(OiPr)3}2N2] (13). With 9a,b the reaction led to formation of [Fe-(CO)2(PEt3)2)2N2] (14) and [{Fe(CO)2-(PEt3)2}2(μ-N2)] (15). In solution at low temperature (-90 to 0°C), the dinitrogen complexes 14 and 15 are in equilibrium with each other. Complexes 13, 14, and 15 were characterized by IR, 1H, 13C, 31P, and 15N NMR spectroscopy. The structures of 5a, 6b, 14, and 15 were determined by X-ray diffraction studies.
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    Graphical Abstract (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. i 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010903
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  • 188
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    The Design of Selective Chelating Agents: 1,3,5-Trideoxy-1,3,5-tris-(dimethylamino)-cis-inositol, a Powerful Ligand for Hard and Highly Charged Metal Ions1,3,5-Triamino-1,3,5-trideoxy-cis-inositol, a Ligand with a Remarkable Versatility for Metal Ions, Part 7. Part 6: K. Hegetschweiler. M. Ghisletta, T. F. Fässler, R. Nesper, Angew. Chem. Int. Ed. Engl. 1993, 32, 1426. (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 74-88 
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    ISSN: 0947-6539
    Keywords: chelate ligands ; hydrogen bonds ; ligand design ; mass spectrometry ; stability constants ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of compounds containing the mononuclear complexes [M(tdci)2]3+ (tdci = 1,3,5-trideoxy-1,3,5-tris(dimethylamino)-cis-inositol, M = Al, Fe, Ga, In) and [M(tdci)2]4+ (M = Ti, Ge, Sn) was prepared and characterized by elemental analysis, NMR spectroscopy, and FAB mass spectrometry. Characteristic fragmentation reactions in the mass spectra were elucidated. X-ray analysis of the AlIII, FeIII, GaIII, and InIII complexes revealed that two neutral, zwitterionic tdci ligands coordinate to the metal cation exclusively through deprotonated alkoxo groups. The six coordinated oxygen donors and the six N—H protons form a hydrophilic pocket, whereas the two cyclohexane rings and the twelve methyl groups form two hydrophobic shells. The hydrophilic pocket is filled with twelve water molecules, which are arranged as a second and a third coordination sphere around the metal cation. The reactivity in aqueous solution was investigated by potentiometric measurements. The bis complexes proved to be stable at pH 7. The evaluated formation constants show an increase of stability in the order AlIII〈InIII〈GaIII〈FeIII. The measurements established that tdci is one of the most effective tridentate ligands for small (r ≤ 0.8Å) and highly charged cations. The different chelating properties of tdci and of the unmethylated 1,3,5-triamino- 1,3,5-trideoxy-cis-inositol are discussed in terms of different steric requirements and different types of solvation of the corresponding complexes in aqueous solution.
    Additional Material: 10 Ill.
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    The Stereochemistry of Carbenoid Cyclopropanation ReactionsChiral Organometallic Reagents, Part XV. For Part XIV, see ref. [1]. (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 619-624 
    Details
    ISSN: 0947-6539
    Keywords: alkenes ; carbenoids ; carbolithiations ; cyclopropanations ; mechanistic studies ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stereochemical course of the intramolecular carbenoid cyclopropanation reaction has been studied for the epimeric carbenoids 12a and 12b. In these reactions the tert-butyldimethylsilyloxy substituent serves as an internal stereochemical reference point. It was found that 12b cyclizes rapidly at -110°C in a complexation-assisted concerted process to give the bicyclo[3.1.0]hexane 16. The diastereomer 12a cyclizes more slowly at -100°C to give both 16 and 17; the former is probably formed by a complexation-assisted carbolithiation pathway.
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    Masthead (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996) 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020102
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  • 191
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    The Role of Porphyrin-to-Porphyrin Linkage Topology in the Extensive Modulation of the Absorptive and Emissive Properties of a Series of Ethynyl- and Butadiynyl-Bridged Bis- and Tris(porphinato)zinc Chromophores (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 645-651 
    Details
    ISSN: 0947-6539
    Keywords: conjugation ; connectivity ; electronic coupling ; metalloporphyrins ; photosynthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new method for the regulation of the photophysical properties of highly conjugated porphyrin arrays is described. The absorptive and emissive signatures of such supramolecular structures can be modulated to an impressive degree by regulation of: i) the extent of the steric interactions that define the barrier to rotation about the conjugated bridge between the porphyrin chromophores, and ii) the magnitude of ground state chromophore-chromophore electronic communication within the supermolecule. The power of this approach is illustrated by the straightforward synthesis as well as the electronic and emission spectra of eight different porphyrin arrays in which (5,10,15,20-tetraphenylporphinato)zinc(11) and (10,20-diphenylporphinato)zinc(11) complexes are joined by ethyne or butadiyne groups. The points of connectivity of these bridges between the chromophoric building blocks are systematically varied to produce a series of supramolecular structures with meso-to-meso, meso-to-β, or β-to-β linkage topologies. These variations allow excellent control of the ground- and excited-state characteristics of the arrays in the series by regulating the degree of both excitonic and electronic porphyrin-to-porphyrin coupling. Our approach shows the precision with which photophysical properties can be engineered in appropriately designed supramolecular systems.
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  • 192
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    Thermochemistry of Metal Nitrides in the Ca/Zn/N System (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1514-1517 
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    ISSN: 0947-6539
    Keywords: calcium compounds ; calorimetry ; nitrides ; ternary metal nitrides ; zinc compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The energetics of ternary oxide formation is reasonably well understood, but little is known of the energetics of ternary nitride formation. We have developed new procedures for high-temperature oxide melt solution calorimetry on metal nitrides and employed them to study compounds in the Ca/Zn/N system. The calorimetry utilized the easy reduction of MoO3 in the solvent to supply a pathway for rapid oxidation of “N3-” to N2 gas. These experiments represent the first high-temperature solution calorimetry of ternary metal nitrides. The results indicate that Ca3N2 acts as a basic nitride analogous to CaO in oxide systems, while Zn3N2 acts as an acidic nitride (“N3-” acceptor) in this ternary nitride system.
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    Oxygen and Nitrogen in Competitive Situations: Which is the Hydrogen-Bond Acceptor? (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1509-1513 
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    ISSN: 0947-6539
    Keywords: ab initio calculations ; binding studies ; crystal packing ; drug design ; hydrogen bonds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the design of novel protein ligands one of the major challenges is the replacement of functional groups to modify and improve the binding characteristics. Often nitrogen- and oxygen-containing groups are exchanged, or both atoms occur in a competitive situation. We have investigated the hydrogen-bonding abilities of oxygen atoms covalently bound to two non-hydrogen atoms of which at least one is formally assigned to an sp2-type hybridization. In particular, examples in which such oxygen atoms compete with nitrogen atoms in the same molecular segment have been studied. Based on interaction energies obtained from ab initio calculations for complexes of these molecules with water, the oxygen atoms can be classified as rather weak hydrogen-bond acceptors; nitrogen atoms present in the same fragment exhibit much stronger interaction energies. The ab initio results are confirmed by the relative frequencies with which oxygen and nitrogen atoms are found to be involved in hydrogen bonding in the crystal structures of organic molecules containing the fragments of interest.
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    Ruthenium(II)-Catalyzed Oppenauer-Type Oxidation of Secondary Alcohols (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1533-1536 
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    ISSN: 0947-6539
    Keywords: catalysis ; dehydrogenations ; oxidations ; ruthenium complexes ; secondary alcohols ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Highly efficient ruthenium-catalyzed Oppenauer-type oxidations of secondary alcohols to ketones have been developed. The catalytic system consists of [(PPh3)3RuCl2] (1) and K2CO3 or [(C4Ph4COHOCC4Ph4)(μ-H)(CO)4Ru2] (2) in refluxing acetone. The catalytic reaction is of high efficiency and permits a catalyst: substrate ratio of 1:1000 at 56 °C. In some cases the initial turnover rate exceeds 1500 h-1. The reaction was found to be general and compatible with double bonds and oxidation-sensitive aromatics. With some allylic alcohols, isomerization to saturated ketones took place. The reaction proceeds by ruthenium-catalyzed dehydrogenation of the alcohol and subsequent hydrogen transfer to acetone. No primary kinetic isotope effect was observed for the catalytic reaction when α-deuterated 1-phenylethanol was employed as substrate (kH/kD=1.1); this shows that β-hydride elimination from a ruthenium alkoxide intermediate is not the rate-limiting step.
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    Synthesis, Reactions, and Molecular Structures of Ethylzinc Enolates of Chiral N-Substituted β-Carbonyl Sulfoximines (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 312-317 
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    ISSN: 0947-6539
    Keywords: aggregates ; asymmetric syntheses ; stereochemistry ; sulfoximines ; zinc enolates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation, structural characterization, and reactivity of ethylzinc-containing enolates and organometallics derived from β-carbonyl sulfoximines are reported. X-ray crystal structures show significant differences between aggregated species obtained from β-keto and β-amido sulfoximines. Whereas the former gives an O-metalated ethylzinc enolate, the latter crystallizes as C-metalated carbonyl species. NMR investigations reveal the presence of chelated zinc enolates in solution. The relationship between structure and reactivity is demonstrated by the reaction profiles of the ethylzinc-containing compounds. A high diastereoselectivity (〉 90% de) was observed in the aldol reaction between the metalated β-amido sulfoximine and benzaldehyde in the presence of trimethylsilyl chloride.
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    Phase Relationships in the N2O3/N2O4 System and Crystal Structures of N2O3 (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 389-393 
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    ISSN: 0947-6539
    Keywords: crystal structure ; differential thermal analysis ; nitrogen oxides ; phase transitions ; twinning ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Mixtures of N2O3 and N2O4 have been prepared from measured volumes of NO and O2. Phase relationships in the system N2O3/N2O4, which depend on the composition of the samples and on the temperature, were studied by the Guinier technique and differential thermal analysis. Single crystals of phases A and B of N2O3 were grown in situ on a diffractometer and studied at temperatures between -107 and -170°C by X-ray diffraction. The structure analysis of A-N2O3 (tetragonal, space group I41/a, T = -170°C, a = 1625.57 (16), c = 880.49(13) pm, Z = 32, R1 = 0.051 for 1030 unique reflections) is hampered by twinning and additional disorder of one of two crystallographically independent molecules. B-N2O3 is nicely ordered with one molecule in the asymmetric unit (orthorhombic, space group P212121, T = -160°C, a = 506.86(4), b = 647.96(5), c = 863.26(6) pm, Z = 4, R1 = 0.023 for 1352 unique reflections). The most interesting features of the N2O3 molecule are its planarity and the extraordinarily long N—N bond (189.0(1) pm).
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    Graphical Abstract (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. i 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010703
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    Mono- and Bis(pentaisopropylcyclopentadienyl) Cobalt and Rhodium Sandwich Complexes and Other Decabranched Cyclopentadienyl ComplexesDedicated to Professor Henri Brunner on the occasion of his 60th birthday (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 374-381 
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    ISSN: 0947-6539
    Keywords: cobalt compounds ; cyclopentadienyl ligands ; metallocenes ; peralkylations ; rhodium compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The acidity of methyl protons in the 18-electron cationic complexes [MCp*Cp]1PF6- and [MCp2*]+PF6- (M = Co or Rh, Cp = η5-C5H5, Cp* = η5- C5Me5) has been used for novel syntheses of starburst organometallic complexes. [CoCp*Cp]+PF6- was deprotonated at -30 °C with Si2Me6NK (1 equiv) in THF to give the fulvene complex [CoICp(η4-C5Me4CH2)]. This was not stable at 20°C, but was characterized by 1H and 13C NMR at -30 °C. The complexes [MCp*Cp]+PF6- (M = Co or Rh) reacted with excess base (KOH or tBuOK) and alkyl halides (RX = CH3I, C2H5I, CH2=CHCH2Br, or PhCH2Br) to give decasubstituted complexes (i.e., two hydrogens of each methyl group are replaced by two R groups). Distinct endo and exo alkyl groups are observed in the new complexes by NMR at room temperature. Coalescence occurs at higher temperatures; this indicates that the bulky alkyl groups are rotating. The calculated activation parameters (ΔG≠) are 71.3±0.8, 70.3±0.8, and 81.0±0.8 kJmol-1 for [Co(C5iPr5)Cp]+PF6-, [Rh(C5iPr5)-Cp]+PF6- (in C6D5NO2), and [Co{C5-(CHEt2)5}Cp]+PF6 (in o-C6H4Cl2), respectively. The single directionality of these ligands is confirmed by the X-ray crystal structure of [Co(C5iPr5)Cp]+PF6. This structure clearly shows the “paddle wheel” conformation adopted in the C5iPr5 ligand, due to steric hindrance between adjacent isopropyl groups and the staggered conformation of the two rings. The relative E° values measured by cyclic voltammetry show that the electron-donating properties of the new C5(CHR2)5 ligand are between those of C5H5 and C5Me5- With the decamethylcobalticinium salt [CoCp2*]+PF6-, the permethylation reactions with base and CH3 I did not go to completion, even under forcing conditions and with repeated reaction (the maximum number of methyl groups introduced was 14). On the other hand, [RhCp2*]+PF6-, in which the distance between rings is larger than in the Co analogue, reacted with excess KOH and CH3I to give [Rh(C5iPr5)2]+PF6 in 55% yield; only one diastereoisomer was detected by NMR (ΔG≠ = 85.5±0.8 kJ mol-1 in C6D5NO2). The C5iPr5 sandwich complexes are extremely robust, even at the 19-electron (CoII) stage. The 20-electron K+ salt of the CoI anion was regiospecifically protonated by H2O at the Cp ligand to give [Co(C5iPr5)(η4-C5H6)] and was decomplexed at 190°C to K+(C5iPr5)-.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010608
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    The Systematic Definition of Organic Reactions (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 449-453 
    Details
    ISSN: 0947-6539
    Keywords: computer chemistry ; databases indexing ; reaction organization ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A logical system is presented to describe organic reactions. It is based on the net structural change in a reaction, rather than on substructure searching. This system rigorously provides a place for any reaction. It is very simple to use by hand, but, since it is also numerical, it provides a basis for organizing and retrieving reactions in a database by computer. The effectiveness of a program, COGNOS, written to implement and test the system on a large database, lends confidence in this logic for organizing reactions.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010710
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    Cover Page (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. cpi 
    Details
    ISSN: 0947-6539
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010801
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