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  • 1
    Electronic Resource
    Electronic Resource
    Photochemical Behavior of Doubly Bridged Dewar Benzenes - Synthesis of PrismanesDedicated to Professor Horst Prinzbach on the occasion of his 65th birthday. (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 1627-1634 
    Details
    ISSN: 0947-3440
    Keywords: Photochemistry ; Cage compounds ; Dewar benzenes ; Prismanes ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper we report on the photochemistry of Dewar benzenes bridged at the 1,4- and 5,6-positions and substituted at the 2,3-positions. It was found that simple alkyl substitution leads to prismanes only to a minor extent. Introduction of phenyl groups into the 2- or 2,3-positions gives the corresponding doubly bridged prismanes in yields up to 80% Pentamethylene-bridged bis-Dewar benzenes 19 rearrange upon irradiation to 22. Irradiation of the doubly bridged Dewar benzene derivatives with one ester group at the 5-position does not yield isolable products. However, introduction of one tert-butylsulfonyl group such as 30-33 gives almost quantitative yields of isolable prismanes if pentamethylene or hexamethylene bridges are used. The nonbridged species, 2-tert-butylsulfonyl-1,4,5,6-tetramethylbicyclo[2.2.0]hexa-2,5-diene (44), aromatizes upon irradiation into 1-(tert-butylsulfonyl)-2,3,4,5-tetramethylbenzene (45). In contrast to the pentamethylene-bridged monosulfone 47, the corresponding disulfone 38 undergoes no photochemical reaction. This could be explained by the X-ray structure, which reveals a strong interaction between one of the tert-butyl groups and the pentamethylene chain bridging the double bond in 38.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199619961020
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  • 2
    Electronic Resource
    Electronic Resource
    Syntheses and conformations of persubstituted inverse calixarenes (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 1401-1408 
    Details
    ISSN: 0947-3440
    Keywords: Calix[n]arenes (n = 4-13) ; Macrocycles ; Calculations, force-field ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of ten inverse calix[n]arenes (2-11) bearing four to thirteen benzene units were prepared by starting from 3,4,5-trimethoxybenzaldehyde followed by LC separation on silica gel. In 2-11 the substitution pattern is interchanged compared with the usual calixarenes. The conformational analysis was undertaken by variable temperature 1H-NMR spectroscopy and by MM2 calculations. Calix[4]arene 2 is a rigid molecule and shows the 1,3-alternate conformation which in addition was proven by X-ray analysis. At low temperatures the calix[5]arene 3 adopts the uudod conformation, where a methyl group of one benzene unit residues in the cavity of the macrocycle. At low temperature calix[6]arene 4 forms an 1:2 equilibrium between the 1,3,5-alternate (ududud; 4E) and the uududu (4B) conformation. Conformation 4B can be regarded as an intramolecular combination of a cone and an alternate arrangement of the benzene units. The calix[8]-arene shows the highest ΔG* value of the series and adopts an uuududdd conformation at low temperature. The inverse calixarenes 5 and 7-11 bearing seven and nine to thirteen aromatic units, respectively, are conformationally highly flexible systems even at low temperatures.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199508190
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  • 3
    Electronic Resource
    Electronic Resource
    Carbocylic cis-[1.1.1]-Tris-σ-homobenzenes - Syntheses by Triple Epoxide → Cyclopropane Conversions, Structural Data, [σ2s+σ2s+σ2s] Cycloreversions (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 967-989 
    Details
    ISSN: 0947-3440
    Keywords: cis-[1.1.1]-Tris-σ-homobenzenes ; [σ2s+σ2s+σ2s] Cycloreversions ; Substituent effects ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By triple epoxide → cyclopropane transformation starting from cis-benzene trioxide the 3α,6α,9α-tris(TIPS-ethynyl) (1b), -tris(alkoxycarbonyl) (1d, e), -tricyano (1f), and -tris(ammoniomethyl) (1j) derivatives of the still elusive parent cis-[1.1.1]-tris-σ-homobenzene (1a) have been synthesized. Out of a number of carbon nucleophiles tested, a weakly basic mixed cyanocuprate of Li-TIPS-propyne proved the reagent of choice: Eliminations were largely avoided, the scylloDescriptors scyllo, chiro, allo, cis are used as in inositol nomenclature; TIPS- = iPr3Si-.-2,4,6-tris(TIPS-propargyl)cyclohexane-1,3,5-triol (13a), obtained in a stereoselective one-pot threefold epoxide opening (up to 69%), allowed the pertinent functional group manipulations. The selectivity of the base-induced triple cyclopropane ring closure in the flexible cyclohexane precursors strongly depends on the activating groups and is promoted by fixation of the “all-axial” conformation as an adamantoid orthophosphate. The ΔG≠ values determined for the generally neat 3σ → 3π isomerizations [28.5 (1e), 29.0 (1f), 22.6 (1j) kcal mol-1] are in line with concerted reaction courses ([σ2s+σ2s+σ2s]). For the trinitrile 1f an X-ray structure analysis confirmed a nearly planar cyclohexane ring and a relatively large cyclohexane/cyclopropane interplanary angle (113°).
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970528
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  • 4
    Electronic Resource
    Electronic Resource
    Chemistry of the Ginkgolides, IX.Part VIII: Ref. [1] Ozonolysis of (10R)-10-Acetoxy-3,14-didehydroginkgolide (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1755-1756 
    Details
    ISSN: 0947-3440
    Keywords: Ginkgolide A ; Didehydroginkgolide A ; Ozonolysis ; Spiro compounds ; Structure elucidation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ozonolysis of (10R)-10-acetoxy-3,14-didehydroginkgolide (1) did not lead to the expected α-hydroxy ketone 3b. Instead, ring-opening of the acetal ring C occurred leading, after acetylation, to the spiroacylal 2. Its structure was confirmed by crystal structure analysis.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970818
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  • 5
    Electronic Resource
    Electronic Resource
    Trapping reactions of sulfenes generated from sulfonic acid derivatives and bases, 1. Cyclopentadiene, methylcyclopentadiene and 1,2,3,4-tetraphenylcyclopentadiene used as sulfene scavengers. [4 + 2] cycloaddition reactions and sulfonylations (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 2137-2149 
    Details
    ISSN: 0947-3440
    Keywords: Sulfenes ; [4 + 2] Cycloaddition ; Cyclopentadiene ; (+)-10-Camphorsulfonyl chloride ; Sulfonyl cyclopentadienides ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The bulky sulfenes generated in situ from (+)-10-camphor-, 10-camphane-, and 2-methyl-2-phenylpropanesulfonyl chloride (1a-c) and Et3N can be trapped by cyclopentadiene to give the [4 + 2] cycloadducts 6a-c. The mixture of endo-6a and exo-6a (no other diastereomers) is formed by complete asymmetric induction. In MeCN solution additionally the 1,3-di- and 1,2,4-trisulfonylated cyclopentadienides 4a-c and 5a (X-ray analysis) + 5c were obtained. On acidification, 4a and 5a were transformed into the pentafulvenoid derivatives 8a, 9a, 10a. The reaction of (+)-10-camphorsulfonyl chloride (1a)/Et3N with 1,2,3,4-tetraphenylcyclopentadiene afforded the sulfonylated product 11a, with 2-methylcyclopentadiene 50% endo-12a (X-ray analysis) and 10% exo-12a. From cyclopentadiene and the more electrophilic cyanosulfene (2e) and mesylsulfene (2f, X = Me), generated in situ from cyanomethanesulfonyl chloride (1e)/Et3N and from mesyl chloride/Et3N, the [4 + 2] cycloadducts 6e and 6g were obtained. Similarly, methanedisulfonyl dichloride (1f, X = Cl)/Et3N afforded stereospecifically by two subsequent [4 + 2] cycloadditions the spirodisulfone 16 (X-ray analysis).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199512300
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  • 6
    Electronic Resource
    Electronic Resource
    Trapping reactions of sulfenes generated from sulfonic acid derivatives and bases, 2. [4 + 2] cycloadditions of 1,2,3,4,5-pentamethylcyclopentadiene and 1,3-diphenylbenzo[c]furan with sulfenes (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 2151-2163 
    Details
    ISSN: 0947-3440
    Keywords: 1,2,3,4,5-Pentamethylcyclopentadiene ; 1,3-Diphenylbenzo[c]furan ; Sulfenes ; [4 + 2] Cycloaddition ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Sulfenes 2a-o, generated in situ from sulfonyl chlorides and Et3N, are trapped by 1,2,3,4,5-pentamethylcyclopentadiene (6) to give [4 + 2] cycloadducts 8a-o containing the 7-methyl group in anti position. With mesylsulfene (7), formed in situ from mesyl chloride/Et3N in MeCN solution, the [4 + 2] cycloaddition to endo/exo- 9 (X-ray analyses) is accompanied by a [2 + 2] cycloaddition to 10 (X-ray analysis). (+)-10-Camphorsulfonyl chloride/Et3N afforded only two (and no more) diastereomeric [4 + 2] cycloadducts (endo/exo-8d). Et3N can be replaced by Me3N, N,N,N′,N′-tetramethylnaphthalene- 1,8-diamine or NaH, the sulfonyl chlorides to a limited extent by sulfonyl fluorides, sulfonic acid anhydrides or aryl esters. Formation of 8p from 6 and dichloromethanesulfonyl chloride requires NaH or AgNO3 or tertiary amine/AgNO3. N-(2-Methyl-1-propenyl)pyrrolidine is more reactive than 6 in trapping sulfene 2a. 6, however, is a more efficient sulfene scavenger than 1,3-diphenylbenzo[c]furan (19), which reacts with sulfene 2d by [4 + 2] cycloaddition and SO2 extrusion to give ketone 21d in only 18% yield.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199512301
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  • 7
    Electronic Resource
    Electronic Resource
    Cycloaddition of Functionalized Nitrile Oxides and Fulminic Acid to [60]FullereneDedicated to Professor Klaus Weinges on the occasion of his 70th birthday. (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 1845-1850 
    Details
    ISSN: 0947-3440
    Keywords: Nitrile oxides ; Fullerenes ; Isoxazolines ; Fulminic acid ; [3 + 2] Cycloaddition ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cycloaddition of nitrile oxides to [60]fullerene led to [60]fullereno[1,2-d]isoxazole derivatives 1b-d. [60]Fullereno[1,2-d]isoxazole (1a) is the corresponding cycloadduct with fulminic acid. X-ray structure analyses of compound 1b and 1e were determined.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199619961118
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  • 8
    Electronic Resource
    Electronic Resource
    Preparation and Structures of Cyclotetradeca-4,11-diynone, Cyclotetradeca-4,11-diyne-1,8-dione, Their Exomethylene Derivatives, and 1,8-Dioxacyclotetradeca-4,11-diyneDedicated to Professor Gottfried Huttner on the occasion of his 60th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1545-1550 
    Details
    ISSN: 0947-3440
    Keywords: Medium-sized rings ; Alkynes ; Conformation analysis ; Ketones ; Cyclizations ; Ether ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The following 14-membered ring diynes have been synthesized: cyclotetradeca-4,11-diynone (4), cyclotetradeca-4,11-diyne-1,8-dione (6), the corresponding exomethylene derivatives 5 and 7, as well as 1,8-dioxacyclotetradeca-4,11-diyne (8). The synthesis of the diketal of 4 was achieved by the reaction of the ethylene ketal of 1,5-dibromopentan-3-one (9) with the dilithium salt of 1,8-nonadiyne. Similarly, the diketal of 6 was prepared from the dilithium salt of the ethylene ketal of 1,8-nonadiyn-5-one 11 with 9. The unprotected ketones 4 and 6 were obtained by treating the ketals 10 and 14, respectively, with HCl. The ketones 4 and 6 were transformed to the exomethylene derivatives by a Wittig reaction. The reaction of the dilithium salt of 5-oxanona-1,8-diyne (16a) with 1,5-dibromo-3-oxapentane (15) yielded 8. X-ray investigations of single crystals of 6 and 8 revealed chair conformations with a zig-zag arrangement, employing two anti orientations of the two chains between the triple bonds. A zig-zag arrangement of the chain containing the carbonyl group was also found in 4. In 3b and 7 Ci symmetry was found, with only one anti conformation in each chain. Molecule 6 crystallizes with C2h symmetry and 8 with a center of symmetry.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970734
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  • 9
    Electronic Resource
    Electronic Resource
    Synthesis and Properties of 4,4,9,9-Tetramethyl-1-oxa-cycloundecane-5,6,7,8-tetrone and 5,5,10,10-Tetramethyl-1-oxa-cyclotridecane-6,7,8,9-tetroneDedicated to Professor Richard Neidlein on the occasion of his 65th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 271-277 
    Details
    ISSN: 0947-6539
    Keywords: biomineralization ; medium-sized rings ; calcite ; crystal morphology ; glycoproteins ; polysaccharides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of 4,4,9,9-tetramethyl-1-oxa-cycloundecane-5,6,7,8-tetrone (9) and 5,5,10,10-tetramethyl-1-oxa-cyclotridecane-6,7,8,9-tetrone (10) has been achieved in a multistep procedure. The key steps in this synthesis were the ring closure of 23 and 24 to 25 and 26, respectively, and the oxidation of the triple bond with RuO2/NaIO4 to the dihydroxydiketones 31 and 32. Compound 9 is the first cyclic tetraketone for which an intramolecular donor-acceptor stabilization has been found. A strong transannular interaction between the ether oxygen and the C4O4 unit in 9 was detected by X-ray studies on single crystals of 9. The transannular distance is 2.7-2.8 Å. Further evidence for a strong transannular interaction was obtained from the comparison of the reduction potential and the first band in the UV/Vis spectrum with the corresponding values from other openchain tetraketones. These findings were substantiated by PE investigations on 9. The crystal structures of the dihydroxy-diketones 31 a and 32 a showed that, in the case of the eleven-membered ring (31 a), there are also short transannular distances between the ether oxygen and the C2O2 moiety (2.5 Å and 2.9 Å). In the case of the thirteen-membered ring (32 a), no transannular interactions were found in the solid state.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020307
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  • 10
    Electronic Resource
    Electronic Resource
    Neue helicale Kohlenwasserstoffe, VIII. Enantiomerentrennung, Circulardichroismus, Racemisierung und Röntgenstrukturanalyse des Benzo[2.2]metacyclophans (1983)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 116 (1983), S. 207-214 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: New Helical Hydrocarbons, VIII. Enantiomer Separation, Circular Dichroism, Racemization, and X-Ray Analysis of Benzo[2.2]-metacyclophaneThe title compound 1 was separated into the enantiomers by chromatography on cellulose triacetate: (-)-1 exhibits an enantiomeric purity of 100% with [α]36520 = -3210 ± 135 (acetone). A racemization barrier ΔG≠ = 125 kJ/mol is found by means of a kinetic study. The helicity of the molecule is demonstrated through these results as well as through an X-ray analysis, which is also described.
    Notes: Die Titelverbindung 1 wird chromatographisch an Cellulosetriacetat in die Enantiomeren getrennt: (-)-1 hat mit 100% Enantiomerenreinheit einen Drehwert von [α]36520 = -3210 ± 135 (Aceton). Für die Racemisierung wird kinetisch eine Barriere ΔG≠ = 125 kJ/mol ermittelt. Der helicale Molekülbau ist hiermit und durch die Röntgenstrukturanalyse gesichert, die gleichfalls beschrieben wird.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19831160123
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