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  • 1
    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.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Synthesis, Crystal Structure, and Circular Dichroism Spectra of (1S)-4,8-Diphenylbarbaralane-2,6-dicarbonitrile - Chiroptical Properties of the Transition State of a Degenerate Cope Rearrangement (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1811-1823 
    Details
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Automerisation ; Circular dichroism ; Conformation analysis ; Enantiomeric resolution ; Polycycles ; Solid-state structures ; Solvent effects ; Thermochromism ; Transition states ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Diphenylbicyclo[3.3.1]nonane-2,6-dione rac-3 is resolved in 57 % overall yield by chromatographic separation of the diastereomeric (R)-N-(1-phenylethyl)carbamates 9 which are obtained from (R)-(1-phenylethyl) isocyanate (8) and the 6-hydroxydiphenylbicyclo[3.3.1]nonan-2-ones endo- and exo-4. The enantiomers (1R)- (e.r. = 98:2) and (1S)-3 (e.r. = 97:3) are regenerated from 9 by reduction with lithium aluminium hydride followed by Swern oxidation of the resulting diols 5. The title compound (1S)-1 is synthesised in three steps from (1S)-3 in improved yield on the route that had led to rac-1. The absolute configurations are established by X-ray diffraction analyses of the carbamates endo-(1R)-9 and exo-(1S)-9. X-ray diffraction analyses were also performed of the camphanoate (1R)-7, the intermediates rac-endo-4 and (1S)-3, and the title compound (1S)-1. Hydroxy ketone rac-endo-4 adopts similar conformations in the solid state and in solution as shown by a comparison of vicinal 1H,1H coupling constants from proton spectra with those calculated from torsional angles in the crystal. The molecular structures of (1S)-1 and (1S)-3 closely resemble those of the corresponding racemates investigated previously. These results show (i) that intermolecular interactions in the solid state are of minor importance and (ii) that the unusually long C2-C8 distance of (1S)-1 and rac-1 (168 pm) is a molecular but not an averaged property due to a non-degenerate Cope rearrangement in the crystal. CD spectra are reported for (1R)- and (1S)-3, the unsaturated dicarbonitrile (1S)-13, and (1S)-1. The CD spectrum of (1S)-1 exhibits a weak positive band at 459 nm where rac-1 shows a temperature-dependent absorption which has been assigned to the higher, vibronic state represented by rac-1*. The intensity of the weak CD band depends on the temperature and the solvents in the same way as the UV/Vis absorption of rac-1. This supports the conclusion that both bands originate from the same source, viz. the transition state 1* of the degenerate Cope rearrangement 1 ⇄ 1′.
    Additional Material: 11 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Cycloadditionen von 6H-1,3,4-Oxadiazin-6-onen (4,5-Diaza-α-pyronen), 13[1]. Diels-Alder-Reaktionen mit 6H-1,3,4-Oxadiazin-6-onen als Dienophil (1993)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 1743-1748 
    Details
    ISSN: 0009-2940
    Keywords: 6H-1,3,4-Oxadiazin-6-ones ; 1,2-Bismethylenecyclohexane ; Diels-Alder reactions ; [1,3,4]Oxadiazino[4,5-b]isoquinolin-1-one derivatives ; Bicyclo[2.1.1]hexan-5-one, highly substituted ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cycloadditions of 6H-1,3,4-Oxadiazin-6-ones (4,5-Diaza-α-pyrones), 13[1].-Diels-Alder Reactions with 6H-1,3,4-Oxadiazin-6-ones as Dienophile2,5-Diphenyl-1,3,4-oxadiazin-6-one (1b) reacted as dienophile with 2,3-dimethyl-1,3-butadiene to afford the pyridooxadiazinone 5. Analogously, the oxadiazinoisoquinolines 7c- e were formed on treatment of 2-(4-nitrophenyl)- (1c), 2-(4-tolyl)- (1d), and 2-(4-bromophenyl)-5-phenyloxadiazinone (1e) with 1,2-bis(methylene)cyclohexane (6). In contrast, the methyl oxophenyloxadiazinecarboxylate 1a gave a low yield of the cyclopentenone derivative 8 and 7a in the ratio 2.3:1.0. A third type of product, i.e. the cyclobutanone derivative 9, resulted on exposure of the anisyl(isopropyl)oxadiazinone 1f to 6. The oxadiazinones 1d, e, f have been prepared for the first time. X-ray structure analyses established the identity of the compounds 7d and 9.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19931260734
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  • 4
    Electronic Resource
    Electronic Resource
    Cycloadditionen von 6H-1,3,4-Oxadiazin-6-onen (4,5-Diazaα-pyronen), 11. δ-Chlor-δ-lactone aus γ-Oxoketenen (1992)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 125 (1992), S. 1913-1918 
    Details
    ISSN: 0009-2940
    Keywords: 1,3,4-Oxadiazine-2-carboxylate, methyl 6-oxo-5-phenyl- ; Diels-Alder reactions ; Ketenes, γ-oxo- ; δ-Lactones, δ-chloro- ; β-Lactones ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cycloadditions of 6H-1,3,4-Oxadiazin-6-ones (4,5-Diaza-α-pyrones), 11. - δ-Chloro δ-Lactones from γ-Oxo KetenesPrepared from 1,3,4-oxadiazinone 1 with norbornene, cyclopentene, cyclopentadiene, and indene, the γ-oxo ketenes 2, 5, 6, and 7 have been converted into the δ-chloro δ-lactones 3, 8, 9, and 10, respectively, by treatment with hydrogen chloride. The configuration of 10 has been determined by an X-ray structural analysis. These pseudo chlorides prove to be stable against methanol. Only in the presence of sulfuric acid as catalyst 3 suffers methanolysis to yield diester 4. On thermolysis, the γ-oxo ketenes are transformed into β-lactones. In particular, 6 and 7 gave 13 and 12, respectively. Formed also on photolysis of 6, β-lactone 13 partly isomerized to β-lactone 14 on prolonged heating.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19921250819
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  • 5
    Electronic Resource
    Electronic Resource
    Cycloadditionen von 6H-1,3,4-Oxadiazin-6-onen (4,5-Diaza-α-pyronen), 10. Reaktionen von Bicyclo[2.1.1] hexenen mit 6H-1,3,4-Oxadiazin-6-onen und dynamische Effekte in einem neungliedrigen, überbrückten, α,β-ungesättigten Enollacton 2) (1991)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 124 (1991), S. 1435-1444 
    Details
    ISSN: 0009-2940
    Keywords: 1,3,4-Oxadiazin-6-ones ; Diels-Alder reactions ; Enol lactones ; Lactone conformations ; Line-shape analysis ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cycloadditions of 6H-1,3,4-Oxadiazin-6-ones (4,5-Diaza-α-pyrones), 10 1). - Reactions of Bicyclo[2.1.1]hexenes with 6H-1,3,4-Oxadiazin-6-ones and Dynamic Effects in a Nine-Membered, Bridged, α,β-Unsaturated Enol Lactone 2)The reactions of bicyclo[2.1.1]hexene (2) and its tricyclic derivative 3 with 2,5-diphenyl-6H-1,3,4-oxadiazin-6-one (1 a) gave the 3,4-dihydro-α-pyrones 6 and 7, respectively. In contrast, the methyl phenyloxadiazinonecarboxylate 1 b and 2 afforded a mixture of the nine-membered, bridged, α,β-unsaturated enol lactone 11 and the β-lactone 12 in a ratio of about 10: 1. Olefin 3 reacted with 1 b to furnish small amounts of the bridged derivative 16 of 11 as well as the 2:1 product 14, a saturated δ-lactone. Unlike 16, enol lactone 11 reveals dynamic phenomena, which have been investigated by means of line shape analyses of the temperature dependent 13C-NMR spectra. The interconvertion of the cis- and trans-lactone conformers (11 a ⇄ 11 b), being present in a 1:2 ratio, proceeds with δH
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19911240619
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  • 6
    Electronic Resource
    Electronic Resource
    Cycloadditionen von 6H-1,3,4-Oxadiazin-6-onen (4,5-Diaza-α1-pyronen), 12. Dieckmann-Kondensationen ohne Basen (1993)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 797-802 
    Details
    ISSN: 0009-2940
    Keywords: 1,3,4-Oxadiazine-2-carboxylate, methyl 6-oxo-5-phenyl- ; Diels-Alder reactions ; Ketenes, γ1-oxo- ; 1,2-Cyclopentanedione derivatives ; Adipic acid, substituted 2-oxo-dimethyl esters ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cycloadditions of 6H-1,3,4-Oxadiazin-6-ones (4,5-Diaza-α1-pyrones), 12[1]. - Dieckmann Condensations without BasesPrepared by treatment of methyl 6-oxo-5-phenyl-6H-1,3,4-oxadiazine-2-carboxylate (1) with norbornene, norbornadiene, and styrene, respectively, the γ1-oxoketenes 2, 5, and 7 were allowed to react with methanol. Inter alia, the semiacetals 3, 6, and 10 of 1,2-cyclopentanedione derivatives were formed. The identity of 3 has been established by an X-ray structure analysis. The pathway to these compounds seems to be closely related to the mechanism of the Dieckmann condensation. By using [D4]methanol, it has been shown that the semiacetal methoxy group underwent an intramolecular [1,2] migration. Methanol was eliminated from semiacetal 10 by chromatography on silica gel with formation of the enol 11. In addition to 3 and 10, the dimethyl adipates 4 and 9 were observed as the expected methanolysis products of the γ1-oxoketenes 2 and 7, respectively. The diesters 9 were obtained on a second route from 7. Treatment of 7 with trifluoroacetic acid and subsequent hydrolysis gave rise to the monoesters 12, which were converted into the diesters 9 by conventional esterification.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19931260334
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