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  • Articles  (55)
  • General Chemistry  (51)
  • Diels-Alder reactions  (4)
  • Asymmetric synthesis  (2)
  • 1
    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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  • 2
    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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  • 3
    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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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    Ring Expansion of 2-Alkylidenedihydroquinazolines to Iminodihydro-1,4-benzodiazepines by Methanesulfonyl and Trifluoromethanesulfonyl Azide (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1577-1587 
    Details
    ISSN: 1434-193X
    Keywords: Azides ; Cleavage reactions ; Cycloadditions ; Nitrogen heterocycles ; Polycycles ; Ring expansion ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---2-Alkyl-1-methylquinazolinium hexafluorophosphates 9 are deprotonated by sodium or potassium hydride to afford solutions of 2-alkylidenedihydroquinazolines 10, which were investigated by NMR spectroscopy. Trapping with methanesulfonyl azide (5a) of 10 in situ or subsequent treatment with trifluoromethanesulfonyl azide (5b) gives mixtures of colourless (15) and intensely yellow N-sulfonylimino-1,4-benzodiazepines 16 along with products due to cleavage of the exocyclic double bond of 10, viz. 11 and 13. The ethylidene compound 10b yields the bicyclic products 18 and 19, apparently by complex sequences of reactions that are triggered by removal of the acidic proton at C-2 of 16b and 16f. The structures of the products are based on spectroscopic evidence and X-ray diffraction analyses performed on 15b, 16d, 16e, and 19.
    Additional Material: 6 Ill.
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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    Extension of Saunders' Isotopic Perturbation Method as Probe for the Structures in Solution of 2,4,6,8-Substituted Barbaralanes - NMR-Spectroscopic Evidence for the Coexistence of Localised and Delocalised States (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 691-693 
    Details
    ISSN: 1434-193X
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---No Abstract.
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  • 8
    Electronic Resource
    Electronic Resource
    Tetraacylethenes as Dienophiles and Hetero Dienes in Two-Step Diels-Alder Reactions (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3343-3351 
    Details
    ISSN: 1434-193X
    Keywords: C-C coupling ; Cycloadditions ; Dehydrogenations ; Electron deficiency ; Isomerisations ; Oxidations ; Zwitterionic intermediates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oxidation with barium manganate of the enol of tetraacetylethane (10) affords tetraacetylethylene (7a) in good yield. Treatment of the 1,3-diketones 15a and b with iodosobenzene in the presence of boron trifluoride does not result in oxidative coupling yielding 10 and diacetyldibenzoylethane 17, respectively, as has been reported by Moriarty et al. Instead the known difluoroborylenolates 16 are formed. Oxidative coupling of the sodium enolate of 15b with iodine affords the meso-tetraketone meso-17 and diacetyldibenzoylethylene (E)-7b besides small amounts of rac-17 and the bisenol 19. In the presence of 1,4-diazabicyclo[2.2.2]octane, meso-17 and 19 tautomerise yielding identical equilibrium mixtures of meso-17, rac-17, and 19 (26:29:45). Dehydrogenation with 5,6-dichloro-2,3-dicyanobenzoquinone of meso-17 yields (E)-7b and an isomer (77:23) which was assigned structure (Z)-7b on the basis of spectroscopic evidence. - Tetraacetylethylene (7a) reacts with 1,2-dimethylenecyclohexane to afford two different [4+2]cycloadducts, viz. the spirocyclic dihydropyran 25 (30 %) and the tetraacetyloctalin 27. Whereas the latter is stable, the former isomerises to the latter on heating. Formation of both [4+2]cycloadducts and the isomerisation 25 → 27 are interpreted by invoking the zwitterion 26 as common intermediate. Monoolefines that cannot generate stable carbenium ions don't give [4+2]cycloadducts with 7a. In contrast, α-methylstyrene yields the oxa Diels-Alder product 30. The structures of (E)-7b, 19, 25, and 27 are established by X-ray diffraction analyses.
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  • 9
    Electronic Resource
    Electronic Resource
    Ring Expansion of 2-Alkylidenedihydroquinolines to 2-Iminodihydro-1-benzazepines by Phenyl, Methanesulphonyl, and Trifluoromethanesulphonyl Azide[1] (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 507-520 
    Details
    ISSN: 1434-193X
    Keywords: Azides ; Cleavage reactions ; Cycloadditions ; Nitrogen heterocycles ; Photolysis ; Ring expansion ; Spiro compounds ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---2-Alkyl-1-methylquinolinium hexafluorophosphates 1 are deprotonated by sodium or potassium hydride to afford solutions of 2-alkylidenedihydroquinolines 2, which are investigated by NMR spectroscopy. 1,3-Dipolar cycloaddition of phenyl azide to 2 yields the spirocyclic products 10. While, at 80-110 °C, the [3 + 2] cycloaddition that afforded (u)-10f is reversible and accompanied by epimerisation to give (l)-10f, thermolysis of the dimethyl compounds 10b and d affords the ring-expanded products 14b and d, respectively, in good yields along with molecular nitrogen. Irradiation of 10d with light of λ 〉 320 nm results in the formation of similar amounts of 14d and [3 + 2] cycloreversion products, viz. 2-diazopropane (5b) and the N-phenylimine 15d. - Trapping of 2 by methanesulphonyl azide (18a) gives mixtures of the products of ring expansion (21b, d-f, 10-50 %) and [3 + 2] cycloreversion (22a, d, 10-80 %) of the apparently very labile intermediate spirocyclic cycloadducts 19. The ratio of 21 vs. 22 is significantly improved when 18a is replaced by trifluoromethanesulphonyl azide (18b), which affords the iminodihydrobenzazepines 21i-k in 50-75 % yield. The structures of the products are based on NMR evidence and X-ray diffraction analyses performed with 21b, d, and (ax,E)-21e.
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  • 10
    Electronic Resource
    Electronic Resource
    Selective Reactions, Resolution and Absolute Configuration of Bridged Hydroazulenes (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2651-2657 
    Details
    ISSN: 1434-193X
    Keywords: Functionalized hydroazulenes ; Wittig reaction ; Selective additions ; Resolution ; X-ray analyses ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Treatment of the bridged oxepine (±)-1 with a large excess of powdered sodium methoxide in Et2O or with triphenylphosphonium methylide leads to the functionalized hydroazulenes (±)-2 (69%) and (±)-3 (81%). Regioselective and stereoselective cyclopropanation of (±)-2 leads to the dibromocyclopropane derivative (±)-4. Epoxidation gives the epoxides (±)-5 and (±)-6. The resolution of the hydro-azulenone (±)-2 is achieved by fractional crystallization of the quinine salt (-)-8 of the corresponding mono acid (±)-7. The absolute configuration of (+)-7 is established by X-ray analysis of the quinine salt (-)-8.
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