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  • 1
    Electronic Resource
    Electronic Resource
    Electrophile-induced cyclizations of silyl-substituted 4-alken-1-olsDedicated to Professor Wolfgang Lüttke on the occasion of his 75th birthday. (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 501-507 
    Details
    ISSN: 0947-3440
    Keywords: Tetrahydrofurans, formation of ; Cyclization, stereocontrolled ; Vinylsilanes ; Allylsilanes ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Silyl-substituted 4-alken-1-ols cyclize in the presence of a wide range of electrophilic reagents to give substituted tetra-hydrofurans. The silyl group accelerates ring closure by its β-effect and its position determines the efficiency of stereo-control. Thus, a vinylic silyl group as in 1, 3-9 gives mixtures of 2,5-disubstituted tetrahydrofurans 2, 10-21, favoring formation of the trans isomer. In contrast, an allylic silyl group as in 28-30 exerts a high degree of stereocontrol, generally affording 2,3-trans-disubstituted tetrahydrofurans 31-36.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199519950369
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  • 2
    Electronic Resource
    Electronic Resource
    α-Oxo- und α-Thioxothioamide aus Methylketonen (1983)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1983 (1983), S. 1116-1132 
    Details
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: α-Oxo- and α-Thioxothioamides from Methyl KetonesMixtures of α-(chloro)sulfenyl chlorides 5 and trisulfides 6 are obtained from the reaction of thionyl chloride with methyl ketones in the presence of pyridine. From these mixtures as well as from the pure trisulfides 6, with amines the α-oxothioamides 1-4 are formed with good yields. Thionation of the thioamides 1 and 2 yields the deeply coloured α-thioxothioamides 16 and 17, the structure of which has been especially characterized by X-ray structure analyses.
    Notes: Bei der Reaktion von Methylketonen mit Thionylchlorid in Gegenwart von Pyridin entstehen Gemische aus α-(Chlor)sulfenylchloriden 5 und Trisulfiden 6, die - ebenso wie die reinen Trisulfide 6 - mit Aminen hohe Ausbeuten an α-Oxothioamiden 1-4 liefern. - Schwefelung der Thioamide 1 und 2 ergibt die tieffarbigen α-Thioxothioamide 16 und 17, deren Struktur insbesondere durch Röntgenstrukturanalysen charakterisiert wird.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.198319830705
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  • 3
    Electronic Resource
    Electronic Resource
    Zur Chemie der α-Thiocarbamoylcarbodiimide (1979)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1979 (1979), S. 1322-1336 
    Details
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chemistry of α-ThiocarbamoylcarbodiimidesThe dipolar species 2a can be detected in equilibrium with the α-thiocarbamoylcarbodiimide 1a by protonation and reduction to give 3 and 4, respectively. On heating, 1a rearranges to afford the photochromic dipole 7a. In addition to the formation of the derivatives 10 - 13, the molecular structure of 7a was confirmed by X-ray structure analysis. In a subsequent rearrangement, 7a isomerizes to give 9a. The α-carbamoylcarbodiimide 21 can be synthesized from the thiourea 20; the course of thiolysis to furnish the urea 24 indicates an equilibrium contribution of the dipolar species 22. The equilibrium compounds 1a, c ⇋ 2a, c undergo 2 + 2 cycloadditions with diphenylketene (25) to yield the four-membered heterocycles 26a and b. The α-carbamoylcarbodiimide 21 reacts with 25 to afford the ß-lactam 30 and the 1:2 adduct 31.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.197919790907
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  • 4
    Electronic Resource
    Electronic Resource
    Reactions of N-sulfonylalkylamines with ynamines  -  formation of 2H-1,2-thiazete 1,1-dioxides, novel thioketene S,S-dioxide dimers, and other s,n-heterocycles (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 1795-1800 
    Details
    ISSN: 0947-3440
    Keywords: [2 + 2] Cycloadditions ; 2H-1,2-Thiazete 1,1-dioxides ; Amidinosulfenes, in situ formation of ; Diaminothioketene S,S-dioxide ; 1,3-Dithietane 1,1,3,3-tetraoxide ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: N-Sulfonylalkylamines 2a, b react with ynamines 3 to give primarily 2H-1,2-thiazete 1,1-dioxides 4. But, except for the 4-triphenylsilyl species 4a, b, these products are unstable and undergo electrocyclic ring opening to very reactive amidinosulfenes 5, which are transformed into different products, depending on the ynamine substituents R2. The 1,3-dithietane 1,1,3,3-tetraoxide 8 is formed from N-sulfonylisopropylamine (2a) and the trimethylsilyl-substituted ynamine 3b via amidinosulfene 5c and probably thioketene S,S-dioxide 7. On the other hand, (isopropylamidino)sulfene 5d dimerizes to the 2H-1,5,2-dithiazine 9 and also gives the [2 + 4] cycloadducts 10a, 11a by reaction with 2a and ynamine 3c, respectively. In contrast, it was possible to trap phenyl-substituted amidinosulfenes 5e-h by addition of water or methanol.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199510251
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  • 5
    Electronic Resource
    Electronic Resource
    Synthesis of Functionalized Cyclopentanes, Cyclohexanes and Cycloheptanes by a Silicon-Induced Domino Reaction (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 1811-1821 
    Details
    ISSN: 0947-3440
    Keywords: Domino reaction ; Functionalized cyclopentanes, -hexanes and -heptanes ; Tetrahydrofurans ; Oxetanes ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,3-Functionalized cyclopentanes, -hexanes and -heptanes are obtained by addition of lithiated silyldithioacetals 7 to epoxyhomoallyl tosylates 4-6, The reaction involves a cascade of epoxide ring opening, of Brook 1,4-rearrangement and tosylate substitution. The method is particularly suitable for the preparation of cyclopentanes, whereas cyclohexanes and -heptanes are formed in yields only up to 49%. Use of enantiomerically pure epoxides provides optically active cyclopentanes (S)-10b, d, 11a as well as oxetanes (S)-14a, b. Hydrolysis of the dithioacetal function leads to the corresponding ketones 12, Cyclization of epoxide 24b gives an anellated cyclopentane 26, the configuration of which was established by X-ray structural analysis of dinitrobenzoate 27. Use of epoxide 29b provides the anellated tetrahydrofuran 30.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199619961115
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  • 6
    Electronic Resource
    Electronic Resource
    Cycloadditionsreaktionen von Heterokumulenen, XXI. [2: 1]- und [3: 1]-Addukte aus Isocyanaten und 3-Dimethyl-amino-2H-azirinen (1981)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1981 (1981), S. 264-276 
    Details
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Cycloaddition Reactions of Heterocumulenes, XXI.  -  [2: 1]- and [3: 1]-Adducts from Isocyanates and 3-Dimethylamino-2H-azirinesThe alkyl isocyanates 1a and b react with the aminoazirines 2a and b, respectively, to give [3: 1]-adducts, the spiro structure of which is established by the X-ray structural investigation on 6a. In contract, the sterically hindered isocyanates 1c and 2b yield the [1: 1]-adduct 10b. While 6 and 10 result from 1,2 bond cleavage of the original azirines 2, isocyanates 1 effect 1,3 bond rupture in the 2-monosubstituted azirine 13. Thus, starting from the alkyl compounds 1a and d, addition of a second isocyanate molecule leads to the oxazoles 15, whereas the aryl isocyanates 1e and f give 21 via the readily hydrolyzed imidazolines 20. These constitutions are derived from the X-ray structure analysis of 21b.
    Notes: Die Alkylisocyanate 1a und b treten mit den Aminoazirinen 2a bzw. b zu [3: 1]-Addukten zusammen, deren Spiro-Struktur 6 durch die Röntgenstrukturanalyse von 6a belegt ist. Das sterisch gehinderte Isocyanat 1c bildet mit 2b dagegen nur das [1: 1]-Addukt 10b. Während sich 6 und 10 von einer 1,2-Bindungsspaltung der eingesetzten Azirine 2 ableiten, bewirken die Isocyanate 1 beim 2-monosubstituierten Azirin 13 1,3-Ringöffnung. Dabei resultieren nach Anlagerung eines zweiten Isocyanat-Moleküls ausgehend von den Alkyl-Verbindungen 1a und d die Oxazole 15, während die Arylisocyanate 1e und f über die hydrolyseempfindlichen Imidazoline 20 und 21 reagieren. Diese Konstitutionen ergeben sich aus der Röntgenstrukturanalyse von 21b.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.198119810211
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  • 7
    Electronic Resource
    Electronic Resource
    Cycloadditionsreaktionen von Heterokumulenen, XXII. Umsetzung von Thioketenen mit 3-Dimethylamino-2H-azirinen (1981)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1981 (1981), S. 277-289 
    Details
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Cycloaddition Reactions of Heterocumulenes, XXII.  -  Reactions of Thioketenes with 3-Dimethylamino-2H-azirinesThioketenes 1 effect C = N cleavage in the aminoazirine 2 to give the dipoles 5a - c or the ketenimines 6d - h, depending on the substituents of the thioketene system. Except for 6d, hydrolysis of 6 proceeds via 5 to afford 2-thiazolin-5-ones 7 and α-carbamoylthioamides 9. Thermally the ketenimines 6 isomerize in a formal [3.3]-sigmatropic shift to furnish ketene S,N-acetals 8. Also in the 2-monosubstituted azirine 11, 1,3-bond cleavage occurs with 1 and yields thiazoles 13. In contrast, the 2-phenylazirine 16 opens at the 1,2-bond in the reaction with 1, and leads to 2-thiazolin-4-ones 20A via 19. The constitution of 20c was proved by an X-ray structural analysis.
    Notes: Thioketene 1 bewirken beim Aminoazirin 2 C = N-Spaltung, wobei je nach den Substituenten des Thioketen-Systems die Dipole 5a - c oder die Ketenimine 6d - h entstehen. Die Hydrolyse von 6 verläuft außer bei 6d über 5 zu 2-Thiazolin-5-onen 7 und α-Carbamoylthioamiden 9. Thermisch isomerisieren sich die Ketenimine 6 in einer formalen [3.3]-sigmatropen Verschiebung zu den Keten-S,N-acetalen 8. Auch beim 2-monosubstituierten Azirin 11 tritt mit 1 1,3-Ringöffnung ein, die hier Thiazole 13 ergibt. Dagegen öffnet das 2-Phenylazirin 16 in der Reaktion mit 1 die 1,2-Bindung und führt über 19 zu 2-Thiazolin-4-onen 20A. Die Konstitution von 20c konnte durch eine Röntgenstrukturanalyse bewiesen werden.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.198119810212
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