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  • 1
    Electronic Resource
    Electronic Resource
    Asymmetric michael additions via SAMP/RAMP hydrazones enantioselective synthesis of 2-substituted 4-oxophosphonates (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 1177-1184 
    Details
    ISSN: 0947-3440
    Keywords: SAMP/RAMP Hydrazones ; Asymmetric synthesis ; Michael addition ; 4-Oxophosphonates ; Michael Michael tandem addition ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Asymmetric Michael addition of lithiated methyl ketone SAMP hydrazones (S)-3 to a variety of alkenylphosphonates (E)-2 followed by oxidative cleavage of the 1,4-adducts (S,S)-4 by ozonolysis afforded 2-substituted 4-oxophosphonates (S)-5 in usually moderate to very good overall yields (14-77%) and with mostly high enantiomeric excesses (ee = 20-〉95%). In addition, asymmetric Michael Michael tandem additions were carried out in good overall yields by trapping the intermediate lithio phosphonate anions with alkenylphosphonate or enoate Michael acceptors.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199507160
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  • 2
    Electronic Resource
    Electronic Resource
    Zinc-Mediated Asymmetric Epoxidation of α-EnonesDedicated to Professor Günther Maier on the occasion of his 65th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1101-1113 
    Details
    ISSN: 0947-3440
    Keywords: Asymmetric epoxidation ; oxa-Michael addition ; Enones ; Eliminations ; Zinc ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new efficient method for the asymmetric epoxidation of α-enones with oxygen in the presence of diethylzinc and a chiral amino alcohol is presented. The epoxidation proceeds in moderate to excellent yields, complete diastereoselectivity and enantiomeric excesses of up to 〉99% by using enantiomerically pure (1R,2R)-N-methylpseudoephedrine 7 as a chiral additive. The amino alcohol auxiliary 7 employed can be almost completely recovered with unchanged enantiomeric purity.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970609
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  • 3
    Electronic Resource
    Electronic Resource
    Diastereo- and enantioselective synthesis of the 18-membered lichen macrolide (+)-aspicilinDedicated to Professor Hans-Dieter Scharf on the occasion of his 65th birthday. (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 1185-1191 
    Details
    ISSN: 0947-3440
    Keywords: (+)-Aspicilin ; Macrolide, asymmetric synthesis of ; SAMP/RAMP hydrazones, diastereoselective alkylation ; 2,2-Dimethyl-1,3-dioxan-5-one ; Baeyer-Villiger reaction ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The asymmetric synthesis of the lichen macrolide (+)-aspicilin (1) was realised in 19 steps and with high stereoselectivity (de ≥ 91 %, ee ≥ 96%). Three of the four stereogenic centres were generated by employing the SAMP/RAMP hydrazone method. Key steps of the synthesis are the α,α′-double alkylation of RAMP hydrazone (R)-10 of 2,2-dimethyl-1,3-dioxan-5-one B and the enantioselective synthesis of the bromo alcohol (S)-9 (subunit A) by a combination of SAMP hydrazone α-alkylation with subsequent Baeyer-Villiger oxidation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199507161
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  • 4
    Electronic Resource
    Electronic Resource
    Chemical Reactions of the Stable Carbene 1,3,4-Triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 2019-2028 
    Details
    ISSN: 0947-3440
    Keywords: Stable carbene ; Nucleophilic carbene ; Insertion ; Cycloaddition ; Betaines ; Triazolium salts ; Spiro compounds ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The title compound 1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene (1), a stable carbene, is chemically characterized via its reactivity towards a multitude of organic substrates. Its behaviour in insertion, addition and cycloaddition reactions allows its classification as a typical representative of nucleophilic carbenes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199619961212
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  • 5
    Electronic Resource
    Electronic Resource
    Diastereo- and Enantioselective Synthesis of 4,5,6-Trisubstituted and 6-Monosubstituted Piperidin-2-onesDedicated to Professor Friedrich Asinger on the occasion of his 90th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1115-1123 
    Details
    ISSN: 0947-3440
    Keywords: 4,5,6-Tri- and 6-monosubstituted piperidin-2-ones ; SAMP/RAMP hydrazone method ; Michael additions ; Alkylative aldehyde amination ; Lactams ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A convenient, versatile and highly diastereo- and enantioselective synthesis of 4,5,6-trisubstituted piperidin-2-ones 1 in satisfactory overall yields is described. The procedure involves the efficient and highly anti-diastereo- and enantioselective Michael addition of aldehydes to enoates via their lithiated SAMP hydrazones, followed by nucleophilic 1,2-addition of organometallic reagents to the C=N double bond of the corresponding aldehyde SAMP hydrazone-lithium ester enolate and subsequent lactamisation. In addition, 6-monosubstituted piperidin-2-ones 8 are prepared with enantiomeric excesses of ee = 79-92% via a similar three-step sequence starting from ethyl 5-oxovalerate (9).
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970610
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  • 6
    Electronic Resource
    Electronic Resource
    Asymmetric Synthesis of Primary Amines by Nucleophilic Addition of Alkyllithium Compounds to Aldehyde SAMP/RAMP Hydrazones (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1089-1100 
    Details
    ISSN: 0947-3440
    Keywords: Asymmetric synthesis ; Primary amines ; Nucleophilic 1,2-addition ; N—N bond cleavage ; Hydrazones ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The aldehydes 1 or 5 are converted to the SAMP hydrazones 2 or the α-alkylated SAMP hydrazones 7 and treated with organolithium compounds at low temperature. Cleavage of the N—N bond of the resulting hydrazines 3 and 8 with Raney-Ni/H2, or of the N-methoxycarbonylhydrazines 9 with Li/NH3, yield the amines 4 with 61-90% ee, the amines 11 with 45-96% de and 93 → 99% ee. The absolute configuration of the amines 11 was established by X-ray analysis of an appropriate MTPA derivative.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970608
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  • 7
    Electronic Resource
    Electronic Resource
    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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  • 8
    Electronic Resource
    Electronic Resource
    Lithiierte Methylnitrosamine Nucleophile α-sek.-Aminomethylierung (1975)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 108 (1975), S. 1293-1320 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Lithiated Methylnitrosamines Nucleophilic α-sec-AminomethylationIf at all. CH-hydrogens adjacent to the nitrogen of amines can only be abstracted as hydride. For secondary methlamines it is shown in this paper that N-nitrosation acidifies the α-position to an extend which allows quantitative H/Li-exchange under appropriate conditions lithium diisopropylamide/THF/-80°C/5 min). The (lithiomethyl)nitrosamines thus generated are highly reactive nucleophiles towards alkyl halides and carbonyl compounds. As products substituted nitrosamines are isolated which are readily converted to the parent amines. Thus the sequence of nitrosation, metalation, reaction with electrophiles, and removal of the nitroso group represents a method of electrophilic substitution at the methyl groups of secondary methylamines. To avoid handling of the carcinogenic nitrosamines, a “one pot procedure” was developed without isolation of these intermediates.
    Notes: CH-Wasserstoffe neben dem Stickstoff von Aminen lassen sich allenfalls als Hydrid abstrahieren. Hier wird am Beispiel von sekundären Methylaminen gezeigt, daß die α-Stellung durch N-Nitrosierung so stark acidifiziert wird, daß unter geeigneten Bedingungen quantitative Metallierung (Lithium-diisopropylamid/THF/-80°C/5 min) möglich ist. Die entstehenden (Lithiomethyl)-nitrosamine erweisen sich als hochreaktive Nucleophile gegenüber Alkylhalogeniden und Carbonyl-verbindungen. Die Produkte sind höher substituierte Nitrosamine, deren Entnitrosierung die zugrundeliegenden Amine liefert. Die Sequenz Nitrosierung, Metallierung, Reaktion mit Elektrophilen und Entnitrosierung ist damit eine Methode der elektrophilen Substitution an der Methylgruppe von sek. Methylaminen. Um das Hantieren mit den carcinogenen Nitrosaminen zu vermeiden, wurde eine „Eintopfvariante“ ohne Isolierung dieser Zwischenstufe entwickelt.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19751080436
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  • 9
    Electronic Resource
    Electronic Resource
    Lithiierung und elektrophile Substitution an α-Methylengruppen von Nitrosaminen Umpolung der Reaktivität sekundärer Amine (1977)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 110 (1977), S. 1852-1865 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Lithiation and Electrophilic Substitution at α-Methylene Groups of Nitrosamines Reactivity Umpolung of Secondary Amines1,2)The electrophilic substitution at the α-position of nitrogen of secondary amines (A → B) has a broad scope. H/Li-exchange can be carried out with lithium diisopropylamide (LDA) at -78°C in THF at methylene groups of open chain (1) and cyclic (9-12) nitrosamines. The resulting lithio derivatives react in high yields with alkyl, allyl, and benzyl halides as well as with aldehydes and ketones to give products 3 and 13-16 under C—C-bond formation. The reaction is also used for cyclizations (°11, 18—20). Most of the nitrosamines prepared are denitrosated to the parent amines.
    Notes: Die elektrophile Substitution in α-Stellung zum Stickstoff sek. Amine (A → B) über metallierte Nitrosamine besitzt große Anwendungsbreite. Der H/Li-Austausch gelingt bei - 78°C in THF an Methylengruppen von offenkettigen (1) und cyclischen (9-12) Nitrosaminen mit Lithium-diisopropylamid (LDA). Umsetzung der Li-Derivate mit Alkyl-, Allyl- und Benzylhalogeniden sowie mit Aldehyden und Ketonen führt in hohen Ausbeuten unter C—C-Verknüpfung zu den Produkten 3 und 13—16. Die Reaktion wird auch für Cyclisierungen zu 11 und 18-20 eingesetzt. Die meisten der hergestellten Nitrosamine werden zu den freien Aminen entnitrosiert.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19771100529
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  • 10
    Electronic Resource
    Electronic Resource
    Herstellung und synthetische Verwendung von metallierten Dimethylhydrazonen Regio- und stereoselektive Alkylierung von Carbonylverbindungen (1978)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 111 (1978), S. 1337-1361 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Generation and Synthetic Use of Metallated Dimethylhydrazones Regio and Stereoselective Alkylation of Carbonyl CompoundsDimethylhydrazones (DMH's) 6-10 of enolizable aldehydes and ketones can be metallated quantitatively in α-position by n-butyllithium and/or lithium diisopropylamide in tetrahydrofuran. The lithio derivatives thus obtained (11-14) are highly reactive carbon nucleophiles. Their application as enolate equivalents is demonstrated via the sequence carbonyl compound, DMH-derivative, metallation, reaction with alkyl halides (→ 16, 18, 19), and cleavage to the α-substituted carbonyl compound (17) in a number of examples. Apart from some special cases, the alkylations occur regiospecificly at the less substituted carbon atom. Cyclohexanone derivatives are selectively axially alkylated, allowing for example the preparation of trans-disubstituted cyclohexanones. An efficient new conversion of dimethylhydrazones to carbonyl compounds under mild conditions (pH 7, room temperature) by oxidative hydrolysis has been developed. Advantages of the procedure are discussed briefly.
    Notes: Dimethylhydrazone (DMH's) 6-10 von enolisierbaren Aldehyden und Ketonen können mit n-Butyllithium und/oder Lithium-diisopropylamid in Tetrahydrofuran quantitativ in α-Stellung metalliert werden. Die so erhaltenen Lithiumderivate 11-14 sind hochreaktive Kohlenstoffnucleophile. Ihre Verwendung als Enolatäquivalente wird über die Sequenz Carbonylverbindung, DMH-Derivat. Metallierung, Reaktion mit Alkylhalogeniden (→ 16, 18, 19) und Spaltung zur α-substituierten Carbonylverbindung (17) an einer Anzahl von Beispielen demonstriert. Die Alkylierungen erfolgen, von Spezialfällen abgesehen, regiospezifisch am weniger substituierten Kohlenstoffatom. Cyclohexanonderivate werden stereoselektiv axial alkyliert, was zur Darstellung von trans-disubstituierten Cyclohexanonen ausgenutzt wird. Zur quantitativen Spaltung der Dimethylhydrazone zurück zu den Carbonylverbindungen unter milden Bedingungen (pH 7, Raumtemperatur) wurde eine neue oxidative Hydrolyse entwickelt. Die Vorteile der Methode werden kurz diskutiert.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19781110413
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