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  • 1
    Electronic Resource
    Electronic Resource
    Enantioselektive Synthese mit Lithium/(-)-Spartein-Carbanion-PaarenProfessor Dieter Seebach zum 60. Geburtstag gewidmet (1997)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 109 (1997), S. 2376-2410 
    Details
    ISSN: 0044-8249
    Keywords: Asymmetrische Synthesen ; Chirale Synthesebausteine ; Lithium ; (-)-Spartein ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: „Chirale Carbanionen“ - gemeint sind enantiomerenangereicherte Lithium-Carbanion-Paare, in denen das carbanionische Zentrum die chirale Information trägt - galten bis vor kurzem als „Exoten“. In den vergangenen zehn Jahren wurde deutlich, daß sie eine bedeutsame Rolle in der enantioselektiven Synthese spielen können, da die Substitution des Lithiumatoms stereospezifisch - meistens unter Retention der Konfiguration - verläuft. Auch sind sie leichter und allgemeiner zugänglich als ursprünglich vermutet. Der Kniff besteht in der Verwendung von Lithium-Kationen mit chiralen Liganden, sei es bei der kinetisch gesteuerten enantiotopos-differenzierenden Deprotonierung mit Alkyllithiumverbindungen als Base oder bei der thermodynamisch gesteuerten Gleichgewichtseinstellung in konfigurativ labilen, epimeren Ionenpaaren. Als chiraler zweizähniger Ligand hat sich das Lupinen-Alkaloid (-)-Spartein bestens bewährt, seine Effizienz und Anwendungsbreite sind bislang unerreicht. Der Aufsatz gibt einen Überblick über die Herstellung chiraler Reagentien - vorwiegend umgepolte Synthone wie Homoenolate, 1-Oxyalkanide mit breitem Substitutionsmuster und α-Aminobenzyl-Anionen.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19971092105
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  • 2
    Electronic Resource
    Electronic Resource
    Herstellung und Reaktionen einer hoch enantiomerenangereicherten, ungewöhnlich konfigurationsstabilen α-BenzylthiolithiumverbindungProfessor Waldemar Adam zum 60. Geburtstag gewidmetDiese Arbeit wurde von der Deutschen Forschungsgemeinschaft und vom Fonds der Chemischen Industrie unterstützt. (1997)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 109 (1997), S. 2872-2874 
    Details
    ISSN: 0044-8249
    Keywords: Carbanionen ; Chiralität ; Ionenpaare ; Konfigurationsumkehr ; Lithium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19971092412
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  • 3
    Electronic Resource
    Electronic Resource
    Enantioselective Synthesis with Lithium/(-)-Sparteine Carbanion PairsDedicated to Professor Dieter Seebach on the occasion of his 60th birthday (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 36 (1997), S. 2282-2316 
    Details
    ISSN: 0570-0833
    Keywords: asymmetric synthesis ; chiral building blocks ; lithium ; (-)-sparteine ; Asymmetric synthesis ; Chiral building blocks ; Lithium ; (-)-Sparteine ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: “Chiral carbanions” - that is, enentiomerically enriched lithium-carbanion pairs in which the carbanionic center carries the chiral information - were regarded until recently as “exotic species.” In the past ten years it has become clear that they can, in fact, play a meaningful role in enantioselective synthesis, since substitution for lithium occurs here stereospecifically, usually with retention of configuration. They are also more readily and commonly accessible than was originally assumed. The trick lies in the use of lithium cations with chiral ligands, whether in the form of alkyllithium species used as bases in kinetically controlled, enantiotopically discriminating deprotonation, or in thermodynamically controlled equilibration in configurationally labile epimeric ion pairs. The lupine alkaloid (-)-sparteine has shown itself admirably suited as a chiral bidentate ligand, and its efficiency and breadth of application are so far unsurpassed. This contribution constitutes an overview of the preparation of chiral reagents, convering primarily “umpoled” synthons such as homoenolates. 1-oxyalkanides with a broad pattern of substitution, and α-aminobenzyl anions.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199722821
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  • 4
    Electronic Resource
    Electronic Resource
    α-Metalated Isocyanides in Organic Synthesis. New synthetic methods (6) (1974)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 13 (1974), S. 789-804 
    Details
    ISSN: 0570-0833
    Keywords: Isocyanides ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: α-Alkali-metalated isocyanides, which can be obtained from isocyanides and bases, can be used for nucleophilic introduction of (masked) α-aminoalkyl groups. Intramolecular ring-closure may then follow if a nucleophile combines at the electron sextet of the isocyanide carbon. Treatment of α-alkali-metalated isocyanides with electrophilic agents permits rapid and efficient synthesis of, inter alia, 2- and 3-amino alcohols, straight-chain, branched, and β-functional α-amino acids, olefins, vinyl isocyanides, and of a large number of mainly five-, but also six- and seven-membered aza-, diaza-, oxa-aza-, and thia-aza heterocycles.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.197407891
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  • 5
    Electronic Resource
    Electronic Resource
    The Homoaldol Reaction, or How to Overcome Problems of Regio- and Stereo-selectivityMetalated Nitrogen Derivatives of Carbonic Acid in Organic Synthesis, Part 28. - Part 27: [72b].Dedicated to Professor Wolfgang Lüttke on the occasion of his 65th birthday (1984)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 23 (1984), S. 932-948 
    Details
    ISSN: 0570-0833
    Keywords: Homoaldol reaction ; Stereoselectivity ; Synthetic methods ; Regioselectivity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Even today, there are conspicuous gaps in the register of organic synthetic methods. Thus, numerous types of homoenolate reagents are listed; yet no generally applicable method for the homologue of the aldol addition, viz. the homoaldol addition, is to be found. The methods documented up to 1980 offer only singular solutions, and, moreover, are not stereoselective. The present article gives an overview of the existing possibilities and then describes how the gap can be closed by using a new class of homoenolate reagents: 2-alkenyl esters of N,N-diisopropylcarbamic acid are lithiated and the resulting allyllithium compounds tailored to high regio- and diastereoselectivity in addition reactions to the carbonyl group via metal exchange. Altogether, the homoaldol reactions now offer a general and reliable, highly stereoselective entry to γ-hydroxycarbonyl compounds, whereby the C(β)—C(γ) bond is formed. Furthermore, it is demonstrated how problems associated with the application of allyl anions as synthetic reagents can be solved today.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198409321
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