Catalytic Enantioselective Protonation of Lithium Enolates with Chiral Imides

The catalytic enantioselective protonation of simple enolates was achieved using a catalytic amount of chiral imides and stoichiometric amount of achiral proton sources. Among the achiral proton sources examined in the protonation of the lithium enolate of 2,2,6-trimethylcyclohexanone catalyzed by (...

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Bibliographic Details
Published in:Journal of organic chemistry 2000-05, Vol.65 (10), p.2979-2983
Main Authors: Yanagisawa, Akira, Watanabe, Tsuyoshi, Kikuchi, Tetsuo, Yamamoto, Hisashi
Format: Article
Language:English
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Summary:The catalytic enantioselective protonation of simple enolates was achieved using a catalytic amount of chiral imides and stoichiometric amount of achiral proton sources. Among the achiral proton sources examined in the protonation of the lithium enolate of 2,2,6-trimethylcyclohexanone catalyzed by (S,S)-imide 1, 2,6-di-tert-butyl-p-cresol (BHT) and its derivatives gave the highest enantiomeric excess. For example, 90% ee of (R)-enriched ketone was obtained when (S,S)-imide 1 (0.1 equiv) and BHT (1 equiv) were used. Use of 0.01 equiv of the chiral catalyst still caused a high level of asymmetric induction. For catalytic protonation of the lithium enolate of 2-methylcyclohexanone, chiral imide 6 possessing a chiral amide portion was superior to (S,S)-imide 1 as a chiral proton source and the enolate was effectively protonated with up to 82% ee.
ISSN:0022-3263
1520-6904
DOI:10.1021/jo991565k