title: Catalytic enantioselective protonation of lithium enolates with chiral imides
abstract: 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.
authors.affiliation: Graduate School of Engineering, Nagoya University, CREST, Japan Science and Technology Corporation (JST), Chikusa, Nagoya 464-8603, Japan.
authors.initials: A
authors.lastname: Yanagisawa
authors.initials: T
authors.lastname: Watanabe
authors.initials: T
authors.lastname: Kikuchi
authors.initials: H
authors.lastname: Yamamoto