Dimethylsilyl Ketene Acetal as a Nucleophile in Asymmetric Michael Reaction: Enhanced Enantioselectivity in Oxazaborolidinone-Catalyzed Reaction
摘要:
Dimethylsilanyl [Me2Si(H)] ketene SO-acetal 6b is an effective nucleophile that retards the undesirable Si+-catalyzed racemic pathway in the oxazaborolidinone-catalyzed asymmetric Michael reaction. Through the further suppression of the Si+-catalyzed pathway by carrying out the reaction in the presence of 2,6-diisopropylphenol and t-BuOMe as additives, enantioselectivity up to 98% ee could be achieved for a variety of acyclic enones.
[GRAPHICS]O-(2-Naphthoyl)-N-tosyl-L-allo-threonine B-phenyloxazaborolidinone catalyzes the asymmetric Mukaiyama-Michael addition of simple acyclic enones to give adducts of 54-85% ee, 2,6-Diisopropylphenal as an additive is demonstrated to effectively retard the undesirable Si+-catalyzed racemic pathway.