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.
Asymmetric Mukaiyama Aldol Reaction of Nonactivated Ketones Catalyzed by <i>allo</i>-Threonine-Derived Oxazaborolidinone
作者:Shinya Adachi、Toshiro Harada
DOI:10.1021/ol802087u
日期:2008.11.6
Asymmetric Mukaiyama aldol reaction of nonactivated ketones is realized for the first time by using an oxazaborolidinone catalyst derived from O-benzoyl-N-tosyl-allo-threonine. By employing a dimethylsilyl ketene S,O-acetal as a nucleophile, a variety of acetophenone derivatives afford the corresponding tertiary beta-hydroxy carbonyl compounds with high enantioselectivity up to 98% ee.