Enantioselective phase-transfer catalytic -benzylation and -allylation of -tert-butoxycarbonyllactones

Abstract

A new enantioselective -benzylation and -allylation of -tert-butoxycarbonyllactones was devloped. -Benzylation and -allylation of -tert-butoxycarbonylbutyrolactone and -tert-butoxycarbonylvalerolactone under phase-transfer catalytic conditions (50% cesium hydroxide, toluene, 60 degrees C) in the presence of (S,S)-3,4,5-trifluorophenyl-NAS bromide (1mol%) afforded the corresponding -substituted -tert-butoxycarbonyllactones in very high chemical yields (up to 99%) and optical yields (up to 99% ee). The synthetic potential of this method has been successfully demonstrated by the asymmetric synthesis of unnatural -quaternary homoserines, 3-alkyl-3-carboxypyrrolidine and 3-alkyl-3-carboxypiperidine.