A new enantioselective α-benzylation and α-allylation of α-tert-butoxycarbonyllactones was devloped. α-Benzylation and α-allylation of α-tert-butoxycarbonylbutyrolactone and α-tert-butoxycarbonylvalerolactone under phase-transfer catalytic conditions (50% cesium hydroxide, toluene, −60 °C) in the presence of (S,S)-3,4,5-trifluorophenyl-NAS bromide (1 mol%) afforded the corresponding α-substituted α-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 α-quaternary homoserines, 3-alkyl-3-carboxypyrrolidine and 3-alkyl-3-carboxypiperidine.
