Enantioselective Alpha-Alkylation Of Benzylideneamino Tert-Butyl Malonates By Phase-Transfer Catalysis

A new enantioselective synthetic method for the synthesis of alpha,alpha-dialkylmalonates with a quaternary carbon center was developed via alpha-alkylation of prochiral malonates by phase-transfer catalysis (PTC). Asymmetric alpha-alkylation of benzylideneamino tert-butyl alpha-methylmalonates under phase-transfer catalytic conditions in the presence of (S,S)-3,4,5-trifluorophenyl-NAS bromide afforded the corresponding alpha,alpha-dialkylmalonates in high yields (up to 97%) with excellent enantioselectivities (up to 98% ee). The products were then selectively hydrolyzed to chiral malonic monoacids under basic, acidic, or catalytic hydrogenation conditions.