Enantioselective phase-transfer catalytic α-alkylation of 2-methylbenzyl tert-butyl malonates.

A new asymmetric synthetic method to prepare α,α-dialkylmalonates for the construction of a quaternary carbon center via phase-transfer catalytic (PTC) alkylation has been developed. Enantioselective α-alkylation of 2-methylbenzyl tert-butyl α-methylmalonates under phase-transfer catalytic conditions in the presence of (S,S)-3,4,5-trifluorophenyl-NAS bromide () afforded the corresponding α,α-dialkylmalonates in high chemical (up to 99%) and optical yields (up to 91% ee), which were selectively hydrolyzed to malonic monoacids under alkali basic conditions for conversion to versatile chiral intermediates.