The phase-transfer catalytic alkylation of N,N-dialkylmalonamic tert-butyl esters in the presence of 1 mol% of (S,S)-3,4,5-trifluorophenyl-NAS bromide afforded highly enantioselective (S)-mono-alpha-alkylated products (up to 96% ee), which could be readily converted into versatile chiral building blocks without loss of chirality.