An efficient asymmetric synthesis of biologically important (2S,3S)-3-methyl- and (2S,3S)-3-trifluoromethylpyroglutamic acid has been developed. We method consists of diastereoselective Michael addition reaction between ethyl crotonate or ethyl 4,4,4-trifluorocrotonate and a Ni(II) complex of the chiral non-racemic Schiff base of glycine with (S)-o-[N-(N-benzylprolyl)amino]benzophenone (BPB) followed by decomposition of the addition products by aq. HCl and treatment of the resultant glutamic acid derivatives with NH4OH to afford the target pyroglutamic acids along with recovery of the chiral auxiliary BPB. The stereochemical outcome of the addition reactions was found to be subjected to kinetic control. A mechanistic rationale for the observed stereochemical preferences is discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.