Stereochemically defined C-substituted glutamic acids and their derivatives. 1. An efficient asymmetric synthesis of (2S,3S)-3-methyl- and - 3-trifluoromethylpyroglutamic acids

Article abstract of DOI:10.1016/S0040-4020(99)00711-5

An efficient asymmetric synthesis of biologically important (2S,3S)-3- methyl- and (2S,3S)-3-trifluoromethylpyroglutamic acid has been developed. The 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.