Chiral salen-metal complexes as novel catalysts for the asymmetric synthesis of α-amino acids under phase transfer catalysis conditions

Chiral salen-metal complexes have been tested as catalysts for the C-alkylation of Schiffs basis of alanine and glycine esters with alkyl bromides under phase-transfer conditions (solid sodium hydroxide, toluene, ambient temperature, 1-10 mol% of the catalyst). The best catalyst, which was derived from a Cu(II) complex of(1R, 2R or 1S,2S)-[N,N'-bis(2'-hydroxybenzylidene)]-1,2-diaminocyclohexane, gave alpha -amino and alpha -methyl-alpha -amino acids with enantiomeric excesses of 70-96%. (C) 2001 Elsevier Science Ltd. All rights reserved.