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 Schiffʹs bases 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 α-amino and α-methyl-α-amino acids with enantiomeric excesses of 70–96%.