Chiral salen-metal complexes as novel catalysts for asymmetric phase transfer alkylations

Abstract

Chiral, salen-metal complexes have been tested as catalysts for the C-alkylation of aldimine Schiff's bases of alanine esters with alkyl bromides under phase-transfer conditions (solid sodium hydroxide, toluene, ambient temperature, 1–10% of the catalyst). The best catalyst, which was derived from a Cu(II) complex of (1 R,2 R or 1 S,2 S)-[ N,N′-bis(2′-hydroxybenzylidene)]-1,2-diaminocyclohexane, gave α-methyl-α-amino acids with enantiomeric excesses of 70–96%.