Asymmetric Synthesis of (2S,3S)- and (2R,3R)-α,β-Dialkyl-α-amino Acids via Alkylation of Chiral Nickel(II) Complexes of Aliphatic α-Amino Acids with Racemic α-Alkylbenzyl Bromides

This study has demonstrated that the stereochemical outcome of the direct alkylation of nickel(II) complexes derived from chiral Schiff bases of glycine, alanine, 2-aminobutyric acid, and leucine with racemic α-methylbenzyl bromide depends on the steric bulk of the corresponding amino acid residue. In particular, the alkylation of the alanine complex was found to proceed with a synthetically useful level (90% de) of stereoselectivity offering a concise synthesis of enantiomerically pure (2S,3S)- or (2R,3R)-α,β-dimethylphenylalanines.