The first catalytic highly enantioselective alkylation of ketimines--a novel approach to optically active quaternary alpha-amino acids.

A series of novel ketimines with intrinsic protecting group anchoring was synthesized and allowed to react with various silylketene acetals in the presence of 5-10 mol % of a chiral Zn(OTf)(2)-(R,R)-Ph-pybox-aqua complex. The corresponding optically active quaternary alpha-amino acid derivatives were obtained in high yields and with enantioselectivities ranging from 34 % up to 95 % ee. The catalyst was studied by (1)H NMR spectroscopy and X-ray crystallography, and a dynamic equilibrium of two species was identified in solution.