C2 symmetric copper (II) complexes of l-valine and l-phenyl alanine based chiral diimines for catalytic asymmetric Henry reaction

Abstract

New C2 symmetric chiral diimines were synthesized from the amino acids l-valine and l-phenyl alanine. In situ copper (II) complexes of the chiral diimine ligands were found to catalyze asymmetric Henry reaction. The chiral nitro aldols were formed in excellent yield (99%) and ee (99%). The synthetic utility of the chiral catalysts were screened with various substituted prochiral aromatic and heteroaromatic aldehydes. Possible catalytic cycle for the chiral diimine copper complex catalyzed asymmetric Henry reaction has been proposed. The stereoselectivity of the asymmetric Henry reaction was discussed based on the transition state in the catalytic cycle.