Asymmetric synthesis of acyclic amines through Zr- and Hf-catalyzed enantioselective alkylzinc reagents to Imines

Readily available chiral amino acid-based ligands are used in metal-catalyzed additions of alkyl-zinc reagents to various aromatic and aliphatic imines; the desired amine products are formed efficiently and in high levels of optical purity. In cases where the more Lewis acidic Zr salts afford lower efficiency, Hf-based catalysts deliver significantly higher yields with similar enantioselectivities. Critical structural features of the N-activating groups as well as the optimal chiral ligands are discussed. A mechanistic working model is presented to rationalize the existing data and to serve as a predictive tool.