Al-catalyzed enantioselective alkylation of α-ketoesters by dialkylzinc reagents.: Enhancement of enantioselectivity and reactivity by an achiral Lewis base additive

An Al-catalyzed enantioselective method for additions of Me2Zn and Et2Zn to alpha-ketoesters bearing aromatic, alkenyl, and alkyl substituents is disclosed. Transformations are promoted in the presence of a readily available amino acid-based ligand and afford the desired products in excellent yields and in up to 95% ee. Investigations described illustrate that the presence of a Lewis basic additive can lead to significant enhancements in efficiency and enantioselectivity. A mechanistic model that provides a rationale for such effects is provided.