Enantioselective Mannich‐Type Reaction Catalyzed by a Chiral Brønsted Acid

No metal required: The Mannich-type reaction of ketene silyl acetals 2 with aldimines 1 proceeded highly enantioselectively to afford the syn isomer of β-aminoesters 3 with up to 96 % ee under the influence of a chiral Brønsted acid 4 derived from (R)-BINOL. The enantioselective Mannich-type reaction of an enolate or an enolate anion equivalent with aldimines constitutes a useful method for the preparation of chiral β-amino carbonyl compounds, which are the precursors of biologically important compounds such as β-lactams and β-amino acids. The development of chiral catalysts for the asymmetric Mannich-type reaction has attracted the attention of synthetic organic chemists.1 Although stoichiometric amounts of…