Enantioselective Direct Mannich Reactions of Cyclic β‑Ketoesters Catalyzed by Chiral Phosphine via a Novel Dual-Reagent Catalysis

A combination of
an amino acid derived chiral phosphine catalyst
and methyl acrylate efficiently catalyzed the direct Mannich reaction
of cyclic β-ketoesters and N-Boc-aldimines.
The dual-reagent catalysis was presumed to function through the formation
of a zwitterion, which catalyzed the reaction with excellent stereocontrol
via a hydrogen-bonding assisted chiral ion-pair pathway.