Asymmetric Mannich Reactions Promoted by a Bifunctional Charge-Activated Thiourea Catalyst.

A bifunctional thiourea featuring a pyridinium cation is employed as an asymmetric organocatalyst in the Mannich reactions of protected aromatic aldimines and various carbon nucleophiles. This charged catalyst is 20 times more active than a neutral analog under identical conditions, enabling reduced catalyst loadings and shortened reaction times. Excellent enantioselectivities are accompanied by high diastereoselectivities in several cases with prochiral β-ketoesters.