Chiral Brønsted Acid-Catalyzed Direct Mannich Reactions via Electrophilic Activation.

This article presents a study on the chiral Brønsted acid-catalyzation through direct Mannich reactions via electrophilic activation. It is a well-accepted that nearly a "proton"-like character is required for activating a substrate efficiently and hence chiral Brønsted acids could not provide a chiral environment to a reactive intermediate. Researchers have developed highly enantioselective Strecker reactions and Mannich reactions catalyzed by peptide-based thiourea derivatives as chiral Brønsted acids. Their achievement has clearly indicated that a chiral Brønsted acid could recognize enantiotopic faces of an imine substrate via hydrogen bonding and has opened up a new avenue in asymmetric catalysis.