Cooperative Thiourea-Bronsted Acid Organocatalysis: Enantioselective Cyanosilylation of Aldehydes with TMSCN

We report a new thiourea-Bronsted acid cooperative catalytic system for the enantioselective cyanosilylation of aldehydes with yields up to 90% and enamioselectivities up to 88%. The addition of an achiral acid was found to be crucial for high asymmetric induction. Mechanistic investigations using a combination of NMR, ESI-MS, and density functional theory computations (including solvent corrections) at the M06/6-31G(d,p) level of theory suggest that the key catalytic species results from the cooperative interaction of bifunctional thioureas and an achiral acid that form well-defined chiral hydrogen-bonding environments.