Catalyst-Directed Guidance of Sulfur-Substituted Enediolates to Stereoselective Carbon-Carbon Bond Formation with Aldehydes

A highly chemo-, regio-, and stereoselective glycolate aldol reaction of sulfur-substituted enediolates with aldehydes was developed by employing a l-cyclohexylglycine-derived chiral iminophosphorane as a catalyst. The key for establishing this protocol is the distinct ability of the iminophosphorane catalyst to precisely direct the equilibrium mixture of the enediolates toward the intermolecular carbon-carbon bond formation with simultaneous yet rigorous control of relative and absolute stereochemistry. The critical importance of the cyclohexyl substituents on the catalyst backbone in dictating the reaction pathway and the stereochemical outcome was elucidated through an extensive quantum analysis by density functional theory calculations.