Mechanistic insights into bicyclic guanidine-catalyzed reactions from microscopic and macroscopic perspectives.

Chiral bicyclic guanidine can act as an efficient chiral Brønsted base catalyst in enantioselective reactions, delivering good yields with high enantioselectivities. There is interest in understanding the detailed mechanisms of these guanidine-catalyzed reactions. Herein, we performed a detailed kinetic study of three different types of chiral bicyclic guanidine-catalyzed reactions, determining the bifunctionality of our guanidine catalyst. Although these three reactions share a similar catalytic cycle, their intrinsic kinetic behaviors are significantly different from each other because of the difference in the rate-determining step. The calculated theoretical rate expression for each reaction, as a result of the mechanism elucidated with density functional theory calculations, agrees well with the respective experimentally observed rate equation.