from Microscopic and Macroscopic Perspectives
Hansong Xue, Danfeng Jiang, Huan Jiang, Choon Wee Kee, Hajime Hirao, Takahiro Nishimura, Ming Wah Wong and Choon-Hong Tan
J. Org. Chem. 2015, 80, 5745-5752
Abstract: 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.
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