Origin of asymmetric induction in bicyclic guanidine-catalyzed thio-Michael reaction: A bifunctional mode of Lewis acid-Brønsted acid activation

Abstract

In addition to a bifunctional Brønsted acid activation mode, an unconventional bifunctional mode of Lewis and Brønsted acid activations was revealed in a DFT study of bicyclic guanidine-catalyzed thio-Michael reaction. This activation mode provides an alternate reaction pathway for the C-S bond forming step and influences the final stereochemical outcome. The calculated turnover frequencies of the R- and S-products, based on the energetic span model, are in good accord with the observed high stereoselectivity toward the S-product. © 2012 American Chemical Society.