Theoretical insights into phosphine‐catalyzed [4 + 2] annulation of allenoates with thiazolone‐derived alkenes

Abstract

In this article, the mechanism of [4 + 2] annulation of allenoates with thiazolone‐derived alkenes catalyzed by phosphine has been studied using density functional theory (DFT). This work adopted the two different phosphine catalysts (named as Cat1 and Cat2) to participate in the theoretical calculation. Catalyst Cat1 was used as a chiral catalyst to obtain optically active products in good yield with excellent enantioselectivity. With the use of Cat2 as the achiral catalyst, products were not enantioselective. The calculated results indicate that the CC bond formation is not only the rate‐determining step but also the stereoselectivity‐determining step. The R‐configured product is predicted as the dominant product catalyzed by Cat1, which is consistent with the experimental results. Moreover, global reaction index (GRI), natural bond orbital (NBO), and frontier molecular orbital (FMO) analyses indicate that the phosphine catalyst can enhance the nucleophilicity of reactant R1 and reduce the energy gap of the interacting HOMO and LUMO orbitals. The revealed mechanism would provide valuable clues in novel catalyst design.