Theoretical study of the NHC-catalyzed C–S bond cleavage and reconstruction reaction: mechanism, stereoselectivity, and role of catalysts

Abstract

A theoretical study of the mechanism of the N-heterocyclic carbene (NHC)-catalyzed C–S bond cleavage and reconstruction reaction of unsaturated thioesters was conducted using density functional theory (DFT). The origin of stereoselectivity and the role of the NHC were also explored based on the established mechanism. The computational results showed that C–S bond cleavage was the rate-determining step, giving an α,β-unsaturated acyl azolium intermediate and sulfur anion species. Stereoselectivity can be generated by the sequential Michael addition process, preferentially generating an S-configured product. Topological analysis of the stereocontrolling transition states revealed that stronger weak interactions, such as π⋯π, C–H⋯O, LP⋯π and C–H⋯π interactions, were key for controlling the stereoselectivity. The key role of the NHC was also determined by electron localization function (ELF) analysis.