DFT Study on Rhodium(III)-Catalyzed Redox-Neutral [3 + 2] Cyclization of Sulfoxonium Ylides with Alkynes: Mechanism and Solvent Effect

The [3 + 2] cycloaddition mechanism of the rhodium-catalyzed redox-neutral cyclization of sulfoxonium ylides with 1,4-diphenyl-1,3-butadiyne has been investigated using density functional theory. The calculations indicate that the active catalyst is [Cp*Rh(OAc)₂]. The reaction proceeds sequentially through C(sp²)-H bond cleavage, alkyne insertion into the Rh-C(sp²) bond, intramolecular nucleophilic addition, protodemetalation, and stepwise proton migration, ultimately affording the product 3-phenyl-2-(phenylethynyl)-1-indenone. Additionally, based on the computational results, we propose that the rate-determining step of the catalytic cycle is governed by both C-H activation and intramolecular nucleophilic addition, rather than being controlled by a single step alone.