Rh(III)-Catalyzed Reaction of α-Carbonyl Sulfoxonium Ylides and Alkenes: Synthesis of Indanones via [4+1] Cycloaddition

The synthesis of indanone derivatives by the Rh(III)-catalyzed reaction of alpha-carbonyl sulfoxonium ylides with activated alkenes is reported. The reaction shows a high tolerance for functional groups and furnishes a variety of substituted indanone derivatives via a formal [4 + 1] cycloaddition. Highly stable sulfoxonium ylides were used as substrates in this C-H functionalization, and their bifunctional character could be effectively exploited using Rh(III) catalysis via sequential double C-C bond formation. Based on mechanistic studies including deuterium-labeling experiments, the reaction is proposed to proceed as follows: Rh(III)-catalyzed C-H oxidative alkenylation via beta-hydride elimination, readdition of H-Rh species, a 1,2-carbon shift with the elimination of DMSO, and protonation.