Synthesis of Cyclic Sulfoxonium Ylides and Sulfoximines Via [3 + 2] Annulation.

A regio- and stereoselective formal [3 + 2] annulation of dimethyl sulfoxonium methylide with propargyl propiolates is reported. In contrast to its conventional C1 reactivity, the ylide functions as a multiatom synthon, enabling efficient access to endocyclic sulfoxonium ylides under mild conditions. The protocol features broad substrate scope and good functional group tolerance and is further extended to the synthesis of cyclic sulfoximines. Mechanistic investigations, including control experiments and DFT studies, support a pathway involving initial 1,2-addition followed by 5-exo-dig cyclization.