Divergent Domino Reactions of Prop-2-ynylsulfonium Salts: Access to Sulfur-Containing Benzo-Fused Dioxabicyclo[3.3.1]nonanes and Dihydrofuro[2,3‑c]chromenes

Solvent-controlled divergent domino annulation reactions between 2-hydroxy-2-methylchromene derivatives and prop-2-ynylsulfonium salts have been developed. Specifically, a sequential [4 + 2] and [4 + 2] annulation reaction occurred in 1,2-dichloroethane affording sulfur-containing benzo-fused dioxabicyclo[3.3.1]­nonanes. In contrast, by changing the solvent to toluene, the reaction course switched to a [4 + 2] and [4 + 1] annulation reaction to afford dihydrofuro­[2,3-c]­chromenes. It is noteworthy that the prop-2-ynylsulfonium salt participates in the transformation with its γ-carbon atom for the first time.