Divergent Synthesis of Alkenyl Sulfur Ylides and Sulfides through Base-Controlled Cascade Reactions of Prop-2-ynylsulfonium Salts and α,α-Dicyanoalkenes

A base-controlled divergent reaction between α,α-dicyanoalkenes and prop-2-ynylsulfonium salts is described. Treatment of Cs₂CO₃ enables selective transformation of various α,α-dicyanoalkenes and prop-2-ynylsulfonium salts into 2,3-dienyl sulfur ylides through a 1,3-intramolecular rearrangement pathway. In contrast, when CsOAc is employed in the presence of AcOH, the reaction proceeds through a protonation-demethylation sequence pathway to afford 1,4-dienyl sulfides. The chemistry features mild reaction conditions, broad substrate compatibility, and scalability for practical applications.