Copper-Catalyzed Dehalogenative Cyclization/Sulfonylation of Alkynes: Synthesis of Pyrrolidone-Based Vinyl Sulfones.

Herein, we report an efficient copper-catalyzed dehalogenative cyclization/sulfonylation of alkynes with potassium metabisulfite (K2S2O5) and electrophiles via sulfur dioxide insertion, enabling straightforward access to a wide range of 2-pyrrolidone-based vinyl sulfones. The readily available industrial feedstock K2S2O5 plays a dual role as a sulfur dioxide surrogate and an electron donor, thereby sustaining the copper catalytic cycle without additional reductants. This reaction exhibits broad compatibility with diverse electrophiles, including alkyl iodides, benzyl bromides, and α-carboxyl alkyl bromides. Mechanistic studies indicate that the transformation involves sequential dehalogenation, intramolecular radical cyclization, sulfur dioxide insertion, and electrophilic trapping in a single operation.