An efficient Pd-catalyzed cyclization/sulfonylation reaction of N-allylbromoacetamides with Na2S2O4 and allyl esters via "SO2" insertion has been developed, enabling the first synthesis of 2-pyrrolidinone-functionalized allylic sulfones. In this protocol, inexpensive and readily available Na2S2O4 functions dually as a sulfur dioxide source and a single-electron donor, thereby sustaining the catalytic cycle. The reaction exhibits a broad substrate scope and excellent tolerance to diverse functional groups, affording a wide range of allylic sulfones with exclusive (E) selectivity. Mechanistic studies suggest a reaction pathway involving intramolecular radical cyclization, the insertion of "SO2," and subsequent allylic substitution of a π-allyl-Pd(II) intermediate in a single reaction.
Li et al. (2026) studied this question.