Mn(OAc)₃-Promoted Sulfonation–ipso-Cyclization Cascade via the SO₃^– Radical: The Synthesis of Spirocyclic Sulfonates

A radical sulfonation-ipso-cyclization cascade promoted by Mn(OAc)3·2H2O using functionalized alkynes or alkenes and potassium metabisulfite (K2S2O5) is reported. A total of 30 spirocyclic sulfonates were synthesized under mild conditions. We also demonstrate a modular synthesis approach in multiple steps for the preparation of various azaspiro[4,5]-trienone-based sulfonamides and sulfonate esters.