Generation of Sulfonyl Radicals from Aryldiazonium Tetrafluoroborates and Sulfur Dioxide: The Synthesis of 3‐Sulfonated Coumarins

Abstract A catalyst‐free approach for the generation of sulfonyl radicals from aryldiazonium tetrafluoroborates in the presence of DABCO⋅(SO 2 ) 2 is realized. The combination of aryldiazonium tetrafluoroborates, DABCO⋅(SO 2 ) 2 , and aryl propiolates affords 3‐sulfonated coumarins in good to excellent yields. This tandem reaction process involves radical addition, spirocyclization, and 1,2‐migration of esters. Additionally, the in situ diazotization of a number of anilines allows the directional synthesis of desired 3‐sulfonated coumarins in a one‐pot, two‐step process.