Metal- and base-free tandem sulfonylation/cyclization of 1,5-dienes with aryldiazonium salts the insertion of sulfur dioxide.

A metal- and base-free 5--trig sulfonylative cyclization between 1,5-dienes, aryldiazonium salts and SO (from SOgen) is presented. This method could successfully produce sulfonylated pyrrolin-2-ones in one pot with excellent regioselectivity and good-to-excellent yields. This strategy features mild reaction conditions and broad substrate scope. Moreover, a scale-up reaction and three synthetic applications demonstrate the practicality of this method. Lastly, control experiments indicate that the 5--trig sulfonylative cyclization may proceed in a radical pathway.