Substituted Hantzsch esters as radical reservoirs with the insertion of sulfur dioxide under photoredox catalysis.

A three-component reaction between 4-substituted Hantzsch esters, DABCO·(SO2)2, and vinyl azides in the presence of photoredox catalysts under visible light irradiation is developed. Substituted Hantzsch esters as radical reservoirs are used in the reaction between sulfur dioxide and vinyl azides. A range of (Z)-2-(alkylsulfonyl)-1-arylethen-1-amines is obtained in moderate to good yields with good regioselectivity and stereoselectivity. The transformation proceeds efficiently under mild conditions with a broad reaction scope. A plausible mechanism is proposed, which involves a radical process with the insertion of sulfur dioxide initiated by an alkyl radical from the 4-substituted Hantzsch ester.