Oxidative Cascade Sulfonylation/Cyclisation of N‐Propargylindoles with Hantzsch Esters via Sulfur Dioxide Insertion

Abstract An oxidative sulfonylation/cyclisation of N ‐propargylindoles with Hantzsch esters through sulfur dioxide insertion has been developed. The method uses Na 2 S 2 O 5 as sulfur dioxide source along with 4‐alkyl‐substituted Hantzsch esters as radical precursors for accessing sulfonyl radicals, and allows for the synthesis of 2‐sulfonated 9 H ‐pyrrolo[1,2‐ a ]indoles.