K2S2O8‐Mediated Access to Alkylsulfonated Spiro[4,5] Trienones from N‐Arylpropiolamides with the Insertion of Sulfur Dioxide

Abstract A four‐component reaction of N ‐arylpropiolamides, Hantzsch esters, Na 2 S 2 O 5 and water via a radical cascade cyclization process with the insertion of sulfur dioxide mediated by K 2 S 2 O 8 is reported. A series of alkylsulfonated spiro[4,5] trienones are prepared up to 86% yield with a good functional group tolerance and substrate applicability. Preliminary mechanism experiments indicate that carbonyl oxygen of spiro[4,5] trienones originated from water.