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

A four-component reaction of N-arylpropiolamides, Hantzsch esters, Na2S2O5 and water via a radical cascade cyclization process with the insertion of sulfur dioxide mediated by K2S2O8 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.