Traditional methods for the transformation of N-allyl ynamides rely on the formation of a ketenimine intermediate or its equivalent, while novel reaction modes remain to be developed. Herein, a cascade trifluoromethylation/cyclization of N-allyl sulfonylynamides is realized, which provides a facile access to azetidine-fused tricyclic compounds under very mild reaction conditions. It represents a rare example of 4-exo-dig radical cyclization, thus opening up a new opportunity for constructing synthetically attractive azetidines from the readily available N-allyl ynamides.