A Tandem Regiospecific [3 + 2] Annulation/Ring Cleavage Reaction for the Synthesis of ß-Ketoenamides.

A series of ß-ketoenamines was synthesized from various phenacyl sulfoxides bearing 1-methyl-1H-tetrazole and oximes in moderate to excellent yields. The proposed mechanism involved the generation of α-sulfines from sulfoxides through thermolytic elimination, regiospecific formal [3 + 2] annulations, and elimination of SO2. This protocol provides convenient access to a variety of synthetically valuable N-unprotected ß-enaminones with absolute Z selectivity.