Cu-Catalyzed Three-Component Cascade Synthesis of 1,3-Benzothiazines from ortho-Aminohydrazones and Bromodifluoroacetamides

An efficient and convenient synthesis of benzo[d][1,3]thiazine has been developed by employing a copper-catalyzed transformation of readily available ketone-derived hydrazones with elemental sulfur and bromodifluoroalkylative reagents. The strategy involves an S₈-catalyzed selective triple-cleavage of bromodifluoroacetamides, which acts as a C1 synthon at the 2-position of benzo[d][1,3]thiazine. A mechanism proceeding through a Cu-carbene intermediate is proposed for the C-S bond formation.