Transition-Metal-Free and HI-Catalyzed Synthesis of 2,3-Dihydrobenzothiazin-4-one Derivatives

A transition-metal-free strategy for the synthesis of 2,3-dihydrobenzothiazin-4-one derivatives has been established. Using HI as the catalyst, various 2-substituted, N-substituted compounds and variations on the benzamide ring were synthesized in excellent yields via the reaction between 2-mercaptobenzamides and aldehydes. In addition, an easy experimental procedure, broad substrate scope, and excellent functional group tolerance demonstrate that this catalytic protocol provides a valuable complementary approach for accessing 2,3-dihydrobenzothiazin-4-one derivatives.