Synthesis of Sulfonimidamide‐Based 1,2‐Benzothiazines by [4+2] Oxidative Annulation of Sulfonimidamides and Alkynes in Water under Visible Light

Abstract

AbstractHerein, we disclose a visible‐light‐induced rhodium‐catalyzed oxidative C−H/N−H bond activation of sulfonimidamides (SIAs) and subsequent [4+2] annulation with an alkyne in water to yield SIA‐based 1,2‐benzothiazines in good to high yields in short reaction times. Further, the C=C bond of the benzothiazine can be cleaved under environmentally friendly conditions (oxygen atmosphere and blue LEDs) to deliver o‐acyl‐N‐acyl SIAs. Interestingly, o‐acyl‐N‐acyl SIAs can also be synthesized directly from SIAs in very good yields without isolating the benzothiazine. The selective and efficient reduction of the benzothiazine C=C bond in the presence of InCl3/R3SiH led to the formation of a hitherto unknown SIA‐based dihydro‐1,2‐benzothiazine in quantitative yield.