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

Herein, 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. Sulfonimidamide (SIA)-based 1,2-benzothiazines were prepared by a [4+2] annulation reaction. The products were further transformed into o-acyl-N-acyl SIAs and a SIA-based dihydro-1,2-benzothiazine through oxidative C=C cleavage and selective C=C reduction, respectively.image