Synthesis of Furanone-Fused 1,2-Benzothiazine by Rh(III)-Catalyzed C-H Activation: Regioselective Oxidative Annulation Leading to in Situ Lactonization in One Pot.

A sulfoximine-directed C-H activation strategy catalyzed by a Rh(III)-catalyst leads to an efficient synthesis of furanone-fused 1,2-benzothiazine. In this reaction, cascade C-H activation, regioselective annulation, and lactonization occur in one pot. 4-Hydroxy-2-alkynoates, as coupling partners, form unsymmetrical alkynes, which undergo lactonization after C-H activation and regioselective annulation. The method shows a good scope with a wide-range of sulfoximine and alkynoates and displays regioselectivity in forming single regioisomers in good yields.