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.