Rhodium-Catalyzed Annulative Coupling of Isothiazoles with Alkynes through N–S Bond Cleavage

A Rh­(III)-catalyzed annulative coupling of 3,5-diarylisothiazoles and alkynes is reported. The N–S bond in the isothiazole ring acts as an internal oxidant to regenerate the Rh­(III) species in combination with an external Cu­(II) oxidant, and the corresponding 1:2 coupling products are obtained. The remarkable difference in the reaction outcome between isothiazoles and the relevant isoxazoles has been investigated by DFT calculations, revealing that the relative stability of the enolate intermediates dictates the product selectivity.