Redox-Neutral Assembly of Selenobenzothiazine 1-Oxides via Rh(III)-Catalyzed Cascade [4 + 2] Annulation/Selenylation

The Rh(III)-catalyzed redox-neutral [4 + 2] annulation/selenylation of sulfoximines with vinyl selenones was realized to deliver the selenobenzothiazine 1-oxides with good compatibility and regioselectivity. The use of vinyl selenones achieves the effect of “three birds with one stone”, which acted as the acetylene surrogate, the selenium source, and the internal oxidant. Further asymmetric synthesis was achieved with good enantioselectivity using an achiral Rh(III)/chiral phosphoric acid hybrid catalytic system, and the mechanistic study probed the sequential [4 + 2] annulation followed by the site-selective selenylation with the in situ-formed diselenide.