Metal-free [3+3] heteroannulation of thioamides with alkynyl NHPI-esters to access 2H-1,3-thiazin-4(3H)-ones

Abstract

The first chemo- and regioselective one-pot convergent synthesis of 2H-1,3-thiazin-4(3H)-ones has been successfully realized employing β-ketothioamides and alkyne derivatives of N-hydroxyphthalimide (NHPI)-ester under mild conditions in good to excellent yields. The process is triggered by the in-situ generation of dienolate intermediate followed by intramolecular selective N-cyclization. Remarkably, metal- and additive-free conditions, an open atmosphere, non-hazardous reagents, and easy purification are added characteristics to this cascade [3 + 3] annulative strategy. This heteroannulative approach will not only provide an effective method to access various 1,3-thiazin-4-ones but also augment the research domain of thioamides.