Synthesis of Isothiochroman-3-ones via Metal-Free Oxidative Cyclization of Alkynyl Thioethers

A novel Brønsted acid-catalyzed oxidative C–H functionalization of alkynyl thioethers has been developed. This method allows the practical synthesis of valuable isothiochroman-3-ones in mostly moderate to good yields under mild reaction conditions and features a broad substrate scope and wide functional group tolerance. Moreover, this metal-free oxidation can also be used to promote formal N–H insertion involving an unexpected 1,2-sulfur migration, affording useful 1,4-benzothiazin-3-ones.