Metal-free and Selectfluor-mediated diverse transformations of 2-alkylthiobenzamides to access 2,3-dihydrobenzothiazin-4-ones, benzoisothiazol-3-ones and 2-alkylthiobenzonitriles

Abstract

Diverse transformations of 2-alkylthiobenzamides have been established to synthesize 2,3-dihydrobenzothiazin-4-ones, benzoisothiazol-3-ones and 2-alkylthiobenzonitriles in the presence of Selectfluor. Both NaI–HI and TFA–Ac₂O systems control the selective C–S bond cleavage and C–H bond functionalization to access 2,3-dihydrobenzothiazin-4-ones and 2-substituted 2,3-dihydrobenzothiazin-4-ones, respectively. Notably, this is the first example of using Selectfluor as a methylene source to construct important 2,3-dihydrobenzothiazin-4-ones. In the presence of HCl, benzoisothiazol-3-ones were obtained in good yields. Furthermore, 2-alkylthiobenzonitriles could also be prepared using the same NaI–HI system via a thioether-directed and Selectfluor-mediated dehydration of 2-alkylthiobenzamides.