Ring-closure reaction of N-arylthiomethylaroylamides to 1,3-benzothiazines

N-Arylthiomethylaroylamides substituted with an electron-donating group in the meta position undergo two-directional cyclization in the presence of phosphorus oxychloride to give both positional isomers of the 4H-1,3-benzothiazine derivative. The structures of the products were confirmed by ¹H and ¹³C nmr spectroscopy. Mixed ring-closure reactions of several N-arylthiomethylaroylamides 3, 6, 9, 13 have shown that these conversions are introduced by a proton-catalyzed intermolecular rearrangement.