Aromatic ring transfer—a new synthesis of 2,4-diaryl-4H-3,1-benzothiazines

A new synthetic approach to 2,4-diaryl-4H-3,1-benzothiazines is described based on the rearrangement of 2-isothiocyano triarylmethanes in the presence of AlCl3. An aryl ring is found to migrate to the carbon atom of an isothiocyano group followed by intramolecular cyclization as a result of electrophilic attack of the benzhydryl carbocation on the sulfur atom.