From benzil arylimines to 2H-benzo-1,4-thiazines, benzothiazoles or indoles

A series of benzil monoarylimines (1) was treated with phosphorus pentasulfide in refluxing toluene or xylene. Thionation of 1 occurred readily to afford either 2H-benzo-1,4-thiazines (2) or indoles (4) via annulation reactions, depending strongly on the nature of the meta substituent of the arylamino group. Mechanisms for these rearrangements were proposed. Furthermore, subsequent oxidation of 2 provided benzothiazoles (3). All compounds were fully characterized by IR, MS, 13C and 1H NMR.