Dithieno‐ and thienobenzothiazines

The synthesis of some isomeric dithienothiazine systems has been described. These thiazines were made by an Ullman type cyclization reaction, starting with the appropriate dithienyl‐sulphides. During the ring closure reaction hydrogen chloride was eliminated from the β‐chloro‐propionyl side chain resulting in the formation of the acryloylthiazines5, 7and11. This reaction was studied under various conditions and some of the byproducts were identified. The general applicability of the reaction was demonstrated by the synthesis of two isomeric thienobenzothiazines14and16. Addition ofN‐methylpiperazine afforded the (N‐methylpiperazinyl)propionylthienothiazines, which were isolated as their hydrochloride salts. The latter compounds were tested for neuroleptic and antidepressive properties, but were shown to be devoid of activity. This lack of activity is discussed in terms of the hampered formation of the radicalcations, as was shown by the electrochemical oxidation of these compounds. Efforts to reduce the carbonyl function to give the propyl chain failed, due to an elimination of the side chain.