New synthesis of pyrrolobenzothiazine and pyrrolobenzoxazine ring systems

Abstract

A new and simple synthesis of pyrrolobenzothiazine and pyrrolobenzoxazine ring sytems is described. Thus, 2-aminophenol and 2-aminothiophenol reacted with maleic anhydride at room temperature to give the acids 7 which were converted into their acid chlorides 9 and then their amides 10. Subsequent pyrolysis of the latter in polyphosphoric acid for 15 h gave the title compounds in good yield. [1,4]Benzothiazino[2,3-d][1,6]benzothiazocin-6-(7H)-one, a new type of phenothiazine heterocycle, was also isolated.