Synthesis of 7,7′-azoimidazo[2,1-b]thiazolium salts

Abstract

The preparation of 4H-thiazolo[2,3-c]-as-triazines from acetophenone thiazol-2-ylhydrazone and α-halogeno-ketones is described. Boiling concentrated hydrobromic acid failed to effect ring contraction of the 4H-thiazolotriazines to the corresponding 7-aminoimidazo[2,1-b]thiazolium salts. These last compounds were, however, prepared in high yield by treating the appropriate imidazo[2,1-b]thiazole bases with O-mesitylsulphonylhydroxylamine; oxidation of the 7-aminoimidazothiazolium salts with saturated aqueous bromine gave the title compounds.