4-Phenyl-1,2-dithiolium perchlorate reacts with ammonia in ethanol to yield 4-phenyl-isothiazole. The reaction is general for dithiolium salts. When unsymmetrical dithiolium salts are treated with ammonia, the major product and, under many conditions, the only product is the 5-substituted isothiazole. Of the four possible mechanisms for these reactions, an addition-elimination mechanism has been shown