Certain 1,2-dithiolium salts react with primary amines in alcoholic solution to provide 1-aminopropene-3-thiones, which can be oxidized by iodine to form isothiazolium salts. These react with sulfur in pyridine to form isothiazole-3-thiones, which react with methyl iodide to form 3-methylthioisothiazolium iodides.