Ring transformation of 3-hydroxy-1,2,5- and -1,2,4-thiadiazoles and -isothiazoles into isothiazole,thiazole and thiophene derivatives

Ring transformation of 3-hydroxy-1,2,5-thiadiazole ( 1 ), 3-hydroxy-1,2,4-thiadiazole ( 14 ), and 3-hydroxyiso-thiazole ( 18 ) by the reaction with acetic anhydride in the presence of DBU afforded isothiazoles 2-5 and 13 , thiazoles 15 and 16 and thiophenes 21-25 , respectively. The reaction of 1 with propionic anhydride gave isothiazole 13 . The formation pathway of the products is mentioned.