Efficient syntheses of thiadiazoline and thiadiazole derivatives by the cyclization of 3-aryl-4-formylsydnone thiosemicarbazones with acetic anhydride and ferric chloride

3-Aryl-4-formylsydnone 4′-phenylthiosemicarbazones and 3-aryl-4-formylsydnone thiosemicarbazones are effective precursors of sydnonyl-substituted heterocycles. The thiosemicarbazones reacted with acetic anhydride () to give 4-acetyl-2-phenylamino-5-(3-arylsydnon-4-yl)-4,5-dihydro-[1,3,4]thiadiazoles and 4-acetyl-2-(N-phenylacetamido)-5-(3-arylsydnon-4-yl)-4,5-dihydro-[1,3,4]thiadiazoles . However, under similar method, thiosemicarbazones produced only 4-acetyl-2-acetamido-5-(3-arylsydnon-4-yl)-4,5-dihydro-[1,3,4]thiadiazoles in high yield. The sydnonyl-substituted thiadiazole derivatives were also obtained successfully by the cyclization of 3-aryl-4-formylsydnone thiosemicarbazones with ferric chloride (). In the cyclization, the thiosemicarbazones are more reactive than the thiosemicarbazones .