Thiadiazole derivatives [I; R = Ph, p-XC6H4 (wherein X = halo, NO2, Me, MeO), furyl, 2,4-Br2C6H3] are prepared by acid-catalyzed cyclization of thiosemicarbazide derivatives II. II (R = Ph) (1 mmol) in HOAc was refluxed 2-3 h to give 91.7% I (R = Ph). Use of H2SO4 for cyclization gave 64.0% yield.

Key words: PHENOXY GROUP, CATALYSIS, AMIDES P, THIOUREAS, PHENOXYACETIC ACID P, CYCLIZATION, THIADIAZOLE