Abstract The reaction of hydrazide with carbonyl chloride in the presence of sodium carbonates leads to the corresponding 1, 2-diacylhydrazines [1a–t, R 1 C (O) NHNHC (O) R 2, R 1= aryl, R 2= aryl or alkyl] in moderate to excellent yield (57–90%). The latter reacts with 2, 4-diphenyl-1, 3-diselenadiphosphetane-2, 4-diselenide (Woollins' reagent, WR) in refluxing toluene to give a series of new 2, 5-disubstituted 1, 3, 4-selenadiazoles (2a–t, 51 ...