Phosphorus oxychloride → 2-(Chloromethyl)-5-(4-chlorophenyl)-1,3,4-oxadiazole

To a mixture of 4-chlorobenzohydrazide 5 (1 g, 5.86 mmol) and K2CO3 (0.97 g, 7.03 mmol) in acetonitrile (30 mL) was added 2-chloroacetyl chloride (0.68 g, 6.08 mmol) dropwise at ambient temperature. The resulting mixture was stirred at ambient temperature for 16 hours. The solid was collected, washed with H2O and ether, and dried to afford 4-chloro-N′-(2-chloroacetyl)benzohydrazide 6 (1.2 g, 82%) which was used for the next step without further purification. A mixture of 4-chloro-N′-(2-chloroacetyl)benzohydrazide 6 (0.6 g, 2.43 mmol) and phosphorous oxychloride (0.37 g, 2.43 mmol) in acetonitrile (20 mL) was stirred under reflux for 16 hours and concentrated. The residue was subjected to flush column chromatography eluting with 10-25% acetone/hexanes to give compound 7 (0.45 g). Yield: 82%.