An anomalous reaction of 7-chloro-2-hydrazono-5-phenyl-1,2-dihydro-3H-1,4-benzodiazepine with sodium acetate and 1,1′-carbonyldiimidazole

The addition of 7-chloro-2-hydrazono-5-phenyl-1,2-dihydro-3H-1,4-benzodiazepine 3 to a mixture of sodium acetate and 1,1′-carbonyldiimidazole 1 at room temperature gave, in moderate yields, carbonyl-1,1′-bis7-chloro-5-phenyl-1,2-dihydro-3H-1,4-benzodiazepin-2-ylidene hydrazone] 7 instead of the expected 2-acetylhydrazono-7-chloro-5-phenyl-1,2-dihydro-3H-1,4-benzodiazepine 4 .