Abstract Pyridazines 1a, b on treatment with potassium cyanide/benzoyl chloride in a mixed solvent system gave 2-benzoyl-2, 5-dihydro-3-pyridazinecarbonitriles 3a, b together with products resulting from attack of one mole of cyanide ion and three moles of benzoyl chloride (5a, b). The structures of these novel compounds are proved. A plausible reaction mechanism is proposed, involving rearrangement of initially formed 2a, b into 3a, b. ...