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. Furthermore, the synthesis of the pyridazine Reissert compound 2a is reported.