3.0 g (11.2 mmol) of 6-(4-chloro-3-nitro-phenyl)-4,5-dihydro-5-methyl-3(2H)-pyridazinone, 3.7 g (22.4 mmol) of 1-(2-pyrimidyl)-piperazine and 0.9 g (11.2 mmol) of pyridine are boiled under reflux in 50 ml of dioxane. A further 1.9 g (11.6 mmol) of 1-(2-pyrimidyl)-piperazine is added after 6 hours and the reaction mixture is boiled for a further 4 hours. When the reaction mixture has cooled, it is poured out on 300 ml of ice water and the precipitated solid is suction filtered, washed with a small quantity of diethyl ether and recrystallized from 40 ml of 2-methoxyethanol. 3.1 g (70%) of orange red crystals, m.p. 232° to 233° C., are obtained.
