The mixture of 315 mg of 1-[2-(2-imidazolylmethyl)phenylthiocarbamoyl]-4-methylpiperazine, 3.3 ml of dimethylformamide, 276 mg of potassium carbonate, 116 mg of cyanogen bromide and 50 mg of 8-crown-6 ether is stirred at room temperature under nitrogen for 3 hours. It is diluted with ethyl acetate, washed with saturated aqueous sodium chloride, dried and evaporated. The residue is dissolved in acetone, the solution treated with 116 mg of maleic acid and diluted with diethyl ether, to yield 5-(4-methyl-1-piperazinyl)-11H-imidazo[1,2-c][1,3]benzodiazepine monomaleate of example 1.
