A mixture of 1.42 g (5 mmol) of ethyl 5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a][1,4]benzodiazepine-3-carboxylate, 100 mg of potassium cyanide and 10 ml of ethyleneglycol is stirred at 130° C. for 6 hours, subsequently diluted with chloroform, washed with water, dried over magnesium sulphate and evaporated. After recrystallisation of the residue from ethyl acetate, there is obtained 2-hydroxyethyl-5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a][1,4]benzodiazepine-3-carboxylate of melting point 222°-223° C.
