A phosgene was mixed with ethanol, then cooling by ice-water the solution of
8-chloro-1-phenyl-2,3,4,5-tetrahydro-1H-1,5-benzodiazepine-2-one in
chloroform was added dropwise, mixed and allowed to stand. Then the
reaction mixture was concentrated, and crystals was filtered off. So the 7-
chloro-2,3,4,5-tetrahydro-4-oxo-5-phenyl-1H-1,5-benzodiazepine-1-carboxylic
acid ethyl ester was obtained, melting point 172°-173°C (dec.).
