Ethyl 3-aminobenzoate (69 mg) was dissolved in tetrahydrofuran (10 ml), the solution was cooled on ice-water. Triphosgene (45 mg) was added at internal temperature 5° C., triethylamine (162 mg) was added thereto over 10 minutes period, the mixture was allowed to come to room temperature and stirred for 10 minutes. A solution of 1-tert-butylcarbonylmethyl-2-oxo-3-amino-5-(2-fluorophenyl)-1,3,4,5-tetrahydro-2H-1,5-benzodiazepine (150 mg) in tetrahydrofuran (5 ml), the mixture was additionally chloride. The organic layer was successively washed with water and saturated brine, dried over anhydrous sodium sulfate, the solvent was evaporated under reduced pressure, and the residue was purified by silica gel column chromatography(n-hexane:ethyl acetate=3:1), to thereby obtain 190 mg of the title compound as colorless crystals (Yield: 83%).
