A mixture of palladium acetate (1.3 mg), 2-dicyclohexylphosphino-2′,4′,6′-triisopropyl-1,1′-biphenyl (7.2 mg), phenylboronic acid (0.9 mg) and tert-butanol (2 mL) was stirred at room temperature for 20 minutes under argon atmosphere. To the reaction mixture were added N-[4-(3-chloro-4-fluorophenyl)-2,2-dimethyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazin-7-yl]methanesulfonamide (compound obtained in Example 13, 60 mg), potassium carbonate (62 mg), tert-butyl carbamate (35 mg) and tert-butanol (5 mL), and the mixture was refluxed for 3 hours. To the reaction mixture were further added palladium acetate (1.3 mg), 2-dicyclohexylphosphino-2′,4′,6′-triisopropyl-1,1′-biphenyl (7.2 mg), potassium carbonate (62 mg) and tert-butyl carbamate (35 mg), and the mixture was further refluxed for 20 hours. After cooling, the reaction mixture was diluted with ethyl acetate, and the mixture was washed successively with water and brine, dried over sodium sulfate and concentrated in vacuo. The resultant residue was purified by column chromatography on silica gel (solvent; n-hexane/ethyl acetate =4/1→3/7) to give tert-butyl (5-{2,2-dimethyl-7-[(methylsulfonyl)amino]-3-oxo-2,3-dihydro-4H-1,4-benzoxazin-4-yl}-2-fluorophenyl)-carbamate (83 mg) as a colorless powder.
