Methanol → Methyl 4-bromo-2-(methylsulfonyl)benzoate

To 4-bromo-2-methanesulfonylbenzoic acid (5 g) were added methanol (45 mL) and concentrated sulfuric acid (1.8 mL), and the mixture was stirred with heating under reflux. After completion of the reaction, the solvent was evaporated, and the residue was neutralized with 1N aqueous sodium hydroxide solution, and the mixture was extracted with ethyl acetate. The organic layer was washed with saturated brine, and the solvent was evaporated to give methyl 4-bromo-2-methanesulfonylbenzoate (3.34 g). To a mixture of the obtained methyl 4-bromo-2-methanesulfonylbenzoate (3.34 g), tris(dibenzylideneacetone)dipalladium(0)-chloroform adduct (295 mg), 2-(dicyclohexylphosphino)biphenyl (399 mg), tripotassium phosphate (3.39 g) and benzophenonimine (2.5 mL) was added 1,2-dimethoxyethane (25 mL), and the mixture was stirred with heating under reflux. After completion of the reaction, water was added to the reaction mixture, and the mixture was extracted with ethyl acetate. The organic layer was washed with saturated brine, and the solvent was evaporated. The obtained residue was dissolved in tetrahydrofuran (26 mL), 1N hydrochloric acid (100 mL) was added, and the mixture was stirred at room temperature for 1 hr. The reaction mixture was neutralized with sodium hydrogen carbonate, and the mixture was extracted with ethyl acetate. The organic layer was washed with saturated brine, and the solvent was evaporated to give methyl 4-amino-2-methanesulfonylbenzoate (1.46 g). Using the obtained methyl 4-amino-2-methanesulfonylbenzoate (1.46 g) and 3-chloropropane-1-sulfonyl chloride (1.03 mL) and by the reaction and treatment in the same manner as in Preparation Example 16, the title compound (0.53 g) was obtained.