In toluene/ethanol/water (10/1/1.2 ml) was dissolved methyl 7-bromo-1,1-dioxo-2,3-dihydro-1-benzothiepine-4-carboxylate (800 mg), and to the solution were added 4-methyl-2-thienyl borate (524 mg) and potassium carbonate (935 mg). The mixture was stirred at room temperature for 30 minutes, and to the mixture was added tetrakistriphenylphosphinepalladium (152 mg). The mixture was stirred at 100° C. for 16 hours and cooled to room temperature. To the mixture was added water, and the mixture was extracted with ethyl acetate, washed with saturated brine and dried with magnesium sulfate. Under reduced pressure, the solvent was evaporated, and the residue was purified with silica gel column chromatography (hexane/ethyl acetate=3/1) to give methyl 7-(4-methyl-2-thienyl)-1,1-dioxo-2,3-dihydro-1-benzothiepine-4-carboxylate (510 mg).
