To a mixture of 88.3 g (F.W. 235.46, 375 mmol) of 4-bromo-2-chlorobenzoic acid (3), 57.8 g (F.W. 154.165, 375 mmol) of 3,5-dimethoxyphenol (13), 93.2 g (F.W. 138.21, 670 mmol) of potassium carbonate and 400 mL of N-methyl-2-pyrrolidone was added benzene (200 mL), and the resulting solution was dried by a Dean-Stark water separator (140-170° C.) for three hours and then, 6.0 g (F.W. 63.55, 93.7 mmol) of copper (powder) and 17.8 g (F.W. 190.45, 93.7 mmol) of copper (I) iodide were added thereto and stirred at 120° C. for 30 minutes. This reaction mixture was cooled by standing and ice water and ethyl acetate were added thereto and then, the obtained solution was made pH 2 with concentrated hydrochloric acid and filtered. The organic layer was separated and then, thoroughly washed with water and subjected to salting out with a saturated sodium chloride aqueous solution. The resulting solution was dried with anhydrous magnesium sulfate and concentrated and the residue was purified by silica gel column chromatography (developing solvent; ethyl acetate:hexane=1:3) and recrystallized from ethyl acetate-hexane to obtain 75.4 g (57%) a desired compound (20). (TLC; ethyl acetate:hexane=1:2 or 1:1).
