Ethyl 4-[2-(3,5-dichloro-4-pyridyl)-1-hydroxyethyl]-7-methoxybenzofuran-2-carboxylate (10 g) was dissolved in acetone (200 ml), a Jones reagent (a 2.76 mmol/L solution, 9.7 ml) was dropwise added thereto under cooling on ice, and the mixture was stirred for 20 minutes. Isopropanol was added thereto, and the mixture was stirred at room temperature for 30 minutes. The solvent was distilled off under reduced pressure and the residue was extracted with chloroform. The extract was washed with a saturated aqueous sodium chloride solution and dried over magnesium sulfate, and the solvent was distilled off under reduced pressure. The residue was suspended in isopropanol and the precipitated crystals were collected by filtration to give the desired compound (8.34 g, 84%) as colorless crystals.
