5-(3,4,5,6-Tetramethoxy-2-methylbenzyl)-2-(3-pyridyl) benzoic acid (500 mg, 1.1820 mmol) was dissolved in a mixed solvent of acetonitrile (30 ml) and water (10 ml), then CAN (1.62 g, 2.9562 mmol) was added thereto at room temperature and the mixture was stirred for 3 hour. The reaction solution was poured into water, neutralized with a 1N aqueous solution of sodium hydroxide and extracted with ethyl acetate. The extract was washed with water and dried and the solvent was evaporated therefrom. The residue was purified by silica gel column chromatography (10% methanol-methylene chloride) to give the title compound (270 mg, 0.6870 mmol, 58%).
