A mixture of {5-[4-(4-methoxyphenyl)piperazin-1-yl]-2,4,6,7-tetramethyl-2,3-dihydro-1-benzofuran-2-yl}acetonitrile (260 mg, 0.641 mmol) synthesized in Example 140, 8N sodium hydroxide aqueous solution (2.0 mL) and ethanol (10 mL) was stirred under heated reflux for 15 hours. After cooled to room temperature, 1N hydrochloric acid (16 mL) was added thereto, and the reaction solution was distributed using water and ethyl acetate. The organic layer was washed with saturated saline and dried using anhydrous magnesium sulfate, and then the solvent was removed under reduced pressure. The obtained residue was purified by silica gel chromatography (hexane-ethyl acetate 90:10-70:30) and crystallized from ethyl acetate-hexane to obtain 150 mg of the title compound (yield 55%). Melting point was 171 to 174° C. (decomposition).
