To methyl 2-(4-phenylbenzyloxy)-6,7-dihydro-5H-benzocycloheptene-8-carboxylate (1.22 g, 3.17 mmol) dissolved in a mixed solvent of methanol (20 ml) and THF (35 ml) was added a 1N aqueous solution of sodium hydroxide (10 ml), and the resulting mixture was stirred at room temperature for 18 hours and 60° C. for 2 hours. The reaction mixture was mixed with 1 N hydrochloric acid (12 ml) at room temperature, was concentrated under reduced pressure and was mixed with water, and an insoluble material was collected by filtration. The insoluble material was washed successively with water and hexane, and was dried under reduced pressure to obtain 2-(4-phenylbenzyloxy)-6,7-dihydro-5H-benzocycloheptene-8-carboxylic acid (1.38 g).
