Toluene (50 ml) and p-toluenesulfonic acid monohydrate (0.15 g) were added to 1-(4-ethoxy-2,3-difluorophenyl)-4-(3-propylcyclopentyl)cyclohexanol (5.0 g) obtained in the first step, in a reaction vessel equipped with a Dean-Stark apparatus under an atmosphere of nitrogen. The mixture was refluxed for 1.5 hour, while forming water was removed with a Dean-Stark apparatus. After the mixture had been cooled to room temperature, the reaction solution was washed with water and dried over anhydrous magnesium sulfate, and the solvent was distilled off under reduced pressure. The residue was purified by silica gel chromatography (eluent: ethyl acetate/n-heptane=1/10 by volume) to give 1-ethoxy-2,3-difluoro-4-(4-(3-propylcyclopentyl)cyclohex-1-enyl)benzene (3.9 g).
