Ethyl 2,2-difluoro-3-hydroxy-3-phenylpropionate acid (9 g) prepared in Synthesis Example 1-4 and 1-adamantanecarbonyl chloride (9.5 g) were dissolved in methylene chloride (60 g), and a mixed solution of triethyl amine (6 g), 4-dimethyl aminopyridine (0.5 g) and methylene chloride (20 g) was dropped into the obtained solution under ice cooling. After aging overnight, 5% by mass hydrochloric acid was added to the product and quenched, and then the reaction solution was washed with water, and concentrated. Methylisobutyl ketone was added to the concentrated solution, and was concentrated again to obtain a target compound, or 1-adamantane carboxylic acid 2-ethoxycarbonyl-2,2-difluoro-1-phenyl-ethyl ester (15 g) as a colorless oily matter (yield: 68%).
