After stirring a mixed solution of 1-adamantane carboxylic acid 2-ethoxycarbonyl-2,2-difluoro-1-phenyl-ethyl ester (6.6 g) prepared in Synthesis Example 1-5, 1,4-dioxane (20 g) and 25% by mass of caustic soda (2.5 g) for 2 hours, water (30 g) was added to the reaction solution and washed with n-hexane to prepare an aqueous solution of sodium 3-(adamantane-1-carbonyloxy)-2,2-difluoro-3-phenyl propionate. An aqueous solution of triphenylsulfonium chloride (32 g) and methylene chloride (100 g) were added to the product, stirred for 30 minutes, and then an organic layer was isolated and washed with water, and thereafter was concentrated under reduced pressure. Methylisobutyl ketone was added to the concentrated solution, and concentrated again. Diisopropyl ether was added to the concentrated solution for crystallization, and a solid obtained was dried under reduced pressure to obtain a target compound, or triphenylsulfonium 3-(adamantane-1-carbonyloxy)-2,2-difluoro-3-phenyl propionate (5.5 g) as a white crystal (yield: 58%).
