A mixture of 2.6 g of ethyl difluoro-(2-hydroxyadamantan-2-yl)acetate, prepared in Synthesis Example 1-8, 30 g of 1,4-dioxane, 4.0 g of 25 wt % sodium hydroxide, and 10 g of water was stirred for 2 hours. To the reaction solution, 1.0 g of 35 wt % hydrochloric acid was added, and then 66 g of an aqueous solution of 4-fluorophenyldiphenylsulfonium chloride and 100 g of methylene chloride were added. After stirring for 30 minutes, the organic layer was taken out, washed with water, and concentrated under reduced pressure. Methyl isobutyl ketone was added to the concentrate, which was concentrated again. Diisopropyl ether was added to the concentrate. The supernatant was removed, leaving 2.4 g of the target compound, 4-fluorophenyldiphenylsulfonium difluoro-(2-hydroxyadamantan-2-yl)acetate as vitreous solids (yield 45%).
