In a 100-ml flask, 31 g of an aqueous solution of 5 mass % sodium hydroxide was placed. The solution was cooled, with stirring, by immersing the flask in an ice water bath. Then, 15.0 g of 2-hydroxy-1,1-difluoroethanesulfonic acid triphenylsulfonium (purity: 95%, 0.035 mol) was gradually added to the solution. The solution was returned to room temperature and stirred for 30 minutes. The solution was again cooled by immersing the flask in the ice water bath. After that, a solution of 6.5 g of tert-butyl 2-bromomethylacrylate (0.029 mol) in 10 g of acetonitrile was dropped into the above solution. The mixed solution was further stirred for 1.5 hours at room temperature. The thus-obtained reaction solution was separated into upper and lower layers. The lower layer was mixed with 20 g of chloroform and washed three times with 24 g of water. The resulting solution was solidified by concentration under reduced pressure. The solid product was dissolved in 10 g of methyl ethyl ketone at 40° C. Into the product solution, 25 g of diisopropyl ether was slowly dropped. The product solution was then stirred for 1 hour at room temperature. After confirming the deposition of a crystalline substance, the crystalline substance was filtered out and dried under reduced pressure. With this, 10 g of the target compound (PAG-1) was obtained as a white solid substance (purity: 99%, yield: 88%).
