Ethyl 2-[3-cyclopropyl-4-(cyclopropylsulfonyl)phenyl]-3-[(2S,3S,7R)-2,3-diphenyl-1,4-dioxaspiro[4.4]non-7-yl]acrylate (1.77 g, (E), (Z) mixture) was dissolved in a mixed solvent of methanol (21.2 mL) and dioxane (21.2 mL), and to this solution was slowly added 8 M aqueous potassium hydroxide solution (21.2 mL), which had been separately prepared. It was stirred at room temperature for 10 minutes, and then stirred in an oil bath at 70° C. for 2 hours under heating. It was left to be cooled to room temperature, and hydrochloric acid was carefully added thereto under ice-cooling. The mixture was stirred for 2 hours under heating in an oil bath at 90° C., and cooled to room temperature again. Chloroform was added thereto and the organic layer was separated. The aqueous layer was extracted with chloroform, combined with the organic layer, dried over anhydrous sodium sulfate and then concentrated under reduced pressure. The residue was purified by silica gel column chromatography to obtain (2E)-2-[3-cyclopropyl-4-(cyclopropylsulfonyl)phenyl]-3-[(1R)-3-oxocyclopentyl]acrylic acid (952 mg).
