After adding 0.04 g of tetrabutylammonium bromide to 8 ml of 50% aqueous solution of sodium hydroxide, the mixture is heated to 120° C. Thereto is dropwise added a solution of 0.40 g of benzyl (2S,4R)-4-hydroxy-2-(4-methyl-1-pentenyl)-1-pyrrolidinecarboxylate and 0.65 ml of 3-chloro-2-methyl-1-propene in 0.8 ml of toluene over a period of 5 minutes. The mixture thus obtained is heated under reflux for 30 minutes with stirring. The reaction mixture is cooled to ambient temperature, toluene and water are added, and the organic layer is separated. The organic layer thus obtained is washed with water and saturated aqueous solution of sodium chloride successively and dried over anhydrous magnesium sulfate, and then the solvent is distilled off under reduced pressure. The residue thus obtained is purified by silica gel column chromatography (eluent; n-hexane:ethyl acetate=10:1) to obtain 0.31 g of benzyl (2S,4R)-2-(4-methyl-1-pentenyl)-4-[(2-methyl-2-propenyl)oxy]-1-pyrrolidinecarboxylate as a colorless oily product.
