A solution of Intermediate 35 (21.06 g), 1,1′-azobis(N,N-dimethylformamide) (64.11 g) and p-anisic acid (23.03 g, Tokyo Kasei Kogyo) in tetrahydrofuran (400 ml) was added with tri(n-butyl)phosphine (35.6 ml) at room temperature and stirred at 50° C. for 2.5 hours. The reaction mixture was cooled to room temperature, then added with ethyl acetate (200 ml) and successively washed with saturated aqueous sodium hydrogencarbonate twice (200 ml each) and 0.1 N aqueous sodium hydroxide (50 ml), and dried over anhydrous sodium sulfate. The solvent was evaporated under reduced pressure, and the residue was purified by silica gel column chromatography (n-hexane:ethyl acetate=5:1) to obtain the title compound (32.92 g).
