Tetrahydrofuran (3.0 vol), ethyl acetate (1.5 vol), compound 8 were mixed. After the mixture was cooled to 0 °C, 52% propylphosphonic anhydride/ethyl acetate solution (2.8 equiv.) was added dropwise to the mixture. Pyridine (2.4 equiv.) was added to the mixture, and then a solution of compound 11 (1.3 equiv.) dissolved in tetrahydrofuran (3.0 vol) was added dropwise to the mixture. After stirring at 0 °C for 6 h, the reaction mixture was added dropwise to a mixture of ethyl acetate (10.0 vol) and 5% sodium bicarbonate aqueous solution (10.0 wt). After stirring at 0 °C for 1 h, the aqueous layer was separated.