Synthesis of compound vi: Compound v (2.57 mmol) was dissolved in 26 mL of anhydrous dichloromethane, and the reaction lasted for 2.5 h under the condition of ice-water bath with slow passage of dry HCl gas. After completion of the reaction, the reaction solution was washed with 19.5 mL of ice water and the organic layer was separated. The organic layer was washed sequentially with saturated sodium bicarbonate solution until the aqueous layer was weakly basic, and then washed with ice water until the aqueous layer was neutral. The organic layer was dried with anhydrous sodium sulfate for more than 4 hours and subsequently concentrated under reduced pressure to give a light yellow syrupy product. The syrup was recrystallized using a solvent mixture of hexane and dichloromethane to give the white solid compound vi in 65.1% yield.1H NMR (CDCl3) δ ppm: 7.36-8.14 (m, 15H, OBz), 6.68 (d, J = 4.4 Hz, 1H, H-1), 5.59 (dd, 1H, H-3), 4.64-4.80 ( m, 4H, H-2, H-4 and H-5). Melting point: 139-140°C.
