To a stirred solution of 21 (1.18 g; 2.52 mmol) in anhydrous THF (43 mL) was added 95% NaH powder (128 mg; 5.07 mmol). The suspension was stirred at room temperature for 45 min. Allyl bromide (240 μL, 2.79 mmol) was then added at 0° C. and the reaction was stirred at room temperature for 14 h with exclusion of moisture. Saturated aqueous NaHCO3 (10 mL) was added at 0° C. and stirred for 10 min. Most THF was evaporated and the residue was dissolved in ethyl acetate (150 mL). The solution was washed by saturated aqueous NaHCO3 and NaCl respectively, and dried over anhydrous Na2SO4. After evaporation of the solvent, the residue was purified by flash column chromatography over silica gel using ethyl acetate as the eluent to afford 22 as white solid (537 mg; 42% yield): 1H NMR (400 MHz, CD3OD) δ 8.15 (s, 1H, 6-H), 6.12 (dd, J=5.6, 8.0 Hz, 1H, 1′-H), 4.17 (m, 1H, 4′-H), 4.14 (m, 1H, 3′-H), 3.98-4.10 (m, 2H, CH2CH═CH2), 3.93 (dd, J=2.8, 11.5 Hz, 1H, one of 5′-H), 3.83 (dd, J=2.8, 11.5 Hz, 1H, one of 5′-H), 2.53-2.60 (ddd, J=1.7, 5.6, 13.6 Hz, 1H, one of 2′-H), 1.94-2.02 (ddd, J=5.9, 8.0, 13.6 Hz, 1H, one of 2′-H), 0.94 (s, 9H, C(CH3)3), 0.17 (s, 3H, one of SiCH3), 0.16 (s, 3H, one of SiCH3); 13C NMR (100 MHz, CD3OD) δ 165.4, 156.7, 147.7, 135.5, 117.2, 88.2, 87.0, 80.4, 70.9, 64.8, 57.3, 40.1, 26.7, 19.4, −4.7, −4.9; HRMS (FAB+) calcd for C18H31O4N3SiI (M+H+): 508.1129. Found: 508.1123.
