Reaction Steps
A solution of 171 (6.50 g, 15.99 mmol) in anhydrous DMF (27.5 mL) was added dropwise to a stirred suspension of NaH (0.422 g, 0.704 g of a 60% dispersion in mineral oil, 18.34 mmol) at 0° C. and the reaction mixture was allowed to stir for 30 minutes. A solution of SEM chloride (3.11 mL, 2.93 g, 17.59 mmol) in anhydrous DMF (5 mL) was added dropwise to the stirred reaction mixture at 0° C. and allowed to stir at room temperature for 16 h. The reaction mixture was poured into water (200 mL) to afford a white precipitate, which was extracted with diethyl ether (4×300 mL). The organic layer was washed with water (2×50 mL), brine (2×50 mL) and dried over anhydrous MgSO4. Filtration and evaporation of the solvent in vacuo afforded the crude product, which was purified by flash column chromatography using an 80:20 mixture of petroleum ether:EtOAc as eluent. Pure fractions were combined and evaporated in vacuo to afford the product (172) as a yellow oil (7.01 g, 13.1 mmol, 82%). 1H NMR (270 MHz, CDCl3) δ7.35 (s, 1H, ArH), 7.24 (s, 1H, ArH), 5.52 (d, 2H, J=9.89 Hz, SEM amino acetal CH2), 4.65 (d, 2H, J=9.90 Hz, SEM amino acetal CH2), 4.61-4.56 (m, 1H, 2), 4.23 (dd, 1H, J=4.40 Hz, 8.24 Hz, 11a), 3.94 (s, 3H, OMe), 3.92 (s, 3H, OMe), 3.68 (m, 4H, SEM 1′ CH2+3), 2.86 (m, 1H, 1), 2.02 (m, 1H, 1), 0.98 (t, 2H, J=8.25 Hz, SEM 2′ CH2), 0.88 (s, 9H, TBDMS t-Bu CH3), 0.10 (s, 6H, 2×TBDMS SiCH3), 0.03 (s, 9H, 3× SEM SiCH3); 13C NMR (67.8 MHz, CDCl3) δ170.0, 165.6, 151.8, 147.1, 133.9, 121.5, 111.2, 105.5, 78.1, 69.6, 67.0, 56.5, 56.2, 56.1, 53.6, 35.5, 25.7, 18.4, −1.3, −4.8.
