Reaction Steps
To a solution of crude 28 (approx. 1.23 mmol) in THF/DMF (9:1, 10 ml) at 0° C., BnBr (0.18 ml, 1.50 mmol) and NaH (36 mg, 1.50 mmol) were added. The solution was warmed to room temperature over 2 h, then cooled to 0° C. again and further BnBr (0.18 ml, 1.50 mmol) was added. The reaction was warmed to room temperature over 30 min, cooled to 0° C. and quenched by the addition of water. After dilution with Et2O the phases were separated and the aqueous layer extracted with Et2O. The organic phase was then dried over MgSO4, filtered and concentrated. Column chromatography on silica gel (hexanes/ethyl acetate) afforded 29 (797 mg, 1.08 mmol, 88%). 1H-NMR (400 MHz, CDCl3) δ 8.14-7.00 (m, 18H, Ar—H), 5.31 (dd, 1H, J1=10.1 Hz, J2=8.9 Hz, 2-H), 4.83 (app. d, 1H, J=11.3 Hz, benzyl-Ha), 4.72 (d, 1H, J=10.2 Hz, 1-H), 4.63 (app. d, 1H, J=11.0 Hz, benzyl-Hb), 4.58 (app. d, 2H, J=3.1 Hz, benzyl-H), 3.95 (app. t, 1H, J=8.7 Hz, 3-H), 3.78-3.51 (m, 4H, 4-H, 5-H, 6-H), 2.15 (s, 3H, S—CH3), 1.25 (s, 9H, S-tBu), 0.79 (s, 9H, TBS-tBu), 0.00 (s, 3H, TBS-CH3), −0.16 (s, 3H, TBS-CH3); 13C-NMR (100 MHz, CDCl3) δ 165.6, 149.7, 138.2, 136.5, 133.2, 130.5, 130.1, 129.8, 129.2, 128.5, 128.4, 128.0, 127.72, 127.68, 127.6, 124.7, 88.0 (C-1), 79.5 (C-5), 78.9 (C-4), 77.0 (C-3), 75.1, 73.6 (C-2), 73.5, 69.0 (C-6), 31.4, 25.8, 20.3, −3.9, −4.1; HRMS (ESI): Calcd for C44H56O6SSiNa+ [M+Na]+ 763.3459. found: 763.3500
