The mixture of diol 23 (585 mg, 2.07 mmol), TBSCl (1.0 g, 6.63 mmol), and imidazole (564 mg, 8.28 mmol) in DMF (5.0 mL) was stirred at 70° C. for 20 h under nitrogen. After being quenched by aqueous NH4Cl, the reaction mixture was extracted with diethyl ether (3×20 mL). The organic layers were washed with brine, dried over Na2SO4, concentrated via rotary evaporation, and further dried in vacuo. The crude residue was dissolved in THF (20 mL), and a THF solution (2.3 mL, 2.3 mmol, 1M) of TBAF was added at room temperature. After being stirred at room temperature for 30 min, the solution was quenched with aqueous NH4Cl solution, and the product was extracted with ethyl acetate (3×10 mL). The organic layers were dried over Na2SO4 and concentrated via rotary evaporation. The crude product was purified by flash column chromatography (ethyl acetate/hexanes; 1:4) to afford 690 mg (84%) of 38 as a white solid. Mp 106.6-108.5° C.; 1H NMR (CDCl3, 300 MHz): δ 7.86 (d, J=7.5 Hz, 2H), 7.48-7.62 (m, 3H), 7.00 (d, J=2.1 Hz, 1H), 4.13 (d, J=9.3 Hz, 1H), 3.54 (s, 1H), 2.27 (q, J=6.9 Hz, 1H), 2.01 (s, 1H), 1.78 (m, 1H), 1.24 (d, J=7.2 Hz, 3H), 1.09 (d, J=6.3 Hz, 3H), 0.64 (s, 9H), −0.06 (s, 3H), −0.35 (s, 3H); 13C NMR (CDCl3, 75 MHz): δ 142.8, 140.4, 139.4, 133.3, 129.2, 128.2, 77.9, 70.7, 37.7, 36.3, 25.6, 18.5, 17.7, 14.9, −4.7, −5.3. Anal. Calcd for C20H32O4SSi: C, 60.57; H, 8.13. Found: C, 60.82; H, 8.07.
