Reaction Steps
A DCM (20 mL) solution of 38 (794 mg, 1.57 mmol, 1 equiv.) and triethylamine (131 μL, 0.940 mmol, 0.6 equiv.) was cooled to −95° C. in a 100-mL recovery flask, and a DCM solution of bromodimethylborane (1.59 M, 5.9 mL, 9.4 mmol, 6 equiv.) was added slowly over 5 min. The resulting bright yellow solution was stirred at −95° C.±3° C. for 10 min, whereupon it was quenched through the sequential addition of NEt3 (6 mL) and saturated aqueous NaHCO3 at −95° C. The mixture was warmed to room temperature and extracted thrice with EtOAc. The organic extracts were combined, washed successively with 2 N HCl, H2O, saturated aqueous NaHCO3, and brine, dried over Na2SO4, filtered, and concentrated in vacuo to a yellow foam. Flash column chromatography (150 mL SiO2, 8:2 to 7:3 hexane:EtOAc) afforded 471 mg (0.897 mmol, 57% yield) of 39 as a white flocculent solid. TLC Rf 0.30 (7:3 hexane:EtOAc). 1H NMR (600 MHz; CDCl3): δ 5.46 (s, 1H), 5.26 (d, J=10.3 Hz, 1H), 3.74 (s, 3H), 3.61 (dd, J=11.8, 5.3 Hz, 1H), 3.55 (s, 1H), 3.25 (s, 3H), 2.87-2.82 (m, 2H), 2.25 (d, J=14.2 Hz, 1H), 1.95 (t, J=12.4 Hz, 1H), 1.73 (s, 3H), 1.70-1.65 (m, 4H), 1.43 (td, J=13.0, 4.2 Hz, 1H), 1.39-1.35 (m, 1H), 1.32-1.27 (m, 3H), 1.21 (s, 3H), 1.20 (s, 3H), 1.09 (s, 3H), 0.93 (t, J=7.9 Hz, 9H), 0.55 (q, J=7.6 Hz, 6H). 13C NMR (126 MHz; CDCl3): δ 198.2, 176.0, 137.4, 122.1, 104.1, 100.6, 73.8, 73.3, 57.6, 56.5, 51.1, 48.5, 45.9, 40.9, 39.4, 37.0, 30.8, 30.0, 29.4, 26.2, 18.0, 17.0, 7.3, 7.0. HRMS-ESI (m/z): [M+Na]+ calculated for C29H52O6Si, 547.3425. found, 547.3404.
