Reaction Steps
A DCM (3 mL) solution of 32 (160. mg, 0.316 mmol, 1 equiv.) and triethylamine (26.5 μL, 0.189 mmol, 0.6 equiv.) was cooled to −78° C. in a 10-mL recovery flask, and a DCM solution of bromodimethylborane (1.26 M, 1.5 mL, 1.89 mmol, 6 equiv.) was added slowly. After stirring the bright yellow solution at −78° C. for 40 min, a 1:1 mixture of NEt3 and MeOH (3 mL) and saturated aqueous NaHCO3 were added in succession at −78° C. The mixture was then allowed to warm to room temperature and thrice extracted with EtOAc. The organic extracts were combined, washed successively with saturated aqueous NH4Cl, H2O, and brine, dried over Na2SO4, filtered, and concentrated in vacuo to an off-white foam. Flash column chromatography (60 mL SiO2, 7:3 hexane:EtOAc) afforded 73 mg (0.15 mmol, 47% yield) of 33 as a white flocculent solid. TLC Rf 0.17 (7:3 hexane:EtOAc). 1H NMR (600 MHz; C6D6): δ 5.59 (t, J=7.0 Hz, 1H), 5.39 (s, 1H), 3.59 (dd, J=11.8, 5.2 Hz, 1H), 3.07 (s, 1H), 3.03 (s, 3H), 3.02 (s, 3H), 2.98 (s, 3H), 2.76 (dd, J=15.4, 7.6 Hz, 1H), 2.44 (dd, J=15.4, 6.2 Hz, 1H), 2.29-2.22 (m, 1H), 1.91 (t, J=12.4 Hz, 1H), 1.82 (dtd, J=15.4, 10.2, 5.1 Hz, 2H), 1.74-1.71 (m, 13H), 1.60 (s, 3H), 1.21 (s, 3H). 13C NMR (126 MHz; C6D6): δ 197.0, 178.3, 130.8, 123.2, 104.2, 103.5, 73.2, 68.5, 58.9, 55.7, 52.5, 50.8, 50.2, 48.7, 40.7, 40.0, 36.4, 35.3, 30.9, 26.1, 20.3, 18.6, 17.7. HRMS-ESI (m/z): [M+H]+ calculated for C24H39BrO5, 487.2054. found, 487.2050.
