Reaction Steps
Compound 39 (77 mg, 0.18 mmol) was dissolved in dry methylene chloride (2.0 mL), and cooled to −78° C. To this cold solution were added 2,6-lutidine (32 μL, 0.27 mmol), followed by TBSOTf (50 μL, 0.22 mmol) under nitrogen. After stirring for 2 h at −78° C. (the reaction was monitored by TLC until completionusing a mixture of 1:1 EA/hexanes), 0.2 mL of methyl alcohol was then added to quench the excess of TBSOTf. The resulting solution was concentrated via rotary evaporation and the residue was purified by flash column chromatography (ethyl acetate/hexane, 1:5) to afford 97 mg (99% yield) of 52 as a white solid. mp 81.0-83.0° C.; [α]20D=+38.8 (c=1.3, CHCl3); 1H NMR (CDCl3, 300 MHz) δ 7.83-7.86 (m, 2H), 7.50-7.71 (m, 3H), 7.37 (d, J=7.8 Hz, 1H), 4.29 (br s, 1H), 3.81 (d, J=4.5 Hz, 1H), 3.56 (dd, J=2.1 Hz, 8.7 Hz, 1H), 2.79 (m, 1H), 2.53 (br s, 1H), 2.45 (m, 1H), 1.22 (d, J=7.2 Hz, 3H), 0.99 (d, J=7.2 Hz, 3H), 0.88 (s, 9H), 0.81 (s, 9H), 0.077 (s, 3H), 0.052 (s, 3H), −0.14 (s, 3H), −0.35 (s, 3H). 13C NMR (CDCl3, 75 MHz) δ 148.8, 139.6, 139.5, 133.5, 129.4, 128.1, 77.7, 73.3, 70.6, 40.3, 36.3, 26.1, 18.3, 18.1, 17.6, 17.5, −4.11, −4.54, −4.61, −4.90. LRMS (CI): m/z 541 [M+H]+; HRMS (CI) calculated for C27H48O5SSi2, 541.2839; found, 541.2834.
