A THF (0.5 mL) solution of 45 (7.0 mg, 11 μmol, 1 equiv.) was cooled to −78° C. in a 10-mL test tube, and a freshly prepared THF solution of lithium tetramethylpiperidide (0.50 M, 113 μL, 57 μmol, 5 equiv.) was added dropwise. The resulting yellow-orange solution was stirred at −78° C. for 10 min and at 0° C. for 10 min. The solution was then cooled to −78° C., and isobutyryl chloride (6.0 μL, 57 μmol, 5 equiv.) was added. The resulting yellow solution was stirred at −78° C. for 50 min, was slowly warmed to 0° C. over 50 min, and subsequently quenched with saturated aqueous NaHCO3. The mixture was warmed to room temperature and extracted thrice with EtOAc. The organic extracts were combined, washed with H2O and brine, dried over Na2SO4, filtered, and concentrated in vacuo to a yellow residue. Preparatory thin-layer chromatography (3×98:2 hexane:EtOAc) afforded 1.8 mg (2.6 μmol, 24% yield) of 46 as a colorless residue along with 1.7 mg (2.8 μmol, 25% recovery) of 45. TLC Rf 0.47 (95:5 hexane:EtOAc). 1H-NMR (600 MHz; CDCl3): δ 5.00-4.96 (m, 2H), 3.90 (s, 3H), 2.55 (dd, J=14.6, 6.4 Hz, 1H), 2.41 (dd, J=14.5, 7.7 Hz, 1H), 2.08 (d, J=15.0 Hz, 1H), 1.97 (septet, J=6.5 Hz, 1H), 1.92-1.85 (m, 2H), 1.79-1.72 (m, 1H), 1.68 (s, 3H), 1.66 (s, 3H), 1.57-1.56 (m, 3H), 1.55-1.53 (m, 3H), 1.50-1.42 (m, 2H), 1.39-1.31 (m, 3H), 1.30-1.24 (m, 2H), 1.17 (s, 3H), 1.17 (s, 3H), 1.13 (d, J=6.5 Hz, 3H), 1.02 (d, J=6.5 Hz, 3H), 0.98 (s, 3H), 0.92 (t, J=7.9 Hz, 9H), 0.54 (q, J=7.9 Hz, 6H), 0.26 (s, 9H). HRMS-ESI (m/z): [M+Na]+ calculated for C40H70O5Si2, 709.4654. found, 709.4626.
