Reaction Steps
Alkyne 29 (4.12 g, 10.0 mmol) was dissolved in THF (100 mL) and cooled to −78° C. n-BuLi (6.25 mL, 1.6 M hexane solution) was added slowly. After 5 min, the mixture was warmed to 0° C. and stirred for 30 min. The mixture was then cooled to −78° C. and amide 15 (6.47 g, 11.3 mmol) in THF (5 mL) was added slowly. After 5 min, the solution was warmed to 0° C. and stirred for 30 min. The reaction was quenched with saturated aqueous NH4Cl and the mixture was partitioned in a separatory funnel. The aqueous phase was extracted with Et2O (3×20 mL). The combined organic extracts were washed with brine and dried over MgSO4. Filtration and concentration under reduced pressure, followed by flash chromatography on silica gel (hexane/EtOAc 19:1), afforded the ynone 32 (9.70 g, 93%) as a pale yellow oil: IR (CHCl3) 2955, 2928, 2856, 2209, 1676, 1471, 1462, 1252, 1085, 836, 774 cm−1; 1H NMR (300 MHz, CDCl3) ε7.56 m, 6H), 7.36 (m, 9H), 5.80 (dd, J=15.6, 7.1 Hz, 1H), 5.69 (dt, J=15.7, 4.8 Hz, 1H), 4.37 (m, 1H), 3.69 (d, J=4.7 Hz, 2H), 3.61 (m, 1H), 3.58 (dd, J=9.7, 5.0 Hz, 1H), 3.43 (dd, J=9.7, 6.5 Hz, 1H), 2.87 (m, 1H), 2.73 (m, 1H), 2.46 (m, 1H), 1.88 (m, 1H), 1.76 (m, 1H), 1.59 (m, 1H), 1.31 (d, J=7.1 Hz, 3H), 1.15 (d, J=6.8 Hz, 3H), 1.05 (m, 1H), 1.00 (m, 3H), 0.194 (s, 3H), 0.190 (s, 3H), 0.17 (s, 3H), 0.15 (s, 3H), 0.14 (s, 6H); 13C NMR (75 MHz, CDCl3) δ 186.1, 144.2, 132.9, 128.6, 127.7, 126.9, 96.8, 86.8, 83.1, 71.5, 68.0, 64.9, 50.0, 42.3, 38.1, 34.4, 33.2, 32.1, 26.01, 25.96, 25.85, 18.3, 18.0, 17.9, 17.2, 15.5, 15.4, −3.8, −4.1, −4.6, −4.7, −5.4; LRMS (ESI) 947.5 [M+Na]+, 562.3, 243.1; HRMS (ESI) calcd for C56H88O5Si3Na 947.5837 [M+Na]+, found 947.5875; [α]20D−12.0 (c 0.54, CHCl3).
