Reaktionsschritte
A solution of Compound 60 (1.657 g, 5.69 mmol) in dichloromethane (10 mL) was treated with 2,6-lutidine (2.00 mL, 17.1 mmol) and triethylsilyl trifluoromethanesulfonate (2.58 mL, 11.4 mmol) at zero degrees C. The solution was stirred 30 minutes, anhydrous methanol (2 mL) was added, the mixture was poured into brine (50 mL) and extracted with dichloromethane (3×50 mL). The organic extracts were dried (Na2SO4), concentrated and purified by flash chromatography (20% Et2O in petroleum ether) to give Compound 61 (2.204 g, 96 percent) as a white solid, m.p. =108 °-109° C. (from CH2Cl2); Rf =0.43 (30 percent Et2O in petroleum ether); [a]D25 =-15.4° (c 2.8, CH2Cl2); IR (thin film) νmax 3307, 2116, 1721, 1646 cm-1 ; 1H NMR (500 MHz, CDCl3) δ 9.50 (s, 1 H, C=CH--O), 6.57 (s, 1 H, C=CH--CO2), 4.38-4.31 (m, 2 H, ethylene ketal), 4.18-4.10 (m, 2 H, ethylene ketal), 3.74 (s, 3 H, CO2Me), 2.66 (s, 1 H, C}C--H), 2.61 (ABq, J =14.0 Hz, Δν =34 Hz, 2 H, CH2), 0.92 (t, J =7.9 Hz, 9 H, Si(CH2CH3)3), 0.70 (q, J =7.9 Hz, 6 H, Si(CH2CH3)3); 13C NMR (125 MHz, CDCl3) δ 166.5, 161.3, 160.7, 143.8, 114.5, 111.9, 100.6, 83.2, 76.9, 70.9, 65.0, 64.8, 51.6, 49.8, 6.8, 5.9; FAB HRMS (NBA/CsI) m/e 538.0652, M+Cs+ calcd for C20H27NO6Si 538.0662.
