Reaction Steps
To a solution of Compound 210 (9.5 g, 13.6 mmol) in wet CHCl3 (150 mL) cooled at zero degrees C. was added BF3.OEt2 (8.4 mL, 68.0 mmol) followed by stirring at 25° C. for 10 minutes. The reaction mixture was diluted with CH2Cl2 (400 mL), washed with saturated aqueous NaHCO3, dried over anhydrous Na2SO4, and concentrated in vacuo. The residue was then dissolved in THF (50 mL) and treated with 48 percent aqueous HBr (5 mL) at 25° C. for 40 minutes with stirring. The reaction mixture was diluted with ethyl ether (400 mL), washed with saturated aqueous NaHCO3 and brine, dried over anhydrous Na2SO4, and concentrated in vacuo. Flash column chromatography of the residue (silica gel, 33 percent ethyl ether in petroleum ether) gave Compound 211 (2.80 g, 34 percent) and Compound 212 (1.30 g, 18 percent). Compound 211: Rf =0.52 (silica, 50 percent ethyl ether in petroleum ether); IR (CHCl3) νmax 2970, 1719, 1681, 1606, 1494, 1381, 1307, 1179, 1123, 846 cm-1 ; 1H NMR (300 MHz, CDCl3) δ 8.26 (d, J=8.7 Hz, 1 H, H1), 7.45-7.18 (m, 6 H, H4 and aromatic), 6.98 (dd, J=8.7, 2.4 Hz, 1 H, H2), 6.11 (d, J=0.9 Hz, 1 H, H6), 5.84 (d, J=11.1 Hz, 1 H, olefinic), 5.72 (dd, J=11.1, 1.7 Hz, 1 H, olefinic), 2.90 (dt, J=18.9, 4.5 Hz, 1 H, H9), 2.77-2.53 (m, 3 H, H7 and H9), 2.24-2.12 (m, 2 H, H8), 1.34 (s, 9 H, COC(CH3)3), 0.21 (s, 9 H, Si(CH3)3); MS (FAB+) m/e (rel intensity) 698 (M+Cs, 100), 565 (6); HRMS for C34H35NO5SiCs (M+Cs), calcd 698.1339, found 698.1339.
