Reaction Steps
To a solution of Compound 209 (mixture of diastereomers, 13.0 g, 19.06 mmol) in CH2Cl2 (100 mL) cooled at zero degrees C was added mCPBA (50 percent, 7.9 g, 22.98 mmol) followed by stirring at 25° C. for one hour. The reaction mixture was diluted with CH2Cl2 (500 mL), washed with saturated aqueous NaHCO3, dried over anhydrous Na2SO4, and concentrated in vacuo. The residue was purified by flash column chromatography (silica gel, 10 percent ethyl ether in petroleum ether) to afford Compound 210 (9.5 g, 71 percent) as a mixture of diastereomers. Major isomer: Rf =0.38 (silica, 10 percent ethyl ether in petroleum ether); IR (CHCl3) νmax 2958, 2933, 1730 (shoulder), 1721, 1382, 1307, 1118, 846 cm-1 ; 1H NMR (300 MHz, CDCl3) δ 7.28 (d, J=8.6 Hz, 1 H, H1), 7.40-7.10 (m, 6 H, H4 and aromatic), 6.95 (dd, J=8.6, 1.9 Hz, 1 H, H2), 5.84-5.62 (m, 3 H, H6 and olefinic), 4.76 (dd, J=9.6, 5.7 Hz, 1 H, H10), 2.45 (dd, J=14.5, 4.6 Hz, 1 H, H7), 1.97- 1.57 (m, 5 H, H7, H8 and H9), 1.31 (br s, 9 H, COC(CH3)3), 0.87 (s, 9 H, SiC(CH3)3), 0.19 (s, 12 H, Si(CH3)3 and SiCH3), 0.06 (s, 3 H, SiCH3); MS (FAB+) m/e (rel intensity) 830 (M+Cs, 100), 681 (6), 624 (9), 534 (11); HRMS for C40H51NO6Si2Cs (M+Cs), calcd 830.2309, found 830.2361. Minor isomer: Rf =0.22 (silica, 10 percent ethyl ether in petroleum ether); IR (CHCl3) νmax 2958, 2933, 1747 (shoulder), 1721, 1494, 1381, 1306, 1256, 1181, 1118, 909, 844 cm-1 ; 1H NMR (300 MHz, CDCl3) δ 7.58 (d, J=8.7 Hz, 1 H, H1), 7.40-7.10 (m, 6 H, H4 and aromatic), 6.95 (dd, J=8.7, 2.5 Hz, 1 H, H2), 5.80-5.60 (m, 3 H, H6 and olefinic), 4.89 (d, J=2.4 HZ, 1 H, H10), 2.66-2.50 (m, 1 H, H7), 2.18-1.63 (m, 5 H, H7, H8 and H9), 1.31 (br s, 9 H, COC(CH3)3), 0.94 and 0.79 (s, 9 H, SiC(CH3)3), 0.23, 0.21 and 0.19 (s, 9 H, Si(CH3)3), 0.14 (s, 3 H, SiCH3), 0.06 (s, 3 H, SiCH3); MS (FAB+) m/e (rel intensity) 830 (M+Cs, 100), 708 (8), 640 (13), 534 (7); HRMS for C40H51NO6Si2Cs (M+Cs), calcd 830.2309, found 830.2296.
