Reaction Steps
A suspension of 6.1 g (34.4 mmol) of NBS and 4 g of silica gel in 125 ml of dry dichloromethane was stirred under argon for 30 min. Then a solution of 4.56 g (17.2 mmol) of (S)-4-(1-methylheptyloxy)-2-nitro-toluene in 150 ml of dichloromethane was added via syringe. The reaction mixture was stirred at room temperature for 72 h. The resulting suspension was filtered through a short silica gel pad and the pad was washed several times with dichloromethane. The solvent was evaporated and the crude product extracted with a mixture of hexanes/ethyl acetate [95/5]. The suspension was filtered, the solvent removed and the residue was purified by flash chromatography using hexanes as eluent, affording 4.6 g (78%) of (S)-α-Bromo-4-(1-methylheptyloxy)-2-nitrotoluene (Compound 35, Scheme VI, R1 =(S)--OCH(CH3)C6H13) as a yellow liquid; Rf [hexanes/ethyl acetate 98/2]: 0.26; 1H NMR (300 MHz, CDCl3): δ 0.86(t, 3 H, J=6.7 Hz), 1.18-1.48(m, 8 H), 1.30(d, 3 H, J=6.1 Hz), 1.58(m 1 H), 1.70(m, 1 H), 4.40(m, 1 H), 4.77(s, 2 H), 7.06(dd. 1 H, J=2.7 Hz, J=8.5 Hz), 7.40(d, 1 H, J=8.5 Hz), 7.50(d, 1 H, J=2.7 Hz); 13C NMR (300 MHz, CDCl3): δ 13.98, 19.36, 22.50, 25.28, 29.10, 29.25, 31.67, 36.12, 75.00, 111.93, 121.08, 124.14, 133.61, 148.69, 158.92; IR (CHCl3): 3020, 2930, 2850, 1625, 1525, 1500, 1350, 1320, 1250, 1100, 975, 850, 825 cm-1 ; Mass spectrum, m/z(rel.intensity): 345(M+ +1 1.38), 343(M+ -1 1.35), 264(37), 152(100), 112(28), 71(59), 57(93), 55 (38), 43(93), 41(70).
