[N:1]1([CH:10]2[CH2:15][CH2:14][N:13]([C:16]([O:18][C:19]([CH3:22])([CH3:21])[CH3:20])=[O:17])[CH2:12][CH2:11]2)[C:9]2[C:4](=[CH:5][CH:6]=[CH:7][CH:8]=2)[CH2:3][CH2:2]1.[Br:23]N1C(=O)CCC1=O>CN(C=O)C.O>[Br:23][C:6]1[CH:5]=[C:4]2[C:9](=[CH:8][CH:7]=1)[N:1]([CH:10]1[CH2:15][CH2:14][N:13]([C:16]([O:18][C:19]([CH3:22])([CH3:21])[CH3:20])=[O:17])[CH2:12][CH2:11]1)[CH2:2][CH2:3]2A solution of compound 2 (2.0 g, 6.61 mmol) in dry DMF (10 mL) was treated with N-bromosuccinimide (1.17 g, 6.61 mmol) in DMF (10 mL) at 0° C. over a period of 30 min. The reaction was stirred at same temperature for 3.5 h. The reaction was diluted with water (200 mL) and product was extracted into ethyl acetate (3×25 mL). The combined ethyl acetate layer was washed with water (2×50 mL), brine (25 mL) and dried (Na2SO4). Solvent was evaporated and crude was purified by column chromatography (ethyl acetate:hexanes, 1:4) to obtain compound 3 (2.5 g, 99%) as a syrup. 1H NMR (CDCl3) δ 7.13-7.10 (m, 2H), 6.27 (d, 1H, J=9.0 Hz), 4.28-4.20 (m, 2H), 3.50-3.40 (m, 1H), 3.35 (t, 2H, J=8.4 Hz), 2.93 (t, 2H, J=8.4 Hz), 2.75 (t, 2H, J=12.9 Hz), 1.78-1.72 (m, 2H), 1.60-1.49 (m, 2H), 1.46 (s, 9H); ESI-MS (m/z, %) 381, 383 (MH+, 3), 325, 327 (100).
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