[CH3:1][C:2]1[N:3]=[C:4]2[N:8]([C:9]=1[C:10]([O:12][CH2:13][CH3:14])=[O:11])[CH:7]=[CH:6][S:5]2.N(C(C)(C)C#N)=NC(C)(C)C#N.[Br:27]N1C(=O)CCC1=O>C(Cl)(Cl)(Cl)Cl.C(OCC)(=O)C.O>[Br:27][CH2:1][C:2]1[N:3]=[C:4]2[N:8]([C:9]=1[C:10]([O:12][CH2:13][CH3:14])=[O:11])[CH:7]=[CH:6][S:5]2To a stirred solution of Step 1 intermediate (2.60 g, 12.366 mmol) and azobisisobutyronitrile (AIBN) (0.041 g, 0.247 mmol) in carbon tetrachloride (40 mL) at reflux temperature was added N-bromosuccinimide (2.40 g, 13.602 mmol). After refluxing for 18 h, the reaction mixture was cooled to room temperature and diluted with ethyl acetate (200 mL) and water (100 mL). The layers were separated. Aqueous layer was extracted with ethyl acetate (2×50 mL) and the combined organic layers were washed with brine (2×50 mL), dried (Na2SO4) and filtered. The filtrate was concentrated under reduced pressure. The residue obtained after the evaporation of the solvent was purified by silica gel column chromatography using 5% ethyl acetate in petroleum ether to obtain 1.95 g of the product as a white solid; 1H NMR (300 MHz, DMSO-d6) δ 1.36 (t, J=6.6 Hz, 3H), 4.36 (q, J=7.2 Hz, 2H), 4.85 (s, 2H), 7.52 (d, J=4.5 Hz, 1H), 8.10 (d, J=4.5 Hz, 1H); ESI-MS (m/z) 291.58 (MH)+.
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