[CH2:1]([O:3][C:4](=[O:20])/[CH:5]=[C:6](/[O:8][C:9]1[CH:14]=[CH:13][CH:12]=[C:11]([O:15][C:16]([F:19])([F:18])[F:17])[CH:10]=1)\[CH3:7])[CH3:2].[Br:21]N1C(=O)CCC1=O.C(OOC(=O)C1C=CC=CC=1)(=O)C1C=CC=CC=1.O>C(Cl)(Cl)(Cl)Cl>[CH2:1]([O:3][C:4](=[O:20])/[CH:5]=[C:6](/[O:8][C:9]1[CH:14]=[CH:13][CH:12]=[C:11]([O:15][C:16]([F:18])([F:19])[F:17])[CH:10]=1)\[CH2:7][Br:21])[CH3:2]
To a stirred mixture of (E)-3-(3-trifluoromethoxy-phenoxy)-but-2-enoic acid ethyl ester (9.87 g, 0.034 mol) in carbon tetrachloride (60 mL) under a nitrogen atmosphere was added N-bromosuccinimide (9.08 g, 0.051 mol) and benzoyl peroxide in water (75%, 1.09 g, 0.003 mol). Nitrogen gas was bubbled through the mixture for 5 min, and the resulting mixture was heated to reflux for 4 h. The reaction mixture was then placed in the refrigerator overnight. The solids formed were removed by filtration and the filtrate concentrated in vacuo. The crude product obtained was purified using flash column chromatography (silica gel (100-200 mesh), ethyl acetate/hexanes) to afford (E)-4-bromo-3-(3-trifluoromethoxy-phenoxy)-but-2-enoic acid ethyl ester (3.70 g, 29%) as a yellow oil.
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