[Cl:1][C:2]1[CH:7]=[CH:6][C:5]([C:8](=[O:10])[CH3:9])=[CH:4][C:3]=1[F:11].[Br-:12].[Br-].[Br-].C([N+](CCCC)(CCCC)CCCC)CCC.C([N+](CCCC)(CCCC)CCCC)CCC.C([N+](CCCC)(CCCC)CCCC)CCC.CCCCCC.C(OCC)(=O)C>C(Cl)Cl.CO>[Br:12][CH2:9][C:8]([C:5]1[CH:6]=[CH:7][C:2]([Cl:1])=[C:3]([F:11])[CH:4]=1)=[O:10]
To a solution of 1-(4-chloro-3-fluorophenyl)ethanone (3.4 g, 19.7 mmol), prepared in the previous step, in methylene chloride:methanol (1:3) was added tetrabutylammonium tribromide (9.5 g, 19.7 mmol) in portions. The reaction was monitored by TLC (3:1 hexane:ethyl acetate) until the starting material was consumed. The reaction solution was concentrated in vacuo and the residue was partitioned between diethyl ether and water. The layers were separated and the organic layer was dried over anhydrous sodium sulfate, filtered and concentrated in vacuo to give 4.2 g of crude product. The crude product was purified on silica gel using 5% ethyl acetate:hexane to give 2-bromo-1-(4-chloro-3-fluoro-phenyl)-ethanone (3.4 g, 69%) as desired product, MS (ES) m/z 252 [M+H+].
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