[F:1][C:2]([F:15])([F:14])[O:3][C:4]1[CH:9]=[CH:8][C:7]([O:10][CH:11]2[CH2:13][CH2:12]2)=[CH:6][CH:5]=1.C([Li])(C)(C)C.[Br:21]C(Br)(F)C(F)(F)F>O1CCCC1>[Br:21][CH:13]1[CH2:12][CH:11]1[O:10][C:7]1[CH:6]=[CH:5][C:4]([O:3][C:2]([F:14])([F:15])[F:1])=[CH:9][CH:8]=14-(Trifluoromethoxy)cyclopropoxybenzene (3 g) was dissolved in tetrahydrofuran (100 ml) and the solution was cooled to −78° C. under a nitrogen atmosphere. tert-Butyllithium (22.9 ml, 1.5M in pentane) was added dropwise and the solution was stirred for 3 hours. Dibromotetrafluoroethane (8.2 ml) was added dropwise and the reaction mixture was stirred at −78° C. for 2 hours. The reaction was quenched by the dropwise addition of water (50 ml). The product was extracted with diethyl ether. The combined organic fractions were dried (brine, MgSO4) and concentrated in vacuo. The residue was purified on silica using hexane as eluant, to yield the product as a colourless oil (2.2 g). 1H NMR (360 MHz, CDCl3) δ 0.86 (4H, m), 3.79 (1H, m), 7.15 (1H, dd, J 8.9, 2.7 Hz), 7.24 (1H, d, J 8.9 Hz), 7.42 (1H, d, J 2.7 Hz).
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