[Br:1]Br.[CH2:3]([O:7][CH:8]=[CH:9][C:10](=[O:15])[C:11]([F:14])([F:13])[F:12])[CH2:4][CH2:5][CH3:6].C(N(CC)CC)C.Cl>CCCCC>[Br:1][C:9](=[CH:8][O:7][CH2:3][CH2:4][CH2:5][CH3:6])[C:10](=[O:15])[C:11]([F:13])([F:14])[F:12]8.0 g (0.05 mole) of bromine, dissolved in 100 ml pentane, are added dropwise to a solution of 9.75 g (0.05 mol) of 4-n-butoxy-1,1,1-trifluorobut-3-en-2-one in 50 ml of pentane cooled to -20° C. After stirring for 1 hour at -20° C., a solution of 6.0 g (0.06 mole) of triethylamine in 100 ml pentane is added dropwise at the same temperature. After being allowed to stand overnight at 25° C., the mixture is poured into ice water and acidified by means of 1N hydrochloric acid and the phases are separated. Conventional work-up gives 12.1 g of almost homogeneous crude 3-bromo-4-n-butoxy-1,1,1-trifluorobut-3-en-2-one, which is freed from the small amount of impurities by distillation under reduced pressure. Boiling point 113°-115° C./16 mbar, nD20 =1.4640.
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