[F:1][C:2]([F:8])([F:7])[CH2:3][CH2:4][CH:5]=[O:6].[Br:9]Br>O1CCOCC1>[Br:9][CH:4]([CH2:3][C:2]([F:8])([F:7])[F:1])[CH:5]=[O:6]To a mixture of 4,4,4-trifluorobutyraldehyde (5 g, 39.68 mmol) in 1,4-dioxane (5 ml) cooled to 0° C., was added bromine (2.24 ml, 43.65 mmol), dropwise. The reaction mixture was stirred at 0° C. for 2 h. The resulting reaction mixture was filtered through a pad of diatomaceous earth and the filtrate was washed with NaHCO3 (aqueous sat. solution). The organic layer was separated, dried (MgSO4) and evaporated in vacuo to yield compound D8 (6.2 g, 76%) that was used in the next reaction step without further purification.
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