[CH:1](=[O:6])[CH2:2][CH2:3][CH2:4][CH3:5].Br[C:8]1[CH:13]=[C:12]([F:14])[CH:11]=[C:10]([F:15])[CH:9]=1.[Mg].[Cl-].[NH4+]>CCOCC.C1COCC1>[F:15][C:10]1[CH:9]=[C:8]([CH:1]([OH:6])[CH2:2][CH2:3][CH2:4][CH3:5])[CH:13]=[C:12]([F:14])[CH:11]=1A solution of pentanal (19.0 g, 0.22 mol) in dry ether (75 ml) was added dropwise to a stirred solution of the Grignard reagent at room temperature, under dry nitrogen, prepared from 1-bromo-3,5-difluorobenzene (50.2 g, 0.26 mol) and magnesium (7.25 g, 0.30 mol) in dry THF (100 ml). The stirred mixture was heated under reflux for 2 h, cooled and a saturated solution of ammonium chloride (300 ml) was added. The product was extracted into ether (twice), and the combined ethereal extracts were washed with water and dried (MgSO4). The solvent was removed in vacuo to give a pale-orange liquid (51.1 g) which was distilled to yield a colourless liquid. Smaller quantities of crude product were purified by column chromatography (silica gel/dichloromethane) to yield a colourless liquid (92%).
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