[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:14][C:12]1[CH:13]=[C:8]([CH:1]([OH:6])[CH2:2][CH2:3][CH2:4][CH3:5])[CH:9]=[C:10]([F:15])[CH:11]=1
A solution of pentanal (19.0 g, 0.22 mol) in dry ether (75 ml) is added dropwise to a stirred solution of the Grignard reagent at room temperature, under dry nitrogen, prepared from 1-bromo-3,5-difluoro-benzene (50.2 g, 0.26 mol) and magnesium (7.25 g, 0.30 mol) in dry THF (100 ml). The stirred mixture is heated under reflux for 2 h, cooled and a saturated solution of ammonium chloride (300 ml) is added. The product is extracted into ether (twice), and the combined ethereal extracts are washed with water and dried (MgSO4). The solvent is removed in vacuo to give a pale-orange liquid (51.1 g) which is distilled to yield a colourless liquid. Smaller quantities of crude product are purified by column chromatography (silica gel/dichloromethane) to yield a colourless liquid, bp 90° C. at 0.5 mm Hg.
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