[Mg].II.Br[CH2:5][CH2:6][CH:7]=[CH2:8].[F:9][C:10]1[CH:17]=[C:16]([F:18])[CH:15]=[CH:14][C:11]=1[CH:12]=[O:13]>C(OCC)C>[OH:13][CH:12]([C:11]1[CH:14]=[CH:15][C:16]([F:18])=[CH:17][C:10]=1[F:9])[CH2:8][CH2:7][CH:6]=[CH2:5]To a stirred suspension of magnesium turnings (16.9 gm) in dry diethyl ether (1.5L) was added (argon atmosphere) a crystal of iodine and 4-bromobutene (2 ml). Soon after the reaction was initiated the remaining 4-bromobutene (101 gm) in dry diethyl ether (500 mL) was added at such a rate to maintain gentle reflux. After complete addition, the mixture was heated to reflux for 1 hour. 2,4-Difluorobenzaldehyde (100 gm) in dry diethyl ether (400 mL) was then added dropwise with a gentle reflux. The mixture was now heated for 2 hours and allowed to cool to room temperature. The entire contents of the flask were poured on 6L ice-water containing 200 ml concentrated HCl. The organic phase was separated, washed with water, saturated NaHCO3, water and dried (Na2SO4). Removal of ether in vacuo provided crude 5-hydroxy-5-(2,4-difluorophenyl)pentene as an oil (136.5 gm) which was used in the next step.
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