[Cl:1][C:2]1[CH:3]=[C:4]([CH2:9][C:10]#[N:11])[CH:5]=[CH:6][C:7]=1[Cl:8].[CH:12]([N-]C(C)C)([CH3:14])[CH3:13].[Li+].C(Br)C=C.Cl>O1CCCC1.C1CCCCC1>[C:10]([CH:9]([C:4]1[CH:5]=[CH:6][C:7]([Cl:8])=[C:2]([Cl:1])[CH:3]=1)[CH2:14][CH:12]=[CH2:13])#[N:11]3,4-Dichlorophenylacetonitrile (80 g) was dissolved in anhydrous tetrahydrofuran (800 ml) under a nitrogen atmosphere, cooled to −70° C., and lithium di-isopropylamide (320 ml of a 1.5M solution in cyclohexane) added. The mixture was stirred at −70° C. for 30 minutes, allyl bromide (63 g) added over 15 minutes and the mixture stirred for a further 30 minutes. 2N Aqueous hydrochloric acid solution (600 ml) was then added and the mixture extracted twice with diethyl ether. The organic extracts were combined and the solvent removed under reduced pressure. The resulting residue was dissolved in dichloromethane, dried over anhydrous sodium sulphate and the solvent removed under reduced pressure to give a red mobile oil. This was chromatographed on silica gel eluting with 4:1, by volume, hexane:dichloromethane to give 4-cyano-4-(3,4-dichlorophenyl)but-1-ene (94.8 g) as an oil.
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