[Cl:1][C:2]1[CH:7]=[CH:6][C:5]([Mg]Br)=[CH:4][CH:3]=1.[CH3:10][C:11]([CH3:15])=[CH:12][CH:13]=[O:14].O>O1CCCC1.[Cu]Br>[Cl:1][C:2]1[CH:7]=[CH:6][C:5]([C:11]([CH3:15])([CH3:10])[CH2:12][CH:13]=[O:14])=[CH:4][CH:3]=1Under a nitrogen atmosphere, a stirred solution of 21.6 grams (0.10 mole) of 4-chlorophenylmagnesium bromide (1M in diethyl ether) in 100 mL of tetrahydrofuran is cooled to -15° C., and 0.7 grams (catalyst) of copper(I) bromide is added in one portion. Upon completion of addition, 9.7 mL (0.10 mole) of 3-methyl-2-butenal is added dropwise during a 1.5 hour period, while maintaining the reaction mixture temperature below -10° C. Upon completion of addition, the reaction mixture is allowed to warm to ambient temperature, where it is stirred for about 18 hours. The reaction mixture is then poured into 300 mL of water and extracted with two 200 mL portions of diethyl ether. The combined extracts are dried with magnesium sulfate and filtered. The filtrate is concentrated under reduced pressure to a residue. The residue is subjected to column chromatography on silica gel, using 50% petroleum ether in methylene chloride as the eluant. The appropriate product-containing fractions are combined and concentrated under reduced pressure, yielding 7.6 grams of 3-(4-chlorophenyl)-3-methylbutyraldehyde. The NMR spectrum is consistent with the proposed structure. The reaction is repeated.
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