Ammonium Chloride → 3-(4-Fluorophenyl)-3-methylbutyraldehyde

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Under a nitrogen atmosphere, a stirring solution of 66.6 grams (0.334 mole) of 4-fluorophenylmagnesium bromide (1M in diethyl ether) is cooled to -10° C., and 2.2 grams (0.015 mole) of copper(I) bromide is added in one portion. Upon completion of addition, a solution of 25.0 grams (0.297 mole) of 3-methyl-2-butenal in 20 mL of tetrahydrofuran is added dropwise at a rate to maintain the reaction mixture temperature at about 5° C. The complete addition requires about one hour. Upon completion of addition, the reaction mixture is stirred for one additional hour and then is stored in a refrigerator for about 18 hours. After this time the reaction mixture is poured into 500 mL of aqueous ammonium chloride and extracted with four portions of diethyl ether. The combined extracts are concentrated under reduced pressure to a residue. The residue is subjected to column chromatography on silica gel, using methylene chloride as the eluant. The product-containing fractions are combined and concentrated under reduced pressure to a residue. The residue is subjected to a second column chromatography on silica gel, using 100% petroleum ether and combinations of methylene chloride in petroleum ether. The product-containing fractions are combined and concentrated under reduced pressure, yielding about 23.0 grams of 3-(4-fluorophenyl)-3-methylbutyraldehyde. The NMR spectrum is consistent with the proposed structure.

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