C1(P(C2C=CC=CC=2)C2C=CC=CC=2)C=CC=CC=1.[C:20]([Br:24])(Br)(Br)[Br:21].[CH:25]([CH:27]1[CH2:32][CH2:31][C:30](=[O:33])[CH2:29][CH2:28]1)=O>C(Cl)Cl>[Br:21][C:20]([Br:24])=[CH:25][CH:27]1[CH2:32][CH2:31][C:30](=[O:33])[CH2:29][CH2:28]1A solution of 36.72 g of triphenylphosphine in 200 ml of methylene chloride was treated slowly at -20° C. with 23.22 g of carbon tetrabromide and stirred for a further 10 minutes. Subsequently, the mixture was added dropwise by means of a cannula to a solution, cooled to -60° C., of 6.30 g of 4-formylcyclohexanone in 100 ml of methylene chloride. The mixture was stirred at -60° C. for a further 15 minutes and then partitioned in water/methylene chloride. The aqueous phases were extracted a further twice with methylene chloride. The organic phases were washed twice with water, dried over magnesium sulphate and evaporated. Low-pressure chromatography of the resulting, pale yellow oil (16 g) on silica gel with ethyl acetate/petroleum ether (vol. 10:90) gave 12.08 g (85.8%) of 4-(2,2-dibromovinyl)cyclohexanone as a pale yellow liquid.
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