A solution of 5.44 g of tetrabromomethane in 80 ml of methylene chloride was placed at 0° C. under argon gasification in a sulphonation flask equipped with a mechanical stirrer and treated within 10 minutes with a solution of 8.6 g of triphenylphosphine in 20 ml of methylene chloride. After completion of the addition, the clear orange solution was stirred at 0° C. for a further 5 minutes and then a solution of 2.08 g of p-(5-pentyl-2-pyrimidinyl)benzaldehyde in 15 ml of methylene chloride was added dropwise within 5 minutes. The mixture was subsequently stirred at 0° C. for a further 30 minutes, then the flask content was poured into 700 ml of hexane and the precipitate which thereby separated was filtered off (rinsing with hexane). The concentrated filtrate was digested with 200 ml of hexane, left to stand at 0° C. for 18 hours, filtered (rinsing with hexane) and the filtrate was concentrated. Low-pressure chromatography (0.5 bar) of the residue (3.7 g) on silica gel with 3% ethyl acetate/petroleum ether gave 2.70 g (80%) of 2-[p-(2,2-dibromovinyl)phenyl]-5-pentylpyrimidine as colourless crystals (purity 94.5%); m.p. 74° C.
