At -25° C., 94 g of 3-acetylaminophenyl-3-pyridylketone are added to a mixture of 217 g of 4-carboxybutyl-triphenylphosphonium bromide and 154 g of potassium tert.butoxide in 1.8 litres of tetrahydrofuran. After 2 hours stirring at ambient temperature, 200 ml of water are added to the reaction mixture and then it is evaporated down. The residue is taken up in 500 ml of water and washed with ethyl acetate. The agueous phase is then neutralised by the addition of citric acid and extracted with ethyl acetate. The organic phase is evaporated down and the residue is recrystallised from ethyl acetate/acetone.
