Process for preparing compounds of the formula (III) in which Ar is the group, where R 1 , R 2 , R 3 , R 4 and R 5 are the same or different and are each independently hydrogen, amino, cyano, nitro, halogen, optionally halogen-substituted C 1 -C 6 -alkyl, C 1 -C 6 -thioalkyl, thiophenyl, C 1 -C 6 -alkoxy, C 6 -C 10 -aryloxy, phenyl, -CO-C 6 -C 10 -aryl, -CO-C 1 -C 3 -alkyl, -COO-C 1 -C 6 -alkyl or -COO-C 6 -C 10 -aryl, the Ar radical may additionally also be a heteroaromatic radical or the Ar radical may also be 1- or 2-naphthyl, and R 6 and R 7 are each independently optionally substituted C 1 -C 8 -alkyl, phenyl, aryl, or NR 8 R 9 , where R 8 and R 9 are the same or different and are each independently C 1 -C 4 -alkyl, or phenyl optionally substituted by optionally fluorine- or chlorine-substituted C 1 -C 3 -alkyl, by nitro, cyano or di-C 1 -C 3 -alkylamino, or together with the nitrogen atom to which they are bonded are a saturated or unsaturated, substituted or unsubstituted cycle, characterized in that aryl or heteroaryl halides of the formula (I) Ar-Hal (I) in which Hal is chlorine, bromine or iodine and Ar is as defined above, are reacted with malonic esters of the formula (II) in which R 6 and R 7 are each as defined above in the presence of a palladium catalyst, of a phosphine ligand and B) of a mixture of inorganic bases, without using caesium carbonate and caesium bicarbonate, optionally using an organic solvent. R 1 , R 2 , R 3 , R 4 and R 5 are the same or different and are each independently hydrogen, amino, cyano, nitro, halogen, optionally halogen-substituted C 1 -C 6 -alkyl, C 1 -C 6 -thioalkyl, thiophenyl, C 1 -C 6 -alkoxy, C 6 -C 10 -aryloxy, phenyl, -CO-C 6 -C 10 -aryl, -CO-C 1 -C 3 -alkyl, -COO-C 1 -C 6 -alkyl or -COO-C 6 -C 10 -aryl, the Ar radical may additionally also be a heteroaromatic radical or the Ar radical may also be 1- or 2-naphthyl, and R 6 and R 7 are each independently optionally substituted C 1 -C 8 -alkyl, phenyl, aryl, or NR 8 R 9 , where R 8 and R 9 are the same or different and are each independently C 1 -C 4 -alkyl, or phenyl optionally substituted by optionally fluorine- or chlorine-substituted C 1 -C 3 -alkyl, by nitro, cyano or di-C 1 -C 3 -alkylamino, or together with the nitrogen atom to which they are bonded are a saturated or unsaturated, substituted or unsubstituted cycle, characterized in that aryl or heteroaryl halides of the formula (I) Ar-Hal (I) in which Hal is chlorine, bromine or iodine and Ar is as defined above, are reacted with malonic esters of the formula (II) in which R 6 and R 7 are each as defined above in the presence of a palladium catalyst, of a phosphine ligand and B) of a mixture of inorganic bases, without using caesium carbonate and caesium bicarbonate, optionally using an organic solvent. Hal is chlorine, bromine or iodine and Ar is as defined above, are reacted with malonic esters of the formula (II) in which R 6 and R 7 are each as defined above in the presence of a palladium catalyst, of a phosphine ligand and B) of a mixture of inorganic bases, without using caesium carbonate and caesium bicarbonate, optionally using an organic solvent. R 6 and R 7 are each as defined above in the presence of a palladium catalyst, of a phosphine ligand and B) of a mixture of inorganic bases, without using caesium carbonate and caesium bicarbonate, optionally using an organic solvent. <EOS>