presence of a suitable lewis acid catalyst and a phase transfer catalyst catalysis by n n dimethylformamide dmf is also possible suitable lewis acid catalysts are e g mgcl 2 mgbr 2 sncl 2 sncl 4 zncl 2 ticl 4 alcl 3 fecl 3 bf 3 et 2 o bf 3 bbr 3 bcl 3 b oet 3 b ome 3 b o ipr 3 preferably a boron based lewis acid catalyst is used the types of phase transfer catalyst which can be used include halides of aromatic or aliphatic ammonium salts for example tetramethylammonium chloride tetrabutylammonium chloride or benzyl triethylammonium chloride or phosphonium salts for example butyltriphenylphosphonium chloride or tetraphenylphosphonium chloride the catalysts are used in an amount of from 0 1 to 20 mol each preferably 0 5 to 10 mol based on the moles of 5 cyanophthalide the reaction with the catalysts can be performed without any solvent but if a solvent is used any inert high boiling solvent such as toluene xylene chlorobenzene or dichlorobenzene can be used the halogenation reagent used can be any suitable reagent used for halogenation e g thionyl chloride pcl 3 pcl 5 ccl 4 in triphenyl phosphine oxalyl chloride or cyanuric chloride in trialkyl amine the reagents for preparing the corresponding bromo compound can be e g pbr 3 pbr 5 pph 3 br 2 thionyl bromide or oxalyl.