Reinvestigating the synthesis of N-arylbenzamidines from benzonitriles and anilines in the presence of AlCl3

The preparation of N-phenylbenzamidine 3a from the reaction between benzonitrile 1a and aniline in the presence of AlCl3 is reinvestigated with respect to mode of reagent addition, reaction temperature and Lewis acid catalysis. Pre-forming the nitrile-Lewis acid complex prior to the addition of aniline allows for milder reaction conditions, allowing for the higher yielding synthesis of N-phenylbenzamidine 3a (83%). Using these modified conditions several N-(4-substituted phenyl)benzamidines can be prepared including the N-(4-methoxyphenyl)benzamidine 3b (93%) and the previously unobtainable 2-amino-N-(4-methoxyphenyl)benzamidine 3l (56%). All new compounds are fully characterised.