A convenient method has been developed for direct conversion of nitriles to amidines in high yields; The method can also be applied to the preparation of guanidines from N-alkyl cyanamides.
An efficient one step preparation of an amidine by the direct nucleophilic addition of an amine to the parent nitrile is an extremely desirable transformation for which no mild and practical methods exist. 1 Methods currently available for amidine synthesis involve multistep processes which proceed in moderate to poor yields.1 Weinreb etul. have demonstrated that aluminum amides efficiently add to carboxylic esters to afford the corresponding carboxamides in a single step.2 We reasoned that these aluminum amides might similarly add to nitriles, thus affording amidines. Insertion of diethylaluminum dimethylamide into benzonitrile was first studied in 1969.4 In these early studies 334 dimeric aluminum amidine derivatives were isolated and studied spectroscopically.
However, the application of these reagents for the preparation of amidines was never demonstrated. Apart from these preliminary studies, there are no reports of the use of aluminum amides in the preparative conversion of nitriles to amidines .5 We have found that alkylchloroaluminum amides, which are conveniently generated from trimethyl aluminum and ammonium chloride or amine hydrochlorides,2b efficiently add to nitriles and afford the desired amidines in high yields. MeAI(CI)NR'R" H20 NH RCN Toluene, 80Β°C -R_ &NR'R