A simple general synthesis of 1-aryl-6-azaisocytosine-5-carbonitriles is described. This method is based on coupling diazonium salts with cyanoacetylcyanamide and then cyclization of the formed 2-arylhydrazono-2-cyanoacetylcyanamides . The 6-azaisocytosines were studied with respect to tautomeric equilibrium and the transformation of functional groups, and used in the synthesis of the condensed heterocyclic compounds: Purine isosteric imidazo[2,1-]-[1,2,4]triazine and the 1,2,4-triazino[2,3-]quinazolines -.