5-Azidotetrazolo[1,5-a]quinazoline (formally known as 2,4-diazidoquinazoline) undergoes regioselective nucleophilic aromatic substitution with amines at C(5) and provides corresponding 5-amino derivatives of tetrazolo[1,5-a]quinazoline. For the first time the molecular structure of the latter tricyclic system is unambiguously proved by X-ray diffraction analysis. Tautomeric equilibrium between tetrazolo[1,5-a]quinazolines and 2-azido-quinazolines permits their use in the copper catalyzed azide-alkyne 1,3-dipolar cycloaddition reaction. In this way a series of N4-substituted derivatives of 4-amino-2-(1,2,3-triazol-1-yl)-quinazolines were obtained.