The reactions of anthranilonitrile and 5-bromoanthranilonitrile with sodium hydride in dimethyl sulphoxide yield 4-amino-2-(2-aminophenyl)quinazoline (7) and its dibromo-analogue (8), respectively. Nitrosation of the diamines affords unstable diazonium salts which cyclise to either quinazolino[3,2-c]- or quinazolino[1,2-c]-[1,2,3]benzotriazines. These tetracyclic triazines readily undergo ring opening in the presence of secondary-amines to form the title compounds. 1,3-Bis-(2-cyano-4-bromophenyl)triazene (12) is smoothly transformed into dibromoquinazolines (18) in boiling secondary amines.

4-Amino-2-[2-(piperidin-1-ylazo)phenyl]quinazoline (17a) behaves as a masked diazonium compound and decomposes in mineral acids, in acetic acid containing copper-bronze, in hot ethylene glycol, on photolysis in methanol or ethanol, or on reduction. The triazene linkage of (17a) is resistant to alcoholic potassium hydroxide but the 4-aminoquinazoline nucleus is hydrolysed to the corresponding quinazolin-4(3H)-one system. Methylation of (17a) with methyl iodide in tetrahydrofuran affords an N(1) methiodide (29) which is hydrolysed to the corresponding 1-methylquinazolin-4(1H)-one (30) in aqueous alkali. The unusual properties of this and other 1-methylquinazolin-4(1H)-ones can be attributed to their dipolar character. This renders the 1-methyl group liable to removal in acidic conditions.