The ZnCl2-promoted intramolecular hetero-Diels-Alder reaction of N-(ortho-propargylphenyl)-N'-arylcarbodiimides, in which the aryl-N=C moiety functioned as a 2-azabuta-1,3-diene, 4π component, has been achieved. By this method, very rare 5,12-dihydrodibenzo[b,g][1,8]naphthyridines and fully aromatized dibenzo[b,g][1,8]naphthyridines were successfully synthesized.