Synthesis of some 3-substituted [1,8]naphthyrido[3,2-c][1,8]naphthyridines. A new heterocyclic ring system

Some 3-substituted-5,6-dihydro1,8]naphthyrido3,2-c]1,8]naphthyridines (V) were obtained by the condensation of 7-substituted-2,3-dihydro-1,8-naphthyridin-4-(1H)ones (IV) with 2-aminonicotinaldehyde. All of the 5,6-dihydro derivatives V were transformed into the fully aromatic compounds VI by refluxing with nitrobenzene.