Fused quinoline heterocycles III: Synthesis of first annulated 1,4,5,6,6a-pentaazabenzo[a]indacenes, 1,3,5,6-tetraazaaceanthrylenes and 5,7,9,11-tetraazabenzo[a]fluorenes

An easy and efficient synthesis of the versatile, hitherto unreported methy l 3-amino-4-chloro-1-ethyl-pyrrolo[3,2-c]quinoline-2-carboxylate (9) is des cribed. Reaction of 9 with sodium azide gives the corresponding tetracyclic ring system 10 in near quantitative yield. With isothiocyanates 13a,b the corresponding new 1,3,5,6-tetraazaaceanthrylenes 14a and 14b are formed, re spectively. Refluxing 9 with an excess of morpholine (15a) in boiling ethan ol yields the corresponding pyrrolo[3,2-c]quinolines 16a which react with i sothiocyanates 13a,c to afford the new 5,7,9,11-tetraazabenzo[a]fluorenes 1 7a,b. Refluxing 9 with an excess of butylamine affords the corresponding in termediate 16b, which reacts with ethyl chloroformate and triethyl orthofor mate to furnish the novel 1,3,5,6-tetraazaaceanthrylenes 18 and 19, respect ively. On the other hand, reacting 16b with acetic anhydride does not give the expected tetracyclic compound 20, but instead, the interesting pyrrolo[ 3,2-c]quinolines 21 is obtaind.