The dye plant Isatis tinctoria yields a number of heterocyclic compounds with interesting antiinflammatory and cytotoxic properties, formed mainly in an unknown manner by post-harvest treatment. A synthesis of the incidently isolated 5,7-dihydrodibenzo[b,f][1,7]naphthyridine-6,12-dione (4a) is presented. Starting from different 1,2-diarylhydrazines, adducts 11 with acetylenedicarboxylates (¼ but-2-ynedioates) are thermally treated (Scheme). In a Fischer-type rearrangement, 3-(arylamino)quinolinecarboxylic acids 9 are obtained, which can be cyclized under Friedel -Crafts conditions to yield a number of analoga 4 of the title compound.