Abstract
Abstractmagnified imageThe dye plant Isatis tinctoria yields a number of heterocyclic compounds with interesting anti‐inflammatory 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 (=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.
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