Synthesis of heterocycle-annelated naphthyridones with a bridgehead nitrogen atom
The condensed naphthyridones thus obtained may also be regarded as interesting building blocks for the construction of other polyfunctional heterocyclic compounds, as exemplified by the conversion of the benzimidazo[1,2-b][2,7]naphthyrid-12-one 9 into the [1,2,4]triazolo[2,3-b][2,7]naphthyridone 21. The latter tricycle, which represents another new heterocyclic system [15], can be obtained in 76% yield simply by refluxing 9 with hydrazine hydrate in the presence of potassium carbonate in dimethylformamide solution - conditions which have been recently used for similar transformations in the isoquinolone series [16]. Obviously, this ring transformation is initiated by hydrazinolytic opening of the lactam ring, followed by addition of the hydrazone N-H to the nitrile function and subsequent condensation of the intermediate vic-diamino compound thus formed with one equivalent of the solvent.
