Synthesis of Heterocycle-Annelated Naphthyridones with a Bridgehead Nitrogen Atom
A benzimidazo[1,2-b][2,7]naphthyridine - [1,2,4]triazolo[2,3-b][2,7]naphthyridine ring transformation
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 ,
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 .
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.
nh, 9 May 1996