The Chemistry of Azaindoles [Pyrrolo[2,3]pyridines]

The review discusses the chemical properties and the biological activity of aza-analogues of indole compounds, i.e. substances containing fused pyridine and pyrrole systems.
The interest taken in azaindole derivatives is due on the one hand to the ever broadening application during recent years of the principle of building up aza-analogues of biologically active substances (purines, pyrimidines, steroids, etc.) as bases in the search for new medicinal preparations, and on the other hand to the appearance in such systems of characteristic chemical properties, indicating a redistribution of electron density caused by the interaction of the "π-electron-deficient" and "π-electron-excessive" rings involved in the fusion.
The above problems are fully reflected in the review. Considerable attention is paid to discussing the chemical peculiarities of azaindoles associated with the presence in the fused systems of rings which have directly opposite displacements of π-electrons relative to carbon atoms, describing the features of lactam–lactim and amino–imino tautomerism in azaindole and azaindoline systems, and also examining routes and methods for introducing substituents both into the pyridine and into the pyrrole parts of the molecule. Exhaustive consideration is given to data on the biological activity of azaindoles. A special section is concerned with the choice of methods for building up azaindole systems and the characteristics of ring-closure in azaindoles compared with indoles.
The review covers all information available in the world's literature on the chemistry and the biological activity of azaindoles. The list of references comprises 159 items.