We present the results of our study towards the synthesis of 2,3-disubstituted 7-azaindoles by cyclization of 2-pyridylhydrazones of aliphatic and alkylaromatic ketones under the conditions of Fischer reaction, catalyzed by polyphosphoric acid.

A simple synthesis of some hard-to-reach heterocycles containing 2,3-disubstituted 5-bromo-1H-pyrrolo[2,3-b]pyridine framework by Fisсher indole cyclization in polyphosphoric acid has been developed. A particularly valuable feature of this synthetic route is the possibility to build a 5-bromo-7-azaindole scaffold with alkyl or aryl substituents at positions 2 and 3 from available starting materials.

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