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.
An efficient and high-yielding strategy to prepare “unsymmetrical”
4-aryl-isoxazol-3,5-dicarboxylic acid derivatives from nitroacetic
esters and aromatic aldehydes has been developed. The strategy is
based on the isolation and usage of the previously missed intermediate
of the Dornow reaction5-hydroxy-6-oxo-4-aryl-6H-1,2-oxazine-3-carboxylates. In addition, the mechanism of the Dornow
reaction was partially revised.
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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