A Multicomponent Approach to the Assembly of a Novel 3 H ‐Furo[3,2‐ d ]Pyrazolo[3,4‐ b ]Pyridine Core

A general method for the synthesis of a previously unknown 3 H ‐furo[3,2‐ d ]pyrazolo[3,4‐ b ]pyridine system was elaborated. The considered route is based on the annulation of the furan ring to the pyrazolo[3,4‐ b ]pyridine framework via a multicomponent reaction with various arylglyoxals and Meldrum's acid. Employing the aforementioned protocol, a series of target 3 H ‐furo[3,2‐ d ]pyrazolo[3,4‐ b ]pyridin‐8‐yl acetic acids was prepared in yields up to 83%. The designed approach enables the application of a wide range of readily available starting 5‐hydroxypyrazolo[3,4‐ b ]pyridines and α‐ketoaldehydes with diverse substituents in the aromatic fragments. The synthetic utility of the obtained furylacetic acids was demonstrated by further conversion of the carboxyl group into an ester moiety.