Synthesis of Substituted Pyrrolo[2,3‐ c ]Pyrazol‐4‐Ylacetic Acids via Acid‐Catalyzed Rearrangement of Aroyl‐Containing Pyrazolo[3,4‐ b ]Pyridin‐6‐Ones

For the first time, the behavior of pyrazolo[3,4‐ b ]pyridin‐6‐ones bearing aroyl substituent in acidic media was investigated. It was shown that previously unknown recyclization into pyrrolo[2,3‐ c ]pyrazol‐4‐ylacetic acids proceeds under action of hydrochloric acid. Based on the disclosed reaction the efficient method for the synthesis of target products was elaborated. Employing the designed procedure 17 examples of final pyrrolo[2,3‐ c ]pyrazol‐4‐ ylacetic acids were obtained with yields up to 94%. The advantages of presented approach are atom economy, easily available starting compounds and simple isolation of target products avoiding chromatography. The structure of one of synthesized products was unambiguously confirmed by X‐ray analysis.