Synthesis of the Substituted 5‐Hydroxy‐1,7‐Dihydro‐ 6 H ‐Pyrazolo[3,4‐ b ]Pyridin‐6‐Ones by Interaction of 5‐Aminopyrazoles With Ethyl Bromopyruvate

In the present work, we describe the first example of constructing the 3‐hydroxypyridin‐2(1 H )‐one core based on the interaction of heterocyclic enamines with ethyl bromopyruvate. Utilizing a wide range of substituted 5‐aminopyrazoles as an enamine component we have shown that the considered condensation leads to the formation of pyrazolo[3,4‐ b ]pyridin‐6‐one derivatives containing a hydroxyl group. Relying on the investigated reaction a general approach to the synthesis of the target bicyclic system was developed. The application of elaborated protocol to a set of diverse 5‐aminopyrazoles allowed us to obtain an array of 5‐hydroxy‐1,7‐dihydro‐6 H ‐pyrazolo[3,4‐ b ]pyridin‐6‐ones with yields up to 82%. The undoubted advantages of the presented method are easily available starting materials, atom economy and facile isolation of the final products without chromatographic purification. The structure of the prepared compounds was confirmed employing 1 H and 13 C NMR spectroscopy, high‐resolution mass spectrometry as well as data of X‐ray analysis.