Synthesis of 2H-pyrazolo[3,4-b]pyridin-3-oles via cyclization of pyrazolacrylonitriles

The reaction of 1-acyl-3-amino-5-pyrazolones 1 with ethyl ethoxymethylenecyanoacetate and ethoxymethylenemalononitrile 2 is described. Thermal cyclization in phenyl ether of the obtained pyrazol-acrylonitriles 3 provides good yields of pyrazolopyridin-3-ol derivatives 4.