A new and straightforward route to synthesize novel pyrazolo[3,4-b]pyridine-5-carboxylate scaffolds from 1,4-dihydropyrano[2,3-c]pyrazole-5-carbonitriles

Among many acidic catalysts, amorphous carbon-supported sulfonic acid (AC-SO(3)H) has been evaluated as a new-generation solid catalyst with outstanding activity. Because of the –SO(3)H groups, the surface properties of the amorphous carbon catalyst were improved, which made the catalytic activity of the amorphous carbon-supported sulfonic acid many times greater than that of sulfuric acid. The amorphous carbon-supported sulfonic acid exhibited several advantages such as low cost, non-toxicity, porosity, stability, and easily adjustable chemical surface. In this paper, we introduce a new pathway for the synthesis of pyrazolo[3,4-b]pyridine-5-carboxylate scaffolds from 1,4-dihydropyrano[2,3-c]pyrazole-5-carbonitriles and aniline at room temperature under ethanol in the presence of AC-SO(3)H as the catalyst. This method provided the desired products with moderate to good yields. The gram-scale synthesis of the major product was carried out with good yields (up to 80%). This strategy involves a sequential opening/closing cascade reaction. This approach presents several advantages, including room temperature conditions, short reaction time, and operational simplicity.