Preparation of 4,7‐Dihydro‐1H‐pyrazolo[3,4‐b]pyridine‐5‐nitriles in a Multicomponent Domino Process

Abstract

AbstractIn this article we present the unprecedented preparation of 4,7‐dihydro‐1H‐pyrazolo[3,4‐b]pyridine‐5‐nitriles and pyrazolo[3,4‐b]pyridine‐5‐nitrile derivatives by the reaction of mono‐substituted aryl/heteroarylhydrazines with 3‐aryl‐3‐oxopropanonitriles in ethanol in the presence of HNO3 (conc.). This multi‐component reaction requires the in situ oxidation of the ethanol (used as a solvent) to acetaldehyde, resulting in a domino assemblage of the starting materials. The resulting products were unambiguously and rigorously characterised based on IR, NMR (1D and 2D techniques), MS and X‐ray crystallography studies. Based on the results obtained from a series of reactions we also propose a mechanism for this unexpected synthesis which confirmed the involvement of in situ oxidation of ethanol and intermediacy of a 5‐aminopyrazole species.