Synthesis of Chiral Nopinane‐Annelated Pyrazolo[3,4‐ b ]pyridines From 5‐Aminopyrazoles and Myrtenal

Abstract

A series of 1‐aryl‐5‐aminopyrazoles was synthesized from 3‐iminobutanenitrile and substituted arylhydrazines under microwave irradiation (115°C–120°C) in ethanol, affording the target compounds in moderate to excellent isolated yields (28%–89%). Subsequently, the synthesized 1‐aryl‐5‐aminopyrazoles were reacted with myrtenal under catalyst‐free microwave conditions (140°C–165°C) to afford a series of novel nopinane‐annelated pyrazolo[3,4‐ b ]pyridines in isolated yields of 31%–68%. A reasonable mechanism for the condensation of 5‐aminopyrazoles with myrtenal is proposed. The structures of the newly synthesized compounds were established by spectroscopic methods, supported by density functional theory (DFT) calculations, and confirmed by single‐crystal x‐ray diffraction analysis. Owing to the presence of a rigid chiral nopinane framework and multiple nitrogen donor sites, the synthesized pyrazolo[3,4‐ b ]pyridines represent promising candidates for the development of chiral ligands for luminescent metal complexes.