Switchable electrosynthesis of C-1-unsubstituted imidazopyridines.

Abstract

Oxidative coupling and cyclocondensation reactions to produce imidazopyridine have been attractive methodologies because of their inherent atom- and step-economy, which have been well established using exogenous oxidants, especially I₂. However, the straightforward and efficient preparation of C-1-unsubstituted-imidazopyridine remains an unsolved challenge, because the core features of imidazopyridine are low oxidation potential and can be easily oxidized to give the C-1-substituted byproduct. Herein, we developed a highly efficient and clean electrosynthesis of C-1-unsubstituted imidazo[1,5-<i>a</i>]pyridine using a user-friendly undivided cell under exogenous oxidant- and transition metal-free conditions. Moreover, the switchable access to imidazo[1,5-<i>a</i>]pyridine was achieved from the oxidative cyclization of two equivalents of pyridin-2-ylmethylamine or the oxidative cyclocondensation of pyridin-2-ylmethylamine and aryl methyl ketones.