A wide variety of functionalized 2-aryl benzimidazoles can be prepared by a solvent-free cobalt- or iron-catalyzed redox condensation of 2-nitroanilines and benzylamines. The cascade including benzylamine oxidation, nitro reduction, condensation, and aromatization occurs without any added reducing or oxidizing agent. The method can be extended to other alkylamines as reducing components or 2-nitrobenzamides as oxidizing components when using an iron/sulfur catalyst to afford various diazaheterocycles.

This work highlights the unexpected and unprecedented outcome of the reactivity with DABCO-bis(sulfur dioxide). The use of this reagent led to the exclusive introduction of a sulfur atom on the C-3 position of imidazopyridines instead of a sulfone group. The reaction methodology turned out to be robust, scalable and suitable for various imidazopyridines and [a]