Electrochemical synthesis of biomass-derived aromatic N-heterocycles by using Ni-based hierarchical nanosheets catalysts

Electrochemical valorization of biomass to aromatic N-heterocycles is a pioneering field and an eco-friendly synthetic strategy. Herein, electro-oxidative cyclocondensations of biomass-based furoin with 1,2-phenylenediamines are developed for quinoxalines syntheses (16 examples) in 97∼80% yields by using Ni-based electro catalyst with KI as electrolyte and mediator. The electrocatalyst is developed as Ni-nanosheets densely assembled on a knitted carbon cloth with a hierarchical 3D-open network. The electrochemical furoin-to-quinoxaline transformation involves a tandem reaction of Ni-promoted I⁻-to-[I⁺] electro-oxidation, [I⁺]-induced furoin-to-furil oxidation, and furil/1,2-phenylenediamine cyclocondensation. The high performance of Ni catalyst is ascribed to its promotion effect on quick and selective I⁻-to-[I⁺] electro-oxidation, thus triggering a [I⁺]-mediated furoin oxidation. In contrast, the competitive reaction of direct 1,2-phenylenediamine oxidation is significantly suppressed on the anodic Ni surface. This research thus highlights a sustainable way for the productions of high value-added aromatic N-heterocycles by electro catalytic transformation of biomass-based compounds with earth-abundant transition-metal catalyst.