Electrochemical ammonium-cation-assisted pyridylation of inert N-heterocycles via dual-proton-coupled electron transfer

A straightforward and practical strategy for pyridylation of inert N-heterocycles, enabled by ammonium cation and electrochemical, has been described. This protocol gives access to various N-fused heterocycles and bidentate nitrogen ligand compounds, through dual-proton-coupled electron transfer (PCET) and radical cross-coupling in the absence of exogenous metal and redox reagent. It features broad substrate scope, wide functional group tolerance, and easy gram-scale synthesis. Various experiments and density functional theory (DFT) calculation results show the mechanism of dual PCET followed by radical cross-coupling is the preferred pathway. Moreover, ammonium salt plays the dual role of proton-ation reagent and electrolyte in this conversion, and the resulting product 9-(pyridin-4-yl)acridine compound can be used for fluorescence recognition of Fe2+ and Pd2+ with high sensitivity.

Automated summary

A straightforward and practical strategy for pyridylation of inert N-heterocycles, enabled by ammonium cation and electrochemical, has been described. This protocol allows for the synthesis of various N-fused heterocycles and bidentate nitrogen ligand compounds without the need for exogenous metal and redox reagents. The reaction shows broad substrate scope, high functional group tolerance, and can be easily scaled up. Experimental and theoretical results support the proposed mechanism, and the resulting product can be used for fluorescence recognition of Fe2+ and Pd2+ with high sensitivity.