Synthesis Of N-Heteroaromatics Via Anodic N-H/C-H Cross-Coupling Reactions

N-Heterocycles are ubiquitous motifs with good physiological activities that play a critical role in both medicinal chemistry and biology.The nitrogen-centered radicals(NCRs)are important intermediate in organic synthesis that play an important role in the construction of N-C bond and the synthesis of heterocyclic aromatic compounds.Herein,we report electrochemical oxidation of N-H bonds for generating NCRs,through N-H/C-H cross-coupling methods to construct N-heterocycles,including benzimidazoles and pyridoimidazoles,phenanthridines and structurally related N-heteroaromatic products.This dissertation is divided into the following sections mainly:In the first part,we report herein an atom-economical and sustainable approach to access amidinyl radical intermediates through the anodic cleavage of N-H bonds.The resulting nitrogencentered radicals undergo cyclizations with(hetero)arenes,followed by rearomatization,to afford functionalized tetracyclic benzimidazoles in a highly straightforward and efficient manner.This metal-and reagent-free C-H/N-H cross-coupling reaction exhibits a broad substrate scope and proceeds with high chemoselectivity.In the second part,an unprecedented synthesis of N-heteroaromatics from biaryl aldehydes and NH3 through reagent-free C-H/N-H cross-coupling has been developed.The electrosynthesis uses NH3 as an inexpensive and atom-economic nitrogen donor,requires no oxidizing agents or salt additives,and allows efficient and regioselective access to a wide range of phenanthridines and structurally related polycyclic N-heteroaromatic products.Based on the experimental and theoretical studies,a possible radical cation reaction mechanism was proposed.