Tandem Electrochemical Oxidation of Polycyclic Aromatic Amines Towards Carbazoles and Phenazine‐based Aza‐helicenes

• Published in: Chemistry : a European journal 2024-05, Vol.30 (25), p.e202400614-n/a
• Main Authors: Yan, Boning, Lei, Ming, Tang, Zefeng, Liao, Hengyi, Xu, Kang
• Format: Article
• Language: English
• Subjects: Amines; Atomic structure; Carbazole; Carbazole Based Aza-helicenes; Carbazoles; Chemical reactions; Density distribution; Electrochemical Oxidation; Electrochemistry; Electron spin; Electrostatic properties; Factor analysis; Free radicals; Nitrogen; Oxidation; Phenazine; Phenazine Based Aza-helicenes; Polycyclic Aromatic Amine; Population studies; Pyrazine; Regioselectivity; Rrgioselectivity; Steric hindrance; Substrates; Tautomers
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202400614

Experimental and theoretical study of the regioselectivity and mechanism of polycyclic aromatic amine (PAA) electrochemical oxidation is important for designing nitrogen doped large π‐conjugated functional molecules. Herein, we used binary‐, ternary‐, and quaternary‐fused PAAs as electro‐oxidative reaction substrates to investigate the yield changes of carbazole and phenazine based aza‐helicene other than oligomers, which were obtained through pyrrole and pyrazine annulation pathways. Combined with the restrained electrostatic potential (RESP) and steric hindrance factor analysis of the substrate, the electron spin density distribution of free radical resonance hybrid and the spin population analysis of the atoms in the structure of each free radical tautomer indicate that the degree of delocalized dispersion of N free radical and the resulting change in the spin density distribution of C free radical tautomers determine the reaction regioselectivity. The potential charge of the K‐region, Bay‐region, and L‐region adjacent to the C(α)−C(β1) bond is higher than that of other regions within the molecule, and the charge in these high RESP regions tends to delocalize more strongly toward electron‐deficient N free radicals. Thus, the activity of N−C(α)−C(β1) region is increased, which supports the proposed free radical addition and free radical coupling mechanism for the electro‐oxidative reaction of PAA. Experimental and theoretical study revealed that high activity of N−C(α)−C(β1) region of the free radical hybrid determine the regioselectivity of polycyclic aromatic amines (PAAs) electrochemical oxidation towards carbazole and phenazine based aza‐helicenes. This work would pave the way for precise construction of heteroatom fused helical large π‐conjugated system using direct splicing strategy from PAHs derivatives.