Facile Synthesis of Nitrogen Cation-Doped Polycyclic Aromatic Hydrocarbons by Anodic Intramolecular Pyridination

Abstract

The bottom-up synthesis of heteroatom-doped polycyclic aromatic hydrocarbons (PAHs) has attracted attention in the development of models of doped graphene. Among PAHs, nitrogen-cation (N +)-doped PAHs are known to exhibit superior optoelectronic functionalities; however, practical methods for synthesizing N +-doped PAHs are limited and challenging [1]. In our previous study, the SNAr reaction was used for the intramolecular cyclization of phenylpyridine derivatives possessing an electron-deficient perfluoroaryl moiety to give the corresponding N +-doped triphenylene in high yields under moderate conditions without the use of a transition-metal catalyst [2,3]. However, one of the challenges in the synthesis of N +-doped PAHs via the SNAr reaction is poor functional-group tolerance.Here, a facile and selective synthesis method for N +-doped PAHs has been established via anodic intramolecular cyclization, inspired by the Yoshida’s protocol for C–H amination without a transition-metal catalyst or an oxidant [4]. The reaction mechanism, in particular the reaction selectivity, was elucidated using density functional theory (DFT) calculations. The N +-doped PAH products were found to have a donor–acceptor structure composed of an arene moiety and a pyridinium moiety, as evidenced by DFT calculations, UV–vis analysis, and electrochemical measurements. The proposed intramolecular anodic pyridination is a practical strategy for the late-stage introduction of N+ into π-electron systems and broadens the scope of molecular design of N +-doped PAHs.