Radical and ionic <i>meta</i>-C-H functionalization of pyridines, quinolines, and isoquinolines.

Carbon-hydrogen (C-H) functionalization of pyridines is a powerful tool for the rapid construction and derivatization of many agrochemicals, pharmaceuticals, and materials. Because of the inherent electronic properties of pyridines, selective <i>meta</i>-C-H functionalization is challenging. Here, we present a protocol for highly regioselective <i>meta</i>-C-H trifluoromethylation, perfluoroalkylation, chlorination, bromination, iodination, nitration, sulfanylation, and selenylation of pyridines through a redox-neutral dearomatization-rearomatization process. The introduced dearomative activation mode provides a diversification platform for meta-selective reactions on pyridines and other azaarenes through radical as well as ionic pathways. The broad scope and high selectivity of these catalyst-free reactions render these processes applicable for late-stage functionalization of drugs.