Visible‐Light‐Mediated C‐2 Functionalization and Deoxygenative Strategies in Heterocyclic N‐Oxides.

Heterocyclic N‐oxides are prevalent in numerous natural products with broad applications in pharmaceuticals, agrochemicals, material sciences, and asymmetric synthesis. Owing to their profound biological and physiological activity and unique chemical reactivity, the importance of these compounds has stimulated substantial interest among organic synthetic chemists. More importantly, C‐2 functionalization of heterocyclic N‐oxides, including pyridine‐, isoquinoline‐, pyrazine‐, quinoxaline‐, and quinoline N‐oxides, is among the most important strategies for heterocyclic functionalization. Besides, deoxygenation of heterocyclic N‐oxides has also emerged as a reaction of significance in organic chemistry. In the past decade, visible light photoredox catalyzed C‐2 functionalization and deoxygenation of these heterocyclic N‐oxides have drawn substantial attention owing to their mild reaction conditions. This review has been categorized based on visible‐light‐mediated nondeoxygenative C‐2 functionalization (alkylation, fluoroalkylation, arylation, acylation, and amination), deoxygenative C‐2 functionalization (sulfonylation, alkynylation, alkylation, and acylation), and deoxygenation (without C−H functionalization) of heterocyclic N‐oxides. For most part of the work, the substrate scope, limitation, and mechanism of the reactions have been discussed. [ABSTRACT FROM AUTHOR]