Light Induced Transformations of the NO2 Group in Nitroarenes.

This review provides a comprehensive overview of recent advances and breakthroughs in visible-light photocatalytic chemistry of nitroarenes, highlighting how photoexcitation endows them with unique reaction pathways that overcome the inherent limitations of conventional thermal reactions. The discussion is systematically organized around the multifaceted roles of nitroarenes in excited-state transformations, including their applications as hydrogen atom transfer (HAT) and oxygen atom transfer (OAT) reagents to enable the functionalization of inert C─H bonds and the oxidative cleavage of alkenes and arenes. Their utility as nitrene precursors for the construction of complex heterocycles is also summarized. Furthermore, nitroarenes can act as energy transfer (EnT) catalysts and proton-coupled electron transfer (PCET) reagents, and the nitro group serves as a leaving group under light irradiation. Relying on the distinct electronic configurations of singlet and triplet excited states, these strategies allow diverse transformations such as cross-couplings, cyclization reactions, and skeletal editing to proceed under mild and sustainable conditions. This emerging field not only enriches the synthetic toolkit for the assembly of valuable molecular frameworks but also provides new avenues for the late-stage modification of pharmaceuticals and fine chemicals.