Pyridine N-oxides as hydrogen atom transfer reagents for site-selective photoinduced C(sp3)–H functionalization

Photoinduced C(sp3)–H functionalization through hydrogen atom transfer (HAT) processes is pivotal in organic synthesis because of the mild reaction conditions and applicability to late-stage functionalization of complex molecules, such as pharmaceuticals and agrochemicals. Despite promise, achieving precise site-selectivity and overcoming the high bond dissociation energy (BDE) of unactivated aliphatic C–H bonds in photoinduced C(sp3)–H functionalization reactions, through HAT, are challenging. In this landscape, pyridine N-oxides have emerged as potent HAT reagents due to their easily tunable nature. This Perspective highlights studies showcasing the potential of pyridine N-oxides as HAT reagents in site-selective hydrogen atom abstraction from unactivated C(sp3)–H bonds and explores their structure–activity relationship with multiple hydrocarbon substrates. Pyridine N-oxides have become promising reagents in environmentally friendly synthesis owing to their cost-effectiveness, tunability and applicability in (heterogeneous) catalysis. Ongoing research on the use of pyridine N-oxides as HAT reagents will probably offer additional avenues for efficient and selective C(sp3)–H bond functionalization. Photoinduced C(sp3)–H functionalization reactions, through hydrogen atom transfer (HAT) processes, have become a useful tool in synthesis, but challenges remain. This Perspective showcases the potential of pyridine N-oxides as HAT reagents in photoinduced C(sp3)–H functionalization reactions, highlighting how they can be readily tuned to achieve site-selectivity.