Radical‐Mediated Formal C(sp2)–H Functionalization of Aldehyde‐Derived N,N‐Dialkylhydrazones

Recent advances in formal C(sp2)–H functionalization of aldehyde‐derived N,N‐dialkylhydrazones (substitution at the azomethine carbon atom) are highlighted, with a focus on radical‐mediated processes that open up new opportunities for C–C bond formation, such as alkylation reactions with the aid of hypervalent iodonium reagents or polyhaloalkanes, as well as for carbon–heteroatom bond formation (C–N, C–P). Cascade sequences based on these reactions, and leading to (hetero)cyclic frameworks, are also discussed. Radical addition to the hydrazone C=N bond generates a hydrazinyl radical adduct that can follow one‐electron oxidation/H‐elimination pathways, enabling the hydrazone functionality to be restored to its original state. This non‐classical pattern of hydrazinyl radical behavior has recently become established as a new strategy for achieving formal C(sp2)–H functionalization of aldehyde‐derived hydrazones.