Hydrazine Derivatives as C-Centered Radical Precursors for C-C Bond Formation Reactions

Organic monosubstituted hydrazine derivatives (Ar-NHNH₂, RC(O)-NHNH₂, Alkyl-NHNH₂) are synthetically available, atom-efficient and stable sources of C-centered radicals upon oxidation with extrusion of the energetically favorable N₂ molecule. This review summarizes the synthetic application of monosubstituted hydrazine derivatives (arylhydrazines, carbazates, acylhydrazides, hydrazine carboxamides and alkylhydrazines) in free-radical C-C bond-forming reactions. The main application directions in this field are (a) alkene difunctionalization, (b) cascade cyclization initiated by the addition of hydrazine-derived C-centered radicals to acrylamides and isonitriles, and (c) CH-functionalization of (hetero)arenes via C-centered radical addition followed by oxidative dehydrogenation (re-aromatization).