Transition Metal-Free Reductive Transformations Using Organic Electron Donors

Abstract

This review highlights recent progress in transition metal-free reductive transformations using organic electron donors. According to previous reports, pyridine-derived super electron donors enable the selective reduction of nitrobenzenes to azobenzenes and phenazines, while also promoting the efficient desulfurization of thioacetals and thioethers under mild conditions. These transformations proceeded with a broad substrate scope and good functional group compatibility. Additionally, a sodium hydride (NaH)/1,10-phenanthroline system developed for radical-mediated C–C bond formation promoted the hydroarylation and hydroalkylation of styrenes with high anti-Markovnikov selectivities. Mechanistic studies suggested that the in situ-generated anilide anion acts as both an electron donor and a hydrogen source, supporting a radical-based reaction pathway. These works demonstrate the potential of organic electron donors for use as sustainable and practical alternatives to conventional transition metal-based reductive methods in organic synthesis.