N-Alkoxyphtalimides as Versatile Alkoxy Radical Precursors in Modern Organic Synthesis

O-substituted derivatives of N-hydroxyphthalimide (NHPI) have attracted much attention recently as synthetically available, stable, and convenient reagents for the generation of free radicals under mild conditions. The single-electron reduction by a photoredox catalyst or another reagent results in the N-O bond cleavage of an NHPI derivative with the release of free radicals that undergo selective synthetic transformations. Whereas N-acyloxyphtalimides (NHPI esters) are well known as a convenient C-radical source due to the facile one-electron reduction followed by the decarboxylation, N-alkoxyphtalimides are much less studied as radical precursors. The present review shows that N-alkoxyphtalimides are effective reagents for free-radical transformations starting from the generation of alkoxy free radicals. Visible light induced reactions are discussed first, these processes are classified according to the way how intermediate alkoxy radicals transformed to C-centered radicals: via hydrogen atom transfer to oxygen atom (HAT, including 1,5-HAT, 1,2-HAT, and intermolecular HAT) or via beta-scission. Other photochemical radical reactions of alkoxyphthalimides and non-photochemical tin-mediated processes are discussed separately.