Oxime‐Derived Iminyl Radicals in Selective Processes of Hydrogen Atom Transfer and Addition to Carbon‐Carbon π‐Bonds

Abstract

Oximes represent one of the fundamental organic compound classes with a wide range of synthetic applications. In the last decade O-substituted oximes were recognized as the synthetically available and versatile precursors of iminyl radicals via one-electron oxidation or one-electron reduction employing visible light photoredox catalysts, salts of abundant metals (such as Cu or Fe), or other convenient reagents. Iminyl radicals are powerful synthons for various processes of cyclization, ringopening, CH-functionalization, and coupling. The present review is focused on the synthetic methods based on oxime-derived iminyl radicals developed in the last few years excluding ring opening reactions of cyclic iminyl radicals that were summarized in recent publications. The review consists of two main parts:(1) reactions of iminyl radicals involving 1,n-hydrogen atom transfer (n = 5 in most cases) and (2) reactions involving the addition of iminyl radical to the carbon-carbon π-bond.

Access to Fully Substituted Dihydropyrimidines via Dual Copper/Photoredox‐Catalyzed Domino Annulation of Oxime Esters and Imines

“…Visible‐light‐driven photoredox catalysis has come forth as a powerful activation mode in synthetic chemistry, which offers the opportunity to realize chemical transformations in a generally efficient, mild, selective, and environmentally friendly way [7] . In this context, the strategy of visible‐light‐induced N−O bond breakage of oxime esters has recently been achieved, which enables a range of iminyl radical‐triggered transformations to access various structural skeletons [4f,g,5] . In the past decade, the efficient syntheses of various five‐membered N ‐heterocycles, such as pyrazoles, [8] thiazoles, [9] oxazoles, [10] imidazoles, [11] triazoles, [12] pyrroles, [13] and indoles, [14] have been achieved by the N−O bond cleavage of oxime esters.…”

Recent Advance in Iminyl Radical Triggered C–H and C–C Bond Functionalization of Oxime Esters via 1,5-HAT and β-Carbon Scission

“…Several reviews on the corresponding C(sp 3 )−C(sp 3 ) bond functionalization have been published recently. 34 Hence, we herein will focus on our recent progress in -fragmentation and further C−C bond functionalization in this section.…”

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

“…In order to generate alkoxyl radicals under mild conditions for selective transformations various reagents were proposed, and compounds with a weak N−O bond are especially popular and versatile radical precursors. Alkoxy, [3,8–11] aminyl, [12–14] imidyl, [15] iminyl, [16–18] and C‐centered radicals [19–21] can be selectively generated upon the N−O bond cleavage depending on the structure of N−O containing substrate. Between such substrates N ‐hydroxyphthalimide (NHPI) derivatives are especially popular due to their synthetic availability, stability, and reactivity in reductive single electron transfer (SET) induced N−O bond cleavage (Scheme 1).…”