Recent Advances in Iminyl Radical Cyclizations

Abstract

Iminyl radical cyclizations have emerged as important tools for constructing five-and six-membered nitrogen-containing heterocycles. Both aromatic and nonaromatic ring systems are readily accessible from a variety of radical precursors. This short review focuses on recently discovered iminyl radical cyclizations. Methods that use heat, transition metals, or oxidants to generate the radicals are discussed, as are protocols employing either UV irradiation or visible light. Many of these newly developed procedures should be quite useful to the organic synthesis community due to their utilization of mild and convenient conditions.

CH‐Functionalization of Heterocycles with the Formation of C−O, C−N, C−S/Se, and C−P Bonds by Intermolecular Addition of Heteroatom‐Centered Radicals

“…Recently, we have witnessed the flourishing of new approaches to the generation of heteroatom‐centered radicals including photocatalysis and electrosynthesis. Such advances have undoubtedly expanded their application in selective transformations [46–50] . The chemistry of heteroatom‐centered radicals has been rapidly developing, but it is still less studied than the chemistry of C‐centered radicals.…”

“…However, hydrogen atom abstraction and β‐scission processes are also typical for heteroatom‐centered radicals, especially O‐centered [58,59] and N‐centered [56] ones, whereas not so frequently observed in C‐centered radical chemistry. Heteroatom‐centered radicals are capable of mediating atom or group transfer or can directly abstract a hydrogen atom from saturated C( sp 3 )−H bonds with the generation of C‐centered radicals [49,55–58,60–64] . These reactions constitute a large family of advanced synthetic methods for the functionalization of C−H bonds [65–71] .…”

“…As the topic is broad, [33,46,47,49–51,56,58,79–84] the present review mainly focuses on addition reactions of heteroatom‐centered radical to heteroaromatic π‐systems (Scheme 1). However, papers, in which non‐aromatic heterocycles participate in the reaction, have been also reported, and some of them are mentioned here.…”

Regioselective Synthesis of Unsymmetrical Vicinal Diamines via Azidoimination of Alkenes with TMSN3 and Ketimines

“…Accordingly, N -centered radicals have drawn considerable attention from the synthetic community because their unique properties and high activities for C–N bond construction . Among various developed nitrogen-centered radicals, the ambiphilic iminyl radicals have received considerable attention recently, which were generally obtained by the cleavage of N–O bond of oxime derivatives via an electron-acceptor heterolytic manner or photoinduced energy-transfer homolytic pathway . To the best of our knowledge, all reported examples on radical amination can accommodate only single or undifferentiated amino functionalities.…”

Stereochemical modulation of ketyl radical cyclization enabled by pyridine-boryl radicals: catalytic diastereoselective synthesis of trans-2-alkyl-1-indanols

“…Radical cyclization is a powerful synthetic method for the construction of complex cyclic molecules owing to its high functional group tolerance and atom economy. 1 A particularly advantageous feature is the highly predictable 5- exo regioselectivity, 2 which has been extensively utilized in a cascade manner for the total synthesis of polycyclic natural products. 3 Among intramolecular radical–π-bond couplings, the reaction between a ketyl radical and an alkene can afford numerous cyclic alcohols that are prevalent in biologically active molecules.…”