Nitrogen-centered radical-mediated C–H imidation of arenes and heteroarenes via visible light induced photocatalysis

Abstract

The C-H imidation of arenes and heteroarenes has been achieved via visible light induced photocatalysis. In the presence of an iridium(III) photoredox catalyst, the reaction of aromatic substrates with N-chlorophthalimide furnishes the N-aryl products at room temperature through a nitrogen-centered radical mediated aromatic substitution.

Visible‐Light‐Mediated Generation of Nitrogen‐Centered Radicals: Metal‐Free Hydroimination and Iminohydroxylation Cyclization Reactions

“…[4] MacMillan [5] and coworkers have developed an asymmetric visible-light-mediated amination of aldehydes by enamine catalysis,a nd the groups of Sanford, [6] Lee, [7] Yu, [8] and Luo [9] have reported the photoredox generation of phthalimidyl and saccharyl radicals and their use in Minisci-type reactions.T he groups of Zheng [10] and Knowles [11] have developed am ethod for the photoredox generation of diaryl and aryl alkyl aminium radical cations and employed them in CÀNb ond-forming reactions.…”

“…[1a,2] Thed evelopment of amild, selective,and general method to catalytically generate NCRs from readily available precursors would enable the facile construction of many N-heterocycles,w hich are privileged motifs in natural products and therapeutic agents. [3] Photoredox catalysis has emerged as apowerful technique through which single electron transfer (SET) reactions can be performed under mild conditions.[4] MacMillan [5] and coworkers have developed an asymmetric visible-light-mediated amination of aldehydes by enamine catalysis,a nd the groups of Sanford, [6] Lee, [7] Yu, [8] and Luo [9] have reported the photoredox generation of phthalimidyl and saccharyl radicals and their use in Minisci-type reactions.T he groups of Zheng [10] and Knowles [11] have developed am ethod for the photoredox generation of diaryl and aryl alkyl aminium radical cations and employed them in CÀNb ond-forming reactions.Drawing inspiration from the work of Forrester, [12] Narasaka, [13] and Walton, [14] we speculated that appropriately functionalized O-aryl oximes could serve as general, benchstable NCR precursors that could deliver iminyl radicals upon photoredox activation under mild conditions.[15] Such an approach would clearly benefit from the facile synthesis of aryl oximes,and we hoped that the high structural modularity of the O-aryl hydroxylamines would allow us to identify substrates that do not require the use of transition-metalbased photocatalysts.[16] Herein, we describe the successful implementation of this approach and the development of novel, transition-metal-free,v isible-light-mediated hydroimination and iminohydroxylation cyclization reactions (Scheme 1B).Theg uiding principle of our photoredox NCR synthesis capitalized on the evidence that electron-poor aromatic compounds have reduction potentials compatible with SET reduction by visible-light-excited photocatalysts, [17] as shown by MacMillan and co-workers.[18] Our envisaged photoredox iminyl NCR generation was initiated by the visible-lightpromoted excitation of ap hotocatalyst (PC! *PC) [19] followed by SET reduction of the aryl unit of oxime A to give radical anion B (Scheme 2A).…”

One-pot synthesis of Pd@PdPt core–shell nanocubes on carbon supports

“…Their removal prior to catalytic reactions is very important; however, the particular shape is oen destroyed during the removal process. [17][18][19] Previously, we showed that Pt cubes could be synthesized directly on the carbon support without using surface-capping agents. 20 Many types of Pt-Pd bimetallic nanoparticles have been prepared using surface-capping agents.…”

Light on Unsaturated Hydrocarbons – “Gotta Heterofunctionalize Them All”

“…NCRs can be generated from different starting materials, which can be prefunctionalized or not. Several preactivated N-containing substrates that can be converted into radicals are N-acyloxyphthalimides, [11] N-halogenophthalimides, [12] acyl azides, [13] benzoylhydroxylamines, [14] and N-aminopyridinium salts. [15] Through this concept, Leonori and coworkers recently disclosed a new application of activated dinitro-substituted aryl-hydroxylamines as NCR precursors.…”