Recent advances in radical-based C–N bond formation via photo-/electrochemistry

Abstract

The employment of nitrogen sources with free N-H bonds for amination is considered to be most straightforward and desirable, especially when the C-N bonds are prepared from N-H bonds and non-functionalized carbon sources, such as C-H bonds and C-C double/triple bonds, since this obviates the needs for the pre-installation of reactive groups in the starting materials and leads to a high atom and step economy. Recently, radical chemistry has been resuscitated owing to its great value in organic synthesis, and notable advances have been made in the direct use of N-H bonds for radical-based C-N bond formation with photo-/electrotechniques. Apart from the well-studied N-radical species addition pathway, radical-mediated aminations also proceed through N-atom nucleophilic addition, C-/N-radical cross-coupling, and a hydrogen-atom transfer (HAT) process. This review highlights the recent advances in this area with emphasis on the related reaction mechanisms.

Photocatalysis with organic dyes: facile access to reactive intermediates for synthesis

“…The reductive cleavage of weak N-X (X = halogen, S, O) bonds using a stoichiometric initiator or high temperatures set the path for key developments for the generations of NCRs, for instance, in the Hofmann-Löffler-Freytag reaction. With the rise of photoredox catalysis, they could be accessed under milder conditions in the last years [125][126][127][128][129][130][131][132].…”

“…Each of these steps generates a C-centered radical, later subject to termination. The variety of possible transformations has already been reviewed [125][126][127][128][129][130][131][132].…”

Cathode Material Determines Product Selectivity for Electrochemical C−H Functionalization of Biaryl Ketoximes

“…[1] Recently,r adical-mediated CÀN bond construction has gained traction because the relatively high reactivity of the open-shell species provides opportunities for the development of transformations that are difficult using the two-electron manifold. [2] In this context, many research groups have employed the easily available oximes and their derivatives as radical precursors in radical CÀN coupling reactions. [3] Thecleavage of the OÀHbond in oxime produces a s-type iminoxyl radical with both ar eactive oxygen and nitrogen atom.…”

Electrochemical Synthesis of O‐Phthalimide Oximes from α‐Azido Styrenes via Radical Sequence: Generation, Addition and Recombination of Imide‐N‐Oxyl and Iminyl Radicals with C−O/N−O Bonds Formation

“…[7] Such processes are often accompanied by the formation of reactive radical species that play a key role in the formation of the desired structures. [8] Electric current is extensively used as a convenient tool for the direct or indirect generation of C-, [9] O-, [10] N- [11] and S-centered [12] radicals.…”