Redox-Tag Processes: Intramolecular Electron Transfer and Its Broad Relationship to Redox Reactions in General

Abstract

Explosive growth in the use of open shell reactivity, including neutral radicals and radical ions, in the field of synthetic organic chemistry has been observed in the past decade, particularly since the advent of ruthenium complexes in 2008. These complexes generally induce single-electron transfer (SET) processes via visible-light absorption. Additionally, recent significant advancements in organic electrochemistry involving SET processes to provide open shell reactivity offer a complementary method to traditional polarity-driven reactions described by two-electron transfer processes. In this Review, we highlight the importance of intramolecular SET processes in the field of synthetic organic chemistry, which seem to be more elusive than the intermolecular versions, since they are net redox-neutral and thus cannot simply be regarded as oxidations or reductions. Such intramolecular SET processes can rationally be understood in combination with concomitant bond formations and/or cleavages, and are regulated by a structural motif that we call a "redox tag." In order to describe modern radical-driven reactions involving SET processes, we focus on a classical formalism in which electrons are treated as particles rather than waves, which offers a practical yet powerful approach to explain and/or predict synthetic outcomes.

Mo‐Based Oxidizers as Powerful Tools for the Synthesis of Thia‐ and Selenaheterocycles

“…The first oxidation peak of the veratrole derivative is a similarly clear peak as the first oxidation of the precursor 9 b , whereas the alkyl disulfide shows a broader oxidation wave at 1.03 V. We conclude that similarly to observations by Chiba et al. the first oxidation occurs at the activated arene . A fast single electron transfer (SET) oxidizes the disulfide, which then forms the active trisulfide cation (Scheme ).…”

“…the first oxidation occurs at the activated arene. [17] Af ast single electron transfer (SET) oxidizes the disulfide, whicht hen forms the active trisulfide cation (Scheme 7). This cation is known from "cation pool" methods and is then attacked intramolecularly by the arene.…”

Radical‐Cation‐Induced Crossed [2+2] Cycloaddition of Electron‐Deficient Anetholes Initiated by Iron(III) Salt

“…Thus far, various one‐electron oxidants have been developed as initiators for the crossed [2+2] cycloaddition of anetholes. In general, an initiator oxidizes anethole 1 to give a key radical cation 1 .+ . The resulting 1 .+ reacts with styrenes 2 to give 3 .+ .…”

“…In general, an initiator oxidizes anethole 1 to give a key radical cation 1 * + . [6,7] The resulting 1 * + reacts with styrenes 2 to give 3 * + . The final step is reduction of 3 * + by 1 as chain propagation.…”

Mechanistic Insights on Concentrated Lithium Salt/Nitroalkane Electrolyte Based on Analogy with Fluorinated Alcohols

“…A previous study proposed that the use of a fluorinated alcohol such as HFIP or 2,2,2-trifluoroethanol (TFE) is efficient both as a solvent and as an additive for electrochemical hole catalysis. [7] On the other hand, our group has also reported the use of lithium salt/nitroalkane as a promising electrolyte for hole catalysis, [9] such as in a Diels-Alder reaction, [10][11][12] [2+2] cycloaddition [13][14][15][16][17] and olefin metathesis. [18] Despite its great potential as a reaction medium in hole catalysis, the exact role of this electrolyte has been a long-standing mystery.…”