Intermolecular Reactions of Pyridyl Radicals with Olefins via Photoredox Catalysis

Seath, Ciaran P.; Jui, Nathan T.

doi:10.1055/s-0037-1611527

Cited by 9 publications

(3 citation statements)

References 45 publications

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“…The Jui group has published a collection of elegant photocatalytic olefin hydro-heteroarylation protocols proceeding through heteroarene radical generation via the reductive PCET activation of heteroaryl halides. 1026 In a 2017 report, the group demonstrated a reductive Meerwein-type heteroarylation of electron-deficient alkenes with heteroaryl halides via radical generation and conjugate addition ( Scheme 360 ). 1027 The combination of [Ir(dF(CF 3 )ppy) 2 (dtbbpy)]PF 6 ([ Ir-6 ]PF 6 ) photocatalyst and HE as a stoichiometric reductant in 25% aq.…”

Section: Reductive Transformations Of Heteroarenes Through Photochemical and Electrochemical Pcet Processesmentioning

confidence: 99%

Photochemical and Electrochemical Applications of Proton-Coupled Electron Transfer in Organic Synthesis

et al. 2021

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We present here a review of the photochemical and electrochemical applications of multi-site proton-coupled electron transfer (MS-PCET) in organic synthesis. MS-PCETs are redox mechanisms in which both an electron and a proton are exchanged together, often in a concerted elementary step. As such, MS-PCET can function as a non-classical mechanism for homolytic bond activation, providing opportunities to generate synthetically useful free radical intermediates directly from a wide variety of common organic functional groups. We present an introduction to MS-PCET and a practitioner’s guide to reaction design, with an emphasis on the unique energetic and selectivity features that are characteristic of this reaction class. We then present chapters on oxidative N–H, O–H, S–H, and C–H bond homolysis methods, for the generation of the corresponding neutral radical species. Then, chapters for reductive PCET activations involving carbonyl, imine, other X=Y π-systems, and heteroarenes, where neutral ketyl, α-amino, and heteroarene-derived radicals can be generated. Finally, we present chapters on the applications of MS-PCET in asymmetric catalysis and in materials and device applications. Within each chapter, we subdivide by the functional group undergoing homolysis, and thereafter by the type of transformation being promoted. Methods published prior to the end of December 2020 are presented.

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Section: Reductive Transformations Of Heteroarenes Through Photochemical and Electrochemical Pcet Processesmentioning

confidence: 99%

Photochemical and Electrochemical Applications of Proton-Coupled Electron Transfer in Organic Synthesis

et al. 2021

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“…For this purpose, the fluorinated N -methyl anilide ( 1a ) was chosen as a model tertiary amide substrate and protected dehydroalanine (DHA) derivative ( 2 ) was chosen as a suitably reactive nucleophilic radical acceptor that would ultimately afford medicinally relevant amino acid products ( 3a ) (Scheme ). , …”

Section: Results and Discussionmentioning

confidence: 99%

Reverse Polarity Reductive Functionalization of Tertiary Amides via a Dual Iridium-Catalyzed Hydrosilylation and Single Electron Transfer Strategy

et al. 2020

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A new strategy for the mild generation of synthetically valuable α-amino radicals from robust tertiary amide building blocks has been developed. By combining Vaska's complex-catalyzed tertiary amide reductive activation and photochemical single electron reduction into a streamlined tandem process, metastable hemiaminal intermediates were successfully transformed into nucleophilic α-amino free radical species. This umpolung approach to such reactive intermediates was exemplified through coupling with an electrophilic dehydroalanine acceptor, resulting in the synthesis of an array of α-functionalized tertiary amine derivatives, previously inaccessible from the amide starting materials. The utility of the strategy was expanded to include secondary amide substrates, intramolecular variants and late stage functionalization of an active pharmaceutical ingredient. DFT analyses were used to establish the reaction mechanism and elements of the chemical system that were responsible for the reaction's efficiency. Scheme 1. α-Functionalization strategies for amine synthesis from tertiary amides Scheme 3. Optimization studies for (A) Vaska's catalyzed amide hydrosilylation. (B) The photocatalytic reductive coupling of the silyl hemiaminal intermediate with DHA derivative. stituted structures delivered tertiary amine products, although a steric increase vs. reaction efficiency trend was observed. 19 Intramolecular Cyclization. We recognized the opportunity that this tandem amide activation protocolthrough tethering an alkene acceptor to the alkyl chain of the amide starting material-could be suitably leveraged towards the synthesis of complex heterocyclic amine frameworks. Accordingly, model substrates bearing a pendant α,β-unsaturated ester (1s-1t) were prepared, but initial studies demonstrated that these motifs did not readily undergo hydrosilylation using Vaska's catalyst (only around 80% conversion was achieved after 8 hours of reaction time), and furthermore significant quantities of over reduction side-product were isolated following the photocatalytic step. 20 Nevertheless, these initial challenges were circumvented when a derivative of Vaska's complex bearing triphenylphosphite ligands-previously reported by Nagashima 21-was employed in the hydrosilylation step instead (Scheme 5). Pleasingly, clean conversion to a stable silyl hemiaminal species was achieved within one hour, and subsequent subjection to the optimized photoredox conditions delivered the desired cyclic pyrrolidine (4s) and piperidine (4t) products in good yields. Scheme 5. Extension of the Vaska-photoredox system for reductive cyclization of tertiary amides Secondary Amide Activation. Recent endeavors by Chida and Sato, and Huang have demonstrated the utility of [Ir(COE)2Cl]2 complex in conjunction with Et2SiH2 reductant for the nucleophilic reductive functionalization of secondary amide building blocks, affording the corresponding α-branched secondary amine products. 4e,f Scheme 6. Reverse polarity, photocatalytic reductive functionalization of seconda...

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“…Classical approaches toward aryl radical species from the corresponding halides would involve halogen abstraction or single-electron reduction processes using chemical reagents; however, these methods have some drawbacks, such as reagent toxicity/stability and limited substrate scope [12][13][14]. While recent advances in photochemistry have remarkably expanded the synthetic utility of (hetero)aryl radicals in organic synthesis [15][16][17][18][19][20], visible-light-mediated alkene hydroarylation commonly requires external reductants and/or hydrogen atom sources to complete the catalytic cycle [21][22][23][24][25]. Over the past few decades, electrochemistry has proven to be an environmentally benign and convenient approach for accessing open-shell intermediates through a single-electron transfer process [26][27][28][29][30][31].…”

Section: Introductionmentioning

confidence: 99%

Transition-metal-catalyst-free electroreductive alkene hydroarylation with aryl halides under visible-light irradiation

Yamamoto,

Arita,

Kuriyama

et al. 2024

Beilstein J. Org. Chem.

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The radical hydroarylation of alkenes is an efficient strategy for accessing linear alkylarenes with high regioselectivity. Herein, we report the electroreductive hydroarylation of electron-deficient alkenes and styrene derivatives using (hetero)aryl halides under mild reaction conditions. Notably, the present hydroarylation proceeded with high efficiency under transition-metal-catalyst-free conditions. The key to success is the use of 1,3-dicyanobenzene as a redox mediator and visible-light irradiation, which effectively suppresses the formation of simple reduction, i.e., hydrodehalogenation, products to afford the desired products in good to high yields. Mechanistic investigations proposed that a reductive radical-polar crossover pathway is likely to be involved in this transformation.

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Intermolecular Reactions of Pyridyl Radicals with Olefins via Photoredox Catalysis

Cited by 9 publications

References 45 publications

Photochemical and Electrochemical Applications of Proton-Coupled Electron Transfer in Organic Synthesis

Photochemical and Electrochemical Applications of Proton-Coupled Electron Transfer in Organic Synthesis

Reverse Polarity Reductive Functionalization of Tertiary Amides via a Dual Iridium-Catalyzed Hydrosilylation and Single Electron Transfer Strategy

Transition-metal-catalyst-free electroreductive alkene hydroarylation with aryl halides under visible-light irradiation

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