1.9 Oxygen-Centered Radicals

2021 ◽  
Author(s):  
J. Zhang ◽  
D. Liu ◽  
Y. Chen
Keyword(s):  
Hydrogen Atom ◽  
Visible Light ◽  
Organic Synthesis ◽  
Reactive Intermediates ◽  
Radical Addition ◽  
Hydrogen Atom Transfer ◽  
Reaction Conditions ◽  
Recent Advances ◽  
Carbon Carbon Bonds ◽  
Induced Reaction

AbstractOxygen-centered radicals (R1O•) are reactive intermediates in organic synthesis, with versatile synthetic utilities in processes such as hydrogen-atom transfer (HAT), β-fragmentation, radical addition to unsaturated carbon–carbon bonds, and rearrangement reactions. In this review, we focus on recent advances in the generation and transformation of oxygen-centered radicals, including (alkyl-, α-oxo-, aryl-) carboxyl, alkoxyl, aminoxyl, phenoxyl, and vinyloxyl radicals, and compare the reactivity of oxygen-centered radicals under traditional reaction conditions with their reactivity under visible-light-induced reaction conditions.

scholarly journals Investigations on the 1,2-Hydrogen Atom Transfer Reactivity of Alkoxyl Radicals under Visible-Light-Induced Reaction Conditions

Synlett ◽  
2020 ◽  
Author(s):  
Yiyun Chen ◽  
Dan Liu ◽  
Jing Zhang
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Atom ◽  
Visible Light ◽  
Organic Synthesis ◽  
Hydrogen Atom Transfer ◽  
Atom Transfer ◽  
Reaction Conditions ◽  
Alkoxyl Radical ◽  
Induced Reaction ◽  
Key Questions

AbstractThe alkoxyl radicals have demonstrated superior hydrogen atom transfer reactivity in organic synthesis due to the strong oxygen–hydrogen bond dissociation energy. However, only the intermolecular hydrogen atom transfer (HAT) and intramolecular 1,5-HAT have been widely studied and synthetically utilized for C(sp3)–H functionalization. This Account summarizes our investigations on the unusual 1,2-HAT reactivity of alkoxyl radicals under visible-light-induced reaction conditions for the α-C–H functionalization. Various mechanistic investigations were discussed in this Account to address three key questions to validate the 1,2-HAT reactivity of alkoxyl radicals.1 Introduction2 Could Aldehydes/Ketones Be the Sole Reaction Intermediate for the α-C–H Allylation? NO3 Is the Alkoxyl Radical Absolutely Involved in the Reaction? YES4 Does the 1,2-HAT of Alkoxyl Radicals Irrefutably Exist? YES5 Conclusion

scholarly journals A Bond-Weakening Borinate Catalyst that Improves the Scope of the Photoredox α-C–H Alkylation of Alcohols

Synthesis ◽  
2020 ◽  
Vol 52 (15) ◽  
pp. 2171-2189
Author(s):  
Kounosuke Oisaki ◽  
Motomu Kanai ◽  
Kentaro Sakai
Keyword(s):  
Hydrogen Atom ◽  
Visible Light ◽  
Organic Synthesis ◽  
Hydroxy Group ◽  
Functional Group ◽  
Chemical Yield ◽  
Catalyst System ◽  
Hydrogen Atom Transfer ◽  
Hybrid Catalyst ◽  
Site Selective

The development of catalyst-controlled, site-selective C(sp3)–H functionalization reactions is currently a major challenge in organic synthesis. In this paper, a novel bond-weakening catalyst that recognizes the hydroxy group of alcohols through formation of a borate is described. An electron-deficient borinic acid–ethanolamine complex enhances the chemical yield of the α-C–H alkylation of alcohols when used in conjunction with a photoredox catalyst and a hydrogen atom transfer catalyst under irradiation with visible light. This ternary hybrid catalyst system can, for example, be applied to functional-group-enriched­ peptides.

Remote C–C bond formation via visible light photoredox-catalyzed intramolecular hydrogen atom transfer

2020 ◽  
Vol 18 (24) ◽  
pp. 4519-4532 ◽  
Author(s):  
Hui Chen ◽  
Shouyun Yu
Keyword(s):  
Hydrogen Atom ◽  
Visible Light ◽  
Bond Formation ◽  
Hydrogen Atom Transfer ◽  
Atom Transfer ◽  
Photoredox Catalysis ◽  
Recent Advances ◽  
Intramolecular Hydrogen

Visible light photoredox catalysis combined with intramolecular hydrogen atom transfer (HAT) can serve as a unique tool for achieving remote C–C bond formation. Recent advances in photoredox-catalyzed remote C–C bond formation are summarized.

scholarly journals Visible light-mediated difluoroalkylation of electron-deficient alkenes

2018 ◽  
Vol 14 ◽  
pp. 1637-1641 ◽  
Author(s):  
Vyacheslav I Supranovich ◽  
Vitalij V Levin ◽  
Marina I Struchkova ◽  
Jinbo Hu ◽  
Alexander D Dilman
Keyword(s):  
Double Bond ◽  
Hydrogen Atom ◽  
Visible Light ◽  
Blue Light ◽  
Radical Addition ◽  
Hydrogen Atom Transfer ◽  
Atom Transfer ◽  
Sodium Cyanoborohydride

A method for the reductive difluoroalkylation of electron-deficient alkenes using 1,1-difluorinated iodides mediated by irradiation with blue light is described. The reaction involves radical addition of 1,1-difluorinated radicals at the double bond followed by hydrogen atom transfer from sodium cyanoborohydride.

Direct Cyclization of Alkenyl Thioester via Transition Metal‐hydrogen Atom Transfer/radical‐polar Crossover Mechanism

2019 ◽  
Author(s):  
Shiori Date ◽  
Kensei Hamasaki ◽  
Karen Sunagawa ◽  
Hiroki Koyama ◽  
Chikayoshi Sebe ◽  
...  
Keyword(s):  
Natural Products ◽  
Hydrogen Atom ◽  
Transition Metal ◽  
Hydrogen Atom Transfer ◽  
Synthetic Method ◽  
Atom Transfer ◽  
Reaction Conditions ◽  
Hydride Hydrogen ◽  
Sulfur Heterocycles ◽  
One Step

<div>We report here a catalytic, Markovnikov selective, and scalable synthetic method for the synthesis of saturated sulfur heterocycles, which are found in the structures of pharmaceuticals and natural products, in one step from an alkenyl thioester. Unlike a potentially labile alkenyl thiol, an alkenyl thioester is stable and easy to prepare. The powerful Co catalysis via a cobalt hydride hydrogen atom transfer and radical-polar crossover mechanism enabled simultaneous cyclization and deprotection. The substrate scope was expanded by the extensive optimization of the reaction conditions and tuning of the thioester unit.</div>

Visible light photoredox-catalysed remote C–H functionalisation enabled by 1,5-hydrogen atom transfer (1,5-HAT)

2021 ◽  
Author(s):  
Weisi Guo ◽  
Qian Wang ◽  
Jieping Zhu
Keyword(s):  
Hydrogen Atom ◽  
Visible Light ◽  
Hydrogen Atom Transfer ◽  
Atom Transfer

The generation of heteroatom-centred radicals followed by intramolecular 1,5-HAT and functionalisation of the translocated carbon-centred radical is an efficient way to functionalize chemo- and regio-selectively the remote unactivated C(sp3)–H bond.

Ligand-Driven Advances in Iridium Catalyzed sp3 C-H Borylation: 2,2’-Dipyridylarylmethane

Synlett ◽  
2020 ◽  
Author(s):  
Margaret R Jones ◽  
Nathan D. Schley
Keyword(s):  
Recent Work ◽  
Organic Synthesis ◽  
Functional Group ◽  
Reaction Conditions ◽  
Recent Advances ◽  
Additional Ligand ◽  
Limited Application ◽  
Hydrocarbon Substrates ◽  
Phenanthroline Ligands

The field of catalytic C-H borylation has grown considerably since its founding, providing a means for the preparation of synthetically versatile organoborane products. While sp2 C-H borylation methods have found widespread and practical use in organic synthesis, the analogous sp3 C-H borylation reaction remains challenging and has seen limited application. Existing catalysts are often hindered by incomplete consumption of the diboron reagent, poor functional group tolerance, harsh reaction conditions, and the need for excess or neat substrate. These challenges acutely affect C-H borylation chemistry of unactivated hydrocarbon substrates, which has lagged in comparison to methods for the C-H borylation of activated compounds. Herein we discuss recent advances in sp3 C-H borylation of undirected substrates in the context of two particular challenges: (1) utilization of the diboron reagent and (2) the need for excess or neat substrate. Our recent work on the application of dipyridylarylmethane ligands in sp3 C-H borylation has allowed us to make contributions in this space and has presented an additional ligand scaffold to supplement traditional phenanthroline ligands.

Carbonylative Coupling of Simple Alkanes and Alkenes Enabled by Organic Photoredox Catalysis

2021 ◽  
Author(s):  
Ling Chen ◽  
Jing Hou ◽  
Ming Zheng ◽  
Le-Wu Zhan ◽  
Wan-Ying Tang ◽  
...  
Keyword(s):  
Hydrogen Atom ◽  
Visible Light ◽  
Transfer Process ◽  
Hydrogen Atom Transfer ◽  
Atom Transfer ◽  
Photoredox Catalysis ◽  
Visible Light Driven

A visible-light-driven direct carbonylative coupling of simple alkanes and alkenes via the combination of the hydrogen atom transfer process and photoredox catalysis has been demonstrated. Employing the N-alkoxyazinium salt as...

scholarly journals Dual Cobalt and Photoredox Catalysis Enabled Intermolecular Oxidative Hydrofunctionalization

2020 ◽  
Author(s):  
Han-Li Sun ◽  
Fan Yang ◽  
Wei-Ting Ye ◽  
Jun-Jie Wang ◽  
Rong Zhu
Keyword(s):  
Hydrogen Atom ◽  
Visible Light ◽  
Electrochemical Analysis ◽  
Hydrogen Atom Transfer ◽  
Redox Process ◽  
Photochemical Oxidation ◽  
Atom Transfer ◽  
Photoredox Catalysis ◽  
Wide Range ◽  
Selective Alkylation

A general protocol has been developed for the Markovnikov-selective intermolecular hydrofunctionalization based on visible-light-mediated Co/Ru dual catalysis. The key feature involves the photochemical oxidation of an organocobalt(III) intermediate derived from hydrogen atom transfer, which is supported by electrochemical analysis, quenching studies and stoichiometric experiments. This unique redox process enables the efficient branch-selective alkylation of pharmaceutically important nucleophiles (phenols, sulfonamides and various N-heterocycles) using a wide range of alkenes including moderately electron-deficient ones. Moreover, light-gated polar functionalization via organocobalt species was demonstrated.

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