scholarly journals Generation of non-stabilized alkyl radicals from thianthrenium salts for C–B and C–C bond formation

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Cheng Chen ◽  
Zheng-Jun Wang ◽  
Hongjian Lu ◽  
Yue Zhao ◽  
Zhuangzhi Shi
Keyword(s):  
Chemical Reactivity ◽  
Bond Formation ◽  
High Chemical ◽  
Alternative Source ◽  
Sulfonium Salts ◽  
Alkyl Radicals ◽  
Aryl Radicals ◽  
Efficient Construction ◽  
Electron Reduction ◽  
Positively Charged

AbstractSulfonium salts bearing a positively charged sulfur atom with three organic substituents have intrigued chemists for more than a century for their unusual structures and high chemical reactivity. These compounds are known to undergo facile single-electron reduction to emerge as a valuable and alternative source of aryl radicals for organic synthesis. However, the generation of non-stabilized alkyl radicals from sulfonium salts has been a challenge for several decades. Here we report the treatment of S-(alkyl) thianthrenium salts to generate non-stabilized alkyl radicals as key intermediates granting the controlled and selective outcome of the ensuing reactions under mild photoredox conditions. The value of these reagents has been demonstrated through the efficient construction of alkylboronates and other transformations, including heteroarylation, alkylation, alkenylation, and alkynylation. The developed method is practical, and provides the opportunity to convert C–OH bond to C–B and C–C bonds.

scholarly journals Free radicals in synthesis. Clean reagents affording oxidative or reductive termination

2000 ◽  
Vol 72 (7) ◽  
pp. 1327-1334 ◽  
Author(s):  
John A. Murphy
Keyword(s):  
Polar Group ◽  
Hypophosphorous Acid ◽  
Sulfonium Salts ◽  
Oxidative Functionalization ◽  
Radical Chemistry ◽  
Alkyl Radicals ◽  
Aryl Radicals ◽  
Tributyltin Hydride ◽  
Alkyl Bromides ◽  
By Products

Neurotoxic organotin reagents currently play a key role in radical chemistry. As a result, this is an important area for development of new clean replacement reactions. The pharmaceutical industry in particular has had to avoid use of radical methodology for the formation of carbon_carbon bonds for this reason. With the current dawn in green chemistry, a host of new clean radical methods is beginning to flourish. Our aim has been to develop new nontoxic methodology for carbon_carbon bond formation by radical chemistry, which would provide either reductive termination (giving a hydrogen atom to the ultimate radical, as happens with tributyltin hydride), or oxidative functionalization, installing a useful polar group at the site of the ultimate radical. Two methods for effecting radical reactions in an environmentally friendly way are presented: (i) The tetrathiafulvalene (TTF)-mediated radical-polar crossover reaction converts arenediazonium salts to aryl radicals, which have sufficient lifetime to cyclize onto alkenes—the resulting alkyl radicals couple with TTF+• to afford sulfonium salts which, in turn, undergo solvolysis to alcohols, ethers or amides. The method provides the key step in a synthesis of (±)-aspidospermidine. (ii) Hypophosphite salts and hypophosphorous acid, on the other hand, form C_C bonds with reductive termination. These economical reagents afford radicals efficiently, starting from aryl iodides, alkyl bromides, and alkyl iodides, and give very easy separation of products from by-products.

Visible-Light Photocatalytic Reduction of Sulfonium Salts as a Source of Aryl Radicals

2013 ◽  
Vol 355 (8) ◽  
pp. 1477-1482 ◽  
Author(s):  
Simon Donck ◽  
Abdulkader Baroudi ◽  
Louis Fensterbank ◽  
Jean-Philippe Goddard ◽  
Cyril Ollivier
Keyword(s):  
Visible Light ◽  
Photocatalytic Reduction ◽  
Sulfonium Salts ◽  
Aryl Radicals ◽  
Visible Light Photocatalytic

1.11 Generation of Radicals from Organoboranes

2021 ◽  
Author(s):  
E. André-Joyaux ◽  
L. Gnägi ◽  
C. Melendez ◽  
V. Soulard ◽  
P. Renaud
Keyword(s):  
Organic Synthesis ◽  
Coupling Reactions ◽  
Alkyl Radicals ◽  
Aryl Radicals ◽  
Cross Coupling Reactions ◽  
Oxidative Reactions ◽  
Radical Cascade ◽  
Cascade Processes ◽  
A Chain ◽  
Boronic Acid Derivatives

AbstractRadicals can be generated by the cleavage of the C—B bond of alkylboranes or boronic acid derivatives. The fragmentation process may result from a nucleohomolytic substitution process or from a redox process. The nucleohomolytic substitution is ideal for the generation of alkyl radicals and is usually part of a chain-reaction process. Redox processes (mainly oxidative reactions) have been used to generate both alkyl and aryl radicals. The use of stoichiometric oxidizing agents can be avoided by employing photoredox catalysis. A broad range of synthetic applications such as radical cascade processes, multicomponent reactions, and cross-coupling reactions in the presence of suitable metal catalysts are now possible. In their diversity, organoboron compounds represent one of the most general sources of radicals. The merging of radical chemistry with the classical chemistry of organoboron derivatives opens tremendous opportunities for applications in organic synthesis.

Iminyl-Radical-Triggered C–C Bond Cleavage of Cycloketone Oxime Derivatives: Generation of Distal Cyano-Substituted Alkyl Radicals and Their Functionalization

Synthesis ◽  
2020 ◽  
Vol 52 (11) ◽  
pp. 1585-1601 ◽  
Author(s):  
Tiebo Xiao ◽  
Lei Zhou ◽  
Hongtai Huang ◽  
Devireddy Anand
Keyword(s):  
Halogen Bond ◽  
Cyano Group ◽  
Bond Cleavage ◽  
Bond Formation ◽  
Radical Reaction ◽  
Building Blocks ◽  
Aromatic Rings ◽  
Organometallic Reagents ◽  
Alkyl Radicals ◽  
Oxime Derivatives

Alkyl nitriles are versatile building blocks in organic synthesis because the cyano group can be easily converted into other functional groups. Iminyl-radical-triggered C–C bond cleavage of cycloketone oxime­ derivatives provides a practical route to access distal cyano-substituted alkyl radicals, which has given chemists a new radical reaction platform for the synthesis of diverse alkyl nitriles. This review provides an overview of various types of radical cyanoalkylation via ring opening of cycloketone oxime derivatives.1 Introduction2 C–C Bond Formation2.1 Alkenes as Radical Acceptors2.2 Aromatic Rings as Radical Acceptors2.3 Organometallic Reagents as Radical Acceptors2.4 Cyanoalkyl-Radical-Triggered Cyclization Reactions2.5 Miscellaneous3 C–Heteroatom Bond Formation3.1 C–O Bond Formation3.2 C–N Bond Formation3.3 C–S Bond Formation3.4 C–Halogen Bond Formation3.5 C–B Bond Formation4 Conclusion

scholarly journals Alcohol-Initiated Dediazoniation of Aryldiazonium Ions to Aryl Radicals: A Simple and Efficient Route to Arylboronates

2018 ◽  
Vol 42 (9) ◽  
pp. 481-485
Author(s):  
Xiulian Zhang ◽  
Zhicheng Zhang ◽  
Yongbin Xie ◽  
Yujie Jiang ◽  
Ruibo Xu ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Bond Formation ◽  
Single Electron ◽  
Single Electron Transfer ◽  
Aryl Radical ◽  
Radical Species ◽  
Aryl Radicals ◽  
Efficient Access ◽  
Efficient Route ◽  
Operational Simplicity

A simple and efficient access to arylboronates was achieved with methanol-initiated borylation of aryldiazonium salts. Reduction of aryldiazonium ions by single electron transfer from methanol affords aryl radical species, which undergo a subsequent C–B bond formation with bis(pinacolato)diboron. This highly practical borylation process, which can be carried out on the gram-scale, enjoys operational simplicity as well as mild and catalyst-free conditions.

Transition-Metal-Free Catalysis for the Reductive ­Functionalization of CO2 with Amines

Synlett ◽  
2018 ◽  
Vol 29 (05) ◽  
pp. 548-555 ◽  
Author(s):  
Liang-Nian He ◽  
Xiao-Fang Liu ◽  
Xiao-Ya Li ◽  
Chang Qiao
Keyword(s):  
Transition Metal ◽  
Energy Content ◽  
Bond Formation ◽  
Energy Storage Materials ◽  
One Pot ◽  
Metal Free ◽  
Recent Developments ◽  
Electron Reduction ◽  
Reduction Of Co2 ◽  
Hierarchical Reduction

Reductive functionalization of CO2 with amines and a reductant, which combines both reduction of CO2 and C–N bond formation in one pot to produce versatile chemicals and energy-storage materials such as formamides, aminals, and methylamines that are usually derived from petroleum feedstock, would be appealing and promising. Herein, we give a brief review on recent developments in the titled CO2 chemistry by employing transition-metal-free catalysis, which can be catalogued as below according to the diversified energy content of the products, that is formamides, aminals, and methylamines being consistent with 2-, 4-, and 6-electron reduction of CO2, respectively. Notably, hierarchical reduction of CO2 with amines to afford at least two products, for example, formamides and methylamines, could be realized with the same catalyst through tuning the hydrosilane type, reaction temperature, or CO2 pressure. Finally, the opportunities and challenges of the reductive functionalization of CO2 with amines are also highlighted.1 Introduction2 2-Electron Reduction of CO2 to Formamide3 6-Electron Reduction of CO2 to Methylamine4 4-Electron Reduction of CO2 to Aminal5 Hierarchical Reduction of CO2 with Amines6 Conclusion

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