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.

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.

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

scholarly journals Copper-catalyzed direct alkylation of heteroarenes

2017 ◽  
Vol 8 (5) ◽  
pp. 3465-3470 ◽  
Author(s):  
Cédric Theunissen ◽  
Jianjun Wang ◽  
Gwilherm Evano
Keyword(s):  
Alkyl Radicals ◽  
Alkyl Bromides ◽  
Tertiary Alkyl

An efficient and broadly applicable process is reported for the direct alkylation of heteroarene C–H bonds, based on the copper-catalyzed addition of alkyl radicals generated from activated secondary and tertiary alkyl bromides to a range of arenes, and their benzo-fused derivatives.

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.

Irradiation-Induced Palladium-Catalyzed Direct C–H Alkylation of Heteroarenes with Tertiary and Secondary Alkyl Bromides

Synthesis ◽  
2018 ◽  
Vol 50 (15) ◽  
pp. 2908-2914 ◽  
Author(s):  
Rui Shang ◽  
Yao Fu ◽  
Guang-Zu Wang
Keyword(s):  
Blue Light ◽  
Palladium Catalyst ◽  
Light Emitting Diodes ◽  
Oxidative Addition ◽  
Phosphine Ligands ◽  
Light Emitting ◽  
Alkyl Radicals ◽  
Alkyl Bromides ◽  
Palladium Catalyzed ◽  
Tertiary Alkyl

A palladium catalyst in combination with two types of phosphine ligands efficiently catalyzes direct C–H alkylation of heteroarenes with secondary and tertiary alkyl bromides under irradiation conditions. Irradiation of blue light-emitting diodes (blue LEDs) effectively excites phosphine-ligated palladium catalyst to facilitate oxidative addition with alkyl bromides, and also excites the alkylpalladium species to enable the generation of alkyl radicals to react with heteroarenes.

Intramolecular Homolytic Displacement. XXIII. Selectivity in the Induced Decomposition of Ethyl t-Butylperoxymethylpropenoate by Radicals Formed From Methyl Propanoate and Derivatives

1995 ◽  
Vol 48 (2) ◽  
pp. 233 ◽  
Author(s):  
M Degueilcastaing ◽  
C Navarro ◽  
F Ramon ◽  
B Maillard
Keyword(s):  
Thermal Decomposition ◽  
Double Bond ◽  
Iodine Atom ◽  
Hydrogen Abstraction ◽  
Alkyl Iodide ◽  
Alkyl Radicals ◽  
Tributyltin Hydride ◽  
Induced Decomposition ◽  
Derivatives Of ◽  
Methyl Propanoate

Thermal decomposition of t-butyl peracetate in a solution of ethyl t- butylperoxymethylpropenoate in methyl propanoate led to the products of substitution of the three different hydrogens in the molecule of the methyl ester by the 2,3-epoxy-2-ethoxycarbonylpropyl group. An SHi reaction on the peroxide function, following the addition to the double bond, is responsible for the formation of these epoxides . Such a result is due to the low regioselectivity of the hydrogen abstraction from methyl propanoate by t- butoxyl radicals, and no improvement could be obtained by changing the relative ratios of the reactants, in converse to previous results described for similar reactions. Thus, selective creation of alkyl radicals was developed through the generation of tributylstannyl radicals as mediator radicals, by reaction of t- butoxyl radicals on tributyltin hydride or hexabutylditin ; the mediator radicals abstract an iodine atom from the alkyl iodide. Application of this methodology to the three iodo derivatives of methyl propanoate permitted us to obtain selectively each of the three epoxides.

scholarly journals Reduction of arenediazonium salts by tetrakis(dimethylamino)ethylene (TDAE): Efficient formation of products derived from aryl radicals

2009 ◽  
Vol 5 ◽  
Author(s):  
Mohan Mahesh ◽  
John A Murphy ◽  
Franck LeStrat ◽  
Hans Peter Wessel
Keyword(s):  
Electron Transfer ◽  
Radical Cyclizations ◽  
Single Electron Transfer ◽  
Aryl Radical ◽  
Relative Ease ◽  
Aryl Radicals ◽  
Radical Intermediates ◽  
Arenediazonium Salts ◽  
First Time ◽  
By Products

Tetrakis(dimethylamino)ethylene (TDAE 1), has been exploited for the first time as a mild reagent for the reduction of arenediazonium salts to aryl radical intermediates through a single electron transfer (SET) pathway. Cyclization of the aryl radicals produced in this way led, in appropriate substrates, to syntheses of indolines and indoles. Cascade radical cyclizations of aryl radicals derived from arenediazonium salts are also reported. The relative ease of removal of the oxidized by-products of TDAE from the reaction mixture makes the methodology synthetically attractive.

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