scholarly journals Visible-light-induced addition of carboxymethanide to styrene from monochloroacetic acid

2020 ◽  
Vol 16 ◽  
pp. 398-408
Author(s):  
Kaj M van Vliet ◽  
Nicole S van Leeuwen ◽  
Albert M Brouwer ◽  
Bas de Bruin
Keyword(s):  
Nucleophilic Substitution ◽  
Monochloroacetic Acid ◽  
Reductive Activation ◽  
Radical Species ◽  
Radical Intermediates ◽  
Nonpolar Solvents ◽  
Electron Reduction ◽  
Reaction Works ◽  
Chlorine Bond ◽  
Full Conversion

Where monochloroacetic acid is widely used as a starting material for the synthesis of relevant groups of compounds, many of these synthetic procedures are based on nucleophilic substitution of the carbon chlorine bond. Oxidative or reductive activation of monochloroacetic acid results in radical intermediates, leading to reactivity different from the traditional reactivity of this compound. Here, we investigated the possibility of applying monochloroacetic acid as a substrate for photoredox catalysis with styrene to directly produce γ-phenyl-γ-butyrolactone. Instead of using nucleophilic substitution, we cleaved the carbon chlorine bond by single-electron reduction, creating a radical species. We observed that the reaction works best in nonpolar solvents. The reaction does not go to full conversion, but selectively forms γ-phenyl-γ-butyrolactone and 4-chloro-4-phenylbutanoic acid. Over time the catalyst precipitates from solution (perhaps in a decomposed form in case of fac-[Ir(ppy)3]), which was proven by mass spectrometry and EPR spectroscopy for one of the catalysts (N,N-5,10-di(2-naphthalene)-5,10-dihydrophenazine) used in this work. The generation of HCl resulting from lactone formation could be an additional problem for organometallic photoredox catalysts used in this reaction. In an attempt to trap one of the radical intermediates with TEMPO, we observed a compound indicating the generation of a chloromethyl radical.

Application of α-Amino Radicals as the Reaction Activators

Synthesis ◽  
2021 ◽  
Author(s):  
Yong-liang Su ◽  
Michael P. Doyle
Keyword(s):  
Halogen Atom ◽  
Building Blocks ◽  
Short Review ◽  
Single Electron ◽  
Radical Species ◽  
Sulfonium Salts ◽  
Radical Intermediates ◽  
Organic Halides

α-Aminoalkyl radicals are easily accessible through multiple pathways from various precursors. Apart from their utilization as N-containing building blocks, they have recently been used as halogen atom abstraction reagents or single-electron reductants to transform organic halides or sulfonium salts to their corresponding highly reactive radical species. Benefiting from the richness of various halides and the diverse reactivity of radical intermediates, new transformations of halides and sulfonium salts have been developed. This short review summarizes this emerging chemistry that uses α-amino radicals as the reaction activators.

scholarly journals Oxidative Generation of Boron-Centered Radicals in Carboranes

2019 ◽  
Author(s):  
Harrison A. Mills ◽  
Joshua Martin ◽  
Arnold L. Rheingold ◽  
Alexander Spokoyny
Keyword(s):  
Direct Oxidation ◽  
Radical Species ◽  
Boron Cluster ◽  
Radical Intermediates ◽  
Substitution Chemistry ◽  
Indirect Observation ◽  
Electronic Environments ◽  
Oxidative Generation

<div><div><div><p>We report the first indirect observation and use of boron vertex-centered carboranyl radicals generated by the oxidation of modified carboranyl precursors. These radical intermediates are formed by the direct oxidation of a B−B bond between a boron cluster cage and an exopolyhedral boron-based substituent (e.g., −BF3K, −B(OH)2). The in situ generated radical species are shown to be competent substrates in reactions with oxygen-based radicals, dichalcogenides, and N-heterocycles, yielding the corresponding substituted carboranes containing B−O, B−S, B−Se, B−Te, and B−C bonds. Remarkably, this chemistry tolerates various electronic environments, providing access to facile substitution chemistry at both electron-rich and electron-poor B−H vertices in carboranes.</p></div></div></div>

scholarly journals Enzymatic single-electron reduction and aerobic cytotoxicity of tirapazamine and its 1-oxide and nor-oxide metabolites

Chemija ◽  
2018 ◽  
Vol 29 (4) ◽  
Author(s):  
Jonas Šarlauskas ◽  
Aušra Nemeikaitė-Čėnienė ◽  
Audronė Marozienė ◽  
Lina Misevičienė ◽  
Mindaugas Lesanavičius ◽  
...  
Keyword(s):  
Side Effects ◽  
Anticancer Agent ◽  
Redox Cycling ◽  
Nitroaromatic Compounds ◽  
Single Electron ◽  
Reductive Activation ◽  
Cell Nuclei ◽  
Electron Reduction ◽  
Phenylene Diamine

Aerobic cytotoxicity of 3-amino-1,2,4-benzotriazine-1,4-dioxide (tirapazamine, TPZ), a bioreductively activated hypoxia-specific anticancer agent, is responsible for TPZ side effects in chemotherapy. In order to clarify its mechanisms, we examined the aerobic cytotoxicity of TPZ and its main metabolites, 3-amino-1,2,4-benzotriazine-1-oxide and 3-amino-1,2,4-benzotriazine in murine hepatoma MH22a cells, and their reduction by NADPH:cytochrome P-450 reductase (P-450R) and ferredoxin:NADP+ reductase (FNR). Analogous studies of several quinones and nitroaromatic compounds with similar values of single-electron reduction midpoint potentials (E17) were carried out. In single-electron reduction by P-450R and FNR, the reactivity of TPZ and its monoxide was similar to that of quinones and nitroaromatics, and increased with an increase in their E17. The cytotoxicity of TPZ and its metabolites possessed a prooxidant character, because it was partly prevented by an antioxidant N,N’-diphenyl-p-phenylene diamine and desferrioxamine, and potentiated by 1,3-bis(2-chloroethyl)-1-nitrosourea. Importantly, the cytotoxicity of TPZ and, possibly, its 1-N-oxide, was much higher than that of quinones and nitroaromatics with similar values of E17 and redox cycling activities. A possible additional factor in the aerobic cytotoxicity of TPZ is its reductive activation in oxygen-poor cell nuclei, leading to the formation of DNA-damaging species similar to those forming under hypoxia.

1.10 Boron-Centered Radicals

2021 ◽  
Author(s):  
F.-L. Zhang ◽  
Y.-F. Wang
Keyword(s):  
Organic Synthesis ◽  
Bond Formation ◽  
Radical Species ◽  
Reduction Reactions ◽  
Radical Intermediates ◽  
Radical Catalysis ◽  
Bond Formation Reactions

AbstractBoryl radicals have emerged as powerful radical intermediates in organic synthesis. This review summarizes recently developed transformations involving boryl radical species, including C—B bond formation reactions, reduction reactions, and radical catalysis.

EPR spin trapping evidence of radical intermediates in the photo-reduction of bicarbonate/CO2 in TiO2 aqueous suspensions

2015 ◽  
Vol 14 (5) ◽  
pp. 1039-1046 ◽  
Author(s):  
Alessandra Molinari ◽  
Luca Samiolo ◽  
Rossano Amadelli
Keyword(s):  
Spin Trapping ◽  
Reaction Intermediates ◽  
Reductive Activation ◽  
Radical Intermediates ◽  
Aqueous Suspensions ◽  
Epr Spin Trapping

Storage of CO2 as carbonates is a strategy for its reductive activation. Carbonates are reduced at pH 5.5–7.5 with photoexcited TiO2. EPR is convenient for detecting reaction intermediates.

Electron transfer mechanism of aromatic 'nucleophilic' substitution

1972 ◽  
Vol 25 (10) ◽  
pp. 2133 ◽  
Author(s):  
PR Singh ◽  
R Kumar
Keyword(s):  
Electron Transfer ◽  
Nucleophilic Substitution ◽  
Potassium Iodide ◽  
Transfer Mechanism ◽  
Salt Solutions ◽  
Aromatic Nucleophilic Substitution ◽  
Electron Transfer Mechanism ◽  
Heterolytic Cleavage ◽  
Radical Intermediates ◽  
Photochemical Catalysis

Mechanistic implications of the ready formation of aryl iodides from aryldiazonium salt solutions and the iodide ion (in contrast with the general need for cuprous or other catalysts with other halides) have been studied. The reaction between benzenediazonium fluoroborate and potassium iodide in methanol at 0�C has been investigated. A new mechanism involving initial one-electron transfer from the iodide anion to the benzenediazonium cation, resulting in the formation of radical intermediates by heterolytic cleavage of a bond, has been proposed in order to account for the products, viz. iodobenzene, benzene, biphenyl, iodine, anisole, and formaldehyde, and the effect of photochemical catalysis.

scholarly journals Reverse Polarity Reductive Functionalization of Tertiary Amides via a Dual Iridium Catalyzed Hydrosilylation & SET Strategy

2020 ◽  
Author(s):  
Tatiana Rogova ◽  
Pablo Gabriel ◽  
Stamatia Zavitsanou ◽  
Jamie Leitch ◽  
Fernanda Duarte ◽  
...  
Keyword(s):  
Active Pharmaceutical Ingredient ◽  
Building Blocks ◽  
Chemical System ◽  
Secondary Amide ◽  
Reductive Activation ◽  
Tertiary Amide ◽  
New Strategy ◽  
Tandem Process ◽  
Electron Reduction ◽  
Tertiary Amides

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.

Production of radical species and modification of DNA through one-electron reduction with indium metal

2007 ◽  
Vol 48 (18) ◽  
pp. 3167-3169 ◽  
Author(s):  
Kazuo Tanaka ◽  
Taku Kamei ◽  
Akimitsu Okamoto
Keyword(s):  
Radical Species ◽  
Indium Metal ◽  
Electron Reduction
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