Microwave‐Assisted Free Radical Chemistry Using the Persistent Radical Effect.

Wetter, Christian; Studer, Armido

doi:10.1002/chin.200419134

Cited by 3 publications

(3 citation statements)

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“…Later, the synthesis was improved by ionic Horner–Wadsworth–Emmons-type olefination reaction under microwave (MW)-induced heating to generate α, β-unsaturated oxindoles. Interestingly, using MW irradiation, a 430-fold acceleration was achieved upon switching from classical heating to MW-induced heating . Later on, steric effects in the nitroxide moiety on the outcome of the PRE-mediated radical alkoxyamine isomerization and intermolecular addition reaction were demonstrated …”

Section: Tempo In Chemical Transformationmentioning

confidence: 99%

TEMPO in Chemical Transformations: From Homogeneous to Heterogeneous

et al. 2019

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The organic nitroxyl radical, TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl), finds a variety of industrial applications for chemical transformations. Because of economic and environmental concerns, the recovery and reuse of TEMPO with maintained high activity are of the utmost importance. In this Review, we summarize the most important advances made by the scientific community in TEMPO immobilization on various organic and inorganic support materials for recovery and reuse, and we discuss the activity and stability, as well as the procedures. Also summarized is the wide range of applications of TEMPO in both homogeneous and heterogeneous forms in chemical transformations, beginning from methodology tuning in synthetic chemistry to the use in polymer chemistry.

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Section: Tempo In Chemical Transformationmentioning

confidence: 99%

TEMPO in Chemical Transformations: From Homogeneous to Heterogeneous

et al. 2019

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“…1 ) 28 29 . However, if a persistent radical and a transient radical simultaneously exist in one reaction system, selective cross-coupling would probably occur according to the persistent radical effect 30 31 . As we know, radical species could be affected through some patterns by transition metals 32 33 , which can catalyze radical reaction 34 .…”

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confidence: 99%

Tuning the Reactivity of Radical through a Triplet Diradical Cu(II) Intermediate in Radical Oxidative Cross-Coupling

Zhou

Zhu

et al. 2015

Sci Rep

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Highly selective radical/radical cross-coupling is paid more attention in bond formations. However, due to their intrinsic active properties, radical species are apt to achieve homo-coupling instead of cross-coupling, which makes the selective cross-coupling as a great challenge and almost untouched. Herein a notable strategy to accomplish direct radical/radical oxidative cross-coupling has been demonstrated, that is metal tuning a transient radical to a persistent radical intermediate followed by coupling with another transient radical. Here, a transient nitrogen-centered radical is tuned to a persistent radical complex by copper catalyst, followed by coupling with a transient allylic carbon-centered radical. Firstly, nitrogen-centered radical generated from N-methoxybenzamide stabilized by copper catalyst was successfully observed by EPR. Then DFT calculations revealed that a triplet diradical Cu(II) complex formed from the chelation N-methoxybenzamide nitrogen-centered radical to Cu(II) is a persistent radical species. Moreover, conceivable nitrogen-centered radical Cu(II) complex was observed by high-resolution electrospray ionization mass spectrometry (ESI-MS). Ultimately, various allylic amides derivatives were obtained in good yields by adopting this strategy, which might inspire a novel and promising landscape in radical chemistry.

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“… Around the same time our group disclosed the intermolecular reaction of TEMPO–malonates with alkenes via malonyl radical addition to alkenes and subsequent trapping with TEMPO . Later it was found that such thermal alkoxyamine addition or isomerization reactions can be conveniently conducted under microwave conditions or in a flow reaction set up or be combined with a Tsuji–Trost allylation . In addition, this formal C–O bond insertion of an alkene was also applied to chemically modify surfaces or to functionalize polymers. , Gigmes and co-workers generated secondary α-carbonyl radicals from the corresponding alkoxyamines and radical addition reactions leading to monocyclic, bicyclic, spirocyclic, and 8-membered lactones and lactams …”

Section: Nitroxides In Free-radical Chemistrymentioning

confidence: 99%

Organic Synthesis Using Nitroxides

Leifert

Studer

2023

Chem. Rev.

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Nitroxides, also known as nitroxyl radicals, are long-lived or stable radicals with the general structure R 1 R 2 N−O • . The spin distribution over the nitroxide N and O atoms contributes to the thermodynamic stability of these radicals. The presence of bulky N-substituents R 1 and R 2 prevents nitroxide radical dimerization, ensuring their kinetic stability. Despite their reactivity toward various transient C radicals, some nitroxides can be easily stored under air at room temperature. Furthermore, nitroxides can be oxidized to oxoammonium salts (R 1 R 2 N�O + ) or reduced to anions (R 1 R 2 N−O − ), enabling them to act as valuable oxidants or reductants depending on their oxidation state. Therefore, they exhibit interesting reactivity across all three oxidation states. Due to these fascinating properties, nitroxides find extensive applications in diverse fields such as biochemistry, medicinal chemistry, materials science, and organic synthesis. This review focuses on the versatile applications of nitroxides in organic synthesis. For their use in other important fields, we will refer to several review articles. The introductory part provides a brief overview of the history of nitroxide chemistry. Subsequently, the key methods for preparing nitroxides are discussed, followed by an examination of their structural diversity and physical properties. The main portion of this review is dedicated to oxidation reactions, wherein parent nitroxides or their corresponding oxoammonium salts serve as active species. It will be demonstrated that various functional groups (such as alcohols, amines, enolates, and alkanes among others) can be efficiently oxidized. These oxidations can be carried out using nitroxides as catalysts in combination with various stoichiometric terminal oxidants. By reducing nitroxides to their corresponding anions, they become effective reducing reagents with intriguing applications in organic synthesis. Nitroxides possess the ability to selectively react with transient radicals, making them useful for terminating radical cascade reactions by forming alkoxyamines. Depending on their structure, alkoxyamines exhibit weak C−O bonds, allowing for the thermal generation of C radicals through reversible C−O bond cleavage. Such thermally generated C radicals can participate in various radical transformations, as discussed toward the end of this review. Furthermore, the application of this strategy in natural product synthesis will be presented.

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Microwave‐Assisted Free Radical Chemistry Using the Persistent Radical Effect.

Abstract: For Abstract see ChemInform Abstract in Full Text.

Cited by 3 publications

References 1 publication

TEMPO in Chemical Transformations: From Homogeneous to Heterogeneous

TEMPO in Chemical Transformations: From Homogeneous to Heterogeneous

Tuning the Reactivity of Radical through a Triplet Diradical Cu(II) Intermediate in Radical Oxidative Cross-Coupling

Organic Synthesis Using Nitroxides

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