An efficient and practical aerobic oxidation of benzylic methylenes by recyclable <i>N</i>-hydroxyimide

Wang, Jian; Zhang, Cheng; Ye, Xiaoqing; Du, Wenting; Zeng, Shenxin; Xu, Jie; Yin, Hong

doi:10.1039/d0ra10475b

Cited by 9 publications

(5 citation statements)

References 59 publications

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“…In the present work we provide a robust exhibition of this approach by comparing a previously dismissed ,, HAT catalyst, succinimide- N -oxyl (SINO), to PINO. The current understanding is that SINO is an inferior HAT mediator compared to PINO, ,, ascribed mostly to a “likely” lower stability. , Consequently, the use of the NHS/SINO redox couple in reaction development has been seldom reported. − We demonstrate that SINO has higher activity than PINO when assessed appropriately, and as such, could be an attractive alternative in the context of HAT catalysis. On one hand, the succinimide species can be easily prepared via Diels–Alder reactions between maleic anhydride and a variety of dienes, providing an open-ended opportunity for catalyst design.…”

Section: Introductionmentioning

confidence: 83%

Revisiting the Reactivity of the Dismissed Hydrogen Atom Transfer Catalyst Succinimide-N-oxyl

Yang,

Farmer,

Pratt

et al. 2024

J. Am. Chem. Soc.

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Phthalimide-N-oxyl (PINO) and related radicals are promising catalysts for C−H functionalization reactions. To date, only a small number of N-oxyl derivatives have demonstrated improved activities over PINO. We postulate that the lack of success in identifying superior catalysts is associated not only with challenges in the design and synthesis of new structures, but also the way catalysts are evaluated and utilized. Catalyst evaluation typically relies on the use of chemical oxidants to generate N-oxyl radicals from their parent N-hydroxy compounds. Herein we provide an example where a potential-controlled electrochemical analysis reveals that succinimide-N-oxyl (SINO) compares favorably to PINO as a hydrogen atom transfer (HAT) catalyst−in contrast to previous claims based on other approaches. Our efforts to understand the basis for the greater reactivity of SINO relative to PINO have underscored that the HAT kinetics are significantly influenced by factors beyond changes in thermodynamics. This is perhaps best illustrated by the similar reactivity of tetrachloro-PINO and SINO despite the latter engaging in substantially more exergonic reactions. The key role of HAT transition state (TS) polarization prompted the design and initial characterization of a chlorinated SINO derivative, which we found to be the most reactive N-oxyl HAT catalyst reported to date.

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Section: Introductionmentioning

confidence: 83%

Revisiting the Reactivity of the Dismissed Hydrogen Atom Transfer Catalyst Succinimide-N-oxyl

Yang,

Farmer,

Pratt

et al. 2024

J. Am. Chem. Soc.

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“…As mentioned for the benzylic and allylic oxidation using oxygen as terminal oxidant (Scheme a), different conditions were reported (without initiator) , and also different metal-based , initiators or cocatalysts such as Co(acac) 2 , Mn(acac) 2 , Cu(acac) 2 , − Co(OAc) 2 , , CoCl 2 , cobalt zeolitic imidazolate framework ZIF-67, SiO 2 /Al 2 O 3 -supported cobalt or manganese, [WZn{Co(H 2 O)} 2 (ZnW 9 O 34 ) 2 ] 12– , CuCl, , CuCl 2 , NaCr 2 O 7 , Fe(NO 3 ) 3 , Fe(acac) 3 /phenanthroline, Fe(BF 4 ) 2 /KHB(Ar) 3 , hemin, nonheme iron(IV)–oxo complexes, horseradish peroxidase/H 2 O 2 , Fe(NO 3 ) 3 , α-Fe 2 O 3 / h ν, , Rh 2 (esp) 2 , cerium oxide-modified CuFe 2 O 4 , and vanadium(IV) complexes were used. In addition, transition-metal-free processes have been developed applying electrochemistry, − using excitation of ketones, , naphthalene imides, a dicyanopyrazine-derived chromophore, and graphitic carbon nitride or other (radical) starters such as azobis(isobutyronitrile) (AIBN), − 2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70), peroxides, acridine yellow/Br 2 , tert -butyl nitrite, , dimethylglyoxime, acetaldehyde, and sodium periodate .…”

Section: Oxidation Reactionsmentioning

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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“…The following three points could be summarized from relevant literatures for the synthesis of 1-tetralone. 1) the synthetic routes to 1-tetralone are still limited, mainly focus on intramolecular Friedel-Crafts reaction [12][13][14]; 2) In general, most 1-tetralones are synthesized through the oxidation reaction of corresponding tetralin derivatives, by directly reacting with oxidants such as PCC or indirectly reacting with oxygen in the presence of catalyst, such as Cr, Cu, Mn, Ru [15][16][17]; 3)1-tetralones could also be yielded from tetralinol via oxidation reaction [18][19][20].…”

Section: Synthesis Strategy Of Tetralonesmentioning

confidence: 99%

Research progress in pharmacological activities and structure-activity relationships of tetralone scaffolds as pharmacophore and fluorescent skeleton

Sheng

Song

Fan

et al. 2022

European Journal of Medicinal Chemistry

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An efficient and practical aerobic oxidation of benzylic methylenes by recyclable N-hydroxyimide

Abstract: An efficient and practical benzylic aerobic oxidation catalyzed by cheap and simple N-hydroxyimide organocatalyst has been achieved with high yields and broad substrate scope.

Cited by 9 publications

References 59 publications

Revisiting the Reactivity of the Dismissed Hydrogen Atom Transfer Catalyst Succinimide-N-oxyl

Revisiting the Reactivity of the Dismissed Hydrogen Atom Transfer Catalyst Succinimide-N-oxyl

Organic Synthesis Using Nitroxides

Research progress in pharmacological activities and structure-activity relationships of tetralone scaffolds as pharmacophore and fluorescent skeleton

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