Reactivity of phthalimide-N-oxyl : A kinetic study.

Ueda, Chihiro; Noyama, Masahito; Ohmori, Hidenobu; Masui, Masaichiro

doi:10.1248/cpb.35.1372

Cited by 121 publications

(144 citation statements)

References 2 publications

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“…[6] Further support for the ionic mechanism of Scheme 2 has been sought, as opposed to the electron transfer (ET) route suggested for the laccase/ABTS system, [4,15Ϫ17] or for the radical H-abstraction (HAT) route suggested for the laccase/HBT and laccase/HPI systems [ABTS: 2,2Ј-azinobis(3-ethylbenzothiazoline-6-sulfonic acid); HBT: 1-hydroxybenzotriazole; HPI: N-hydroxyphthalimide]. [5,7,18,19] Oxidation of 4-MeO-benzyl alcohol (1) and 1-(4-MeO-phenyl)ethanol (3) in a competition experiment with the laccase/TEMPO system (Table 1) [7] afforded the carbonylic products 2 and 4, the relative amounts of which allowed for calculation of the relative reactivity of oxidation of a primary (1) vs. a secondary (3) benzylic alcohol. The k 1 /k 3 ratio obtained (i.e., 0.7) is consistent with the slightly higher nucleophilicity of a secondary vs. primary alcohol, [20] thereby supporting the theory of a nucleophilic attack of the alcohol onto the oxoammonium ion (Scheme 2).…”

Section: Substrate Reactivitymentioning

confidence: 99%

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A Mechanistic Survey of the Oxidation of Alcohols and Ethers with the Enzyme Laccase and Its Mediation by TEMPO

et al. 2002

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The oxidation of alcohols and ethers by O2 with the enzyme laccase, mediated by the stable N‐oxyl radical TEMPO, affords carbonylic products. An ionic mechanism is proposed, where a nucleophilic attack of the oxygen lone‐pair of the alcohol (or ether) onto the oxoammonium form of TEMPO (generated by laccase on oxidation) takes place leading to a transient adduct. Subsequent deprotonation of this adduct α to the C−O bond leads to the carbonylic product. Additional mechanistic considerations for the laccase‐mediated oxidation of ethers and thioethers are offered. The proposed mechanism is supported by: (i) investigating the inter‐ and intramolecular selectivity of oxidation with appropriate substrates, (ii) thermochemical considerations, and (iii) attempting a Hammett correlation for the oxidation of a series of 4‐X‐substituted benzyl alcohols, wherein a shift of the rate‐determining step as a function of the 4‐X‐substituent results. Based on the above points, the lack of mediation efficiency of another stable N‐oxyl radical (viz., IND‐O·) can be explained. (© Wiley‐VCH Verlag GmbH & Co KGaA, 69451 Weinheim, Germany, 2002)

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Section: Substrate Reactivitymentioning

confidence: 99%

“…In 4-(methylthio)benzyl alcohol (17), the laccase/TEMPO system could, in principle, oxidise either the alcohol or the thioether group of the substrate. Only the former was oxidised, as 4-(methylthio)benzaldehyde (18) was the unique product. Analogously, 9-hydroxyxanthene (19; viz.…”

Section: Substrate Selectivitymentioning

confidence: 99%

A Mechanistic Survey of the Oxidation of Alcohols and Ethers with the Enzyme Laccase and Its Mediation by TEMPO

et al. 2002

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“…We found that substituting the methoxy group with more electron-deficient 2,2,2-trifluoroethoxy (6) or acetophenone (9) moieties led to improved yields of 45% and 39%, respectively (entries 3, 4). 7-Trifluoromethyl-and 4,5,6,7-tetrafluoro-substituted precatalysts 20 and 34 also afforded improved yields (entries 2 vs. 5,8), probably on account of their increased electron-withdrawing properties. Whereas the combination of the 7-trifluoromethyl and the acetophenone moieties in 28 proved to be mismatched (entries 4 vs. 7), the combination of a 7-trifluoromethyl substitution pattern with a 2,2,2-trifluoroethoxy group (21) displayed an additive effect, resulting in the formation of ketone 37a in 66% yield (entries 3, 5 vs. 6).…”

Section: Radical Catalystsmentioning

confidence: 98%

“…poor solubility in common organic solvents and rapid autodecomposition. 8,9) Introducing substituents at the aromatic ring of 1 has been reported to enhance its solubility and stability (Fig. 1).…”

Section: 4)mentioning

confidence: 99%

“…2-Hydroxy-3-(2,2,2-trif luoroethoxy)-3-trif luoromethy lisoindolin-1-one (6) According to the procedure B, benzyl ether 4 (1.45 g, 3.58 mmol) was converted into 6 (1.07 g, 95%). White powder; 2-Benzyloxy-3-(2-oxo-2-phenylethyl)-3-trif luoromethy lisoindolin-1-one (8) To a suspension of AgOTf (437 mg, 1.70 mmol) in toluene (1.0 mL), chloride 2 (342 mg, 1.00 mmol), Et 3 N (279 µL, 2.00 mmol) and [(1-phenyl-1-ethenyl) oxy] trimethylsilane (7) (385 mg, 2.00 mmol) in toluene (1.0 mL) were added at 0°C. The reaction mixture was stirred for 1 h at 0°C, and for 35 h at rt.…”

Section: General Procedures For Hydrogenolysis Of Benzyl Ether (Procedmentioning

confidence: 99%

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Enhanced Structural Variety of Nonplanar <i>N</i>-Oxyl Radical Catalysts and Their Application to the Aerobic Oxidation of Benzylic C–H Bonds

Kadoh

Oisaki

Kanai

2016

CHEMICAL & PHARMACEUTICAL BULLETIN

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The design and synthesis of structurally variable, nonplanar N-oxyl radical catalysts and their application to the aerobic oxidation, etherification, and acetoamidation of benzylic C-H bonds are described. The catalytic oxidation of C-H bonds represents a powerful tool to synthesize oxygenated functional molecules from simple hydrocarbons in a straightforward way. Electron-deficient N-oxyl radical catalysts, such as phthalimidoyl N-oxyl (PINO) radical, generated from N-hydroxyphthalimide (1), have attracted much attention because of their applications in the oxidation of C-H bonds with high bond dissociation energy (BDE). However, a few sites in 1 are available for structural modifications and improvements of the catalytic performance. By replacing one carbonyl group in 1 with a trifluoromethyl (CF 3 )-substituted sp 3 -carbon, we generated an additional tunable site and a nonplanar backbone, while retaining the desirable electronwithdrawing properties and increasing the lipophilicity with respect to 1. We synthesized a variety of Nhydroxy pre catalysts containing such a CF 3 moiety, and investigated their utility in the aerobic oxidation of benzylic C-H bonds. Precatalysts with electron-withdrawing substituents, such as trifluoroethoxy and the acetophenone moieties, afforded higher yields than a corresponding methoxy-substituted analogue. The introduction of substituents at the aromatic ring was also effective, as evident from the performance of 7-CF 3 and 4,5,6,7-tetrafluoro precatalysts. Especially the combination of trifluoroethoxy-and 4,5,6,7-tetrafluoro substitution afforded a superior performance. These catalyst systems exhibited high functional group tolerance during the aerobic oxidation of C-H bonds, and benzylic etherification and Ritter-type reactions could be carried out at room temperature when a selected precatalyst and N-bromosuccinimide (NBS) were used.

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Electrochemistry of Hydroxylamines, Oximes and Hydroxamic Acids

Onomura

2010

Patai's Chemistry of Functional Groups

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Reactivity of phthalimide-N-oxyl : A kinetic study.

Cited by 121 publications

References 2 publications

A Mechanistic Survey of the Oxidation of Alcohols and Ethers with the Enzyme Laccase and Its Mediation by TEMPO

A Mechanistic Survey of the Oxidation of Alcohols and Ethers with the Enzyme Laccase and Its Mediation by TEMPO

Enhanced Structural Variety of Nonplanar <i>N</i>-Oxyl Radical Catalysts and Their Application to the Aerobic Oxidation of Benzylic C–H Bonds

Electrochemistry of Hydroxylamines, Oximes and Hydroxamic Acids

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