The Only Stable Organic Sigma Radicals: Di‐
            <i>tert</i>
            ‐Alkyliminoxyls

Ingold, K. U.

doi:10.1002/9780470666975.ch6

Cited by 12 publications

(27 citation statements)

References 33 publications

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“…Most of the iminoxyl radicals with alkyl and aryl substituents at the carbon atom, except for the di-tert-butyliminoxyl radical, [99,100,[104][105][106] are unstable at room temperature even in solutions. [98,102,106] It is necessary to use flow techniques [98] or generate radicals by irradiation of the sample in the cavity of the spectrometer [102] in order to detect these radicals by ESR spectroscopy.…”

Section: Resultsmentioning

confidence: 99%

“…[98][99][100][101][102][103] However, only a few reactions with oxime (iminoxyl) radicals were described in the literature. The synthetic application of these radicals has long been limited to reactions of the stable di-tert-butyliminoxyl radical: [99,100] the oxidation of amines to imines, [104] the oxidative addition to phenols, [105] and the replacement of allylic hydrogen in cyclohexene. [106] First selective reactions involving unstable iminoxyl radicals generated in situ were realized only recently: the intramolecular hydrogen atom abstraction by oxime radical followed by cyclization [107] and the intramolecular addition to the C=C double bond [108] were performed.…”

Section: Introductionmentioning

confidence: 99%

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Iminoxyl Radical‐Based Strategy for Intermolecular CO Bond Formation: Cross‐Dehydrogenative Coupling of 1,3‐Dicarbonyl Compounds with Oximes

et al. 2014

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Cross-dehydrogenative C À O coupling of 1,3-diketones and 1,3-keto esters with oximes was realized for the first time. The reaction proceeds in the presence of the oxidants [KMnO 4 , /KMnO 4 ] system; yields are 27-92%. The synthesis can be easily scaled up to gram quantities of the target products. Appa-rently, the reaction proceeds via a radical mechanism in which the oxidizing agent serves to generate radicals from oximes and perform the one-electron oxidation of 1,3-dicarbonyl compounds. The formation of oxime radicals was confirmed quantitatively by electron spin resonance (ESR) spectroscopy. The coupling described in the present study is the first example of the selective intermolecular reaction involving unstable iminoxyl radicals generated in situ. Scheme 1. Cross-dehydrogenative C À O coupling of 1,3-dicarbonyl compounds 1a-l with oximes 2a-i.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Iminoxyl Radical‐Based Strategy for Intermolecular CO Bond Formation: Cross‐Dehydrogenative Coupling of 1,3‐Dicarbonyl Compounds with Oximes

et al. 2014

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“…To record EPR spectra, a flow system was used, which allowed observation of radicals with lifetimes of about 10 −2 s [39]. The EPR spectra of iminoxyl radicals are characterized by large values of the hyperfine splitting constants of an unpaired electron with a 14 N nucleus (a N ≈ 28-33 G [35][36][37][38]), which are very different from those for other N-oxyl radicals, such as imidoxyl (a N ≈ 4.2-4.9 G [40]), amidoxyl (a N ≈ 5-8 G [41,42]), and aminoxyl (a N ≈ 15 G [43]). The characteristic 14 N hyperfine splitting constant makes EPR spectroscopy a convenient method for the identification of iminoxyl radicals, and for many of them, EPR is the only observation method due to low stability, and therefore low concentration in investigated systems.…”

Section: Reviewmentioning

confidence: 99%

“…The proposed scheme for the decomposition of di-tert-butyliminoxyl radical (8) is presented in Scheme 3 [35,45]. It includes formation of C-O dimer 4f followed by the fragmentation to iminyl radical 12, ketone 9, and nitric oxide.…”

Section: Reviewmentioning

confidence: 99%

“…The chemistry of iminoxyl radicals (including their generation, structure, EPR spectroscopy, and reactions) was reviewed in 1978 before the discovery of their substantial synthetic potential [34]. A book chapter was dedicated to the chemistry of stable di-tert-alkyl iminoxyl radicals [35]. Kinetic [36] and EPR data [37] of iminoxyl radicals were previously compiled in tabular form.…”

Section: Introductionmentioning

confidence: 99%

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Oxime radicals: generation, properties and application in organic synthesis

Krylov¹,

Paveliev²,

Budnikov³

et al. 2020

Beilstein J. Org. Chem.

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N-Oxyl radicals (compounds with an N–O• fragment) represent one of the richest families of stable and persistent organic radicals with applications ranging from catalysis of selective oxidation processes and mechanistic studies to production of polymers, energy storage, magnetic materials design and spectroscopic studies of biological objects. Compared to other N-oxyl radicals, oxime radicals (or iminoxyl radicals) have been underestimated for a long time as useful intermediates for organic synthesis, despite the fact that their precursors, oximes, are extremely widespread and easily available organic compounds. Furthermore, oxime radicals are structurally exceptional. In these radicals, the N–O• fragment is connected to an organic moiety by a double bond, whereas all other classes of N-oxyl radicals contain an R2N–O• fragment with two single C–N bonds. Although oxime radicals have been known since 1964, their broad synthetic potential was not recognized until the last decade, when numerous selective reactions of oxidative cyclization, functionalization, and coupling mediated by iminoxyl radicals were discovered. This review is focused on the synthetic methods based on iminoxyl radicals developed in the last ten years and also contains some selected data on previous works regarding generation, structure, stability, and spectral properties of these N-oxyl radicals. The reactions of oxime radicals are classified into intermolecular (oxidation by oxime radicals, oxidative C–O coupling) and intramolecular. The majority of works are devoted to intramolecular reactions of oxime radicals. These reactions are classified into cyclizations involving C–H bond cleavage and cyclizations involving a double C=C bond cleavage.

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DPPH (2,2-di(4-tert-octylphenyl)-1-picrylhydrazyl) radical scavenging mixed-mode colorimetric assay(s)

Nenadis

Tsimidou

2017

Measurement of Antioxidant Activity &Amp; Capacity

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The Only Stable Organic Sigma Radicals: Di‐ tert ‐Alkyliminoxyls

Cited by 12 publications

References 33 publications

Iminoxyl Radical‐Based Strategy for Intermolecular CO Bond Formation: Cross‐Dehydrogenative Coupling of 1,3‐Dicarbonyl Compounds with Oximes

Iminoxyl Radical‐Based Strategy for Intermolecular CO Bond Formation: Cross‐Dehydrogenative Coupling of 1,3‐Dicarbonyl Compounds with Oximes

Oxime radicals: generation, properties and application in organic synthesis

DPPH (2,2-di(4-tert-octylphenyl)-1-picrylhydrazyl) radical scavenging mixed-mode colorimetric assay(s)

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