Iminoxyl radicals<i>vs. tert</i>-butylperoxyl radical in competitive oxidative C–O coupling with β-dicarbonyl compounds. Oxime ether formation prevails over Kharasch peroxidation

Krylov, Igor B.; Paveliev, Stanislav A.; Shumakova, N. S.; Syroeshkin, Mikhail A.; Shelimov, B.N.; Nikishin, G. I.; Terent’ev, Alexander O.

doi:10.1039/c7ra13587d

Cited by 17 publications

(16 citation statements)

References 72 publications

(131 reference statements)

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“…Based on these results, it can be concluded that the oxidative C−H activation of alkyl benzenes and benzyl alcohols to the corresponding benzyl alcohols and aryl aldehydes, respectively, mainly is done in the presence of TBAB and TBHP and finally desired ester will produced via the cross‐dehydrogenative coupling of aryl aldehyde and benzyl alcohol in the presence of NMZI‐CuO‐9 : 1. According to these results and some reports about the generation of radicals with Cu 2+ /TBHP as well as Br − /TBHP systems, we proposed a multistep pathway for the synthesis of esters through the reaction of alkyl benzenes and benzyl alcohols in the presence of NMZI‐CuO‐9 : 1 and TBAB (Scheme ). The addition of butylated hydroxytoluene (BHT) (a strong radical inhibitor) to the model reaction of toluene ( 1 a ) and benzyl alcohol ( 2 a ) completely inhibited the reaction under the optimized reaction conditions.…”

Section: Resultsmentioning

confidence: 69%

Nanostructured Mesoporous Zinc‐Incorporated Copper Oxide (NMZI‐CuO): An Efficient and Reusable Nanocatalyst for the Synthesis of Esters through C−H Functionalization

et al. 2019

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Nanostructured mesoporous zinc-incorporated copper oxide (NMZI-CuO), an efficient and reusable heterogeneous nanocatalyst, was successfully prepared and fully characterized by XRD analysis, IR spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), inductively coupled plasma atomic emission spectroscopy (ICP-OES), Brunauer-Emmett-Teller analysis (BET), energy-dispersive X-ray (EDX) spectroscopy, and X-ray photoelectron spectroscopy (XPS) methods and was successfully applied for the synthesis of esters through a direct sp 3 CÀ H functionalization of alkyl benzenes. Using this method a broad range of benzyl alcohols as well as aryl aldehydes and alkyl benzenes were reacted via a cross-dehydrogenative coupling (CDC) process and all desired esters were obtained in good to excellent yields after relatively short times. The catalyst was recovered and reused several times without any detectable loss of activity. Moreover, presented catalyst was successfully applied for selective 5' esterification of nucleosides using alkyl benzenes without protecting the 2' and 3' hydroxyl groups.

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Section: Resultsmentioning

confidence: 69%

Nanostructured Mesoporous Zinc‐Incorporated Copper Oxide (NMZI‐CuO): An Efficient and Reusable Nanocatalyst for the Synthesis of Esters through C−H Functionalization

et al. 2019

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“…radicals by reactions of Cu centres within the [Cu 2 (O 2 CR) 4 ] paddlewheel. [ 1 , 18 , 19 , 20 ] The reactive tert ‐butoxy and tert ‐peroxy derived radicals abstract a hydrogen atom from the benzylic position of the substrate, and the resultant C radical is then converted to the product via O‐transfer. Rietveld refinement of the SPXRD data of t BuOOH‐loaded MFM‐170 confirmed binding of t BuOOH to the vacant metal site within the [Cu 2 (O 2 CR) 4 ] paddlewheel (Figure 2 , Figure S9) with Cu⋅⋅⋅O of 2.840(2) Å.…”

mentioning

confidence: 99%

The Origin of Catalytic Benzylic C−H Oxidation over a Redox‐Active Metal–Organic Framework

Kimberley

Sheveleva

et al. 2021

Angew Chem Int Ed

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Selective oxidation of benzylic CÀH compounds to ketones is important for the production of a wide range of fine chemicals, and is often achieved using toxic or precious metal catalysts. Herein, we report the efficient oxidation of benzylic C À H groups in a broad range of substrates under mild conditions over a robust metal-organic framework material, MFM-170, incorporating redox-active [Cu 2 II (O 2 CR) 4 ] paddlewheel nodes. A comprehensive investigation employing electron paramagnetic resonance (EPR) spectroscopy and synchrotron X-ray diffraction has identified the critical role of the paddlewheel moiety in activating the oxidant t BuOOH (tertbutyl hydroperoxide) via partial reduction to [Cu II Cu I -(O 2 CR) 4 ] species.

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“…Later, the Cu(BF 4 ) 2 (cat. )/t-BuOOH oxidative system [87] was proposed as an alternative to stoichiometric metal-containing oxidants, such as KMnO 4 , Mn(OAc) 3 , and KMnO 4 /Mn(OAc) 3 (Scheme 16).…”

Section: Methodsmentioning

confidence: 99%

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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Iminoxyl radicalsvs. tert-butylperoxyl radical in competitive oxidative C–O coupling with β-dicarbonyl compounds. Oxime ether formation prevails over Kharasch peroxidation

Abstract: The Kharasch peroxidation system Cu(ii)cat./t-BuOOH, the source oft-BuOO˙ radicals, can be switched to generate iminoxyl radicals by adding various oximes.

Cited by 17 publications

References 72 publications

Nanostructured Mesoporous Zinc‐Incorporated Copper Oxide (NMZI‐CuO): An Efficient and Reusable Nanocatalyst for the Synthesis of Esters through C−H Functionalization

Nanostructured Mesoporous Zinc‐Incorporated Copper Oxide (NMZI‐CuO): An Efficient and Reusable Nanocatalyst for the Synthesis of Esters through C−H Functionalization

The Origin of Catalytic Benzylic C−H Oxidation over a Redox‐Active Metal–Organic Framework

Oxime radicals: generation, properties and application in organic synthesis

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