Mechanistic Insight into Phenol Dearomatization by Hypervalent Iodine : Direct Detection of a Phenoxenium Cation
Phenol dearomatization is one of several oxidation reactions enabled by hypervalent iodine reagents. However, the presence of a proposed free phenoxenium intermediate in phenol dearomatization is a matter of debate in the literature. Here, we report the unambiguous detection of a free phenoxenium intermediate in the reaction of an electron-rich phenol, 2,4,6-trimethoxyphenol, and (diacetoxyiodo)benzene using UV-vis and resonance Raman spectroscopies. In contrast, we predominantly detect single electron oxidation products of less electron-rich phenols or alkoxy-substituted aromatics in their reaction with (diacetoxyiodo)benzene using UV-vis and electron paramagnetic resonance (EPR) spectroscopies. We conclude that the often-postulated free phenoxenium intermediate, while possible with highly stabilizing substituents, is unlikely to be a general mechanistic pathway in the reaction of typical phenols with hypervalent iodine reagents. The polar solvent 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) or the use of more strongly oxidizing hypervalent iodine reagents, such as [bis(trifluoroacetoxy)iodo]benzene (PIFA) or [hydroxy(tosyloxy)iodo]benzene (HTIB), can help reduce the formation of radical byproducts and favors the formation of phenoxenium intermediates.
| Medienart: |
E-Artikel |
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| Erscheinungsjahr: |
2022 |
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| Erschienen: |
2022 |
| Enthalten in: |
Zur Gesamtaufnahme - volume:87 |
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| Enthalten in: |
The Journal of organic chemistry - 87(2022), 21 vom: 04. Nov., Seite 14274-14283 |
| Sprache: |
Englisch |
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| Beteiligte Personen: |
Juneau, Antoine [VerfasserIn] |
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| Links: |
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| Anmerkungen: |
Date Revised 07.11.2022 published: Print-Electronic Citation Status PubMed-not-MEDLINE |
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| doi: |
10.1021/acs.joc.2c01765 |
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| funding: |
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| Förderinstitution / Projekttitel: |
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| PPN (Katalog-ID): |
NLM347309364 |
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| 245 | 1 | 0 | |a Mechanistic Insight into Phenol Dearomatization by Hypervalent Iodine |b Direct Detection of a Phenoxenium Cation |
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| 500 | |a Citation Status PubMed-not-MEDLINE | ||
| 520 | |a Phenol dearomatization is one of several oxidation reactions enabled by hypervalent iodine reagents. However, the presence of a proposed free phenoxenium intermediate in phenol dearomatization is a matter of debate in the literature. Here, we report the unambiguous detection of a free phenoxenium intermediate in the reaction of an electron-rich phenol, 2,4,6-trimethoxyphenol, and (diacetoxyiodo)benzene using UV-vis and resonance Raman spectroscopies. In contrast, we predominantly detect single electron oxidation products of less electron-rich phenols or alkoxy-substituted aromatics in their reaction with (diacetoxyiodo)benzene using UV-vis and electron paramagnetic resonance (EPR) spectroscopies. We conclude that the often-postulated free phenoxenium intermediate, while possible with highly stabilizing substituents, is unlikely to be a general mechanistic pathway in the reaction of typical phenols with hypervalent iodine reagents. The polar solvent 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) or the use of more strongly oxidizing hypervalent iodine reagents, such as [bis(trifluoroacetoxy)iodo]benzene (PIFA) or [hydroxy(tosyloxy)iodo]benzene (HTIB), can help reduce the formation of radical byproducts and favors the formation of phenoxenium intermediates | ||
| 650 | 4 | |a Journal Article | |
| 700 | 1 | |a Lepage, Iannick |e verfasserin |4 aut | |
| 700 | 1 | |a Sabbah, Sami G |e verfasserin |4 aut | |
| 700 | 1 | |a Winter, Arthur H |e verfasserin |4 aut | |
| 700 | 1 | |a Frenette, Mathieu |e verfasserin |4 aut | |
| 773 | 0 | 8 | |i Enthalten in |t The Journal of organic chemistry |d 1945 |g 87(2022), 21 vom: 04. Nov., Seite 14274-14283 |w (DE-627)NLM000006343 |x 1520-6904 |7 nnns |
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