Direct Experimental Characterization of a Bridged Bicyclic Glycosyl Dioxacarbenium Ion by 1 H and 13 C NMR Spectroscopy : Importance of Conformation on Participation by Distal Esters
© 2021 Wiley-VCH GmbH..
Low-temperature NMR studies with a 4-C-methyl-4-O-benzoyl galactopyranosyl donor enable the observation and characterization of a bridged bicyclic dioxacarbenium ion arising from participation by a distal ester. Variable-temperature NMR studies reveal this bridged ion to decompose at temperatures above ≈-30 °C. In the absence of the methyl group, the formation of a bicyclic ion is not observed. It is concluded that participation by typical secondary distal esters in glycosylation reactions is disfavored in the ground state conformation of the ester from which it is stereoelectronically impossible. Methylation converts the secondary ester to a conformationally more labile tertiary ester, removes this barrier, and renders participation more favorable. Nevertheless, the minor changes in selectivity in model glycosylation reactions on going from the secondary to the tertiary esters at both low and room temperature argue against distal group participation being a major stereodirecting factor even for the tertiary system.
| Medienart: |
E-Artikel |
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| Erscheinungsjahr: |
2021 |
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| Erschienen: |
2021 |
| Enthalten in: |
Zur Gesamtaufnahme - volume:60 |
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| Enthalten in: |
Angewandte Chemie (International ed. in English) - 60(2021), 48 vom: 22. Nov., Seite 25397-25403 |
| Sprache: |
Englisch |
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| Beteiligte Personen: |
Upadhyaya, Kapil [VerfasserIn] |
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| Links: |
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| Themen: |
Bridged Bicyclo Compounds, Heterocyclic |
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| Anmerkungen: |
Date Completed 15.12.2021 Date Revised 04.04.2024 published: Print-Electronic Citation Status MEDLINE |
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| doi: |
10.1002/anie.202110212 |
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| funding: |
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| Förderinstitution / Projekttitel: |
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| PPN (Katalog-ID): |
NLM330853821 |
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| 245 | 1 | 0 | |a Direct Experimental Characterization of a Bridged Bicyclic Glycosyl Dioxacarbenium Ion by 1 H and 13 C NMR Spectroscopy |b Importance of Conformation on Participation by Distal Esters |
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| 500 | |a Date Revised 04.04.2024 | ||
| 500 | |a published: Print-Electronic | ||
| 500 | |a Citation Status MEDLINE | ||
| 520 | |a © 2021 Wiley-VCH GmbH. | ||
| 520 | |a Low-temperature NMR studies with a 4-C-methyl-4-O-benzoyl galactopyranosyl donor enable the observation and characterization of a bridged bicyclic dioxacarbenium ion arising from participation by a distal ester. Variable-temperature NMR studies reveal this bridged ion to decompose at temperatures above ≈-30 °C. In the absence of the methyl group, the formation of a bicyclic ion is not observed. It is concluded that participation by typical secondary distal esters in glycosylation reactions is disfavored in the ground state conformation of the ester from which it is stereoelectronically impossible. Methylation converts the secondary ester to a conformationally more labile tertiary ester, removes this barrier, and renders participation more favorable. Nevertheless, the minor changes in selectivity in model glycosylation reactions on going from the secondary to the tertiary esters at both low and room temperature argue against distal group participation being a major stereodirecting factor even for the tertiary system | ||
| 650 | 4 | |a Journal Article | |
| 650 | 4 | |a Research Support, N.I.H., Extramural | |
| 650 | 4 | |a dioxacarbenium ion | |
| 650 | 4 | |a distal group participation | |
| 650 | 4 | |a glycosylation | |
| 650 | 4 | |a variable-temperature NMR | |
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| 650 | 7 | |a Glycosides |2 NLM | |
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| 700 | 1 | |a Crich, David |e verfasserin |4 aut | |
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