Epimerization, transacylation and bromination of dihydroquercetin acetates; synthesis of 8-bromodihydroquercetin
| Autor: | Eberhard Kiehlmann, Monica G. Szczepina |
|---|---|
| Rok vydání: | 2011 |
| Předmět: |
Chemistry
Halogenation General Chemistry Nuclear magnetic resonance spectroscopy dihydroflavonol acetylation intermolecular acetyl transfer Catalysis taxifolin chemistry.chemical_compound Acetic anhydride Transacylation cis-2 3-dihydroflavonols 6 8-dibromoflavanonols Yield (chemistry) Materials Chemistry Organic chemistry Epimer QD1-999 Sodium sulfite |
| Zdroj: | Open Chemistry, Vol 9, Iss 3, Pp 492-498 (2011) |
| ISSN: | 2391-5420 |
| DOI: | 10.2478/s11532-011-0032-8 |
| Popis: | Dihydroquercetin (dhq) and its 3-acetate react with acetic anhydride in the absence of a base catalyst to yield mixtures of partially acetylated products. Three new esters were characterized by NMR spectroscopy as dhq 3,7,3′-triacetate, 3,7,4′-triacetate and 5,7,3′,4′-tetraacetate. At its melting point neat dhq 3,7,3′,4′-tetraacetate is partially converted to dhq 3,3′,4′-triacetate and dhq pentaacetate by intermolecular acetyl transfer. Dhq 7,3′,4′-triacetate yields exclusively dhq 3′,4′-di- and 3,7,3′,4′-tetraacetate under these conditions. The acetylation/deacetylation reactions are accompanied by partial epimerization: 3 new acetates with 2,3-cis stereochemistry (dhq 3-, 3,7,3′,4′-tetra- and penta-) were identified. Dhq and its 3,7,3′,4′-tetraacetate undergo regiospecific dibromination at C-6 and C-8 with excess N-bromosuccinimide in polar solvents, and 6,8-dibromo-dhq can be regioselectively debrominated to 8-bromo-dhq with sodium sulfite. |
| Databáze: | OpenAIRE |
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