Use of acyl substituents to favour 2,3-epoxidation of 5,7-dioxygenated flavones with dimethyldioxirane |
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Authors: | Benjamin J ComptonLesley Larsen Rex T Weavers |
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Institution: | a Department of Chemistry, University of Otago, Box 56, Dunedin 9054, New Zealandb The New Zealand Institute for Plant and Food Research, Department of Chemistry, University of Otago, Box 56, Dunedin 9054, New Zealand |
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Abstract: | The reaction of 5,7-dimethoxyflavone with dimethyldioxirane (DMDO) gives the 2,3-epoxide rapidly at first. However, low levels of ring A hydroxylated by-products are also formed. With increasing proportions of DMDO, demethylation at C-5 becomes apparent and consumption of substrate is not matched by further significant build-up of the epoxide. Deactivation of ring A by the use of acyl groups removes this complication. 5,7-Diacylflavones give excellent yields of epoxides and monoacyl derivatives also react in good yield. Ionization potential maps derived from density functional theory calculations (B3LYP/6-31G∗), provide good visual indicators of the relative reactivity of the key nucleophilic loci. The epoxides may be isolated as such, or transformed into flavonols by treatment with p-toluenesulfonic acid. |
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Keywords: | Flavone Epoxidation Dimethyldioxirane Acylation |
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