Aurone epoxides

The mass spectra of aurone epoxides have been thoroughly investigated. ... 

The mechanisms of the cyclisation of 2 -hydroxychalcone derivatives which can lead to flavanones, flavones and aurones have been reviewed <95MI1> and the formation of 3-hydroxy- chromanones and -flavanones from l-(2-hydroxyphenyl)-2-propen-l-ones via the epoxide has been optimised <96JOC5375>. 

Scheme 3 presents substrates which carry both electron-donating and electron-withdrawing substituents. These systems, in comparison with the previous set of substrates, were considerably less reactive so that longer reaction times and excess oxidant were necessary for complete epoxidations. In the rosette are displayed the oxidation of p-oxo enol phosphates [13] 13, dihydrofuranone [17] 14, p-alkoxycyc-lohexenones [17] 15, alkoxymethylenecyclohexanones [17] 16, benzalphthalide [12a] 17, aurones [18] 18, flavones [19] 19, and isoflavones [18] 20. Many of these epoxides, which have become available for the first time, constitute valuable building blocks for natural product chemistry. 

X-Ray analysis of (-)-6-bromocryptostrobin (127 R Br, R2 Me) has confirmed the differentiation between crystostrobin (127 Rl=H, R2=Me) and strobopinin (127 R1=Me, R2=H). As a consequence of this work, the structures of several other natural products (lawin-al, unonal, etc) have had to be revised.135 The reaction of nucleophiles with 3-methanesulphonyloxyflavanones gives a mixture of two or more products which arise by elimination (to give flavones), substitution (to produce 3-substituted flavanones), ring contraction (to aurones) and additon-intramolecular substitution (to form 3,4-epoxides).136... 

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