Flavonoid epoxides. Part 18. Solvolysis products of 2-arylmethylenebenzo[b]furan-3(2H)-one (aurone) epoxides
Aurone epoxides readily undergo solvolysis with aqueous acetone, methanol, and ethanol under neutral conditions, and also with acetic acid to give α,β-dihydroxy, α-hydroxy-β-alkoxy, and α-hydroxy-β-acetoxy aurones, which equilibrate in solution, through ring-chain tautomerism (Scheme 1), giving predominantly the cyclic benzofuranone diastereoisomers of the solvolysis products. Acetyl derivatives of the cyclic products and quinoxaline derivatives of the open-chain products have been prepared and characterised. Methanolysis of aurone epoxides under acid conditions gave α-methoxy-β-hydroxyaurone derivatives. 1H N.m.r. spectroscopy was used in the tentative assignment of the configurations of the solvolysis products.