CYCLIZATION AND SUBSEQUENT REACTIONS OF 2'-HYDROXY-6'-METHOXYCHALCONE EPOXIDE AND RELATED-COMPOUNDS

2'-Hydroxy-6'-methoxychalcone epoxide reacts in neutral aqueous acetonitrile solution to give a 6:1 ratio of the alpha- and beta-cyclisation products, erythro-4-methoxyaurone hydrate [erythro-2-(alpha-hydroxybenzyl)-4-methoxycoumaran-3-one] and trans-3-hydroxy-5-methoxyflavanone; the dominance of alpha-cyclisation may be associated with a stereoelectronic preference for a conformation favourable for alpha- but not beta-cyclisation when the carbonyl group is forced by the 6'-substituent to lie out-of-plane with the aromatic ring. In more basic solutions, erythro-threo isomerisation of aurone hydrate occurs, and 4-methoxycoumaran-3-one and 4-methoxyaurone are formed. Other 6'-substituted 2'-hydroxychalcone epoxides show a similar strong preference for alpha- over beta-cyclisation.