Kinetics and mechanism of the cyclisation of some 2′-hydroxy-chalcone epoxides and subsequent elimination reactions of aurone hydrates
作者:Christopher J. Adams、Lyndsay Main
DOI:10.1016/s0040-4020(01)92283-5
日期:1992.11
Analysis of the pH-rate profile for the cyclisation of the monoanion of 2′-hydroxychalcone epoxide which gives 3-hydroxyflavanone and of some 6′-alkoxy-substituted analogues which give mostly hydrate, gives rate coefficients which quantify the preference for α over β cyclisation when 6′-substituents are present. These are considered in terms of stereoelectronic factors which may be responsible for
Cyclisation and subsequent reactions of 2′-hydroxy-6′-methoxychalcone epoxide and related compounds
作者:Christopher J Adams、Lyndsay Main
DOI:10.1016/s0040-4020(01)80961-3
日期:1991.1
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.