KINETICS AND MECHANISM OF THE CYCLIZATION OF SOME 2'-HYDROXYCHALCONE EPOXIDES AND SUBSEQUENT ELIMINATION-REACTIONS OF AURONE HYDRATES

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 aurone hydrate, gives rate coefficients which quantify the preference for alpha over beta cyclisation when 6'-substituents are present These are considered in terms of stereoelectronic factors which may be responsible for the preference. Also reponed are rate coefficients for the subsequent reaction of aurone hydrates in which aurones and coumaranones are formed.