13C NMR SPECTROSCOPY OF CARBONYL COMPOUNDS. 2. COMFORMATIONAL AND CONFIGURATIONAL DEPENDENCE OF THE (Z)-EPOXYENONE/FURAN ISOMERIZATION

Article abstract of DOI:10.1016/S0040-4020(01)88624-5

The furan derivative 4 which has been isolated upon photolysis of the epoxyenone compound (E)-1 results from a thermal isomerization of the intermediate (Z)-isomer (Z)-1.The latter reaction can best be understood as a multi-centre process implying a nucleophilic attack of the carbonyl oxygen upon the oxirane ring.Inspection of related epoxyenones (e.g. 2 and 3) reveals that the ease of the above isomerization sensitively depends upon the conformation with respect to the C-6/C-7 single bond.The conformational properties of a series of epoxyenones as well as of related dienones and epoxydienes have been studied by dinamic 13C NMR spectroscopy.The chemical and spectroscopic information is combined to describe the stereochemical course of the epoxyenone/furan isomerization.As a consequence we can control the thermal reactivity of the title compounds by creating an appropriate conformational behaviour.