TOWARD THE SYNTHESIS OF (-)-CODEINE BY CHIRAL AUXILIARY -MEDIATED NITRONE CYCLOADDITION

摘要

Application of a C-2-symmetric dioxolane moiety as chiral auxiliary for an asymmetric intramolecular nitrone cycloaddition was studied as a possible key step for the enantioselective synthesis of (-)-codeine. A cycloaddition precursor bearing a 1,2-diphenylethylene acetal was selected that was readily accessible in ten steps from isovanillin. It underwent nitrone cycloaddition and after a consecutive transformation, an isoxazolidine intermediate with the absolute and relative configuration required for (-)-codeine was obtained.