Abstract: | The complete stereochemistry of the Δ6-dihydrothebaine → 7-bromodihydrocodeinone dimethyl ketal → codeinone dimethyl ketal → thebaine sequence of transformations has been elucidated by NMR studies of the isotopically labeled compounds prepared using diimide-d2, methyl hypobromite-[14C], and methyl hypobromite-d3. Final elimination of methanol from codeinone dimethyl ketal proceeds in a stereospecific manner: cis under acid catalysis with POC13, and trans under alkaline catalysis with EtO?. As a result of these reactions, variously isotopically labeled thebaines can be prepared. |