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Communication | Regular issue | Vol 51, No. 3, 1999, pp.501-504
Published online, 1st January, 1970
DOI: 10.3987/COM-98-8434
Model Studies on Interconversion of Roxburghine-Type Alkaloids. Acid-catalysed Epimerization of C-12b Substituted Indolo[2,3-a]quinolizidine Derivatives

Mauri Lounasmaa,* Mathias Berner, Anders Månsus, and Arto Tolvanen

*Laboratory for Organic and Bioorganic Chemistry, Technical University of Helsinki, P.O. Box 6100, FIN-02150 Espoo, Finland

Abstract

C-12b Methyl substituted indolo[2,3-a]quinolizidines possessing different structural features were prepared as model compounds to investigate whether different roxburghine alkaloids can be obtained by acid-catalysed epimerization. When they were subjected to epimerization under strongly acidic conditions (TFA), indoloquinolizidines (7) and (8) and lactams (12) and (13) epimerized as expected but the vinylogous urethanes (4) and (5) remained unaffected. The results indicate that the mechanism starting with protonation at the β-position of indole (Mechanism 1) is active in the acid-catalysed epimerization of vinylogous urethanes. This further suggests that roxburghine alkaloids do not epimerize at C-19.