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Acid-catalysed epimerization of indolo[2,3-a]quinolizidine derivatives: Role of the nitrogen lone pairs in the mechanism

✍ Scribed by Mauri Lounasmaa; Mathias Berner; Martin Brunner; Harri Suomalainen; Arto Tolvanen

Publisher
Elsevier Science
Year
1998
Tongue
French
Weight
545 KB
Volume
54
Category
Article
ISSN
0040-4020

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✦ Synopsis

The role of the nitrogen lone pairs in the mechanism of the acid-catalysed epimerization of indolo[2,3-a]quinolizidines is investigated using laetams as model compounds. Deethylebumamonine (3) did not epimerize with trifluoroacetic acid (TFA), whereas deethyldihydroeburnamenine (7) underwent epimerization smoothly. Under treatment with TFA, lactams 12 and 13 both epimerized with ease to a mixture of lactams 12 and 13. An analogous equilibrium was achieved when the experiment was repeated with lactams 18 and 19. Intermediate 20 was trapped (Zn reduction) in the acid-catalysed epimerization of lactam 12, allowing conclusions about the mechanism.

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