Acid-catalysed epimerization of indolo[2,3-a]quinolizidines. 1-, 2- and 3-monosubstituted alkyl derivatives

✍ Scribed by Mauri Lounasmaa; Lars Miikki; Arto Tolvanen

• Publisher: Elsevier Science
• Year: 1997
• Tongue: French
• Weight: 444 KB
• Volume: 53
• Category: Article
• ISSN: 0040-4020
• DOI: 10.1016/s0040-4020(97)00197-x

✦ Synopsis

Acid-eatalysed epimerization of 1-, 2-and 3-monosubstituted 1,2,3,4,6,7,12,12boctahydroindolo[2,3-a]quinolizine alkyl derivatives in refluxing trifluoroacetic acid (TFA) leads to an equilibrium mixture of C-12b diastereomers. The thermodynamically more stable epimer predominates over the kinetically favoured epimer in a ratio of about 85:15 unless the substituent is at C-I, in which ease the ratio is 55:45. The proton at C-12b is exchanged when the epimerization is performed in refluxing TFA-d. New stereoselective synthesis of the missing 2-ethylindolo[2,3a]quinolizidines is described.