ACID-CATALYSED EPIMERIZATION OF INDOLO[2,3-A]QUINOLIZIDINES - 1-, 2- AND 3-MONOSUBSTITUTED ALKYL DERIVATIVES

摘要

Acid-catalysed epimerization of 1-, 2- and 3-monosubstituted 1,2,3,4,6,7,12,12b-octahydroindolo[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-l, in which case 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[2,3-a]quinolizidines is described. (C) 1997 Elsevier Science Ltd. [References: 31]