Stereochemical course of the alkaline decarboalkoxylative cyclization of C(4)- C(5)- and C(4) ,C(5)-substituted 1-[2-(3-indolyl)ethyl-3-methoxycarbonyl -1,4,5,6-tetrahydropyridines to C(2)- , C(3)- and C(2) ,C(3)-substituted indolo[2,3-a quinolizidines
Alkaline decarboalkoxylative cyclization of C(4)-monosubstituted 1-[2-(3-indolyl) ethyl-3methoxycarbonyl-1,4,5,6-tetrahydropyridines 1a and 1d leads mainly to C(2)-monosubstituted indolo[2,3-a quinolizidines 2a and 2d possessing the C(12b)H-C(2)H cis relationship [corresponding to the C(3)H-C(15)H cis relationship when the biogenetic numbering of indole alkaloids is used