Abstract
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 usedThe C(5)-monosubstituted 1-[2-(3-indolyl) ethyl-3-methoxycarbonyl-1,4,5,6- tetrahydropyridine 1e yields almost exclusively C(3)-monosubstituted indolo[2,3-3 quinolizidine 3e [C(12b)H-C(3)H trans relationship. In the case of the C(4),C(5)-disubstituted analogues 1f and 1g, the C(12b)H-C(2)H relationship is strongly influenced by the C(4)H-C(5)H relationship (cis or trans) of the original 1,4,5,6- tetrahydropyridine. Thus 1-[2-(3-indolyl)ethyl-3-methoxycarbonyl-4- methyl-5-ethyl-1,4,5,6-tetrahydropyridine 1f [C(4)H-C(5)H cis relationshipleads to 2-methyl-3-ethylindolo[2,3-a quinolizidines 1f and 1f [C(12b)H-C(2)H trans and cis relationships, respectively in about 98:2 ratio, whereas 1-[2-(3-indolyl)ethyl-3-methoxycarbonyl-4-methyl-5-ethyl-1,4,5,6-tetrahydropyridine 1g [C(4) H-C(5)H trans relationshipyields exclusively 2-methyl-3-ethylindolo[2,3-a quinolizidine 2g [C(12b)H-C(2)H cis relationship
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