a new strategy for the synthesis of tricyclic and tetracyclic systems of indole alkaloids

reaction of tryptamine 1 with dimethyl -3-methoxyallylidenemalonate 2 afforded n?-[4,4-bis (methoxycarbonyl)-1,3-butadienyl] tryptamine 3 which in combination with acetylchloride and pyridine in dichloromethane gave n?, n?-[acetyl]-[(4,4-dinethoxycarbonyl) 1,3butadienyl] tryptamine 4. treatment of 3 with sodium hydroxide afforded 2h[n-(3-indolyl) ethyl] 2-oxo-3-methoxycarbonyl-1-pyridine 5. cyclization of 2 with trifluoroacetic acid gave methyl-2-(methoxycarbonyl) 4-(2,3,4,9-tetrahydro-1h-pyrido [3,4-b] indole-1-yle) butanoate 6. heating of the latter in ethylacetate at reflux temperature afforded a new tetracyclic system methyl 4-oxo 1, 4, 6, 7, 12, 12b-hexahydro indolo [2, 3-a] quinolidine 3 carboxylate 7.