SYNTHESIS OF SEMPERVIRINE, A PENTACYCLIC ANHYDRONIUM INDOLE ALKALOID

Sempervirine etrahydro-1H-benz[g]indolo[2,3-a]quinolizin-6-ium, 1) the pentacyclic anhydronium indole alkaloid of Gelsemium sempervirens Ait . f. (Loganiaceae), has been synthesized in three steps from hexahydro isochroman-3-one (6) and N-2-(3-indolyl)-ethylamine (tryptamine, 7). T he condensation product, -2-(hydroxymethyl)-trans-hexahydro-phenylacet amide (8) arising from 6 and 7 on double cyclization with phosphoryl c hloride yielded the 3,4-dehydroyohimbane derivative 9. Aromatization o f rings C and D of compound 9 with 2,3-dichloro-5,6-dicyanobenzoquinon e (DDQ) in glacial acetic acid, followed by basification, generated se mpervirine (1).