METHODS FOR INDOLE ALKALOID SYNTHESIS - ENANTIOSPECIFIC SYNTHESIS OF PENTACYCLIC DESETHYLASPIDOSPERMA-TYPE ALKALOIDS USING AN EXCEPTIONALLY MILD RETRO-DIELS-ALDER REACTION

Using an enantiomerically pure [2.2.1] system in the indole-2,3-quinodimethane cyclization, the construction of either enantiomer of desethylaspidospermidine-type alkaloids is described. The adduct 10 from the imine 9 and the [2.2.1] acid chloride 7 (X = Cl) was thermolyzed at 180-190.degree. C to give the retro-Diels-Alder product 11, thereby introducing the 6,7 double bond. The adducts 10 and 11 were separately converted into the pentacyclic adduct 12 and its enantiomeric purity established as .gtoreq. 95% by the chiral solvating agent (+)-2,2,2-trifluoro-1-(9-anthryl)ethanol.