Novel syntheses of tetrahydropyrroloquinolines: Applications to alkaloid synthesis

Two novel routes involving the intramolecular olefin insertion with a zirconium--benzyne complex, followed by a palladium-catalyzed aryl amination, have been developed for the synthesis of tetrahydropyrroloquinolines. In one approach, exemplified in the six-step total synthesis of the South American toad poison dehydrobufotenine (1), the tricyclic system was formed via the Pd-catalyzed ring closure of a functionalized tryptamine derivative. In the second, cyclization of an appropriately substituted quinoline yields 13, an intermediate in the synthesis of damirones A and B, and also makaluvamine C, a topoisomerase II inhibitor exhibiting antitumor properties.