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.