A Fully Palladium-Mediated Construction of Phenanthrenes and Naphthoxindoles

A fully palladium-catalyzed synthesis of unusual naphthoxindole alkaloids through a key intramolecular direct C-H arylation step leading to the formation of the phenanthrene core is described. The three-step process involves a highly efficient Heck coupling of aryl diazonium salts with phenyl-acrylates, giving the corresponding cis-stilbenes. Cyclization of stilbenes into phenanthrenes through a direct intramolecular C-H arylation, followed by a palladium-mediated cyclization of an amino ester, led to the formation of novel naphthoxindoles.