Catalytic palladium-mediat{approaches the limit}d tetraene carbocyclizations: Enamine trapping reagents

The palladium-catalyzed carbocyclization of a tetraene substrate in the presence of an enamine effects efficient cyclization of the substrate with concomitant formation of a second carbon-carbon bond via allylation of the enamine. A brief survey of the roles of the reaction medium, ligand, enamine reagent, and to a lesser extent the substrate and palladium catalyst in determining the catalytic efficiency, mode-selectivity, and stereoselectivity of the cyclization is described. In one example, indole is shown to also function as an efficient trapping reagent.