Pd-catalyzed cascade carbopalladation-annulation reaction of 3-(2-iodobenzyl)-indoles into fused 6/5/7/6-and 6/5/5/6-heterocyclic systems

Polycyclic indole structures, possessing fused seven-membered rings were efficiently synthesized via the Pd-catalyzed intramolecular carbopalladation-annulation of 3-(2-iodobenzyl)-indoles and alkynes. A remarkable base effect on the chemoselectivity of this transformation has been found: switching from Et3N to CsOAc completely reverses the reaction path to intramolecular cyclization forming fused five-membered rings.