Silver-Catalyzed Carbon Dioxide Fixation on Alkynylindenes

The synthesis of polycyclic indene derivatives via silver-catalyzed carbon dioxide fixation on 2-alkynylindene derivatives was achieved by nucleophilic addition of the indenyl anion to carbon dioxide involving carbon-carbon bond formation and subsequent intramolecular cyclization to the alkyne part activated by a silver catalyst. This cascade process could be applied to various substrates to obtain the corresponding products in high yields. The endo/exo selectivity of the cyclization could be controlled by the steric or electronic effect of the substituents on the substrates, and 6-endo-selective cyclization was realized to afford α-pyrone-fused indenes.