Double Carboxylation of O-Alkynyl Acetophenone with Carbon Dioxide.

A copper-catalyzed double carboxylation of o-alkynyl acetophenone using carbon dioxide to afford 1(3H)-isobenzofuranylidene dicarboxylic esters in good yields is described. The reaction proceeds via a carboxylation/intramolecular cyclization/carboxylation sequence. Alkyl-substituted substrates show much higher double carboxylation product selectivities than aryl-substituted substrates.