Nickel-mediated cyclization of enynes under an atmosphere of carbon dioxide

Nickel-mediated carboxylation of alpha,omega-enyne was investigated. In the presence of a stoichiometric amount of zero-valent nickel complex, enynes having an electron-withdrawing group on alkene reacted with carbon dioxide via intramolecular cyclization to afford cvclic carboxylic acids in good yields. Various heterocyclic compounds were prepared by this carboxylative cyclization protocol. The reaction seems to proceed through oxidative cycloaddition of the alpha,omega-enyne moiety to a zero-valent nickel complex. regioselective insertion of carbon dioxide at the Csp(3) -nickel bond, and hydrolysis of the resulting oxanickelacycle intermediate. (c) 2006 Elsevier Ltd. All rights reserved.