Double ring closure of diacetylenic compounds with activated olefins in the presence of a cobalt(0) catalyst

Abstract

Ring formation from 1,6- or 1,7-diynes and activated olefins is catalysed by cobalt(0) complexes through cobaltacyclopentadiene intermediates. If steric hindrance is sufficiently low the reaction proceeds further and products containing two molecules of olefin per molecule of diyne are obtained. With terminally alkyl-substituted and conformationally rigid diynes the reaction must be carried out stoichiometrically because of the incursion of a new acid/base-catalysed reaction, which is independent of cobalt.