Reaction of Dialkyl-substituted Alkynes with Carbon Dioxide Catalyzed by Nickel(0) Complexes. Incorporation of Carbon Dioxide in Alkyne Dimers and Novel Cyclotrimerization of the Alkynes

Article abstract of DOI:10.1246/bcsj.53.3329

Ni(cod)2-Ph2P(CH2)4PPh2 system (cod=1,5-cyclooctadiene) catalyzed the reaction of 3-hexyne, for example, with CO2 to give a CO2 incorporated product, i.e., tetraethyl-2-pyrone, in a fairly good yield together with novel two cyclotrimers of the alkyne having cyclopentadiene structures, i.e., pentaethyl-5-(1-propenyl)-1,3-cyclopentadiene and pentaethyl-5-allyl-1,3-cyclopentadiene.The novel two cyclotrimers were formed selectively on Ni(cod)2-PPh3 system under CO2, whereas under N2 the main trimer was hexaethylbenzene.A nickelacyclopentadiene intermediate has been proposed for the pyrone formation.The novel two cyclotrimers were also formed on the oligomerization catalyzed by a cationic nickel hydride complex, OCOCF3, together with a novel dimer having a methylenecyclobutane structure, i.e., 1,2,4-triethyl-3-ethylidenecyclobutene.The effect of posphine added and that of active-hydrogen compounds on the novel oligomerization are mentioned.