Dramatic Influence on the Olefinic Geometry in the Nickel(0)-Catalyzed Coupling Reaction of 1,3-Dienes and Aldehydes Using N-Heterocyclic Carbene as a Ligand

The use of N-heterocyclic carbene 2 as a ligand in a nickel(0)-catalyzed coupling reaction of 1,3-diene and aldehyde was investigated. It was found that the Ni(0)−carbene complex showed a unique property in the reaction of 1,3-diene 4 and aldehyde 5 to give the coupling product Z-6, having a (Z)-olefin in high yield in a highly stereoselective manner. Since the same reaction using the Ni(0)−PPh₃ complex gave E-6a in a stereoselective manner, this result indicates that the Ni(0)−carbene complex has a property different from that of the traditional Ni(0)−phosphine complex.