Nickel-catalyzed cycloisomerization of enynes: catalyst generation via C–H activation of carbene ligands

The combination of Ni(0) and an N-heterocyclic carbene acts as a precatalyst for the cycloisomerization of enynes to afford 1,3-dienes. During the course of the reaction, a nickel hydride is formed from oxidative addition of the ortho C–H on the carbene ligand. Deuterium labeling studies are presented.