Nickel-catalyzed [4+2+2]-type annulation reaction of cyclobutanones with diynes and enynes

In the presence of a nickel(0) catalyst, cyclobutanones reacted with diynes to produce bicyclic eight-membered ring ketones. Cyclobutanones acted its it C4 unit in the formal [4+2+2]-type annulation reaction, which proceeded through a ring-expansion of it spirocyclic seven-membered oxanickelacycle to a nine-membered nickelacycle via beta-carbon elimination. A similar annulation reaction was also examined with enynes.