Nickel-Catalyzed Intermolecular [2+2] Cycloaddition of Conjugated Enynes with Alkenes

A nickel-catalyzed intermolecular [2 + 2] cycloaddition of conjugated enynes with alkenes has been developed. A variety of electron-deficient alkenes as well as electronically neutral norbornene and 1-decene were applicable to this reaction. The use of conjugated enynes circumvented possible side rections, such as oligomerizations and cyclotrimerizations. The isolation of reaction intermediate complexes revealed that the eta(3)-butadienyl coordination is the key for the selective formation of cyclobutene.