Nickel-catalyzed intermolecular [3+2+2] cocyclization of ethyl cyclopropylideneacetate and alkynes. Synthesis of seven-membered carbocycles

[Graphics] The [3 + 2 + 2] cocyclization of ethyl cyclopropylideneacetate (1a) and various alkynes proceeded smoothly in the presence of Ni(cod)(2)-PPh3. The cycloheptadiene derivatives were synthesized in highly selective manners. The unique reactivity of la was essential for the progress of the reaction. The observed regioselectivity of the product formation and the mechanism of the reaction are discussed.