Novel type of carbozirconation reaction of alkynes is reported. Treatment of zirconocenealkyne complexes, zirconacyclopentenes, or zirconacyclopentadienes with allylic compounds gave allylzirconation products of alkynes. Carbozirconation of alkynes with zirconacyclopentenes or zirconacyclopentadienes involved β, β′-CC bond cleavage reaction of zirconacycles. Reactions of zirconacyclopentenes with homoallyl bromides ...