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Today discovering and developing efficient approaches and strategies to synthesize ring compounds,which are building blocks or skeletons of materials,drugs and natural products,have been extremely expected.However,the formation of strained ring,such as 4-or 8-membered ring,is still a stern challenge.In the last decades,zirconacyles,prepared in situ by the reaction of 14e of “Cp2Zr(Ⅱ)”species and unsaturated molecules have emerged as high reactive intermediate in the synthesis of ring compound.[1] The two or more C-Zr bonds show special behaviors compared with those in the acyclic skeletons.a-Methylenyl zirconacyclopentene 1,selectively prepared via the cross-coupling of allene and alkyne,shows especial reactivity contrast to the zirconacyclopentadiene containing two conjugative double bonds.[2] In the case of a-methylenyl zirconacyclopentene 1,the exocyclic double bond leads to an unconjugative zirconacyclopentene,based on which the chemistry of 1 absolutely differ from that of the zirconacyclopentadiene.The reaction of 1 with dimethyl acetylenedicarboxylate(DMAD)/CuCl system led to the formation of the methylenyl cyclobutene 2 rather than the compound involved DMAD skeleton.When treated with o-di(bromomethyl)benzene in the presence of Cu(Ⅰ),the benzocyclooctene derivative 3 could be obtained in high regio-and stereoselectivity,which could be used in the synthesis of cyclooctanone,cyclooctanol,etc..