Carbon-carbon bond cleavage and selective transformation of zirconacycles

This account describes recent development in carbon-carbon bond cleavage reactions and selective transformation of 5-membered zirconacycles, including zirconacyclopentanes, zironacyclopentenes, and zirconacyclopentadienes. These zirconacycles can be prepared by coupling of unsaturated compounds such as alkenes and/or alkynes, but the zirconacycles also undergo beta,beta'-C-C bond cleavage, which has been further applied to organic transformation reactions. Combination of the beta,beta'-C-C bond cleavage and the C-C bond formation on zirconocene provided a highly selective and novel transformation. Vinylzirconation of alkynes, regioselective allylzirconation of alkynes, and coupling of alkynes with nitriles or ketones were achieved by this method. Zirconacyclopentadienes prepared symmetrically or unsymmetrically were converted into naphthalene, diene, and benzene derivatives. Preparation of benzene derivatives from three different alkynes was performed by combination of C-C bond cleavage and C-C bond formation on zirconocene in one-pot in high yield with excellent selectivity.