Carbon-carbon bond cleavage and selective transformation of zirconacycles

This account describes recent development in carbon-carbon bond cleavage re actions and selective transformation of 5-membered zirconacycles, including zirconacyclopentanes, zironacyclopentenes, and zirconacyclopentadienes. Th ese 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 transformat ion. Vinylzirconation of alkynes, regioselective allylzirconation of alkyne s, and coupling of alkynes with nitriles or ketones were achieved by this m ethod. Zirconacyclopentadienes prepared symmetrically or unsymmetrically we re converted into naphthalene, diene, and benzene derivatives. Preparation of benzene derivatives from three different alkynes was performed by combin ation of C-C bond cleavage and C-C bond formation on zirconocene in one-pot in high yield with excellent selectivity.