Selective intermolecular coupling of alkynes with nitriles and ketones via β,β′ carbon-carbon bond cleavage of zirconacyclopentenes

Selective intermolecular coupling of alkynes with nitriles and ketones was performed by the reaction of a mixture of alkynes and Cp2ZrEt2 with nitriles and ketones, respectively. Hydrolysis of the mixture gave alpha,beta-unsaturated ketones and allylic alcohols in good to excellent yields, respectively. These reactions proceeded via zirconacyclopentenes which were prepared by the reaction of alkynes with Cp2ZrEt2. The structure of zirconacyclopentene, which was prepared from diphenylacetylene and Cp2ZrEt2, was determined by X-ray analysis. It clearly indicated that there is a single bond between the beta- and beta'-carbons of the zirconacyclopentene. The reaction of zirconacyclopentenes with nitriles or ketones proceeded via the beta,beta' carbon-carbon bond cleavage of the zirconacyclopentenes. In a similar way, addition of PMe3 to the zirconacyclopentene afforded a zirconocene-alkyne complex in 87% yield.