SELECTIVE INTERMOLECULAR COUPLING OF ALKYNES WITH NITRILES AND KETONES VIA BETA,BETA' 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 wi th nitriles and ketones, respectively. Hydrolysis of the mixture gave alpha,beta-unsaturated ketones and allylic alcohols in good to excelle nt yields, respectively. These reactions proceeded via zirconacyclopen tenes which were prepared by the reaction of alkynes with Cp2ZrEt2. Th e structure of zirconacyclopentene, which was prepared from diphenylac etylene and Cp2ZrEt2, was determined by X-ray analysis. It clearly ind icated 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 c leavage of the zirconacyclopentenes. In a similar way, addition of PMe 3 to the zirconacyclopentene afforded a zirconocene-alkyne complex in 87% yield.