Tandem insertion of halocarbenoids and lithium acetylides into zirconacycles: a novel rearrangement to zirconium alkenylidenates by β-addition to an alkynyl zirconocene.

Tandem insertion of 1,1-dihalo-1-lithio species (halocarbenoids) and lithium alkynides into zirconacyclopentenes and zirconcyclopentanes affords carbocyclic products in high yields via an unusual rearrangement that probably involves addition of an organolithium species to the β-position of a zirconium-alkyne complex to give an alkenylidene-zirconate species. A wide variety of cyclopentanoid organic structures are rapidly assembled in good yield using this multicomponent coupling. The main side reaction, which becomes exclusive in some cases, is β-hydride elimination of an intermediate cyclopentyl- or cyclopentenyl zirconocene.