Copper(I)-catalyzed tandem inter–intramolecular cyclization reactions of zirconacycles: formation of highly substituted styrenes, vinylcyclohexadienes, and related compounds

1,2,3,4-Tetrasubstituted cyclopentadienes and their applications for metallocenes: efficient synthesis through zirconocene- and CuCl-mediated intermolecular coupling of two alkynes and one diiodomethane

1,2,3,4-Tetrasubstituted cyclopentadienes and indene derivatives with identical or different substituents were obtained in good to excellent isolated yields through a zirconocene- and CuCl-mediated intermolecular coupling process. This synthetic procedure involved three organic partners, including one CH2 I2 , and two different or identical alkynes. Two alkynes or one diyne undergo Cp2Zr(II)-mediated (Cp = η(5)-C5H5) pair-selective reductive coupling to afford the corresponding zirconacyclopentadiene derivatives, which react, in the presence of CuCl and 1,3-dimethyl-3,4,5,6-tetrahydro-2(1 H)-pyrimidinone (DMPU), with CH2I2 through intermolecular followed by intramolecular coupling to afford the cyclopentadiene derivatives. An application of the prepared tetrasubstituted cyclopentadiene derivatives was demonstrated by the facile synthesis of the corresponding zirconocene complexes [((4R)Cp)2ZrCl2] and [((4R)Cp)2ZrR'2] (R' = Me, Et, or nBu). The unique 1,2,3,4-tetrasubstituted cyclopentadiene ligands and the corresponding metallocenes are expected to have further applications in organometallic chemistry and organic synthesis.

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.