Synthesis of Ferrocenylbenzenes via Cp*RuCl-Catalyzed Partially Intramolecular Cyclotrimerization of Ferrocenylalkynes

In the presence of catalytic amounts of Cp*RuCl(cod), the [2 + 2 + 2] cycloaddition of 1,6-diynes with ethynylferrocene proceeded at ambient temperature to afford ferrocenylbenzenes in 62-72% yields. An unsymmetrical 1,6-diyne bearing a ferrocenyl terminal was allowed to react with monoalkynes to give the corresponding meta-substituted cycloadducts selectively as single regioisomers. On the other hand, Bis(ferrocenyl)ruthenacyclopentatriene was formed from a diyne bearing a ferrocenyl group on both terminals and excess Cp*RuCl(cod).