Formation of Carbon-Carbon Bonds using Zirconocene-Butene Complex (”Cp₂Zr”) as a Synthetic Tool

An efficient formation of the allylic zirconocene species by treatment of allylic ether derivatives with a low-valent zirconocene complex (”Cp₂Zr”) through an easy β-alkoxyl group elimination of the primarily formed zirconacyclopropane compounds was developed. This procedure is applicable to the generation of γ-alkoxy allylic zirconium and allenyl zirconium species from α,β-unsaturated aldehyde acetals and propargylic ethers, respectively. This methodology can also be applied to the unprecedented and highly diastereoselective formations of optically pure carbocycles and pyrrolidines by ring contractions of vinylsugar and vinylmorpholine derivatives. In the ring contraction of vinylsugar compounds, we could explain the high diastereoselectivity of the reaction by isolating a nine-membered cyclic zirconocene intermediate, which includes a Z-allylic zirconocene portion in the ring. Useful applications of the ”Cp₂Zr”-mediated ring contraction to the preparation of bioactive compounds is discussed.

zirconocene equivalent - allylic zirconocene - ring contraction - oxetanocin - macronecine