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 beta-alkoxyl group elimination of the primar ily formed zirconacyclopropane compounds was developed. This procedure is applicable to the generation of gamma-alkoxy allylic zirconium and allenyl zirconium species from alpha,beta-unsaturated aldehyde acetal s and propargylic ethers, respectively. This methodology can also be a pplied to the unprecedented and highly diastereoselective formations o f 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 interm ediate, which includes a Z-allylic zirconocene portion in the ring. Us eful applications of the ''Cp2Zr''-mediated ring contraction to the pr eparation of bioactive compounds is discussed.