[Development of novel carbon-carbon bond forming reactions using zirconocene complex]

Novel zirconium-mediated carbon-carbon bond-forming reactions were developed. The allylic, gamma-alkoxyallylic, allenyl, and gamma, gamma-dialkoxyallylic zirconium species can be prepared from corresponding ethers under mild conditions through the addition of a zirconocene-butene complex to the carbon-carbon multiple bond of the ethers and subsequent beta-elimination of the alkoxyl group. The gamma,gamma-dialkoxyallylic zirconium species reacts with carbonyl compounds at the beta-position of the zirconium atom like a ketene dialkyl acetal in the presence of stoichiometric amounts of Lewis acid and gave cyclopropane and/or cyclobutane derivatives. Intramolecular reaction of allylic zirconium species with acetal also develops as a ring contraction reaction of carbohydrates and morpholine derivatives. This method is useful for the construction of chiral highly functionalized carbocycles and pyrrolidines. The intramolecular ester transfer reaction through the zirconium-mediated coupling reaction of alkenyl carbamates gave gamma-aminobutyric acid derivatives and pyrrolidine-3-carboxylic acids.