Copper-Catalyzed Conjugate Additions of Organozirconocenes. Synthetic and Mechanistic Studies.

Article abstract of DOI:10.1016/S0040-4020(01)85058-4

In the presence of 3-10 mol percent of Cu(I) salts such as CuBr*SMe2 or CuCN, alkylzirconocenes add readily to α,β-unsatuatred ketones, aldehydes, and sulfones.The reaction yield is sensitive to the presence of Lewis acids and bases.Steric hindrance as well as a broad range of functional groups are tolerated in the conjugate addition process.Unsaturated N-acyl oxazolidinones give high diastereoselectivities for the formation of the new asymmetric carbon.The resulting zirconium enolates can be used for tandem aldol addition reactions to aldehydes.Depending on the type of copper salt used, slow or fast formation of copper mirror occurs, but no intermediate copper species is detected spectroscopically.Therefore, a mechanism involving enone complexation by the Lewis-acidic zirconocene followed by inner-spere transfer of the alkyl substituent to chelated Cu(I) is proposed.