Transmetalation Reactions of Alkenylalanes: Copper-Catalyzed Conjugate Adition to Enones

Article abstract of DOI:10.1021/jo00037a040

An improved synthetic strategy for the in situ preparation of vinyl cuprates from alkynes is presented and used for the stereospecific synthesis of di-, tri-, and tetrasubstituted olefins.Hydroalumination or Cp2ZrCl2-catalyzed carboalumination of alkynes, followed by in situ transmetalation to bis-alkynyl-copper complex <(C4H9C<*>C)2CuCN>Li2 and addition of enones, led to the isolation of 1,4-addition products in high yields.Stoichiometric or catalytic amounts of copper complex gave similar results.However, in the presence of less than 10 mol percent of Cu(I) complex, side products were formed and a significant drop in the yield of the desired conjugate addition product was observed.An ate-transfer mechanism is postulated for the rapid exchange of vinyl ligands from Al(III) to Cu(I) at low temperatures.