ADDITION OF ME2CULI TO ENONES AND ENOATES - EFFECTS OF SOLVENT AND ADDITIVES ON THE YIELD AND STEREOSELECTIVITY

High yields of diastereomeric 1,4-addition products are obtained on addition of 1, 2 or 3 to [Me2CuLi]2 in toluene, hexane or CH2Cl2. The stereoselectivity is strongly influenced by the choice of solvent as well as by addition of TMSCl or TMSI. The diastereoselectivity of the reaction between S-1 and [Me2CuLi]2 changed from 13.5:1 RS:SS ratio when the reaction was performed in thiophene, to 10:1 in toluene, to 1:14 in CH2Cl2 with TMSI. The RS configuration obtained with non-polar solvents such as toluene is attributed to chelation control of the stereoselectivity while the reaction under "non-chelation" conditions, i e ether and TMSCl or TMSI, shows low stereoselectivity.