[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-polarsolvents such