Addition of Me2CuLi to Enones and Enoates Effects of Solvent and Additives on the Yield and Stereoselectivity

Article abstract of DOI:10.1016/S0040-4020(01)88500-8

High yields of diastereomeric 1,4-addition products are obtained on addition of 1, 2 or 3 to 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 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. Key words: lithium diorganocuprates; conjugate addition; stereoselectivity; solvent effects; effects of additives.