Stereoselectivity in the Michael Addition Reaction of Dialkylcuprates to the 2-Cyclohexenones with C-4 Ester Substituents

Abstract

  Stereoselectivity in the Michael addition of (Me₂C=CH)₂CuMgBr and (Me₂C=CH)₂CuLi to 3-alkyl/H-4-[(tert-butoxycarbonyl)alkyl]-2-cyclohexenone was studied. (Me₂C=CH)₂CuMgBr showed stereoselectivity in all cases (3-H, Me: anti; 3-n-Bu: syn). This stereoselectivity disappeared in the reaction of (Me₂C=CH)₂CuLi with 4-[(tert-butoxycarbonyl)methyl]-3-butyl-2-cyclohexenone. However, the stereoselectivity was recovered by elongating the 4-alkyl chain of 2-cyclohexenone to show the same selectivity as that of (Me₂C=CH)₂CuMgBr.