ChemInform Abstract: Regio- and Stereo-Selectivity in the Reaction of Methyl 4,5-Epoxy-2-hexenoate with Methylcopper Reagents.
Abstract
The reaction of the title compound (I) with MeCu (II) (or, similarly, with Me2CuLi or with BF3 complexes of (II) and Me2CuLi) gives predominantly the γ-methylated product (IV) via an SN2 process whereas the reaction of (I) with the cyanocuprate (V) or with higher order dimethylcyanocuprate and their BF3 complexes affords preferentially the α-methylated product (III) via an SN2' process.
ChemInform Abstract
The reaction of the title compound (I) with MeCu (II) (or, similarly, with Me2CuLi or with BF3 complexes of (II) and Me2CuLi) gives predominantly the γ-methylated product (IV) via an SN2 process whereas the reaction of (I) with the cyanocuprate (V) or with higher order dimethylcyanocuprate and their BF3 complexes affords preferentially the α-methylated product (III) via an SN2' process. Anti-diastereoselectivity is always observed in the reactions with (II), Me2CuLi, (V), or Me2CuCNLi2; the presence of BF3·Et2O, however, increases the formation of the syn isomers of (III) and (IV). In addition, the by-product (VI) is formed in most cases. - The regio- and stereoselectivities of the reactions are discussed on the basis of CNDO/2 calculations.
