DIASTEREODIFFERENTIATION IN SN2' ADDITIONS OF METHYLCUPRATES TO NONRACEMIC ACYCLIC VINYLOXIRANES

S(N)2' additions of Me2CuLi, MeCu(CN)Li, and Me2Cu(CN)Li2 to the 2S and 2R alkoxy cis-(Z)- and -(E)- vinyloxiranes 8, 9, 13, and 14 were examined as possible routes to acrylic subunits of polypropionate natural products. Highest antisyn ratios were found for the (2S)- and (2R)-hydroxy-(E)-vinyloxiranes 13a and 14a followed by the (2R)-MTM ether analogue 14c. In both cases Me2CuLi gave higher ratios than either of the cyanocuprates (> 99:1 vs 14:1 for 13a/13b and > 40:1 vs approximately 24:1 for 14c).