Synthesis of (E)-α,β-unsaturated esters with total or high diastereoselectivity from α,β-epoxyesters

[GRAPHICS] High stereoselective beta-elimination in 2,3-epoxyesters 1 was achieved using samarium diiodide, yielding alpha,beta-unsaturated esters 2, in which the C=C bond is di-, tri- or tetrasubstituted. The starting compounds 1 are easily prepared by reaction of the corresponding lithium enolates of alpha-chloroesters with aldehydes or ketones at -78 degreesC. The influence of the reaction conditions and the structure of the starting compounds in the stereoselectivity of the beta-elimination reaction is also discussed.