Samarium-Mediated beta-Elimination in Dihalo Alcohols: Diastereoselective Synthesis of (Z)-Vinyl Halides.

High diastereoselectivity in beta-elimination reactions of O-acetyl 1,1-dihaloalkan-2-ols to give (Z)-vinyl halides was achieved by using samarium diiodide [Eq. (1)]. The reaction was also highly diastereoselective and totally chemoselective when a mixture of diastereoisomers was used as substrate (X(1), X(2)=halogen; X(1) not equal X(2)).