AsymmetricSimmons-Smithreactions of α,β-unsaturated acetals derived from chiral dialkyl tartrate or (2R,4R)-2,4-pentanediol are described. Treatment of the acetal with diethylzinc and methylene iodide gives a cyclopropane with high diastereoselectivity. The acetal group is readily transformed to the aldehyde or the ester group. In addition, the method is successfully applied to the enantioselective