(<i>Z</i>)-α-Haloacrylates: An Exceptionally Stereoselective Preparation via Cr(II)-Mediated Olefination of Aldehydes with Trihaloacetates

(Z)-α-Fluoro-, (Z)-α-chloro-, and (Z)-α-bromoacrylates were obtained with unprecedented yield and stereocontrol (>99%) via addition of the corresponding commercial trihaloacetates to aldehydes at room temperature using stoichiometric Cr(II) salts or catalytic Cr(II) with a regeneration system. The intermediate 2,2-dihalo-3-hydroxy adducts could be isolated in good yields under conditions of limited reagent at 0 °C.