Stereospecific synthesis of (E)- and (Z)-1-chloro-1,2-difluorostyrenes

(Z)-2-chloro-1,2-difluoro-1-iodoethene and the (E)-2-chloro-1,2-difluoro-1-iodoethene react with activated zinc at 50 °C to stereospecifically generate the corresponding zinc reagents in 95% yields. These zinc reagents could be selectively coupled in a Negishi type coupling process with substituted aryl iodides to produce the corresponding (E)- and (Z)-1-chloro-1,2-difluorostyrenes in high yields. Both electron donating and electron withdrawing substituents on the aryl ring successfully participate in the Negishi coupling process. In some cases a 1-chloro-1,2,3,4-tetrafluoro-4-arylbutadiene was formed as a byproduct - indicative of the reactive nature of the vinyl chlorine in the 1-chloro-1,2-difluorostyrenes.