Nickel(0)-catalyzed coupling of vinylzirconiums to alpha-bromo-alpha,alpha-difluoro esters. Convenient generation of a functionalized allyldifluoro moiety

Vinylzirconium reagents couple with alpha-bromo-alpha,alpha-difluoro esters in the presence of a Ni(PPh3)(4) catalyst to form alkenyl difluoro esters in good yields. This reaction exemplifies a novel mode of reactivity for al pha-bromo-alpha,alpha-difluoro esters wherein the inherent electrophilicity of the carbon-bromine bond is utilized in the course of the reaction rathe r than being formally reduced in Reformatzsky-type reactions. The choice of ester group in the reactant is critical to the success of this reaction wi th the isopropyl group, formed via a novel transesterification procedure, g iving the best yields. (C) 2000 Elsevier Science Ltd. All rights reserved.