Ni-Catalyzed Defluorination for the Synthesis of gem-Difluoro-1,3-dienes and Their [4+2] Cycloaddition Reaction

A nickel-catalyzed defluorination of alpha-trifluoromethylated allyl/propargyl carbonates using bis(pinacolato)-diboron (B(2)pin(2)) as a reactant is described. The reaction proceeds under relatively mild reaction conditions, providing conjugated gem-difluoroalkenes in moderate to good yields. Applications of the resulting 1,1-difluoro-1,3-dienes by [4 + 2] cycloaddition reactions with maleimide led to cyclic fluorinated products efficiently.