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

A nickel-catalyzed defluorination of α-trifluoromethylated allyl/propargyl carbonates using bis­(pinacolato)­diboron (B<sub>2</sub>pin<sub>2</sub>) as a reactant is described. The reaction proceeds under relatively mild reaction conditions, providing conjugated <i>gem</i>-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.