Earth-Abundant Metal-Catalyzed Cross-Coupling Reactions of 1-Bromocyclobut-1-enes with Grignard Reagents

Cross-coupling reactions have been developed between C2-substituted 1-bromocyclobut-1-enes and Grignard reagents using two effective catalysts, e.g., Fe(acac)₃ and Ni(acac)₂. The iron catalyst works in THF but requires NMP as the co-solvent, with the advantage of achieving cross-coupling reactions with alkyl Grignard reagents. The nickel catalyst was able to promote the reactions in THF without any additive and showed high reactivity with electron-rich aryl Grignard reagents. These catalysts gave various types of substituted cyclobutenes in good yields.