Cyclopropanation of Electron-deficient Olefins with Dibromomethane by Ni(0) Complexes and Zinc

Article abstract of DOI:10.1246/bcsj.56.1025

A new method for the synthesis of cyclopropane derivatives is described. It involves treatment of electron-deficient olefins with dibromomethane in the presence of Ni(0) complex/zinc/Lewis acid (or alkali halide) systems. Ni(PPh3)4/Zn/ZnBr2 system was effective for the cyclopropanation of methyl acrylate and acrylonitrile, but was ineffective for that of methyl vinyl ketone and acrylaldehyde. Ni(COD)2/Zn/NaI system was applicable to the cyclopropanation of methyl vinyl ketone as well as to that of methyl acrylate and acrylonitrile. Alternative catalytic systems which were easy to handle were exploited, involving in situ generated Ni(0) complexes prepared from NiBr2(PPh3)2 and zinc, or nickel bromide, sodium iodide, zinc, and an olefin. Catalytic amounts of nickel compounds are sufficient for the cyclopropanation of methyl acrylate, acrylonitrile, and methyl vinyl ketone, but a 1:2 nickel:acrylaldehyde mole ratio results in the best yield. A mechanism is proposed which involves metallacyclobutane as an intermediate.