Cyclopropanation via a Simple Barbier Reaction in DMF

Jean Paul Paugam and co-workers from France have published a simple cyclopropanation reaction between α,α-trihalomethyl or α,α-dihalomethyl aromatics and activated olefins. In a typical reaction magnesium is suspended in DMF and dichlorodiphenylmethane (DCDPM) and dimethyl itaconate are added via a dropping funnel. Yields are typically in the region of 50-70%, with substrates such as DCDPM, α,α-dibromotoluene and methyl trichloroacetate reacting with olefins such as itaconate esters, cyclohexenone, ethyl acrylate, vinyl ketones and acrylonitrile.  The reaction is thought to proceed by initial conjugate addition of the Grignard reagent to the olefin followed by SN_i cyclisation although an alternative pathway via formation of a carbene from the Grignard reagent cannot be ruled out.(Synlett, 2003, (4), 485-488).