Synthesis of gem-dialkoxycarbonylcyclopropane derivatives from olefins by the reaction with dibromomalonic esters and copper in dimethyl sulphoxide

A novel method for the synthesis of gem-dialkoxycarbonylcyclopropane derivatives is reported which involves the reaction of olefins with dibromomalonic esters and Cu in dimethyl sulphoxide. The reaction was applicable to a wide range of olefins and proceeded smoothly at moderate temperature to give the cyclopropane derivatives often in good yields. Cu was converted to Cu(II) bromide during the reaction. The reaction was weakly electrophilic and proceeded non-stereospecifically, and a stepwise mechanism involving addition and elimination appeared favourable for the reaction. In contrast, in the previously reported examples of the cyclopropanation of olefins by organic gem-dihalides and Cu in an aromatic hydrocarbon, Cu was converted to Cu(I) halides and a concerted cycloaddition of carbenoid intermediates appeared favourable.