ELECTROCHEMICAL REDUCTION OF 1,1-DIHALO-2,2-DISUBSTITUTED CYCLOPROPANES

The electrochemical reduction of 1,1-dihalo-2-R-2-methylcyclopropanes was studied by polarography and preparative electrolysis. A mixture of stereoisomeric monoboro- and monochlorocyclopropanes was obtained wit h preparative yield of 60-70% in preparative electroreduction in metha nol against a background of 0.1 M LiClO4. In the case of bromine deriv atives of cyclopropanes (except when R = CN) an effect was found on th e part of the current density on the ratio of cis and trans isomers, w hich was interpreted as a change, in dependence on current density, of the contributions of the reactions of reduction of the starting compo unds (SN2 mechanism) and ionic pairs (S(N)1 mechanism). The effect of the solvent (CHCl3, DMF, DMSO, MeOH) and background salt (LiClO4, Et4N Br) on the ratio of stereoisomers is in agreement with this interpreta tion.