ELECTROCHEMICAL STUDY OF THE FORMATION OF CYCLOPROPANES FROM GEM-DIHALOCOMPOUNDS AND ALKENES CATALYZED BY COPPER 1,10-PHENANTHROLINE COMPLEXES

The reactions between four gem-dihalides 1, 2, 3, and 4 and styrene in the presence of copper-1,10-phenanthroline complexes were investigate d. The formation of a cyclopropane derivative was only observed in the case of dimethyl dibromomalonate 1, while with the other gem-dihalide s the addition products were formed by a radical chain addition mechan ism. A study by cyclic voltammetry and chronoamperometry showed that t he reduction of 1 by the copper(I) complex is a redox catalysis which is kinetically controlled by the rate of the concerted electron-transf er carbon-bromine bond-breaking. In the presence of styrene the format ion of the cyclopropane proceeds by a radical addition followed by a c oncerted electron-transfer bond-breaking process. (C) 1997 Elsevier Sc ience Ltd.