R. Hazard, S. Jaouannet, A. Tallec
1982
Citations
0
Influential Citations
23
Citations
Journal
Tetrahedron
Abstract
Abstract The electrochemical behaviours of 1-bromo-2,2-diphenylcyclopropane carboxylic acid, its methyl ester and 1,1-dibromo-2,2-diphenylcyclopropane are investigated in the presence of strongly adsorbed alkaloids: yohimbine, emetine, brucine, strychnine and methylstrychninium cations. The polarographic study evidences the existence of interactions between the alkyl bromides and nitrogen cations; these interactions make easier the 2 e cleavage of the carbon-halogen bond. Whatever the alkaloid used, rather poor optical yields are obtained after electroreduction of monobromo compounds. On the contrary, notably optically active products are obtained from the dibromide derivative, but only when the inductor can act as a protonating species; 45% optical yield can be achieved in the presence of emetine. The mechanism of asymmetric electrochemical synthesis is interpreted in terms of (i) preferential presentation of one of the two stereotopic faces of the substrate at the mercury cathode, made chiral by the adsorption of the alkaloid and (ii) protonation by the acidic form of the inductor of the carbanion resulting from a 2 e reduction.