Stereoselective reduction of meso- and dl-1,2-dibromo-1,2-diphenylethane at the mercury electrode

Abstract

Meso- and dl-1,2-dibromo-1,2-diphenylethane are both reduced to ∼100% trans-stilbene at the mercury electrode in DMF containing 0.1 M Et4NClO4. Polarographic, coulometric and controlled-potential experiments as well as u.v. spectra substantiate a two-electron process giving the trans-olefin and Br− ions. Reduction performed in the presence of weak or strong proton donors gave the same results as in the absence of acids. Arguments in favour of a “synchronous concerted” mechanism are discussed.