Vitamin B12-mediated electrochemical cyclopropanation of styrene

Vitamin B12 (a cobalt corrin complex) mediated the reduction of methylene chloride in the presence of styrene to give cyclopropylbenzene in quantitative yields in DMF containing tetrabutylammonium bromide (TBAB) and acetic acid with current efficiency 45% and turnover rate 4-fold larger than a typical vitamin B12-mediated 6membered ring cyclization. A pathway involving formation and electroreductive cleavage of a chloromethylene-CoIII intermediate to yield a chloromethylene radical that adds to styrene is suggested. The reaction is highly sensitive to solvent composition, and water in the solvent acts as a proton donor to facilitate production of 1-chloro-3-phenylpropane in a competitive pathway.