Selective Cyclization and Pinacolization Directed by Tetraalkylammonium Ions

Article abstract of DOI:10.1021/jo00357a018

The effect of the electrolyte composition on the cathodic reduction of cyclohexanone and 6-hepten-2-one was investigated.It was found that addition of catalytic amounts of certain tetraalkylammonium salts to the electrolysis solution alters the reaction pathways.Using a mercury cathode in DMF, dimethylpyrrolidinium (DMP⁺) tetrafluoroborate, shifts the potential required for preparative reduction to less negative values and changes the reaction products.Cyclohexanone yields the corresponding pinacol and 6-hepten-2-one is stereoselectively cyclized to cis-1,2-dimethylcyclopentanol (95percent).In the absence of DMP⁺ both substrates are reduced to the corresponding simple alcohols.Stereoselective reductive cylization in DMF can also be induced by tetraethylammonium cations (TEA⁺) on mercury and by either DMP⁺ or TEA⁺ on graphite electrodes.The combination of DMR⁺ and mercury results in excellent chemical yield and current efficiency.On the basis of results of preparative electrolyses under various conditions and cyclic voltammograms, a mechanism involving the initial reduction of the catalyst cation with participation of the electrode material is proposed.It is suggested that catalysis by specific tetraalkylammonium ions can lead to a preference for one-electron reaction routes.