Electrochemical reduction mechanism of rotenone. Part 2. Effect of proton donors

Abstract

The effect of proton donors on the electrochemical reduction mechanism of rotenone (I) in acetonitrile and on the yield and nature of the electrolysis products has been examined. In the presence of acetic acid one-electron reduction of the carbonyl group leads to the formation of the neutral ketyl radical which dimerizes to the corresponding pinacol (a new derivative in the rotenoid series) as established by ¹³C n.m.r. analysis. On the basis of ¹H n.m.r. spectra a trans-12a-H, 12-OH configuration is proposed for this compound. If phenol is used as proton donor, rotenol (or its reduction products) is obtained as well as the pinacol. The latter can be formed through keto-enol isomerization of the ketyl radical and/or rotenone itself catalysed by the conjugated base of the proton donor which is formed during the electrolysis.