Electrochemical reduction of bicyclo[3,3,1]nonadienediones: synthesis of substituted barbaralanes

Abstract

Electrochemical reduction of 4,8-dimethylbicyclo[3.3.1]nona-3,7-diene-2,6-dione in the first cathodic wave at –2.0 V gave dihydro-dimer products. In contrast, reduction in the second cathodic wave at –2.75 V in the presence of acetic anhydride gave a substituted barbaralane, 2,6-diacetoxy-4,8-dimethyltricyclo[3.3.1.0^2,8]nona-3,6-diene. Similarly by reduction of 4,6-dimethylbicyclo[3.3.1]nona-4,6-diene-2,8-dione in the second wave at –2.75 V, a further substituted barbaralane, 4,6-diacetoxy-2,8-dimethyltricyclo[3.3.1.0^2,8]nona-3,6-diene was obtained. The effect of substituents on the stability of the valence isomers of barbaralanes is discussed. The mechanism of electrochemical reduction is analysed on the basis of data obtained from cyclic voltammetry, and chronamperometry.