Direct electrochemical oxidation of abietane diterpene acids

Abietic and dehydroabietic acids are widely present in gum rosin (colophony). Transformation of the corresponding methyl ester derivatives of these abietane diterpenes have been reported, including several oxidation protocols. However, direct oxidation of the naturally occurring carboxylic acids has been less investigated. Herein we report an electrochemical method for the benzylic oxidation of dehydroabietic acid and for the olefin oxidation of abietic acid, which allows the sustainable preparation of the corresponding abietane-type ketones in gram-scale. Moreover, this method can be applied to the corresponding methyl ester derivatives. Furthermore, we conducted competitive experiments between the two acids and show that the methodology can be applied directly to the gum rosin.