Electrochemical oxidation of 3,4-dihydroxybenzoic acid (I) and 4-tert-butylcatechol (V) in the presence of 4-hydroxycoumarin (II) as nucleophile in aqueous solution has been studied using cyclic voltammetry and controlled-potential coulometry. The results indicate that I via a 1,4-addition (Michael) reaction under electro-decarboxylation reaction converts to coumestan TV, and V via 1,4-(Michael) and 1,6-addition reactions converts to new coumestan VII. The electrochemical synthesis of IV and VII has been performed successfully in an undivided cell in good yield and purity.