A Convergent Paired Electrochemical Synthesis of New Heterocyclic Compounds. Reaction of Benzoquinones with 3-Amino-4-hydroxycoumarin
D. Nematollahi* and H. Karbasi
Faculty of Chemistry, Bu-Ali-Sina University, P. O. Box 65174, Hamedan, Iran
Electrochemical oxidation of catechols (1) has been studied in the presence of cathodically generated 3-amino-4-hydroxycoumarin(3a) as a nucleophile in aqueous solutions, using cyclic voltammetry and controlled-potential coulometry. The results indicate that the o-benzoquinones derived from catechols (1) participate in Michael addition reaction with 3-amino-4-hydroxycoumarin(3a) to form the corresponding new heterocyclic compounds (7) (oxidized form of coumestan derivatives). The electrochemical process consists of a multi-step including (a) cathodic reduction of 4-hydroxy-3-nitrocoumarin (3) to 3-amino-4-hydroxycoumarin (3a), (b) anodic oxidation of catechols (1) to related o-benzoquinone (2), (c) the Michael addition reaction of 3-amino-4-hydroxycoumarin (3a) to o-benzoquinone (2), and (d) anodic oxidation of formed adduct. The paired electrochemical synthesis of compounds 7a and 7b has been successfully performed in a one-pot process at carbon rods as working and counter electrodes in an undivided cell.
Keywords: 4-Hydroxy-3-nitrocoumarin, Catechol, Paired electrochemical synthesis, Cyclic voltammetry, 3-Amino-4-hydroxycoumarin