Electrosynthesis of a Biaurone by Controlled Dimerization of Flavone: Mechanistic Insight and Large-Scale Application

• Published in: Journal of organic chemistry 2020-08, Vol.85 (16), p.10658-10669, Article acs.joc.0c01220
• Main Authors: Hosseini, Seyyedamirhossein, Thapa, Bishnu, Medeiros, Maria J, Pasciak, Erick M, Pence, Michael A, Twum, Eric B, Karty, Jonathan A, Gao, Xinfeng, Raghavachari, Krishnan, Peters, Dennis G, Mubarak, Mohammad S
• Format: Article
• Language: English
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/acs.joc.0c01220

The electrochemistry of flavone (1) has been carefully investigated at glassy carbon cathodes in dimethylformamide containing 0.10 M tetra-n-butylammonium tetrafluoroborate as supporting electrolyte. In this medium, a cyclic voltammogram for a reduction of 1 exhibits a reversible cathodic process (E pc = −1.58 V and E pa = −1.47 V vs SHE) that is followed by an irreversible cathodic peak (E pc = −2.17 V vs SHE). When water (5.0 M) is introduced into the medium, the first peak for 1 becomes irreversible (E pc = −1.56 V vs SHE), and the second (irreversible) peak shifts to −2.07 V vs SHE. Bulk electrolyses of 1 at −1.60 V vs SHE afford flavanone, 2′-hydroxychalcone, 2′-hydroxy-3-phenylpropionate, and two new compounds, namely (Z)-1,6-bis­(2-hydroxyphenyl)-3,4-diphenylhex-3-ene-1,6-dione (D1) and (Z)-2,2′-(1,2-diphenylethene-1,2-bis­(benzofuran-3­(2H))-one) (D2), obtained in significant amounts, that were characterized by means of 1H and 13C NMR spectrometry as well as single-crystal X-ray diffraction. Along with the above findings, we have proposed a mechanism for the electroreduction of 1, which has been further corroborated by our quantum mechanical study.