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

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journal contribution
posted on 2020-08-03, 04:48 authored by Seyyedamirhossein Hosseini, Bishnu Thapa, Maria J. Medeiros, Erick M. Pasciak, Michael A. Pence, Eric B. Twum, Jonathan A. Karty, Xinfeng Gao, Krishnan Raghavachari, Dennis G. Peters, Mohammad S. Mubarak
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 (Epc = −1.58 V and Epa = −1.47 V vs SHE) that is followed by an irreversible cathodic peak (Epc = −2.17 V vs SHE). When water (5.0 M) is introduced into the medium, the first peak for 1 becomes irreversible (Epc = −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.