Radical-capturing reaction of 5,7,3′,4′-tetramethylquercetin with the AIBN radical initiator

Article abstract of DOI:10.1271/bbb.64.173

In order to clarify the mechanism for the radical-capturing reaction which is initiated at the C₃-hydroxyl group of flavonols, 5,7,3′,4′-tetramethylquercetin (TMQ) was reacted with the 2,2′-azobis-isobutyronitrile (AIBN) radical initiator in benzene. Six products, one depside and its two hydrolytic products, one nitrite adduct, and two others, were isolated from the reaction mixture, and their structures were determined by instrumental analyses. The quantitative change to the four main products against the reaction time was measured by an HPLC method. The radical-capturing reaction pathway for TMQ with AIBN is proposed from these products and their quantitative changes. The pathway dividing into two clearly reveals that one subpath formed the depside and its hydrolytic products, while the other formed the nitrite adduct. The reactivity of each two sub-path was nearly the same, different from the case of TMQ and the 2,2′-azobis-2,4-dimethylvaleronitrile (AMVN) radical initiator.