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

In order to clarify the mechanism for the radical-capturing reaction which is initiated at the C-3-hydroxyl group of flavonols, 5,7,3',4'-tetramethylq uercetin (TMQ) was reacted with the 2,2'-azobis-isobutyronitrile (AIBN) rad ical initiator in benzene. Six products, one depside and its two hydrolytic products, one nitrile adduct, and two others, were isolated from the react ion mixture, and their structures were determined by instrumental analyses. The quantitative change to the four main products against the reaction tim e was measured by an HPLC method. The radical-capturing reaction pathway fo r TMQ with AIBN is proposed from these products and their quantitative chan ges. The pathway dividing into two clearly reveals that one subpath formed the depside and its hydrolytic products, while the other formed the nitrile 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.