130689-57-5Relevant academic research and scientific papers
Dioxygen Transfer from 4a-Hydroperoxyflavin Anion. 4. Dioxygen Transfer to Phenolate Anion as a Means of Aromatic Hydroxylation
Moto, Shigeaki,Bruice, Thomas C.
, p. 2284 - 2290 (2007/10/02)
Potassium 2,6-di-tert-butylphenolate (1-) in the presence of N5-ethyl-4a-hydroperoxy-3-methyllumiflavin anion (4a-FlEtOO-) yields (30 deg C, absolute t-BuOH; anaerobic) 2,6-di-tert-butylbenzoquinone (2), 4,4'-dihydroxy-3,3',5,5'-tetra-tert-butylbiphenyl (4), and 3,3',5,5'-tetra-tert-butyl-4,4'-diphenoquinone (5).The 4a-FlEtOO- is converted in turn to N5-ethyl-3-methyllumiflavin radical (FlEt.) and 1,5-dihydro-N5-ethyl-3-methyllumiflavin anion (FlEt-).Kinetic and product studies establish the sequence of eq A to be competent.The product 4 is proposed to arise by rearrangement of 3,3',5,5'-tetra-tert-butyl--4,4'-dione (3), which is known to be a product of dimerization of 1.In separate experiments, the rearrangement 3 -> 4 has been shown to occur (absolute t-BuOH) spontaneously (k = 1.3 * 10-4 s-1) and to be catalyzed by t-BuO-K+ (k = 3.5 * 103 M-1 s-1).The transfer of the peroxy substituent from 4a-FlEtOO- to 1-, yielding the quinone 2 and FlEt-, undoubtedly occurs via the cyclohexadienone peroxide anion (as shown).This is supported by the finding that the rate constant for conversion of 4a-FlEtOO- to reactive intermediate (X) is the same (0.37 s-1) as found previously for peroxidation of other ambident nucleophiles by 4a-FlEtOO- (i.e., 0.375 +/- 0.016 s-1).Of possible relevance to the mechanism of dioxygen transfer are the findings that 1- undergoes 1e- oxidation by FlEt. (k = 2.45 * 104 M-1 s-1) (products FlEt- + 1/2 4), a feature shown by other ambident nucleophilic substrates, and that the second-order rate constant for reaction of 1- with 3O2 (k ca. 0.9 M-1 s-1) is too small for this to be of importance in the formation of 2.It is pointed out that, since dioxygen transfer from 4a-FlEtOO- to 1- yields reduced flavin (FlEt-) and a quinone (2) and since FlEt- reduces quinones to hydroquinones, the oxygen-transfer mechanism could serve as a means of hydroxylation of phenols.
