Arenes oxidations

Phenolic compounds are commonplace natural products Figure 24 2 presents a sampling of some naturally occurring phenols Phenolic natural products can arise by a number of different biosynthetic pathways In animals aromatic rings are hydroxylated by way of arene oxide intermediates formed by the enzyme catalyzed reaction between an aromatic ring and molecular oxygen... 

One ammo acid often serves as the biological precursor to another L Phenylala nine is classified as an essential ammo acid whereas its p hydroxy derivative L tyro sine IS not This is because animals can convert L phenylalanine to L tyrosine by hydrox ylation of the aromatic ring An arene oxide (Section 24 7) is an intermediate... 

Although details vary for particular cases, a common synthetic route to diol epoxides such as (30) frequently begins with the ketone (33) (78MI50700). The final epoxidation is often highly stereoselective. A general route to non-K-region arene oxides has been described (75JA3185). 

Arene oxides of heterocycles such as pyridine have often been postulated as photoisomerization intermediates (81H(15)1569,72JOC3592) but to date they have not been isolated or extensively studied. 

Dihydro-9,10-epoxyphenanthrene and related arene oxides are of considerable interest as carcinogens formed by polycyclic aromatic hydrocarbons in vivo.45 Phenanthrene oxide does not isomerize to the corresponding dibenzoxepin under thermal conditions. Photolysis of... 

Thermolysis of 3-oxaquadricyclanes in which the bond between Cl and C2 is part of a cyclohexane structure gives a,/J-annulated oxepins 11 in good yield.133 The enlargement of the an-nulated ring favors the arene oxide structure.134... 

Vol. E19b, p 1866f).190 191 Bulky substituents in the 2- and 7-positions, sueh as /erf-butyl groups, prevent the isomerization to arene oxides.191... 

Numerous reactions have been described in which the oxygen of the oxepin system is removed to give benzene derivatives. The formation of the aromatic products can be rationalized by an arene oxide as intermediate. A suitable reagent for the elimination of an oxygen atom from this heterocycle is triphenylphosphane, e.g. formation of l,24 2a,12 and 2b.1,9... 

Transition-metal complexes such as [Rh(CO)2Cl]2,204 Rh(butadiene)2Cl,205 or Cr(CO)3(NH3)312 have also been used for the deoxygenation of oxepins to give 312,204 205 and benzoxepins to give 4.12,204 Occasionally, substantial amounts of phenolic compounds have been isolated due to the competing NIH shift of the arene oxide.204 1-Benzoxepin and 3-benzoxepin resist oxygen extrusion under these conditions probably due to their inability to form arene oxi-des.133,204... 

Forgue, S.T. et al. (1980). Direct evidence that an arene oxide is a metabohc intermediate of 2,2, 5,5 -TCB In Abstracts of the I9th Meeting of the Society of Toxicology (Abstract No. 383). 

Arene oxides can be intermediates in the bacterial transformation of aromatic compounds and initiate rearrangements (NIH shifts) (Dalton et al. 1981 Cerniglia et al. 1984 Adriaens 1994). The formation of arene oxides may plausibly provide one mechanism for the formation of nitro-substituted products during degradation of aromatic compounds when nitrate is present in the medium. This is discussed in Chapter 2. 

Cerniglia CE, JP Ereeman, EE Evans (1984) Evidence for an arene oxide-NIH shift pathway in the transformation of naphthalene to 1-naphthol hy Bacillus cereus. Arch Microbiol. 138 283-286. 

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