ARENE OXIDES OF POLYNUCLEAR AROMATIC HYDROCARBONS

Benzene monoxide-oxepin and its sulfur analog are treated elsewhere (Chapter 5.1.7) (67AG(E)385). However, we point out here that electron-withdrawing substituents often favor the benzene oxide tautomer. The first study on oxides of the environmentally hazardous polychloro- and polybromo-biphenyls shows that they exist mainly in the benzene oxide form (81JOC3721). Oxides of polynuclear aromatic hydrocarbons (PAH) also exist mainly in the fused-ring oxirane form. 

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). 

DNA binding of (30) and its analogs depends on nucleophilic attack on the oxirane ring at C(10), the preferred position because it is benzylic. With strong nucleophiles such as 

Fused-ring Oxiranes, Oxirenes, Thiiranes and Thiirenes 

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. 

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The synthesis of quinones from arenes is an area which demands further research, despite the number of reagents presently available for this transformation. This is highlighted by the synthesis of the naphthoquinone (3). Direct oxidation of the dibromoarene (1) was unsatisfactory, and therefore Bruce and coworkers had to resort to a multistep sequence involving nitration, reduction, diazotization, displacement by hydroxide and finally oxidation of the phenol (2) with Fremy s salt (Scheme 1). Although there are examples of the oxidation of polynuclear aromatic hydrocarbons to quinones, the direct oxidation of an arene to a quinone is a process not encountered in the synthesis of more complex mt ecules. 

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