Quinone diacetals aromatization

Phenols can be mononitrated in a two-phase system (ether/water) by sodium nitrate and aqueous hydrochloric acid in the presence of a catalytic amount of lanthanum(III) nitrate in yields genei ly above 80%. Phenol itself gives 2 1 ortho.para nitration, while phenols substituted in the para position give predominantly ortho nitration with some meta nitration (equation 21). As shown recently nitration of phenols in the two-phase system occurs even without lanthanum(III) nitrate. By use of sodium nitrate, aqueous sulfuric acid and a catalytic amount of sodium nitrite in the two-phase system mononitration of phenols can be achieved in high yields. Under these conditions starting from 3-substituted phenols in addition to the nitro compounds formation of quinones has been observed. Polyhydroxy aromatics are typically difficult to nitrate directly. Thus, 4,6-dinitroresorcinol (45) has been synthesized from resorcinol diacetate (44) with nitric acid or mixed solutions of nitric acid/sulfuric acid containing urea as a nitrous trap (equation 22). ... 

Phenols are oxidized by NaBiO3 to polyphenylene oxides, quinones, or cyclohexa-2,4-dienone derivatives, depending on the substituents and the reaction conditions [263]. For example, 2,6-xylenol is oxidized in AcOH to afford a mixture of cyclohexa-dienone and diphenoquinone derivatives (Scheme 14.123) [264] and is oxidatively polymerized in benzene under reflux to give poly(2,6-dimethyl-l,4-phenylene) ether (Scheme 14.124) [265]. Substituted anilines and a poly(phenylene oxide) are oxidatively depolymerized by NaBiO, to afford the corresponding anils [266]. Nal iO, oxidizes olefins to vicinal hydroxy acetates or diacetates in low to moderate yield [267]. Polycyclic aromatic hydrocarbons bearing a benzylic methylene group are converted to aromatic ketones in AcOH under reflux (Scheme 14.125) [268]. 

Oxidation of benzoquinones and naphthoquinones by palladium diacetate in arene-containing acetic acid gave the corresponding aryl-substituted quinones (eq 70). Treatment of 1,4-naphthoquinone with aromatic heterocycles, for example furfural, 2-acetylfuran, 2-acetylthiophene, and 4-pyrone, yielded the corresponding 2-heteroaryl-substituted 1,4-naphthoquinones. 

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