Cerium ammonium nitrate hydroquinones oxidation

Moore et al. investigated the thermal rearrangements of differently substituted cyclobutenones. Reactions of 4-alkenyl-4-hydroxycyclobute-nones such as 18, in which the triple bond is replaced by a double bound, are complementary to the ring expansions of 4-alkynyl-4-hydroxycyclobute-nones and provide a route to the differently substituted benzoquinones, such as aurrantiogliocladin 19. The reaction proceeds via enyne-ketene 20. Since cyclization produces a derivative of hydroquinone 21, an additional oxidation step is required that is accomplished with the use of cerium ammonium nitrate on silica. This ring expansion process is independent of the... 

Monofluorinated hydroquinone and quinone are obtained by stepwise oxidation of 2-fluorophenol(l) using different oxidation agents.167 In the first stage, potassium peroxydisulfate is applied and the resulting hydroquinone 2 is further oxidized to 3 by ammonium cerium(IV) nitrate.167... 

Catechols and hydroquinones can be converted (91-98%) into quinones by cerium(IV) salts coated onto silica as free-flowing yellow powder from impregnation with cerium(IV) ammonium nitrate. This reaction is usually performed in the presence of magnesium sulfate. The same (NH4)2Ce(N03)6 SiQ2 reagent in the dry state effects oxidative nitrations of arenes. For example a-mq>hthol is converted to the Orth) (42%) and the para (38%) nitro compounds, while its metiiyl or ethyl ethers give exclusively the para nitration product (equation 4). In solution, the products are cmtaminated with the products of dinitration and of oxidation into quinones. ... 

Quinones can he prepared hy the oxidation of phenols, dihydroxy-henzenes, dimethoxyhenzenes and anilines. For example, 1,4-dihydroxy-henzene (hydroquinone) can he oxidized in good yield using sodium chlorate in dilute sulfuric acid in the presence of vanadium pentoxide and also hy manganese dioxide and sulfuric acid and hy chromic acid. Other reagents which convert hydroquinones to quinones include Fremy s salt [potassium nitrosodisulfonate, (KS03)2N0] and cerium(IV) ammonium nitrate [CAN, Ce(NH4)2(N03)J. 

The hydroquinone dimethyl ether moiety of (+)-74 was oxidatively cleaved with ammonium cerium(IV) nitrate ((NH4)2Ce(N03)6), yielding xestoquinone (12b5)-(+)-4 as crystals mp 213-216°C dec natural, mp 212-214°C dec (Scheme 15). Xestoquinone (12bS)-(+)-4 was finally reduced with sodium hydrosulfite to afford xestoquinol (12bS)-62 in an almost quantitative yield. Although xestoquinol 62 has not been isolated yet as a natural product, the spectroscopic data of the synthetic sample reasonably support its structure. The first total synthesis of (+)-xestoquinone and xestoquinol has been thus achieved. 

Reactions of ammonium hexanitratocerate(IV) with organic substrates other than benzyl alcohol have also been examined, and 1,4-hydroquinone was quantitatively transformed into 1,4-quinone. Anisole and naphthalene can be nitrated. For the cerium-mediated oxidation reactions in ionic liquids, high reaction temperature is beneficial because of the formation of smaller amounts of by-products. 

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