Cerium ammonium nitrate benzylic alcohols

Cerium(IV) ammonium nitrate in aqueous acetonitrile will also cleave a p-methoxyp/zeny/ ether (presumably to benzoquinone).335 The reaction was used in a synthesis of Stigmastellin A [Scheme 4.183] to release a primary alcohol in the presence of a benzyl ether.339 In an extension of the method, a bidirectional strategy for the synthesis of 2,3 5-trisubstitute d tetrahydrofuran components of annonaceous acetogenins benefited from the simultaneous protection of two primary hydroxyls as their Cj-symmetric hydroquinone ether [Scheme 4.184].340... 

Primary benzylic alcohols (equation 10) can be oxidized in the presence of saturated primary alcohtris using a catalyst derived from ammonium cerium(IV) nitrate supported on charcoal with air as the cooxidant (under these conditions a-hydroxy ketones are oxidized to a-diketones). ... 

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. 

Benzaldehydes can be prepared in good yield from benzyl alcohols by means of various oxidants, including dinitrogen tetroxide (for its preparation see Park and Partington412) in chloroform or carbon tetrachloride,413 concentrated nitric acid,414a aqueous hypochlorite,414b or cerium(iv) ammonium nitrate in 50% acetic acid.415... 

Cerium(IV) has been used extensively, and the two most common reagents are ceric ammonium sulfate [Ce(S04)2 2(NH4)2S04 2 H2O] and ceric ammonium nitrate [Ce(NH4)2(N03)6].l 3 Modified cerium reagents such as Ce(OH)302Hl 4 d [(N03)3Ce]3H2l06l - have been used by Firouzabadi et al. or the oxidation of primary alcohols, especially benzylic and allylic alcohols. 

The p-methoxyphenyl group has recently been found suitable for alcohol protection, as the resulting ethers are stable both to acidic and basic conditions and can be cleaved by brief treatment with ceric ammonium nitrate. The same principle can be applied to carboxylic acid protection.Thus, the rather stable benzyl (64) and phenyl (65) esters can be cleaved as indicated by oxidation with DDQ or cerium(IV)(at pH 3) respectively. A recent total synthesis of (+)-Antimycin-A features the use of a... 

Oxalic and malonic acids, as well as a-hydroxy acids, easily react with cerium(IV) salts (Sheldon and Kochi, 1968). Simple alkanoic acids are much more resistant to attack by cerium(IV) salts. However, silver(I) salts catalyze the thermal decarboxylation of alkanoic acids by ammonium hexanitratocerate(IV) (Nagori et al., 1981). Cerium(IV) carboxylates can be decomposed by either a thermal or a photochemical reaction (Sheldon and Kochi, 1968). Alkyl radicals are released by the decarboxylation reaction, which yields alkanes, alkenes, esters and carbon dioxide. The oxidation of substituted benzilic acids by cerium(IV) salts affords the corresponding benzilic acids in quantitative yield (scheme 19) (Hanna and Sarac, 1977). Trahanovsky and coworkers reported that phenylacetic acid is decarboxylated by reaction with ammonium hexanitratocerate(IV) in aqueous acetonitrile containing nitric acid (Trahanovsky et al., 1974). The reaction products are benzyl alcohol, benzaldehyde, benzyl nitrate and carbon dioxide. The reaction is also applicable to substituted phenylacetic acids. The decarboxylation is a one-electron process and radicals are formed as intermediates. The rate-determining step is the decomposition of the phenylacetic acid/cerium(IV) complex into a benzyl radical and carbon dioxide. 

N03)j, a newcomer to the arena of oxidants, is useful for the acetoxylation of aromatic side chains in benzylic positions [415, 416] and for the oxidation of methylene or methyl groups that are adjacent to aromatic rings to carbonyl groups [238, 415, 417]. The reagent also oxidizes alcohols to aldehydes [418, 419, 420, 421] and phenols to quinones [422, 423], cleaves vicinal diols to ketones and a-hydroxy ketones to acids [424, 425], and converts diaryl sulfides into sulfoxides [426]. A specialty of ammonium cerium nitrate is the oxidative recovery of carbonyl compounds from their oximes and semicarbazones [422, 427] and of carboxylic acids from their hydrazides [428] under mild conditions. 

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