Benzylic cerium ammonium nitrate

CAN = cerium-ammonium nitrate, (NH4)jCe(N03)5 products are benzylic acetates. 

Table 4-1 compares two different reactions, namely, anode oxidation and oxidation with cerium ammonium nitrate (which are bona fide electron-transfer processes) and bromination by /V-bromosuccinimide in the presence of azobis(iso-butyro)nitrile (which is bona fide hydrogen-atom-transfer process). Both electron-transfer and hydrogen-atom-transfer processes have the benzylic radical as a common intermediate, but positional selectivity is stronger for electron-transfer processes. Another important point is the preference of the 2-positioned methyl group over the 1-positioned group, in terms of selectivity. For 1,2,3-tetramethylbenzene, such a preference reaches values from 16 to 55, and it is over 200 for 5-methoxy-1,2,3-tctramcthylbcnzcnc. 

PMB ethers can be cleaved oxidatively with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)11 in dichloromethane/water tor with cerium ammonium nitrate (CAN) in acetonitrile/water.12 Many other protecting groups such as esters, isopropylidene acetals, benzyl ethers, allyl ethers and f-butyldiphenyl silyl (TBDMS) ethers are stable to these conditions (Scheme 2.4). The cleavage reaction, with DDQ is initiated with a single-... 

Recently it was pointed out [6] that potassium and sodium bromate oxidize arenes in good yields in a 3 2 dioxane-water solution by using cerium ammonium nitrate (CAN) as catalyst. Toluene derivatives are oxidized to ca. 1 1 mixture of benzaldehydes and benzoic acids, while ethylbenzenes are converted to acetophenones. According to the proposed mechanistic scheme, water either influences the polarity of the reaction medium or acts as the reagent, reacting with the intermediate benzylic carbonium ion to give a hydroxy derivative, which is oxidized from either Ce or BrOa ions. 

Cerium(IV) ammonium nitrate, 67 Dimethyl sulfate, 239 Other ethers Allyltrimethylsilane, 11 Benzyl trichloroacetimidate, 32 (E)-(Carboxyvinyl)trimethylammonium betaine, 67... 

Cerium(IV) ammonium nitrate (CAN) in acetic acid oxidizes potassium bromide and, consequently, brominates methylbenzenes at a benzylic position with 50-80% yield293. f-Butyl hydroperoxide (TBHP) oxidizes CuBr2 which a-brominates toluenes to benzyl... 

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... 

A diastereoisomeric mixture of dicobalt hexacarbonyl complexes 33 reacted with trifluoroborane etherate at -20 °C to give the reduced product 3.3 (minus a benzyl ether) as a single diastereoisomer after decomplexation of the metal with cerium(IV) ammonium nitrate. Suggest a mechanism for the formation of 33 which accounts for the stereochemistry of the product. 

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). ... 

Benzyltrimethylsilanes, on the other hand, give products of C-Si cleavage, i.e. benzyl nitrate and acetate, on treatment with cerium(IV) ammonium nitrate in AcOH based on ring substituent effects, a one-electron transfer mechanisms seems to be in operation. 

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... 

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. 

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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