Oxidations cerium ammonium nitrate

Preparation of a-fluoro ketones or aldehydes can also be achieved by cerium ammonium nitrate oxidation of the corresponding silyl nitronates. C-acylation compounds derived from nitroalkanes can be... 

Cerium ammonium nitrate oxidation of camphorquinone gives (201 X = C02Me) as the major product along with the exo-double-bond isomer, methyl 3-methoxy-2,2,3-trimethylcyclopentane-l-carboxylate, and dimethyl camphor ate. 

Dihydropyrans [71] and 4-dihydropyranones [72] have been prepared by BF3 or Me2AlCl catalyzed Diels-Alder reactions of alkyl and aryl aldehydes with dienes 72 and 73 (Equations 3.20 and 3.21). Allylic bis-silanes are useful building blocks for synthesizing molecules of biological interest [73], 4-Pyra-nones have been obtained by cerium ammonium nitrate (CAN) oxidation of the cycloadducts. 

Goumont et al. exploited this kind of reactivity for the nucleophilic substitution of the hydrogen atom in position 5 by carbon nuclophiles <20030BC2192> (Scheme 18). These authors reported that 6,8-dinitrotetrazolo[l,5- ]pyr-idine 11 easily reacts with potassium nitropropenide to yield an adduct similar to those obtained with alcohols 12. This adduct when oxidized by cerium ammonium nitrate yields the nitroalkyl-substituted aromatic compound 64. 

A Greek team also reported on oxidation of partially saturated heterocycles to fully heteroaromatic rings <1996JHC599> 5-/>-anisyl-4,5-dihydro[l,2,3]triazolo[5,l-/][l,2,4]triazine 91, when treated with cerium ammonium nitrate, underwent an oxidative hydrolysis giving heteroaromatic product 92 in poor yield (20%). 

To generate 8O3 in acidic mediums, the reaction between sodium hydrogen sulfite and cerium ammonium nitrate should be employed. In (NH4)2Ce(N03)g, cerinm has 4+ oxidation state. In acidic mediums, (NH4)2Ce" +(N03)g easily oxidates the sulfite ion + 803 —> +... 

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-bromo-succinimide in the presence of azobis(iA(9butyro)nitrile (which is a bona fide hydrogen-atom-transfer... 

The head-to-head trans-cyclorimer 92 of 9-vinylcarbazole (see Section II,C,2) undergoes C—C bond fission by a one-electron oxidative process on treatment with cerium ammonium nitrate or tris-(p-bromophenyl)ammo-niumyl hexachloroantimonate in methanol giving 93. ... 

Treatment of the 3,l-benzoxazin-2-one derivative 249 with cerium ammonium nitrate (CAN) resulted in removal of the /i-methoxybenzyl substituent, by oxidation of its a-position, which led to the human immunodeficiency vims-1 (HIV-1) reverse transcriptase inhibitor efavirenz 250 and anisaldehyde (Equation 24) <1998JOC8536>. 

Trisubstituted (3-lactams have been reported to be obtained through oxidative removal of the /V-alkyl group from more complex (3-lactams by treatment with cerium ammonium nitrate [260], Anologous methodology was employed for a general synthesis of cis- and trans-(3-lactams bearing a quinone moiety at the N-l, the C-3, or the C-4 position (I, II and III, respectively, Fig. 8), [261]. 

Oxidation of benzo-fused 1,3-dioxepane 79 with cerium ammonium nitrate afforded the />-diquinone 80 <2006T635>, and oxidation of 2-hydroxydioxepin 81 with manganese dioxide gave l,3-dioxa-4-cyclohepten-6-one 82 <2004RJ01830> (Scheme 14). 

The oxidation reaction of alkylaromatic compounds with cerium-ammonium nitrate in acetic acid medium is crucial for understanding the problem (Baciocchi, Rob, Man-dolini 1980) ... 

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. 

The alkaline oxidative cleavage of softwood lignin to vanillin is an other important reaction of wood chemistry. Such typical one-electron oxidants as nitrobenzene, cupric salts, and cerium ammonium nitrate are used. The reaction includes a cation radical step and pro-... 

Despite the ionic reactions, other reactions (presented in Scheme 44) show that free-radical mechanisms can also take place. Catalyzed by ebselen, TBHP oxidation of alkylarenes to alkyl aryl ketones (141) [240], anthracene to anthraquinone (142), 1,4-dimethoxyarenes to 1,4-quinones (e.g., menadione 143) [244], and oxidative coupling of 2-aminophenol to phenoxazinone (144) [245] gave results similar to these when one-electron oxidants such as Ce(IV), Ag(II), or Mn(III) were the reagents. Moreover, oxidation of azine derived from 2-acetylpyridine gave a mixture of ketone (145) and condensed triazole (146) [240], The same result was found when cerium ammonium nitrate was used as the reagent. This suggests that the... 

In particular, A-arylsuccinimidate 62 (obtained from anizidine in three steps) with t-BuOK in THF produces the corresponding carbanion, which instantly cyclizes into crH-adduct 63. The latter, on oxidation with cerium ammonium nitrate (CAN) gives lactame 64 in 53% yield (Scheme 19). 

Thioamides of 3-oxoacids 118 are transformed into 1,2,4-dithiazolidines 29 by treatment with cerium ammonium nitrate (CAN) in MeOH or with CF3SC1 in CH2CI2 (Equation 16) <1996SC4165, 2001SC189>. The thermal conversion of 6/7-1,3,5-oxathiazine A-oxides 119 in refluxing benzene results in 1,2,4-oxathiazolines 20 with extrusion of R CHO. This reaction involves the heterodiene intermediate 120, which can be independently trapped by the reaction with EtOH (Scheme 32) <2003TL2517, 2004HAC175>. 

The C-Si bond of an SMA can also be cleaved by oxidizing reagents like cerium ammonium nitrate (CAN). Starting from (V-bis(trimethylsilyl)methylazetidinones, treatment with CAN probably leads to the oxidation product of the two C-Si bonds, i.e., the corresponding disilylketal that is hydrolyzed into the formamide to give the N-H azetidinones (yields >80%). This constitutes an alternate and more efficient way to sequential fluoride-induced desilylation. Peterson olefination, ozonolysis, and formamide decomposition when deprotection of bis(trimethylsilyl)methylated azetidinones into NH-azetidinones is required.228,230... 

The direct oxidation of arenes to quinones is a reaction with a limited scope [41], Only substrates that form stable quinones give good yields. For example, oxidation of anthracene to stable 9,10-anthraquinone with chromic acid is practiced on industrial scale. Such oxidations are believed to proceed through a series of one-electron oxidation/solvolysis steps. Yields and selectivity may be improved by using a strong one-electron oxidant such as cerium ammonium nitrate (CAN), as in the oxidation of phenanthrene to phenanthrenequinones (Eq. 9) [42]. 

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-... 

One-electron oxidation of the p-allyloxy nitroalkane (85) by cerium ammonium nitrate (CAN) produces a tetrahydrofuran derivative (86) (eq. 3.31). 

Two short syntheses of P-lapachone from readily available naphthols and 3-methylbut-2-enal via a mild phenyl-boronic acid mediated cyclization to 2//-chromenes have been reported. Catalytic hydrogenation of 2H-chromenes with H /Pd-C in ethyl acetate afforded the corresponding naturally occurring chromanes (72) and (73). Oxidation of the adequate chromane with an excess of cerium ammonium nitrate (CAN) furnished P-lapachone in 62% yield [153]. 

Transient oxonium ions could be generated from 2-tetrahydrofuranylsilanes <1996TL9119> and 2-tetrahydrofur-anylstannanes <2006TL3607> by oxidation with cerium ammonium nitrate. Intramolecular capture of the cations by the hydroxyl group provided furo[2,3-3]pyrans, as depicted in Equation (145). 

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