Cerium ammonium nitrat

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. 

A similar process can be performed with the use of cerium ammonium nitrate (CAN) for generation of radicals from another CH acid, viz., methyl nitroacetate (72b) (Scheme 3.22, Eq. 2). 

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 —> +... 

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-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>. 

Pyranone 127 reacts with alkenes in the presence of cerium ammonium nitrate via a cyclization reaction that leads to the formation of furo[2,3-3]- and furo[3,2-f]-pyranones in moderate yields (Equation 60). This reaction can be extended to the synthesis of furoquinolinones <1999H(51)2881>. Dihydropyran 128, with either / -diketones or /3-keto esters, undergoes cycloaddition reactions promoted by ceric ammonium nitrate to generate furo[2,3-3]pyrans in good yields (Equation 61) <1996T12495>. 

Ceric-Ammonium Nitrate or Cerium-Ammonium Nitrate. See under Nitrates... 

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. 

Yamashiro et al. 1972), boron trifluoride etherate in acetic acid (Schnabel et al. 1971), trimethylsylil triflate (Schmidt et al. 1987), trimethylsilyl perchlorate (Vorbrueggen Krolikiewicz 1975), and, most frequently, trifluoroacetic acid (Farowicki Kocienski 1995 and references therein). Deprotection of the /-HOC group under neutral conditions was not described until recently, yet it is highly desirable. Now it has been found that the tert-butoxycarbonyl protecting group for amines, alcohols, or thiols is removed efficiently (90-99% yield) with use of 0.2 equivalent of cerium ammonium nitrate in acetonitrile at 80°C (Hwu et al. 1996) ... 

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>. 

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