Cerium IV Ammonium Nitrate CAN

The use of cerium(IV) ammonium nitrate (CAN) as a catalyst for an aza-Diels-Alder reaction was reported in two different publications. In one report Perumal and co-workers react a variety of anilines 86 and aldehydes 87 with enamine 88 in the presence of 5 mol% CAN to form a series of tetrahydroquinolines 89. The reactions were performed at room temperature with very short reaction times and in good yields. In addition, the resulting tetrahydroquinolines could be oxidized to the corresponding substituted quinolines using 2.5 eq of CAN in high yields <06TL3589>. 

Partially or fully reduced thiadiazoles can be oxidized to yield 1,3,4-thiadiazoles. The 2,5-disubstituted 3-acyl-l,3,4-thiadiazole 157 can be deacylated by numerous methods <2004H(63)2243>. The oxidative deacylation of compound 157 to thiadiazole 158 can be achieved using oxidants such as KMn04, cerium(iv) ammonium nitrate (CAN), and (diacetoxy)iodobenzene (Equation 58). Better yields and cleaner products are obtained using CAN as oxidant. 

An interesting sequence, again overall an isomerization, is the stoichiometric formation of the manganese complexes 68, which, on basic alumina, isomerize to the allenyl complexes 69 from the latter the allenes 70 can be liberated with cerium(IV) ammonium nitrate (CAN) in good yields [128] (Scheme 1.30). 

The use of cerium(IV) salts as catalytic oxidation mediator is restricted by their insolubility in non-aqueous media. Cerium(IV) ammonium nitrate (CAN) may be used in organic solvents upon the addition of quaternary ammonium salts, but cerium(IV) sulphate is not transferred under analogous conditions. Bis(tetra-/t-butyl-ammonium) hexanitratocerate(IV) is obtained in a solid form by metathesis of CAN... 

More recently, Menendez et al. reported a closely related four-component access to tetrahydropyridines, the amino alcohol being replaced by a primary amine and an alcohol. Thus, the cerium(IV) ammonium nitrate (CAN)-catalyzed reaction between primary aliphatic amines, 1,3-dicarbonyls, cx,p-unsaturated aldehydes, and alcohols resulted in the formation of 6-aUcoxy-2-methyl-l,4,5,6-tetrahydropyridines with... 

Another transient aminoxyl radical has been generated , and employed in H-abstraction reactivity determinations" . Precursor 1-hydroxybenzotriazole (HBT, Table 2) has been oxidized by cyclic voltammetry (CV) to the corresponding >N—O species, dubbed BTNO (Scheme 9). A redox potential comparable to that of the HPI —PINO oxidation, i.e. E° 1.08 V/NHE, has been obtained in 0.01 M sodium acetate buffered solution at pH 4.7, containing 4% MeCN". Oxidation of HBT by either Pb(OAc)4 in AcOH, or cerium(IV) ammonium nitrate (CAN E° 1.35 V/NHE) in MeCN, has been monitored by spectrophotometry , providing a broad UV-Vis absorption band with A-max at 474 nm and e = 1840 M cm. As in the case of PINO from HPI, the absorption spectrum of aminoxyl radical BTNO is not stable, but decays faster (half-life of 110 s at [HBT] = 0.5 mM) than that of PINO . An EPR spectrum consistent with the structure of BTNO was obtained from equimolar amounts of CAN and HBT in MeCN solution . Finally, laser flash photolysis (LFP) of an Ar-saturated MeCN solution of dicumyl peroxide and HBT at 355 nm gave rise to a species whose absorption spectrum, recorded 1.4 ms after the laser pulse, had the same absorption maximum (ca 474 nm) of the spectrum recorded by conventional spectrophotometry (Scheme 9)59- 54... 

Cerium(IV) ammonium nitrate (CAN) is effective for oxidative hydrolysis of phenyl esters substituted by hydroxyl, methoxyl, and dimethylamino groups in CH3CN-H20 at 0°. 

Apart from sodium hypochlorite, a number of alternative secondary oxidants for TEMPO-mediated alcohol oxidations can be employed. These include cerium (IV) ammonium nitrate (CAN),24 trichloroisocyanuric acid (TCCA),25 oxone ,26 MCPBA,2,3,7 PhI(OAc)2,27 W-chlorosuccinimide,28 sodium bromite,29 electrooxidation,8,21 H5IO626 and a polymer-attached diacetoxybromide (I) complex.30... 

Cerium(IV) ammonium nitrate (CAN) has been reported to catalyse a facile and efficient aza-Michael addition of aromatic and aliphatic amines to a -unsaturated esters in the absence of solvent under ultrasound irradiation.136 a,/l-Unsaturated ketones react in aqueous solutions under these conditions but only with aliphatic (not aromatic) amines.137... 

The ring opening of 2,2 -diphenyloxetane has been achieved using cerium(iv) ammonium nitrate (CAN) as a redox catalyst (Equation 7) <2003TL4585>. The first step involves oxidation of the oxetane by Ce(rv) to a cyclic radical cation. Equilibration to the ring-opened distonic version 42 with a stabilized cation, then quenching of the cation with methanol and reduction of the alkoxide radical by Ce(lll) to the anion, completes the catalytic cycle. 

Hydroxycoumarin can react with alkenes in the presence of cerium(iv) ammonium nitrate (CAN) to form a mixture of furochromones and furocoumarins in modest yield (Equation 316) <1999H(51)2881>. 

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... 

The cyclohexadiene complex 29 has been further elaborated to afford either the cydo-hexenone 34 or the cyclohexene 36 in moderate yields (Scheme 1) [21]. The addition of HOTf to 29 generates the oxonium species 33, which can be hydrolyzed and treated with cerium(IV) ammonium nitrate (CAN) to release the cyclohexanone 34 in 43 % yield from 29. Alternatively, hydride reduction of 33 followed by treatment with acid eliminates methanol to generate the r 3-allyl complex 35. This species can be trapped by the conjugate base of dimethyl malonate to afford a cyclohexene complex. Oxidative decomplexation of this species using silver trifluoromethanesulfonate liberates the cyclohexene 36 in 57 % overall yield (based on 29). 

Titanium- and cerium-based reagents have been used to prepare binaphthol structures [95, 96]. Jiang showed that treatment of 2-naphthol (68a) with cerium(IV) ammonium nitrate (CAN) leads to the biaryl product 69a in yields of around 90 % (Scheme 32). Crosscoupling of differently substituted naphthols can be accomplished using the same reagents, albeit in lower yields. 

Electrophilic aromatic substitution of 5-hydroxy-2,4-dimethoxy-3-methylaniline by reaction with the iron complex salts affords the corresponding aryl-substituted tricarbonyliron-cyclohexadiene complexes. O-Acetylation followed by iron-mediated arylamine cydization with concomitant aromatization provides the substituted carbazole derivatives. Oxidation using cerium(IV) ammonium nitrate (CAN) leads to the carbazole-l,4-quinones. Addition of methyllithium at low temperature occurs preferentially at C-1, representing the more reactive carbonyl group, and thus provides in only five steps carbazomycin G (46 % overall yield) and carbazomycin H (7 % overall yield). 

In a nice illustration of the impact of metal coordination upon the reactivity of phospholes, a methodology for the functionalization of these heterocycles in the /3-position has been described (see also Scheme 22) <2001JOM105>. Here, coordination of both the P-lone pair and the cyclic diene system was undertaken. The resulting multimetallic complex 79 was treated with lithium diisopropylamide (LDA) to afford the lithium salt 350 (Scheme 118). This readily undergoes nucleophilic substitution with a variety of electrophiles to afford the corresponding substituted phosphole complexes 351-353. The free phospholes can be isolated following decomplexation with cerium(iv) ammonium nitrate (CAN). 

The regioselective oxidation of aziridines to a-tosylamino ketones has been accomplished via NBS and cerium(iv) ammonium nitrate (CAN) <2005TL4111>. Both styryl aziridines, 388, and aliphatic aziridines, 390, have been oxidized. A related report uses /3-CDs in addition to NBS to catalyze the same transformation <2005TL1299>. These reaction conditions also work well for epoxides to provide the corresponding a-hydroxy ketones (Scheme 99). 

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. 

Cerium (IV) ammonium nitrate (CAN) [NH4]2[Ce(N03)6], is a water-soluble oxidant, classical in organic chemistry [197], which has sometimes been used in or-ganometallic chemistry to disengage ligands from metal centers [211]. It can be used... 

Considerable interest has been shown recently in the use of cerium (IV) salts as oxidizing agents. Cerium (IV) ammonium nitrate can also be a nitrating agent 1125]. It can also act in the presence of acetic acid 1119]. In the presence of nitric acid [120] it can form nitrate esters from the methyl group, viz. ... 

Silica gel supported cerium(IV) ammonium nitrate (CAN) has been employed for controlled nitration of some naphthalene derivatives. While treatment of hydroxynaphthalenes and polynuclear arenes with cerium(IV) ammonium nitrate absorbed on silica gel without a solvent affords mononitro derivatives, the reaction of the same substrates with cerium(IV) ammonium nitrate in solution alfords a considerable per-... 

A similar reaction with cerium(IV) ammonium nitrate (CAN) can be used preparative I y for cleaving the C-Sn bond (e.g. equation 5-47). 

In 2007, MacMillan and co-workers reported conceptually novel reactions employing MacMillan s catalyst 5b [39]. This catalyst worked as a singly occupied molecular orbital (SOMO) catalyst in the presence of cerium (IV) ammonium nitrate (CAN) as a single-electron oxidant and the enantioselective a-allylation of aldehydes... 

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