Ammonium cerium nitrate, reaction with

Like the double bond, the carbon-carbon triple bond is susceptible to many of the common addition reactions. In some cases, such as reduction, hydroboration and acid-catalyzed hydration, it is even more reactive. A very efficient method for the protection of the triple bond is found in the alkynedicobalt hexacarbonyl complexes (.e.g. 117 and 118), readily formed by the reaction of the respective alkyne with dicobalt octacarbonyl. In eneynes this complexation is specific for the triple bond. The remaining alkenes can be reduced with diimide or borane as is illustrated for the ethynylation product (116) of 5-dehydro androsterone in Scheme 107. Alkynic alkenes and alcohols complexed in this way show an increased structural stability. This has been used for the construction of a variety of substituted alkynic compounds uncontaminated by allenic isomers (Scheme 107) and in syntheses of insect pheromones. From the protecting cobalt clusters, the parent alkynes can easily be regenerated by treatment with iron(III) nitrate, ammonium cerium nitrate or trimethylamine A -oxide. ° ... 

A facile approach to polysubstituted chiral dihydrofiirans starts from pyranose triflates and monoanions of 1,3-dicarbonyl compounds <94CC173S>. Treatment of cyclopropylsulfides of type 9 with ammonium cerium nitrate (CAN) gives furans by a tandem oxidative ring cleavage-cylization reaction <94CC1S29>. 

Cerium(IV) was checked in the form of its sulfate Ce(S04)2 and, because of its better solubility, also with ammonium cerium nitrate (NH4)2Ce(N03)s in aqueous solution. Despite the high reactivity of cerium(lV) resulting in a very rapid reaction, the PEDOT from oxidation by Ce(lV) had a disappointing low conductivity of not more than 0.075 S/cm. ... 

Ammonium cerium(IV) nitrate on reaction with acetone or acetophenone generates acetyl- or benzoylformonitrile oxides, respectively (99). These nitrile oxides dimerize to furoxans and give, in the presence of alkenes and alkynes, 3-acetyl- or 3-benzoyl-4,5-dihydroisoxazoles and 3-acetyl- or 3-benzoylisoxazoles, respectively the yield of the isoxazole derivatives was improved on using ammonium cerium(III) nitrate tetrahydrate-formic acid (99). 

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 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-... 

Acetyl- and 3-benzoylisoxazoles have been conveniently obtained by one-pot reactions of alkynes with ammonium cerium(IV) nitrate or ammonium cerium(III) nitrate tetrahydrate in acetone or acetophenone these processes probably involve 1,3-DC of nitrile oxides formed by nitration of the carbonyl compound by cerium salts <02TL7035>. 

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). 

Cyclic ethers are oxidized to lactones in the presence of cerium(IV) salts. Treatment of tetrahydiofu-ran with cerium(rV) ammonium nitrate in the presence of primary, secondary or tertiary alcdiols leads to the formation of the corresponding tetrahydrofuranyl ethers in quantitative yield. Fuitfaermoie, 4-meth-oxybenzyl ether derivatives of carbohytbates are selectively deprotected to the parent alcohols on reaction with cerium(IV) ammonium nitrate in aqueous acetonitrile. ... 

The oxidative cleavage of Al-Boc groups with ammonium cerium(IV) nitrate (CAN) in acetonitrile has been reported,0 1 but the fact that, again, acidic or Lewis acidic rather than oxidative reaction conditions noight affect the reaction (CAN is, at least in aqueous solution, strongly acidic) should be kept in nnind. Boc-protected amino acids have been reported to be stable against other oxidative reagents. 

Acetyl- and 3-benzoylisoxazoles 389 (and isoxazolines) have been prepared by one-pot reactions of alkynes (and alkenes) with ammonium cerium(iv) nitrate (CAN(lv)) or ammonium cerium(lll) nitrate tetrahydrate (CAN(m))-formic acid, in acetone or acetophenone. These processes probably involve 1,3-dipolar cycloaddition of nitrile oxides produced via nitration of the carbonyl compound by cerium salts. The existence of nitrile oxides as reaction intermediates was proved by the formation of the dimer furoxan 390 when the above reaction was carried out in absence of any dipolarophile (Scheme 95) <2004T1671>. An analogous improved procedure has been applied to alkynyl glycosides as dipolarophiles for the preparation of carbohydrate isoxazoles <2006SL1739>. 

The action of n-butyllithium in THF at low temperature leads to the anion. After reaction with an electrophilic compound, e hydrolysis can generally be carried out in polar solvents (acetone, alcohols, acetonitrile) in the presence of mercury(II) chloride or oxide and water.In other cases, NBS, - chloramine T, cerium(IV) ammonium nitrate, n-tributyltin hydride, trialkyloxonium tetrafluorobor-ate, thallium nitrate or photochemistry can be used. Desulfurization by Raney nickel gives hydro-carbons. ... 

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). 

Oxidation of the hydroxymalonic acid ene adducts with cerium(IV) ammonium nitrate in aqueous acetonitrile or sodium periodate results in oxidative didecarboxylation to give an allylcarboxylic acid. The two step process ene reaction with diethyl oxomalonate and oxidative didecarboxylation provides a general procedure for the conversion of alkenes to allylcarboxylic acids. 

The 2,5-dihydro-l,2,3-triazines 20, obtained by reaction of 1,2,3-triazines 19 with ketene silyl acetals or silyl enol ethers in the presence of 1-chloroethyl chloroformate, can be readily oxidized and hydrolyzed with ammonium cerium(lV) nitrate (CAN) in acetonitrile/water to afford 5-substituted 1,2,3-triazines 21.3 64... 

The reactions of several alkenes and alkynes with ammonium cerium(lV) nitrate [CAN(IV)] or ammonium cerium(III) nitrate tetrahydrate [CAN(III)]-formic acid in acetone under reflux gave 3-acetyl-4,5-dihydroisoxazoles 4 (R = Me) and 3-acetylisoxazoles 5 (R = Me), respectively through nitrile oxide 1,3-dipolar cycloaddition (1,3-DC). The... 

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