Ammonium cerium nitrate, reaction

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). 

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>. 

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 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... 

For the synthesis of PEDOT in a PVAc matrix, 1 g PVAc was dissolved in 8 mL acetone and stirred magnetically at room temperature until a homogenous solution was obtained (Fig. 6.6c). EDOT was added dropwise to PVAc solutions 25, 50, and 72 iL EDOT were used for the reaction (S25, S50, and S75, respectively). Synthesis was carried out with excess oxidant 1 2 (EDOT ammonium cerium(lV) nitrate). A solution of CAN (respectively, 0.258, 0.515, and 0.773 mmol) dissolved in 2 mL acetone was then introduced at once. 

Mononitration of 1-hydroxynaphthalene could be obtained by use of ammonium hexanitra-tocerate(IV) supported on silica gel in acetonitrile (Chawla and Mittal, 1985) (scheme 39). The same reaction with CAN in acetic acid give the 2,4- and 4,6-dinitro derivatives. By the same method, 2-hydroxy naphthalene is converted into l-nitro-2-hydroxy naphthalene and 4-nitro-2-hydroxynaphthalene (scheme 40). The 1-alkoxynaphthalenes can be mononitrated regioselectively in the 4-position (scheme 41). The lower reactivity of CAN supported on silica gel is also evident from the fact that naphthalene derivatives are not oxidized into 1,4-naphthoquinones. The authors noticed that no reaction could be observed when ammonium hexanitratocerate(IV) was replaced by a mixture of ammonium nitrate and ammonium cerium(IV) nitrate. Silica supported CAN has also been used for the nitration of methoxyben-zenes (Grenier et al., 1999) and less electron rich aromatic compounds like benzene, toluene, chlorobenzene and bromobenzene (Mellor et al., 2000) (scheme 42). For the less electron rich aromatics, dichloromethane is used as solvent instead of acetonitrile. In most cases, the yields are good to excellent. 

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. 

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