Oxidation nitrites, oxime synthesis

Triketone (57), a key intermediate in the synthesis of 4,4,7,7,11,11-hexanitropentacyclo [6.3.0.0 .0 °.0 ]undecane (61) (Zlj-hexanitrotrishomocubane), has been synthesized independently by both Marchand and co-workers, and Fessner and Prinzach. Marchand and co-workers prepared the trioxime (58) from the corresponding triketone (57). Oxidation of (58) with peroxytrifluoroacetic acid in acetonitrile provides a direct route to the trinitro derivative (59) in 35 % yield, this yield reflecting an efficiency of 70 % for the oxidation of each oxime group. Subsequent oxidative nitration of (59) with sodium nitrite and potassium ferricyanide in aqueous sodium hydroxide yields the target T>3-hexanitrotrishomocubane (61). 

Nitrosomethane (1) is known to be less stable than its isomer formaldoxime 2 and original attempts to isolate this species failed owing to its facile isomerization to the oxime 2. Already Bamberger and Seligman considered in 1903 that it would be difficult to isolate nitrosomethane after oxidation of methylamine due to its rapid isomerization to 2. Hence, 2 is always present in the synthesis of the nitrosomethane. Nitrosomethane is produced in the pyrolysis or photolysis of tcrf-butyl nitrite and by the reaction of methyl radicals with nitric oxide. Early results were confusing since the final product obtained is dimeric nitrosomethane. It was first isolated in 1948 by Coe and Doumani from the photolysis of gaseous ferf-butyl nitrite according to the overall reaction shown in equation 2. 

A regiospecific synthesis of A -substituted (aminopyridinyl)imidazole 1286 started with ketone 1282 (cf. Section 4.02.9.2(i)). a-Oximination of ketone 1282 with isoamyl nitrite under basic condition provides oxime isomers 1283. Both as- and /ra t-oximes 1283 participate in the cyclization process when treated with l,3,5-trimethyl-l,3,5-triazinane, leading to imidazole iV-oxide 1284 that is then reduced with 2,2,4,4-treta-methyl-cyclobutane-l,3-dithione to give 1285 (Scheme 326) <2003JOC4527, 1999JME2180> (see also Section 4.02.9.3(i)). 

Nitrosolysis of camphor ethyl acetal with ethanolic ethyl nitrite in sulphur dioxide yields the orthoester oxime (205) which is rapidly dehydrated by excess acetal to the orthoester nitrile which then reacts with sulphur dioxide to form the ester nitrile and diethyl sulphite.Further papers in this section include the full paper on ozonolysis of silyl ethers (Vol. 5, p. 33), another synthesis of camphor-enol trimethylsilyl ether (cf. Vol. 6, p. 41)/°° the conversion of camphor oxime with Grignard reagents into the corresponding imine with no aziridine formation/° the preparation of (206) by treating bornylene with trichloroacetyl isocyanate/ the oxidation of thiocam-phor to the 5-oxide and alkylation in the presence of thallium(i) ethoxide to a/S-unsaturated sulphoxides/ and the free-radical C-3 alkylation of camphor with alkenes. " ... 

CAN-mediated nitration provides a convenient route for the introduction of a nitro group into a variety of substrates. Alkenes on treatment with an excess of sodium nitrite and CAN in chloroform under sonication afford nitroalkenes. When acetonitrile is used as the solvent, nitroacetamidation occurs in a Ritter-type fashion. However, the attempted nitroacetamidation of cyclo-pentene-1 -carboxaldehyde under similar conditions resulted in the formation of an unexpected dinitro-oxime compound. A one-pot synthesis of 3-acetyl- or 3-benzoylisoxazole derivatives by reaction of alkenes (or alkynes) with CAN in acetone or acetophenone has been reported. The proposed mechanism involves a-nitration of the solvent acetone, oxidation to generate the nitrile oxide, and subsequent 1,3-dipolar cycloaddition with alkenes or alkynes. The nitration of aromatic compounds such as carbozole, naphthalene, and coumarins by CAN has also been investigated. As an example, coumarin on treatment with 1 equiv of CAN in acetic acid gives 6-nitrocoumarin in 92% yield. ... 

Remote Oxidation.—Remote oxidation reactions generally involve intramolecular hydrogen abstraction. The best known example is the Barton reaction (photolysis of nitrite esters). "- One of the most important applications of this reaction was to the synthesis of aldosterone acetate. The yield of this reaction has been substantially improved (55%) by irradiating the dienone nitrite ester (172) in which the extended conjugation ensures that sufficient separation between C-19 and the 11/3-oxygen atom exists to suppress functionalization at C-19 in favour of attack at C-18. Another recent application of the Barton reaction occurred in the synthesis of perhydrohistrionicotoxin (175), where the key step was the stereoselective formation of the oxime (174) from the nitrite ester (173). °... 

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