Oximes pyrolysis

Isoxazoline-3,5-dicarboxylic acid, 4-oxo-diethyl ester synthesis, 6, 106 Isoxazoline-4,5-dione, 3-methyI-4-oxime pyrolysis, 6, 42 Isoxazolines... 

Thermolysis of 4-methyl(4-phenyl)isoxazolin-5-one produced a-cyanophenylacetic acid <67JHC533). The pyrolysis of 3-methylisoxazoline-4,5-dione 4-oxime generated fulminic acid, which was trapped in a liquid N2 cooled condenser for further study. Pyrolysis of metal salts such as Ag or Na produced the corresponding highly explosive salts of fulminic acid 79AG503). Treatment of the oxime with amines generated bis-a,/3-oximinopropionamides (Scheme 65) <68AC(R)189). 

The analogous transformation of 125, also realized by flash vacuum pyrolysis, gave rise to allenic oximes 126 [165], which are not directly accessible by the classical route starting from allenyl ketones and hydroxylamine (see Section 7.3.2) [122], Because compounds 125 are prepared from allenyl ketones and furan by [4 + 2]-cycloaddition followed by treatment with hydroxylamine, the retro-Diels-Alder reaction 125 —> 126 is in principle the removal of a protecting group (see also Scheme 7.46). 

Particularly good yields of the cydoadduct 329 are obtained if R1 = R2 = H is valid for the allenyl ketone 328 [165]. The Diels-Alder products 329 can undergo many chemical transformations, for example to the oximes 330, which yield the modified allenes 331 after a subsequent flash vacuum pyrolysis. The oximes 331 generated by retro-Diels-Alder reaction are not available from ketones 328 and hydroxylamine hydrochloride directly [122] (see also Scheme 7.19). 

Kinetics and mechanisms of gas-phase pyrolysis of sulfonyl hydrazones and their oxime analogues have been reported for the first time " it is proposed that cyanoarene formation arises in each case via a six-membered transition state (60). The lower limit... 

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. 

Thermolysis of tetrazole oximes (478) in a suitable hydrocarbon solvent, or pyrolysis without it, produces 3,5-disubstituted 1,2,4-oxadiazoles (480) (Scheme 75) (81BSB193 87BSB675 91MIP137367). in the case of 5-unsubstituted tetrazoles (478 R = H), the reaction goes by two concomitant pathways, which imply elimination of hydrazoic acid or nitrogen. 

Mesomalonodialdehyde 1,3-dioxime is treated with arylhydrazines to give the mesoaldehyde 1,3-dioxime-2-arylhydrazones (685), which are O-acetylated with acetic anhydride to afford the mono-and di-acetyl derivatives (Scheme 139). Both intermediates are cyclized to 2-aryl-1,2,3-triazole-4-carbaldehyde oximes (686) and (687) with caesium carbonate. Triazoles (687) are converted to 4-cyanotriazoles by refluxing with acetic anhydride followed by pyrolysis <83JHC1561>. 

This compound is easily available by the pyrolysis of D-galactose [25] or, on the small scale, by Angyal and Beveridge s method [26]. Regioselective catalytic oxidation led to the corresponding 5-ulose which, via the oxime and subsequent reduction, could be converted into inhibitor (5) in approximately 6% overall... 

Pyrolysis of di-n-butylmercury in the presence of nitric oxide in a flow system produced mixtures of oximes and nitroso compounds [51]. 

Pyrolysis of alkyl or aryl azides 8-18 Reaction between oxime sulfonates and organometallic compounds... 

Amide reduction with lithium aluminum hydride, 39, 19 Amine oxide formation, 39, 40 Amine oxide pyrolysis, 39, 41, 42 -Aminoacetanilide, 39, 1 Amino adds, synthesis of, 30, 7 2-Amino-4-anilino-6-(chloro-METHYl) -S-TRIAZINE, 38, 1 -Aminobenzaldehyde, 31, 6 hydrazone, 31, 7 oxime, 31, 7 phenylhydrazone, 31, 7 > -Aminobenzoic add, 36, 95 2-Aminobenzophenone, 32, 8 c-Aminocaproic acid, 32, 13 6-Aminocaproic acid hydrochloride,... 

Glyoidonrcrile itself has not been prepared directly from acrylonitrile, but was eyatheaized recently1311 from glycidaldehyde by pyrolysis of the corresponding oxime acetate, as shown in Eq, (67). 

Later on, the same results were obtained with a- and /3-0-(phe-nylvinyl)acetophenone oximes (86,89), which readily rearranged to the corresponding pyrroles 88 and 91 in KOH/DMSO, while under the conditions of noncatalytic pyrolysis (150°C, 10 min), they resinified to give only trace amounts (TLC) of the expected pyrroles (Scheme 43). 

The pyrolysis of 4//-isoxazolin-5-ones of general structure 323 proceeds readily with loss of CO2 and RCN to give the corresponding carbenes X=C . This has provided a convenient route for the generation of fulminic acid, HO—N=C , by pyrolysis of oximes... 

A new synthesis of isoxazoles is by successive treatment of a ketoxime with butyllithi-um, the ester of a carboxylic acid and sulfuric acid, e.g. 1 -> 2 (94S989). Hitrovinyl oximes 3 (R1, R3 = alkyl or aryl) undergo oxidative cyclization to isoxazoles 4 by the action of DDQ or iodine/potassium iodide (94JHC861). Flash-vacuum pyrolysis of the 1,3-dipolar cycloadduct 5 of acrylonitrile oxide to norbornadiene results in a retro-Diels-Alder reaction to give cyclopentadiene and 3-vinylisoxazole 6 (94CC2661). 

Later the estrone produced for commercial purposes was obtained from diosgenin. Diosgenin was first oxidized to its l,4,6-triene-3-one derivative, which was aromatized by pyrolysis at 500-600°C,50 subjected to the Marker degradation and the 17-acetyl group removed by Beckmann rearrangement of the 20-oxime. The overall Syntex process51 for the manufacture of Norethindrone from diosgenin (XVIII) is outlined in Scheme 5. 

Reagents i, several published steps ii, U-NH3 (stereospecific) iii, oximation iv, PC15 v, Me2S04-H0 vi, LiH-3-furoyl chloride vii, hydrolysis to acid viii, CaO, pyrolysis ix, NaBH4... 

Again, the configuration of the oxime is of significance. The acetate (20, R = Ph) provides the indoxazene smoothly on pyrolysis, while its isomer (21) gives only a small yield of the same product.42 A Beckmann rearrangement diverts the pyrolysis of some of the oxime benzoate (22) to the formation of the benzoxazole (23).43... 

Oxido-reduction of nitro compounds 117 Oximes, oxidation of 60 (V131) 4-Oximmoizoxazol-5(4H)-oncs. photolysis and pyrolysis leading to esters of ful-minic acid 469... 

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