Oximes mechanisms

Jousserandot, A., Boucher, J. L., Henry, Y., Niklaus, B., Clement, B., Mansuy, D., Microsomal cytochrome P450 dependent oxidation of N-hydroxyguanidines, amidoximes, and ket oximes mechanism of the oxidative cleavage of their C=N(OH) bond with formation of nitrogen oxides, Biochemistry 37 (1998),... 

Nevertheless, concluding this section, one can state that all now available experimental data correlate better with the O-vinyl oxime mechanism. At the same time, it should be remembered that all, even the most plausible, mechanistic schemes cannot be considered adequate if they do not explain why the pyrrole synthesis from ketox-imes and acetylene successfully proceeds only in the presence of specific superbase systems KOH/DMSO. 

In a 250 ml. conical flask mix a solution of 14 g. of sodium hydroxide in 40 ml. of water and 21 g. (20 ml.) of pure benzaldehyde (Section IV,115). Add 15 g. of hydroxylamine hydrochloride in small portions, and shake the mixture continually (mechanical stirring may be employed with advantage). Some heat is developed and the benzaldehyde eventually disappears. Upon coohiig, a crystalline mass of the sodium derivative separates out. Add sufficient water to form a clear solution, and pass carbon dioxide into the solution until saturated. A colourless emulsion of the a or syn-aldoxime separates. Extract the oxime with ether, dry the extract over anhydrous magnesium or sodium sulphate, and remove the ether on a water bath. Distil the residue under diminished pressure (Fig. 11,20, 1). Collect the pure syn-benzaldoxime (a-benzald-oxime) at 122-124°/12 mm. this gradually solidifies on cooling in ice and melts at 35°. The yield is 12 g. 

Synthesis from Aldehydes and Ketones. Treatment of aldehydes and ketones with potassium cyanide and ammonium carbonate gives hydantoias ia a oae-pot procedure (Bucherer-Bergs reactioa) that proceeds through a complex mechanism (69). Some derivatives, like oximes, semicarbazones, thiosemicarbazones, and others, are also suitable startiag materials. The Bucherer-Bergs and Read hydantoia syntheses give epimeric products when appHed to cycloalkanones, which is of importance ia the stereoselective syathesis of amino acids (69,70). 

In a number of cases the intermediate oxime has been isolated in the reaction of hydroxylamine and /3-keto esters. The reaction of ethyl acetoacetate with hydroxylamine generated an oxime which cyclized on base treatment (Scheme 144) (70MI41600). Likewise, treatment of an analogous amide with hydroxylamine generated a ring opened material which cyclized on treatment with HCl (Scheme 144) (67T831). The presence of a minor contaminant in the standard reaction of ethyl acetoacetate with hydroxylamine was discovered and identified as an isomeric isoxazolin-3-one. The mechanism of product formation has been discussed (70BSF2685). 

The treatment of 2-hydroxyacetophenone with hydroxylamine-O-sulfonic acid in dilute aqueous base produced 3-methyl-1,2-benzisoxazole. The mechanism was reported to be a C(2)—C(3) ring closure via intermediate (560) (Scheme 171). Salicylaldehyde failed to cyclize with dilute base, but with 20% KOH and hydroxylamine-O-sulfonic acid the transformation to 1,2-benzisoxazole succeeded (76MI41600). Kemp and Woodward isolated an oxime sulfonate (561) from salicylaldehyde and hydroxylamine-O-sulfonic acid and the subsequent decomposition gave 1,2-benzisoxazole in 95% yield (65T3019). 

Thebainone (Schopf), CigHjjOgN. This substance, which must be distinguished from Pschorr s thebainone (metothebainone of Schopf (see p. 248) ), is formed, along with the latter in the reduction of thebaine by stannous chloride in hydrochloric acid, and was isolated by Schopf and Hirsch. Its prior isolation by Pschorr, as confirmed by Morris and Small, has been referred to already. It crystallises with 0-5 HjO, has m.p. 151-2°, yields a hydriodide, m.p. 258-9°, methiodide, m.p. 223°, and an oxime, m.p. 185-6°. On catalytic hydrogenation it yields dihydrothebainone (LI), and can be degraded to 3 4 6-triacetoxyphenanthrene, m.p. 165-7°. On this basis formula (XLIX) is assigned to it. The mechanism of the formation of codeinone, thebainone and mefathebainone from thebaine is discussed by Schopf and Hirsch. ... 

Mechanism The reaction of and A -steroids with nitrosyl fluoride to form ni trimines is best discussed in conjunction with the nitrosyl chloride reaction leading tothe5a-chloro-6 -nitro steroids (33). Since nitroso alkanes are oxidized with nitrosyl chloride to nitro alkanes it is believed that 5a-chloro-6j5-nitro steroids are formed in this way from an initially formed 5a-chloro-6 -nitroso adduct. The same is true for nitrosyl fluoride up to the stage of the nitroso fluoride (56). Since NOF is a weaker oxidizing agent than NOCl the nitroso fluoride tautomerizes to the fluoro oxime (57) at a rate... 

A -Methylation of the NH of heterocycles using 1 is also known as exemplified by the methylation of indole/ The interesting mechanism is delineated below. O-methylation of weak acids such as phenols, carboxylic acids and oximes as well as 5-methylation such as A -phenylisorhodanine, certain thioketones, and dithiocarboxylic acids have also been reported." ... 

The aforementioned mechanism is supported by the following experimental data. When oxime 13 was treated with Grignard reagent, 3% of the indole 15 was isolated, indicating the possible existence of nitrene intermediate 14. A 2-phenylazirine intermediate, on the other hand, has been isolated and characterized from the reaction under carefully controlled conditions (adding Grignard reagent to the oxime in toluene). ... 

The mechanism of the original Knorr pyrrole synthesis entails in situ reduction of the oxime moiety to an amine, condensation with the second carbonyl compound, and cyclization with loss of a second molecule of water to give a pyrrole for example, 10 + 11 to 12. Several studies have demonstrated that different pathways and pyrrole products obtain depending on the substrates. 

The reaction is thought to occur by nucleophilic addition of the N-alkyl-hydroxylamine to the keto acid as if forming an oxime (Section 19.8), followed by decarboxylation and elimination of wrater. Show the mechanism. 

Carbons adjacent to a Z group (as defined on p. 548) can be nitrosated with nitrous acid or alkyl nitrites. The initial product is the C-nitroso compound, but these are stable only when there is no tautomerizable hydrogen. When there is, the product is the more stable oxime. The situation is analogous to that with azo compounds and hydrazones (12-7). The mechanism is similar to that in 12-7 R—H —> R + N=0 — R—N=0. The attacking species is either NO or a carrier of it. When the substrate is a simple ketone, the mechanism goes through the enol (as in halogenation 12-4) ... 

In the pH range 2—3.5 the phosphonate (78) hydrolyses with loss of ROH at approximately 10 times the rate of comparable esters lacking the vicinal oxime function or in which this function is methylated on oxygen. An intramolecular general-acid catalysis mechanism was proposed, but it was not possible to exclude entirely an intramolecular nucleophilic attack at phosphorus. Intramolecular attack by the vicinal dimethylamino-group takes place preferentially at carbon rather than phosphorus in the phos-phonofluoridate (79). ... 

It is believed that SCR by hydrocarbons is an important way for elimination of nitrogen oxide emissions from diesel and lean-burn engines. Gerlach etal. [115] studied by infrared in batch condition the mechanism of the reaction between nitrogen dioxide and propene over acidic mordenites. The aim of their work was to elucidate the relevance of adsorbed N-containing species for the F>cNOx reaction to propose a mechanism. Infrared experiments showed that nitrosonium ions (NO+) are formed upon reaction between NO, NOz and the Brpnsted acid sites of H—MOR and that this species is highly reactive towards propene, forming propenal oxime at 120°C. At temperatures above 170°C, the propenal oxime is dehydrated to acrylonitrile. A mechanism is proposed to explain the acrylonitrile formation. The nitrile can further be hydrolysed to yield... 

The structures of the oxime complex Co(NO)(dmg)2 (84) and its diphenylglyoxime analog exhibit strongly bent Co—NO groups, which are easily oxidized to the corresponding nitro compound.353 A mechanistic study of NO transfer from Co(NO)(dmg)2 to hemoglobin established that the reaction involves NO association with the protein subsequent to dissociation of NO from the Co complex.354 This mechanism is also consistent with the observation of nitrato complexes in reactions... 

Hydrolysis of oximes catalyzed by transition-metal complexes has not been studied prior to a report by Kostic et al. They have reported kinetics of hydrolysis of acetoxime to acetone catalyzed by two palladium(II) complexes, identified active species in the hydrolysis reaction, proposed a reaction mechanism, and fully characterized a bis(acetoxime) complex that is relatively stable toward hydrolysis.458... 

Irradiation of a mixture of androstane (28) and cholestane (29) followed by oxidation of the product oximes to nitriles and mass spectrometric analysis revealed a N15/N14 ratio of 1 1.32 for the product derived from (28) and a N16/N14 ratio of 1 1.25 for the product derived from (29). Thus mechanism (a) is effectively eliminated, see top of facing page. 

A choice between mechanisms (b) and (c) was achieved by photolyzing a mixture of a 14N-nitrite in the pregnane series and the 15N-nitrite (29) to half-completion. Rearrangement of the nitroso dimers thus obtained to a mixture of oximes followed by oxidation of the pure oxime from (29) to the ketonitrile and mass spectrometric analysis indicated the N15/N14 ratio to be 1.15 1.00. Analysis of pure unreacted (29) gave a ratio of 1.00 0.00. These results indicate that mechanism (c) is operative in nitrite photolyses. 

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