Oximes, acid catalyzed with nitroso compounds

An aqueous solution of sodium nitrite that is treated with HC1 contains nitrosyl cations 0=N . These can react with the enol E of the malonic acid diethyl ester (cf. Figure 12.9, bottom). First, a nitroso compound (F) is formed, which then undergoes acid-catalyzed isomerization to give the oxime A. Usually, the oxime is reduced by zinc, which is dissolved in acetic acid, to yield an amine that normally undergoes in situ acetylation in acetic acid. In this way the (acetamido)malonic acid diethyl ester B is obtained as the reduction/acetylation product, which can be employed, for example, in the synthesis of amino acids (Figure 13.39). 

Aromatic and aliphatic primary amines can be oxidized to the corresponding nitro compounds by peroxy acids and by a number of other reagents. The peroxy acid oxidations probably go by way of intermediate hydroxylamines and nitroso compounds (Scheme 2). Various side reactions can therefore take place, the nature of which depends upon the structure of the starting amine and the reaction conditions. For example, aromatic amines can give azoxy compounds by reaction of nitroso compounds with hy-droxylamine intermediates aliphatic amines can give nitroso dimers or oximes formed by acid-catalyz rearrangement of the intermediate nitrosoalkanes (Scheme 3). 

Ketones having an a-methylene group, that is, —CH2 bound to the carbonyl group, can react with nitrous acid, nitrite esters, or nitrosyl chloride to form nitroso compounds and oximes. These reactions are catalyzed by acids or bases. 

Incorporation of natural amino acids (114, 115,116, 117, 118) and homologs (119,120,121) without further chain lengthening (VII to XVI) proceeds with retention of the a-amino nitrogen (119, 120, 122). An enzyme catalyzing the oxidation and decarboxylation of the N-hydroxyamino acid VIII to the aldoxime XI (123,124) has been purified 1400-fold (125). It is stimulated by FMN, O2 uptake is observed, and the a-keto acid oxime V is not used as a substrate (124,125). Decarboxylation may occur via the a-nitroso acid IX. Incorporation of the nitro compound XIII (126) presumably occurs via the acf-nitro compound XII which was suggested by Ettlinger and Kjaer (72) as an intermediate. The addition of thiols to... 

Scheme 31 Copper-catalyzed reactions of arylbOTonic acids with sulfoximines, oximes, nitroso aromatic compounds, azodicarboxylates and aryl azides...

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