Hydroxylamino Derivatives formation

Carbon-Oxygen Bond Formation The cathodic reduction of some nitrocarhonyl compounds in aqueous acidic medium gives the hydroxylamino derivatives that can undergo a ring-closure reaction affording anthrandic compounds or isoxazolones [102-104] (Schemes 70 and 71). 

Nitro compounds are easily reduced, catalytically or chemically, to amino compounds. Incomplete reduction can lead to a hydroxylamino derivative or to binuclear azo, azoxy, and hydrazo compouds, e.g., 789 790, 791. Examples include reduction of 3-nitropyridines using aqueous sodium hydrosulfite at room temperature <2005JME5104> and of 2-nitropyridine by transfer hydrogenation in the presence of 10% Pd/G and recyclable polymer-supported formate, prepared from aminomethylpolystyrene resin and ammonium formate <2005SC223>. A nitro group can be reduced in the presence of an A-oxidc group, e.g., 784 782. 

Nitroaromatic compounds can be initially reduced to aniline derivatives via the intermediary formation of nitroso- and hydroxylamino derivatives (Fig. 3). Subsequently, the amines can be reductively deaminated, yielding benzene derivatives and ammonium (5,6). Several bacteria are only capable of partial degradation of nitroaromatic compounds and either use the released ammonium as a nitrogen source for growth without further degradation of the aromatic ring (5, 6, 45), or use the nitroaromatic compound only as an electron acceptor under anaerobic conditions (2, 3, 12, 34, 38, 47). In the latter case, the amine produced by the reduction of the nitroaromatic compound is not further converted. 

Everninomidn D is the principal component from cultures of Micromonos-pora carbonacae. Chemical modification of the nitro group in everninomicin D has resulted in the formation of amino, mono- and clialky-lamino, Ar-acylamino, and N-hydroxylamino (and its nitrone derivatives) everninomidn D, all of which possess great antibiotic activity against gram-positive bacteria. 

Isotellurazoles 4 were obtained in low yields (3-11%) by the one-pot reaction of alkynyl ketones with hydroxylamino-O-sulfonic acid and K2Te in aqueous solution containing sodium acetate (83S824 87H1587). A plausible mechanism of the reaction includes formation of the oxime derivative and subsequent nucleophilic addition of telluride anion to the triple bond followed by cyclization to 4. The reaction is accompanied by the formation of telluro bis(alkenyl ketones) 5 in yields approximately equal to those of 4. When alkynyl aldehydes are used instead of ketones, the single reaction products are the tellurobis(alkenyl nitriles) 6 (83S824). 

A reductive coupling is possible whenever two aromatically bonded nitro groups are in such a position that a 6- or 7-membered ring may be formed. The coupling occurs probably between a hydroxylamino group and an intermediate nitroso group with the formation of a cyclic azoxy derivative, a heterocyclic V-oxide. 

Amino-3-(pyrrol-2-yl)isoxazoles 348 were selectively prepared by treatment of cyano-ethylthio-ethenylpyrroles 347 with hydroxylamine in methanol, probably through replacement of their SEt group with a hydroxylamino moiety. With carbamoyl derivatives 347 (R = CONH2), minor amounts of regioisomers 349 were also isolated and their formation was increased (12-48%) operating in the presence of aqueous NaOH (Scheme 84) <2005T4841>. 

In reduction, three peaks appear at -0.598 V, -0714 V, and 0891 V, corresponding to the consecutive formation to nitroso, hydroxylamino, and amino-derivatives (Fig. 14.16). 

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