Aldehyde nitroxides

Sodium hydrogen telluride, (NaTeH), prepared in situ from the reaction of tellurium powder with an aqueous ethanol solution of sodium borohydride, is an effective reducing reagent for many functionalities, such as azide, sulfoxide, disulfide, activated C=C bonds, nitroxide, and so forth. Water is a convenient solvent for these transformations.28 A variety of functional groups including aldehydes, ketones, olefins, nitroxides, and azides are also reduced by sodium hypophosphite buffer solution.29... 

Bis(trifluoromethyl) nitroxide abstracts aldehydic hydrogen atoms from perfluorobenzaldehyde with great case, to give the ( [bis(trifluoromethyl)amino]oxyjcarbonyl)arene in almost quantitative yields.188 The reaction has also been extended to other classes of compounds (vide infra).189... 

Possibly, the reaction is driven by the electrophilicity of the ketenic and nitroxide-type mesomer. In effect, it leads to the oxidation of the aldehyde and the reduction of the nitro function. 

By extrapolating data of Lattimer and coworkers (24, 40), it may be anticipated that the ozonation of DPPD proceeds most probably via nitroxide and aminyl formation pathways. Dinitrone and N-N or N-C and C-C coupling products should therefore be considered as ozonation products formed via free radical intermediates. The reactivity of DPPD with aldehydes will be very limited. All these mechanistic features together with the low ozonation rate of DPPD in comparison with N,N -disec.alkyl PD (26) may be responsible for the generally reported poor antiozonant efficiency of N,N -diaryl PD in comparison with N-sec.alkyl-N -aryl and N,N -disec.alkyl PD. 

The oxidation of alkanes leads to aldehydes. Toda et al. [81] and Felder [82] suggested that the formation of the nitroxide is related to the oxidation of the aldehydes formed. 

Inactive A-acylhydroxylamines 135 result in free-radical scavenging of acyl radicals by nitroxides (Scheme 24, pathway a) [126, 173, 174, 191]. Alternative pathways b and c starting with NOH were proposed as well [26] and include reactivity with aldehydes or carboxylic acids formed in oxidized PO. Aldehydes generate hemiacetals 136 in the first step and are transformed into 135 after scavenging ROO. ... 

Further syntheses with nitroxide. alpha.,.beta.-unsaturated aldehydes and allylic bromides... 

Oxammonium salts such as 81 are new and powerful oxidizing agents for the selective oxidation of alcohols to aldehydes or ketones. 28 Such salts can be generated catalytically from small amounts of a nitro-xide in the presence of a secondary oxidation procedure, either chemical or electrochemical,. 29 or with two equivalents of acid and 2 equivalents of a nitroxide. When 81 was mixed with acetylenic alcohol 82 in dichloromethane, aldehyde 83 was isolated in 93% yield. The reaction can be monitored as the initial yellow slurry changes to a white slurry and the presence of unreacted oxidant can be checked with starch. 3l It is not necessary to use anhydrous conditions, and it was discovered that the rate of reaction was enhanced by the presence of silica gel. This reagent is compatible for the mild oxidation of many alcohols, including aliphatic primary and secondary as well as allylic and benzylic alcohols. 

Pentafluorobenzalddiyde reacts with bistrifluoromethyl nitroxide (see also p. 414) to give the amino-oxy-compound C6Fs CX>2-N(CF3)s, with the monohydrazide of cyclic trimeric phosphonitrile fluoride to give the hydrazone (117), and with ethyl acetoacetate and ammonia to give the expected dihydropyridine derivative (118). (Pfcntajauorophenyl)acetaldehyde is obtained in excellent yield from 2-(pentafluoropheny])ethanol and sodium dichromate in dimethyl sulphoxide the solvent may prevent further oxidation of the aldehyde. ... 

Many of these mechanisms are based on radical scavenging in which a nitroxide plays a key role. In the first reaction the amine is converted into a nitrox-yl radical. For this reaction several mechanisms are proposed. Sedlar et al. [110] proposed a reaction of a hydroperoxide with the amine to form an alkoxy-amine, which reacts with a peroxy radical to form a nitroxide. Carlsson et al. [Ill] published a mechanism involving an aminyl radical which is oxidized to a nitroxide. Geuskens andNedelkos [112] suggested that the reaction of an amine with a peroxy radical leads to the nitroxide and an alcohol. Toda et al. [113] and Felder [114] suggested that the formation of the nitroxide is related to the oxidation of aldehydes that are formed by oxidation. Toda et al. [113] assumed that the nitroxide is formed by a reaction of a peracid... 

Polarization of the C=N bond also causes electrophilic substitution of the alkyl group hydrogen in the a-position. Interaction of 1-hydroxy-3-imidazoline-3-oxide (6a) with aromatic aldehydes in the presence of bases, similar to the case observed for heterocyclic iV-oxides (Ochiai, 1967 Katritzky and Lagowski, 1971 Hansen and Boyd, 1970), leads to l-hydroxy-4-arylvinyl-3-imidazoline-3-oxides (41), oxidation of which generates nitroxides 42. The action of an equimolar amount of amyl nitrite on l-hydroxy-4-methyl- and l-hydroxy-4-ethyl-3-imidazoline-3-oxides... 

Thus, the interaction of a-haloalkylnitrones 64a,b with amines and hydrazine leads to products that contain no iV-oxide oxygen atom. This allows aldehyde and ketone derivatives of 3-imidazoline nitroxide to be synthesized the latter are of interest as spin labels for biological systems (Schlude, 1973). The interaction of the same compounds (64a,b) with nitrogenous nucleophiles, which contain a more electronegative nitrogen atom than that in amines or hydrazine, as well as the interaction with C-, S-, and O-nucleophiles, proceeds with the preservation of the nitrone group and leads to nucleophilic substitution products. Dehydrobromination of 4-bromoalkyl derivatives leads to reactive a,j8-unsaturated nitrones... 

Alkali treatment of 4-dihalomethyl derivatives 65a leads not to aldehyde 83a, but to acid 46. Nitroxyl aldehyde 83a was prepared by acid hydrolysis of 4-iminomethyl-3-imidazoline-3-oxide nitroxide (78). Alkaline hydrolysis of 4-a,a-dichloroethyl nitroxide (65b, X = Cl) leads to ketone 83b (Grigor ev et al, 1979b). 

The nitroxide also oxidizes the alcoholic group of 4-hydroxymethyl-(84a) and 4-(l-hydroxyethyl)- (84b) 3-imidazoline-l-oxyls obtained by reduction of aldehyde 71a and ketone 71b with NaBH4 (Grigor ev and Volodarsky, 1978). 

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