Nitro nitrone

The nitroparaffins are named as derivatives of the corresponding hydrocarbons by usiag the prefix "nitro" to designate the NO2 group (1), eg, 1,1-dinitroethane, CH2CH(N02)2- The salts obtained from nitroparaffins and the so-called nitronic acids are identical and may be named as derivatives of either, eg, sodium salt of i7ti-nitromethane, or sodium methanenitronate [25854-38-0]. 

The nitro isomer is weaMy acidic the nitronic acid isomer (aci form) is much more acidic. A comparison of the ionisation constants of the two forms ki water at 25°C is given ki Table 4. 

In solution, a nitronic acid either isomerizes slowly into its more stable nitro form or undergoes some kreversible transformation. The isomerization occurs sufficiently slowly that it can be measured by conductometric or halometric methods. 

Nitrones or aci-nitro esters react with alkenes to give in some cases A/-substituted isoxazolidines and in others 2-isoxazolines. When the intermediate isoxazolidines were observed, a number of procedures transformed them into the 2-isoxazolines. Acrylonitrile and phenyl rzcf-nitrone esters produced an A/-methoxyisoxazolidine. Treatment with acid generated a 2-isoxazole while treatment with base generated an oxazine (Scheme 118) (68ZOR236). When an ethoxycarbonyl nitrone ester was reacted with alkenes, no intermediate isoxazolidine was observed, only A -isoxazolines. Other aci-mtro methyl esters used are shown in Scheme 118 and these generate IV-methoxyisoxazolidines or A -isoxazolines which can be further transformed (72MI41605). 

Alicyclic hydroxamic acids undergo several specific oxidative cleavage reactions which may be of diagnostic or preparative value. In the pyrrolidine series compounds of type 66 have been oxidized with sodium hypobromite or with periodates to give y-nitroso acids (113). Ozonolysis gives the corresponding y-nitro acids. The related cyclic aldonitrone.s are also oxidized by periodate to nitroso acids, presumably via the hydroxamic acids.This periodate fission was used in the complex degradation of J -nitrones derived from aconitine. 

Cycloaddition reactions of nitro compounds, nitrones, and nitrile oxides 99JCS(P1)749. 

The conversion of a primary or secondary nitro alkane 1 to a carbonyl compound 3 via an intermediate nitronate 2 is called the Nef reaction. Since carbonyl compounds are of great importance in organic synthesis, and nitro alkanes can on the other hand be easily prepared, the Nef reaction is an important tool in organic chemistry. 

Various side-reactions may complicate the course of the Nef reaction. Because of the delocalized negative charge, the nitronate anion 2 can react at various positions with an electrophile addition of a proton at the a-carbon reconstitutes the starting nitro alkane. 1. The nitrite anion can act as leaving group, thus leading to elimination products. 

The required nitro compounds are easy to prepare, and are useful building blocks for synthesis. Treatment with an appropriate base—e.g. aqueous alkali—leads to formation of nitronates 2. Various substituted nitro compounds, such as nitro-ketones, -alcohols, -esters and -nitriles are suitable starting materials. 

Several approaches based on nitro-aldol for the synthesis of amino sugars have been reported Alumina-catalyzed reaction of methyl 3- nitropropanoate with O-benzyl-o-lactaldehyde gives the o-ribo-nitro-aldol fanti, and isomeri in 63% yield, which is converted into L-dannosamine fsee Secdon 3 3 Jager and coworkers have reported a short synthesis of L-acosamine based on the stereoselective nitro-aldol reaction of 2-O-benzyl-L-lactaldehyde with 3-nitropropanal dimethyl acetal as shovm in Scheme 3 10 The stereoselecdve nitro-aldol reacdon is carried ont by the silyl nitronate approach as discussed in Secdon 3 3... 

An experimentally simple ptocedure for stereoselecdvely preparing fi-nitro alcohols has been developed. The alkyl nitronates, formed by the acdon of u-butyUithiumonnitroalkanes in THF soludon, react v/ith aldehydes in the presence of isopropoxydtanium trichloride at room temperanire to give the fi-nitro alcohols enriched in the ruiri-thastereoisomers fEq. 3.711. 

Scheme 3.20. Proposed mechanism of asymmetric nitro-aldol reactions catalyzed by LLB, LLB-II, or LLB-LI nitronate...

Mosher and coworkers have adopted this strategy for the enandoselecdve synthesis of 2,3-thdeoxy-3-nitro-furanosides and pyranosides using chirM nitronate dianions, as shown in Eq. 5.5."... 

In d sumldf way, a-nitroselenides are prepared via the reacdon of nitronates with phenylse-lenyl bromide, which gives a new synthedc method of 1-nitroalkenes from nitroalkanes The sequence of ct-selenadon, nitro-aldol reacdon, and oxidadon provides a nsefid method for the preparadon of nitroalkenes with a hydroxymethyl group fEq 5 81 ... 

The reduction of y-nitroketone acetals as in Eq. 6.50 v/ith ammonium formate in the presence of Pd/C gives the correspondmg amines in good yields. However, the reduction ofy-nitro ketones are reduced to cyclic nitrones fEq. 6.51. This reduction is far superior to the classical method using Zn/T4HlCl due to improved yield and simple workup. 

Stereoselective preparation of CEi-allyl alcohols via radical elimination from ruin -y-phenylthio-fi-nkro alcohols has been reported. The requisiteruin -fi-nitro sulfides are prepared by protonadon of nitronates at low temperanire Isee Chapter 4, and subsequent treatment v/ith Bu-vSnH induces and eliminadon to givelE -alkenes selecdvely IseeEq. 7.112. Unfortunately, it is difficult to get the pure syu-fi-nitro sulfides. Treatment of a rruxnire of syu- and ruin -fi-nitrosulfides v/ith Bu- SnH results in formadon of a rruxnire of (Ey and lZ -alkenes. 

Nitro compounds have been converted into various cyclic compounds via cycloaddidon reactions. In particular, nitroalkenes have proved to be nsefid in Diels-Alder reactions. Under thermal conditions, they behave as electron-deficient alkenes ind react v/ith dienes to yield 3-nitrocy-clohexenes. Nitroalkenes c in also act as heterodienes ind react v/ith olefins in the presence of Lewis acids to yield cyclic alkyl nkronates, which undergo [3- 2 cycloaddidon. Nitro compounds are precursors for nitnie oxides, alkyl nitronates, and trialkylsilyl nitronates, which undergo [3- 2 cycloaddldon reacdons. Thus, nitro compounds play important roles in the chemistry of cycloaddidon reacdons. In this chapter, recent developments of cycloaddinon chemistry of nitro compotmds and their derivadves are summarized. 

N-(p-Dimetliylaminophenyl)-Qr-(o-nitro-phenyl)nitrone from reaction of o-nitrobenzylpyridinium bromide and -nitrosodimethylaniline, 46, 82... 

CONVERSION OF NITRO TO CARBONYL BY OZONOLYSIS OF NITRONATES 2,5-HEPTANEDIONE... 

Analytical. Mannitol Hexanitrate can be hydrolyzed in basic soln and the soln acidified in the presence of NITRON to quanty ppt NITRON nitrate (Ref 16). A procedure is described for. the quant detn of nitrate esters, including Mannitol Hexanitrate, in the presence of aromatic nitro compds in Ref 17. It gives a yellow color when treated in et ale or acet with 5% aq K hydroxide, then 5% aq ammonia (Ref 24), It can be quanty detd by reduction with Devarda s alloy (Encycl 5, D-l 110) or A1 wire in aq et ale and titration of the evolved... 

N-Nitro-amine werden in der Regel durch Hydride nicht angegriffen (s. S. 365), Nitrone an der C=N-Doppelbindung hydriert (s.S. 373). Zur Reduktion von Furoxanen s.S. 378. 

The nitro form is much more stable than the aci form in sharp contrast to the parallel case of nitroso-oxime tautomerism, undoubtedly because the nitro form has resonance not found in the nitroso case. Aci forms of nitro compounds are also called nitronic acids and azinic acids. 

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