Nitro compounds oxime synthesis

Indirect conversion of oximes to nitro compounds viact-halo nitro compounds has provided a useful method for synthesis of nitro compounds, as shown m Scheme 2 1... 

As discussed in Chapter 6, nitro compounds are converted into amines, oximes, or carbonyl compounds. They serve as usefid starting materials for the preparation of various heterocyclic compounds. Especially, five-membered nitrogen heterocycles, such as pyrroles, indoles, ind pyrrolidines, are frequently prepared from nitro compounds. Syntheses of heterocyclic compounds using nitro compounds are described partially in Chapters 4, 6 and 9. This chapter focuses on synthesis of hetero-aromadcs fmainly pyrroles ind indolesi ind saturated nitrogen heterocycles such as pyrrolidines ind their derivadves. 

Reductive alkylations have been carried out successfully with compounds that are not carbonyls or amines, but which are transformed during the hydrogenation to suitable functions. Azides, azo, hydrazo, nitro and nitroso compounds, oximes, pyridines, and hydroxylamines serve as amines phenols, acetals, ketals, or hydrazones serve as carbonyls 6,7,8,9,12,17,24,41,42,58). Alkylations using masked functions have been successful at times when use of unmasked functions have failed (2). In a synthesis leading to methoxatin, a key... 

Oxidation of oximes to nitro compounds with m-CPBA has been applied to the synthesis of dialkyl 1-nitroalkanephosphonates (Eq. 2.63),124 which are useful reagents for conversion of carbonyl compounds to nitroalkenes.125... 

Nitro compounds are versatile precursors for diverse functionalities. Their conversion into carbonyl compounds by the Nef reaction and into amines by reduction are the most widely used processes in organic synthesis using nitro compounds. In addition, dehydration of primary nitro compounds leads to nitrile oxides, a class of reactive 1,3-dipolar reagents. Nitro compounds are also good precursors for various nitrogen derivatives such as nitriles, oximes, hydroxylamines, and imines. These transformations of nitro compounds are well established and are used routinely in organic synthesis. 

I.2. Oxidation of Amines Oxidation of primary amines is often viewed as a particularly convenient way to prepare hydroxylamines. However, their direct oxidation usually leads to complex mixtures containing nitroso and nitro compounds and oximes. However, oxidation to nitrones can be performed after their conversion into secondary amines or imines. Sometimes, oxidation of secondary amines rather than direct imine oxidation seems to provide a more useful and convenient way of producing nitrones. In many cases, imines are first reduced to secondary amines which are then treated with oxidants (26). This approach is used as a basis for a one-pot synthesis of asymmetrical acyclic nitrones starting from aromatic aldehydes (Scheme 2.5) (27a) and 3,4-dihydroisoquinoline-2-oxides (27b). 

Methods for preparation of hydroxylamine derivatives have been reviewed in detail recently. Here, mainly new developments concerning the synthesis of hydroxylamines by substitution processes with heterobond formation are presented. Reduction of nitro, nitroso, oxime and nitrone derivatives as well as direct oxidation of amines leading to hydroxylamine compounds will not be considered. 

As mentioned above, nitro compounds are obviously of great importance in organic chemistry and aryl nitro compounds are an important source of aniline derivatives (secs. 4.2.C.V, 4.8.D). Both amine oxides and nitrones have been synthetically exploited. Alkyl nitroso derivatives, however, usually cannot be isolated since they decompose in solution, although the aromatic derivatives are more stable in solution and can be used in synthesis (sec. 2.1 l.E). Treatment of a primary amine with excess peroxyacid is a useful preparative route to alkyl nitro compounds.588 Yields are highest for tertiary alkyl primary amines next come secondary, followed by primary alkyl. Peroxyacid oxidation of oximes also provides a route to alkyl nitro compounds.589 This method is convenient for preparing aromatic nitro compounds as in the oxidation of 2,6-dichloroaniline to 2,6-dichloronitrobenzene (441).590 Nitrones are 1,3-dipoles and have been used in 1,3-dipolar cycloaddition reactions (sec. ll.ll.D). 

The synthesis and deamination of the 3-aminopinanes, including the unknown 3a-amino-rrans-pinane (354) is described. The latter was made by oxidation of fruns-pinocamphone oxime (355) to the nitro-compound, which was catalytically reduced, direct catalytic reduction of the oxime giving the 3jS-amino-isomer (356). The various conformations ascribed to the four possible amines were... 

The [Ru(bpy)3] photocatalyst was also applied in the following novel visible-light driven processes (i) synthesis of indazolo[2,3-a]quinoline derivatives from 2-(2-nitrophenyl)-l,2,3,4-tetra-hydroquinolines (ii) azido- and amino-trifluoromethylation of alkenes (iii) reduction of nitro compounds to oximes (iv) generation of aryl radicals by visible-light photocatalytic reduction of sulfonium salts. ... 

A number of modern industrial processes are based on the catalytic carbonyl at 1 on of organic substrates by carbon monoxide. ll In contrast, the application of carbon monoxide as reductant in organic synthesis is confined to relatively few exampl es. 2l In recent years the catalytic carbonyl at I on of nitro compounds has become a ery intense field of research. This is due to the fact that 3 series of industrially important compounds can be obtained - om nitro compounds and carbon monoxide in a single step azo compounds, amides, amines, oximes, ureas, urethanes and isocyanates [ 3] and indoles. Ureas and urethanes are important final products and intermediates in the synthesis of ert ll eps and pesticides. On the other hand mono and di-1 socyanates are very important intermed 1 a es in the manu-i-acture of pesticides, polyurethane foam plastics, synthetic leather, adhesives and coatings. 

The reduction of ketoximes with titanium(iu) chloride is noted in a partial synthesis of erythromycylamine in this case, the intermediate imine is stable and can be further reduced, though normally imine hydrolysis is rapid and ketones are obtained in high yield. This observation has been utilized to effect conversion of a nitro-compound into a ketone. In search of a route to 1,4-diketones via conjugate addition of a masked carbonyl anion to an ajS-unsaturated ketone, McMurry considered Michael addition with a nitro-alkane. Treatment of the resulting y-nitroketone with titanium(m) chloride afforded the required 1,4-diketone (148) in excellent yield, presumably by sequential intermediacy of the oxime and the imine this mild conversion avoids the harsh conditions of the alternative Nef procedure (Scheme 69). 

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