Nitro compounds carbonylation

Hydrogenation of double bonds, acid chlorides, aromatic nitro compounds, carbonyl groups, partial reduction of triple bonds, etc. 

Keywords Nitro-compounds, carbonyl compounds, dialkyl or trialkyl phosphites. Indium (In) metal, hydrochloric acid, water, room temperature, reductimi of nitro-group, imines, hydro-phosphorylation, a-aminophosphonates... 

Nowadays a broad range of different 1,3-dipoles, ozone, azides ° and diazoalkanes on the one hand as well as dipoles like nitrones, nitro compounds, carbonyl ylides, nitrile oxides, nitrile imines and ylides on the other hand, are well-established. The addition of these 1,3-dipoles to an alkene is one of the most frequently used cycloaddition reactions in organic synthesis. ... 

Reductive carbonylation of nitro compounds is catalyzed by various Pd catalysts. Phenyl isocyanate (93) is produced by the PdCl2-catalyzed reductive carbonylation (deoxygenation) of nitrobenzene with CO, probably via nitrene formation. Extensive studies have been carried out to develop the phosgene-free commercial process for phenyl isocyanate production from nitroben-zene[76]. Effects of various additives such as phenanthroline have been stu-died[77-79]. The co-catalysts of montmorillonite-bipyridylpalladium acetate and Ru3(CO) 2 are used for the reductive carbonylation oLnitroarenes[80,81]. Extensive studies on the reaction in alcohol to form the A -phenylurethane 94 have also been carried out[82-87]. Reaction of nitrobenzene with CO in the presence of aniline affords diphenylurea (95)[88]. 

Reduction of an azide a nitrile or a nitro compound furnishes a primary amine A method that provides access to primary secondary or tertiary amines is reduction of the carbonyl group of an amide by lithium aluminum hydride... 

Attempts have been made to develop methods for the production of aromatic isocyanates without the use of phosgene. None of these processes is currently in commercial use. Processes based on the reaction of carbon monoxide with aromatic nitro compounds have been examined extensively (23,27,76). The reductive carbonylation of 2,4-dinitrotoluene [121 -14-2] to toluene 2,4-diaLkylcarbamates is reported to occur in high yield at reaction temperatures of 140—180°C under 6900 kPa (1000 psi) of carbon monoxide. The resultant carbamate product distribution is noted to be a strong function of the alcohol used. Mitsui-Toatsu and Arco have disclosed a two-step reductive carbonylation process based on a cost effective selenium catalyst (22,23). 

These reversible reactions are cataly2ed by bases or acids, such as 2iac chloride and aluminum isopropoxide, or by anion-exchange resias. Ultrasonic vibrations improve the reaction rate and yield. Reaction of aromatic aldehydes or ketones with nitroparaffins yields either the nitro alcohol or the nitro olefin, depending on the catalyst. Conjugated unsaturated aldehydes or ketones and nitroparaffins (Michael addition) yield nitro-substituted carbonyl compounds rather than nitro alcohols. Condensation with keto esters gives the substituted nitro alcohols (37) keto aldehydes react preferentially at the aldehyde function. 

In general, peroxomonosulfates have fewer uses in organic chemistry than peroxodisulfates. However, the triple salt is used for oxidizing ketones (qv) to dioxiranes (7) (71,72), which in turn are useful oxidants in organic chemistry. Acetone in water is oxidized by triple salt to dimethyldioxirane, which in turn oxidizes alkenes to epoxides, polycycHc aromatic hydrocarbons to oxides and diones, amines to nitro compounds, sulfides to sulfoxides, phosphines to phosphine oxides, and alkanes to alcohols or carbonyl compounds. 

Another important feature of the Nef reaction is the possible use of a CH-NO2 function as an umpoled carbonyl function. A proton at a carbon a to a nitro group is acidic, and can be abstracted by base. The resulting anionic species has a nucleophilic carbon, and can react at that position with electrophiles. In contrast the carbon center of a carbonyl group is electrophilic, and thus reactive towards nucleophiles. 1,4-Diketones 4 can for example be prepared from a-acidic nitro compounds by a Michael additionfNef reaction sequence " ... 

Conversion of carbonyl to nitro groups fretro Nef Reacdoni is tin importiint method for the preparadon of nitro compounds. Such conversion is generally effected vii oximes using strong oxidiints such as CF-vCOaH. 

Thus, various kmds of bases are effective in inducing the Henry reaction The choice of base and solvent is not crucial to carry out the Henry reaction of simple nitroalkanes v/ith aldehydes, as summarized in Table 3 1 In general, sterically hindered carbonyl or nitro compounds are less reactive not to give the desired ni tro-aldol products in good yield In such cases, self-condensation of the carbonyl compound is a serious side-reaction Several mochfied procedures for the Henry reaction have been developed... 

When the substrate does not contain a reactive carbon-carbon double bond, the ozonolysis procedure appears to provide a convenient and efficient method for the conversion of primary and secondary nitro compounds into carbonyl compounds fEq. 6.7. ... 

The Nef reacaon can also be earned out with reducing agents. Aqueous Qtatuum chlonde reduces nitro compounds to iirunes, which are readily hydrolyzed to carbonyl compounds fEq. 

The Henry reaction of ketones with nitroalkanes in the presence of etbylenediamine gives allylic nitro compounds, which give a,fi-imsanirated carbonyl compounds via the Nef reaction fEq. 6.30. ... 

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. 

The Michael reaction occurs with a variety of a,/3-unsaturated carbonyl compounds, not just conjugated ketones. Unsaturated aldehydes, esters, thio-esters, nitriles, amides, and nitro compounds can all act as the electrophilic acceptor component in Michael reactions (Table 23.1). Similarly, a variety of different donors can be used, including /3-diketones, /3-keto esters, malonic esters, /3-keto nitriles, and nitro compounds. 

With this reaction available, a simple synthesis of unsymmctrical dibenzyl ketones (21) can be planned. The carbonyl group can be derived from a nitro group (22) by TlClg-catalysed hydrolysis (p T 183 ). Reversing the selective reduction gives (23) and a,6-dlsconnection separates this Into aldehyde (24) and nitro compound (25), available by reduction of (20). 

These oxidants are generally too feeble to attack monofunctional compounds except thiols, carbonyl- and nitro-compounds in their enolic forms, phenols and aromatic amines. However, ferric rWj-o-phenanthroline readily oxidises cyclohexanone. 

The addition reaction of enolates and enols with carbonyl compounds is of broad scope and of great synthetic importance. Essentially all of the stabilized carbanions mentioned in Section 1.1 are capable of adding to carbonyl groups, in what is known as the generalized aldol reaction. Enolates of aldehydes, ketones, esters, and amides, the carbanions of nitriles and nitro compounds, as well as phosphoms- and sulfur-stabilized carbanions and ylides undergo this reaction. In the next section we emphasize the fundamental regiochemical and stereochemical aspects of the reactions of ketones and aldehydes. 

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. 

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