Nitro nitroalkanes

Chemoselective C-alkylation of the highly acidic and enolic triacetic acid lactone 104 (pAl, = 4.94) and tetronic acid (pA, = 3.76) is possible by use of DBU[68]. No 0-alkylation takes place. The same compound 105 is obtained by the regioslective allylation of copper-protected methyl 3,5-dioxohexano-ate[69]. It is known that base-catalyzed alkylation of nitro compounds affords 0-alkylation products, and the smooth Pd-catalyzed C-allylation of nitroalkanes[38.39], nitroacetate[70], and phenylstilfonylnitromethane[71] is possible. Chemoselective C-allylation of nitroethane (106) or the nitroacetate 107 has been applied to the synthesis of the skeleton of the ergoline alkaloid 108[70]. 

Nitroparaffias (or nitroaLkanes) are derivatives of the alkanes ia which one hydrogen or more is replaced by the electronegative nitro group, which is attached to carbon through nitrogen. The nitroparaffins are isomeric with alkyl nitrites, RONO, which are esters of nitrous acid. The nitro group ia a nitroparaffin has been shown to be symmetrical about the R—N bond axis, and may be represented as a resonance hybrid ... 

A,V,V-trifliioroalkylamidines N-halogen compounds N-metal derivatives Nitroalkanes, c-nitro, and polynitroaryl compounds... 

This reaction can also be applied to tertiary nitroalkanes lacking any additional functional group. The reactions with nitro compounds lacking additional anion-stabilizing groups are carried out in DMSO solution ... 

Nitroalkanes, C-Nitro and Polynitroaryl compounds Polynitroalkyl compounds... 

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... 

Another method for improving the reactivity of nitro compounds is provided by the double deprotonadon of nitroalkanes. In this case, the reacdon with ketones affords fi-nitro alcohols in 4Q-6Q% yield CEq.d.lQi ... 

Proazaphosphao-ane, PrRNCH-,CH-j,N, is an efficient catalyst for the Henty reacdon, and arious ketones give nitro-aldols by the reacdon with nitromethane and other nitroalkanes fEq. 

Condensadon of glyoxalic acid, nitroalkanes, and amines provides a simple method for fi-nitro-ct-airino acids fEq 4 116 ... 

The reaedvity of carbon is much enhanced by the double deprotonated intermediates of nitro compounds. Except for nitromuhane, other nitroalkanes are alkylated to give the C-alkylated products in 50-60% yield by this procedure fsee Eq. 5.4. ... 

Because the anioas of nitroalkanes are stable, retro-acyladoc smoothly In the presence of a base catalyst. This type of reacdo organic synthesis." Nucleophilic attack of water or alcohol to ct-the ring cleavage v/ith the formadon of Oj-nitro acids and Oj-niti... 

Gem-nitro Lmidd2Qlyl ilkdnes undergo Spj l reacdons with the anion of various nitroalkanes, as shown in Eq 5 36 The nitro group is replaced by hydrogen in 80-90% yield oi with Bn-vSnH fsee Chapter 7, which discusses radicM denitradoni... 

Wade and coworkers have found that ct-nitro siilfones are useful reagents in organic synthesis because they are converted into nitroalkanes, nitnles, or carboxylic acids fsee Eq 5 52 ... 

In general, heterocyclic nitro compounds undergo cine snbsdtudon reacdons more readily than nltrobenzenes For example, the reacdon of 5-acyl- or 5-alkoxycarbonyl-2-nitrofurans v/ith the anion of nitroalkanes gives cine snbsdtudon products in excellent yields fEq 5 66 ... 

Barton and co workers have explored the aryladon of various nucleophiles inclndmg nitroalkanes using bismuth reagents Reacdon of 2-nitropropane v/ith triphenylbismnth carbonate gives 2-nitro-2-phenylpropane in 80% yield Recently, this aryladon has been used for the synthesis of unusual amino acids Aryladon of ct-nitro esters v/ith triphenylbismnth dichloride followed by redncdon gives unique ct-amino acids fEq 5 68 ... 

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 ... 

TheNef reaction of primary nitro compounds gives iildehydes or carboxylic acids, depending on the reaction conditions. Each transformation provides an important tool in organic synthesis. Primary nitro compotmds are converted into carboxylic acids vrith concentrated mineriil acids. Because such harsh conditions iilso lead to side reactions, a milder method is required inorganic synthesis. Basic phosphate-buffered KMnO rapidly converts primary nitroalkanes into carboxylic acids in 90-99% yield fEq. 6.13. "... 

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. ... 

Nitro Alcohols 7 General Procedure from Nitroalkanes l22 ... 

A variety of 1,5-dialdehydes 9 react in a double nitroaldol reaction with nitroalkanes to give 6-membered carbo- and heterocyclic owMran. -2-nitro-l,3-diols 10 which can be transformed into the enantiomcrically pure derivatives via enantiosclcctive saponification of their diacetates with pig liver esterase5. 

The condensation of nitro compounds and imines, the so-called aza-Henry or nitro-Mannich reaction, has recently emerged as a powerful tool for the enantioselective synthesis of 1,2-diamines through the intermediate /3-amino nitro compounds. The method is based on the addition of a nitronate ion (a-nitro carbanion), generated from nitroalkanes, to an imine. The addition of a nitronate ion to an imine is thermodynamically disfavored, so that the presence of a protic species or a Lewis acid is required, to activate the imine and/or to quench the adduct. The acidic medium is compatible with the existence of the nitronate anion, as acetic acid and nitromethane have comparable acidities. Moreover, the products are often unstable, either for the reversibility of the addition or for the possible /3-elimination of the nitro group, and the crude products are generally reduced, avoiding purification to give the desired 1,2-diamines. Hence, the nitronate ion is an equivalent of an a-amino carbanion. 

In practice, the condensation of nitroalkane (60) and aldehyde (59) gives nitro lactone (57) directly. Synthesis ... 

Whereas secondary nitroalkanes such as 1-nitrocyclohexane 1766 are reduced to the corresponding oximes, for example 1767 [24], primary nitro compounds such as a-nitro-o-xylene 1768 or unsaturated nitro compounds such as 1770 are transformed into nitriles such as 1769 and 1771 [24] (Scheme 12.6). 

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