Nitro groups arenes

With these homogeneous catalysts, it is possible to selectively reduce the C=0 group without any competitive reduction of the carbon-carbon double bond, nitro group, arenes and aryl-halide bond. 

The nucleophilic substitution of the nitro group in nitro-arene complexes works almost as well as that of Cl" and such substitutions were achieved by Chowdhurry et al. with O, S, and N nucleophiles and with stabilized carbanions [97,98] Eq. (28) and Table 8. 

As a consequence of the strong electron-withdrawing properties of the nitro group, conjugated nitroalkenes behave as powerful Michael acceptors. An example of conjugate addition of Reformatsky reagents to (2-nitrovinyl)arenes 107 is given in equation 63150. 

Glutathione conjugation Glutathione (GSH) GSH-S-transferase (cytosol, microsomes) Epoxides, arene oxides, nitro groups, hydroxylamines Acetaminophen, ethacrynic acid, bromobenzene... 

Cross-linked polystyrene can be directly nitrated with fuming nitric acid at low temperatures (-25 °C to 0°C) [189,203,374] polymers with up to one nitro group per arene result [203]. Partial nitration can be achieved with milder nitrating agents, such as acetyl nitrate [203]. Because direct nitrations are not compatible with most linkers (which are often acid- or oxidant-labile), nitro compounds are generally not prepared on supports but in solution, and are then linked to the support. 

The structure of the tetranitro derivative was confirmed by X-ray diffraction in the solid state, this compound does not possess any symmetry element. The conformation of the calixarene structure is less symmetrical than for calix[4]arene(bis crown-6). The nitro groups appear to strongly modify the usual conformation of this calixarene, and a decrease in the preorganization toward cesium complexation can be expected. 

This reduction is carried out in the same way as reduction of an arene that contains only a single nitro group. In this case hydrogenation over a nickel catalyst gave the desired product in 90% yield. 

Benzylic electrophiles bearing electron-withdrawing groups at the arene do not always yield the expected products of nucleophilic substitution on treatment with a nucleophile. One important side reaction is the dimerization of these compounds to yield 1,2-diarylethenes (stilbenes). This dimerization does not require such highly activated systems as the example sketched in Scheme 4.28, but can even occur with, for example, 2- or 4-nitrobenzyl chloride [120, 121]. The latter compounds are converted into the corresponding stilbenes by treatment with KOH in ethanol [120]. Di-arylmethyl halides behave similarly and can yield tetraarylethenes on treatment with a base. These reactions presumably proceed via the mechanism sketched in Scheme 4.27, in which the amphiphilic character of the nitro group plays a decisive role (metalated nitroalkanes or 4-nitrobenzyl derivatives can act as nucleophiles and as electrophiles). 

Similarly, nitroarenes can also be lithiated (Scheme 5.43), but reactions of meta-lated nitroarenes with electrophiles only proceed cleanly if the metalation is performed in the presence of the electrophile [403], Otherwise, the metalated arene can reduce nitro groups to nitroso groups, which quickly react with additional organo-metallic reagent to yield hydroxylamines [404, 405], Nitroarylmagnesium halides can be prepared by iodine-magnesium exchange at -80 °C to -40 °C, and react with electrophiles in the expected way [6] (Scheme 5.43). 

The one-pot Stille cross-coupling reaction of compound 256 produced all four isomeric thieno[3,2-c]naphthyridines (1994JHC11). The stepwise formation of the C(7)-C(7a) and C(4)-N(5) bonds of the thieno[3,2-c]pyridine system can be considered as a modification of the above-described approaches. For example, aldehyde 256 reacts with arene 265 to give 266 reduction of its nitro group is accompanied by cyclization to form thieno[3,2-c]isoquinoline A-oxide (267) (1990JHC1127). 

Several works have been reported for selective substitution of nitro groups at the upper rim of the calix[4]arene [39,40], The selectively i/Avo-nilraled p-tert-butylcalix[4]arene was used as starting material for the preparation of bisphthaloni-trile 5. Nitro groups at the upper rims of 6 were coupled with nitro groups of four unsymmetrical Pcs 7 in order to obtain the hexanuclear zinc Pc 8, Fig. 2 [41],... 

The introduction of nitro groups at the upper rim of calix[4]arenes is a quick and useful method for the preparation of functionalized calix[4]arenes. This reaction is quite general and can be conveniently carried out on a wide variety of calix[4]arenes substituted at the lower rim. When the starting calix-arene is partially substituted at the lower rim, the substitution takes place at the more reactive phenol rings. 

Particularly convenient is the reaction carried out on tetraalkoxytetra-t-butylcalix[4]arenes in which concomitant removal of the f-butyl groups and introduction of four nitro groups occurs (ipso nitration) in 37-67% yield (Scheme 7.13).29... 

Dry ozonization is also an efficient proc ure for oxidation of aliphatic primary amines into nitro groups, with yields of about 70%. Arylamines are also oxidized to nitro aronutics, albeit witii low yields. Ozone on silica gel has also been shown to oxidize arenes in some cases. ... 

In some cases it is also possible to add fluorine and another element to arenes, for example, fluorine and bromine, " or fluorine and a nitro group by the use of hydrogen fluoride and nitric acid as the nitrofluorinalion reagent." "... 

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