Nitro group rearrangement

A further type of nitro-group rearrangement gives rise to a cyclic hydroxamic ether. Noland e.t aL describe the action of cold, dilute sulfuric acid on the sodium salt of 5-nitronorbornene (98), which results in conversion to the oxazinone (101). This complex rearrangement is rationalized by the sequence 98 101 involving intermediate formation of the nitrile oxide (99) and the hydroxamic acid (100). 

Nitro group rearrangements have also been postulated during aromatic nitration reactions, particularly those associated with reaction pathways involving ipso attack by the reagent (N02+ or NO2). This topic is more fully discussed elsewhere in this volume and so just a few examples will be presented here. 

The proposed mechanism for the photochemical cleavage of nBn ethers (see Scheme 3) involves a n tt transition of the nitrogroup and an intramolecular, benzylic hydrogen abstraction by the excited nitro group. Rearrangement leads to a hemiacetal that decomposes to a free alcohol and to 2-nitrosobenzaldehyde that undergoes further thermal and photochemical reactions. 

Trinitrochloroethane (202) and 2,2,2-trinitroethyl acetate (203) also undergo nitro group rearrangement in the presence of potassium nitrite to give the di-potassium salt of 1,1,2,2-tetranitroethane (74) in both cases. ... 

Initial nitration of pyrazole derivatives with nitric acid in acetic or trifluoroacetic anhydrides leads to A-nitropyrazoles, which rearrange to the C-nitrated product on stirring in concentrated sulfuric acid at subambient temperature. This N -> C nitro group rearrangement often occurs in situ when pyrazoles are nitrated with mixed acid. 

Similarly generated diarylnitrilimines carrying o-nitro groups rearrange thermally to benzotriazoles (Eq. 40).196... 

These features will not be dealt with here. Two points of importance should be stressed however. First, the formation of an ipso adduct may give rise to either nitro group rearrangement... 

Allylic nitro compounds form rr-allylpalladium complexes by displacement of the nitro group and react with nucleophiles, and allylation with the tertiary nitro compound 202 takes place at the more substituted side without rearrangement to give 203[8,9,128]. 

Diaminoazobenzene was reported by Nietzki to have been prepared by diazotizing -nitroaniline and coupling the product with aniline. The resulting 4-nitrodiazoaminobenzene is rearranged and the nitro group reduced. The submitters tried several times to carry out this procedure but were unsuccessful. 4,4 -Diaminoazobenzene has been prepared by the oxidation of -nitroaniline with potassium persulfate followed by the reduction of the nitro groups. ... 

Nucleophilic displacement of a nitro group by aniline in 5,6-dinitrobenzofuroxan has been reported. Rearrangements of 4-nitro-benzofuroxans are discussed in Section VIII. 

The literature contains several examples of the rearrangement of a nitro group to a hydroxamic acid function. In two cases an adjacent carbonyl group is present, so that the rearrangement products are A-hydroxyimides. 

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