Fischer-Hepp reaction

We mention Williams work briefly here because it may also explain Blangey s observations strongly basic primary amines unequivocally form 7V-nitrosoanilinium ions in strongly acidic media. In contrast to the rate-limiting deprotonations of the less basic aromatic and heteroaromatic nitrosoamine cations discussed in this section, the TV-nitroso cation of a strongly basic amine deprotonates extremely slowly. Therefore, the nitroso rearrangement, the Fischer-Hepp reaction, competes effectively with the 7V-deprotonation. 

In contrast to the other mechanistically related mechanisms in this section, there do not appear to be any examples of the Fischer-Hepp reaction in synthesis on aU-carbon aryl systems (i.e., benzene). That said, there is a recent heterocychc example that claims to be the first example of the Fischer-Hepp-type rearrangement in pyrimidines, although its details will not be included here [72]. 

The Fischer-Hepp rearrangement generally gives only the 4-isomer and, apart from examples in the naphthyl series, the 2-isomer has rarely been identified. Now the 2-isomer has been characterized96 as the minor product from the reaction of the diphenylamine derivative 96. The 2-nitroso product gives the cyclized product 97 on treatment with hydrogen peroxide (Scheme 17). 

Quite different from the Fischer-Hepp rearrangement is the reaction of N-nitrosodehydromorpholine 98 which, in methylene chloride containing HC1, gives at room temperature l-azo-4-oxa-3-oximinocyclohexene 99, which ring-opens on treatment... 

One of the best-knbwn methods for the preparation of aromatic nitroso compounds is the Fischer-Hepp rearrangement of A-nitrosoamines (Eq. 2). In effect, this reaction is the C-nitrosation of secondary aromatic amines. 

A side-chain methylenamino group reacts with a nitroso group (introduced in situ) when the compound is heated with mineral acid [2466]. An unusual reaction occurred when the nitro-t-amine (103.4) was refluxed with acetic anhydride and zinc chloride the course of this reaction may involve an A -oxide [2039]. When an o-nitroalkylamine is heated with ethoxide, the two functions are converted into a 1-hydroxyimidazole ring [3004]. Nitrosation of the pyrim-idinone (103.5) involves several steps including a Fischer-Hepp rearrangement of an iV-nitroso to a ring-C-nitroso the final product is a 6-(4 -nitrophenyl-amino)purin-2-one [2667]. In a weakly basic medium, the nitroamine (103.6) is cyclized to either the benzimidazole (when R == H), or the benzimidazolone (when R H). 

This reaction is related to Fischer-Hepp Rearrangement, Orton Rearrangement, and Reilly-Rickinbottom Rearrangement... 

Scheme 10.42. The Fischer-Hepp rearrangement. A representation of diazotization of ami-nobenzene (aniline) with nitrons acid and subsequent reaction of the diazonium ion with N-methylaminobenzene (A-methylanihne) to yield a nitrogen-substituted derivative, which then undergoes intramolecular rearrangement to the corresponding 4-substituted azo derivative.

The nucleophilic attack on the nitrogen atom of a nitroso group is the limiting stage of condensation reactions of nitroso compounds with amines, methylene-active, and organomagnesium compounds, of Ehrlich-Sachs, Fischer-Hepp, Burton, and other reaction [161,162]. 

A number of papers on aspects of nitrous acid chemistry have appeared. Kinetic work on the Fischer-Hepp rearrangement has provided information on the selectivity of ONCl and ONSCN as electrophilic nitrosating agents, and has shown a very close similarity between ONSCN and [ONSC(NH2>2]+. The electrophilic nitro-sation of hydrazine, methylhydrazine, 1,1-dimethylhydrazine, and various aryl-hydrazines has been described. These reactions seem to be close to encounter-controlled processes. Evidence of a second nitrosation of the primary product has been obtained ... 

Fischer-Hepp rearrangement org chem The rearrangement of a nitroso derivative of a secondary aromatic amine to a p-nitrosoarylamine the reaction is brought about by an alcoholic solution of hydrogen chloride. fish ar hep re a rani mant) Fischer indole synthesis orgchem A reaction to form indole derivatives by means of a ring closure of aromatic hydrazones.. fish ar in.dol. sin tha sas )... 

The influence of the nitrite trap HN3 on the Fischer-Hepp rearrangement of N-nitrosoani-line [21], on its denitrosation by an excess of a secondary amine [22], and on other reactions of the starting material [23] were investigated. 

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