Electrophilic nitrogen

Electrophilic nitrogen, in the forms of NO2, NO+, or ArN., has been well authenticated in aromatic substitution. However, while there is evidence for electrophilic addition mechanisms involving nitrogen , very little kinetic work has been carried out on such systems. Of the two which have been studied, the addition of 2A-dinitmbenzenediazonium ion to olefins seems to 

It is evident that substitution at the carbon atom undergoing attack is considerably diminished by a phenyl group, although this has the normal accelerating effect when steric hindrance is not serious. Solvent effects have not been studied in this system, nor have the effects of other diazonium ions been investigated kinetically.  

The kinetics of addition of nitrosyl chloride to a number of olefins have been examined. In chloroform, methyl and phenyl substituents enhance the rate while electron-withdrawing groups (e.g. chlorine) retard it. Such be-haviour would be consistent with electrophilic attack by the dipole NO-CP. The effect of changes in the solvent was not simple, although more polar solvents (nitrobenzene, chloroform) speeded the reaction (compared with toluene or carbon tetrachloride). Methanol appeared to be a remarkably poor reaction medium, perhaps due to interaction with the reactant the low reactivity of nitrosyl chloride in diethyl ether was attributed to strong bonding between the solvent and the incipient NO cation. 

While evidence has been presented of other electrophiles resulting from Group V elements, no kinetic studies appear to have been made. 

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Ring closures which depend on the conversion of the heteroatom into an electrophile are mostly associated with the formation of thiophene, selenophene and tellurophene rings and some illustrative examples are shown in Scheme 17. The last example which concerns the conversion of reaction with isocyanides is of particular interest since it appears to entail the attack of an electrophilic nitrogen species on the aryl ring. 

Electrophilic nitrogen compounds, such as arenesulfonyloxyamines, can convert alkenes to aziridines without the intervention of free nitrenes (80CC560). 

There is some debate in the literature as to the actual mechanism of the Beirut reaction. It is not clear which of the electrophilic nitrogens of BFO is the site of nucleophilic attack or if the reactive species is the dinitroso compound 10. In the case of the unsubstituted benzofurazan oxide (R = H), the product is the same regardless of which nitrogen undergoes the initial condensation step. When R 7 H, the nucleophilic addition step determines the structure of the product and, in fact, isomeric mixtures of quinoxaline-1,4-dioxides are often observed. One report suggests that N-3 of the more stable tautomer is the site of nucleophilic attack in accord with observed reaction products. However, a later study concludes that the product distribution can be best rationalized by invoking the ortho-dinitrosobenzene form 10 as the reactive intermediate. 

Carbon-Nitrogen Bond Formation A carbon-nitrogen bond can result either from the reaction between an anodically produced cationic center and an amino group or from the reaction between a nucleophilic center and an electrogenerated electrophilic nitrogen... 

Electrophilic amination is an important reaction in which an electrophilic nitrogen atom (R2N+) carried out by an amination reagent (R R N—L) is transferred to all kinds of nucleophiles (Nu ) (equation 1). The leaving group L is displaced by the nucleophile in the amination reaction. 

This methodology is also an important and potentially valuable method for C—N bond formation using the amination of carbon nucleophiles with electrophilic nitrogen transfer reagents (Scheme 1) Amination of ordinary carbanions and a-carbanion derived from carbonyl compounds and nitriles provides an important method for the synthesis of amines and a-amino carbonyl compounds and nitriles", respectively. For this purpose, a number of electrophilic amination reagents, which are synthetic equivalents of the R2N+ synthon, have been developed and the synthetic potential of electrophilic amination of carbon nucleophiles has been studied in detail . ... 

Amines are generally prepared by nucleophilic amination, which is a coupling of carbon electrophiles with a nucleophilic amination reagent, NR2, and Ni and Pd catalyzed reaction of aryl halides with arylamines (Hartwig-Buchwald amination) . Thus, the direct C—N bond formation between carbon nucleophiles and electrophilic nitrogen functionality R2N+ constitutes an example of the umpolung methodology. 

The conversion of alkenes to amines has a considerable synthetic value and hydrob-oration-amination methodology has been applied using different protocols. However, only two of the three organyl groups can be aminated because of the low reactivity of RB(NHR)2 towards electrophilic nitrogen (equation 2). 

Radhakrishna and coworkers also found a direct substitution on the electrophilic nitrogen of enolates in their reaction with DPH ". ... 

Recently, a direct kinetic study on the amination of substituted phenyhnagnesium bromides using Af,Af-dimethyl O-mesitylenesulfonyl hydroxylamine 3b as amination reagent has been reported by Erdik and Ate Ulkii . Rate data, the Hammett relationship and activation entropy support an Sn2 displacement of the carbon nucleophile on the electrophilic nitrogen. These results are consistent with the competition kinetics for electrophilic amination of substituted phenyl Grignard reagents with O-methylhydroxylamine In. ... 

There have been numerous specific reactions attributed to nitrenium ions over the years. Space constraints prohibit an exhaustive catalogue, so that the reactions described below should be understood to be typical examples that highlight important trends, rather than a comprehensive listing. In particular, we emphasize reactions where the involvement of the nitrenium ion has been well established or at least widely acknowledged. As noted above, there are numerous reactions of electrophilic nitrogen species in which the involvement of a nitrenium ion is possible but where the data are insufficient to permit any firm conclusion. Interested readers are encouraged to consult the Additional Reading section for further examples. 

Arylazo tosylates of type 248, which are readily obtained from aniline derivatives 249 in a two-step procedure (equation 162), can be alternatively used as starting materials. This electrophilic nitrogen equivalent 248 reacts with a broad range of functionalized Grignard reagents under mild conditions. Subsequent allylation of the addition products with allyl iodide, followed by reductive cleavage of the resulting hydrazine derivatives... 

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