Nitrene cation

A few groups of investigators, however, proposed another mechanism, in which the radical cation undergoes a de-protonation reaction first, followed by another electron transfer, to form a nitrene cation [49-52] according to the classical ECE (electrochemical-chemical-electrochemical) route, i.e.. 

The aniline nitrene cation (couples with a neutral aniline molecule to produce head-to-tail. 

Park et al. [51] concluded from their spectroelec-trochemical experiments that the nitrene cation must be the intermediate species. They showed from derivative cyclic voltabsorptometry (DCVA) experiments that the 420 ran band, which happens to be located at the same wavelength as that of oxidized benzidine, does not actually originate from the oxidized benzidine. The... 

As pointed out, the dihydrazozene would undergo a rapid benzidine rearrangement reaction to benzidine. When the nucleophile is water, which is also a good nucleophile, the product would be p-aminophenol (PAP), which is produced from the hydrolysis reaction of the nitrene cation according to the reaction. 

Interestingly, no SO 2 was evolved in this reaction as in the photolysis of a-toluenesulphonyl azide. This could be explained on the basis of a cation-radical anion pair which collapses as in Eq, (8) to give a sulphon-amido radical, and no free nitrene is formed 21>. 

Furthermore, the first direct amination of benzene has been achieved and has generated the aniline derivative in an acceptable yield (Equation (103)). Recently, a cationic copper(i) complex 132-catalyzed nitrene transformation to the C-H bonds of the electron-rich arene was reported by Sadighi and co-workers (Equation (104)).285... 

Anodic oxidation of benzenesulphenanilides 56 leads to cleavage of the nitrogen-sulphur bond in the radical-cation with the formation of a nitrenium ion, which deprotonates to the nitrene. The intermediate dimerises to a phenazine [168]. 

These results indicate that vacuum curing occurs through a radical reaction mechanism and is terminated by reaction of the ring-opened epoxy group with the azide group (not nitrene) under exposure. There is a possibility that polymerization initiated by an exposure-induced radical cation may occur. Furthermore, it is thought that reaction products from both the azide and epoxide serve as dissolution inhibitors, because the sensitivity of EAP is almost the same as that of EP, as shown in Figures 1 and 2. 

Oxidation of 1-aminobenzimidazoles with manganese dioxide or lead tetraacetate can give either 1,1 -azobenzimidazoles (735) or 3-substituted benzo-l,2,4-triazines (736). Electrochemical measurements have shown that the first step in this reaction is removal of an electron from a ir-orbital of benzimidazole rather than from the A-amino group. Because the cation radical which is formed must be stabilized by loss of a proton, for (736) to form the 2-substituent must contain an NH or OH group. This is unnecessary for the formation of the azo product (735) which may form via a nitrene intermediate. 

In 1991, Evans et al. reported that cationic Cu(I) ions catalyzed the nitrene-transfer reaction smoothly (Scheme 6B.29) [74]. Since then, many studies on asymmetric aziridination have been carried out with chiral copper(I) complexes as catalysts. 

A number of other groups have investigated the clustering reactions of small cation silicon species with silanes and other small molecules. The ion-molecule reactions occurring between SiHv+ (x = 0-3) cations and neutral ammonia, as well as the reactions between NHt+ cations and SiH4 were studied by FIMS113,114. The main channel for the reaction between SiHv+ ions and NH3 was found to correspond to the elimination-addition reaction, well-known for silanes (equation 20), which formally corresponds to the transfer of a nitrene-unit (NH)113. 

The nitrene transfer from PhI=NTos to alkenes catalyzed by the CpFe(CO)2+ fragment gave better results (85% for styrene) [25], but the characteristics of the chemistry of the cationic intermediates as postulated by the reaction mechanism are closely connected to the alternative formation of aziridines by a carbene transfer... 

Aziridines. The synthesis of aziridines has been covered in several major reviews <2003CRV2905, 2004T2701, B-2006MI1 >. The intermolecular cycloaddition of an electron-deficient species such as a nitrene, a nitrenium cation, or a carbene (or their formal equivalents) to the -bond of an alkene, alkyne, imine, or nitrile is a significant approach to aziridines and azirines (Scheme 5). These reactions are often named aziridinations. 

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