Kinetic studies superelectrophile

Dinitrobenzofuroxan (DNBF) is known as a superelectrophile due to its high reactivity both as an electrophile and in its pericyclic addition reactions. NMR studies show that reaction with 2-aminothiazole and its 4-methyl derivative yield anionic carbon-bonded adducts such as (11) by reaction at the 5-position, whereas the 4,5-dimethyl derivative reacts via the exocyclic amino group. Kinetic studies of the first two compounds, both in acetonitrile and in 70 30 (v/v) water-DMSO, have been used to assess their carbon nucleophilicities and place them on the Mayr nucleophilicity scale.55 In a related study, the nucleophilic reactivity, in acetonitrile, of a series of indoles with both DNBF and with benzhydryl cations have been compared and used to determine nucleophilicity parameters for the indoles.56... 

The concept of superelectrophilic activation was first proposed 30 years ago.20 Since these early publications from the Olah group, superelectrophilic activation has been recognized in many organic, inorganic, and biochemical reactions.22 Due to the unusual reactivities observed of superelectrophiles, they have been exploited in varied synthetic reactions and in mechanistic studies. Superelectrophiles have also been the subject of numerous theoretical investigations and some have been directly observed by physical methods (spectroscopic, gas-phase methods, etc.). The results of kinetic studies also support the role of superelectrophilic activation. Because of the importance of electrophilic chemistry in general and super-acidic catalysis in particular, there continues to be substantial interest in the chemistry of these reactive species. It is thus timely to review their chemistry. 

These examples illustrate how electrophilic systems can exhibit enhanced reaction rates and yields with increasing strength of the acidic reaction media. Both qualitative and quantitative kinetic studies strongly suggest the involvement of superelectrophilic species in reactions. 

Shudo and Ohwada have developed and used acid systems composed of varying ratios of CF3SO3H and CF3CO2H in order to obtain solutions having acidities between Hq — 7.7 and Hq — 13.7.27 These acid systems have been used in kinetic studies related to superelectrophiles... 

Our book is about the emerging field of Superelectrophiles and Their Reactions. It deals first with the differentiation of usual electrophiles from superelectrophiles, which show substantially increased reactivity. Ways to increase electrophilic strength, the classification into gitionic, vicinal, and distonic superelectrophiles, as well as the differentiation of superelec-trophilic solvation from involvement of de facto dicationic doubly electron deficient intermediates are discussed. Methods of study including substituent and solvent effects as well as the role of electrophilic solvation in chemical reactions as studied by kinetic investigations, spectroscopic and gas-phase studies, and theoretical calculations are subsequently reviewed. Subsequently, studied superelectrophilic systems and their reactions are discussed with specific emphasis on involved gitionic, vicinal, and distonic superelectrophiles. A brief consideration of the significance of superelectrophilic chemistry and its future outlook concludes this book. 

This study reports on the reactions of ambident nucleophiles with electron-deficient nitroaromatic and heteroaromatic substrates anionic complex formation or nucleophilic substitution result. Ambident behavior is observed in the case of phenoxide ion (O versus C attack) and aniline (N versus C attack). O or N attack is generally kinetically preferred, but C attack gives rise to stable thermodynamic control. Normal electrophiles such as 1,3,5-trinitrobenzene or picryl chloride are contrasted with superelectrophiles such as 4,6-dinitrobenzofuroxan or 4,6-dinitro-2-(2,4,6-trinitrophenyl)benzotriazole 1-oxide (PiDNBT), which give rise to exceptionally stable a complexes. Further interesting information was derived from the presence in PiDNBT of two electrophilic centers (C-7 and C-l ) susceptible to attack by the ambident nucleophilic reagent. The superelectrophiles are found to exhibit lesser selectivity toward different nucleophilic centers of ambident nucleophiles compared with normal electrophiles. 

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