Electrophiles chemistry

Because the protonation of ozone removes its dipolar nature, the electrophilic chemistry of HOs, a very efficient oxygenating electrophile, has no relevance to conventional ozone chemistry. The superacid-catalyzed reaction of isobutane with ozone giving acetone and methyl alcohol, the aliphatic equivalent of the industrially significant Hock-reaction of cumene, is illustrative. 

Taken as a whole, the collection should serve as a reasonable representation of how the field is progressing and evolving and should serve as a model for gauging the current trends. It is hoped that the book can inspire the younger researchers who are still trying to find their niche and can be a useful source for students who are in the process of deciding whether or not to enter into this area. There is no doubt in my mind that much remains to be learned and that electrophilic chemistry and electron-deficient reactive intermediates will continue to play a pivotal role in structural/mechanistic and synthetic chemistry, both in the traditional sense and as applied to interdisciplinary areas. 

Although this work probably does not cover all the details of the developments in electrophilic chemistry of fluoroolefins, it has nevertheless attempted to provide a strategic overview in this area, hoping that chemists working on related subjects should be able to find answers to basic questions associated with reaction conditions, types of electrophiles, reactivity of olefins and orientation of addition. We also wish to acknowledge the tremendous work accomplished in the last 30 years in the area of electrophilic reactions of fluoroolefins that has made this review possible. 

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. 

The diprotonated benzoquinone monooximes have also been studied. Using low temperature NMR, dications such as 203 can be directly observed (eq 70)64. Little work has been done to study the electrophilic chemistry of these ionic species, although Shudo and Okamato generated dication 204 in superacid and found it capable of reacting with phenol (eq 71).65... 

Finally, some miscellaneous fused systems containing thiophene rings have attracted some interest. The electrophilic chemistry of several thia-PHAs has been investigated, among others benzo[Z>]naphtho[2,l-c/]thiophene , whereas an approach to related partially saturated systems from tetrahydrothiophene-3-one has been published <07TL4715>. It should also be mentioned that a 4-armno-7-ar ithieno 3,2-<7 pyrimidine library has been prepared <07JCC431>. 

Among catalytic alkane conversions, the most important is the Shilov system and its descendents [108]. Discovered around 1970, these involve Pt(II) salts in aqueous solvents. Initially, the reaction studied was H/D exchange with D2O, where polydeuteration of alkanes was seen. The selectivity for attack at the terminal methyl groups of long chain alkanes made it clear that one was not dealing with classical electrophilic chemistry. The intervention of colloidal Pt was also excluded. 

It seems that the intervening years have justified that prediction to a significant degree. The electrophilic chemistry of alkanes has rapidly expanded and has started to occupy a significant role even in the conversion of methane. 

Bearing in mind the value of Hg(II) in the electrophilic chemistry of alkenes, alkynes etc. (see below), any new manipulations of the C-Hg bond attract interest. Although a number of transformations of this bond are available the direct conversion of RCH2 CH2HgX into RCH=CH2 is at present a low-yielding process. A solution to this problem has been proposed and relies on the... 

This may be contrasted with the D SO -promoted hydrogen-deuterium exchange at an arene (Eq. 1.1). In this case, the electrophilic chemistry occurs at the polarized deuterium-oxygen bond, where the deuterium atom carries a significant positive charge. Although the various S Ar synthetic reactions do share a common basic mechanism (Scheme 1.2), they often differ considerably in the means or mechanisms by which the electrophiles are generated. Several of the common mechanistic types are described below. 

The issue of transmetalation reactions, or metathesis or redistribution reactions (all terms have been used to describe this) is an important one in the chemistry of organostannanes The typical electrophilic chemistry of allylstannanes involves reaction with an electrophile in an Se2 process. Since all of the Lewis acids we are using to mediate this process are electrophilic, one can easily envision the sequences outlined in Fig.2. Thus a... 

Another example of electrophilic chemistry is provided by the myrcene complex 10.48 (Scheme 10.15). The iron tricarbonyl complex 10.48 undergoes cyclization via a carbocation 10.49 on acid treatment. The 16e rr-allyl complex 10.50 produced may then lose a proton (in a way similar to benzene in electrophilic cyclization) to give a V-diene complex 10.51 or gain an additional ligand, CO if supplied, to give a stable ISe-ir-allyl complex 10.52. 

A series of bimolecular coupling reactions was developed, utilizing the electrophilic chemistry of aromatic cations (Scheme 48). For example, 27/-chromene (236) reacts... 

Condensation of nitrile (63) with 2-butanone gave pyridone (64). However, attempts to introduce an amino substituent into the 3-position of (64) by various electrophilic reactions gave only phenyl ring-substitution products (55, 58). This work clearly indicated the inherent difficulties associated with functionalization of pyridine C-ring precursor by electrophilic chemistry in the presence of a highly oxygenated D-ring. 

---