Electrophilic reactions super-electrophiles

Ees in these reactions increased with the electrophilic super-delocalizability [Sj j at the carbonyl oxygen, a measure of susceptibility to nudeophUic attack, consistent with the idea that Lewis add coordination of the aldehyde is important for enantiocontrol [24]. 

Arbuzova, S.N., Gusarova, N.K., Malysheva, S.F., Brandsma, L., Albanov, A.I., and Trofimov, B.A., Reaction of red phosphorus with electrophiles in super-basic systems. Part 8. Reaction of red phosphorus and phosphine with aryl alkenes, Zh. Obshch. Khim., 66, 56, 1996. 

Such reactions can take place under severe conditions. For example, electrophilic addition could be accomplished wiihF,C=CHF in super-acid solutions Olah Mo J. Org. Chem. 1972,. 7, 1028) although F,C=CF, did not react under these conditions. For reviews of electrophilic additions to fluoroolcfins. sec Bclcn kii German Sov. Sci. Rev. Seel B 1984, 5. 183-218 Dyatkin Mochalina Knunyants Russ. Chem. Rev. 1966, 35. 417-427. Fluorine Chem. Rev. 1969,3. 45-71. Ref. 62. pp. 77-81. 

Some interesting reactions of the super-electrophile 4,6-dinitrobenzofuroxan (151) with aryloxide ions have been reported 130 (151) with phenoxide ion gives the O-bonded ff-adduct (152) which has been fully characterized for the first time. On... 

There have been several studies utilizing the ability of 4,6-dinitrobenzofuroxan (DNBF) to act as a super-electrophile. It has been shown that the initial product of its reaction with phenoxide ions is the O-bonded adduct (29), although this rearranges to give die C-bonded adduct.117 The reaction of DNBF with ethyl vinyl ether yields a dihydrooxazine A -oxidc cycloadduct as a mixture of two diastereoisomers, and in the presence of excess ether a di-adduct (30) is formed.118 Rate constants have been reported for the reaction of DNBF with 3-methoxythiophene in DMSO-water mixtures. The reaction results in a er-adduct which is the product of Se-At substitution in the thiophene, and the results were used to probe the carbon basicity of the thiophene derivative.119... 

Reactions of PhO with the super-electrophilic substrate (163) have been examined by 400 MHz 1 H NMR spectroscopy in MeCN-DME (1 1) as a function of temperature (—40 to 23 °C) and in DMSO at room temperature (Scheme 34). The <9-bonded c-adduct (164), resulting from the attack at C(7) of (163), has been observed and characterized for the first tune no C(5) adduct was detected at —40 °C or in subsequent monitoring the reaction. Apparently, the C(7) attack is favoured by both kinetics and thermodynamics. Upon warming the reaction mixture to ambient temperature, (164)... 

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. 

Carboxonium ions are indicated to be involved in a number of super-electrophilic reactions. In several cases, the direct observation of the superelectrophiles and reactive dications has been possible using low... 

Tetramethyl-2,4-pentanediol forms the oxonium dication 230 in superacid, and dehydration is followed by carbon- carbon bond cleavage. Although such cleavage reactions can occur with monocationic onium ions, in this case the cleavage reaction is likely an indication of the super-electrophilic nature of the dicationic intermediate(s). 

For the chemist practicing polysubstituted aromatic and heteroaromatic synthesis, methods steeped in classical electrophilic (1, Scheme 1) [1] and nucleophilic substitution [2] and SRN1 (2) [3] reactions have been joined and, not infrequently super-ceded, by vicarious substitution (3) [4] and by DoM (4) [5] processes. The Murai ortho CH activation (5) [6] is a recently evolving and potential competitive method to the DoM tactic. The 60 years since its discovery by Wittig and Gilman, and 40 years since its systematic study by the school of Hauser, the DoM reaction has advanced by the contributions of Christensen, Beak, Meyers, and many other... 

At first sight formaldehyde (methanal, CH2=0) seems the ideal electrophilic partner in a mixed aldol reaction. It cannot enolize, (Usually we are concerned with oc hydrogen atoms in an aldehyde. Formaldehyde does not even have a carbon atoms.) And it is a super aldehyde. Aldehydes are more electrophilic than ketones because a hydrogen atom replaces one of the alkyl groups. Formaldehyde has two hydrogen atoms. 

The industrially important direct methane conversion processes comprise oxidative coupling, reductive coupling including pyrolysis reactions, partial oxidation, halogenation and oxyhalogenation,26 and ammoxidation. Other direct conversions include alkylation, electrophilic substitution, and C-H bond activation over various complex and super acid catalysts. Several of these direct conversion technologies remain to be exploited to achieve their full commercial potentials. 

S Ar reactions have been studied mostly with dinitro and trinitro activated benzenes. Recently, the aniline reactions with the highly activated super-electrophile, 4,6-dinitrobenzofuroxan (DNBF), have attracted considerable attention due to its ambident reactivity114. In acidic solvent, where aniline is almost completely protonated, the reaction by nitrogen attack is inhibited. However, a carbon-carbon bonded adduct is slowly formed by reaction at the 4-position of the aniline. Kinetic studies in H2O-DMSO have shown that this adduct formation involves two steps a carbon-carbon bond formation ( a), followed by elimination of a proton, Kiep (vide infra). The reactions of anilines with DNBF in DMSO have shown that the N-bonded adduct (a-N) is kinetically preferred, but the C-bonded adduct (a-C), formed in equilibrium with its deprotonated form, is the thermodynamically favored product (Scheme 14). 

Salts with carbenium ions and SbFg as counteranion have already been described, such as magic methyl CHj SbFg. However, these super-electrophilic species can be involved in electrophilic additions to double bonds and carbenium cations, and are therefore not suitable for fluorination reactions. 

Nitro- and Cyano-stabilized Anions.—Further publications have appeared which describe the reactions of the doubly deprotonated nitroalkanes (35) with electrophiles. If R = ArCH2 in (35), then the dianion (36) is obtained which functions as a super enamine and reacts to give /3-functionalized nitroalkanes. " ... 

Generally, one may state that the PES of the reaction of electrophilic substitution in the region of a transition state is much simplified as compared with the nucleophilic substitution. Therefore, the effects of solvation and small amounts of catalysts, particularly those coordinating the metal centers in XXIV, may considerably exceed the magnitude of the above-examined structural effects. One may appropriately point to the calculations on the hydrated methonium ion performed by the CNDO/2 method with a special parametrization in super-molecular approximation, and with the surrounding of 5 and 10 water molecules taken into account. They led to the conclusion that the pyramidal C4V structure, rather than the structures or Dj, is in solution energetically the most favored [83]. The structure of the first hydrated shell is shown by the formula XXVI ... 

A theoretical study of the hydrolysis of arenediazonium ions, combining Marcus theory with density functional theory (DPT) calculations, indicates the possibility of reaction by an 5 2 pathway, with the transition state (1), rather than an 5 1 pathway There has been a survey of the use of arenediazonium ions in synthetic reactions including their use as aryl radical precursors, aryl cation precursors, and super-electrophiles in transition-metal-catalysed reactions ... 

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