Superoxide nucleophilic reactions

Contents Introduction and Principles. - The Reaction of Dichlorocarbene With Olefins. - Reactions of Dichlorocarbene With Non-Olefinic Substrates. -Dibromocarbene and Other Carbenes. - Synthesis of Ethers. - Synthesis of Esters. - Reactions of Cyanide Ion. - Reactions of Superoxide Ions. - Reactions of Other Nucleophiles. - Alkylation Reactions. - Oxidation Reactions. - Reduction Techniques. - Preparation and Reactions of Sulfur Containing Substrates. -Ylids. - Altered Reactivity. - Addendum Recent Developments in Phase Transfer Catalysis. 

Both the basic and nucleophilic reactions within the cage are totally inhibited by the presence of one equivalent of Na + PFg in THF. Double ion exchange between the two ion pairs is favored which removes superoxide from the cage Eq. (10) ... 

Hence, nucleophilic reactions of the superoxide ion are typical. This ion can be compared with the thiophenoxide and thiocyanate ions with respect to nucleophilicity. The cause of such high nucleophilicity lies in a so-called a-effect In 0—0 ion, an attacking site (O ) adjoins directly to a site (O ) with a significant electronegativity. This effect usually confers special activity to nucleophiles. The effect can be additionally enhanced by including the 0—0 group in sulfenate. 

Similarly, when both the Cp and arene ligands are permethylated, the reaction of 02 with the Fe1 complex leads to C-H activation of the more acidic benzyl bond [57]. When no benzylic hydrogen is present, superoxide reacts as a nucleophile and adds onto the benzene ligand of the FeCp(arene)+ cation to give a peroxocyclohexadienyl radical which couples with a Fe Cp(arene) radical. A symmetrical bridging peroxo complex [(Fe"Cp)2(r 5-C6H60)2] is obtained. The C-H activation reactions of the 19e Fe1 radicals BH can be summarized as follows... 

Two alternatives to conventional acid/base hydrolyses for cleaving esters are Sn2 displacement of the carboxylate group by reactive nucleophiles and nucleophilic attack at the carbonyl carbon. In this latter context we investigated the reaction of S-b-MM with potassium trimethylsilanolate, a so-called potassium superoxide equivalent (15). One advantage that this reagent has over potassium... 

Displacement by cyanide works particularly well, and many other nucleophilic substitution reactions are enhanced by PTC. Most monovalent anions can be transferred, including alkoxides, phenoxides, thiocyanates, nitrates, nitrites, superoxides and all of the halides. Divalent anions are usually too hydrophilic to be transferred into the organic phase. 

It has been shown that when nucleophilic aromatic photo-substitution reactions are carried out in non-deoxygenated solutions of aprotic solvents, such as DMSO and acetonitrile, destructive superoxide anions may be formed from aromatic radical anions. Such solvents are best avoided. There has been a review of mechanistic aspects of photo-substitutions of the cyano group in aromatic compounds. ... 

As noted earlier, the superoxide ion reacts with effective electron acceptors. It is a one-electron reductant of moderate strength. However, the superoxide ion can act as a nucleophile if a substrate has a decreased electron affinity. For instance, alkyl halides react with the ion O2 RCH2OO -h HaE. This reaction initiates the next ones RCH2OO ... 

The reaction of alkyl isothiocyanates, RNCS, with diphenylphosphinic hydrazide (338) in benzene has been reported.308 The bis(diethylamino)[(methylthio)thiocarbon-yl]carbenium salts (339 X = I or BF4) display ambident reactivity and can react either at carbenium carbon (hard nucleophiles) or at the thiocarbonyl sulfur atom (soft nucleophiles).309 Electrochemically generated superoxide reacts with dithioic S,S -diesters (dicarbothiolates) (340 Ar = C5H3N or C6H4) to give the monocarboxylate anions in 100% yield before giving the dicarboxylate anions.310... 

As seen from the scheme, the initial step of the reaction between the superoxide ion and alkylhalides is a bimolecular nucleophilic substitution. Reactions of K02 with optically active alkylhalides proceed with the configurational inversion. Moreover, the reactivity changes in the same order as that of the usual SN2 reactions (primary > secondary tertiary I > Br > Cl) (Sawyer Gibian 1979). Nevertheless, the SN2 scheme does not exclude a possibility of one-electron transfer according to Scheme 1-77 ... 

More recent examples of nucleophilic aromatic substitution reactions include the reactions of C6F6 with the superoxide ion, 02 to give F and, presumably, C6F502 278 and with the acetic acid enolate anion, as shown in Scheme 42, which also indicates how the anionic reagent was formed279. It should be noted that reaction of gas-phase F" with a suitably silylated precursor is one of the best and most specific reactions to prepare gas-phase anions280. 

The synthesis, structure, and superoxide dismutase mimetic activity in vitro and the protection against reactive oxygen species in vivo of mononuclear copper complexes with 2-(4-methylphenylsulfamoyl)-6-nitrobenzothiazole have been reported [602], Like 1,2,3-benzoxadiazoles, nitroderivatives of 1,2,3-benzothiadiazoles were obtained on diazotization of the corresponding or/Zzo-aminothiophcnolcs [213, 218, 583], The initial or/Zzo-thiophcnols for this reaction were synthesized by nucleophilic substitution of halogen in ort/zo-halogenoanilines. It turned out that 4-nitro- and... 

The superoxide ion, O , produced by the electron-transfer reduction of dioxygen (O2 + e O ), is a strong Bronsted base and an effective nucleophile. Because of rapid hydrolysis and disproportionation, the lifetime of O in aqueous solution is limited. This has led to investigations of its reaction chemistry in dipolar non-HBD solvents [632]. Under these conditions, the superoxide ion attacks haloalkanes by Sn2 displacement of the halides to eventually give dialkyl peroxides in a multi-step reaction [632]. 

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