Carbanion, reaction with aromatic nitro

Reaction of the carbanion derived from 1,3-dithiane 1,1-dioxide with aromatic nitro compounds results in oxidative nucleophilic substitution of hydrogen rather than SnAt displacement of even halogen (94T4913). 

Solvent for Displacement Reactions. As the most polar of the common aprotic solvents, DMSO is a favored solvent for displacement reactions because of its high dielectric constant and because anions are less solvated in it (87). Rates for these reactions are sometimes a thousand times faster in DMSO than in alcohols. Suitable nucleophiles include acetyUde ion, alkoxide ion, hydroxide ion, azide ion, carbanions, carboxylate ions, cyanide ion, hahde ions, mercaptide ions, phenoxide ions, nitrite ions, and thiocyanate ions (31). Rates of displacement by amides or amines are also greater in DMSO than in alcohol or aqueous solutions. Dimethyl sulfoxide is used as the reaction solvent in the manufacture of high performance, polyaryl ether polymers by reaction of bis(4,4 -chlorophenyl) sulfone with the disodium salts of dihydroxyphenols, eg, bisphenol A or 4,4 -sulfonylbisphenol (88). These and related reactions are made more economical by efficient recycling of DMSO (89). Nucleophilic displacement of activated aromatic nitro groups with aryloxy anion in DMSO is a versatile and useful reaction for the synthesis of aromatic ethers and polyethers (90). 

The latter reagent also methylates certain heterocyclic compounds (e.g., quinoline) and certain fused aromatic compounds (e.g., anthracene, phenanthrene). The reactions with the sulfur carbanions are especially useful, since none of these substrates can be methylated by the Friedel-Crafts procedure (11-12). It has been reported that aromatic nitro compounds can also be alkylated, not only with methyl but with other alkyl and substituted alkyl groups as well, in ortho and para positions, by treatment with an alkyllithium compound (or, with lower yields, a Grignard reagent), followed by an oxidizing agent such as Bra or DDQ (P- 1511). 

There are not many successful examples of arylation of carbanions by nucleophilic aromatic substitution. A major limitation is the fact that aromatic nitro compounds often react with carbanions by electron-transfer processes.111 However, such substitution can be carried out under the conditions of the SRN1 reaction (see Section 11.4). 

Electron-transfer from carbanions to aromatic hydrocarbons like anthracene has been known from the beginning of this century. For example, the oxidation of triphenyl carbanions, Ph3Cr, by benzophenone was described by Schlenk in 1916. Sufficiently powerful acceptors such as aromatic nitro-compounds may acquire electrons from poor donors such as alkoxides or thiolates. Butyllithium is oxidized by sterically hindered olefines, e.g., its reaction with 1,2,3,4-tetra-phenyl butadiene leads to electron transfer instead of addition. 

Miscellaneous reactions of cr-sulphonyl carbanions with electrophiles include processes involving arylsulphonylmethyl methyl ether anions, cr-sulphinyl sulphone anions, perfluorobutylsulphonylmethylmagnesium halides, nucleophilic substitution in aromatic nitro-compounds by cr-halogenosulphonyl... 

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