Methylsulfinyl carbanion, with

On treatment with a strong base such as sodium hydride or sodium amide, dimethyl sulfoxide yields a proton to form the methylsulfinyl carbanion (dimsyl ion), a strongly basic reagent. Reaction of dimsyl ion with triphenylalkylphosphonium halides provides a convenient route to ylides (see Chapter 11, Section III), and with triphenylmethane the reagent affords a high concentration of triphenylmethyl carbanion. Of immediate interest, however, is the nucleophilic reaction of dimsyl ion with aldehydes, ketones, and particularly esters (//). The reaction of dimsyl ion with nonenolizable ketones and... 

A 1.5 to 2 M solution of methylsulfinyl carbanion in dimethyl sulfoxide is prepared under nitrogen as above from sodium hydride and dry dimethyl sulfoxide. An equal volume of dry tetrahydrofuran is added and the solution is cooled in an ice bath during the addition, with stirring, of the ester (0.5 equivalent for each 1 equivalent of carbanion neat if liquid, or dissolved in dry tetrahydrofuran if solid) over a period of several minutes. The ice bath is removed and stirring is continued for 30 minutes. The reaction mixture is then poured into three times its volume of water, acidified with aqueous hydrochloric acid to a pH of 3-4 (pH paper), and thoroughly extracted with chloroform. The combined extracts are washed three times with water, dried over anhydrous sodium sulfate, and evaporated to yield the jS-ketosulfoxide as a white or pale yellow crystalline solid. The crude product is triturated with cold ether or isopropyl ether and filtered to give the product in a good state of purity. 

Treatment of dimethylsulfoxide (DMSO) with sodium hydride generates methylsulfinyl carbanion (dimsyl ion), which acts as an efficient base in the production of ylides. The Wittig reaction appears to proceed more readily in the DMSO solvent, and yields are generally improved over the reaction with -butyl lithium (i). Examples of this modification are given. 

The most convenient method for the preparation of sodium acetylide appears to be by reaction of acetylene with sodium methylsulfinyl carbanion (dimsylsodium). The anion is readily generated by treatment of DMSO with sodium hydride, and the direct introduction of acetylene leads to the reagent. As above, the acetylide may then be employed in the ethynylation reaction. 

Methylsulfinyl carbanion (dimsyl ion) is prepared from 0.10 mole of sodium hydride in 50 ml of dimethyl sulfoxide under a nitrogen atmosphere as described in Chapter 10, Section III. The solution is diluted by the addition of 50 ml of dry THF and a small amount (1-10 mg) of triphenylmethane is added to act as an indicator. (The red color produced by triphenylmethyl carbanion is discharged when the dimsylsodium is consumed.) Acetylene (purified as described in Chapter 14, Section I) is introduced into the system with stirring through a gas inlet tube until the formation of sodium acetylide is complete, as indicated by disappearance of the red color. The gas inlet tube is replaced by a dropping funnel and a solution of 0.10 mole of the substrate in 20 ml of dry THF is added with stirring at room temperature over a period of about 1 hour. In the case of ethynylation of carbonyl compounds (given below), the solution is then cautiously treated with 6 g (0.11 mole) of ammonium chloride. The reaction mixture is then diluted with 500 ml of water, and the aqueous solution is extracted three times with 150-ml portions of ether. The ether solution is dried (sodium sulfate), the ether is removed (rotary evaporator), and the residue is fractionally distilled under reduced pressure to yield the ethynyl alcohol. 

Other carbanionic groups, such as acetylide ions, and ions derived from a-methylpyridines have also been used as nucleophiles. A particularly useful nucleophile is the methylsulfinyl carbanion (CH3SOCHJ), the conjugate base of DMSO, since the P-keto sulfoxide produced can easily be reduced to a methyl ketone (p. 549). The methylsulfonyl carbanion (CH3SO2CH2 ), the conjugate base of dimethyl sulfone, behaves similarly, and the product can be similarly reduced. Certain carboxylic esters, acyl halides, and DMF acylate 1,3-dithianes (see 10-10. )2008 Qxj(jatjye hydrolysis with NBS or NCS, a-keto aldehydes or a-... 

Aromatic nitro compounds can be methylated with dimethyloxosulfonium methylide203 or the methylsulfinyl carbanion (obtained by treatment of dimethyl sulfoxide with a strong base) 206... 

Diphenylacetylene reacts with methylsulfinyl carbanion to give 2,3-diphenylbutadiene.1113 Neither the scope nor the mechanism of the reaction seems to have been investigated. 

The method was used in studies of a fungal heterogalactan.150 The polysaccharide was subjected to successive tritylation, methylation, detritylation, p-toluenesulfonylation, reaction with sodium iodide, and, finally, reaction with sodium p-toluenesulfinate. The product was then treated with sodium methylsulfinyl carbanion in dimethyl sulfoxide, the product remethylated, and the polysaccharide material recovered by gel chromatography. The polymer was hydrolyzed, and the sugars in the hydrolyzate were analyzed, as the alditol acetates, by g.l.c.-m.s.1 The analysis revealed that —60% of the hexose residues that were unsubstituted at C-6 had been eliminated. As the product was still polymeric, it was concluded that these residues had constituted a part of side chains linked to a main chain of (1 — 6)-linked D-galactose residues. 

Most of the applications of sulfoxides in synthesis make use of the reactions of sulfur-stabilized carbanions with electrophiles [385, 386]. Thus the methylsulfinyl methylene carbanion, conveniently generated through the interaction of sodium hydride with DMSO [387], is a powerful nucleophile. 

Methylsulfinyl Carbanion. Strong bases, eg., sodium hydride or sodium amide, react with DMSO producing solutions of methylsulfinyl carbanion, known as the dimsyl ton, which arc synthetically useful. The solutions also provide a strongly basic reagent for generating other carbanions. 

The great majority of experimental variants discussed for benzylation (see Sect. 2.1) has also been applied for the preparation of allyl ethers. Among them, the alkylation with allyl bromide and sodium hydride in a dipolar aprotic solvent is most frequently used for complete allylation. Reaction with the methylsulfinyl carbanion in DMSO to form an alkoxide, followed by the reaction with allyl bromide provides a convenient high-yield route to 2,3,6-tri-O-allyl-amylose [227], With the limited amount of reagent, 35% of methyl 2-0-allyl-3,6-dideoxy-a-D-xy/o-hexopyranoside was synthesized from the corresponding glycoside [228]. The 2-allyl ether was the major product (43 % yield) of the reaction of methyl 4,6-0-benzylidene-a-D-glucopyranoside with allyl bromide and 1.1 equiv. of sodium hydride in benzene [71]. 

Preliminary examinations of dextran structures were conducted by optical rotation, infrared spectroscopy and periodate-oxidation reactions. More detailed results can be achieved by methylation analysis [19]. The hydroxyl groups are methylated with methyl iodide after activation with sodium methylsulfinyl carbanion (Fig. 2). The methyl dextran is hydrolysed to the corresponding different methylated monosaccharides, which are furthermore reduced and peracetylated. The resulting alditol acetates of methylated sugars are separated by gas chromatography and identified by their retention times. In particular, a combined capillary gas-liquid chromatography/mass... 

Corey and Chaykovsky described the reduction of carboxylic esters to ketones by way of / -keto sulfoxides. The ester is treated in tetrahydrofuran with a solution of methylsulfinyl carbanions in a mixture of dimethyl sulfoxide and tetrahydrofuran at 0°. This yields a j8-keto sulfoxide which is reduced with aluminum amalgam in 90% aqueous tetrahydrofuran.527 The methylsulfinyl carbanions are formed by the action of sodium hydride on dimethyl sulfoxide under nitrogen at 65-70°. 

In order to increase the solubility of the para wholly aromatic polyamide, PPTA, Katayose succeeded in producing the AT-substituted polyamide using a metalation reaction. The polyamide was reacted with a solution of sodium methylsulfinyl carbanion in DMSO this anion being formed from reaction of powdered sodium hydride with excess dry DMSO [67a] (Scheme 12). 

The most important development in methylation technique is due to Hakomori, who used as the base methylsulfinyl carbanion, formed by reaction of methyl sulfoxide with sodium hydride, and thus extended to carbohydrates the reaction developed by Corey and Chaykovsky/ In certain cases, completely methylated polysaccharide may be obtained in high yield by one treatment within an hour. This method was used by Sandford and Conrad in a re-examination of the polysaccharide from Aerobacter aerogenes, and their paper should be consulted for the excellent experimental details contained therein. These authors showed that this polysaccharide has a simple, repeating structure, and previous suggestions that it is complicated and highly branched arose from interpretation based on products of incomplete methylation. 

This reaction has been modified to become the Haworth Methylation, which was extended to treat sugars with sodium methylsulfinyl carbanion and methyl iodide for the purpose of per-O-methylation in one step7 ... 

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