Dimsyl ion

The dimsyl ion also adds to carbon—carbon double bonds, and if the mixture is heated for several hours, methanesulfenate is eliminated. The overall result is methylation, and for compounds such as quinoline or isoquinoline (eq. 20), yields ate neady quantitative (50). The reaction sequence for isoquinoline to 1-methyhsoquinoline is as follows ... 

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... 

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. 

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. 

The lyate ion of DMSO (Cl l SOCI l2 ) is called dimsyl ion. Its alkali metal salts have been used as titrant in DMSO [25 a]. 

Perturbation Molecular Orbital (PMO) theory has been used to account for the regioselectivity of the reaction of naphthyridines (l)-(6) with amide and dimsyl anions. The reaction with the amide ion (a hard nucleophile) is under charge control, whereas the reaction with the dimsyl ion (a soft nucleophile) is determined by the distribution of the LUMO <91PJC1449>. 

Methyl sulfinyl carbanion (CH3SOCH2 ) has been given the trivial name dimsyl ion and is involved in the majority of the base-catalyzed reactions in DMSO, in spite of the fact that the equilibrium lies far to the left (K = 1.5x10 ). The equilibrium of reaction (10.17) is established quickly [4] and even though the dimsyl ion is present in very low concentrations, it is orders of magnitude more reactive than the r-butoxide ion [4]. 

Beside the metal oxide, dimsyl ions formed by reaction of metal alkoxide with DMSO [Eq. (10.17)] take part in the initiation of polymerization. With potassium as gegenion both alkoxide and dimsyl ion pairs are completely dissociated in DMSO at salt concentrations less than 0.1 M [5. The initial rate of polymerization may be given by the expression [cf. Eq. (10.15)] ... 

Treatment of trequinsin (19) with dimsyl ion gave the ring-opened product 114 when a short reaction period (5 min) was applied, but a longer reaction period led to a mixture of 115 and 114 (reaction period 15 min), or a mixture of 116 and 115 (reaction period 45 min) (90JOC5117). Similar... 

Hg(OAc)2-EDTA afforded ring-opened products. Treatment of trequinsin (34), and other 6,7-dihydro derivatives of the 5,6-benzologue of (10) with dimsyl ion gave various ring-opened products <90JOC5117,91CB111>. 

Similarly, with phenoxide ions, oxygen attack is kineticaUy favored, while attack by the para- or ortho-ring carbons gives thermodynamically more stable adducts [130]. It is worth noting that earlier work was hampered by the competition with phenoxide of attack by hydroxide ions formed from small amounts of water in the solvent. Ambident attack by pyrrolide anions may involve reaction at nitrogen or carbon centers [132]. DMSO usually acts as an inert solvent for these measurements, but attack by its anion, the dimsyl ion, may involve successive reaction at oxygen, sulfur, and carbon centers [133]. 

The use of DMSO also led us to a study of the decomposition of dimsyl ion at elevated temperatures. The identification of methyl mercaptide, methylsulfenate and methylsulfInate ions and a number of methylated butadienes was accounted for by the scheme on the next page. 

Several papers report studies on the anionic polymerization of EO in DMSO. The use of potassium tert-butoxide (t-BuOK) as initiator was reported to yield living poly(EO)s with molar masses controlled by the ratio [monomer]/[initiator] although dimsyl ion resulting from transfer to the solvent... 

Scheme 6 Formation of dimsyl ion through transfer to DMSO.

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