Dimsylsodium

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. 

Kano et al. (161,162) also investigated the Stevens rearrangement of tetrahydroprotoberberine metho salts 302 with dimsylsodium and obtained the spirobenzylisoquinolines 303 in high yield (Scheme 56). Similarly C-homoprotoberberine 304 gave the new spiro compound 305, whereas B-homoprotoberberine 306 afforded only the Hofmann degradation product 307. 

Permethyiation of carbohydrates. One widely used method for this reaction employs dimsylsodium in DMSO and methyl iodide. The. purity of the permethylated products is significantly improved if dimsylpotassium is used as the base.2... 

Dieb-Alder catalyst. The key step in a recent total synthesis of androstanes is a SnCVcatalyzed Diels-Alder reaction of 1 with the (Z)-dienophile 2. The geometry of the diene favors addition ami to the C,0-methyl group, and the catalyst promotes the desired enrfo-orientation. A1C1, and BF3 ctherate are less suitable for additions involving aliphatic bifunctional dienophiles. The initial adduct a can be isolated, but in only 15-20% yield. The synthesis of the androstane 4 is completed by ketalizatioh of 3 followed by a novel cyclization affected with dimsylsodium. ... 

Heating of compound 1 with dimsylsodium in DMSO at 90°C for 21 hours gives a 71% yield of the epimeric ene-diesters 2. 

Long-chain alkanes. Triphcnylphosphonium salts such as 3, prepared as shown from bromo acetals 2, when treated with dimsylsodium form the long-chain bromo acetal 4. The terminal bromine atom can be displaced by lithium trielhylborohydridc. 

OL,fi-Unsaturatedsulfides. The reaction of aromatic aldehydes and DMSO with metallic sodium leads to 2-arylethenyl methyl sulfides with the (E)-ponfiguration. Presumably the actual reagent is dimsylsodium the final product is then formed by reduction of an intermediate sulfoxide by sodium. o... 

Diinethyl sulfoxide-derived reagent (a). Sodium ulethylsulfinyluiethylide (Dimsylsodium),... 

Octamethylnaphthalene. The definitive paper on the preparation of octamethyl-naphthalene (2, 168, ref. 11b) has now been published. The conversion of (3) to (4) with dimsylsodium is essentially quantitative. Isobutyric acid has been identified as a second product. Use of other bases (sodium methoxide in methanol, sodium hydride) was unsuccessful. 

Preparation of ethers. Treatment of secondary and tertiary alcohols with dimsylsodium in DMSO followed by alkylation with a dialkyl sulfate gives ethers in 60-90% yield. The presence of ester and tertiary amino groups and of double bonds docs not interfere with the reaction. However, alkylation of a- or j8-hydroxyketones was not successful by this procedure. 

Tschugaeff reaction (3, 123). Meurling et al. have prepared xanihates in good yield by treating alcohols with an equivalent amount of dimsylsodium in DMSO followed by carbon disulfide and an alkylating agent. The decomposition temperature of the xanthates is lowered when pyrolysis is carried oul in DMSO. 

Treatment of substituted 1,3-dithiolanes 302 with dimsylsodium led to the formation of thiopyranone derivative 304 in 75% yield via the intermediate thioenolate 303 (Scheme 40) <2000SL1804>. 

The Wharton fragmentation was used as a key step in an approach toward the total synthesis of xenicanes by H. Pfander et al. ° Two optically active substituted frans-cyclononenes were synthesized starting from (-)-Hajos-Parrish ketone. First, the bicyclic 1,3-diol was protected regioselectively on the less sterically hindered hydroxyl group with p-toluenesulfonyl chloride in quantitative yield. Next, the monosulfonate ester was exposed to dimsylsodium in DMSO, which is a strong base, to initiate the desired heterolytic fragmentation. 

Dimsylsodium (22) is an important reagent and it can be used for carbon-carbon bond formation (see Chapter 10, p. 187). DMSO may also be used in the Moffatt oxidation (see Chapter 5, p. 66) and by alkylation it can be converted into the corresponding dimethylsulfoxonium ylide which is valuable in organic synthesis (see Chapter 10, p. 187).4... 

Dimethyl sulfoxide (DMSO) (23) can be used in carbon-carbon bond formation it is a weak acid and with strong bases yields dimsylsodium (24) (Scheme 10). 

Dimsylsodium (24) functions as a highly basic sulfur ylide. It can be used to convert phosphonium salts to phosphorus ylides for use in the Wittig reaction. Dimsylsodium also reacts with aldehydes and ketones by nucleophilic addition to form epoxides and with esters by nucleophilic substitution to yield p-ketosulfoxides (25) (Scheme 11). The p-ketosulfoxides (25) contain acidic a-hydrogens which can be readily removed to allow alkylation, and the products (26) suffer reductive desulfuration on treatment with aluminium amalgam to yield ketones (27) (Scheme 11) This procedure can, for instance, be applied to the conversion of ethyl benzoate to propiophenone (28) (Scheme 12). 

In certain cases, dimsylsodium (24) will undergo selective nucleophilic substitution with bromides thus, v/c-dibromides (29) and gem-dibromides (30) are preferentially debrominated to the products (31) and (32) (Scheme 13). 

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