Dimethylsulfoxide general reaction

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. 

Pinocarveol has been prepared by the autoxidation of a-pinene,5 by the oxidation of /S-pinene with lead tetraacetate,6 and by isomerization of a-pinene oxide with diisobutylalumi-num,7 lithium aluminum hydride,8 activated alumina,9 potassium ferf-butoxide in dimethylsulfoxide,10 and lithium diethylamide.11 The present method is preferred for the preparation of pinocarveol, since the others give mixtures of products. It also illustrates a general method for converting 1-methylcy-cloalkene oxides into the corresponding exocyclic methylene alcohols.11 The reaction is easy to perform, and the yields are generally high. 

The enolate ions from acyclic and cyclic aliphatic ketones, and mainly those derived from acetone and pinacolone, are the carbanions most extensively studied so far. In general, the substitution products are obtained in good yield under irradiation in both liquid ammonia and dimethylsulfoxide (DMSO). For example, the anti-inflammatory drug fluorobiprophen 1 can be synthesized by the reaction of... 

The high-boiling polar organic solvents - dimethylsulfoxide, sulfolane, dimethylsulfone, dimethylformamide, dimethylacetamide - are generally used for synthesizing the polyesterketones and polyesteresterketones by means of polycondensation in this case the reaction catalysts are the anhydrous hydroxides, carbonates, fluorides and hydrides of alkali metals. 

In general one has to realize that each deprotection reaction is specifically influenced by the chain length of the polymer-bound peptide and by the acutal N-terminal amino acid residue, because of the differences in solvation of the individual amino acids and of the whole peptide in relation to the properties of the support. For this reason, for example, 5.35 N HCl in dimethylsulfoxide/dichloromethane (1 1) was employed [ 115] to deal with the problem of different solvations. In another example, mercaptoethane sulfonic acid [116] was utilized in diluted solution to deprotect N-terminal Boc-tryptophane without harming the indole moiety. 

Synthesis started with the reaction of commercially available 2-methoxy-4-nitroaniline, 1, with potassium hydroxide in aqueous dimethylsulfoxide to yield a phenol (2). The phenol was alkylated with dibromotetrafluoroethane following the general route described by Rico and Waskselman to give 2 (8). The addition of a catalytic amount of propanethiol is required for this reaction to proceed since it assists in the in-situ generation of tetrafluoroethylene, the electrophile in the reaction. 

Figure 13.9 illustrates the reversible abstraction of a proton of 2,2, 4,4 -tetranitro-phenylmethane by a series of bases in 50% water-50% dimethylsulfoxide, where this acid has a dissociation constant of = 0.90, and that may proceed by general acid-base catalysis [6]. The general expression for the rate constant of this reaction is, according to eq. (13.25),... 

Substitution reactions at secondary hydroxyls are generally performed either for analysis of structure or to serve a protective function during other reactions. Etherification of the nonanomeric hydroxyls was an important structural tool in the analysis of oligosaccharide and polysaccharide structure. Methyl ethers have been employed for structural determination for more than 75 years. Thus, methyl ether formation in a polysaccharide results in substitution only at free hydroxyls. Subsequent analysis of the methylated derivatives reveals positions previously occupied in glycosidic linkage. Reagents used for this purpose have evolved from dimethylsulfate to the commonly employed method of Hakomori using sodium hydride and dimethylsulfoxide. 

General procedure for the Heck reaction/anion-trapping cascade. The palladium catalyst (0.025 equiv), the ligand (0.05 equiv), and NaBr (2 equiv) were added to a solution of triflate (1 equiv) in dimethylsulfoxide (DMSO) (3.6mL/mmol). The mixture was degassed, and the sodium enolate of diethyl (2-((rerr-butyldiphenylsilyl)oxy)ethyl)malonate (0.33 M solution in DMSO, 2 equiv) was added dropwise at room temperature. After the appropriate reaction time, the mixture was cooled, extracted with Et20, and washed with 1-N aqueous HCl and brine. The organic extracts were dried and concentrated. Then, the residue was purified by flash chromatography on silica gel. 

---