Subject sulfonyl stabilization

Ionic liquids are a class of solvents and they are the subject of keen research interest in chemistry (Freemantle, 1998). Hydrophobic ionic liquids with low melting points (from -30°C to ambient temperature) have been synthesized and investigated, based on 1,3-dialkyl imidazolium cations and hydrophobic anions. Other imidazolium molten salts with hydrophilic anions and thus water-soluble are also of interest. NMR and elemental analysis have characterized the molten salts. Their density, melting point, viscosity, conductivity, refractive index, electrochemical window, thermal stability, and miscibility with water and organic solvents were determined. The influence of the alkyl substituents in 1,2, 3, and 4(5)-positions on the imidazolium cation on these properties has been scrutinized. Viscosities as low as 35 cP (for l-ethyl-3-methylimi-dazolium bis((trifluoromethyl)sulfonyl)amide (bis(triflyl)amide) and trifluoroacetate) and conductivities as high as 9.6 mS/cm were obtained. Photophysical probe studies were carried out to establish more precisely the solvent properties of l-ethyl-3-methyl-imidazolium bis((trifluoromethyl)sulfonyl)amide. The hydrophobic molten salts are promising solvents for electrochemical, photovoltaic, and synthetic applications (Bon-hote et al., 1996). 

The alkylation of sulfur-stabilized anions has been the subject of an excellent recent review633. Anions adjacent to a wide range of sulfur functionalities may be alkylated readily, the most common being sulfoxide and sulfone a-anions. In the synthesis of retinoic acid derivatives and vitamin A634-636, a-sulfonyl anions have been alkylated with an co-acetoxy-containing allyl halide in good yield (equation 96). 

When chloromethyl phenyl sulfone (130 Ar = phenyl) was subjected to the Darzens-type reaction with an aldehyde, a thermodynamically stable trans isomer (133) was produced exclusively (equation 32). This is in sharp contrast with the corresponding reaction of chloromethyl phenyl sulfoxide. Tavares proposed that the initial nucleophilic attack of the a-sulfonyl carbanion upon a carbonyl compound is rapidly reversible due to its stability, and that the product-determining step is the ring closure. Thermodynamic equilibrium between the two diastereomers of (132) allows predominant formation of the thermodynamically stable isomer (133) from the preferred transition state. ... 

Villalgordo et al. [22, 23] as well as Gayo and Suto [25] developed a strategy to cleave pyrimidines from the solid support. After oxidation of the thioether-linkage 17, aromatic substitution of the sulfonyl unit was performed with different N-nucleophiles as amines and azides to give free amino- or azido-pyrimidines 19 (Scheme 16.5). To demonstrate the stability of the linker, the resin-bound derivatives were subjected to different reactions such as saponification, ester reduction, acid chloride formation or Mitsunobu alkylation. A similar approach was presented later on by Hwang and Gong in the SPOS of 2-aminobenzoxazoles [26]. 

It is tempting to think that allylic cations would behave similarly to other stabilized cations in their reactions with alkyl azides. " In practice what happens is invariably an initial formal [3+3] cycloaddition of azide to the allylic cation, which is followed by a migration event (typically of hydride) or trapping by a nucleophile. Pearson and coworkers found that when sulfonylindole 27 was treated with SnCk at -78 °C, followed by basic workup, triazoline adducts 28 were obtained as mixture of chloride epimers (Scheme 7.24). When A -alkyl indoles (e.g. 29) were subjected to Lewis acidic conditions, tri-azines such as 30 were obtained as the sole products. In the former case involving an iV-sulfonyl indole, a [3+2] cycloaddition pathway explains the product, whereas the iV-alkyl indoles examined underwent [3+3] cycloaddition. 

To resolve the problems associated with safety, thermal and electrochemical stability and conductivity, new syntheses of new electrolytes are the subject of new and important studies. Not withstanding the importance of the methide salt for which commercial availabhity is expected shortly, a number of important new developments are worth highhghting. Lithium bis(perfluoro-ethyl-sulfonyl)imide, liNCSOzCzFjjz or IJBETI, is very similar to that for the imide salt as it is stable up to 330°C [26]. hi addition to its high thermal stabhity, the LiBElT salt was also shown to be unreactive towards water [27]. The studies by Barthel et al. on chelatoborates [32] such as bis[2,3-pyridinediolato(2-)-0,0"]borate are of special interest as are studies on new methide salts such as Li[C2(S02CF3)4(S204C3F6)] [32]. 

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