Subject trifluoroacetate

Intramolecular Friedel-Crafts reactions can sometimes compete with organosil-icon hydride reductions of benzylic-type alcohols to cause formation of undesired products. An example is the attempted reduction of alcohol 26 to the corresponding hydrocarbon. When 26 is treated with triethylsilane in trifluoroacetic acid at room temperature for 15 hours, a mixture of the two fluorene isomers 27 and 28 is obtained in a combined yield of 45%. None of the hydrocarbon structurally related to the substrate alcohol 26 is obtained.171 Whether this problem could be circumvented by running the reduction at a lower temperature or with a different acid remains subject to experimentation. 

The diastereoselectivity of the reduction of a-substiluted ketones has been the subject of much investigation. The reagent combination of trifluoroacetic acid and dimethylphenylsilane is an effective method for the synthesis of erythro isomers of 2-amino alcohols, 1,2-diols, and 3-hydroxyalkanoic acid derivatives.86,87,276,375 Quite often the selectivity for formation of the erythro isomer over the threo isomer of a given pair is >99 1. Examples where high erythro preference is found in the products are shown below (Eqs. 218-220).276 Similar but complementary results are obtained with R3SiH/TBAF, where the threo isomer product... 

Recoveries of Galacturonic Acid Subjected to Treatment with 2 M Trifluoroacetic Acid"... 

Alkyl halides, alkyl sulfonates and other alkylating agents have also been subject to scmtiny in spheres other than pharmaceuticals, such as in environmental analysis. Various approaches have included two-step SPE, derivatisation with trifluoroacetic anhydride followed by GC/MS (for cyclophosphamide and its analogues in sewage water) SPE on surface water to isolate the antineoplastic agents carmustine, chlorambucil, cyclophosphamide and melphalan for LC-UV and LC-fluorescence measurements and derivatisation of alkyl halides and epoxides with 4-nitrothiophenol followed by HPLC-UV detection (claimed to be better than NBP derivatisation). A patent exists for a field test kit for mustard gases in military use based on NBP derivatisation. 

We have subjected the mechanistic proposal of Fig. 1 to a direct test. N,N-Dimethylformaldimmonium ion was independently prepared as its trifluoroacetate salt and was mixed with a slight excess of silver nitrite in acetonitri1e-d3. The only product identified was dimethylnitrosamine, which was produced in greater than 90% yield ( ). No direct evidence for intermediates of structure I could be obtained, as the reaction was complete within the few minutes required to analyze the mixture by running its NMR spectrum. 

In addition to phosphate and halide anion binding, carboxylate chelation by sapphyrin macrocycles has been the subject of recent investigation. To date, two crystal structures have been solved. A 2 1 complex formed between diprotonated sapphyrin 3 and trifluoroacetic acid shows that the oxyanions are chelated above and below the sapphyrin plane (Figure 10). ° Greater complexity of organi-... 

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). 

Trifluoroethanol [5n] This solvent is strongly acidic and the major impurities are water and trifluoroacetic acid. In its purification, it is dried over potassium carbonate anhydride for a night and then subjected to fractional distillation (reflux ratio 10 1) under atmospheric pressure, the middle fraction being collected. 

Another method, which generated in most cases good yields of N-protected gem-diaminoalkyl compounds, involves N-protected peptidyl or aminoacyl carboxamide derivatives. These are subjected to a Hofmann-type rearrangement with the mild oxidizing reagent iodobenzene bis(trifluoroacetate) (IBTFA). 83 IBTFA is also known as phenyl iodosyl... 

Our retrosynthetic analysis for lipid I is presented below [Scheme 2], Our protected version of lipid I employed acetate protective groups for the carbohydrate hydroxyls, methyl esters for each of the carboxyl groups in the pentapeptide side chain, and trifluoroacetate for the terminal amino group of the lysine residue. These base-cleavable protective groups could be removed in a single operation in the final step of our synthesis and would not subject the sensitive diphosphate linkage to acidic reagents or reaction conditions. 

Among these groups (siloxy, amino, benzotriazolyl, thiolate, cyanide) the methoxy group has been the subject of a large number of studies. To generate the azomethine ylid, essentialy three reagents have been utilized silyl triflate (or iodide), trifluoroacetic acid and lithium fluoride (sometime combined with sonication). Thermal rearrangement has also proven to be efficient. 

---