Fluoride ion displacement

Trifluoromethyl thioethers are produced in a fluoride-catalysed one-pot reaction of alkyl or aryl thiocyanates with trifluoromethyl silanes [37]. The reaction is initiated by fluoride ion displacement of the trifluoromethyl anion from the silane the thioether is formed from the thiocyanate by displacement by the trifluoromethyl anion of the cyanide ion, which then perpetuates the reaction. Trifluoromethyl selenoethers are obtained by an analogous route. In a similar manner, disulphides can be converted into trifluoromethyl thio- or selenoethers [38],... 

The selective introduction of fluorine is of continuing interest not only because of the synthetic challenge but also because of the possibility of a dramatic change in biological activity. The fluoride-ion displacement of carbohydrate trifluoromethanesulfonates using tris(dimethylamino)sulfonium... 

The fluorinase enzyme mediates a substitution reaction whereby fluoride ion displaces L-methionine with formation of a C-F bond and cleavage of a C-S bond. In order to explore the mechanism in detail, the process has been explored both experimentally and theoretically. The stereochemical course of the reaction was of immediate interest, particularly to delineate between direct inversion or double inversion during the substitution process. A direct substitution will proceed with inversion of configuration at the C5 carbon, whereas a double inversion process will proceed with an overall retention of configuration at the C-5 carbon. To explore this, it was important to prepare SAM 8 carrying a stereospecifically... 

The synthesis of fluorine-18-labelled receptor-based radiopharmaceuticals carried out before 1986 have been reviewed331 and the methods applied for the synthesis of 18F-butyrophenone neuroleptics such as spiroperidol (spiperone), haloperidol have been critically evaluated. The synthesis for preparing 7V-(2-[18F]fluoroethyl)spiperone330 involving the [18F]fluoride ion displacement of a suitable leaving group on the ethyl side chain was found to be particularly good (>50% yield). 

The precursor 318 has been prepared in the four steps outlined in equation 136. A-([18F]Fluoroalkyl)spiperone derivatives have also been prepared310 by N-alkylation of spiperone with 2-[18F]fluoroethyl bromide, 3-[18F]fluoropropyl bromide and 4-[18F]fluorobutyl bromide (equation 137), which were prepared in turn by [18F]fluoride ion displacement of the corresponding triflates. The 2-[18F]fluoroethyl, 3-[18F]fluoro-... 

Anhydrous reagent. Two laboratories - have reported that the commercially available trihydrate is converted into almost anhydrous reagent when heated at 40-45° under high vacuum. This material is very effective for various Sn2 fluoride ion displacements, but elimination and hydrolysis to an alcohol can be significant side reactions. 

A very interesting species is [Bi(CF3)4], which is formed by reaction of Bi(CF3)3 with MesSiCFs in the presence of [NMc4]F. Presumably, the fluoride ion displaces CFs from the silyl reagent making it available for reaction with Bi(CF3)3. 

Polyfluoroarenes and polyfluoroolefins are exceptions, since both groups undergo facile fluoride ion displacement by nucleophiles, e.g., to prepare polyfluoroaryl- and polyfluorovinyl-metal compounds from reactions of these precursors with anionic metal complexes ... 

Potassium fluoride on alumina is sometimes used as a base.23 It may be that the fluoride ion displaces some surface hydroxyl from the alumina to produce some potassium hydroxide. Lithium chloride, bromide, and iodide on silica... 

Aryl triflates have been used to generate arynes via other routes than metal-halogen exchange. For example, fluoride ion displacement of the trimethylsilyl group in 26 provides a convenient route to benzyne under mild conditions. The required benzyne precursor 26 was prepared from o-trimethylsilylphenoxytrimethylsilane by sequential treatment with BuLi and (Tf)20. Analogous aryne precursors have also been prepared less directly, as in the case of amide benzyne 31. Examples of 32 include various methylfurans, diphenylsobenzofuran and tetraphenylcyclopentadienone. Examples of nucleophiles include methanol, phenol, lithium thiophenoxide and others. 

L-Xylose has been converted into a 2-deoxy-2-fluoro-P-L-arabinofuranose derivative, by way of a fluoride ion displacement of an imidazolylsulfonate, and then into a range of pyrimidine nucleosides. Displacement of another imidazolylsulfonate with Et3N.3HF initially formed the corresponding sulfonyl fluoride which was subsequently displaced by fluoride ion. Methyl 2,3-dideoxy-3-fluoro-5-0-(4-methylbenzoyl)-a-D-ribofuranoside, an intermediate for the syntheses of some anti-HIV nucleosides, has been synthesized from 2-deoxy-D-ribose in five steps and in 24% yield. ... 

Hydroxylapatite is the mineral in teeth and bone that crystallizes between the collagen fibers and gives strength. When a fluoride ion displaces hydroxyl ions, it becomes fluorapatite. Fluorapatite is even stronger and prevents tooth decay by slowing demineralization and speeding remineralization. 

Fluoride ion displaces McjSiF from compounds of type (102), and on quenching with water the Si-free oxiranes are obtained in good yield. Application of the reaction to derivatives of type (103) gives access to the allene oxide (104). ... 

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