Fluoride ion source

Fluoride ion sources include alkali metal, ammonium, tetraalkylammomum, and silver fluorides. With silver fluoride, the polyfluoroalkylsilver intermediates can be isolated [/, 37] (equation 6)... 

Cyclic sulfates rapidly react with the fluoride ion sources to give monofluoro derivatives Thus, the 2,3-cyclic sulfate of methyl-4 6 O benzylidene p D manno pyranoside cleanly reacts with tetramethylammonium fluoride to give methyl 4,6-0-benzylidene 2 deoxy 2 fluoro-p-D-glucopyranoside-3-sulfate Acid hydrolysis followed by acetylation gives 2 deoxy 2 fluoro-P-D-glucopyranoside triacetate in 84% isolated yield [5S] (equation 38)... 

Fluoride ion is effective in promoting the reduction of aldehydes by organosil-icon hydrides (Eq. 161). The source of fluoride ion is important to the efficiency of reduction. Triethylsilane reduces benzaldehyde to triethylbenzyloxysilane in 36% yield within 10-12 hours in anhydrous acetonitrile solvent at room temperature when tetraethylammonium fluoride (TEAF) is used as the fluoride ion source and in 96% yield when cesium fluoride is used.83 The carbonyl functions of both p-anisaldehyde and cinnamaldehyde are reduced under similar conditions. Potassium bromide or chloride, or tetramethylammonium bromide or chloride are not effective at promoting similar behavior under these reaction conditions.83 Moderate yields of alcohols are obtained by the KF-catalyzed PMHS, (EtO SiH, or Me(EtO)2SiH reduction of aldehydes.80,83,79... 

The electrochemical oxidations of aromatic compounds in the presence of a fluoride ion sources have been widely studied by a number of workers to produce a range of partially fluorinated compounds [9-12]. 

This procedure describes an example of the "aldehyde route". The addition of 2-(trimethylsilyl)thiazole (2-TST) to aldehydes occurs readily and does not require the presence of a fluoride ion source.10 The resulting secondary alcohol is as a rule isolated in very good yield. The sense of the diastereofacial selectivity of the addition reaction to chiral a-amino aldehydes can be controlled by differential protection of the... 

The nucleophile for which increased reactivity is most critical is the fluoride ion [3,4], Water molecules bind tightly to this ion, and their presence dramatically reduces its effective nucleophilicity. A variety of fluoride ion sources have been used in an effort to improve product yields in deoxyfluoro sugar synthesis [26,34]. The yields of substitution and elimination products generated from reactions with fluoride ion from several sources are listed in Table 2 [26]. Currently, the most attractive source of fluoride ion is tris(dimethylanuno)-5ulfur (trimetbylsilyl)difluoride (TASF), which is soluble in a variety of oiganic solvents and produces an anhydrous fluoride ion [33]. 

With the aid of a fluoride ion source, alkynyltrimethylsilanes work as effective alkynyl donors in the Pd-catalyzed cross-coupling with alkenyl iodides.43,43a Recent studies have revealed that the alkynylsilanes react smoothly with aryl iodides and triflates, alkenyl triflates, or alkynyl chlorides under co-catalysis by a Cu or Ag salt.45 46a The use of a Pd/imidazolium chloride system in the presence of Cs2CC>3 and a Cu co-catalyst enables an efficient coupling between alkynyltrimethylsilanes and aryl bromides.47 In some cases, this catalytic system works well under Cu-free conditions. Alkynylsilanols also can be used as alkynyl donors in the coupling with aryl iodides.48 49 When TBAF is employed as activator, the coupling proceeds efficiently without co-catalyst.48... 

Carbon dioxide behaves as a weak fluoride ion acceptor towards naked fluoride ion sources such as tetramethylammonium fluoride, neopentyl(trimethyl)-ammonium fluoride and piperidinium fluoride (pip+F ) in the absence of a solvent and in CH2F2 and CF3CHFCF3 solvents for pip+F [25]. The C02F anion has been characterized in the solid state by 1H 13C MAS NMR spectroscopy and... 

Under an atmospheric pressure of carbon monoxide, aryl- and alkenylsilanes undergo a carbonylative coupling reaction with aryl and alkenyl halides [44,45]. The optimized conditions for arylsilanes involve the use of N,M-dimethyl-2-imidazolidinone (DMI) as a solvent and KF as a fluoride ion source (Eq. 38), whereas alkenylsilanes prefer THF and TBAF (Eq. 39). 

As mentioned above, liquid fluoride salts like EtaN nHF (n = 3-5) and Et4NF-4HF have proved to be highly useful as the electrolytic media and fluoride ion source for selective anodic fluorination. However, this solvent-free method has an atom economy problem because of the use of an excessive amount of liquid salts in place of a solvent. 

Potassium hydrogen fluoride or sodium hydrogen fluoride may serve as a fluoride ion source for the nucleophilic ring-opening reaction of epoxides. Attack of fluoride occurs predominantly at the less-hindered, i.e. least-substituted, site in the epoxide, as discussed in the following examples. 

Tetramcthylammoiiium fluoride and potassium fiuoridc/tetraethylammonium iodide have also been used as the fluoride ion source. ... 

In a similar process to halofluorination, sulphur- [285], selenium- [286] and nitrogen-containing [43] groups and fluorine may be added to hydrocarbon double bonds by reaction of an alkene with an electrophilic reagent of the heteroatom species in conjunction with a fluoride-ion source (Figure 3.66). As expected, Markovnikov addition in trans stereochemistry occurs mainly. 

The reagents for iodine fluoride addition to unsaturated centers are iodine229 or A -iodosuc-cinimide (NIS),221 258 and iodine pentafluoride, hydrogen fluoride,221,258 potassium fluoride, silver(I) fluoride229 278 or ammonium hydrogen difluoride/aluminum trifluoride220 as fluoride ion sources. In addition to the in situ iodofluorinations with iodine monofluoride,l96,22< 227 and (difluoroiodo)methane,194,19 iodofluorination with bis(pyridine)iodonium tetrafluoro-borate219 is described. 

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