Fluoride-promoted

Fluoride promoted alkylation of silyl enol ethers Acc. Cfiem. Res. 1985, 18, 181... 

Cesium fluoride-promoted telomenzation of equimolar amounts of perfluoro 2-butyne and 2-bromoperfluoro-2-butene gives a mixture of hexadienes or, with... 

Dehydrochlorination of bis(tnfluoromethylthio)acetyl chloride with calcium oxide gives bis(trifluoromethylthio)ketene [5] (equation 6) Elimination of hydrogen chloride or hydrogen bromide by means of tetrabutylammonium or potassium fluoride from vinylic chlorides or bromides leads to acetylenes or allenes [6 (equation 7) Addition of dicyclohexyl-18-crown-6 ether raises the yields of potassium fluoride-promoted elimination of hydrogen bromide from (Z)-P-bromo-p-ni-trostyrene in acetonitrile from 0 to 53-71 % In dimethyl formamide, yields increase from 28-35% to 58-68%... 

In contrast, perfluoromethylenecyclopropane (105) failed to give any thermal dimerization (cesium fluoride promotes its dimerization, but not in a [2 + 2] fashion) [29], while tetrafluoroethylene and other 1,1-difluoroalkenes readily undergo thermal [2 + 2] dimerization [123]. 

Fluoride-promoted elimination of HBr from eis-/ -bromo-p-nitrostyrene [1551 under solid-liquid conditions ... 

Mowery and DeShong reported on the use of siloxanes 72 (Figure 16) as versatile transmetallation agents for Pd(dba)3-catalyzed couplings with aryl halides and allylic alcohol derivates, in the presence of TBAF and at high temperature (95 They later used aryl silatrane 73 (Figure 16) as a suitable partner for the fluoride-promoted... 

Unsaturated fluorocarbons are much more reactive toward nucleophiles than then hydrocarbon counterparts owing to fluorine s ability to both stabilize carban ions and inductively increase the electrophihcity of multiple bonds and aromauc rings Nucleophilic attack dominates the chemistry of unsaturated fluorocarbons, and the role of fluoride ion in fluorocarbon chemistry is analogous to that of the proton in hydrocarbon chemistry [729] Lake the related electrophilic reactions for hydrocarbons, there are fluoride-promoted isomenzations and dimerizations (equation 9), oligomerizations (equation 10), additions (equation 11), and amomc Fnedel-Crafts alkylations (equation 12) that all proceed via carbamomc intermediates [729 141]... 

Maleczka, R. E. Geng, F. Synthesis and fluoride-promoted Wittig rearrangements of a-alk-oxysilanes. Org. Lett. 1999, 1,1111-1113. 

Aroyl fluorides promote dipolar cycloaddition of thioimide with dimethyl fumarate.162... 

By analogy to Denmark s proposed mechanism, SCB oxidation is believed to proceed via initial (and rapid) fluoride-promoted ring opening of the SCB, which generates in situ a heteroatom-activated organosilane for subsequent oxidation. 

Under strictly anhydrous conditions which minimize competing protiodesilylation, (Z)-a-silyl vinyl sulfides with an co-carbonyl moiety attached to the S atom undergo a fluoride-promoted intramolecular cyclization which yields 2-alkenyltetrahydropyran-3-ols. The substrates are derived from (Z)-a-silyl enethiols by alkylation with co-halocarbo-nyl compounds (Scheme 157) <2000EJ02391>. 

The Pandey group has developed a silver fluoride-promoted desily lation of tertiary bis(silyl)amines as an interesting alternative method to access azomethine ylides (Scheme 2.10).18 Notably, this method allows the generation of nonstabilized azomethine ylides under essentially neutral conditions. The starting materials are prepared by a three-step process, sometimes coupled into a single operation. For example, Boc-protected pyrrolidine 36 can be sequentially deprotonated and silylated twice in a one-pot reaction (Scheme 2.10). Removal of the Boc group and alkylation of the free amine leads to bis(silyl)amine 37. When this compound is treated with 2 equiv of silver fluoride in the presence of phenyl vinyl sulfone, rapid formation of products 39 as single stereoisomers results. 

The desired extent of fluorination of the starting material may dictate the fluorinating agent to be used. For example, fluorine converts silicon tetrachloride to silicon tetra-fluoride, whereas antimony(III) fluoride promotes the reactions which produce the chlorofluorides, SiCl3F, SiCl2F2, and SiCIFs. 

The fluoride-promoted dehalosilylation of l-trimethylsilyl-2,2-dihalocyclopropanes provides one of the easiest routes to simple monohalocyclopropenes, the products being trapped by [4 + 2]-addition to furan or diphenylisobenzofuran (DPIBF)121. In the same... 

Tetrabutylammonium fluoride promotes the intramolecular nucleophilic attack of the ester group. Oxazoline-5-ones 622 are obtained from carbodiimide 621 in this manner. The reaction is conducted at room temperature in THE and yields of 55-75 % are obtained. ... 

In case of o-carboxylic ester groups, such as in 623, ring closure to give 3,1-benzoxazin-4-ones 624 is observed. The yields in this tetrabutylammonium fluoride promoted reaction are 50-55 %. 

Cesium fluoride promoted oxirane preparation starting from bis(sulfonyl fluorides) has been reported. In general, epoxide formation predominates over furan synthesis. Investigations of cyclohexane derivatives 1 show trans elimination to form 2 this still holds true when the syn chlorine is substituted by a bromine.Epoxide 4 is a versatile, general, enan-liomerically pure building block that is best synthesized by substitution of the mesylate 3. ... 

Treatment of 2 with 3 equiv of 3-phenyl-2-propenal in refluxing toluene-cfe while the reaction progress was monitored by H NMR spectroscopy resulted in the disappearance of the aldehyde hydrogen peak (5 1.56). The IR spectrum of 4 shows a new absorption due to a vC-o stretch at 1448 cm 1. The mass spectrum of the product shows a molecular ion at m/z 538. To our surprise, an X-ray study of 4 showed it to be the insertion product of the two carbonyl ligands into the C-Si bond in 2. The reaction has the potential for developing a new method for double C-C bond formation between the carboranyl unit and carbonyl compounds. Such an insertion of the carbonyl functionality into the o-carborane has been observed in Yamamoto s work on the chemoselective addition of o-carborane to the aldehyde groups by a palladium-catalyzed9 or a fluoride-promoted reaction.10... 

Finally, a recent study by Majetich and Hull has demonstrated the feasibility of the carbanion-accel-erated divinylcyclobutane rearrangement. Whereas the thermal rearrangement of the divinylcyclobu-tane (273 Scheme 38) required extended heating at 180 C and proceeded in modest yield, the corresponding enolate was shown to rearrange smoothly at -35 C in 90% yield. As illustrated in Scheme 39, the enolate-accelerated DVCB rearrangement can be employed in tandem with the intramolecular fluoride-promoted Michael addition of allylsilanes to provide an attractive route to a variety of fused bi-cyclic cyclooctane derivatives. 

Nordin JP, Sullivan DJ, Phillips BL, Casey WH (1999) Mechairisms for fluoride-promoted dissolution of bayerite [p-Al(OH)3(s)] and boehmite [y-A100H(s)]- F-NMR spectroscopy and aqueous surface chemistry. Geochim Cosmochim Acta 63 3513-3524... 

A highly exo-selective asymmetric hetero Diels-Alder reaction was the key step in D.A. Evans total synthesis of (-)-epibatidine. The bicyclic cycloadduct was then subjected to a fluoride-promoted fragmentation that afforded a (f-keto ester, which was isolated exclusively as its enol tautomer. The removal of the ethoxycarbonyl functionality was achieved using the Krapcho decarboxylation. Interestingly, the presence of a metal salt was not necessary in this transformation. Simply heating the substrate in wet DMSO gave rise to the decarboxylated product in quantitative yield. 

Denmark, S. E., Lee, W. Investigations on Transition-State Geometry in the Lewis Acid- (Mukaiyama) and Fluoride-Promoted Aldol Reactions. J. Org. Chem. 1994, 59, 707-709. 

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