1- fluoro-pyridinium triflate

When chiral enolates are allowed to react with W-fluoro-2,4,6-trimethyl-pyridinium triflate (K, Table 3b), moderate diastereomeric excesses are achieved [79] (equation 44)... 

Fluoropyridinium salts, in most cases, are freely soluble in polar solvents such as acetonitrile, but insoluble or sparingly soluble in nonpolar organic solvents.38 39 The solubilities of 1-fluoro-pyridinium triflate, tetrafluoroborate, hexafluoroantimonate and perchlorate in dichloro-methane are 0.63, 0.05, 0.09 and 0.035 mg cm 3, respectively, and of 1-fluoropyridinium triflate in tetrahydrofuran is 1.71 mg cm-3. The salts were dissolved in water and decomposed very slowly at room temperature. When a solution of 1-fluoropyridinium triflate in water was allowed to stand for 14 days at room temperature it decomposed completely to give pyridin-2-ol in 66% yield. 1-Fluoropyridinium salts with non-nucleophilic counteranions are generally stable crystals with high melting points. 

Substituted 1-fluoropyridinium triflates have been used for substitution of hydrogen by fluorine in aromatic compounds (Table 3).46"50 Thus benzene is transformed to fluorobenzene (56 % yield, l-fluoro-2,6-bis(methoxycarbonyl)pyridinium triflate), Af-ethoxycarbonylaniline gives Al-ethoxycarbonyl-2- and -4-fluoroaniline (60 and 27% yield, respectively, 1-fluoropyridinium triflate), and phenylurethane also gives the products of fluorination at position 2 (47%) and 4 (32%) of the aromatic ring [l-fluoro-2,6-bis(methoxycarbonyl)pyridinium triflate]. In the case of fluorination of anisole, 1-fluoropyridinium tetrafluoroborate gives 19% 2- and 17% 4-fluoroanisole.46... 

Chloro- and bromophenols and A -acylhaloanilines can be fluorinated in the ortho or para position by 1-fluoropyridinium triflates and the fluorophenols and iV-acylfluorohaloanilines thus obtained reduced to fluorophenols and iV-acylfluoroanilincs. For example, 4-chlorophenol reacts with 2-chloro-l-fluoro-6-(trichloromethyl)pyridinium tetrafluoroborate in 1,2-dichlo-roethane at 45°C for three hours to give 4-chloro-2-fluorophenol in 68% yield.51... 

Flow fluorination of the 4,4 -bipyridine —boron trifluoride complex gives only mono-fluorinated l-fluoro-4-(4-pyridyl)pyridinium boron trifluoride tetrafluoroborate (31), while fluorination of l-methyl-4-(4-pyridyl)pyridinium triflate in the presence of lithium triflate provides l-fluoro-l -methyl-4,4 -bipyridinium ditriflatc (32) 67... 

Abbreviations Ac acetyl Bn benzyl BSP 1-benzenesulfinyl piperidine BTIB bis(trifluoroacetoxy)iodobenzene DAST (diethylamino)sulfur trifluoride DDQ 2,3-dichloro-5,6-dicyano-/)-benzoquinone DMDO dimethyldioxirane DMTSF dimethyl(methylthio)sulfonium tetrafluoroborate DMTST dimethyl(methylthio)sulfonium triflate DTBMP 2,6-Ai-tert-butyl-4-methylpyridine DTBP 2,6-di-tert-butylpyridine DTBPl 2,6-di-tert-butylpyridinium iodide FDCPT l-fluoro-2,6-dichloropyridinium triflate FTMPT l-fluoro-2,4,6-trimethylpyridinium triflate IDCP iodonium dicollidine perchlorate IDCT idonium dicollidine triflate LPTS 2,6-lutidinium p-toluenesulfonate LTMP lithium tetramethylpiperidide Me methyl MPBT S-(4-methoxyphenyl) benzenethiosulflnate NBS A-bromosuccinimide NIS A-iodosuccinimide NlSac A-iodosaccharin PPTS pyridinium p-toluenesulfonate TBPA tris(4-bromophenyl)ammoniumyl hexachloroantimonate Tf trifluoromethanesulfonyl TMTSB methyl-bis(methylthio)sulfonium hexachloroantimonate TMU tetramethylurea Tr trityl TTBP 2,4,6-tri-tert-butylpyrimidine. 

A novel scandium complex bearing perfluorinated binaphthyl phosphate ligand, Sc[(R)-F8BNP]3, has been synthesized and used as a catalyst for asymmetric electrophilic fluorination reactions of P-keto esters [156]. In combination with 1-fluoro-pyridinium triflate (NFPY-OTf) as a fluorinating agent, the desired a-fluoro-P-keto esters were obtained in moderate to high yields (16-94%) and enantiomeric excesses (47-88%) under mild conditions. 

Shibata et al. described the synthesis of fluorogypsetin and fluo-robrevianamide E (3) by a novel fluorination-cyclization of cyclo-L-Trp-L-AAs. The authors found that A-fluoro-2,4,6-trimethyl-pyridinium triflate (2) was very effective for the fluorination-cyclization sequence and produced the target molecules in good 3uelds (eq 20). ... 

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