Pyridinium triflates

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)... 

Dudley and co-workers have designed pyridinium triflate reagent 58 for the preparation of benzyl ethers <06JOC3923>. This reagent is easily prepared in two steps with good yield. Since it is also bench-stable and preactivated, the benzylation reaction occurs upon warming 58 in the presence of an alcohol with no need for acidic or basic promoters. 

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... 

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... 

CH2C12 (10 mL) containing propane-1,3-diol (3.04 g, 40 mmol) and pyridine (6.94 g, 88 mmol) was added dropwise to a stirred solution of triflic anhydride (24.8 g, 88 mmol) in cold (0°C) CH2C12 (20 mL), The mixture was stirred at 0LC for 30 min then filtered through a 4-cm bed of silica gel to remove pyridinium triflate. The filtrate was concentrated in vacuo at rt to provide a viscous, orange liquid, presumed to be... 

The reaction of methyl nicotinate with / -butyldimethylsilyl triflate gave the A-silylpyridinium salt which on treatment with phenyl Grignard followed by TBAF afforded the N-unsubstituted 4-phenyl-l,4-dihydropyridine <1998TL9275>. An improved preparation of iV-(trimethylsilyl)pyridinium triflate, A-(triphenylsilyl)pyridinium triflate, and A-(triisopropylsilyl)pyridinium triflate involves the reaction of the corresponding allyl silanes with triflic acid followed by pyridine <1997S744>. 

Pyridinium methylides. Trimethylsilylmethyl triflate converts pyridines into N-(trimethylsilylmethyl)pyridinium triflates in high yield. On treatment with cesium fluoride these products are converted into nonstabilizcd pyridinium methylides. which can be trapped by cycloaddition to dimethyl acetylenedicarboxylate to form indolizincs. 

Mohan, H, Gemma, E, Ruda, K, Oscarson, S, Efficient synthesis of spacer-linked dimers of A-acetyllactosamine using microwave-assisted pyridinium triflate-promoted glycosylations with oxazoline donors, Synlett, 1255-1256, 2003. 

Acylation of chiral alcohols The pyridinium triflates and tetrafluoroborates are useful reagents for delivery of acyl groups to chiral secondary alcohols such as a-hydroxy carboxylic esters. 

PhC (OTBDMS)=NPh, (Si-BEZA) catalytic pyridinium triflate, THF or ben-zotrifluoride, 25-50°C, 5-2400 min, 23-99% yield. This is a general method and can be used to prepare TMS, TES, TBDPS, and TIPS ethers even from 3° alcohols and phenols. "... 

Using pyridinium triflate, the deprotonated amide intermediate was estimated to have pKa = 4.20. This low value is consistent with Zn(II) ion stabilization of the deprotonated amide. The formation of this deprotonated amide intermediate occurs in wet DMSO with a microscopic rate constant that corresponds to the intramolecular hydrolysis of coordinated nitrocefin catalyzed by [Zn2L3( i-0H)(N03)2]. Activation parameters for this reaction (A= 77.6 + 8.0kJM-1 and AS = —62.7 + 20.0 JM"1 K-1) are within error of those found for the same reaction in acetone DMSO... 

Pyridinium triflates, 620 (2,6)-Pyridinophanes, 51 2-Pyridones, 479 Pyridoxal pyrophosphate, 114 Pyrocatechase, 429... 

Oscarson et al. [75] performed easy and efBcient synthesis of spacer-linked dimers of N-acetyllactosamine from the corresponding oxazoline donor 97, by applying pyridinium triflate as promoter combined with microwave heating. Compared with the promoter pyridinium p-toluenesulfonate, previously proven to be more effective than other sulfonates [76], the triflate salt increased the yield of dimers 100 by more than 30%. Microwave irradiation reduced the reaction time... 

Reactions with Pyridines. It is well known that the reaction of triflic anhydride with pyridine and pyridine derivatives affords the pyridinium triflate, thus activating the para position for nucleophilic attacks, such as ketene acetals (106), activated arenes (107), azulenes, or A-alkenes. ... 

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