Pentafluoropyridine

FLUORINECOMPOUNDS,ORGANIC - FLUORINATED ALIPHATIC COMPOUNDS] (Vol 11) Pentafluoropyridine [70-16-3]... 

Tri-, Tetra-, and Pentafluoropyridines. 2,4,6-Trifluoropyridine can be prepared in 75% yield by catalytic hydrogenolysis (paHadium-on-carbon, 280°C) of 3,5-dichloro-2,4,6-trifluoropyridine [1737-93-5] (416). The latter is synthesized by exchange fluorination of pentachloropyridine with potassium fluoride in polar solvents such as /V-methy1pyrro1idinone (417,418). 3,5-Dichloro-2,4,6-trifluoropyridine is used to... 

Tetrafluoropyridine can be prepared ia 75% yield from the hydrogenation of pentafluoropyridine under free-radical (catalytic) or nucleophilic (lithium aluminum hydride) conditions (416,419). No practical uses for 2,3,5,6-tetra uoropyridine are known. 

Several methods for the preparation of unsymmetrical sulfur diimides RN=S=NR have been developed. One approach involves the addition of a catalytic amount of an alkali metal to a mixture of two symmetrical sulfur diimides, RN=S=NR and RT8i=S=NR. A second method makes use of alkali-metal derivatives of [RNSN] anions.Eor example, derivatives in which one of the substituents is a fluoroheteroaryl group can be prepared by the reaction of the anionic nucleophile [RN=S=N] with pentafluoropyridine. Sulfur diimides of the type RN=S=NH (R = 2,4,6- Bu3C6H2S) have also been prepared. "... 

Until recently the substitution pattern in pentafluoropyridine was considered to be 4 2 however, several examples have been found where... 

Pentafluoropyridine is less reactive toward addition of fluorine by BrF2+ than polyfluorobenzenes. The product is perfluoro-l-aza-1,3-cyclohexadiene (81JOU879). 

Raman and multinuclear NMR spectroscopy have been used to study the reaction product of pentafluoropyridine with XeF+AsF6 in anhydrous HF. Identified in the mixture was a fluoro(pentafluoropyridine)xenon(II) cation with the Xe bonded to the ring N (88CC257). 

Scheme 7.2 Reactivity of pentafluoropyridine with nickel(O) complexes...

Attempts to perform hydrodefluorination on other polyfluoroarenes using 9c met with mixed success (Table 8.4). Pentafluoropyridine proved to be highly active with a turnover number of 13.6, although the distribution of products revealed up to three hydrodefluorination reactions (Table 8.4, entry 4). Substrates with a lower fluorine content, such as CF.CH, and 1,2- or 1,4-CF,H were unreactive. 

Perfluoroarenes also undergo facile and selective monosubstitution with hydroxyl-amine. This reaction is general and proceeds with different Ai-alkylhydroxylamines and a number of perfluorinated arenes (e.g. 29, equation 19) and pentafluoropyridine. 

Pentafluoropyridine (292) is reduced440 in dry DMF at a mercury cathode to perfluoro-4,4 -bipyridyl (293) in the presence of hydroquinone as proton donor, 2,3,5,6-tetrafluoropyridine (294) is obtained [Eq. (150)]. Pentachloro-pyridine gives on reduction in dry DMF very little bipyridyl derivative, but tetrachloropyridine and bis(tetrachloropyridyl) mercury. 

Perfluorotoluene and pentafluoropyridine have been proposed as reagents for protecting alcohols and phenols as perfluoroaryl ethers, a reaction which takes place under mild PTC conditions. Deprotection involves demethoxylation with NaOMe in DMF at 60 C (Scheme 18 R = phenyl, steroidal).158... 

Pentafluoropyridine, with Ni(0) complexes, 8, 47 -8 Pentagonal bipyramidal complexes, triiron complexes, 6, 310 Pentahapto germolyl complexes, with Hf(IV), 4, 987-989 Pentahapto siloyl complexes, with Hf(IV), 4, 987-989 Pentakis(acetoxymercurio)pentamethylruthenocene, preparation, 6, 630... 

Pentafluoropyridine is known to undergo photocycloaddition with ethylene [89,90] and cycloalkenes [91] at the 3,4-position of the pyridine ring. Recently, Sakamoto et al. reported that metacrylonitrile adds to the 2,3-position of 2-alkoxy-3-cyano-4,6-dimethylpyridines (24a,b) to give 7-azabicyclo[4.2.0]octa-2,7-di-enes (25a,b) [92] (Scheme 10). This work was developed to the photocycloaddition of furan to pyridine ring as a first example (Scheme 10) [93],... 

The Hell spectra of pentafluoropyridine and cyanuric fluoride have been assigned on the basis of HAM/3 and HAM/3 plus STO-3G calculations, respectively. Daamen and Oskam164 have reported Hel/Hell intensity ratios, and Utsonomiya and coworkers165 have measured the Hel angular distribution for pentafluoropyridine. 

Radical anion of 2-fluoropyridine 2,6-difluoropyridine 2,3,4, 6-tetrafluoropyridine pentafluoropyridine... 

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