Xenon difluoride, reaction with pyridine

Pyridine is converted into perfluoropiperidine (82) in low yield by reaction with fluorine in the presence of cobalt trifluoride (50JCS1966) quinoline affords (83) under similar conditions (56JCS783). Perfluoropiperidine can be obtained electrochemically. This is useful, as it may be readily aromatized to perfluoropyridine by passing it over iron or nickel at ca. 600 °C (74HC(14-S2)407). Recently, pyridine has been treated with xenon difluoride to yield 2-fluoropyridine (35%), 3-fluoropyridine (20%) and 2,6-difluoropyridine (11%), but it is not likely that this is simply an electrophilic substitution reaction (76MI20500). 

Sulfanyl groups are active substrates for perfluorodecarboxylation reactions. 2,3,5,6-Tetra-chloro-4-sulfanylpyridine reacts with xenon difluoride and perfluoroalkanecarboxylic acids in dichloromethane at room temperature to form 2,3,5,6-tetrachloro-4-perfiuoroalkylsulfanyl-pyridines in moderate to high yields.87... 

Electrochemical fluorination of pyridine in the presence of a source of fluoride ion gave 2-fluoropyridine in 22% yield (85M11). With xenon difluoride, pyridine formed 2-fluoropyridine (35%), 3-fluoropyridine (20%), and 2,6-difluoropyridine (11%) in a reaction unlikely to be a conventional electrophilic substitution. Xenon hexafluoride has also been used (76JFC179). With cesium fluoroxysulfate at room temperature in ether or chloroform, the major product was 2-fluoropyridine (61 and 47%, respectively). Some 2-chloropyridine was also formed in chloroform solution. In methanol the entire product was 2-methoxypyridine (90TL775). Fluorine, diluted with argon in acetic acid, gave a 42% yield of the 5-fluoro derivative of l-methyl-2-pyridone [82H( 17)429],... 

Anand and Filler123 demonstrated that pyridine reacted with xenon difluoride forming 2-fluoro-, 3-fluoro- and 2,6-difluoropyridine and 8-hydroxyquinoline was converted to 5-fluoro 8-hydroxyquinoline, while nitrogen functionalization was observed by reaction of phthalimide and saccharin in benzene124. A-Fluoroimides were formed in good yields by reactions of xenon difluoride with imides of perfluorinated succinic and glutaric acids125 (Scheme 52). 

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