Reaction with cesium fluoroxysulfate

Fluororesorcinol can be prepared from derivatives of resorcinol and fluo-roxytrifluoromethane [15, 24] (equation 4) or by fluorination of resorcinol with cesium fluoroxysulfate [25] (equation 5). Reaction of acetyl hypofluorite with M-acetyl-O-methyltyrosine methyl ester provides a good route to 3-fluorotyrosine derivatives [26] (equation 6). 

Room-temperature reactions of 1.1-diphenyl-substituted alkenes in dichloromethane with cesium fluoroxysulfate give addition-elimination products, e.g. formation of 1, while the reaction with norbornene gives only 7-fluoronortricyclene and 7-mi-fluoronorbornene.6-7... 

The reaction of 17/ -estradiol (14) with cesium fluoroxysulfate and boron trifluoride-diethyl ether complex in acetonitrile gives the 2-fluoro and 4-fluoro isomers in a 1 1 ratio,17 while the reaction with the hexamethyl ether of gossypol fails under a variety of conditions.21... 

The course of the reaction of methyl-substituted benzene derivatives with cesium fluoroxysulfate in acetonitrile at 35-40 C strongly depends on the structure of the molecule. Toluene (16, R1 = R2 = H) and other alkyl-substituted benzenes 16 and 17 are mainly functionalized on the side chain, while 1,3.5-trimethylbenzene (18) gives mainly ring-substituted products 24 however. 1.2.4,5-tetramethylbenzene (19) and hexamethylbenzene again give mainly or exclusively side-chain products.25... 

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],... 

Table 7. Aryl Fluorides by Reaction of Arylboronic Acid Esters with Cesium Fluoroxysulfate...

The fluorination of adamantane and its derivatives can also be achieved with oxygen difluoride in the presence of sodium hydrogen carbonate as a hydrogen fluoride trap however, this reaction is complicated by competing oxidation.22 When the fluorination of adamantane is performed with cesium fluoroxysulfate, a mixture of monofluorinated products 4 and 5 arising from fluorination at tertiary and secondary sites, respectively, and difluorinated product 6 is obtained.23 The thermally initiated fluorination of adamantane using xenon difluoride gives a similar mixture but includes a small amount of trifluoride 7.24 25... 

The white cesium fluoroxy sulfate precipitates from the reaction medium and may be kept for several months in the cold (0 to -15 °C) Metal surfaces can cause detonation of the reagent. The reaction scope of cesium fluoroxysulfate seems narrower than that of acetyl hypofluorite because of its limited solubility in organic solvents Cesium fluoroxysulfate has not been prepared with a fluorine-18 label. 

Cesium fluoroxysulfate, CsSO.,f (1). Mol. wt. 247.97, stable solid at - I O, stable in CHyCN for about a day. The reagent is prepared by reaction of cesium sulfate in water with fluorine.1... 

Addition of cesium fluoroxysulfate to olefins gives vicinalfluoroalky l sulfates with low regio- and stereoselectivity [762, 165] (equations 12 and 13) Reactions of this reagent with olefins in methanol or acetic acid give vicinalfluoroalkyl methy l ethers or acetates, respectively [164, 165 166] (equation 14), with a predominance... 

Cesium fluoroxysulfate is prepared, usually in minute amounts, from Cs2S04 and elemental fluorine299. Its advantages are the possibility of storage and its relatively mild reactions. On the other hand, it is produced only in minute amounts at a time, its reactions with... 

Xenon difluoride is a better fluorinaling reagent for vinyltin compounds than cesium fluoroxysulfate (compare entry 1 in Tables 1 and 2). Besides this, cesium fluoroxysulfate (which can be prepared from elemental fluorine and cesium sulfate) is known to be shock sensitive and to undergo detonation upon hcaling. However, cesium fluoroxysulfate is the alternative choiee in the ease of some vinyltin compounds, such as 2- and 3-(trimethylstannyl)indolcs (Table 2, entries 5 7), whose reactions with xenon difluoride are not effective. 

Fluoroaromatic compounds 8 are synthesized by reaction of aryltrialkyltin derivatives with electrophilic fiuorinating reagents, such as cesium fluoroxysulfate, trifluoromethyl hypo-fluorite and acetyl hypofluorite, or with elemental fluorine. In Table 4 examples of these reactions arc summarized. 

The reaction of alkenes with acetyl hypofluorite436-439 or with fluorine,451-473-474 2,3,4,5,6-pcntachloro-l-fluoropyridinium trifluoromelhanesulfonate ((V-FPCPy-OTf),441-711 cesium fluoroxysulfate,435 (V-fluorobis(triflyl)amine432 or l-(chloromethyl)-4-fluoro-l,4-diaza-bicyclo[2.2.2]octane tetrafluoroborate431 in acetic acid leads to the simultaneous addition of fluorine and the acetoxy group across the double bond. Examples of these additions are summarized in Table 34. Further examples are the formation of l439 and 2 439... 

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