Cesium Fluoroxysulfate


[70806-67-6]  · CsFO4S  · Cesium Fluoroxysulfate  · (MW 247.96)

(mild fluorinating agent capable of electrophilic addition to C=C bonds1-3 and fluorofunctionalization of saturated hydrocarbons,4,5 aromatics,6-10 ketones and b-diketones,11,12 enol acetates,2,3,11,12 organosilicon11 and organotin13,14 derivatives, etc.)

Solubility: insol cold water; gives 0.07 M soln in acetonitrile.

Analysis of Reagent Purity: iodometric titration.15

Preparative Method: the reagent can be readily prepared from dilute fluorine and Cs2SO4: fluorine (20% mixture with nitrogen) was passed into Cs2SO4 in a polyethylene vessel with cooling to -4 °C. The yellowish-white precipitate is centrifuged, washed with a little water, and dried in vacuo.8,15

Handling, Storage, and Precautions: the synthesis of up to 200 g of CsOSO2OF has been described.8 The reagent is easily handled, provided due care is taken not to cause detonation: avoid mechanical pressure (sharp strikes), any contact with a metallic spatula,15 and do not heat. A protective shield should always be used. The reagent has been stored in a polyethylene vessel at 0 °C for 14 days without significant loss of activity.8


The main result of CsOSO2OF reactions with various organic substrates is electrophilic fluorination, the hypofluorite moiety in the anionic fragment FOSO2O- serving as the F+ synthon.

Unsaturated compounds react readily with CsOSO2OF (1) to yield products of addition, of addition with incorporation of solvent or external nucleophile, and of addition-elimination, depending on the reaction conditions. The reactions of (1) with alkenes gives 1,2-addition products (2), which can be conveniently transformed into ethyl sulfates (3) by treatment with Et3O+BF4- (eq 1).1 The same reaction in the presence of methanol (rt, CH2Cl2) gives b-methoxyalkyl fluorides (4). Analogously, reactions in AcOH and HF give vicinal fluoroacetates (5) and difluorides (6), respectively (eq 2).2,3 In some cases the reaction proceeds to give vinyl fluorides (7) (eq 3). For example, interaction of 1,1-diphenylethylene with (1) gives 2-fluoro-1,1-diphenylethylene.2 Fluorination of norbornene gives a 1:1 mixture of 2-fluoronortricyclene and 7-syn-fluoronorbornene.2

Reaction of the reagent (1) with 1,2-diphenylacetylene in methanol gives a mixture of 1,1-difluoro-2,2-dimethoxy-1,2-diphenylethane and 2,2-difluoro-1,2-diphenylethanone.16

Aromatic and aliphatic aldehydes react with CsOSO2OF, giving acid fluorides in good yields, presumably via radical pathways (eq 4).4

Room temperature fluorination of cyclic enol acetates by (1) gives a-fluorocycloalkanones in high yield (70-90%).2 b-Diketones and barbituric acid give the corresponding gem-difluorinated derivatives.11,12 Room temperature fluorination of uridine in methanol followed by treatment with Et3N gives 5-fluorouridine (79%).11 Similarly, 1,3-dimethyluracil gives the 5-fluoro derivative (89%).11

Cesium fluoroxysulfate is a mild fluorinating agent for activated aromatics,6-10 such as phenols (eq 5), alkoxy-substituted benzenes, and naphthalenes. The reaction is catalyzed by HF, H2SO4, CF3SO3H, FSO3H,6 and BF3.9

The reaction of toluene with CsOSO2OF in acetonitrile gives benzyl fluoride as the principal product,7 but in the presence of catalysts, o- and p-fluorotoluenes (6:1) are produced.6 In some cases of aromatic substitution the formation of fluorinated cyclohexadienones is observed (eq 6).9

Trimethylchlorosilane reacts smoothly with CsOSO2OF to give trimethylfluorosilane.11 Trimethyltin-substituted alkenes give fluoroalkenes (eq 7).13


The reagent (1) easily oxidizes secondary alcohols to ketones, and 1,2-dihydroxy-4-butylbenzene to the quinone derivative.17 Ph3P and dibenzothiophene are oxidized in room temperature reactions with CsOSO2OF.5,11

Related Reagents.

Chlorine Fluoroxysulfate; (2-Chloro-1,1,2-trifluoroethyl)diethylamine; Fluorine; N-Fluoro-N-t-butyl-p-toluenesulfonamide; Dibromomethane.

1. Zefirov, N. S.; Zhdankin, V. V.; Koz'min, A. S.; Fainzilberg, A. A.; Gakh, A. A.; Ugrak, B. I.; Romaniko, S. V. T 1988, 44, 6505.
2. Stavber, S.; Zupan, M. CC 1981, 795.
3. Stavber, S.; Zupan, M. JOC 1987, 52, 919.
4. Stavber, S.; Planinšek, Z.; Zupan, M. JOC 1992, 57, 5334.
5. Stavber, S.; Zupan, M. T 1989, 45, 2737.
6. Appleman, E. H.; Basile, L. J.; Hayatsu, R. T 1984, 40, 189.
7. Ip, D. P.; Arthur, C. D.; Winans, R. E.; Appleman, E. H. JACS 1981, 103, 1964.
8. Stavber, S.; Zupan, M. JOC 1985, 50, 3609.
9. Stavber, S.; Zupan, M. CC 1981, 148.
10. Stavber, S.; Zupan, M. JFC 1981, 17, 597.
11. Stavber, S.; Zupan, M. CC 1983, 563.
12. Stavber, S.; &SScaron;ket, B.; Zajc, B.; Zupan, M. T 1989, 45, 6003.
13. Hodson, H. F.; Madge, D. J.; Widdowson, D. A. SL 1992, 831.
14. Bryce, M. R.; Chambers, R. D.; Mullins, S. T.; Parkin, A. CC 1986, 1623.
15. Appleman, E. H.; Basile, L. J.; Thompson, R. C. JACS 1979, 101, 3384.
16. Stavber, S.; Zupan, M. JOC 1987, 52, 5022.
17. Stavber, S.; Zupan, M. T 1992, 48, 5875.

Nikolai S. Zefirov

Moscow State University, Russia

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