N-Fluoropyridinium Triflate1

[107263-95-6]  · C6H5F4NO3S  · N-Fluoropyridinium Triflate  · (MW 247.17)

(fluorinating agent for many nucleophilic substrates)

Physical Data: mp 185-187 °C.

Solubility: sol polar solvents such as MeCN; 0.6 mg mL-1 in CH2Cl2; 1.7 mg mL-1 in THF; insol Et2O.

Form Supplied in: white crystals; widely available.

Analysis of Reagent Purity: 1H and 19F NMR, IR.2

Purification: recrystallization from MeCN-Et2O at rt.2

Handling, Storage, and Precautions: nonhygroscopic and thermally stable. The reagent should be stored in a dry atmosphere protected from light. Handle in a fume hood.

Fluorination.1

N-Fluoropyridinium triflate (1) is an electrophilic fluorinating agent and is one of a series of N-fluoropyridinium triflates of differing strength. Typical related reagents include N-fluoro-2,4,6-trimethylpyridinium triflate (2), N-fluoro-3,5-dichloropyridinium triflate (3), N-fluoro-2,6-dichloropyridinium triflate (4), and N-fluoropentachloropyridinium triflate (5). The fluorinating power of these compounds varies in the order (2) < (1) < (3) < (4) < (5). The strongest reagent (5) smoothly fluorinates less reactive nucleophiles, while the mildest reagent (2) can be used satisfactorily for the more reactive nucleophiles. Reagents (1) and (3) fluorinate nucleophiles of intermediate reactivity. Because of this variation in strength, N-fluoropyridinium triflates fluorinate a wide range of nucleophiles including carbanions,1 active methylene compounds,1,3-6 sulfides,7 enamines,1 enol alkyl and silyl ethers,1,8 vinyl acetates,1 aromatics,1,9-13 and alkenes.1 In the following representative examples, N-fluoropyridinium triflate fluorinates enol silyl ethers (eq 1), alkyl enol ethers (eq 2), activated vinyl acetates (eq 3), and activated aromatics (eq 4).

In some cases, N-fluoropyridinium triflate exhibits selectivity in the fluorination of silyl enol ethers. As shown in eq 5, a trialkylated enol silyl ether moiety is thus fluorinated preferentially.1

N-Fluoropyridinium triflates (1), (2), (3) and (4) are commercially available. A series of N-fluoropyridinium tetrafluoroborates1,2,7 are also available. The triflates often give better yields because of better solubility in organic solvents.1 Since (3), (4), and (5) readily decompose in water, exposure of these reagents to moisture should be avoided.

Selective Hydrolysis.

Efficient and selective hydrolysis of dithioacetals by (2) was reported.14

Related Reagents.

Other useful electrophilic fluorinating agents which are commercially available include Xenon(II) Fluoride,15 F-+N(CH2CH2)3+N-CH2Cl.2BF4- (6),16 C5H5+N-F(C5H5N)B2F7- (7),17 and (PhSO2)2NF (8).18 XeF2 is not suitable for large scale reactions because of its high cost. The scope of fluorination by each of these reagents (6)-(8) is also covered by the N-fluoropyridinium salts (1)-(5). Acetyl Hypofluorite (MeCO2F), a useful electrophilic fluorinating agent, must be prepared in situ because of instability.19 Perchloryl Fluoride (FClO3) is a potentially explosive material.20


1. (a) Umemoto, T.; Fukami, S.; Tomizawa, G.; Harasawa, K.; Kawada, K.; Tomita, K. JACS 1990, 112, 8563. (b) Umemoto, T.; Kawada, K.; Tomita, K. TL 1986, 27, 4465.
2. (a) Umemoto, T.; Harasawa, K.; Tomizawa, G.; Kawada, K.; Tomita, K. BCJ 1991, 64, 1081. (b) Umemoto, T.; Harasawa, K.; Tomizawa, G.; Kawada, K.; Tomita, K. JFC 1991, 53, 369. (c) Umemoto, T.; Tomita, K.; Kawada, K. OS 1990, 69, 129. (d) Umemoto, T.; Tomita, K. TL 1986, 27, 3271.
3. Shimizu, I.; Ishii, H. CL 1989, 577.
4. Ihara, M.; Kai, T.; Taniguchi, N.; Fukumoto, K. JCS(P1) 1990, 2357.
5. Ihara, M.; Taniguchi, N.; Kai, T.; Satoh, K.; Fukumoto, K. JCS(P1) 1992, 221.
6. Sato, M.; Kitazawa, N.; Kaneko, C. H 1992, 33, 105.
7. Umemoto, T.; Tomizawa, G.; BCJ 1986, 59, 3625.
8. Dauben, W. G.; Greenfield, L. J. JOC 1992, 57, 1597.
9. Page, P. C. B.; Hussain, F.; Maggs, J. L.; Morgan, P.; Park, B. K. T 1990, 46, 2059.
10. Hebel, D.; Kirk, K. L. JFC 1990, 47, 179.
11. Chung, Y.; Duerr, B. F.; McKelvey, T. A.; Nanjappan, P.; Czarnik, A. W. JOC 1989, 54, 1018.
12. Bockman, T. M.; Lee, K. Y.; Kochi, J. K. JCS(P2) 1992, 1581.
13. Naruta, Y.; Tani, F.; Maruyama, K. TL 1992, 33, 1069.
14. Kiselyov, A. S.; Strekowski, L.; Semenov, V. V. T 1993, 49, 2151.
15. Recent papers; (a) Tius, M. A.; Kawakami, J. K. SL 1993, 207. (b) Della, E. W.; Head, N. J.; JOC 1992, 57, 2850.
16. (a) Banks, R. E.; Mohialdin-Khaffaf, S. N.; Lal, G. S.; Sharif, I.; Syvret, R. G. CC 1992, 595. (b) Lar, G. S. JOC 1993, 58, 2791.
17. Poss, A. J.; Van Der Puy, M.; Nalewajek, D.; Shia, G. A.; Wagner, W. J.; Frenette, R. L. JOC 1991, 56, 5962; this formula and structure is indicated to be incorrect.16a
18. (a) Differding, E.; Ofner, H. SL 1991, 187. (b) Differding, E.; Duthaler, O. R.; Krieger, A.; Ruegg, G. M.; Schmit, C. SL 1991, 395.
19. Rozen, S.; Lerman, O.; Kol, M.; Hebel, D. JOC 1985, 50, 4753 and references citied therein.
20. Takeuchi, Y.; Ogura, H.; Kanada, A.; Koizumi, T. JOC 1992, 57, 2196.

Teruo Umemoto

Daikin Industries, Ibaraki, Japan



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