Triethylsilyl Trifluoromethanesulfonate1


[79271-56-0]  · C7H15F3O3SSi  · Triethylsilyl Trifluoromethanesulfonate  · (MW 264.38)

(potent silylating agent;2-4 Lewis acid catalyst)

Physical Data: 85-86 °C/12 mmHg; d 1.169 g cm-3.

Solubility: readily sol hydrocarbons, dialkyl ethers, halogenated solvents. CH2Cl2 is employed most commonly. Reactions in 1,2-dichloroethane proceed faster than those in CCl4 or Et2O. Protic solvents and THF react with trialkylsilyl triflates and are therefore not suitable.

Form Supplied in: neat colorless liquid.

Preparative Methods: can be prepared by reacting Chlorotriethylsilane with Trifluoromethanesulfonic Acid followed by distillation.1

Handling, Storage, and Precautions: trialkylsilyl triflates are generally corrosive and moisture sensitive. Appropriate precautions should be taken to ensure that the reagent is handled and stored under rigorously anhydrous conditions.

Reactive Silylating Agent.

Triethylsilyl ethers are generally more stable towards hydrolysis than are trimethylsilyl ethers, and consequently the Et3Si moiety has gained increasing use as a protecting group for alcohols. However, since it is often difficult to silylate sterically hindered hydroxyl groups using Et3SiCl, Triethylsilyl Perchlorate and triethylsilyl triflate (Et3SiOTf) were introduced to overcome this problem. Although both reagents are much more potent than Et3SiCl, the triflate is considered to be safer than the perchlorate and is more convenient because it is commercially available.

Secondary and tertiary alcohols can be silylated under mild conditions using Et3SiOTf and 2,6-Lutidine or a trialkylamine as a proton scavenger (eqs 1 and 2).2-4

Silyl enol ethers can be conveniently prepared by treatment of ketones with Et3SiOTf and Triethylamine (eq 3).1,5 Similarly, esters can be converted to silyl ketene acetals; however, large amounts of the C-silylated product may also be isolated (eq 4).1,6,7 Equilibration of O- and C-silylated products may occur in the presence of catalytic amounts of Et3SiOTf.1

a-Diazo esters react with Et3SiOTf and Hünig's base (Diisopropylethylamine) to give exclusively a-silyl-a-diazo esters, which can be converted to other silylated compounds by loss of dinitrogen (eq 5).8

Nitroalkanes have been shown to give a-siloxy O-silyloximes upon reaction with two molar equivalents of the silylating agent (eq 6).9 The reaction is believed to proceed via a nitrogen-to-carbon 1,3-silyloxy rearrangement.

Linderman and Ghannam have utilized Et3SiOTf to trap the alkoxide formed from the addition of stannyl anion to aldehydes (eq 7).10 Upon treatment with excess n-Butyllithium, these adducts undergo a reverse Brook rearrangement to afford a-hydroxysilanes.

Lewis Acid Catalyst.

Jefford has reported that condensation reactions of 2-trimethylsiloxyfuran with aldehydes can be catalyzed by Et3SiOTf to give mainly the threo addition product (eq 8).11 Conversely, the erythro adduct is favored when fluoride ion is used as the catalyst.

Fraser-Reid has reported that an equimolar mixture of N-Iodosuccinimide and Et3SiOTf efficiently promotes the glycosylation of hindered glycoside donors with n-pentenyl glycoside acceptors (eq 9).12

Related Reagents.

Chlorotriethylsilane; Triethylsilyl Perchlorate; Trimethylsilyl Trifluoromethanesulfonate.

1. Emde, H.; Domsch, D.; Feger, H.; Frick, U.; Götz, A.; Hergott, H. H.; Hofmann, K.; Kober, W.; Krägeloh, K.; Oesterle, T.; Steppan, W.; West, W.; Simchen, G. S 1982, 1.
2. Fujiwara, K.; Sakai, H.; Hirama, M. JOC 1991, 56, 1688.
3. Higgins, R. H. JHC 1987, 24, 1489.
4. McCarthy, P. A.; Kageyama, M. JOC 1987, 52, 4681.
5. Danishefsky, S.; Harvey, D. F. JACS 1985, 107, 6647.
6. Emde, H.; Götz, A.; Hofmann, K.; Simchen, G. LA 1981, 1643.
7. Emde, H.; Simchen, G. LA 1983, 816.
8. (a) Maas, G.; Brückmann, R. JOC 1985, 50, 2801; (b) Brückmann, R.; Maas, G. CB 1987, 120, 635.
9. (a) Ferger, H.; Simchen, G. LA 1986, 428; (b) Feger, H.; Simchen, G. S 1981, 378.
10. (a) Linderman, R. J.; Ghannam, A. JACS 1990, 112, 2392; (b) Linderman, R. J.; Ghannam, A. JOC 1988, 53, 2878.
11. Jefford, C. W.; Jaggi, D.; Boukouvalas, J. TL 1987, 28, 4037.
12. Konradsson, P.; Udodong, U. E.; Fraser-Reid, B. TL 1990, 31, 4313.

Edward Turos

State University of New York at Buffalo, NY, USA

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