Tetra-n-butylammonium Fluoride (Supported)1


[429-41-4]  · C16H36FN  · Tetra-n-butylammonium Fluoride (Supported)  · (MW 261.53)

(can be used for most fluoride-assisted reactions;1 deprotection of silyl groups;2 catalysis of Michael addition;1 alkylation;3 desilylation;4 fluorination5)

Alternate Name: TBAF.

Form Supplied in: on alumina; on silica gel.

Handling, Storage, and Precautions: TBAF/SiO2 is nonhygroscopic and an air-stable material. Contact with skin may cause irritation.

Desilylation Reagent.

Tetra-n-butylammonium Fluoride is very hygroscopic and absorbed water can greatly effect the reactivity. TBAF/SiO2 is a nonhygroscopic fluoride ion source, which is also very effective for most fluoride-assisted reactions. Desilylations of allyl, benzyl, and heteroaryl silanes generate carbanions, which undergo nucleophilic addition to an electrophilic center.4,6 The benzothiazolyl carbanion obtained from treatment of benzothiazolylsilanes with TBAF/SiO2 or Cesium Fluoride adds to benzaldehyde to give alcohols (eq 1). When cyclohexen-2-one is used as an electrophile, the 1,4-Michael addition product is obtained in reasonable yield (eq 2). d-Valerolactone can be opened under these reaction conditions to give the corresponding keto alcohols (eq 3).

By using TBAF/SiO2 or CsF as catalysts with allylsilanes, different products from addition to cyclohexen-2-one have been obtained (eqs 4 and 5). The a-chloroallyl anion made from a-trimethylsilylallyl chloride with TBAF/SiO2 adds to benzaldehyde with little regioselectivity (eq 6).7

TBAF/SiO2 is also effective for deprotecting silyl groups. TBDMS groups of N-silylated b-sultam derivatives can be removed by TBAF/SiO2 using very mild conditions in good yields (eq 7).2

Fluoride- and Lewis acid-catalyzed intramolecular cyclization of alkylidene 1,3-dioxo compounds with an allylsilane moiety has been observed. It is possible that fluoride cleaves the allylic C-Si bond to give an allylic anion which adds to carbonyl compounds, or more likely, a hypervalent silyl anion is formed as an intermediate (eq 8).8


Activated nitro groups can be displaced by the fluoride of TBAF or TBAF/SiO2. This reaction can provide some very useful fluoroaromatic compounds with a very short synthesis. Heating 1-nitrobenzo[c]cinnoline with TBAF/SiO2 in decalin for several hours gave 1-fluorobenzo[c]cinnoline in reasonable yield (eq 9).5

Use as a Base.

TBAF/SiO2 is an effective and convenient reagent for catalyzing Michael addition, oxidation, sulfenylation, and alkylation. Nitromethane (eq 10) and PhSH (eq 11) undergo Michael addition very smoothly at rt within a few hours.1 When a large excess of reagent was used, esterification of acetic acid was achieved (eq 12).

TBAF/Al2O3 is more effective than KF/Al2O3 and CsF/Al2O3 for methylation of phenol. The reactions are usually complete within a short period of time in quantitative yields (eq 13).3

When using Ethyl Trimethylsilylacetate (ETSA) as a silylating agent and TBAF/SiO2 as a catalyst, regioselective formation of silyl enol ethers has been achieved. 2-Methylcyclohexanone is converted to two silyl enol ether isomers where the kinetic product is predominant (eq 14). Exclusive kinetic product with high (Z) selectivity has been achieved on 2-methylpentan-3-one (eq 15). These reaction conditions can also be used to silylate alcohols with longer reaction times (eq 16).

1. Clark, J. H. CC 1978, 789.
2. Müller, M.; Otto, H.-H. LA 1992, 687.
3. Ando, T.; Yamawaki, J.; Kawate, T.; Sumi, S.; Hanafusa, T. BCJ 1982, 55, 2504.
4. Ricci, A.; Fiorenza, M.; Grifagni, M. A.; Bartolini, G. TL 1982, 23, 5079.
5. Kiliç, E.; Tüzün, C. SC 1992, 22, 545.
6. Ricci, A.; Degl'Innocenti, A.; Fiorenza, M.; Taddei, M.; Spartera, M. A. TL 1982, 23, 577.
7. Julia, M.; Verpeaux, J. N.; Zahneisen, T. SL 1990, 769.
8. Tietze, L. F.; Ruther, M. CB 1990, 123, 1387.

Hui-Yin Li

Du Pont Merck Pharmaceutical Company, Wilmington, DE, USA

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