[429-41-4] · C16H36FN · Tetra-n-butylammonium Fluoride (Supported) · (MW 261.53)
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.
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
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).
Du Pont Merck Pharmaceutical Company, Wilmington, DE, USA