TBAF

Silyl ethers serve as preeursors of nucleophiles and liberate a nucleophilic alkoxide by desilylation with a chloride anion generated from CCI4 under the reaction conditions described before[124]. Rapid intramolecular stereoselective reaction of an alcohol with a vinyloxirane has been observed in dichloro-methane when an alkoxide is generated by desilylation of the silyl ether 340 with TBAF. The cis- and tru/u-pyranopyran systems 341 and 342 can be prepared selectively from the trans- and c/.y-epoxides 340, respectively. The reaction is applicable to the preparation of 1,2-diol systems[209]. The method is useful for the enantioselective synthesis of the AB ring fragment of gambier-toxin[210]. Similarly, tributyltin alkoxides as nucleophiles are used for the preparation of allyl alkyl ethers[211]. 

Early workers using anhydrous tetrabuCylammonium fluonde (TBAF) may have actually used mixtures of TBAF and tetrabutylammonium bifluoride It IS known that excessive drying at 77 °C in a vacuum below 2 torr (1 torr = 133 322 Pa) produces the bifluoride salt [20] TBAF can be obtained by drying commer... 

In contrast to the nature of TBAF, tetrabutylammoniuin bifluoride converts benzyl bromide to its fluoride in 100% yield and 4-chloronitrobenzene to 4 fluoronitrobenzene in 70% yield 1-Bromodecane is transformed by tetrabutyl-atnmonium bifluoride to 1-fluorodecanein 88% yield, and Tchlorododecane forms 1-fluorododecane m 83% yield In neither case are significant amounts of the elimination products formed [25]... 

Tetrabutylammonium fluoride trihydrate (Aldnch) is heated in a round-bottom flask with magnetic stirring at 40-45 C under vacuum (<0.1 mm of Hg) After several hours, the sample liquefies. Heating is continued until the sample loses 20% of its original weight (usually ca 48 h). The resulting anhydrous TBAF (singlet at -99 ppm, F NMR) contains 0 1-03 molar equivalent of water (by NMR) and ca 10% tetrabutylammonium bifluoride (a doublet at -146 ppm, (J = 123 Hz, F NMR) This oil must be used immediately. 

Although potassium fluoride is the preferred nucleophile, tetiabutylam-monium fluoride (TBAF) is successfully used for aromatic fluorodenitration o Fluoronitrobenzene can be obtained in quantitative yield from o-dinitrobenzene in tetra hydrofuran at 25 °C after 1 5 h 7]... 

This group is stable to strong acids and bases, TMSI, Pd-C/H2, DDQ, TBAF, and LAH at low temperatures and thus has the potential to participate in a large number of orthogonal sets/... 

A, A -Bis-TBDMSdimethylhydantoin, cat. TBAF. Primary alcohols are selectively protected. 

CH3C(0TBDMS)=NTBDMS, TBAF, NMP (A-methylpyrrolidinone), 76-99% yield. °... 

TBDMSH, THF, TBAF, it, 1 h, 97% yield. Other silanes react similarly. ... 

The following tables give a comparison of the stability of various silyl ethers to acid, base, and TBAF. The reported half-lives vary as a function of environment and acid or base concentration, but they help define the relative stabilities of these silyl groups. 

Protective BF3 Et20 Group CH2CI2, rt TBAF THF,rt BF3 Et20 Aldehyde, CHjClj... 

Developed as a carboxyl protective group for peptide synthesis because of its stability to hydrogenolysis and acidic conditions, the acetol (hydroxy acetone) ester is prepared by DCC coupling (68-92% yield) of the acid with acetol. It is cleaved with TBAF in THF. ... 

TBAF, THF or DMSO or DMF, 72-98% yield. 4-Nitrobenzyl and trichloroethyl esters of amino acids are also cleaved. 

Photolysis, 350 nm, CH3CN, H2O. The by-product from the reaction is 2-phenyl-benzo[ ]furan. Cleavage with TBAF and PhCH2SH has been demonstrated (70-94% yield). The related 3,5-dimethoxybenzoin analogue is cleaved with a rate constant of >10 sec Photolytic cleavage occurs by heterolytic bond dissociation. ... 

TBAF, TsOH, THF, 20°. Other conditions in this sensitive ivermectin analogue led to decomposition. ... 

TBAF, DMF/THF, 64-100% yield. Cleavage occurs in the presence of TMSE and benzyl esters and acetates. ... 

The Phacm group is stable to the following conditions DIEA-CH2CI2, TFA-CH2CI2, piperidine-DMF, 0.1 M TBAF-DMF, and DBU-DMF for 24 h at It to HF-anisole or / -cresol (9 1) at 0° for 1 h and to TFA-scavengers (phenol, HSCH2CH2SH, p-cresol, anisole) for 2 h at 25°. It is partially stable (>80%) to TFMSA-TFA-/ -cresol for 2 h at 25°. These stability characteristics make the group compatible with BOC- or Fmoc-based peptide synthesis. ... 

The very similar benzenesulfonamide is cleaved with TBAF (THF, reflux, 38-100% yield)." ... 

Bu4N F, ethylenediamine (ethylenediamine was used as a formaldehyde scavenger), 45-98% yield. Neat TBAF under vacuum has been used (90% yield). ... 

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