Tris dimethylamino sulfonium Difluorotrimethylsilicate

Form Supplied in R = Me, white crystalline sohd, 90% pure major impurity is tris(dimethylamino)suIfonium hifluoride [(Me2N)3S+ HF2-]. 

Preparative Methods the methyl derivative is prepared hy the reaction of dimethylaminotrimethylsilane and sulfur tetra-fluoride at —70°C to rt in ether the precipitated solid is filtered off. The ethyl derivative is best prepared hy the reaction of lV,lV-diethylaminosulfur trifluoride (DAST) and diethylaminotrimethylsilane.  

Handling, Storage, and Precautions because of the extreme hygroscopic nature of this compound, it is best handled in a dry box or a polyethylene glove bag filled with high purity nitrogen. Use in a fume hood. 

William J. Middleton Victor J. Tortorelli Ursinus College, Collegeville, PA, USA 

TASF is a source of organic soluble fluoride ion with a bulky noncoordinating counter ion (eq 1).  

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Tris(dimethylamino)sulfonium difluorotrimethylsilicate (TSAF), THF, 0°, 5 h, 64% yield. A TES and two phenolic TIPS groups were also cleaved. 

Tris(dimethylamino)sulfonium Difluorotrimethylsilicate (TASF, 1) Typical Procedure 74... 

However, in the presence of a catalytic amount of tris(dimethylamino)sulfonium difluorotrimethylsilicate ( TASF ), pivaldehyde imine yields the N-unsubstituted adduct, whereas acetone imine leads to the corresponding BSMA amides accompanied with the addition product of THF to DMAD. Formation of amides might be explained by the loss of HC1 from the iminium resulting from condensation of acyl chloride with imine, leading to a vinyl amide which is easily hydrolyzed. No explanation was presented for the formation of the THF adduct.241... 

Attempts to remove the two TBS ethers in 52 1 [Scheme 4.52] resulted in formation of the elimination product 52 2 in 50% yield. By contrast, treatment of the same substrate with tris(dimethylamino)sulfonium difluorotrimethylsilicate [TAS-F, (Me2N)](S+Me3SiF2 ] afforded the desired hemiacetal 523 in 75% yield. Using a range of complex substrates, Roush and co-workers showed that TAS-F in DMF at room temperature is generally useful for the deprotection of TBS, TES, and TBDPS ethers as well as 2- trimethyIsilyl)ethyl carbamates and 2-(tri-methylsilyl)ethyl esters in base-sensitive substrates.82 Selective deprotections may also be achieved as exemplified by the removal of the primary TBDPS group from 52.4 in the presence of a secondary TBS ether. It is not yet possible to remove a secondary TES ether in the presence of secondary TBS ether or a primary TBS ether in the presence of a secondary TBDPS ether. TAS-F is commercially available as an anhydrous solid and it can be prepared by reaction of... 

Tris(dimethylamino)sulfonium difluorotrimethylsilicate [TASF(Me)] has found very little use in the ring-opening fluorination of epoxides. From the experimental conditions that were successfully applied in one ease (THF. reflux. 4d). it can be concluded that TASF(Mc) is not very reactive towards epoxides. 

When activated by anionic catalysts [potassium fluoride, cesium fluoride, tctraalkylammonium fluorides, tris(dimethylamino)sulfonium difluorotrimethylsilicate, phosphazenium, hexa-methylpiperidinium and cobaltoccnium fluorides, tetrabuiylammonium difluoro(triphenyl-silyl)silicatc. the complex tetrakis(dimethylamino)ethene/pcrfluoropropene, ammonium (and phosphonium) periluorocyclobuianc ylides], trimethyl(perfluoroalkyl)silanes will generate C-Rp bonds from carbon-halogen bonds. 

Trimethyl(trifluoromethyl)silanc is easily fluorodesilylated by tris(dimethylamino)sulfonium difluorotrimethylsilicate [TASF(Me)], tetrabutylammonium fluoride, or tris(diethylamino) (methylamino)phosphonium hydrogen difluoride and, if arenesulfonyl fluorides are used to trap the trifluoromethyl anion, trifluoromethyl sulfones arc formed in high yield. Trisfdiethyl-amino)(methylamino)phosphonium phenolate is also an effective catalyst for this reaction, but TASF(Me) is favored as it can achieve the quantitative transformation of ArS02F into aryl trifluoromethyl sulfones.115-117... 

SMDA sodium dihydrobis(2-methoxyethoxy)aluminate TASF tri(dimethylamino)-sulfonium difluorotrimethylsilicate TFAA trifluoroacetic anhydride... 

A variety of fluoride ion sources have been used in an effort to improve product yields in deoxyfluoro sugar synthesis. These salts include cesium fluoride, tetrabutylammonium fluoride, and tetrabutylammonium difluoride (BU4NHF2) [37,38]. And currently, the most successful fluoride source is tri(dimethylamino)-sulfonium difluorotrimethylsilicate (TASF), which is soluble in many organic solvents and produces an anhydrous fluoride ion [39]. 

TASF tris(dimethylamino)sulfonium difluorotrimethylsilicate TMSCN trimethylsilyl cyanide... 

Tris(dimethylamino)sulfonium difluorotrimethylsilicate (TAS-F), DMF, >76% yield. This method was effective where TBAF caused elimination of a 3-acetoxyester. ... 

The final step in a recent synthesis of the antifungal agent Papulacandin D involved deprotection of five O-silyl groups including a di-ferf-butylsilylene group, a triethylsilyl ether and two phenolic tri-isopropylsilyl ethers [Scheme 3.115]. Acid conditions were precluded by the acid lability of the side chain. Use of TBAF was complicated by problems in separating the product from tetrabuty-lammonium salts. The desired global deprotection was accomplished with tris-(dimethylamino)sulfonium difluorotrimethylsilicate (TAS-F). 

TASF Tris(dimethylamino)sulfonium difluorotrimethylsilicate T eoc 2-(Trimethylsilyl)ethoxycarbonyl... 

Because tris(dimethylamino)sulfonium difluorotrimethylsilicate is very hygroscopic, it is best transferred in a dry atmosphere of nitrogen or argon (dry box or glove bag). 

The authors found that phenylsilane/anhydrous cesium fluoride was the preferred reagent combination for this reaction sequence. Other silanes were effective, whereas tributyltin hydride afforded low yields (< 20%) and only in the presence of a fluoride source. Tris(dimethylamino)sulfonium difluorotrimethylsilicate (TASF) and tetrabutylammonium fluoride (TBAF) destroyed the silane. Acetonitrile was the best solvent among the ethers and halogenated solvents evaluated." In a subsequent study " the authors converted a 2,5-disubstimted oxazole 15 (Rl = R3 = CH3, CeHs, or OC2H5, R2 = H) to the oxazolium salt followed by treatment with trimethylsilylcyanide (Scheme 1.290). The resulting intermediate 2-cyano-4-oxazoline 1107 spontaneously ring opened to the stabilized azomethine... 

A nonionic way of polymerizing MVK is the group transfer polymerization (GTP) with dimethylketene methyl trimethylsilyl acetal as intiator and the MegSiFa anion delivered from tris(dimethylamino)sulfonium difluorotrimethylsilicate (TASF2SiMe3)... 

Palladium-Catalyzed Coupling Reaction with Organo-halides. In the presence of tetrakis(triphenylphosphine)-palladium(O), vinyl halides (12) are converted to the corresponding vinylsilanes (13) with the aid of MegSi2 and tris-(dimethylamino)sulfonium difluorotrimethylsilicate (TASF) in 53-92% yields with high chemoselectivity and stereospecificity (eq 6). Similarly, aryl-, benzyl-, and allylsilanes are obtained from the corresponding halides in 57-100, 8 8, and 52-93% yield, respectively. Allyl esters also are transformed by Pd-catalyzed reaction of Me6Si2 into allylsilanes. ... 

Reactions with Carbonyl Compounds. TMSCF3 reacts with aldehydes in the presence of a catalytic amount of tetra-w-butylammonium fluoride (TBAF) in THF to form the corresponding trifluoromethylated carbinols in good to excellent yields following aqueous hydrolysis of the silyl ethers (eq 3) 2.3.6,10 The reaction also works very well for ketones under the same conditions, with the exception of extremely hindered ones such as l,7,7-trimethylbicyclo[2.2.1]heptan-2-one, di-l-adamantyl ketone, and fenchone. The reaction has been characterized as a fluorideinduced autocatalytic reaction. Other initiators such as tris(dimethylamino)sulfonium difluorotrimethylsilicate (TASF), potassium fluoride, Ph3SnF2, andRO can also be used for these reactions. ForthereactionsofTMSCFs and perfluorinated ketones and pentafluorobenzaldehyde, excess of KF is needed. 

Deprotection Conditions. While cesium fluoride (CsF) in DMF and tetrabutylammonium fluoride (TBAF) in THF are the most common reaction conditions for deprotection, other reagents include hydrofluoric acid for deprotection of depsipeptides and tris(dimethylamino)sulfonium difluorotrimethylsilicate... 

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