Trimethylsilyl Trifluoromethanesulfonate silylation

Trimethylsilyl trifluoromethanesulfonate. This is an extremely powerful silylating agent, but probably is more useful for its many other applications in synthetic chemistry... 

Trimethylsilyl trifluoromethanesulfonate (trimethylsilyl triflate) is the most synthetically useful representative of the family of trialkylsilyl perfluoroalkane-sulfonates (for a review, see reference 101) This reagent is commercially available or can be prepared easily by the reaction of chlorotrimethylsilane and triflic acid [101] It has wide application in organic synthesis as an excellent silylating reagent... 

The reaction of 5-methylene-l,3-dioxepanes 386 with trimethylsilyl trifluoromethanesulfonate in the presence of base forms cyclic silyl enol ethers 387 (Scheme 90) <2000TL2171>. 

A solution of 0.125 g (1 mmol) of 2-(2-cyclopentenyl)acetamide and 0.22 (2.2 mmol) of Et3N in 20 mL of dry pentane at 0CC is treated with 0.488 g (2.2 mmol) of trimethylsilyl trifluoromethanesulfonate and stirred for 30 min at 23 t C. The supernatant, which contains iV, -bis-silylated amide, is transferred to a Second dry flask under an Ar atmosphere. The residue is rinsed with additional pentane, which is combined with the supernatant in the second flask, and the pentane is carefully removed. Then 20 mL of THF are added, the solution is cooled to 0CC and 0.556 g (2.2 mmol) of I2 in 20 mL of THF are added in one portion. After 10 min, the solution is quenched with aq Na2S203 and extracted with EtOAc. After drying and removal of the solvent, the residue is purified by chromatography (silica gel, (Et30/ petroleum ether) yield 86% mp 138-139 "C. 

R. Noyori developed a procedure that avoids migration of the double bond during acetalization of a, 3-unsaturated ketones (enones)A Treatment of the enone with the silylated diol l,2-bis[(trimethylsilyl)oxy]ethane in the presence of a catalytic amount of trimethylsilyl trifluoromethanesulfonate (TMSOTf ) affords the acetal without double bond migration (kinetic control). The stability of the Me3Si-0-SiMe3 formed (instead of HjO) drives the reaction to completion. Modifications of Noyori s procedure in which preparation of the silylated diol is circumvented have been reported. ... 

Several different methods have been employed for the preparation of diazo(trimethylsilyl)meth-ane (1). At present, the best synthetic method seems to be the diazo transfer reaction between diphenylphosphoryl azide and (trimethylsilyl)methylmagnesium chloride.However, the product often contains (chloromethyl)trimethylsilane and hexamethyldisiloxane as impurities. This method can also be employed for the synthesis of diazo(triethylsilyl)methane and diazo(di-ethylmethylsilyl)methane. The diazo transfer reaction can also be carried out with (trimethyl-silyl)methyllithium and tosyl azide. Other methods are the silylation of diazomethane with (trimethylsilyl)trifluoromethanesulfonate or chloro(trimethyl)silane and the base-induced cleavage of A-nitroso-A-[(trimethylsilyl)methyl]urea or the related carbamate or acet-amide.2° =... 

Polymer-bound reagents for silylation have been reported. Murata and Noyori treated Nation, a perfluorinated resin-sulfonic acid, with trimethylsilyl chloride to afford a polymer-bound trimethylsilyl ester that functions as a polymer-bound equivalent of trimethylsilyl trifluoromethanesulfonate, converting alcohols, eth-anethiol and diethylamine into the corresponding silylated compounds in high yields (Scheme 6.16) [70]. Acetic acid could also be silylated, albeit with moderate conversion. The corresponding polystyrene-bound reagent is commercially available. 

Aldol-type condensation of enol silyl ethers and acetals or orthoesters can be accontplished by the use of trimethylsilyl trifluoromethanesulfonate (TMSOTf). In these reactions, TMSOTf acts as a true catalyst and is required in 1-S ntol %. The reactions show interesting chemoselectivity in that acetals are highly reactive receptors of enol silyl ethers but the parent aldehydes and ketones do not react under these conditions (Scheme 37). Similarly, trityl perchlorate is found to be an efficient catalyst to promote the reaction between enol silyl ethers and acetals. 

Synthesis of nucleosides. Reaction of shylated heterocycles with a protected 1-0-acyl or 1-0-alkyl sugar in 1,2-dichloroethane with either trimethylsilyl perchlorate or trimethylsilyl trifluoromethanesulfonate, (013)3810802-CF3, as catalyst gives nucleosides in high yield. The reaction is formulated for the reaction of silylated uracil (1) with l-0-acetyl-2,3,5-tri-0-benzoyl- 3-D-ribofuranose (2) either at 22 for a prolonged period or for 4 hr. at reflux temperature. The function of the catalyst is to convert the sugar into the glycosyl... 

Transglycosylation of silylated 3 -azido-3 -deoxythymidines with silylated N -octanoyladenine [33], iV -palmitoylguanine [33] and benzimidazole [40] in acetonitrile and, in the presence of trimethylsilyl trifluoromethanesulfonate, afforded a mixture of the a and P anomers of the corresponding nucleosides of adenine, guanine and benzimidazole. 

The reaction with acetals does not always need the acetal itself to be synthesized it can be made in the same flask by mixing the allylsilane, the aldehyde, the silyl ether of the alcohol, and a catalytic amount of an acid such as diphenylboryl trifluoro-methanesulfonate, trimethylsilyl trifluoromethanesulfonate, or fluorosulfuric acid. ... 

SILYLATION Bis(trimethylsilyl)urea. t-Butyldimethylchlorosilane. t-Butyldimethylsilyl trifluoromethanesulfonate. Chlorotrimethylsilane. Dimethyl(2,4,6-tri-f-butylphenoxy)chlorosilane. Ethyl trimethylsilylacctate. Ketene t-butyldimethylsilyl methyl acetal. N-Methyl-N-(/-... 

As homogeneous acid catalysts, trifluoromethanesulfonic acid (CF3SO3H) and its silylated form, trimethylsilyl triflate (CF3S03SiMc3), were chosen for comparison of the acid catalysis between heterogeneous and homogeneous acids. The reaction of 14a with 15a or 15b proceeded smoothly even at low temperature in the presence of CF3S03SiMe3 as well as CF3SO3H (Table XIV, Entries 8, 10 Table XV, Entries 12, 13, 15). The catalytic behavior of... 

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