Activation trimethylsilyl trifluoromethanesulfonate

High enantioselectivities may be reached using the kinetic controlled Michael addition of achiral tin enolates, prepared in situ, to a,/i-unsaturated carbonyl compounds catalyzed by a chiral amine. The presence of trimethylsilyl trifluoromethanesulfonate as an activator is required in these reactions236. Some typical results, using stoichiometric amounts of chiral amine and various enolates are given below. In the case of the l-(melhylthio)-l-[(trimethylsilyl)thio]ethene it is proposed that metal exchange between the tin(II) trifluoromethanesulfonate and the ketene acetal occurs prior to the 1,4-addition237,395. 

A typical coupling cycle (Scheme 2) for glycosyl trich1oroacet.imidat.es is outlined in Table I. A polystyrene support, functionalized with an olefinic linker, is loaded into a reaction vessel in the instrument.1617 The activating reagent (trimethylsilyl trifluoromethanesulfonate (TMSOTf /... 

Reaction of benzaldehyde and its 4-nitro derivative with the enantiopure diene 796 in DCM and in presence of trimethylsilyl trifluoromethanesulfonate (TMSOTf) afforded the condensed enantiopure oxathiocanes 777 and 778 (50% yield). The reaction path began with the ionic addition of the diene 796 onto the carbon atom of the aldehyde function in 797a,b activated by trimethylsilyl cation attack to the carbonyl oxygen. 

Recent improvements in the standard synthetic procedure using haloacetates have featured the use of trialkyi phosphites and activated acetates in the presence of trimethylsilyl trifluoromethanesulfonate (TMSOTf) as activating reagent. " This reaction has proved to be of great value in constructing complex sugar phosphonates. For example, in the presence of TMSOTf, the Michaelis-Arbuzov reaction between protected ketose acetates and triethyl phosphite takes place in ( 1 FC F at room temperature to produce, after deprotection, the expected diethyl l-(methoxycarbonyl)alkyl-phosphonates in high yields. -" ... 

Tetrazoles are usually prepared by the reaction of an azide with a nitrile, or an activated amide tri-n-butyltin azide and trimethylsilyl azide are more convenient and safer reagents than azide anion is some cases. The second example shown illustrates the use of a cyanoethyl group as a removable protecting group for amide nitrogen. Other variations on this method from nitriles include the use of triethylammonium chloride (instead of ammonium chloride) to avoid the possible sublimation of potentially explosive azides, and the use of micelles as reaction media. Amides can be activated with trifluoromethanesulfonic anhydride, or via formation of the thioamide, or by the use of triphenylphosphine with diethyl azodicarboxylate the equivalent imidochloride will react under phase transfer conditions. ... 

We have also tested the stereodirecting effect of the benzophenone moiety in a-glucosylation, using thioglucosides as donors that were activated with N-iodosuccinimide and trimethylsilyl trifluoromethanesulfonate. In Table II, the data show excellent yields of the desired disaccharides, combined with high a-stereoselectivity. Interestingly, when the donors 10 and 12 were used in a less than equimolar amount, the a-selectivity increased (items 1, 3) relative to the experiments having the donor 10 and acceptors 11 and 14 in a 3 1 molar ratio (items 2, 5). The benzophenone ketal-protected donors 10 and 12 (items 1, 3)... 

In the presence of an amino acid-derived boronate (e.g. 2) or a diamine-tin(II), complex,as Lewis acids, optically active aldol products are obtained in good yields (eq 8). In the addition of KSAs to iminies, a diphosphonium ditriflate (eq 9) or an acidic montmorillonite clay has been claimed to give better results than the originally reported Lewis acids (titanium(IV) chloride and trimethylsilyl trifluoromethanesulfonate ). The products of this reaction are valuable intermediates for the synthesis of p-lactams. Two excellent reviews covering this area have recently appeared. ... 

Kaw cki used optically active sulfonamide 234 to perform an asymmetric aza-Diels-Alder reaction with Rawal diene 235. " The reaction was performed in the presence of a Lewis acid, trimethylsilyl trifluoromethanesulfonate (TMSOTf), to obtain dihydropyridinone 236 as the product with high enantiomeric excess (Scheme 40.51). 

Other base-modifications. Hassan and co-workers reported a novel synthesis of pyrazolone nucleosides and their antimicrobial activities. Mata and his group reported the stereoselective AAglycosylation of 2-deo3ythioribosides. This facile synthesis (shown in Scheme 3) involves N-2-deo3yribosylation of a modified nucleobase with 2-deoiythioriboside in the presence of bis-(trimethylsilyl)acetamide, AT-iodosuccinimide and trimethylsilyl trifluoromethanesulfonate to afford stereoselective nucleosides (19) in excellent yields. 

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