Methyl trifluorosulfonates

The first article on the desilylative route to azomethine ylids appeared in 1979.385 It deals with the action of methyl trifluorosulfonate on iV-(trimethylsilylmethyl)benzylide-nimine to form the corresponding iminium salt which reacts with DMAD in the presence of cesium fluoride to yield corresponding A3-pyrroline. 

Under certain conditions, amides can add directly to alkenes to form N-alkylated amides. 3-Pentenamide was cyclized to 5-methyl-2-pyrrolidinone by treatment with trifluorosulfonic acid. Acylbydrazine derivatives also cyclized in the presence of hypervalent iodine reagents to give lactams. When a carbamate was treated with Bu3SnH, and AIBN, addition to an alkene led to a bicyclic lactam. 

The copper(I) trifluorosulfonate catalyzed photoreaction of cycloheptene (38a) leads to the dimer 95 (114c). Formation of the latter was taken as support for the generation of frans-cycloheptene (39a) as an intermediate. However, isomerization of free (ran,s-cycloheptene (39a) seems to be faster than its cyclodimerization. 7 ran.s-cycloheptene (39a), obtained by photoreaction with methyl benzoate as sensitizer, isomerizes to ds-cycloheptene (38a) at 0°C (114b) but reacts at low temperature with acidified methanol to form 96 or with diazomethane to form 97 (114a). The stereochemistry of the pyrazoline 97 is trans, in accord with the stereospecific addition to trans-cycloheptene (39a). 

Reductive Etherifications and Acetal Reductions. Additional applications of triethylsilane in the reduction of C-0 bonds also continue to surface. The Kusanov-Pames dehydrative reduction of hemiacetals and acetals with trifluorosulfonic acid/EtsSiH has proven especially valuable. Under such conditions, 4,6-O-benzyli-dene acetal glucose derivatives can be asymmetrically deprotected to 6-0-benzyl-4-hydroxy derivatives (eq 28) and thioketone derivatives can be converted to syn-2,3-bisaryl (or heteroaryl) di-hydrobenzoxanthins with excellent stereo- and chemoselectivity (eq 29). Triethylsilane is also useful in a number of related acetal reductions, including those used for the formation of C-glycosides. For example, EtsSiH reductively opens 1,3-dioxolan-4-ones to 2-alkoxy carboxylic acids when catalyzed by HCU. Furthermore, functionalized tetrahydrofurans are generated in good yield from 1,2-0-isopropylidenefuranose derivatives with boron trifluoride etherate and EtsSiH (eq 30). These same conditions lead to 1,4- or 1,5-anhydroalditols when applied to methyl furanosides or pyranosides. ... 

Additionally, as pointed out earlier (Chapter 7, Section D7) with regard to vinyl halides, the Stille vide supra) reaction affords substitution of the leaving group by a carbon nucleophile at the site of unsaturation. Thus, as shown in the Equation 8.26, when the enol trifluorosulfonate (trillate, -OSO2CF3, -OTf) of 4-tert-butylcy-clohexanone (Chapter 9) is treated with tri-n-butylphenylstannane in the presence of a palladium catalyst (tris(dibenzylideneacetone)palladium, Pd2(dba)3) in a polar aprotic solvent (l-methyl-2-pyrrolidinone, A-methylpyrrolidinone [NMP]), substitution is readily affected. 

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