Triethylsilane-Trifluoromethanesulfonic

Alkenes with a 1,1-disubstitution pattern form tertiary carbocations upon treatment with a Brpnsted acid. Consequently, such compounds are often easily reduced (Eq. 72). An example of this is the formation of 2-methylpentane in 93% yield after only 5 minutes when a dichloromethane solution of 2-methyl-1-pentene and 1.4 equivalents of triethylsilane is treated with 1.4 equivalents of trifluoromethanesulfonic acid at —75°.216 Similar treatment of 2,3-dimethyl-l-butene gives a 96% yield of 2,3-dimethylbutane.216... 

In a useful variant of the classical methylation procedure for linkage analysis in the structural determination of oligo- and poly-sacccharides, the fully methylated oligomer is treated with triethylsilane and boron trifluoride etherate or triethylsilane and trimethylsilyl trifluoromethanesulfonate. This procedure produces partially methylated anhydroalditols. These are acetylated and analyzed by GLC-MS.222 223 This reductive-cleavage method makes possible simultaneous determination of identity, ratio, linkage position, and especially the ring size for each monosaccharide component. 

The combination of triethylsilane and trifluoromethanesulfonic acid reduces aryl ketones to the methylene derivative61 (equation 53). 

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