Trimethylsilyl Trifluoromethanesulfonate (TMSOTf)

Abstract

(A) Reaction with aldehydes and ketones gives quantitative yields of the trimethylsilyl enol ethers.5 Triethylamine is often used as an auxiliary base, which produces an insoluble precipitate of triethylammonium triflate in non-polar solvents.6 equation presented (B) tert-Butyl esters can easily be cleaved using TMSOTf to afford, after an aqueous work-up, the free carboxylic acid. Benzyl esters are not attacked under these conditions so selective deprotection of dicarboxylic acids can be achieved.7 Recently Nishizawa et al. reported that a prenyl (3-methylbut-2-enyl) ester is catalytically cleaved by TMSOTf to give a carboxylic acid and isoprene with high chemoselectivity and without causing epimerization of a neighboring chiral center.8 equation presented (C) A significant contribution to the methodology of TMSOTf was made by Noyori et al., who found that TMSOTf, with or without hindered tertiary amines, catalyses directed condensation of enol trimethylsilyl ethers with acetals.9 The reaction of enol silyl ethers and carboxonium triflate ion-pair intermediates occurs via acyclic transition states and exhibits moderate to high erythro-selectivity independent of the geometry (E/Z) of the enol silyl ethers. equation presented (D) TMSOTf when used in equimolar amounts wth DBU can affect the ring opening of epoxides to allylic alcohols.10 The very mild reaction conditions are applicable to cyclic substrates as well as 2,2-di, tri, and tetrasubstituted epoxides. equation presented (E) The treatment of acetals of enolisable ketones and aldehydes with TMSOTf and N,N-diisopropytethylamine gives enol ethers in high yield.11 In the case of cyclic acetals this gives a product retaining the TMS group. equation presented.