Trimethylsilyl triflate glycoside synthesis

Silylation, for instance, providing 1-0-trimethylsilyl glycosides frOTi 1-0-unprotected sugars in an anomerically pure form, has been shown by Tietze and coworicers to be useful in phenyl glycoside and l,l -diacetal (see Section 1.2.5) synthesis with 0-silylated acceptors and trimethylsilyl triflate as catalyst. The diastereoselectivity was dependent on 0-protection. 

Roush WR, Briner K, Sebesta DP. Highly stereoselective synthesis of a-L-olivomycosides via trimethylsilyl triflate mediated glycosidations of l-0-acetyl-4-0-isobutyryl-2,6— dideoxy-2-iodo-3-C-methyl-a-L-mannopyranose. Synlett 1993 264-266. 

We have found that the secret to a successful synthesis of the alkenyl glycosides 64 lies in obtaining the pure -acetate 65 [47]. Condensation of the acetate 65 with the appropriate alkenol,in the presence of a small amount (5-20 mol% depending on the scale) of trimethylsilyl triflate, gave the alkenyl glycosides 64 in excellent yield. Oxidation of the alkene 64 with dimethyldioxirane, followed by deacetylation, then gave the putative enzyme inhibitors 60. 

The synthesis of urdamycinone B (182) by Toshima et al. [76] is an instructive example of the know-how that has been acquired in angucycline chemistry. They directly coupled the unprotected olivose (188) with naphthol 187 using trimethylsilyl triflate as the Lewis acid to afford the C-glycoside 189 after removal of the benzyl ethers and air oxidation in 21 % yield. The strategy essentially developed in our group was then employed in the Diels-Alder reaction of 189... 

Catalysis with protic acids has traditionally been used in Fischer glycosylations. As with the recent variations of the above procedure, Lewis acid catalysis is also valuable for dehydrative glycosylations with protected derivatives (Scheme 4.40). Trimethylsilyl triflate has been shown to promote reactions of glucuronic acid hemiacetals [420], and pyridine and TMSOTf was used for the synthesis of cw-glucosides [421]. Pyridinium / -toluenesulfonate (PPTS) was used for the synthesis of glycosides of the biologically important Kdo [422]. 

Kimura, Y, Suzuki, M, Matsumoto, T, Ahe, R, Terashima, S, Trimethylsilyl trifluoromethanesulfonate (trimethylsilyl triflate) as an excellent glycosidation reagent for anthracycline synthesis. Simple and efficient synthesis of optically pure 4-demethoxydaunoruhicin, Chem. Lett, 501 -504, 1984. 

The electrophilic addition of arylbis(arylthio)sulfonium salts to glycals in the presence of alcohols, directly provide 2-thio-(5-glycosides with good stereoselectivity [162]. Stereoselective syntheses of [5-glycosides were also obtained from the reaction of 1,2-trans acetoxysele-nides, prepared by treatment of glycals with phenylselenyl chloride and silver acetate, in the presence of trimethylsilyl triflate [163]. Combined application of this method and the trichlo-roacetimidate method (see section 3.3) was suggested for the synthesis of functionalized precursors of the olivomycin C-D-E trisaccharide [164] (Scheme 34). 

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