Glycosides thioglycoside

S-Glycosides. Thioglycosides can be prepared from glycosyl bromides by reaction with /3-trimethylsilyIethyl sulfides in the presence of AgBp4. The silver salt provides Ag to assist ionization of the halogen, and also a F to initiate removal of the silylethyl group of the intermediately formed glycosylsulfonium salts. 

SCHEME 13. Synthesis of the trimanoside 59 by glycosidation of a thioglycoside or a trichloroacetimi-date with a diol acceptor in the presence of HC104—Si02. 

Glycosylation of thioglycosides.1 1-Thioglycosides when activated with 1.5 equiv. of C,H,SeOTf, prepared in situ from QH SeCl and AgOTf, react at 0° to -40° with alcohols to form glycosides in 60-95% yield. The reaction is generally p-selective. 

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