1-Thioglycosides reactions

Radical scission of an 5-benzyl derivative with tributylstannane initiated by azo-bis(isobutyronitrile) (AIBN) in refluxing benzene generates a tributylstannyl thiolate that can be used directly in thioglycosidation reactions as shown in Scheme 5.11.2812[Pg.367]

Thioglycosides can be activated for gfycosylation reactions with sulfur electrophiles, e.g., with dimethyl(methylthio)sulfonium triflate or with methanesulfenyi bromide and silver(l +) to form reactive sulfonium intermediates (F. Dasgupta, 1988). 

Fully acetylated hexopyranoses react with thiols in the presence of Lewis acids, such as BF3-Et20.32,33 The reaction is faster with 1,2-trans acetates than with the corresponding 1,2-cij ones and 1,2-trans products predominate. Alkyl, alkenyl, and aryl thioglycosides are produced by this method. Variations on this method include the use of trimethylsilyl34 or stannyl derivatives35 of the thiols. 

This preparation, specifically of acylated aryl thioglycosides, is carried out by reaction of, for instance, a 2,3,4,6-tetra-O-acety 1-1 -thio-P-D-glucopyranose with a di-azonium salt, followed by thermal decomposition of the intermediate diazo product. 

Acylated glycosyl thiocyanates are made by treatment of acylated glycopyranosyl halides with potassium thiocyanate.30 Reaction at —40° with a Grignard reagent affords alkyl or aryl 1-thioglycosides.54... 

TVansfer of the Armed-Disarmed Concept to Thioglycoside Glycosylation Reactions... 

Although the aim of this chapter is specifically to survey the use of thioglycosides in glycosylation reactions, the presentation is incomplete without some information concerning glycosyl sulfoxides and selenoglycosides in glycosylation... 

I am deeply indebted to all of my present and past co-workers who have participated in the unfolding development and use of thioglycosides in glycosylation reactions. 

Scheme 1.6 Test reaction with C2-S5mimetric bis(thioglycosides) ligands.

Scheme 1.19 Test reaction with phosphinite thioglycoside ligands.

B. Mukhopadhyay, B. Collet, and R. A. Field, Glycosylation reactions with disarmed thioglycoside donors promoted by /V-iodosuccinimide and HC104-silica, Tetrahedron Lett., 46 (2005) 5923-5925. 

The oxidation of the a-amino acids has not been completely studied, but it appears to be slow in most cases.8-9 The organic sulfide linkage is oxidized by periodate to a sulfone, with the concomitant liberation of iodine,48 but the oxidation of a 1-deoxy-l-thioglycoside, without occurrence of this side reaction, has been carried out at least once (in very dilute solution).44... 

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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