Thioglycoside trans

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. 

In this classic41 and general method, an acylated glycosyl halide reacts with a thiolate anion to produce a 1-thioglycoside, usually with 1,2-trans configuration. With alkyl thiolates, re-acylation is normally required following this treatment. 

M. Blanc-Muesser, J. Defaye, and H. Driguez, Stereoselective thioglycoside syntheses. Part 4. A new approach to 1,4-linked-thio-disaccharides and synthesis of thiomaltose, J. Chem. Soc., Perkin Trans. 1, (1982) 15-18. 

Lonn, H, Glycosylation using a thioglycoside and methyl trifluoromethanesulfonate — a new and efficient method for cis and trans glycoside formation, J. Carbohydr. Chem., 6, 301-306, 1987. 

Fugedi, P, Garegg, P J, A novel promoter for the efficient constmction of, 2-trans hnkages in glycoside synthesis, using thioglycosides as glycosyl donors, Carbohydr. Res., 149, C9-C12, 1986. 

Veeneman, G H, van Leeuwen, S H, van Boom, J H, lodonium ion promoted reactions at the anomeric centre. II. An efficient thioglycoside mediated approach toward the formation of 1,2-trans linked glycosides and glycosidic esters, Tetrahedron Lett, 31, 1331-1334, 1990. 

An anomeric acetate is efficiently displaced by a thiol under the influence of an acidic catalyst, and this is probably presently the most used and efficient way to produce thioglycosides of simple mercaptans, especially on a large scale. The standard procedure is to react a peracetylated aldose dissolved in dichloromethane with a slight excess of thiol using a hard Lewis acid as promoter, which generally gives a high yield of mainly the 1,2-trans product ( Scheme i) [11]. 

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