Halide ion-catalyzed

Scheme 1 1,2-tranj-glycoside synthesis by Koenigs-Knorr-type glycosidations, and 1,2-cis-glycosides by the halide ion catalyzed method. 

The advances that have led to the almost routine synthesis of tri- and tetrasaccha-rides began in the early 1970s and included a new approach to a-glycosides, the halide-ion catalyzed glycosylation [4], and the introduction of improved heavy metal catalysts such as silver trifluoromethanesulfonate (triflate) [5]. Numerous other technical and conceptual advances punctuated the intervening period and reference to these developments are to be found in the cited literature of several reviews [6—9]. 

Ito, Y, Ogawa, T, An efficient approach to stereoselective glycosylation of A-acetylneuraminic acid use of phenylselenyl group as a stereocontrolling auxiliary. Tetrahedron Lett., 28, 6221-6224, 1987. Lemieux, R U, Hendriks, K B, Stick, R V, James, K, Halide ion catalyzed glycosidation reactions. Syntheses of a-linked disaccharides, J. Am. Chem. Soc., 97, 4056-4062, 1975. 

Shingu, Y, Nishida, Y, Dohi, H, Matsuda, K, Kohayashi, K, Convenient access to halide ion-catalyzed a-glycosylation free from noxious fumes at the donor synthesis, J. Carbohydr. Chem., 21, 605-611, 2002. 

Lemieux, R. U., Hendriks, K. B., Stick, R. V., James, K. Halide ion catalyzed glycosidation reactions. Syntheses of a-linked disaccharides. 

The halide ion-catalyzed glycosidation method of Lemieux and coworkers (12-14) takes advantage of two phenomena to enhance the proportion of a-glycoside formed an increase in... 

Another very valuable principle for glycosidation reactions, introduced by Lemieux,8 is the so-called halide ion-catalyzed glycosidation reaction. In an equilibrium reaction with tetraethylammonium halide, an a-D-glycosyl halide that is more stable can be converted into the thermodynamically less stable /3-D anomer, which may be present in much lower concentrations. The latter, however, reacts... 

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