Halide ion catalyzed glycosidation reactions. Syntheses of .alpha.-linked disaccharides

Synthetic studies on pterin glycosides: the first synthesis of 2′-O-(α-d-glucopyranosyl)biopterin

“…Glycosylation of 23 was then examined by use of tetra-O-benzoyl-α-D-glucopyranosyl bromide (5) as a glycosyl donor in the presence of various activators. While treatment of 23 with 5 in dichloromethane at room temperature in the presence of tetrabutylammonium bromide and N-ethyldiisopropylamine 23 did not proceed, the same reaction in the presence of tin (IV) chloride 13 as an activator resulted in the formation of diol 4, instead of glycosylation, by cleavage of PMB group.…”

Electrochemical Conversion of Thioglycosides to Glycosyl Triflates

“…An increase in b-selectivity with a decrease in OTf concentration is ascribed to a decrease in solvent polarity, which disfavors the formation of SSIP (1a,13). A possibility that a decrease in -OTf concentration decelerates the in situ anomerization to the more reactive b-glycosyl tri‰ate, which yields the a-product, cannot be excluded (14). The increased b-selectivity observed in case of the benzylidene-protected 3b as compared to the benzyl-protected 3a is ascribed to the locking of the C5-C6 bond in its most electron-withdrawing trans-gauche conformation, which limits the concentration of SSIP (15).…”

An unusual glycosylation product from a partially protected fucosyl donor under silver triflate activation conditions

“…24 It has been established that activation of fucosyl donors in the presence of sterically demanding glycosyl acceptors preferentially form the alpha products via both S N 1 and S N 2 type reaction mechanisms. [25][26][27] These reactions are vital for accessing biologically important fucosides with stereocontrol of the glycosidic linkage.…”

“…The activation of glycosyl halides have been studied in detail by Lemieux and co-workers. 24 Given the synthetic novelty of the product, the apparent selectivity and the synthetic interest in one-pot glycosylation systems, we decided to investigate this methodology further to determine the scope and limitations. An optimisation study of the reaction conditions for the fucose dimerisation reaction was performed (Table 1).…”