A New Glycosidation Procedure Utilizing Rare Earth Salts and Glycosyl Fluorides, with or without the Requirement of Lewis Acids

Chemical synthesis and functionalization of clickable glycosylphosphatidylinositol anchors

“…As shown, when performing this reaction with donor 30 at room temperature using any activation reagent and stirring for days, either no reaction or only trace amounts of the desired product were observed. Heating the reaction to reflux in Et 2 O completely consumed the donor, although only moderate yields of desired pseudodisaccharide 31 were obtained with Cp 2 HfCl 2 /AgOTf 48 (22%) or Yb(OTf) 3 /CaCO 3 49 (40%) as promoters (entries 2-3). The remainder of the mass balance was attributed to a side reaction resulting from the increased temperature required for donor activation (Fig.…”

A Catalytic and Stereoselective Glycosylation withβ-Glycosyl Fluorides

“…Preparative methods involving glycosyl fluorides combined with suitable activators were widely studied by many research groups [5]. Activators such as SiF 4 [6], Me 3 SiOTf [6], TiF 4 [7], BF 3Ó Et 2 [8] 3 [12], and La(ClO 4 ) 3´n H 2 O [13] promoted the glycosylation of various glycosyl acceptors and allowed the synthesis of many complex oligosac-charide chains. Several examples involving activation of the glycosyl fluoride by a stoichiometric amount of the activator were studied; in comparison, only a few studies concerning catalytic glycosylation with glycosyl fluorides were reported [6] [8] [13].…”

Galactan synthesis in a single step via oligomerization of monosaccharides

“…The use of the more Lewis acidic [22] Yb(OTf) 3 resulted in a reduction in both overall yield and in the degree of oligomerization (Table 1, entry 6). Shibasaki has previously reported improvements in both yield and reaction time using ZnCl 2 as an additive [19,23], but its inclusion in the reaction did not result in any significant changes (Table 1, entry 7). Finally, the use of Hf(OTf) 4 as a promoter [24] was completely ineffective and no glycosylation was observed (Table 1, entry 8).…”