Rare Earth Salts Promoted Glycosidation of Glycosyl Fluorides

Abstract

A glycosidation reaction of glycosyl fluori des with free 2 acceptors has been found to be promoted effectively by using rare earth metal salts, with or without the requirement of usual Lewis acids such as ZnCI2 and Ba(CIO4)z. Moreover, a glycosidation reaction of glycosyl fluorides with trimethylsilyl ethers ha9 been found to be promoted more effectively by using a catalytic amount of rare earth metal perchlorates. 4B~O* En0

Pre-activation based stereoselective glycosylations: Stereochemical control by additives and solvent

“…Comparison of 1 H NMR spectra with literature values [33] confirmed the identity of compound 7 . 1 H NMR (500 MHz, CDCl 3 ) δ 3.36 (s, 3H, OCH 3 ), 3.44–3.47 (m, 2H), 3.51–3.71(m, 14H), 3.74 (d, 1H, J 3 = 1.5 Hz), 3.76 (d, 1H, J 3 = 2 Hz), 3.84–3.87 (m, 1H), 4.0–4.04 (m, 2H), 4.22 (dd, 1H, J 3 = 2, 11 Hz), 4.39 (d, 1H, J 3 = 8 Hz), 4.50–4.85 (m, 18H), 4.92–4.95 (m, 1H), 4.98–5.02 (m, 3H), 7.14–7.38 (m, 64H, aromatic), 7.81–7.86 (m, 6H, aromatic).…”

Lanthanide Complexes in Multifunctional Asymmetric Catalysis

“…Although this method produces the catalytic species in a high yield, an alternative method for catalyst preparation was investigated to make the catalyst more accessible, employing hydrated LnCl 3 as a widely available and much less expensive lanthanide source. As a result, an equivalently active catalyst ( 4a ) was prepared from LaCl 3 ·7H 2 O, Li 2 (binol) (2.7 mol equiv), and NaO- t -Bu (0.3 mol equiv) in THF . All the preparative methods described above are considered to generate an identical catalytic species ( 4a ).…”

Galactan synthesis in a single step via oligomerization of monosaccharides

“…We surmised that the fluoride ion derived from the activated glycosyl donor was responsible for desilylating 1 during the course of the reaction. We observed no reaction when we used a TMS-protected version of 3 (entry 2, Table 1), even though silyl ethers have been reported as competent acceptors in this reaction [19]. The use of 2,6-di- tert -butylpyridine (DTBP) as the base resulted in a single glycosylation, and no oligomerization products were obtained (entry 3, Table 1).…”

“…We prepared the TBS-protected galactosyl fluoride 1 and carried out a glycosylation with 4-pyrenebutanol ( 3 ) as the acceptor (Fig. 1), using conditions reported by Shibasaki (lanthanum perchlorate and potassium carbonate in acetonitrile) [19]. To our surprise, the reaction provided both the desired monosaccharide 4 1 a as well as significant amounts of the disaccharide 4 2 a and trisaccharide 4 3 a (entry 1, Table 1) [20].…”

“…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).…”