Highly β-selective glucosylations of glycosyl acceptors having a primary hydroxy group with a 6-nitro-2-benzothiazolyl α-glucoside donor 3α proceeded smoothly in the presence of a catalytic amount of trifluoromethanesulfonic acid (TfOH) in CH2Cl2 at −78 °C to afford the corresponding glycosides in high yields. With the use of 3α, β-saccharides could be obtained more dominantly than other α-glucosyl donors such as thioform- and trichloroacet-imidates or fluoride in the glucosylation under the same conditions. Similarly, highly β-selective mannosylations of glycosyl acceptors with a 6-nitro-2-benzothiazolyl α-mannoside donor 18α were carried out smoothly in the presence of a catalytic amount of tetrakis(pentafluorophenyl)boric acid H[B(C6F5)4] to afford the corresponding disaccharides in good to high yields; 18α apparently behaved as a potent donor here for the construction of β-mannoside linkage. Interestingly, in situ anomerization from 18β to 18α was observed when β-mannosyl donor 18β was treated with a catalytic amount of H[B(C6F5)4] in CH2Cl2.
高度β选择性的糖苷化反应使用6-硝基-2-
苯并噻唑基α-
葡萄糖苷供体3α,在−78 °C下,添加催化量的三
氟甲烷磺酸(TfOH)于
CH2Cl2中顺利进行,使得具有一级羟基的糖苷受体生成相应的糖苷,并获得高产率。在相同条件下使用3α时,β-糖苷的生成明显优于其他α-
葡萄糖苷供体,如
硫甲酸酯、三
氯醋
酰亚胺或
氟化物。同样地,使用6-硝基-2-
苯并噻唑基α-
甘露糖苷供体18α进行的
甘露糖苷化反应在催化量的
四氟苯基
硼酸H[B(
C6F5)4]存在下顺利进行,获得相应的二糖,产率良好至高;18α在这里明显表现为有效的供体,用于构建β-
甘露糖苷键。有趣的是,当β-
甘露糖苷供体18β与催化量的H[B( )4]在 中反应时,观察到18β向18α的原位异构化。