Catalytic Stereoselective Synthesis of Glycosides

在催化量的三氟甲磺酸锡（II）或三氟甲磺酸镱（III）的存在下，从1，3，4，6-四-O-乙酰基-2-氨基-β-D-吡喃葡萄糖苷或吡喃半乳糖苷以高产率立体选择性地合成各种2-氨基-β-D-吡喃葡萄糖苷或吡喃半乳糖苷。（2，2，2-三氯乙氧基-羰基氨基）-2-脱氧-β-D-吡喃葡萄糖和吡喃半乳糖或1，3，4，6-四-O-乙酰基-2-烯丙氧基羰基氨基-2-脱氧-β-D-吡喃葡萄糖，使用由锡（IV）产生的催化剂，从相同的糖基供体以几乎完美的立体选择性以高产率分别制备2-氨基-α-D-吡喃葡萄糖苷或吡喃半乳糖苷，在六甲基二硅氧烷和无水硫酸钙的共存下，催化量的活化剂如三氟甲磺酸锡（II），三氟甲磺酸镱，三氟甲磺酸镧或氯化锡（II）平稳地促进1-羟基糖与游离醇、富电子芳族化合物或甲硅烷基化亲核试剂之间的糖基化反应以产生各种O-，C-或N-β-糖苷以高产率立体选择性地获得，而α-核苷主要通过进一步加入高氯酸锂获得。在碳亲核试剂如富电子芳族化合物或衍生自羰基化合物的甲硅烷基烯醇醚的情况下，在存在或不存在高氯酸锂的情况下显示出完美的β-选择性。

In the presence of a catalytic amount of tin (II) trifluoromethanesulfonate or ytterbium (III) trifluoromethanesulfonate, various 2-amino-beta-D-glucopyranosides or galactopyranosides are stereoselectively synthesized in high yields from 1, 3, 4, 6-tetra-O-acetyl-2- (2, 2, 2-trichloroethoxy-carbonylamino) -2-deoxy-beta-D-glucopyranose and galactopyranose or 1, 3, 4, 6-tetra-O-acetyl-2-allyloxycarbonylamino-2-deoxy-beta-D-glucopyranose on treatment with alkyl trimethylsilyl ethers or free alcohols.Further, 2-amino-alpha-D-glucopyranosides or galactopyranosides are respectively prepared in high yields with almost perfect stereoselections from the same glycosyl donors using a catalyst generated from tin (IV) chloride and a silver salt via an anomerization step.In the coexistence of hexamethyldisiloxane and anhydrous calcium sulfate, a catalytic amount of an activator such as tin (II) trifluoromethanesulfonate, ytterbium trifluoromethanesulfonate, lanthanum trifluoromethanesulfonate or tin (II) chloride smoothly promotes the glycosylation reactions between 1-hydroxy sugars and free alcohols, electron-rich aromatic compounds or silylated uncleophiles to produce various O-, C- or N-beta-glycosides stereoselectively in high yields whereas alpha-ribosides are obtained predominantly by the further addition of lithium perchlorate. In the case of carbon nucleophiles such as electron-rich aromatic compounds or silyl enol ethers derived from carbonyl compounds, perfect beta-selectivity is shown either in the presence or absence of lithium perchlorate.