In the presence of hexamethyldisiloxane and anhydrous calcium sulfate, a catalytic amount of 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 nucleophiles to produce various O -, C - or N - glycosides stereoselectively in high yields. In the case of oxygen or nitrogen nucleophiles, β-ribosides are formed, except that α-ribosides are obtained predominantly in the presence of lithium perchlorate. In the case of carbon nucleophiles such as electron-rich aromatic compounds or silyl enol ethers derived from carbonyl compounds, perfect β-selectivity is shown either in the the presence or absence of lithium perchlorate. Further, pyranosyl substrates such as glucose or galactose afford the corresponding α-anomers, except with electron-rich aromatic compounds.
在六甲基二
硅氧烷和无
水硫酸钙的存在下,以催化量的活化剂(如二
氟三氟甲磺酸锡、三
氟三氟甲磺酸镱、三
氟三氟甲磺酸镧或二
氯化锡)顺利促进1-羟基糖与自由醇、富电子芳香化合物或
硅化亲核试剂之间的糖基化反应,高产率地选择性合成各种O-、C-或N-糖苷。对于氧或氮亲核试剂,主要生成β-
核糖苷,但在
高氯酸锂存在下主要得到α-
核糖苷。对于碳亲核试剂(如富电子芳香化合物或来自羰基化合物的
硅基烯醇醚),无论在
高氯酸锂存在或不存在下,均表现出完全的β-选择性。此外,
吡喃糖基底物(如
葡萄糖或半
乳糖)主要生成相应的α-异构体,但对于富电子芳香化合物则例外。