Application Research Of Silica Gel Supported Triflic Acid In The Synthetic Carbohydrate Chemistry

Strong acidic catalysts have been used widely in the modern organic synthesis,especially in the industrial manufacture. But due to their intrinsic strong acidity andcausticity, there are some potential risks in their storage, usage and disposal, and thissomewhat reduces their application especially in industry. Following the urgentdemand of green chemistry and social sustainable development, people prepare thesolid supported acids with the strong acids adsorbed on inorganic supports to avoidthe disadvantages. In recent years, solid supported acids have received considerableattentions in organic synthesis, but their application research in the syntheticcarbohydrate chemistry is relative slow. We study the application of silica gelsupported triflic acid in the synthetic carbohydrate chemistry in this thesis for the firsttime, mainly focused on the glycosylation, functional group transformation and thecarbohydrate hydroxyl group protection and deprotection.1. Study on the deprotection of TBDPS ethers catalyzed by TfOH-SiO₂A rapid, efficient, chemoselective and environment-friendly method for thedeprotection of tert-butyldiphenylsilyl ethers mediated by triflic acid supported onsilica gel is reported. A wide range of tert-butyldiphenylsilyl ethers derived fromcarbohydrate, saponin, alkyl and aryl residues can be smoothly cleaved in thepresence of various types of other protecting groups in good to excellent yields inacetonitrile at50℃. 2. Study on the protection of diols catalyzed by TfOH-SiO2and its applicationto the synthesis of natural products1) Triflic acid immobilized on silica gel has been identified as an excellentcatalyst for the chemoselective O-isopropylidenation of free sugars and functionalizedcarbohydrates with2,2-dimethoxylpropane in acetone at room temperature.2) Silica gel supported triflic acid has been used as an remarkable catalyst for thechemoselective O-benzylidenation of functionalized carbohydrates with benzaldehydedimethylacetal in acetonitrile at room temperature.3) A tetrasaccharide related to the repeating unit of the O-polysaccharide isolatedfrom Salmonella enterica O59is prepared by using NIS/TfOH-SiO2as glycosylationcatalyst and O-isopropylidenated and O-benzylidenated monosaccharide derivativeswhich are synthesized as described before as building blocks.3. Study on the conversion of glycosides into their corresponding thioglycosidescatalyzed by TfOH-SiO₂A new method for the conversion of glycosides into their correspondingthioglycosides mediated by triflic acid supported on silica gel is reported. Thethioglycosides can be obtained by treating a wide range of glycosides derived frommethyl, n-octyl, n-dodecyl, propargyl, and p-methoxyphenyl residues with1.2equiv. thiol in dichloromethane at reflux condition.