Efficient Synthesis Of 2-Thio-S-Acetyl Glycoside Donor

2-Deoxy glycosides are important structural components of many natural products.In the field of carbohydrate chemistry,the synthesis of 2-deoxy glycosides remains important and challenging.Various methods have been developed aimed at stereoselective synthesis2-deoxy sugar.Highly efficient synthesis of the donors are often required.As a temporary directing group,2-thio-S-acetyl can be easily installed and removed.But there are few researcher to apply 2-thio-S-acetyl group in the area of indirect method.We developed twoefficient methods for synthesis of 2-SAc-manosides donor.The research was explored as the following aspects:1.In this paper,we applyed TBAOAc as catalysis to the regioselective acetylation a series of donors.And we found that the regioselective acetylation a series of donors is diffenrent from each other owing to the anomeric substituents.The catalysis was applied to the acetylation of unprotected donor and the isolated yields of the major product are41%-81%.However,the product is decomposed in the progress of 2,4-di-sulfonylation.And we found that S-Phenyl migration occur in the sulfonylation reaction.2.We develop different method to synthesis 2-SAc donor.In the first system,those unprotected donors were prepared,then 2-SAc donor can be synthesized via S_N2displacement after regioselective acetylation.We used galactose and glucose as material,respectively.The result indicated that 2-SAc donor can be synthesized via inversion only using?-glucose as material.The possible mechanism was proposed.Perhaps the failure of the inversion reaction about?-galactose is owing to 4-axial-OH,which can impede S_N2displacement.On the other hand,we observed that C2-OTf group of phenyl1-thio-?-glucoside undergoes a facile nucleophilic displacement by thioacetate anions to afford the 2-SAc-2-deoxymannose compound in high yields,whereas the?-anomers react difficultly.The rule is that in the presence of the?-linkage in glucoside is necessary for achieving success in nucleophilic displacement.3.On the second system,we found a proper catalysis for the conversion from methyl2-SAc-glycoside to phenyl 2-SAc-1-thio-glycoside donor.We can easily synthesis methyl2-SAc-mannoside from methyl galactoside.But phenyl 2-SAc-1-thio-mannoside donor can not be obtained according to this route.Then we tested SnCl₄ as the catalysis,the target compounds can be synthesized under the specified condition,the isolated yields of the major product is 84%.The fact of this experiment indicate that we can synthesize glycoside donors by a new path.