Investigation On The Synthesis Of α-glycosyl Thiols And The Se-acylation With N-acylbenzotriazoles

This dissertation is devoted to the direct and stereospecific synthesis of a-glycosyl thiols, and on the acylation of Se-nucleophiles with N-acylbenzotriazoles. Three chapters are included in the thesis:Chapter one is the preface, consisting of two parts. In the first part, the importance of a-glycosyl thiol in Carbohydrate Chemistry, especially in thioglycoside chemistry, and progress on the preparation of a-glycosyl thiol over the past few years were reviewed. In the second part, the applications of N-acylbenzotriazole in organic synthesis were summarized.Chapter two introduces a highly stereoselective method for the synthesis of a-glycosyl thiols:ring-opening of 1,6-anhydrosugars with commercially available bis(trimethylsilyl)sulfide under the action of TMSOTf smoothly afforded a-glycosyl thiols in moderate to high yields and in a stereospecific way. Here mainly 1,6-anhydrosugars with dis-armed protecting groups were used as the substrates. Fortunately, all the glycosyl thiols were isolated as exclusively the a-anomer despite the reduced rates and yields, which indicated the method could circumvent the traditional neighboring group participation. Thus this one-step procedure provided a concise and efficient access to a-glycosyl thiols, which could be used to synthesize various a-S-linked glycoconjugates.Chapter three describes the acylation of Se-nucleophiles with N-acylbenzotriazoles. Samarium selenolates (RSeSmI2), which were generated by the reductive cleavage of RSeSeR with SmI2, reacted with N-aroyl and N-alkanoylbenzotriazoles smoothly and afforded the corresponding selenol esters in good yields. Treatment of the RSeSmI2 withα,β-unsaturated N-acylbenzotriazoles afforded the anticipatedα,β-unsaturated selenol esters only in moderate yields, due mainly to the side reaction of bis-addition.