Utilization of Sugars in Organic Synthesis. XXIV. Regioselective Monotosylation of Non-protected and Partially Protected Glycosides by the Dibutyltin Oxide Method.
Tosylation of non-protected glycopyranosides with p-toluenesulfonyl chloride in the presence of 4-dimethyl-aminopyridine, after activiation of the glycosides by dibutyltin oxide, gave mono-O-tosylates in good yield. The regioselectivity in this tosylation was different from that in the corresponding benzoylation for some glycosides. The reason for this difference is discussed based on an equilibrium of the tin intermediates and kinetic attack of the tosyl chloride on the intermediates. Thus, by application of this tosylation method to non-protected and partially protected glycosides, various glycoside mono-O-tosylates were synthesized regioselectively.
Novel benzoxaborole derivatives were designed as efficient catalysts for the highly site‐selective and protecting‐group‐free modification of polyols, such as carbohydrate. Additionally, the benzoxaborolecatalyst could tolerate diverse modifications of polyols, including acylation, sulfonylation, alkylation, and glycosylation.
Chiral Benzazaborole‐Catalyzed Regioselective Sulfonylation of Unprotected Carbohydrate Derivatives
作者:Satoru Kuwano、Yusei Hosaka、Takayoshi Arai
DOI:10.1002/chem.201903443
日期:2019.10.8
Chiral benzazaborole-catalyzed regioselective sulfonylations of unprotected carbohydrate derivatives have been developed. This methodology enables direct regioselective functionalization of the secondary OH group in carbohydrate in the presence of the primary OH group. By using the chiral organoboron catalysis, kinetic resolution of the carbohydrate derivatives was also achieved.