Direct Addition of Amides to Glycals Enabled by Solvation-Insusceptible 2-Haloazolium Salt Catalysis.
The direct 2-deoxyglycosylation of nucleophiles with glycals leads to biologically and pharmacologically important 2-deoxysugar compounds. Although the direct addition of hydroxyl and sulfonamide groups have been well developed, the direct 2-deoxyglycosylation of amide groups has not been reported to date. Herein, we show the first direct 2-deoxyglycosylation of amide groups using a newly designed Brønsted acid catalyst under mild conditions. Through mechanistic investigations, we discovered that the amide group can inhibit acid catalysts, and the inhibition has made the 2-deoxyglycosylation reaction difficult. Diffusion-ordered two-dimensional NMR spectroscopy analysis implied that the 2-chloroazolium salt catalyst was less likely to form aggregates with amides in comparison to other acid catalysts. The chlorine atom and the extended π-scaffold of the catalyst played a crucial role for this phenomenon. This relative insusceptibility to inhibition by amides is more responsible for the catalytic activity than the strength of the acidity.
['Nakatsuji|Yuya|Y|', 'Kobayashi|Yusuke|Y|0000-0003-3074-7378', 'Takemoto|Yoshiji|Y|0000-0003-1375-3821']
D000577:Amides D001393:Azoles D002241:Carbohydrates D002384:Catalysis D006863:Hydrogen-Ion Concentration D015394:Molecular Structure D012492:Salts D012995:Solubility
Brønsted acid catalysis carbohydrates glycosylation organocatalysis