AuCl3- and AuCl3-Phenylacetylene-Catalyzed Glycosylations by Using Glycosyl Trichloroacetimidates

Glycosylations of armed and disarmed trichloroacetimidate-based glycosyl donors were carried out by using the AuCl3-phenylacetylene relay catalyst system. The effectiveness of this catalytic system was also compared with that of using AuCl3 alone as a catalyst. Glycosylations with these catalysts proceeded efficiently at room temperature within 5-45 min. Excellent diastereoselectivity was obtained for the glycosylation of 2-O-acetyl-protected disarmed glycosyl donors, whereas armed glycosyl trichloroacetimidates gave rise to a mixture of anomeric glycosides. Acid-sensitive nucleophiles such as Fmoc-serine tert-butyl ester or Fmoc-threonine tert-butyl ester successfully underwent the glycosylations, albeit in moderate yields, under mild conditions at room temperature.