Recent advances in gold-catalyzed glycosylation - Carbohydrate Chemistry: Chemical and Biological Approaches - page 148

Scheme 12
2.7 Gold(III)-catalyzed glycosidation with methyl glycoside donors
The readily available methyl glycosides are known to be inert to diverse
chemical manipulations and rarely used as glycosyl donors. In 2009, a
significant progress was made by Hotha and Vidadala for their discovery
that AuBr 3 could catalyze the reaction of methyl mannopyranoside 56
with various aglycones to afford corresponding 1,2-trans glycoside prod-
ucts 57. The ability of AuBr 3 to activate methyl glycoside was ascribed to
its inherent Lewis and Brønsted acidity. Change of the glycosyl donors to
methyl glucoside and galactoside resulted in decreased stereoselectivity.
This novel glycosylation protocol was successfully applied to the syn-
thesis of tri- and tetra-saccharides from di- and tri-saccharide donors
with disarmed sugar aglycone (Scheme 12). 24 In 2011, Hotha and co-
workers found 2-C-branched methyl glycosides reacted with various
alcohols under similar condition. 25
2.8 Gold(III)-catalyzed glycosylations with thioglycoside donors
In 2013, Zhu and co-workers successfully used S-but-3-ynyl and gem-
dimethyl S-but-3-ynyl thioglycoside donors (''armed'' and ''disarmed'')
for the preparation of various disaccharides and glycoconjugates (61-69)
by Au(III)-catalyzed glycosylation. In general, the use of gem-dimethyl
S-but-3-ynyl thioglycoside donors lead to slightly higher yields than
corresponding S-but-3-ynyl thioglycoside donors, demonstrating the
gem-dimethyl effect (Scheme 13). 26
3 Gold(I)-catalyzed glycosylation
3.1 Gold(I)-catalyzed glycosylation with 1,2-anhydrousugars
In 2008, Yu et al. discovered that Au(I) could effectively catalyzed the
glycosidation of 1,2-anhydrosugars (70, 72, Scheme 14), offering en-
hanced yields compared with ZnCl 2 . 27