Recent advances in gold-catalyzed glycosylation - Carbohydrate Chemistry: Chemical and Biological Approaches - page 155

Scheme 24
Fig. 3
of sequential [1,3]-sigmatropic rearrangement and protodeauration of
118. 42
3.4 Gold(I)-catalyzed glycosylations with s-but-3-ynyl thioglycoside
In 2013, Zhu et al. used 2-deoxy S-but-3-ynyl thioglycosides 123-126 as
donors for the selective synthesis of 2-deoxy (127-130) and 2,6-dideoxy a-
glycosides under the Au(I)-catalyzed condition. Various alcohol acceptors
such as primary, secondary, and tertiary aliphatic alcohols and sugar-
derived primary and secondary alcohols could be used for this O-glyco-
sylation (Scheme 25). The use of corresponding O-glycosides as donors
did not afford any glycosylation products under identical condition,
demonstrating higher reactivity of thioglycoside. This is probably due to
the more nucleophilic nature of the sulfur atom over oxygen atom, which
facilitates the activation of the leaving group by Au(I) catalyst. A plausible
mechanism was proposed based on experimental observations (Fig. 4), 43
which resembles that of Au(I)-catalyzed glycosylation by ortho-alkynyl-
phenyl thioglycosides in every respect.