542
3
Chemical Glycosylation Reactions
⊡ Scheme 37
(Ref. [45])
⊡ Scheme 38
(Ref. [46,47])
Mukaiyama and coworkers also introduced tin-based Lewis acids such as SnCl 4 /Sn(OTf) 2 /
LiClO 4 and SnCl 4 /AgClO 4 for the glycosylation of trimethylsilylated alcohols with the 1-Oacetyl sugar. For example, 1,2-cis-α-ribosides were predominantly obtained from 1-O-acetylriboses and silylated 3β-cholestanol ( > Scheme 37) [45]. On the basis of the effectiveness
of the SnCl 4 /AgClO 4 combination as a promoter [46], they also investigated the glycosylation of silylated alcohols with 1-O-acetyl-2,3,4,6-tetra-O-benzyl-D-glucopyranose using
a series of combinations of other Lewis acids and AgClO 4 . Among them, the catalysts generated from HfCl 4 , GaCl 3 , InCl 3 , SiCl 4 , or GeCl 4 , with AgClO 4 led to the formation of
the corresponding glycosides effectively in high diastereomeric ratios ( > Scheme 38) [47].
⊡ Scheme 39
(Ref. [48])
3
Chemical Glycosylation Reactions
⊡ Scheme 37
(Ref. [45])
⊡ Scheme 38
(Ref. [46,47])
Mukaiyama and coworkers also introduced tin-based Lewis acids such as SnCl 4 /Sn(OTf) 2 /
LiClO 4 and SnCl 4 /AgClO 4 for the glycosylation of trimethylsilylated alcohols with the 1-Oacetyl sugar. For example, 1,2-cis-α-ribosides were predominantly obtained from 1-O-acetylriboses and silylated 3β-cholestanol ( > Scheme 37) [45]. On the basis of the effectiveness
of the SnCl 4 /AgClO 4 combination as a promoter [46], they also investigated the glycosylation of silylated alcohols with 1-O-acetyl-2,3,4,6-tetra-O-benzyl-D-glucopyranose using
a series of combinations of other Lewis acids and AgClO 4 . Among them, the catalysts generated from HfCl 4 , GaCl 3 , InCl 3 , SiCl 4 , or GeCl 4 , with AgClO 4 led to the formation of
the corresponding glycosides effectively in high diastereomeric ratios ( > Scheme 38) [47].
⊡ Scheme 39
(Ref. [48])