636
3
Chemical Glycosylation Reactions
⊡ Table 15
β-Selective arabinofuranosylation of acyl-protected acceptors
Entry
Glycosyl acceptor (ROH)
β/α ratio
Yield β/α ratio (%)
i
99:1
97
ii
7:1
95
iii
β only
95
iv
4:1
95
v
20:1
86
vi
4:1
95
vii
β only
92
viii
2.2:1
95
elective β-arabinofuranosylation processes [211]. They found that the presence of acyl-protective groups on the glycosyl acceptors was essential for attaining β-stereoselective glycosyl
couplings. Thus, reaction of donor 409 with acceptor 398 having benzoyl-protective groups
afforded a β-disaccharide almost exclusively (β/α = 99:1) in 97% yield ( > Table 15, entry i),
while the same reaction with acceptor 42 having benzyl-protective groups gave a mixture of
α- and β-disaccharides (β/α = 7:1) ( > Table 15, entry ii). Further examples in > Table 15