Chemistry Reference
In-Depth Information
i) Ac
2
O, I
2
(cat), rt
ii) HBr/AcOH
saccharide
R
N
N
unprotected
monosaccharide
N
iii) Na
N
3
,
Bu
4
NHSO
4,
NaHCO
3
CuSO
4,
Na ascorbate
CHCl
3
:EtOH:H
2
O, 9:1:1
R
N
N
N
HO
AcO
O
O
O
O
O
HO
OH
O
AcO
O
O
O
O
HO
OH
O
O
OAc
AcO
O
O
D-glucose
4
7
BnO
N
BnO
N
N
O
AcO
O
O
OMe
O
O
O Me
AcO
O
O
O
O
OAc
AcO
5
8
N
O
N
N
O
AcO
O
OAc
O
OAc
O
AcO
OAc
OAc
OAc
AcO
6
9
i) HBr/AcOH
Saccharide
acetate
Glycoconjugate
iii) Na
N
3
,
Bu
4
NHSO
4,
NaHCO
3
CuSO
4,
Na ascorbate
CHCl
3
:EtOH, 9:1, rt,
alkyne
O
O
OMe
O
O
N
N
OAc
AcO
AcO
N
O
O
AcO
OAc
AcO
OAc
D-Ribose tetraacetate
10
SCHEME 5.3
Cu(II)-ascorbate approach form unprotected or acetylated sugars.
(86% yield), but for
1b
and
1c,
the use of (EtO)
3
P.Cu(I)-DIPEA led to higher yields
(96% and 99%, respectively).
Interestingly, microwave irradiation was used here for the first time for CuAAC
reactions, resulting in improved yields. Independently, Appukkutan et al. [23]
reported that microwaves significantly accelerate the click reaction.
To overcome the instability of Cu(I), it was shown that it can be generated by
in
situ
reduction of Cu(II) salts (e.g., copper sulfate) with sodium ascorbate [11, 24].
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