S. Malik et al. / Carbohydrate Research 345 (2010) 867–871
871
Table 3
3.3. Typical procedure-anomerization of methyl 2,3,4,6-tetra-O
-acetyl-b- -galactopyranoside (1b)
Anomerization of aryl glycosides using I2-HMDS systema
D
O
O
To a solution of the b-glycoside (1b, 362 mg, 1 mmol) in anhy-
drous CH3CN (7 mL) was added I2 (254 mg, 1 mmol) followed by
HMDS (732 mg, 5 mmol) and the mixture was stirred at rt until
TLC (EtOAc–hexane 1.5:3.5) showed completion of the reaction
(3 h, see Table 1). The reaction mixture was then diluted with
CH2Cl2 and was washed successively with cold saturated Na2CO3
solution and distilled H2O. The organic layer was then dried
(Na2SO4) and concentrated to dryness under reduced pressure to
I2, Me3SiSiMe3
OR
AcO
AcO
OR
CH3CN, rt
R = aryl
Entry
Substrate (b-anomer)
Time (h)
Product
Yield
a
:bb
AcO OAc
O
OAr
get neat 1a in near quantitative yield as colorless crystals. Spectro-
AcO
AcO
scopic data and the physical constants were in agreement with
1
2
3
4
16 Ar = Ph
2
2
2
8
Only
Only
a
a
-
-
Quantitative
Quantitative
literature.14
18 Ar = 4-MeO-Ph
20 Ar = 4-Cl-Ph
21 Ar = 4-NO2-Ph
90:10
50:50
Acknowledgment
AcO
O
AcO
OAr
Authors sincerely acknowledge the University Grants Commis-
sion, New Delhi for the award of a Senior Research fellowship to S.M.
AcO
AcO
5
6
7
17 Ar = Ph
19 Ar = 4-MeO-Ph
22 Ar = 4-NO2-Ph
3
3
8
Only
Only
a
a
-
-
50:50
References
a
All reactions were carried out in anhydrous acetonitrile (2 mL/100 mg sugar)
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b
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3.2. General procedure for anomerization using I2-HMDS
To a solution of the b-glycoside (1 mmol) in anhydrous CH3CN
(2 ml/100 mg glycoside) was added I2 (1 mmol), followed by HMDS
(5 mmol), and the mixture was allowed to stir at rt until TLC (EtOAc–
hexane 1.5:3.5) showed completion of the reaction. When the reac-
tion was complete, the mixture was diluted with CH2Cl2 and was
washed successively with saturated Na2CO3 solution and distilled
H2O in the cold. The organic layer was then dried (Na2SO4) and con-
centrated to dryness under reduced pressure. The products thus ob-
tained were pure enough in most cases for use elsewhere directly or
else were purified by column chromatography.
Physical constant and spectral data of compounds 2a 23
10a 25 16a 26 17a 27 18a 28 19a 27 20a 27
22a27 were in agreement with the literature data.
,
3 ,
a 23
28. Ichikawa, Y. Chem. Asian J. 2006, 1, 717–723.
29. Temeriusz, A.; Gubica, T.; Rogowska, P.; Paradowskab, K.; Cyran´ ski, M. K.
4
a 23
,
5
a 23
,
6
a 24
,
9
a 23
,
,
,
,
,
,
,
21a 29
,
Carbohydr. Res. 2005, 340, 1175–1184.