Sulfuric acid immobilized on silica: an excellent catalyst for Fischer type glycosylation

Article abstract of DOI:10.1016/j.tetlet.2007.03.165

Fischer glycosylation, a widely used technique for the preparation of simple alkyl or aryl glycosides, has a few drawbacks including the use of strong mineral acids, excess alcohols, high temperature and long reaction times. This manuscript highlights a modification using sulfuric acid immobilized on silica as catalyst for the preparation of glycosides from free sugars such as d-glucose, d-galactose, d-mannose, l-rhamnose, l-fucose, N-acetyl-d-glucosamine and d-maltose with a diverse range of alcohols to afford a series of useful sugar derivatives in good to excellent yields.

Full text of DOI:10.1016/j.tetlet.2007.03.165

Tetrahedron Letters 48 (2007) 3783–3787
Sulfuric acid immobilized on silica: an excellent catalyst for
Fischer type glycosylationI
Bimalendu Roy and Balaram Mukhopadhyay*
Medicinal and Process Chemistry Division, Central Drug Research Institute, Chattar Manzil Palace, Lucknow 226 001, UP, India
Received 1 March 2007; revised 19 March 2007; accepted 30 March 2007
Available online 4 April 2007
Abstract—Fischer glycosylation, a widely used technique for the preparation of simple alkyl or aryl glycosides, has a few drawbacks
including the use of strong mineral acids, excess alcohols, high temperature and long reaction times. This manuscript highlights a
modification using sulfuric acid immobilized on silica as catalyst for the preparation of glycosides from free sugars such as D-glu-
cose, D-galactose, D-mannose, L-rhamnose, L-fucose, N-acetyl-D-glucosamine and D-maltose with a diverse range of alcohols to
afford a series of useful sugar derivatives in good to excellent yields.
ꢀ 2007 Elsevier Ltd. All rights reserved.
Simple alkyl and aryl glycosides of free sugars are extre-
mely useful for both synthetic and biological studies.
For example, benzyl,1 allyl2 or p-methoxybenzyl3 glyco-
sides are used for temporary anomeric protection during
oligosaccharide synthesis as they can be removed when
needed to make glycoconjugates, whereas long chain
alkyl glycosides, for example, n-octyl4 and n-dodecyl
are often used as substrates for enzymatic transforma-
tions and other biological studies. Furthermore, propar-
gyl glycosides are of great interest for ‘Click Chemistry’
approaches to mimic various biodynamic carbohydrate
structures5 and glycoconjugates. Fischer glycosylation
is the best choice for preparing these simple alkyl or aryl
glycosides from free sugars. However, this procedure
suffers from some serious drawbacks such as the use of
a large quantity of alcohol (critical for expensive alco-
hols) and strong mineral acids at reflux conditions for
long reaction times.6 Thus neutralization and purifica-
tion of the final product becomes an issue for these
transformations. Recently, microwave assisted Fischer
type glycosylation has been reported,7 but this is not
suitable for large-scale preparation of these important
starting materials. Moreover, alcohols are not ideal sub-
strates for microwave assisted processes.
dure for Fischer type glycosylation, we envisioned
sulfuric acid immobilized on silica (H2SO4–silica)8 as
an efficient alternative for the required transformation
using a lower quantity of alcohol and shorter reaction
time. Moreover, purification would only require filtra-
tion. Herein, we report our findings on H2SO4–silica9
catalyzed Fischer type glycosylations with various alco-
hols and free sugars.
In a simple reaction, D-glucose (180 mg, 1 mmol) was
suspended in propargyl alcohol (290 lL, 5 mmol) and
stirred at 65 ꢁC. H2SO4–silica (5 mg) was added and stir-
ring was continued until all the solids had dissolved
(ꢀ2.5 h). At this point, TLC (CH2Cl2–MeOH; 5:1)
showed complete conversion of the starting D-glucose
to a faster running component. After cooling to room
temperature, the reaction mixture was transferred to a
short (4 cm · 1 cm) silica gel column and the excess
propargyl alcohol was eluted with CH2Cl2 (20 mL)
followed by elution of the product glycoside with
CH2Cl2–MeOH (15:1) to afford the desired propargyl
glycoside in 75% yield (Scheme 1). For detailed charac-
terization, the product was per-O-acetylated using Ac2O
1
(4 equiv) and catalytic H2SO4–silica. H and 13C NMR
In our ongoing efforts to prepare oligosaccharide mimics
to develop drug-like molecules, we often required glyco-
sides as synthons. In the search for an alternative proce-
OH
O
HO
H2SO4-silica
HO
HO
D
-glucose
HO
O
q CDRI Communication No. 7190.
*
Scheme 1. Synthesis of propargyl glucoside.
Corresponding author. E-mail: sugarnet73@hotmail.com
0040-4039/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2007.03.165

3784
B. Roy, B. Mukhopadhyay / Tetrahedron Letters 48 (2007) 3783–3787
Table 1. Comparison between anomeric selectivities obtained by
different methods
spectroscopy of the per-O-acetylated product revealed
formation of the desired glycoside in a 6:1 (a/b) ratio.
The anomeric mixture was separated by flash chroma-
tography. Although formation of furanoside and acyclic
acetals in small quantities is common with this type of
reaction, no such by-product was evident here.
OH
O
Method A, B or C
HO
HO
D-glucose
HO
O
Method
a/b
Yield (%)
75
A similar reaction was performed except on this occa-
sion the reaction mixture was allowed to stir at room
temperature for 12 h after complete dissolution of the
starting sugar. The product was processed in a similar
way and then per-O-acetylated. After purification of
the acetate, NMR showed a significant improvement
in anomeric selectivity (10:1, a/b) due to the slow shift-
ing of the equilibrium towards the thermodynamic prod-
uct. The same result was obtained when the reaction was
allowed to continue under heating for an additional 3 h.
Comparisons between the anomeric selectivity of prop-
argyl glycoside prepared under different conditions are
illustrated in Table 1. As we were interested in preparing
a library of propargyl glycosides, the reaction was per-
formed with other sugars (mono and disaccharides) fol-
lowing Method C and the results are summarized in
Table 2. For D-mannose, L-rhamnose and N-acetyl-D-
Method A. 2.5 h stirring
6:1
at 65 ꢁC (until complete
dissolution of starting material)
Method B. After 2.5 h heating
at 65 ꢁC, the mixture was allowed
to stir at room temperature for 12 h
Method C. Stirring continued
at 65 ꢁC for an additional 3 h
after complete dissolution
10:1
10:1
81
80
glucosamine, heating for 2 h was sufficient for complete
a-selectivity. It is worth noting that a 100 mmol scale
reaction with D-glucose using the same stoichiometry
and reaction conditions afforded the desired product in
similar yield and anomeric selectivity.
Table 2. Preparation of propargyl glycosides from free sugarsa
Starting material
Product
Time (h)
5.5
Yield (%)
80
a/b
OAc
O
AcO
AcO
D-Glucose
10:1
AcO
O
1
OAc
O
AcO
AcO
D-Galactose
6
2
2
2
4
79
83
80
82
74
10:1
1:0
AcO
O
2
AcO
AcO
OAc
O
D-Mannose
AcO
O
3
OAc
O
AcO
N-Acetyl-D-glucosamine
L-Rhamnose
1:0
AcO
AcNH
4
O
O
Me
O
1:0
AcO
AcO
O
OAc
5
O
Me
L-Fucose
12:1
OAc
O
OAc
AcO
6
AcO
AcO
AcO
OAc
O
D-Maltoseb
AcO
8
69
11:1
O
AcO
7
AcO
O
a 1 mmol of sugar was reacted with 5 mmol of propargyl alcohol and 5 mg H2SO4–silica.
b For maltose, 10 mmol of propargyl alcohol was used for 1 mmol of sugar.

B. Roy, B. Mukhopadhyay / Tetrahedron Letters 48 (2007) 3783–3787
Table 3. Preparation of glycosides of D-glucose with various alcoholsa
3785
Alcohol
Product
Time (h)
Yield (%)
79
a/b
OAc
O
AcO
AcO
Allyl alcohol
6
10:1
10:1
AcO
O
8
OAc
O
AcO
AcO
Benzyl alcohol
p-Methoxybenzyl alcohol
n-Octanol
7
7
6
8
6
78
75
81
76
82
AcO
O
9
OMe
AcO
O
11:1
13:1
12:1
11:1
AcO
AcO
AcO
10
OAc
O
O
AcO
AcO
AcO
11
OC8H17
OAc
O
AcO
AcO
n-Dodecanol
AcO
12
OC12H25
OAc
O
AcO
AcO
2-Bromo ethanol
Br
AcO
O
13
a 1 mmol of D-glucose was reacted with 5 mmol of alcohol and 5 mg of H2SO4–silica in each case.
Next, we focussed our attention on other alcohols in or-
der to generalize the method and to access various gly-
cosides for future use. Thus, D-glucose was used as a
representative sugar and the glycosylation reactions
were performed with benzyl, allyl, p-methoxybenzyl,
2-bromoethyl (which can be converted to the corre-
sponding azido derivative and used in the ‘Click’ reac-
tion), n-octyl and dodecyl alcohol. To our satisfaction,
all the reactions proceeded smoothly to furnish the de-
sired glycosides in good to excellent yields and anomeric
selectivity. The results are described in Table 3. All com-
pounds were characterized as their per-O-acetylated
derivatives by 1H and 13C NMR spectroscopies and
mass spectrometry. NMR data for selected compounds
are given in the reference section.10
pared will be studied as glycomimetics and the results
will be communicated in due course.
Acknowledgements
B.R. is thankful to the CSIR, New Delhi, for providing
a fellowship. Instrumentation facilities from SAIF and
CDRI are gratefully acknowledged. The present work
is supported by DST Fast Track Grant (SR/FTP/CS-
110/2005).
References and notes
As a control, when the glycosylation reaction was per-
formed without H2SO4–silica, no product formation
was evident even after heating for 12 h at 60 ꢁC. This
confirms the utility of H2SO4–silica as a catalyst for
the reaction.
1. Mukhopadhyay, B.; Field, R. A. Carbohydr. Res. 2004,
339, 1285–1291.
2. Kim, I. J.; Park, T. K.; Hu, S.; Abrampah, K.; Zhang, S.;
Livingston, P.; Danishefsky, S. J. J. Org. Chem. 1995, 60,
7716–7717.
´
´
3. Sarabia, F.; Martın-Ortiz, L.; Lopez-Herrera, F. J. Org.
Biomol. Chem. 2003, 21, 3716–3725.
In conclusion, we have shown that H2SO4–silica can be
used successfully as a catalyst to prepare various alkyl
and aryl glycosides from free sugars through Fischer
type glycosylation using less equivalents of alcohol and
in shorter times. The strategy is equally applicable for
large-scale preparations. The propargyl glycosides pre-
4. Wing, C.; Errey, J. C.; Mukhopadhyay, B.; Blanchard, J.
S.; Field, R. A. Org. Biomol. Chem. 2006, 4, 3945–3950.
5. For instance see: (a) Hotha, S.; Kashyap, S. J. Org. Chem.
2006, 71, 364–367; (b) Nepogodiev, S. A.; Dedola, S.;
Marmuse, L.; Field, R. A. Carbohydr. Res. 2007, 342, 529–
540.

3786
B. Roy, B. Mukhopadhyay / Tetrahedron Letters 48 (2007) 3783–3787
6. (a) Kappe, C. O. Angew. Chem., Int. Ed. 2004, 43, 6250–
170.7, 170.2 (3 · COCH3), 169.3 (NHCOCH3), 96.6 (C-1),
78.6 (CH2AC„CH), 75.9 (CH2AC„CH), 71.3, 68.7,
68.4, 62.1 (CH2AC„CH), 55.6 (C-6), 53.7 (C-2), 23.3
(NHCOCH3), 21.0, 20.9, 20.8 (3 · COCH3). HRMS:
Calcd for C17H27O9N2 (M+NH4): 403.1717; found m/z
6284; (b) Heard, D. D.; Barker, R. J. Org. Chem. 1968, 33,
740–746; (c) Ferrier, R. J.; Hatton, L. R. Carbohydr. Res.
1968, 6, 75–86; (d) Freudenberg, K. Adv. Carbohydr.
Chem. 1966, 21, 2–38.
1
7. Bornaghi, L. F.; Poulsen, S.-A. Tetrahedron Lett. 2005, 46,
3485–3488.
403.1720. Compound 5: H NMR (CDCl3, 300 MHz) d:
5.23 (dd, 1H, J 2.4 Hz, 9.6 Hz, H-3), 5.21 (br s, 1H, H-2),
5.02 (t, 1H, J 9.6 Hz, H-4), 4.90 (s, 1H, H-1), 4.24 (d, 2H, J
2.4 Hz, CH2AC„CH), 3.87 (m, 1H, H-5), 2.45 (t, 1H, J
2.4 Hz, CH2AC„CH), 2.16, 2.03, 1.98 (3s, 9H,
3 · COCH3), 1.24 (d, 3H, J 7.2 Hz, H-6). 13C NMR
(CDCl3, 50 MHz) d: 169.8, 169.7 (2) (3 · COCH3), 96.4
(C-1), 78.6 (CH2AC„CH), 75.7 (CH2AC„CH), 71.2,
69.9, 69.3, 67.2, 54.9 (CH2AC„CH), 21.1, 21.0, 20.9
(3 · COCH3), 17.6 (C-CH3). HRMS: Calcd for
C15H24O8N (M+NH4): 346.1502; found m/z 346.1503.
Compound 6: 1H NMR (CDCl3, 300 MHz) d: 5.24 (dd,
1H, J 3.3 Hz, 8.7 Hz, H-3), 5.22 (br d, 1H, J 3.3 Hz, H-4),
5.18 (d, 1H, J 3.6 Hz, H-1), 5.05 (dd, 1H, J 3.6 Hz, 8.7 Hz,
H-2), 4.20 (d, 2H, J 2.4 Hz, CH2AC„CH), 4.16 (q, 1H, J
6.6 Hz, H-5), 2.40 (t, 1H, J 2.4 Hz, CH2AC„CH), 2.13,
2.04, 1.94 (3s, 9H, 3 · COCH3), 1.11 (d, 3H, J 6.6 Hz, H-
6). 13C NMR (CDCl3, 50 MHz) d: 170.0, 169.8, 169.5
(3 · COCH3), 94.9 (C-1), 78.6 (CH2AC„CH), 75.1
(CH2AC„CH), 71.2, 67.7 (2), 64.9, 55.4 (CH2AC„CH),
20.6, 20.5, 20.4 (3 · COCH3), 16.0 (C-CH3). HRMS:
Calcd for C15H24O8N (M+NH4): 346.1502; found
m/z 346.1505. Compound 8: 1H NMR (CDCl3,
300 MHz) d: 5.78 (m, 1H, CH2ACH@CH2), 5.43 (t, 1H,
J 10.2 Hz, H-3), 5.35–5.21 (2d, 2H, CH2ACH@CH2),
5.08 (d, 1H, J 3.9 Hz, H-1), 5.04 (t, 1H, J 6.3 Hz, J
10.2 Hz, H-4), 4.86 (dd, 1H, J 3.9 Hz, 10.2 Hz, H-2), 4.18–
4.11 (m, 2H, CH2ACH@CH2), 4.10–3.99 (m, 3H, H-5, H-
6a, H-6b), 2.10, 2.07, 2.04, 2.01 (4s, 12H, 4 · COCH3).
13C NMR (CDCl3, 50 MHz) d: 170.1, 169.8, 169.2,
168.8 (4 · COCH3), 133.3 (CH2ACH@CH2), 117.9
(CH2ACH@CH2), 94.7 (C-1), 70.6 (CH2ACH@CH2),
70.0, 68.6, 68.3, 67.3, 61.7 (C-6), 20.4 (2), 20.3 (2)
(4 · COCH3). HRMS: Calcd for C17H28O10N (M+NH4):
8. For the use of H2SO4–silica in carbohydrate synthesis see:
(a) Mukhopadhyay, B. Tetrahedron Lett. 2006, 47, 4337–
4341; (b) Rajput, V. K.; Mukhopadhyay, B. Tetrahedron
Lett. 2006, 47, 5939–5941; (c) Rajput, V. K.; Roy, B.;
Mukhopadhyay, B. Tetrahedron Lett. 2006, 47, 6987–
6991; (d) Dasgupta, S.; Roy, B.; Mukhopadhyay, B.
Carbohydr. Res. 2006, 341, 2708–2713; For the use of
H2SO4–silica in organic synthesis see: (e) Zolfigol, M. A.;
Bamoniri, A. Synlett 2002, 1621–1623; (f) Zolfigol, M. A.
Tetrahedron 2001, 57, 9509–9511; (g) Zolfigol, M. A.;
Shirini, F.; Ghorbani Choghamarani, A.; Mohammad-
poor-Baltork, I. Green Chem. 2002, 4, 562–564; (h) Shirini,
F.; Zolfigol, M. A.; Mohammadi, K. Bull. Korean Chem.
Soc. 2004, 25, 325–327.
9. Preparation of H2SO4–silica: To a slurry of silica gel (10 g,
200–400 mesh) in dry diethyl ether (50 mL) was added
commercially available concd H2SO4 (3 mL) with shaking
for 5 min. The solvent was evaporated under reduced
pressure resulting in free flowing H2SO4–silica which was
then dried at 110 ꢁC for 3 h.
10. Analytical data of selected compounds: Compound 1: 1H
NMR (CDCl3, 200 MHz) d: 5.50 (t, 1H, J 9.8 Hz, H-3),
5.30 (d, 1H, J 3.6 Hz, H-1), 5.10 (t, 1H, J 9.8 Hz, H-4),
4.92 (dd, 1H, J 3.6 Hz, 9.8 Hz, H-2), 4.32–4.23 (m, 3H,
CH2AC„CH, H-6a), 4.10–4.03 (m, 2H, H-5, H-6b), 2.47
(t, 1H, J 2.4 Hz, CH2AC„CH), 2.10, 2.08, 2.04, 2.02 (4s,
12H, 4 · COCH3). 13C NMR (CDCl3, 50 MHz) d: 170.5,
170.2, 169.5, 169.3 (4 · COCH3), 94.8 (C-1), 78.5
(CH2AC„CH), 75.9 (CH2AC„CH), 70.7, 70.2, 68.7,
68.1, 61.9 (C-6), 55.9 (CH2AC„CH), 20.9 (4 · COCH3).
HRMS: Calcd for C17H26O10N (M+NH4): 404.1557;
found m/z 404.1561. Compound 2: 1H NMR (CDCl3,
200 MHz) d: 5.47 (br d, 1H, J 2.2 Hz, H-4), 5.36 (dd, 1H, J
3.2 Hz, 9.8 Hz, H-3), 5.32 (d, 1H, J 3.2 Hz, H-1), 5.14 (dd,
1H, J 3.2 Hz, 9.8 Hz, H-2), 4.27 (m, 2H, CH2AC„CH),
4.14–4.07 (m, 3H, H-5, H-6a, H-6b), 2.47 (t, 1H, J 2.4 Hz,
CH2AC„CH), 2.15, 2.10, 2.05, 1.99 (4s, 12H,
4 · COCH3). 13C NMR (CDCl3, 50 MHz) d: 170.2 (2),
1
406.1713; found m/z 406.1711. Compound 11: H NMR
(CDCl3, 300 MHz) d: 5.44 (t, 1H, J 9.6 Hz, H-3), 5.04 (d,
1H, J 3.9 Hz, H-1), 5.02 (t, 1H, J 9.6 Hz, H-4), 4.82 (dd,
1H, J 3.9 Hz, 9.6 Hz, H-2), 4.25 (dd, 1H, J 4.5 Hz,
12.0 Hz, H-6a), 4.06 (dd, 1H, J 2.4 Hz, 12.0 Hz, H-6b),
3.98 (m, 1H, H-5), 3.66, 3.44 [2m, 2H, OCH2–(CH2)6–
CH3], 2.09, 2.06, 2.02, 2.00 (4s, 12H, 4 · COCH3), 1.58 [m,
2H, OCH2–CH2–(CH2)5–CH3], 1.26 [m, 10H, OCH2–
CH2–(CH2)5–CH3], 0.92 [t, 3H, OCH2–CH2–(CH2)5–
CH3]. 13C NMR (CDCl3, 50 MHz) d: 169.9, 169.7 (2),
168.7 (4 · COCH3), 95.5 (C-1), 72.8, 71.7, 68.6 (2), 67.1,
60.1 (C-6), 31.7, 29.2, 26.0 (2), 25.7, 22.5, 20.8, 20.5, 20.4
(2) (4 · COCH3), 14.0 [OCH2–CH2–(CH2)5–CH3].
HRMS: Calcd for C22H40O10N (M+NH4): 478.2652;
found m/z 478.2653. Compound 12: 1H NMR (CDCl3,
300 MHz) d: 5.45 (t, 1H, J 9.9 Hz, H-3), 5.07 (d, 1H, J
3.9 Hz, H-1), 5.04 (t, 1H, J 9.9 Hz, H-4), 4.86 (dd, 1H, J
3.9 Hz, 9.9 Hz, H-2), 4.29 (dd, 1H, J 4.2 Hz, 12.3 Hz, H-
6a), 4.11 (dd, 1H, J 2.1 Hz, 12.3 Hz, H-6b), 3.92 (m, 1H, H-
5), 3.63–3.47 [m, 2H, OCH2–(CH2)10–CH3], 2.11, 2.08,
2.04, 2.01 (4s, 12H, 4 · COCH3), 1.62 [m, 2H, OCH2–
CH2–(CH2)9–CH3], 1.29 [m, 18H, OCH2–CH2–(CH2)9–
CH3], 0.95 [t, 3H, OCH2–CH2–(CH2)9–CH3]. 13C NMR
(CDCl3, 50 MHz) d: 169.8, 169.7, 169.6, 168.9
(4 · COCH3), 95.7 (C-1), 72.6, 71.5, 68.6, 68.4, 67.0, 61.1
(C-6), 32.1, 29.7 (2), 28.5, 28.3, 27.9, 27.6, 26.5, 25.7, 22.5,
20.8 (2), 20.5, 20.4 (4 · COCH3), 14.0 [OCH2–CH2–
(CH2)9–CH3]. HRMS: Calcd for C26H48O10N (M+NH4):
169.8,
169.4
(4 · COCH3),
95.2
(C-1),
78.0
(CH2AC„CH), 75.6 (CH2AC„CH), 68.0, 67.7, 67.2,
67.1, 61.5 (C-6), 55.9 (CH2AC„CH), 21.0 (2), 20.9 (2)
(4 · COCH3). HRMS: Calcd for C17H26O10N (M+NH4):
404.1557; found m/z 404.1559. Compound 3: 1H NMR
(CDCl3, 300 MHz) d: 5.30 (dd, 1H, J 2.4 Hz, 9.3 Hz, H-3),
5.26 (m, 2H, H-2, H-4), 5.02 (s, 1H, H-1), 4.29 (br d, 2H, J
2.1 Hz, CH2AC„CH), 4.28 (dd, 1H, J 4.2 Hz, 12.3 Hz,
H-6a), 4.10 (dd, 1H, J 2.4 Hz, 12.3 Hz, H-6b), 4.08 (m, 1H,
H-5), 2.47 (t, 1H, J 2.1 Hz, CH2AC„CH), 2.20, 2.11,
2.05, 2.00 (4s, 12H, 4 · COCH3). 13C NMR (CDCl3,
50 MHz) d: 170.4, 169.7, 169.6 (2) (4 · COCH3), 96.5
(C-1), 78.3 (CH2AC„CH), 76.1 (CH2AC„CH), 69.6,
69.4, 69.2, 66.3, 62.5 (C-6), 55.6 (CH2AC„CH), 21.1 (2),
20.9 (2) (4 · COCH3). HRMS: Calcd for C17H26O10N
(M+NH4): 404.1557; found m/z 404.1560. Compound 4:
1H NMR (CDCl3, 300 MHz) d: 5.76 (d, 1H, J 9.3 Hz,
NH), 5.18 (t, 1H, J 9.6 Hz, H-3), 5.11 (t, 1H, J 9.6 Hz,
H-4), 5.01 (d, 1H, J 3.9 Hz, H-1), 4.32 (dt, 1H, J 3.9 Hz,
9.3 Hz, 9.6 Hz, H-2), 4.27 (m, 2H, CH2AC„CH), 4.23
(dd, 1H, J 4.5 Hz, 12.3 Hz, H-6a), 4.07 (dd, 1H, J 2.4 Hz,
12.3 Hz, H-6b), 3.96 (m, 1H, H-5), 2.47 (t, 1H, J 2.4 Hz,
CH2AC„CH), 2.09, 2.02, 2.01 (3s, 9H, 3 · COCH3), 1.95
(s, 3H, NHCOCH3). 13C NMR (CDCl3, 50 MHz) d: 171.3,
1
534.3278; found m/z 534.3280. Compound 13: H NMR
(CDCl3, 300 MHz) d: 5.45 (t, 1H, J 9.3 Hz, H-3), 5.13 (d,

B. Roy, B. Mukhopadhyay / Tetrahedron Letters 48 (2007) 3783–3787
3787
1H, J 3.6 Hz, H-1), 5.03 (t, 1H, J 9.3 Hz, H-4), 4.83 (dd,
1H, J 3.6 Hz, 9.3 Hz, H-2), 4.25 (dd, 1H, J 4.8 Hz,
12.3 Hz, H-6a), 4.15–4.07 (m, 2H, H-5, H-6b), 4.00, 3.85
(2m, 2H, OCH2–CH2–Br), 3.52 (t, 2H, J 5.8 Hz, OCH2–
NMR (CDCl3, 75 MHz) d: 170.0, 169.7, 169.5, 169.1
(4 · COCH3), 95.8 (C-1), 70.6, 69.8, 68.6 (OCH2–CH2–
Br), 68.3, 67.6, 61.7 (C-6), 29.6 (OCH2–CH2–Br), 20.5 (2),
20.4 (2) (4 · COCH3). HRMS: Calcd for C16H27O10NBr
(M+NH4): 472.0818; found m/z 472.0819.
CH2–Br), 2.09, 2.08, 2.03, 2.02 (4s, 12H, 4 · COCH3). 13
C