CeCl37H2O: A versatile and efficient reagent for the synthesis of C-pyrrolyl glycosides

Article abstract of DOI:10.1055/s-0030-1258369

1,3-Diketones and β-oxo esters undergo smooth coupling with d-glucosamine in the presence of 25 mol% CeCl₃7H₂O in water at 80 C to furnish C-pyrrolyl glycosides in good to high yields. The reaction of cyclic diketones such as dimedone with d-glucosamine affords the corresponding 2-(3,4-dihydroxytetrahydrofuran-2-yl)-6,7-dihydro-1H-indol-4(5H)- one derivatives. These dihydroxy derivatives are directly converted into acetates using acetic anhydride and 4-(dimethylamino)pyridine. The use of readily available CeCl₃7H₂O makes this procedure quite simple, convenient and practical. Georg Thieme Verlag Stuttgart New York.

Full text of DOI:10.1055/s-0030-1258369

PAPER
337
CeCl3·7H2O: A Versatile and Efficient Reagent for the Synthesis of C-Pyrrolyl
Glycosides
Synthesis of
C
-
Py
a
r
rolyl
G
lyc
s
osides
U
s
iing CeCl3·7H
V
O
. Subba Reddy,* Ruchi Jain, Kudikyala Bhargavi, Manisha Swain, Jhillu S. Yadav
2
Division of Organic Chemistry, Indian Institute of Chemical Technology, Hyderabad 500 007, India
Fax +91(40)27160512; E-mail: basireddy@iict.res.in
Received 1 November 2010
tive solvent in organic synthesis.13 This becomes further
sophisticated if these reactions can be performed using
water-tolerant Lewis acids.
Abstract: 1,3-Diketones and b-oxo esters undergo smooth cou-
pling with D-glucosamine in the presence of 25 mol% CeCl3·7H2O
in water at 80 °C to furnish C-pyrrolyl glycosides in good to high
yields. The reaction of cyclic diketones such as dimedone with D-
glucosamine affords the corresponding 2-(3,4-dihydroxytetrahy-
drofuran-2-yl)-6,7-dihydro-1H-indol-4(5H)-one derivatives. These
dihydroxy derivatives are directly converted into acetates using ace-
tic anhydride and 4-(dimethylamino)pyridine. The use of readily
available CeCl3·7H2O makes this procedure quite simple, conve-
nient and practical.
In this paper, we disclose a simple and practical method
for the synthesis of optically pure C-pyrrolyl glycosides
via a novel cyclization of 1,3-diketones with D-glu-
cosamine. We initially attempted the Knoevenagel con-
densation of D-glucosamine with acetylacetone in the
presence of cerium(III) chloride heptahydrate
(CeCl3·7H2O). Interestingly, we observed the formation
of a C-pyrrolyl furanoside. Thus, treatment of D-glu-
cosamine (1) with acetylacetone (2) in the presence of 25
mol% CeCl3·7H2O in water at 80 °C for four hours, fol-
lowed by acetylation, gave the product 3a in 86% yield
(Scheme 1).
Key words: C-pyrrolyl glycosides, 1,3-diones, glucosamine, ceri-
um(III) salts
Pyrroles are attractive structural scaffolds in medicinal
chemistry.1 They are frequently present in various natural
products such as porphyrins and lamellarins.2 In particu-
lar, they are frequently present in the most promising ther-
apeutic agents such as atorvastatin, anti-inflammatants,
antitumor agents and immunosuppressants.3–5 Polypyr-
roles are of great importance in material science, nonlin-
ear optics, and supramolecular chemistry as molecular
sensors and devices.6–9 Therefore, a great attention has
been paid to developing efficient methods for the synthe-
sis of pyrroles.10 In particular, the synthesis of sugar-
substituted pyrroles is of prime importance due to the
enormous applications of such pyrroles in medicinal
chemistry; however, few methods are known in the litera-
ture for the synthesis of C-furyl and C-pyrrolyl glyco-
sides.11 Recently, an elegant approach has been reported
for the synthesis of sugar-annulated pyrroles by the con-
densation of aldose sugars with enamines.12 In view of en-
vironmental concerns, the use of water as a green solvent
has received considerable interest in organic synthesis. In
addition to its abundance, for economical and safety rea-
sons water has naturally become a substitute and alterna-
The structure of the product 3a was confirmed by NOE
experiments (Figure 1) and also characterized by NMR
and IR spectroscopy, and HRMS.
O
H
H
O
H H
N
H
H
H
AcO OAc
Figure 1 Characteristic NOE correlations for 3a
This result provided an incentive to extend this process to
b-oxo esters. Interestingly, various b-oxo esters partici-
pated effectively in this reaction (Table 1). This method
works well even with heteroaryl b-oxo esters, including
ethyl 3-oxo-3-(pyridin-4-yl)propanoate (Table 1, entry f).
In all cases, the corresponding C-pyrrolyl glycosides were
obtained in good yields (Table 1, entries b–f).
O
OH
O
O
OH
O
a) CeCl3⋅7H2O, H2O, 80 °C
b) Ac2O, DMAP, CH2Cl2
N
+
H
HO
NH2
O
AcO
OAc
OH
2
1
3a
Scheme 1 Reaction between D-glucosamine and acetylacetone
SYNTHESIS 2011, No. 2, pp 0337–0341
x
x
.
x
x
.2
0
1
1
Advanced online publication: 17.12.2010
DOI: 10.1055/s-0030-1258369; Art ID: Z26210SS
© Georg Thieme Verlag Stuttgart · New York

338
B. V. S. Reddy et al.
PAPER
Table 1 CeCl3·7H2O Promoted Synthesis of C-Pyrrolyl Glycosides
Entry
a
D-Glucosamine
1,3-Diketone or b-oxo ester Product 3a
Time (h)
4.0
Yieldb (%)
O
O
O
OH
HO
86
O
HO
OH
NH2
N
H
O
AcO
AcO
OAc
O
O
OH
O
HO
OMe
OEt
OEt
OEt
OEt
b
c
d
e
f
3.5
4.0
3.0
7.0
8.5
81
85
82
75
70
O
O
OMe
HO
OH
NH2
N
H
O
OAc
OAc
O
O
OH
O
O
HO
OEt
OEt
HO
OH
NH2
N
H
O
O
AcO
AcO
AcO
O
O
OH
HO
O
HO
OH
NH2
N
H
OAc
O
O
O
OH
HO
OEt
O
HO
OH
NH2
N
H
O
OAc
O
O
O
OH
HO
OEt
N
O
HO
OH
NH2
N
O
N
H
AcO
AcO
AcO
OAc
O
O
O
OH
HO
g
h
8.5
62
55
O
HO
OH
NH2
N
H
O
OAc
O
O
O
OH
HO
12.0
O
HO
OH
NH2
N
H
O
OAc
a After acetylation with Ac2O and DMAP in CH2Cl2. All products were characterized by NMR and IR spectroscopy, and mass spectrometry.
b Yield refers to pure products after chromatography.
To extend the scope of this method, we next attempted the tetrahydro-1H-indol-2-yl)tetrahydrofuran-3,4-diyl diace-
coupling of cyclic 1,3-diones with D-glucosamine. Inter- tate and (2S,3S,4R)-2-(4-oxo-1,4-dihydroindeno[1,2-
estingly, cyclic diketones such as dimedone and 1,3-in- b]pyrrol-2-yl)tetrahydrofuran-3,4-diyl diacetate, respec-
dandione reacted well with D-glucosamine to give the tively (Table 1, entries g and h; Scheme 2).
corresponding (2S,3S,4R)-2-(6,6-dimethyl-4-oxo-4,5,6,7-
Synthesis 2011, No. 2, 337–341 © Thieme Stuttgart · New York

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Synthesis of C-Pyrrolyl Glycosides Using CeCl3·7H2O
339
O
OH
O
O
OH
O
a) CeCl3⋅7H2O, H2O, 80 °C
N
H
+
b) Ac2O, DMAP, CH2Cl2
HO
NH2
O
AcO
OAc
OH
Scheme 2 Reaction of D-glucosamine with dimedone
–
Ce
Ce(III)
O
O
+
O
HO
O
OH
O
OH
OH
OH
R2
R1
R2
HO
HO
HO
HO
HO
R2
Ce(III)
+
H
R1
NH2
R1
N
O
HO
:
..
N
H
OH
OH
O
O
O
R2
R1
R2
OH
H
OH
OH
HO
HO
HO
HO
O
R2
aromatization
N
H
– H2O
R1
– H2O
N
H
R1
N
H
O
HO
OH
–
Ce
+
Scheme 3 Plausible reaction mechanism
C-Pyrrolyl Glycosides 3; General Procedure
The cyclic diketones, however, gave the products in lower
yields and required longer reaction times compared to the
b-oxo esters (Table 1).
A mixture of D-glucosamine (1; 215 mg, 1.2 mmol), a 1,3-diketone
or a b-oxo ester (1.4 mmol), and CeCl3·7H2O (98 mg, 0.25 mmol)
in H2O (2 mL) was stirred at 80 °C for the appropriate time (see
Table 1). After completion of the reaction, as indicated by TLC, the
mixture was extracted with EtOAc (3 × 10 mL) and the extracts
were concentrated under reduced pressure. The resulting residue
was subjected to acetylation using Ac2O (3 equiv) and DMAP (10
mol%) in CH2Cl2 (6 mL). Then, the reaction mixture was quenched
with H2O (5 mL) and extracted with CH2Cl2 (2 × 10 mL). The com-
bined organic extracts were washed with sat. NaHCO3 soln (10 mL)
followed by H2O (5 mL) and brine soln (10 mL), then dried
(Na2SO4). Removal of solvent followed by purification on a silica
gel column (EtOAc–n-hexane, 7:3) afforded pure diacetate. The
products thus obtained were characterized by IR and NMR spec-
troscopy, and mass spectrometry.
To know the efficacy of CeCl3·7H2O, the reaction of D-
glucosamine with acetylacetone was carried out with oth-
er Lewis acids such as FeCl3, InCl3 and InBr3. Of these,
CeCl3·7H2O gave the best results. In the absence of a cat-
alyst, no reaction was observed, even after a long reaction
time. The scope and generality of this process is illustrated
in Table 1. Mechanistically, the reaction proceeds via the
formation of enamine from glucosamine and the 1,3-dike-
tone. The resulting enamine may undergo intramolecular
aldol condensation with the hemiacetal to give an aldol
product which on subsequent cyclodehydration and arom-
atization would give the C-pyrrolyl glycoside (Scheme 3).
(2S,3S,4R)-2-(4-Acetyl-5-methyl-1H-pyrrol-2-yl)tetrahydrofu-
ran-3,4-diyl Diacetate (3a)
Yield: 0.32 g (86%); viscous solid.
In summary, we have demonstrated an efficient protocol
for the synthesis of C-pyrrolyl glycosides from D-glu-
cosamine and 1,3-ketones or b-oxo esters. The use of in-
expensive and readily available CeCl3·7H2O makes this
method simple, convenient and practical. The versatility
and synthetic usefulness of this methodology was demon-
strated in the synthesis of some interesting C-pyrrolyl gly-
cosides. We believe that these C-pyrrolyl glycosides may
find applications in drug discovery programs.
IR (neat): 3274, 2921, 2852, 2362, 1747, 1641, 1588, 1448, 1374,
1243, 1069, 820 cm–1.
1H NMR (300 MHz, CDCl3): d = 8.64 (s, 1 H), 6.31 (s, 1 H), 5.24
(dd, J = 4.8, 9.7 Hz, 1 H), 5.11 (t, J = 4.8 Hz, 1 H), 4.77 (d, J = 5.8
Hz, 1 H), 4.22 (dd, J = 5.8, 9.8 Hz, 1 H), 3.81 (dd, J = 4.8, 9.7 Hz,
1 H), 2.46 (s, 3 H), 2.29 (s, 3 H), 2.04 (s, 6 H).
13C NMR (75 MHz, CDCl3): d = 194.9, 170.0, 169.9, 135.9, 125.6,
110.2, 108.0, 76.3, 75.0, 71.1, 70.2, 29.7, 20.5, 13.6.
LC-MS: m/z = 310 [M + H]+.
HRMS (ESI): m/z [M + H]+ calcd for C15H20NO6: 310.1290; found:
IR spectra were recorded on a Perkin-Elmer FT-IR 240-c spectro-
photometer using KBr optics. 1H and 13C NMR spectra were record-
ed on Bruker Avance 300 and Inova 500 spectrometers in CDCl3
using TMS as internal standard. Mass spectra were recorded on a
Finnigan MAT 1020 mass spectrometer operating at 70 eV. Column
chromatography was performed using E. Merck silica gel (60–120
mesh).
310.1296.
Methyl 5-[(2S,3S,4R)-3,4-Diacetoxytetrahydrofuran-2-yl]-2-
methyl-1H-pyrrole-3-carboxylate (3b)
Yield: 0.31 g (81%); yellow oil.
Synthesis 2011, No. 2, 337–341 © Thieme Stuttgart · New York

340
B. V. S. Reddy et al.
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IR (neat): 3307, 3019, 2923, 2850, 2363, 1747, 1699, 1455, 1374,
1232, 1096, 1068, 771 cm–1.
Ethyl 5-[(2S,3S,4R)-3,4-Diacetoxytetrahydrofuran-2-yl]-2-(py-
ridin-4-yl)-1H-pyrrole-3-carboxylate (3f)
Yield: 0.33 g (70%); dark brown oil.
1H NMR (500 MHz, CDCl3): d = 9.06 (s, 1 H), 6.40 (s, 1 H), 5.27
(d, J = 4.1 Hz, 1 H), 5.13 (t, J = 6.1 Hz, 1 H), 4.74 (d, J = 6.1 Hz, 1
H), 4.18 (dd, J = 5.1, 10.3 Hz, 1 H), 3.76 (dd, J = 3.1, 10.3 Hz, 1 H),
3.69 (s, 3 H), 2.39 (s, 3 H), 1.99 (s, 6 H).
13C NMR (75 MHz, CDCl3): d = 170.2, 170.0, 165.7, 136.3, 125.8,
111.6, 108.6, 76.0, 75.0, 71.1, 70.5, 50.7, 29.6, 20.6, 13.1.
ESI-MS: m/z = 326 [M + H]+.
HRMS (ESI): m/z [M + Na]+ calcd for C15H19NNaO7: 348.1059;
IR (neat): 3302, 2978, 2362, 1750, 1710, 1370, 1220, 1161, 1032,
762 cm–1.
1H NMR (300 MHz, CDCl3): d = 12.3 (s, 1 H), 8.34 (d, J = 4.5 Hz,
2 H), 7.57–7.50 (m, 2 H), 6.62 (s, 1 H), 6.02 (d, J = 5.8 Hz, 1 H),
5.54 (t, J = 6.0 Hz, 1 H), 4.83 (d, J = 6.4 Hz, 1 H), 4.10 (q, J = 6.9
Hz, 2 H), 3.93–3.88 (m, 2 H), 2.07 (s, 3 H), 1.80 (s, 3 H), 1.23 (t,
J = 6.9 Hz, 3 H).
13C NMR (75 MHz, CDCl3): d = 170.5, 169.9, 164.1, 148.8, 139.8,
134.2, 127.6, 123.7, 114.3, 112.8, 111.1, 76.6, 75.9, 70.6, 69.4,
60.0, 29.6, 20.7, 14.2.
found: 348.1046.
Ethyl 5-[(2S,3S,4R)-3,4-Diacetoxytetrahydrofuran-2-yl]-2-
methyl-1H-pyrrole-3-carboxylate (3c)
ESI-MS: m/z = 403 [M + H]+.
Yield: 0.34 g (85%); yellow oil.
HRMS (ESI): m/z [M + H]+ calcd for C20H23N2O7: 403.1427; found:
IR (neat): 3306, 2924, 2851, 1748, 1699, 1447, 1373, 1235, 1097,
780 cm–1.
403.1476.
(2S,3S,4R)-2-(6,6-Dimethyl-4-oxo-4,5,6,7-tetrahydro-1H-indol-
2-yl)tetrahydrofuran-3,4-diyl Diacetate (3g)
Yield: 0.26 g (62%); light yellow oil.
1H NMR (300 MHz, CDCl3): d = 9.07 (s, 1 H), 6.52 (s, 1 H), 5.41
(d, J = 3.7 Hz, 1 H), 5.27 (dd, J = 5.6, 11.8 Hz, 1 H), 4.91 (d, J = 6.6
Hz, 1 H), 4.25 (q, J = 7.1 Hz, 2 H), 3.91 (dd, J = 3.3, 10.1 Hz, 2 H),
2.47 (s, 3 H), 2.08 (s, 6 H), 1.33 (t, J = 7.1 Hz, 3 H).
13C NMR (75 MHz, CDCl3): d = 170.1, 169.9, 165.4, 136.3, 125.6,
111.7, 108.8, 74.8, 72.6, 71.1, 70.4, 59.3, 29.5, 20.5, 14.3, 13.0.
LC-MS: m/z = 340 [M + H]+.
HRMS (ESI): m/z [M + H]+ calcd for C16H22NO7: 340.1396; found:
IR (neat): 3241, 2924, 2852, 1784, 1635, 1487, 1371, 1246, 1073,
763 cm–1.
1H NMR (300 MHz, CDCl3): d = 9.72 (s, 1 H), 6.48 (s, 1 H), 5.43
(dd, J = 4.9, 8.8 Hz, 1 H), 5.25 (t, J = 6.6 Hz, 1 H), 4.94 (d, J = 6.9
Hz, 1 H), 4.32 (dd, J = 5.2, 10.1 Hz, 1 H), 3.90 (d, J = 5.2 Hz, 1 H),
2.65 (s, 2 H), 2.35 (s, 2 H), 2.12 (s, 3 H), 2.08 (s, 3 H), 1.10 (s, 6 H).
13C NMR (75 MHz, CDCl3): d = 194.1, 169.9, 143.8, 129.3, 119.1,
103.9, 75.6, 74.8, 71.1, 70.6, 51.7, 36.5, 35.6, 30.5, 29.5, 28.6, 20.5,
20.4.
340.1405.
Ethyl 5-[(2S,3S,4R)-3,4-Diacetoxytetrahydrofuran-2-yl]-2-iso-
propyl-1H-pyrrole-3-carboxylate (3d)
Yield: 0.36 g (82%); reddish yellow oil.
LC-MS: m/z = 350 [M + H]+.
IR (neat): 3335, 2973, 2875, 1748, 1699, 1471, 1373, 1227, 1084,
1060, 783 cm–1.
HRMS (ESI): m/z [M + H]+ calcd for C18H24NO6: 350.1603; found:
350.1621.
1H NMR (300 MHz, CDCl3): d = 8.72 (s, 1 H), 6.39 (s, 1 H), 5.31
(dd, J = 5.4, 9.8 Hz, 1 H), 5.17 (t, J = 5.8 Hz, 1 H), 4.83 (d, J = 6.6
Hz, 1 H), 4.31 (dd, J = 5.4, 10.1 Hz, 1 H), 4.20 (q, J = 7.1 Hz, 2 H),
3.88 (dd, J = 3.9, 10.1 Hz, 1 H), 3.41 (m, 1 H), 2.10 (s, 6 H), 1.35
(t, J = 7.1 Hz, 3 H), 1.31 (d, J = 2.4 Hz, 6 H).
13C NMR (75 MHz, CDCl3): d = 170.3, 170.0, 165.2, 146.1, 125.6,
110.7, 108.6, 76.2, 75.2, 74.9, 71.2, 59.3, 26.1, 21.8, 21.7, 20.6,
14.4.
(2S,3S,4R)-2-(4-Oxo-1,4-dihydroindeno[1,2-b]pyrrol-2-yl)tet-
rahydrofuran-3,4-diyl Diacetate (3h)
Yield: 0.23 g (55%); dark brown oil.
IR (neat): 3277, 2924, 2853, 1747, 1703, 1610, 1450, 1373, 1259,
1244, 1093, 724 cm–1.
1H NMR (300 MHz, CDCl3): d = 8.31 (s, 1 H), 7.62 (d, J = 8.3 Hz,
2 H), 7.23 (d, J = 8.4 Hz, 2 H), 6.48 (s, 1 H), 5.56 (d, J = 5.3 Hz, 1
H), 5.21 (t, J = 6.9 Hz, 1 H), 4.95 (t, J = 6.9 Hz, 1 H), 4.59 (d, J = 6.9
Hz, 1 H), 4.36 (dd, J = 5.2, 10.1 Hz, 1 H), 2.22 (s, 3 H), 2.18 (s, 3 H).
LC-MS: m/z = 368 [M + H]+.
HRMS (ESI): m/z [M + H]+ calcd for C18H26NO7: 368.1704; found:
13C NMR (75 MHz, CDCl3): d = 183.4, 166.9, 166.8, 135.5, 133.6,
128.7, 123.3, 116.3, 103.7, 76.3, 75.2, 71.1, 70.8, 29.7, 29.3.
368.1706.
Ethyl 5-[(2S,3S,4R)-3,4-Diacetoxytetrahydrofuran-2-yl]-2-phe-
nyl-1H-pyrrole-3-carboxylate (3e)
Yield: 0.36 g (75%); brown oil.
LC-MS: m/z = 356 [M + H]+.
HRMS (ESI): m/z [M + H]+ calcd for C19H18NO6: 356.1146; found:
356.1129.
IR (neat): 3311, 2924, 1749, 1700, 1459, 1245, 1104, 1072, 766
cm–1.
Acknowledgment
1H NMR (300 MHz, CDCl3): 9.23 (s, 1 H), 7.54 (d, J = 6.2 Hz, 2 H),
7.39–7.32 (m, 3 H), 6.67 (s, 1 H), 5.41 (dd, J = 5.2, 9.4 Hz, 1 H),
5.29 (t, J = 6.0 Hz, 1 H), 4.99 (d, J = 6.2 Hz, 1 H), 4.29 (dd, J = 5.4,
10.1 Hz, 1 H), 4.17 (q, J = 7.1 Hz, 2 H), 3.91 (dd, J = 3.3, 10.1 Hz,
1 H), 2.10 (s, 3 H), 2.08 (s, 3 H), 1.33 (t, J = 7.1 Hz, 3 H).
13C NMR (75 MHz, CDCl3): d = 170.3, 169.9, 164.6, 137.6, 131.7,
128.9, 127.9, 127.7, 112.2, 110.1, 76.2, 75.2, 71.1, 70.5, 59.8, 29.6,
20.5, 14.1.
R.J., K.B. and M.S. thank CSIR, New Delhi for the award of fel-
lowships.
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Synthesis 2011, No. 2, 337–341 © Thieme Stuttgart · New York

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