Synthesis of 1,4-dihydropyridines using Ce(SO4)2-SiO2 as catalyst under solvent-free conditions

Article abstract of DOI:10.1002/cjoc.201090101

A facile and efficient one-pot synthesis of 1,4-dihydropyridines from aldehyde, 1,3-dicarbonyl compounds and ammonium acetate in the presence of Ce(SO₄)₂-SiO₂ at 80 °C under solvent-free conditions is described. Compared with the classical Hantzsch reaction, this novel method consistently has the advantages of excellent yields and short reaction time.

Full text of DOI:10.1002/cjoc.201090101

NOTE
Synthesis of 1,4-Dihydropyridines Using Ce(SO ) -SiO as
4
2
2
Catalyst under Solvent-free Conditions
Pei, Wen*(裴文)
Wang, Qin(王勤)
Li, Xiaonian(李小年)
Sun, Li(孙莉)
College of Chemical Engineering and Materials, Zhejiang University of Technology,
Hangzhou, Zhejiang 310014, China
A facile and efficient one-pot synthesis of 1,4-dihydropyridines from aldehyde, 1,3-dicarbonyl compounds and
ammonium acetate in the presence of Ce(SO ) -SiO at 80 ℃ under solvent-free conditions is described. Com-
4
2
2
pared with the classical Hantzsch reaction, this novel method consistently has the advantages of excellent yields and
short reaction time.
Keywords 1,4-dihydropyridine, Ce(SO ) -SiO , solvent-free, heterogneous catalysis, supported catalyst
4
2
2
Introduction
Ce(SO
4
)
2
-SiO
2
as a heterogeneous acid catalyst can be
removed very easily from the reaction. The catalyst can
be easily prepared from the readily available ingredients,
cerium(IV) sulphate and silica gel. Recently, sol-
vent-free organic syntheses have received considerable
attention because they are operationally simple, often
involve nontoxic materials, and proceed in excellent
1
,4-Dihydropyridines (1,4-DHP) have received
much attention because of their wide range of pharma-
ceutical and biological properties. The current literature
reveals that 1,4-dihydropyridines exhibit several me-
dicinal applications including neuroprotectant and
platelet anti-aggregratory activity, in addition to acting
as a cerebral antiischemic agent in the treatment of
Alzheimer’s disease. These examples clearly demon-
1
2
3
14
yields with high selectivity. Thus, we report an effi-
cient and convenient procedure for the one-pot synthesis
of 1,4-dihydropyridine derivatives in excellent yield
from 1,3-dicarbonyl compounds, aldehydes and ammo-
4
strate the remarkable potential of novel DHP derivatives
as a source of valuable drug candidates. The classical
method for the synthesis of 1,4-dihydropyridines was
reported by Hantzsch and Liebigs more than a century
nium acetate by using heterogeneous catalyst (Ce(SO
SiO ) under solvent-free conditions. To the best of our
knowledge, there was no report for the synthesis of
,4-DHP catalyzed by Ce(SO -SiO (Eq.1).
4 2
) -
2
5
ago. This reaction involves a one-pot condensation of
1
4
)
2
2
an aldehyde with ethyl acetoacetate and ammonia re-
fluxing in alcohol or acetic acid for a long time. The
yields of 1,4-DHP by the Hantzsch method are gener-
6
-9
ally low. A number of modified methods under im-
proved conditions have been reported. However, many
of these methodologies have been associated with sev-
eral shortcomings such as harsh conditions, long reac-
tion time, occurrence of several side products, expen-
sive reagents, low product yields, and difficulty in re-
covery and reusability of the catalysts. Moreover, some
of them were conducted in organic solvents which are
often harmful to the environment. As a result, they are
frequently subjected to government restrictions and high
Results and discussion
1
0
waste disposal costs. Recently, the microwave and
A model reaction of benzaldehyde, ethyl acetoace-
tate and ammonium acetate was catalyzed by
Ce(SO ) -SiO under solvent-free conditions. It was
4 2 2
1
1
ultrasonic techniques have been introduced in the
Hantzsch reaction as well. Thus, the development of
facile synthetic methods to the Hantzsch reaction is de-
manded.
found that the reaction could go smoothly and the cor-
responding product 4a was obtained in high yield (96%),
when the mixture was heated at 80 ℃ for 20 min. But
Cerium(IV) sulphate can be used in many reactions
1
2
13
such as Ritter reaction, esterification and oxidation.
in the absence of Ce(SO
4
)
2
-SiO
2
, the yield could only
*
E-mail: peiwen58@zjut.edu.cn; Tel.: 0086-0571-88320629; Fax: 0086-0571-88320629
Received June 30, 2009; revised October 19, 2009; accepted December 2, 2009.
Project suppored by the Open Foundation of the Key Discipline of Industrial Catalysis of Zhejiang Province.
Chin. J. Chem. 2010, 28, 483— 486 © 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
483

Pei et al.
NOTE
receive 30% under the same conditions. The best molar
ratios of benzaldehyde to ethyl acetoacetate to ammo-
nium acetate is 1∶2∶2. Encouraged by this result, a
series of aldehydes and 1,3-dicarbonyl compounds were
examined under the optimized conditions. The general-
ity and scope of the reaction was summarized in Table
tive use of the recovered catalyst, showing yield varia-
tion of less than 5% in the formation of 1,4-DHP in Ta-
ble 1.
When Ce(SO ) was supported on gel, the activity
4 2
points would be added, so the catalytic activity would
be enhanced. Additionally, it is very easy to isolate and
1
.
4 2 2
recycle. The plausible mechanism was Ce(SO ) -SiO
enhancing the formation of intermediate products that
were synthesized by 1,3-dicarbonyl compounds and
aldehydes.
4 2
Table 1 Synthesis of 1,4-dihydropyridines catalyzed by Ce(SO ) -
SiO
2
under solvent-free conditions
1
2
a
In summary, this paper describes a convenient and
efficient process for the synthesis of 1,4-dihydropy-
ridines using Ce(SO ) -SiO as catalyst under solvent-
4 2 2
Compd.
R
R
Yield /%
OEt
OEt
OEt
C
6
6
H
H
5
5
5
96
b
4
a
C
92
free conditions. The present methodology offers very
attractive features such as reduced reaction time, in-
creased yields and economic viability of the catalyst,
when compared with conventional method as well as
with other catalysts, which will have wide scope in or-
ganic synthesis. The simple procedure combined with
ease of recovery and reuse of this catalyst will make this
method economic, benign and a waste-free chemical
process for the synthesis of 1,4-dihydropyridines.
c
6
C H
30
4
b
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OMe
OMe
OMe
Me
4-CH C H
4
91
92
93
90
95
93
93
90
90
91
95
92
91
94
92
92
93
95
90
3
6
4c
2 6 4
3-O NC H
4
d
4-CH OC H
3
6
4
4e
4-ClC H
6
4
4
f
6 4
4-HOC H
4
g
3 2 6 3
3,4-(CH O) C H
4
h
4-HO-3-CH OC H
3
6
3
Experimental
4i
C H CH＝CH
6
5
4
j
2,4-Cl
2
C
6
H
3
Melting points were determined on a WRS-1B digi-
1
4
k
2-ClC H
tal melting-point instrument and uncorrected. H NMR
6
4
spectra were measured on a Bruker AVANCE 400
spectrometer using TMS as an internal standard and
DMSO-d or CDCl as solvent. IR spectra were re-
6 3
corded on Nicolet Avatar 360 FT-IR instrument. Liquid
aldehydes and 1,3-dicarbonyl compounds were purified
by distillation, and solid aldehydes by recrystallization
prior to use.
4l
4-FC H
6
4
4
m
2-O
2
NC
6
H
4
4
n
(CH ) CH
3
2
4
o
p
q
6
C H
5
4
4-CH
3 6 4
C H
4
3-O NC H
2
6
4
4r
C H
6 5
General procedure
4
s
Me
4-MeOC H
6
4
Preparation of the supported catalyst The cata-
lyst was prepared by mixing silica gel (8.0 g, Merck
grade 60, 230—400 mesh) with a solution of Ce(SO )
4
t
Me
2-Furyl
a
b
Yields of the isolated products. Yields of the catalyst recycling
reactions. Yields of the isolated product without catalyst under
the same conditions.
4
2
c
(2.0 g) in distilled water (10 mL). The resulting mixture
was stirred for 30 min to absorb Ce(SO ) on the surface
4
2
of silica gel. After the removal of water in a rotary
evaporator, the solid powder was dried at 105 ℃ for
2—3 h under reduced pressure.
As can be seen from Table 1, aromatic aldehydes,
,3-dicarbonyl compounds and ammonium acetate in
1
the presence of Ce(SO -SiO without any solvent gave
4
)
2
2
Synthesis of 1,4-dihydropyridines A mixture of
aldehyde (10 mmol), 1,3-dicarbonyl compounds (20
mmol), ammonium acetate (20 mmol) and Ce(SO ) -
the corresponding 1,4-dihydropyridines in good yields
after 20—40 min. A variety of substituted aromatic al-
dehydes carrying either electron-withdrawing groups or
electron-donating groups afford excellent yields of
products. The experimental procedure is very simple
and convenient, and has the ability to tolerate a variety
of other functional groups such as methyl, nitro, hy-
droxyl and halides under the reaction conditions. Every
substituent in aldehyde components has been accom-
modated and remained after the reaction. The heteroge-
neous catalyst could be easily isolated by filteration
4
2
SiO (0.5 g) was heated at 80 ℃ with stirring for
2
20—40 min. After the completion of reaction as indi-
cated by TLC, the reaction mixture was washed with ice
cold water and extracted with ethyl acetate. The organic
layer was washed with water, and then dried with anhy-
drous magnesium sulfate. The solution was concen-
trated under vacuum to afford the crude product. The
pure product was obtained by further re-crystallization
using absolute alcohol. All the products were character-
1
from the reaction mixture. Ce(SO
4
)
2
-SiO
2
was recovered
ized by comparing their IR, H NMR and melting points
and reused without further activation. Only slight reduc-
tion in the catalytic activity was found during consecu-
with those reported in literature.
4
84
www.cjc.wiley-vch.de
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2010, 28, 483— 486

Synthesis of 1,4-Dihydropyridines under Solvent-free Conditions
Characterization of products
(KBr) ν: 3336, 3098, 3023, 2977, 2096, 1688, 1645,
－
1
1
5
1
1
491, 1327, 1121, 770 cm .
4
a: m.p. 157—159 ℃ (Lit. 158—160 ℃); H
1
1
1
4
j: m.p. 108—110 ℃ (Lit. 109—110 ℃); H
NMR (CDCl
3
, 400 MHz) δ: 1.24 (t, J＝7.2 Hz, 6H),
NMR (CDCl
3
, 400 MHz) δ: 1.24 (t, J＝7.2 Hz, 6H),
2
(
1
7
.32 (s, 6H), 4.10 (q, J＝7.2 Hz, 4H), 5.00 (s, 1H), 5.63
2
.13 (s, 6H), 2.49 (s, 3H), 4.13 (q, J＝7.2 Hz, 4H), 5.58
brs, 1H), 7.12—7.31 (m, 5H); IR (KBr) ν: 3341, 3060,
(
s, 1H), 5.94 (brs, 1H), 7.22—7.39 (m, 3H); IR (KBr) ν:
688, 1651, 1488, 1372, 1229, 1211, 1123, 1091, 1020,
－
1
－
1
3
291, 3098, 3023, 2979, 2095, 1696, 1669, 819 cm .
68, 703, 680 cm .
1
1
1
1
5
1
4
k: m.p. 82—84 ℃ (Lit. 83—85 ℃); H NMR
4
b: m.p. 135—137 ℃ (Lit. 136—138 ℃); H
(CDCl
3
, 400 MHz) δ: 1.22 (t, J＝7.2 Hz, 6H), 2.32 (s,
NMR (CDCl
3
, 400 MHz) δ: 1.24 (t, J＝7.2 Hz, 6H),
6
6
3
H), 4.12 (q, J＝7.2 Hz, 4H), 4.62 (s, 1H), 5.65 (s, 1H),
2
(
.27 (s, 3H), 2.32 (s, 6H), 4.10 (q, J＝7.2 Hz, 4H), 5.02
.00 (brs, 1H), 7.20—7.37 (m, 4H); IR (KBr) ν: 3315,
s, 1H), 5.60 (brs, 1H), 7.10 (d, J＝7.2 Hz, 2H), 7.17 (d,
－
1
098, 3023, 2979, 2095, 1696, 1647, 756 cm .
J＝7.2 Hz, 2H); IR (KBr) ν: 3350, 2990, 1700, 1688,
1
8
1
－
1
4
l: m.p. 147—149 ℃ (Lit. 148—150 ℃); H
1
649, 1490, 1390, 1200, 1100, 1090 cm .
1
5
1
3
NMR (CDCl , 400 MHz) δ: 2.23 (s, 6H), 2.34 (s, 6H),
4
c: m.p. 166—168 ℃ (Lit. 165—167 ℃); H
4
7
1
.96 (s, 1H), 5.52 (brs, 1H), 6.87—6.89 (m, 2H), 7.20—
NMR (CDCl
3
, 400 MHz) δ: 1.22 (t, J＝7.2 Hz, 6H),
.23 (m, 2H); IR (KBr) ν: 3344, 3067, 2905, 1687, 1652,
371, 1333, 1170, 1016, 745 cm .
2
(
1
3
1
.37 (s, 6H), 4.10 (q, J＝7.2 Hz, 4H), 5.09 (s, 1H), 5.77
－
1
brs, 1H), 7.38 (t, J＝8.0 Hz, 1H), 7.64 (d, J＝8.0 Hz,
1
8
1
4
m: m.p. 167—169 ℃ (Lit. 168—170 ℃); H
H), 8.00 (d, J＝8.0 Hz, 1H), 8.13 (s, 1H); IR (KBr) ν:
NMR (CDCl
2
3
, 400 MHz) δ: 1.19 (t, J＝7.0 Hz, 6H),
333, 2990, 1700, 1633, 1510, 1475, 1350, 1200, 1110,
－
1
.18 (s, 6H), 4.10 (q, J＝7.2 Hz, 4H), 5.58 (s, 1H), 5.85
010, 800, 750, 700 cm .
1
5
1
(
brs, 1H), 7.44 (dd, J＝8.2, 2.4 Hz, 1H), 7.52—7.55 (m,
4
d: m.p. 154—156 ℃ (Lit. 153—155 ℃); H
2
3
7
H), 7.73 (dd, J＝8.2, 2.4 Hz, 1H); IR (KBr) ν: 3330,
NMR (CDCl
3
, 400 MHz) δ: 1.23 (t, J＝7.2 Hz, 6H),
092, 1695, 1678, 1528, 1489, 1354, 1280, 1100, 1020,
2
(
.33 (s, 6H), 3.77 (s, 3H), 4.10 (q, J＝7.2 Hz, 4H), 5.02
－
1
15 cm .
s, 1H), 5.69 (brs, 1H), 6.75 (d, J＝8.0 Hz, 2H), 7.20 (d,
1
8
1
4
n: m.p. 94—96 ℃ (Lit. 95—97 ℃); H NMR
J＝8.0 Hz, 2H); IR (KBr) ν: 3350, 2990, 1700, 1650,
－
1
(CDCl
3
, 400 MHz) δ: 0.75 (d, J＝6.8 Hz, 6H), 1.31 (t,
1
500, 1380, 1210, 834, 786, 750 cm .
1
5
1
J＝7.2 Hz, 6H), 1.55 (q, J＝6.8 Hz, 1H), 2.31 (s, 6H),
4
e: m.p. 144—146 ℃ (Lit. 143—146 ℃); H
3
.93 (d, J＝6.8 Hz, 1H), 4.15 (q, J＝7.2 Hz, 4H), 5.62
NMR (CDCl
3
, 400 MHz) δ: 1.23 (t, J＝7.2 Hz, 6H),
(brs, 1H); IR (KBr) ν: 3344, 3026, 2872, 1697, 1487,
2
(
2
1
.33 (s, 6H), 4.10 (q, J＝7.2 Hz, 4H), 5.02 (s, 1H), 5.59
－
1
1
216, 105l, 772, 744 cm .
brs, 1H), 7.17 (d, J＝8.0 Hz, 2H), 7.23 (d, J＝8.0 Hz,
1
9
1
4
o: m.p. 196—198 ℃ (Lit. 196—198 ℃); H
H); IR (KBr) ν: 3358, 2987, 1695, 1651, 1507, 1490,
－
1
3
NMR (CDCl , 400 MHz) δ: 2.32 (s, 6H), 3.64 (s, 6H),
210, 1120, 1020 cm .
1
6
1
5
.02 (s, 1H), 5.60 (brs, 1H), 5.59 (brs, 1H), 7.10—7.29
4
f: m.p. 223—225 ℃ (Lit. 222—224 ℃); H
(m, 5H); IR (KBr) ν: 3343, 3081, 3026, 2950, 1699,
NMR (CDCl
3
, 400 MHz) δ: 1.23 (t, J＝7.2 Hz, 6H),
－
1
1
649, 768, 703, 680 cm .
2
(
.32 (s, 6H), 4.10 (q, J＝7.2 Hz, 4H), 5.02 (s, 1H), 5.40
1
9
1
4
p: m.p. 175—177 ℃ (Lit. 174—176 ℃); H
s, 1H), 5.49 (brs, 1H), 6.69 (d, J＝8.0 Hz, 2H), 6.89 (d,
3
NMR (CDCl , 400 MHz) δ: 2.27 (s, 3H), 3.34 (s, 6H),
J＝8.0 Hz, 2H); IR (KBr) ν: 3347, 2987, 2939, 1660,
－
1
3
8
3
.64 (s, 6H), 5.02 (s, 1H), 5.59 (brs, 1H), 7.03 (d, J＝
1
634, 1511, 1488, 1369, 1227, 1171, 1022 cm .
1
6
1
.0 Hz, 2H), 7.17 (d, J＝8.0 Hz, 2H); IR (KBr) ν: 3314,
4
g: m.p. 138—140 ℃ (Lit. 138—140 ℃); H
105, 2942, 1697, 1655, 1495, 1320, 1200, 1133, 1100
NMR (CDCl
3
, 400 MHz) δ: 1.24 (t, J＝7.2 Hz, 6H),
－
1
cm .
2
.34 (s, 6H), 3.82 (s, 3H), 3.84 (s, 3H), 4.11 (q, J＝7.2
1
9
1
4
q: m.p. 210—212 ℃ (Lit. 210—212 ℃); H
Hz, 4H), 4.95 (s, 1H), 5.62 (brs, 1H), 6.72 (d, J＝8.0 Hz,
3
NMR (CDCl , 400 MHz) δ: 2.38 (s, 6H), 3.64 (s, 6H),
1
3
H), 6.80 (d, J＝8.0 Hz, 1H) , 6.88 (s, 1H); IR (KBr) ν:
5
7
.10 (s, 1H), 5.75 (brs, 1H), 7.38 (t, J＝8.0 Hz, 1H),
340, 1700, 1650, 1510, 1470, 1200, 1130, 1030, 780
－
1
.63 (d, J＝8.0 Hz, 1H), 8.01 (d, J＝8.0 Hz, 1H), 8.10
cm .
1
6
1
(
s, 1H); IR (KBr) ν: 3350, 3003, 2960, 1705, 1651, 1527,
4
h: m.p. 158—160 ℃ (Lit. 158—159 ℃); H
－
1
1
090, 1018, 856, 786, 755, 695 cm .
NMR (CDCl
3
, 400 MHz) δ: 1.24 (t, J＝7.2 Hz, 6H),
1
8
1
4
r: m.p. 179—181 ℃ (Lit. 180—182 ℃); H
2
(
1
1
1
1
.33 (s, 6H), 3.83 (s, 3H), 4.10 (q, J＝7.2 Hz, 4H), 4.90
3
NMR (CDCl , 400 MHz) δ: 2.25 (s, 6H), 2.35 (s, 6H),
s, 1H), 5.48 (s, 1H), 5.55 (brs, 1H), 6.68 (d, J＝8.2 Hz,
5
.02 (s, 1H), 5.58 (brs, 1H), 7.12—7.16 (m, 3H), 7.23
H), 6.80 (dd, J＝8.2, 2.0 Hz, 1H), 6.84 (d, J＝2.0 Hz,
H) ; IR (KBr) ν: 3351, 2983, 2953, 1681, 1653, 1598,
514, 1489, 1370, 1303, 1272, 1218, 1160, 1122, 1095,
(
dd, J＝8.8, 2.4 Hz, 2H); IR (KBr) ν: 3321, 3062, 2929,
－
1
1
670, 1475, 1376, 1299, 1113, 936, 790, 727, 703 cm .
1
8
1
－
1
4
s: m.p. 147—149 ℃ (Lit. 148—150 ℃); H
020 cm .
1
7
1
NMR (CDCl
3
, 400 MHz) δ: 1.25 (t, J＝7.2 Hz, 6H),
4
i: m.p. 148—150 ℃ (Lit. 149—150 ℃); H
2
.35 (s, 6H), 3.87 (s, 3H), 4.07 (q, J＝7.2 Hz, 4H), 4.98
NMR (CDCl
3
, 400 MHz) δ: 1.29 (t, J＝7.2 Hz, 6H),
(
s, 1H), 5.60 (brs, 1H), 6.80 (d, J＝8.2 Hz, 2H), 6.98 (d,
2
(
1
.33 (s, 6H), 2.32 (s, 6H), 4.19 (q, J＝6.8 Hz, 4H), 4.62
J＝8.2 Hz, 2H); IR (KBr) ν: 3343, 3096, 2836, 1690,
d, J＝6.8 Hz, 1H), 5.74 (s, 1H), 6.17 (q, J＝6.8 Hz,
－
1
1
610, 1510, 1489, 1253, 1089, 786, 750 cm .
H), 6.23 (d, J＝6.8 Hz, 1H), 7.13—7.71 (m, 5H); IR
Chin. J. Chem. 2010, 28, 483— 486
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
485

Pei et al.
NOTE
1
8
1
4
t: m.p. 166—168 ℃ (Lit. 167—168 ℃); H
Tetrahedron Lett. 2003, 44, 4129.
NMR (CDCl
3
, 400 MHz) δ: 2.28 (s, 6H), 2.35 (s, 6H),
9
0
1
2
3
Sharma, S. D.; Hazarika, P.; Konwar, D. Catal. Commun.
2008, 9, 709.
5
6
3
7
.08 (s, 1H), 5.69 (brs, 1H), 6.06 (d, J＝3.6 Hz, 1H),
.23 (q, J＝3.6 Hz, 1H), 7.25 (s, 1H); IR (KBr) v: 3275,
1
1
1
1
Heldebrant, D. J.; Jessop, P. G. J. Am. Chem. Soc. 2003,
214, 2930, 1666, 1586, 1470, 1351, 1269, 1013, 934,
1
25, 5600.
－
1
87, 740 cm .
Wang, S. X.; Li, Z. Y.; Zhang, J. C.; Li, J. T. Ultrason.
Sonochem. 2008, 15, 677.
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