Silica-supported perchloric acid catalyzed one-pot synthesis of 1,4-dihydropyridines

Article abstract of DOI:10.1002/cjoc.201100032

An environmentally friendly and highly efficient procedure for the preparation of 1,4-dihydropyridines by the reaction between α,β- unsaturated aldehydes, aromatic amines and β-keto esters in the presence of silica supported perchloric acid is described.

Full text of DOI:10.1002/cjoc.201100032

FULL PAPER
Silica-supported Perchloric Acid Catalyzed One-pot Synthesis
of 1,4-Dihydropyridines
Ramesh, Dasari
Reddy, Thummalpally Srikanth
Manasa, Gajji Venkateswarlu, Yenamandra*
Rajaram, Singanaboina
Narasimhulu, Manchala
Mahesh, Kondempudi Chinni
Natural Products Laboratory, Organic Chemistry Division-I, Indian Institute of Chemical Technology,
Hyderabad-500 007, India
An environmentally friendly and highly efficient procedure for the preparation of 1,4-dihydropyridines by the
reaction between α,β-unsaturated aldehydes, aromatic amines and β-keto esters in the presence of silica supported
perchloric acid is described.
Keywords 1,4-dihydropyridines, silica supported perchloric acid, Hantzsch reaction, β-keto esters
6
Introduction
the N-aryl and C5
-C -unsubstituted systems. However
many of these procedures have one or more disadvan-
tages such as refluxing at high temperature, long reac-
tion times (55—85 h), requiring unusual starting mate-
rials, using toxic solvents, forming side products, low
yields, and difficulties in workup. In order to circum-
vent these associated problems with these procedures,
for the first time a multi component procedure has been
developed using CAN for the synthesis of 1,4-dihydro-
pyridines.12 Since, 1,4-dihydropyridine derivatives are
useful and important intermediates in synthesis and
pharmaceuticals, the development of simple, convenient
and high yielding protocols is desirable.
Multi component reactions (MCRs) constitute an
important group of transformations that combine three
or more substrates for an ideal synthesis, which gives
operational simplicity, atom economy, bond-forming
efficiency, the access to molecular complexity from
simple starting materials and so on. The modular char-
acter of this approach is extremely suitable for drug
discovery and therefore it is widely used for the fast
generation of bioactive compounds.1
1,4-Dihydropyridines are important class of hetero-
cycles with a wide range of biological activities such as
radio protective effect,2 HIV protease inhibitors,3 in the
management of cardiovascular diseases4 and some other
pharmacological activities.5 Further 1,4-dihydropyri-
dines are also very important synthetic intermediates for
the synthesis of various nitrogen containing heterocy-
cles.6 The best-known procedure for the preparation of
1,4-dihydropyridines is the classical Hantzsch synthesis
which involves the condensation of two molecules of a
β-ketoester, one molecule of an aldehyde, and one
molecule of ammonia.7 But some important types of
derivatives, including N-aryl-1,4-dihydropyridines8 and
C5-C6-unsubstituted 1,4-dihydropyridines are not al-
lowed to synthesis by this method. Because of their
biological activities and synthetic point of view few
efficient routes have been developed, these are the reac-
tion between α,β-unsaturated imines and β-dicarbonyl
compounds in the presence of sodium ethoxide9 at 150
℃, Michael reaction followed by cyclization between a
β-dicarbonyl compound and α,β-unsaturated imine in
the presence of lithium iodide10 and hetero Diels-Alder
reactions of 1-azadienes and allenic esters11 to generate
Results and discussion
Recently silica supported catalysts13 as well as per-
chloric acid impregnated on silica gel has gained con-
siderable attention in current organic synthesis due to its
ease of preparation, high efficiency, environmental be-
nignity, reusability of the catalyst and its economic vi-
ability. Because of its versatility of the catalyst in or-
ganic transformations14 we investigated employing
HClO4•SiO2 as a catalyst for the synthesis of 1,4-di-
hydropyridines. The catalyst HClO4•SiO2 was prepared
by the following reported procedure15 in which 1 g of
silica gel contains 0.37 mmol of HClO4.
Initially, a reaction was performed between cinna-
maldehyde (1a), aniline (2a), and ethylacetoacetate (3a)
in acetonitrile in the presence of HClO4•SiO2 at room
temperature to afford the corresponding 1,4-dihydro-
pyridine (4a) (Entry 1) (Scheme 1) in 96% yield in 20
min.16
*
E-mail: luchem@iict.res.in; Fax:＋0091(40)27160512
Received June 20, 2011; revised July 13, 2011; accepted July 21, 2011.
Chin. J. Chem. 2011, 29, 2471— 2475
© 2011 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Ramesh et al.
FULL PAPER
Scheme 1
Experimental
Solvents were dried over standard drying agents and
freshly distilled prior to use. The reagents were pur-
chased from Aldrich and Acros and were used without
further purification unless otherwise stated. Organic
solvents were dried over anhydrous Na2SO4 and con-
centrated in vacuo below 40 ℃. All column chroma-
tographic (CC) separations were performed using silica
1
gel (Acme’s 60—120 mesh). H NMR (200 and 300
MHz) spectra were measured with a Varian Gemini
FT-200 and Bruker Avance 300 instrument with
tetramethylsilane as an internal standard in CDCl3; J
values are given in Hz. Mass spectra were recorded on
Agilent Technologies 1100 Series (Agilent Chemista-
tion Software).
General procedure for preparation of compounds
The reaction proceeded very efficiently at room
temperature with excellent yields and without formation
of any side products. This is due to the rapid formation
and activation of the imines by solid HClO4•SiO2.
Similarly several types of anilines containing electron
releasing and electron withdrawing groups at ortho,
para, and meta positions such as alkyl, alkoxy, bromo,
chloro and fluoro were reacted with various β-keto es-
ters such as ethyl, methyl, allyl, and tertiary butyl aceto-
acetates and cinnamaldehyde in a one-pot operation by
using catalytic amount (5 mol%) of HClO4•SiO2 to give
1,4-dihydropyridines in 74%—96% yields (Table 1).
The reaction with aliphatic amines (eg. Benzyl
amine and phenylethylamine) gave complex reaction
mixtures containing only small amounts of the desired
products and the reactions with substituted cinnamal-
dehydes were also unsuccessful.
Moreover, it is noteworthy that this reaction does not
require any inert conditions to get good to excellent
yields without loss of efficiency of the catalyst. After
the completion of reaction, the catalyst was recovered
by filtration, washed with acetonitrile and recycled (af-
ter activation at 120 ℃ for 4—5 h) for four times in
subsequent reactions without substantial loss of its
catalytic activity. The recyclability of the catalyst was
verified on the reaction of cinnamaldehyde, ethylaceto-
acetate and aniline (Entry 1, Table 1) to afford dihy-
dropyridines in 96%, 92%, 85% and 79% yields over
four cycles.
4a— 4w
To a stirred solution of cinnamaldehyde (0.132 g, 1
mmol), aniline (0.094 g, 1 mmol) and ethylacetoacetate
(0.130 g, 1 mmol) in acetonitrile (5 mL), HClO4•SiO2 (5
mol%) was added. The reaction mixture was stirred at
r.t. for 20 min and the reaction was monitored by TLC.
After the completion of reaction mixture, the contents
were filtered (to remove the catalyst). The filtrate was
concentrated by vacuum. The residue was purified by
silica-gel column chromatography by eluting with
AcOEt/PE (1∶9) to afford the pure product in 96%
yield (0.306 g).
Ethyl-2-methyl-1,4-diphenyl-1,4-dihydropyri-
1
dine (4a) Yield 0.306 g (96%), gummy syrup; H
NMR (CDCl3, 200 MHz) δ: 1.19 (t, J＝7.1 Hz, 3H),
2.21 (s, 3H), 4.08 (q, J＝7.1 Hz, 2H), 4.75 (d, J＝5.5
Hz, 1H), 5.07 (dd, J＝5.5, 7.6 Hz, 1H), 6.23 (d, J＝7.6
Hz, 1H),－7.24—7.47 (m, 10H); IR (KBr) ν: 1690, 1568,
＋
1
1221 cm ; ESI-MS m/z: 319 (M ).
Ethy-2-methyl-1-(2-methylphenyl)-4-phenyl-1,4-
dihydropyridine-3-carboxylate (4b) Yield 0.313 g
1
(94%), gummy syrup; H NMR (CDCl3, 200 MHz) δ:
1.1 (t, J＝6.5 Hz, 3H), 2.08 (s, 3H), 2.30 (s, 3H), 4.02 (q,
J＝6.68 Hz, 2H), 4.70 (d, J＝5.28 Hz, 1H), 4.95 (dd,
J＝5.28 Hz, 7.45, 1H), 5.85 (d, J＝7.45 Hz, 1H), 7.10—
7.38 (m,－ 9H); IR (Neat) ν: 3025, 2＋980, 1689, 1568,
1
1225 cm ; ESI-MS m/z: 334 (M＋H) .
Ethyl-1,4-dihydro-1-(4-isopropylphenyl)-2-meth-
yl-4-phenylpyridine-3-carboxylate (4d) Yield 0.346
1
g (96%), gummy syrup; H NMR (CDCl3, 200 MHz) δ:
1.12 (t, J＝6.7 Hz, 3H), 1.28 (d, J＝6.79 Hz, 6H), 2.12
(s, 3H), 2.90—2.92 (m, 1H), 3.98—4.02 (m, 2H), 4.62
(d, J＝5.28 Hz, 1H), 4.90 (dd, J＝7.55, 6.04 Hz, 1H),
6.95 (d, J＝7.54 Hz, 1H), 7.09—7.13 (m, 3H), 7.20—
7.31 (m, 6H);－IR (Neat) ν: 3024, 29＋60, 1682, 1564,
In conclusion, we described a simple, efficient and
practical method for the synthesis of dihydropyridines
through a one-pot three-component coupling of cinnam-
aldehyde, β-keto ester and aromatic amines by using
heterogeneous catalyst, silica supported perchloric acid.
This simple method combined with ease of recovery and
reusability of the catalyst is expected to contribute to the
development of clean, cost effective, and environmen-
tally friendly procedure for the synthesis of 1,4-dihydro-
pyridines.
1
1510, 1220 cm ; ESI-MS m/z: 361 (M ).
Ethyl-2-methyl-1-(4-bromophenyl)-4-phenyl-1,4-
dihydropyridine-3-carboxylate (4e) Yield 0.357 g
1
(90%), gummy syrup; H NMR (CDCl3, 200 MHz) δ:
1.12 (t, J＝7.5 Hz, 3H), 2.12 (s, 3H), 4.02 (q, J＝6.0 Hz,
2H), 4.66 (d, J＝5.2 Hz, 1H), 4.98 (dd, J＝6.04, 7.55
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© 2011 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2011, 29, 2471— 2475

Silica-supported Perchloric Acid Catalyzed One-pot Synthesis of 1,4-Dihydropyridines
Table 1 HClO4•SiO2 catalyzed synthesis of 1,4-dihydropyridinesa
a
1
All products were characterized by H NMR and mass spectral data and spectral data of known compounds compared with reported
compounds.
Hz, 1H), 6.09 (d, J＝7.5 Hz, 1H), 7.06 (d, J＝8.3 Hz,
2H), 7.24—7.28 (m, 5H), 7.53 (d, J＝8.3 Hz, 2H); －IR
Ethyl-2-methyl-1-(4-chlorophenyl)-4-phenyl-1,4-
dihydropyridine-3-carboxylate (4f) Yield 0.324 g
1
1
(Neat) ν: 3061, 2943, 1667, 1567, 1510, 1221 cm ;
(92%), gummy syrup; H NMR (CDCl3, 200 MHz) δ:
ESI-MS: m/z 397 (M)＋.
2.01 (t, J＝6.5 Hz, 3H), 2.08 (s, 3H), 4.05 (q, J＝6.6 Hz,
Chin. J. Chem. 2011, 29, 2471— 2475
© 2011 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Ramesh et al.
FULL PAPER
2H), 4.68 (d, J＝5.2 Hz 1H), 4.98 (dd, J＝5.15, 7.48 Hz,
1H), 6.10 (d, J＝7.4 Hz, 1H), 7.15 (d, J＝8.2 Hz, 2H),
7.22—7.34 (m, 5H), 7.38 (d, J＝8.2 H－z, 2H); IR (Neat)
J＝5.2, 7.5 Hz, 1H), 5.04—5.08 (m, 2H), 5.76 (m, 1H),
6.12 (d, J＝7.5 Hz, 1H), 7.10—7.42 (m, 10H); IR (Neat)
－1
ν: 1698, 1597, 1495, 1222 cm ; ESI-MS m/z: 331
(M)＋.
1
ν: 3026, 2980, 1690, 1567, 1223 cm ; ESI-MS m/z:
354 (M＋H)＋.
Allyl-2-methyl-1-(2-methylphenyl)-4-phenyl-1,4-
dihydropyridine-3-carboxylate (4p) Yield 0.317 g
Ethyl-2-methyl-1-(4-methoxyphenyl)-4-phenyl-
1,4-dihydropyridine-3-carboxylate (4h) Yield 0.314
1
(92%), gummy syrup; H NMR (CDCl3, 200 MHz) δ:
1
g (90%), gummy syrup; H NMR (CDCl3, 200 MHz) δ:
2.10 (s, 3H), 2.30 (s, 3H), 4.44 (d, J＝5.2 Hz, 2H), 4.69
(d, J＝5.2 Hz, 1H), 4.98—5.01 (m, 3H), 5.69—5.72 (m,
1H), 5.83—5.85 (m, 1H), 7.04—7.38 (m, 9H); IR (Neat)
1.1 (t, J＝6.5 Hz, 3H), 2.10 (s, 3H), 3.80 (s, 3H), 3.94 (q,
J＝6.5 Hz, 2H), 4.62 (d, J＝1.5 Hz, 1H), 4.88 (dd, J＝
5.12, 7.3 Hz, 1H), 6.05 (d, J＝7.3 Hz, 1H), 6.88 (d, J＝
8.77 Hz, 2H), 7.12 (d, J＝8.77 Hz, 2H), 7.21—7.29 (m,
5H－); IR (Neat) ν: 3059, 2978, 1687, 1567, 1510, 1221
－1
ν: 3019, 2929, 1688, 1565, 1492, 1223 cm ; ESI-MS
m/z: 346 (M＋H)＋.
Allyl-2-methyl-4-phenyl-1-(4-isopropylphenyl)-
1,4-dihydropyridine-3-carboxylate (4q) Yield 0.352
＋
1
cm ; ESI-MS m/z: 349 (M) .
1
Methyl-2-methyl-1,4-diphenyl-1,4-dihydropyri-
dine-3-carboxylate (4i) Yield 0.289 g (95%), gummy
syrup; 1H NMR (CDCl3, 200 MHz) δ: 2.15 (s, 3H), 3.57
(s, 3H), 4.66 (d, J＝5.8 Hz, 1H), 4.99 (dd, J＝5.8 Hz,
7.3 Hz, 1H), 6.13 (d, J＝7.3 Hz, 1H),－7.14—7.45 (m,
g (94%), gummy syrup; H NMR (CDCl3, 200 MHz) δ:
1.24 (d, J＝6.7 Hz, 6H), 2.16 (s, 3H), 2.88—2.91 (m,
1H), 4.46 (d, J＝6.0 Hz, 1H), 4.69 (d, J＝5.2 Hz, 1H),
4.98 (t, J＝6.04 Hz, 1H), 5.13—5.05 (m, 3H), 5.76—
5.78 (m, 1H), 6.12 (d, J＝7.5 Hz, 1H),－7.20—7.36 (m,
1
1
10H); IR (Neat) ν: 1693, 1569, 1224 cm ; ESI-MS m/z:
9H); IR ＋(Neat) ν: 1692, 1568, 1226 cm ; ESI-MS m/z:
306 (M＋H)＋.
375 (M) .
Methyl-2-methyl-1-(2-methylphenyl)-4-phenyl-
1,4-dihydropyridine-3-carboxylate (4j) Yield 0.306
Allyl-2-methyl-1-(4-chlorophenyl)-4-phenyl-1,4-
dihydropyridine-3-carboxylate (4r) Yield 0.350 g
1
1
g (96%), gummy syrup; H NMR (CDCl3, 200 MHz) δ:
(96%), gummy syrup; H NMR (CDCl3, 200 MHz) δ:
2.05 (s, 3H), 2.25 (s, 3H), 3.52 (s, 3H), 4.65 (d, J＝5.26
Hz, 1H), 4.95 (dd, J＝5.26, 7.54 Hz, 1H), 5.85 (d, J＝
7.54 Hz, 1H), 7.10—7.30 (m, 9H); IR (Neat) ν: 3076,
2.17 (s, 3H), 4.48 (d, J＝5.2 Hz, 2H), 4.68 (d, J＝5.2
Hz, 1H), 5.0 (dd, J＝5.2, 7.5 Hz, 1H), 5.08—5.11 (m,
2H), 5.74—5.77 (m, 1H), 6.08 (d, J＝7.5 Hz, 1H), 7.12
(d, J＝8.3 Hz, 2H), 7.24—7.32 (m, 5H), 7.38 (d, J＝8.3
Hz, 2H); IR (Neat) ν: 3026, 1693, 1565, 1491, 1220
－1
2874, 2753, 1610, 1497, 1227 cm ; ESI-MS m/z: 320
(M＋H)＋.
＋
－1
Methyl-2-methyl-1-(4-isopropylphenyl)-4-phenyl-
1,4-dihydropyridine-3-carboxylate (4k) Yield 0.319
cm ; M/S m/z: 365 (M) .
1
g (92%), gummy syrup; H NMR (CDCl3, 200 MHz) δ:
Acknowledgements
1.25 (d, J＝6.6 Hz, 6H); 2.15 (s, 3H), 2.9—3.01 (m,
1H), 3.55 (s, 3H), 4.7 (d, J＝5.1 Hz, 1H), 4.96 (dd, J＝
5.8, 8.0 Hz, 1H), 6.12 (d, J＝8.08 Hz, 1H), 7.04—7.32
(m, 9H); IR (Neat) ν: 3028, 2959, 2926, 1695, 1566,
The authors thank to Council of Scientific and In-
dustrial Research New Delhi, India, for financial assis-
tance.
＋
－1
1513, 1225 cm ; ESI-MS m/z: 347 (M) .
References
Methyl-2-methyl-1-(4-methoxyphenyl)-4-phenyl-
1,4-dihydropyridine-3-carboxylate (4l) Yield 0.301
g (90%), gummy syrup; H NMR (CDCl3, 200 MHz) δ:
1
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Silica-supported Perchloric Acid Catalyzed One-pot Synthesis of 1,4-Dihydropyridines
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