ZnO nanoparticles: An efficient reagent, simple and one-pot procedure for synthesis of highly functionalized dihydropyridine derivatives

Article abstract of DOI:10.1155/2012/780470

A new and efficient one-pot synthesis of dihydropyridones derivatives by four-component reaction between cyanoacetamide, aryl aldehydes, and ethyl acetoacetate with ammonium acetate using nano ZnO is described. The reaction was performed in ethanol under reflux conditions and afforded good yields of products.

Full text of DOI:10.1155/2012/780470

ISSN: 0973-4945; CODEN ECJHAO
E-Journal of Chemistry
http://www.ejchem.net
2012, 9(2), 615-620
ZnO nanoparticles: An efficient reagent, simple and
One-Pot Procedure for Synthesis of Highly
Functionalized Dihydropyridine Derivatives
MARZIYEH KHAZAEI1, MOHAMMAD ANARY-ABBASINEJAD2, ALIREZA
HASSANABADI3*, and BAHAREH SADEGHI1
1Department of Chemistry, Islamic Azad University, Yazd Branch, P.O. Box 89195-155,
Yazd, Iran
2Department of Chemistry, Rafsanjan Vali-e-Asr University, Rafsanjan, P.O. Box 77176,
Iran
3Department of Chemistry, Islamic Azad University, Zahedan Branch, P.O. Box 98135-978,
Zahedan, Iran
ar_hasanabadi@yahoo.com
Received 20 May 2011; Accepted 15 July 2011
Abstract: A new and efficient one-pot synthesis of dihydropyridones
derivatives by four-component reaction between cyanoacetamide, aryl
aldehydes, and ethyl acetoacetate with ammonium acetate using nano ZnO is
described. The reaction was performed in ethanol under reflux conditions and
afforded good yields of products.
Keywords: Dihydropyridones derivatives, Ammonium acetate, Cyanoacetamide, Aryl aldehydes,
Multi-component reaction, ZnO nanoparticles.
Introduction
Substituted dihydropyridones derivatives are important intermediates in the pharmaceutical,
dye and photo industries.1 pyridones are of interest because of the occurrence of their
saturated and partially saturated derivatives in biologically active compounds and natural
products such as NAD nucleotides, pyridoxol (vitamin B6), and pyridine alkaloids.2 Due to
their π-stacking ability, some pyridines are used in supramolecular chemistry.3 Some
examples are used as pharmaceuticals (as antimalarial, vasodilator, anesthetic,
anticonvulsant, and antiepileptic), dyes, additives (as antioxidant), agrochemicals (as
fungicidal, pesticidal, and herbicidal), veterinary (as anthelmintic, antibacterial, and
antiparasitic), and also in qualitative and quantitative analysis4-7. So far, the most common
synthetic methods for the preparation of pyridine ring systems involve: transformation of
another ring, and cyclizations classified on the basis of the number of ring atoms in each of
the components being cyclized: from six ring atoms by N–Cα, Cα–Cβ, or Cβ–Cγ bond

616 ALIREZA HASSANABADI et al.
formation; by formation of two bonds, from [5+1], [4+2], or [3+3] atom fragments; by formation
of three bonds, from [4+1+1], [3+2+1], or [2+2+2] atom fragments; and by formation of
four bonds, from [3+1+1+1] or [2+2+1+1] atom fragments.8,9 Synthesis of 4-aryl-3-cyano-
2,5-dihydro pyridin-2-one derivatives under solvent-Free conditions we reported10.
Nanomaterials have attracted considerable interest in the last decade because of their
unique properties in physics and chemistry as well as their potential industrial applications.
Among these materials, ZnO is an important semi-conducting material, having a wide range
of properties. The size and morphology of ZnO nanoparticles have great influences on their
performances. Recently, efforts have been made for the synthesis of ZnO particles with
controlled morphologies. Wurtzite-type ZnO crystals are used for a wide variety of
industrial applications, such as semiconductors11 catalysts12, room-temperature UV lasers13,
solar cells14 and sensors15.
Experimental
Melting points were determined with an Electrothermal 9100 apparatus. Elemental analyses
were performed using a Costech ECS 4010 CHNS-O analyzer at analytical laboratory of
Islamic Azad University Yazd branch. Mass spectra were recorded on a FINNIGAN-MAT
8430 mass spectrometer operating at an ionization potential of 70 eV. IR spectra were
1
recorded on a Shimadzu IR-470 spectrometer. H and 13C NMR spectra were recorded on
1
BRUKER DRX-500 AVANCE spectrometer at 500.1 and 125.8 MHz, respectively. H and
13C NMR spectra were obtained on solution in CDCl3 using TMS as internal standard.
Column chromatography was performed with Merck silica gel 60, 230-400 mesh. The
chemicals used in this work were purchased from Fluka (Buchs, Switzerland) and were used
without further purification.
General procedure
In a typical experiment, a mixture of ZnO nanoparticles (10 mol%), aryl aldehydes 1 (1
mmol), and cyanoacetamide 2 (1 mmol) in ethanol (20 mL) was stirred at room
temperature for 3h and was added to it a solution of , ethyl acetoacetate(1 mmol) 3 and
NH4OAc(1 mmol) and was refluxed for 8h. After completion of the reaction, as
indicated by TLC, the product was extracted with ethyl acetate (10 mL). The combined
organic extracts were concentrated in vacuum and the resulting product was purified by
column chromatography on silica gel with ethyl acetate and n-hexane (1:1) as eluent to
afford the pure product.
Ethyl 5-cyano-2-methyl-6-oxo-4-phenyl-1,4,5,6-tetrahydropyridine 3-carboxylate (1A)
White powder, (59 %), m.p. 143–145˚C, IR (KBr) (νmax/cm-1): 3411 (NH), 2234 (CN), 1709
(C=O). MS, m/z (%): 284 (M+., 5). Anal. Calcd for C16H16N2O3 : C, 67.59; H, 5.67; N, 9.85
1
3
%. Found: C, 67.43; H, 5.72; N, 9.75%. H NMR (500.1 MHZ, CDCl3): δ = 0.80(3H, t, JHH
= 7 HZ, CH3), 2.38 (3H, s, CH3), 4.09 (2H, q, 3JHH = 7 HZ, CH2), 4.16 (H, d, 3JHH = 7.1HZ,
3
CH), 4.47 (H, d, JHH = 7.1HZ, CH), 7.26-7.61 (5H, m, aromatic), 13.38(1 H, broad s, NH).
13C NMR (125.7 MHZ, CDCl3): δ = 14.50 and 19.27 (2CH3), 41.66 and 41.97 (2CH), 61.23
(CH2), 108.12 (CN), 114.62 and 146.48 (C=C), 128.25, 128.95, 129.45, 136.47 (aromatic),
163.71 and 165.91 (2C=O).
Ethyl 5-cyano-2-methyl-6-oxo-4-(4-chlorophenyl)-1,4,5,6-tetrahydropyridine 3-
carboxylate (2A)
White powder, (58 %), m.p. 162–164˚C, IR (KBr) (νmax/cm-1): 3403 (NH), 2273 (CN), 1706
(C=O). MS, m/z (%): 318 (M+., 10). Anal. Calcd for C16H15ClN2O3 : C, 60.29; H, 4.74; N,

A Simple and One-Pot Procedure for Synthesis of Highly Functionalized 617
1
8.79%. Found: C, 60.20; H, 4.87; N, 8.63%. H NMR (500.1 MHZ, CDCl3): δ = 1.21(3H, t,
3
3
3JHH = 7 HZ, CH3), 2.49 (3H, s, CH3), 4.13 (2H, q, JHH = 7 HZ, CH2), 3.66 (H, d, JHH
=
7.1HZ, CH), 4.48 (H, d, 3JHH = 7.1HZ, CH), 7.10 -7.38 (4H, m, aromatic), 12.74 (1 H, broad
s, NH). 13C NMR (125.7 MHZ, CDCl3): δ = 14.30 and 18.51 (2CH3), 40,99 and 41.83 (2CH),
60.31 (CH2), 104.62 (CN), 116.05 and 148.30 (C=C), 129.17, 130.04, 132.99, 137.50
(aromatic), 163.28 and 166.10 (2C=O).
Ethyl 5-cyano-2-methyl-6-oxo-4-(4-bromophenyl)-1,4,5,6-tetrahydropyridine 3-car-
boxylate (3A)
White powder, (61 %), m.p.175–177˚C, IR (KBr) (νmax/cm-1): 3414 (NH), 2210 (CN), 1697
(C=O). MS, m/z (%): 363 (M+., 8).Anal. Calcd for C16H15BrN2O3 : C, 52.91; H, 4.16; N,
1
7.71%. Found: C, 52.60; H, 4.25; N, 7.61%. H NMR (500.1 MHZ, CDCl3): δ = 1.22 (3H, t,
3
3
3JHH = 7 HZ, CH3), 2.46 (3H, s, CH3), 4.11 (2H, q, JHH = 7 HZ, CH2), 3.62 (H, d, JHH
=
7.1HZ, CH), 4.47 (H, d, 3JHH = 7.1HZ, CH), 7.12 -7.49 (4H, m, aromatic), 7.84(1 H, broad s,
NH). 13C NMR (125.7 MHZ, CDCl3): δ = 14.12 and 19.03 (2CH3), 40,99 and 41.07 (2CH),
60.97 (CH2), 107.38 (CN), 113.85 and 146.05 (C=C), 122.72, 129.35, 132.26, 134.93
(aromatic), 162.79 and 165.18 (2C=O).
Ethyl 5-cyano-2-methyl-6-oxo-4-(3-methoxyphenyl)-1,4,5,6-tetrahydropyridine 3-car-
boxylate (4A)
White powder, (57 %), m.p. 134–136˚C, IR (KBr) (νmax/cm-1): 3415 (NH), 2220 (CN), 1705
(C=O). MS, m/z (%): 314 (M+., 12).Anal. Calcd for C17H18N2O4 : C, 64.96; H, 5.77; N,
1
8.91%. Found: C, 64.88; H, 5.70; N, 8.95 %. H NMR (500.1 MHZ, CDCl3): δ = 1.24 (3H, t,
3
3JHH = 7 HZ, CH3), 2.44 (3H, s, CH3), 3.80 (3H, s, OCH3), 4.16 (2H, q, JHH = 7 HZ, CH2),
3
3
4.10 (H, d, JHH = 7.1HZ, CH), 4.48 (H, d, JHH = 7.1HZ, CH), 6.79-7.29 (4H, m, aromatic),
7.82 (1 H, broad s, NH). 13C NMR (125.7 MHZ, CDCl3): δ = 14.11 and 18.87 (2CH3), 39.82
and 42.91 (2CH), 55.23 (OCH3), 60.82 (CH2), 107.61 (CN), 113.39 and 146.02 (C=C),
113.08, 114.13, 120.03, 130.07, 137.51 159.87 (aromatic), 163.20 and 165.02 (2C=O).
Ethyl 5-cyano-2-methyl-6-oxo-4-(2-nitrophenyl)-1,4,5,6-tetrahydropyridine 3-car-
boxylate (5A)
White powder, (54 %), m.p. 166–168 ˚C, IR (KBr) (νmax/cm-1): 3400 (NH), 2250 (CN), 1704
1
3
(C=O), 1346 and 1523 (NO2). H NMR (500.1 MHZ, CDCl3): δ = 1.10 (3H, t, JHH = 7 HZ,
3
3
CH3), 2.57 (3H, s, CH3), 4.04 (2H, q, JHH = 7 HZ, CH2), 3.97 (H, d, JHH = 7.1HZ, CH),
4.29 (H, d, JHH = 7.1HZ, CH), 7.20 -7.98 (4H, m, aromatic), 8.03(1 H, broad s, NH). 13C
3
NMR (125.7 MHZ, CDCl3): δ = 13.75 and 18.91(2CH3), 39.93 and 41.95 (2CH), 60.97
(CH2), 106.66 (CN), 114.94 and 147.46 (C=C), 125.58, 128.30, 129.48, 132.90, 134.01,
148.89 (aromatic), 163.08 and 165.22 (2C=O).
Ethyl 5-cyano-2-methyl-6-oxo-4-(3-nitrophenyl)-1,4,5,6-tetrahydropyridine 3-car-
boxylate (6A)
White powder, (68 %), m.p. 190–192 ˚C, IR (KBr) (νmax/cm-1): 3410 (NH), 2230 (CN), 1707
3
(C=O), 1319 and 1525 (NO2).1H NMR (500.1 MHZ, CDCl3): δ = 1.09 (3H, t, JHH = 7 HZ,
3
3
CH3), 2.35 (3H, s, CH3), 4.01 (2H, q, JHH = 7 HZ, CH2), 4.31 (H, d, JHH = 7.1HZ, CH),
4.47 (H, d, JHH = 7.1HZ, CH), 7.46 -8.09 (4H, m, aromatic), 10.54 (1 H, broad s, NH). 13C
3
NMR (125.7 MHZ, CDCl3): δ = 14.04 and 18.87 (2CH3), 44.81 and 45.94 (2CH), 65.28
(CH2), 110.05 (CN), 112.13 and 153.14 (C=C), 120.25, 127.97, 134.80, 139.28, 144.37,
153.49 (aromatic), 163.97 and 166.92 (2C=O).
Ethyl 5-cyano-2-methyl-6-oxo-4-(4-nitrophenyl)-1,4,5,6-tetrahydropyridine 3-car-
boxylate (7A)

618 ALIREZA HASSANABADI et al.
White powder, (63 %), m.p. 183–185 ˚C, IR (KBr) (νmax/cm-1): 3407 (NH), 2255 (CN), 1715
(C=O), 1345 and 1515 (NO2). MS, m/z (%): 329 (M+., 10).Anal. Calcd for C16H13N3O5 : C,
1
58.36; H, 4.59; N, 12.76%. Found: C, 58.50; H, 4.71; N, 12.53%. H NMR (500.1 MHZ,
3
3
CDCl3): δ = 1.06 (3H, t, JHH = 7 HZ, CH3), 2.31 (3H, s, CH3), 3.98 (2H, q, JHH = 7 HZ,
3
3
CH2), 4.13 (H, d, JHH = 7.1HZ, CH), 4.18 (H, d, JHH = 7.1HZ, CH), 7.31 -8.06 (4H, m,
aromatic), 10.28 (1 H, broad s, NH). 13C NMR (125.7 MHZ, CDCl3): δ = 14.48 and 19.00
(2CH3), 41.01and 41.71 (2CH), 61.01 (CH2), 105.54 (CN), 114.59 and 144.77 (C=C),
124.42, 129.40, 148.12, 149.04 (aromatic), 162.34 and 165.70 (2C=O).
Ethyl 5-cyano-2-methyl-6-oxo-4-(4-nitrophenyl)-1,6-dihydropyridine 3-carboxylate (7B)
White powder, (37 %), m.p. 198–200˚C, IR (KBr) (νmax/cm-1): 3395 (NH), 2225 (CN), 1721
(C=O), 1348 and 1593 (NO2). MS, m/z (%): 327 (M+., 3).Anal. Calcd for C16H13N3O5 : C,
1
58.72; H, 4.00; N, 12.84%. Found: C, 58.55; H, 4.15; N, 12.99%. H NMR (500.1 MHZ,
3
3
CDCl3): δ = 0.88 (3H, t, JHH = 7 HZ, CH3), 2.66 (3H, s, CH3), 3.96 (2H, q, JHH = 7 HZ,
CH2), 7.25 -8.37 (4H, m, aromatic), 13.54 (1 H, broad s, NH). 13C NMR (125.7 MHZ,
CDCl3): δ = 13.96 and 18.87 (2CH3), 62.46 (CH2), 105.12 (CN), 114.18, 124.40, 129.01,
142.17, 149.04, 154.22, 159.33, 162.47 (aromatic and olefinic), 164.57 and 165.48 (2C=O).
Results and Discussion
Herein we report a new and efficient one-pot synthesis of polysubstituted dihydropyridones
derivatives by four-component reaction between cyanoacetamide, aryl aldehydes and ethyl
acetoacetate with ammonium acetate using nano ZnO. The reaction was performed in
ethanol under reflux conditions and afforded good yields of products. (Figure 1).
O
O
Ar
O
Ar
H
CN
O
CN
H
CN
H2N
Ar
EtO
O
O
EtO
H3C
Nano ZnO
C2H5OH
+
NH4OAc
+
+
H3C
N
H
EtO
CH3
N
H
O
O
Reflux,
8h
(A)
(B)
H
Entry
Ar
C6H5
8 yield (A/B)
59 (Only A)
58 (Only A)
61(Only A)
57 (Only A)
54 (Only A)
68 (Only A)
63/37
1
2
3
4
5
6
7
4-Cl C6H4
4-Br C6H4
3-Meo C6H4
2-NO2C6H4
3-NO2C6H4
4-NO2C6H4
* Isolated yield
Figure 1 Four-component reaction between cyanoacetamide, aryl aldehydes and ethyl
acetoacetate with ammonium acetate using nano ZnO.
The reaction course without ammonium acetate in the absence of zinc oxide a complex
mixture was obtained from which no product was isolated. The reaction course in the
presence of ammonium acetate without zinc oxide afforded the product in lower yield and
longer reaction time. Using nano ZnO afforded the product in higher yield and shorter

A Simple and One-Pot Procedure for Synthesis of Highly Functionalized 619
reaction time. The structure of compounds A and B was deduced from their elemental
1
analyses and their IR, H, and 13CNMR spectra data. The mass spectrum of compound 7A
displayed the molecular ion peak at m/z = 329 as the base peak. The 500 MHZ 1H NMR
spectrum of compound 7A exhibited a D2O-exchangable broad signal at 10.28 ppm for NH
proton, and displays one sharp line (δ 2.31 ppm ) for the methyl group. Ethyl protons were
observed as a triplet (3JHH = 7 HZ) at 1.06 ppm and a quartet at 3.98 ppm. Two doublet were
observed respectively at 4.13 and 4.18 ppm for methine protons. (3JHH = 7.1 HZ). Aromatic
protons resonated between 7.31 and 8.06 ppm as multiplets. The 13C NMR spectrum of
compound 7A showed 14 distinct resonances in agreement with the proposed structure. The
IR spectrum showed an absorption bond at 3407 cm-1 for NH group. The carbonyl stretching
vibrations observed as strong absorption bonds at 1715 cm-1. The nitrile stretching vibrations
observed absorption bond at 2255 cm-1. The nitro stretching vibrations observed absorption
bonds at 1345 and 1515 cm-1.The mass spectrum of compound 7B displayed the molecular
ion peak at m/z = 327 as the base peak. The 500 MHZ 1H NMR spectrum of compound 7B
exhibited a D2O-exchangable broad signal at 13.54 ppm for NH proton, and displays one
sharp line (δ 2.66 ppm ) for the methyl group. Ethyl protons were observed as a triplet (3JHH
= 7 HZ) at 0.88 ppm and a quartet at 3.96 ppm. Aromatic protons resonated between 7.25
and 8.37 ppm as multiplets. The 13C NMR spectrum of compound 7B showed 14 distinct
resonances in agreement with the proposed structure. The IR spectrum showed an absorption
bond at 3395 cm-1 for NH group. The carbonyl stretching vibrations observed as strong
absorption bonds at 1721 cm-1. The nitrile stretching vibrations observed absorption bond at
2225 cm-1. The nitro stretching vibrations observed absorption bonds at 1348 and 1593 cm-1.
Although the mechanistic details of the above reaction are not known, a plausible
mechanism may be advanced to rationalize product formation.
Resumably a intermediate 3 formed from michael addition of product 1 the addition of
cyanoacetamide with aryl aldehydes using nano ZnO and product 2 the addition of ethyl
acetoacetate with ammonium acetate which could undergo stepwise cyclization to produce A by
elimination of NH3. The amide tautomer is considerably more stable. Admittedly the
exchangeable peak in the 1H NMR spectrum is very high for a NH peak, and would appear to be
more consistent with a OH peak. The A product is finally converted to B by oxidation (Figure 2).
O
O
NC
Ar
O
Nano ZnO
H
Ethanol
NH2
NC
O
+
NH2
Ar
1
2
O
O
NH2
NH4OAc
O
+
EtO
CH3
EtO
CH3
CH3
NH2
NH2
O
Ar
N
O
Ar
EtO
Micheal addition
CN
OH
CN
O
EtO
H3C
EtO
-NH3
Cyclization
Ar
NC
1
2
+
H3C
N
H
3
O
A
O
Ar
CN
O
Oxidation
-H2
EtO
H3C
A
N
H
B
Figure 2. Suggested mechanism for formation of compound A and B.

620 ALIREZA HASSANABADI et al.
Conclusion
In summary, here we reported a four-component reaction between cyanoacetamide, aryl
aldehydes and ethyl acetoacetate with ammonium acetate using nano ZnO. The reaction was
performed in ethanol under reflux conditions and afforded good yields of products. The
present method carries the advantage that not only is the reaction performed under neutral
conditions but also that the substances can be mixed without any activation or modification.
nano ZnO was prepared as previously described in the literature.16
Acknowledgment
We gratefully acknowledge financial support from the Research Council of Islamic Azad
University, Yazd branch and the Islamic Azad University, Zahedan branch.
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