A green solventless protocol for the synthesis of β-Enaminones and β -Enamino esters using silica sulfuric acid as a highly efficient, heterogeneous and reusable catalyst

Article abstract of DOI:10.1155/2010/829547

Silica sulfuric acid is utilized as a green, highly efficient, heterogeneous and recyclable catalyst for the preparation of β-enaminones and β -enamino esters from amines and β -dicarbonyl compounds under solvent-free conditions at 80 °C. Using this method, the title compounds are produced in high to excellent yields and in short reaction times.

Full text of DOI:10.1155/2010/829547

ISSN: 0973-4945; CODEN ECJHAO
E-Journal of Chemistry
2010, 7(4), 1546-1554
http://www.e-journals.net
A Green Solventless Protocol for the Synthesis of
β-Enaminones and β-Enamino Esters Using
Silica Sulfuric Acid as a Highly Efficient,
Heterogeneous and Reusable Catalyst
ALIREZA HASANINEJAD*, ABDOLKARIM ZARE#,
MOHAMMAD REZA MOHAMMADIZADEH,
MOHSEN SHEKOUHY and AHMAD REZA MOOSAVI-ZARE§
Department of Chemistry, Faculty of Sciences,
Persian Gulf University, Bushehr 75169, Iran.
#Department of Chemistry, Payame Noor University (PNU), Iran.
§Faculty of Chemistry, Bu-Ali Sina University,
P. O. Box 4135, Hamedan 6517838683, Iran.
ahassaninejad@yahoo.com
Received 31 July 2009; Accepted 25 September 2009
Abstract: Silica sulfuric acid is utilized as a green, highly efficient, heterogeneous
and recyclable catalyst for the preparation of β-enaminones and β-enamino esters
from amines and β-dicarbonyl compounds under solvent-free conditions at 80 °C.
Using this method, the title compounds are produced in high to excellent yields
and in short reaction times.
Keywords: β-Enaminone, β-Enamino ester, Silica sulfuric acid, Solvent-free, Green chemistry.
Introduction
β-Enaminones and β-enamino esters have been extensively used as key intermediates in
organic synthesis1-3 and the chemistry of these compounds have been reviewed4. In particular
they have been employed as synthons of a wide variety of bioactive heterocycles5-7, as well as
pharmaceutical compounds having anti-epileptic8,9, antibacterial10,11, anti-inflammatory11,
anticonvulsant11,12, antitumor activities11,13 and other therapeutic agents14,15. Due to their
wide range of activity and importance, several methods have been developed for the
synthesis of β-enaminones and β-enamino esters. The most well-known and exploited route
toward these compounds involves the direct condensation of β-dicarbonyl compounds with
amines in refluxing aromatic hydrocarbons with azeotropic removal of water16. Some
improved procedures have been subsequently reported for this transformation using different
catalysts such as P2O5/SiO217, clay K-10/uL trasound18, Zn(ClO4)2.6H2O/MgSO419, NaAuClO420
,

1547
A. HASANINEJAD et al.
26
Bi(TFA)321, CeCl3.7H2O22, Sc(OTf)323, Yb(OTf)324, ionic liquid [EtNH3]NO325, HClO4.SiO2
,
ZrOCl2.8H2O27, iodine28, silica chloride29 and LaCl3.7H2O30. Other synthetic approaches to
β-enaminones include the cyclization of amino acids31, reductive cleavage of isoxazoles32,
condensation of methyl ketones with dimethylformamide dimethylacetal in the presence of
equimolar amounts of [BMIM]BF433, substitution of the imidoylbenzotriazoles, with
trimethylsilyl (TMS) enol ethers34 and aminolysis of dithioacetals mediated by copper
acetate35. However, most of the methods suffer major or minor limitations such as long
reaction times, unsatisfactory yields, low selectivity, tedious work-up procedures, lack of
general applicability, applications of non-available and costly reagents, the use of hazardous
solvents and no agreement with the green chemistry protocols. Moreover, in the case of some
of the Lewis acid-catalyzed reactions, no recycling of the catalyst renders these methods
environmentally unsound. Thus, searching for a facile, efficient and nonpolluting procedure
for the synthesis of β-enaminones and β-enamino esters is still of practical importance.
In the aspect of green catalysis has received considerable attention as a stable,
inexpensive, non-toxic and readily producible catalyst from available materials for various
organic transformations under mild and heterogeneous conditions to afford the
corresponding products in excellent yields with high selectivity. Silica sulfuric acid (SSA) is
certainly one of these green catalysts that is easily prepared36 and has been successfully
applied in various organic transformations37.
As part of our ongoing program to develop more efficient and environmentally benign
methods for organic synthesis using economic and eco-friendly materials as catalysts38-47
,
herein, we report a new, clean and efficient solvent-free method for the synthesis of β-enaminones
and β-enamino esters from aromatic as well as aliphatic amines and β-dicarbonyl compounds
in the presence of catalytic amount of SSA (Scheme 1). It is important to note that this
method has none of the above-mentioned disadvantages at all.
O
NH2
O
SSA
+
80 °C, Solvent-free
5 min
N
H
O
93%
Scheme 1
Experimental
All chemicals were purchased from Merck or Fluka chemical companies. Silica sulfuric acid
was prepared according to the reported procedure36. All known compounds were identified by
comparison of their melting points and spectral data with those in the authentic samples. The 1H
NMR (250 MHz) and 13C NMR (62.5 MHz) were run on a Bruker Avance DPX-250, FT-NMR
spectrometer. Microanalysis was performed on a Perkin-Elmer 240-B microanalyzer. Melting
points were recorded on a Stuart scientific apparatus SMP3 (UK) in open capillary tubes.
General procedure for the synthesis of β-enaminone and β-enamino ester derivatives
To a mixture of amine (1 mmol) and β-dicarbonyl compound (1 mmol) in a 10 mL round-
bottomed flask connected to a reflux condenser was added SSA (0.4 g) and the resulting
mixture was stirred in an oil-bath (80 °C). After completion of the reaction (monitored by
TLC), the reaction mixture was cooled to room temperature and to it was added EtOAc (15 mL),
stirred for 5 min and filtered to separate the catalyst. The solvent of the filtrate was
evaporated and the crude product was purified by recrystallization from EtOH/H2O (1/1).
The recycled catalyst was washed by EtOAc, dried and re-used.

A Green Solventless Protocol
1548
Selected spectral data of the products
4-(5,5-Dimethyl-3-oxocyclohex-1-enylamino)phenyl acetate (Table 3, entry 4)
1
White solid; H NMR (CDCl3): δ 1.13 (s, 6H), 2.10 (s, 2H), 2.24 (s, 2H), 2.76 (s, 3H), 5.73
(s, 1H), 7.02 (d, 2H, J = 7.1 Hz), 7.12 (s, 1H), 7.84 (d, 2H, J = 7.1 Hz); 13C NMR (CDCl3): δ
26.4, 28.1, 32.8, 43.6, 50.3, 100.6, 115.8, 121.2, 140.3, 143.2, 158.8, 196.8, 198.4; Anal.
calcd. for C16H19NO3: C, 70.31; H, 7.01; N, 5.12. Found: C, 70.17; H, 6.90; N, 4.98.
3-(4-Bromophenylamino)-5,5-dimethylcyclohex-2-enone (Table 3, entry 5)
1
White solid; H NMR (CDCl3): δ 1.02 (s, 6H), 2.14 (s, 2H), 2.36 (s, 2H), 5.13 (s, 1H), 6.66
(br., 1H), 6.96 (d, 2H, J = 8.6 Hz), 7.39 (d, 2H, J = 8.6 Hz); 13C NMR (CDCl3): δ 28.5, 31.8,
44.1, 50.4, 100.2, 121.6, 129.8, 132.7, 140.3, 143.2, 198.7; Anal. calcd. for C14H16BrNO: C,
57.16; H, 5.48; N, 4.76. Found: C, 57.29; H, 5.58; N, 4.67.
3-(5,5-Dimethyl-3-oxocyclohex-1-enylamino)benzonitrile (Table 3, entry 6)
1
White solid; H NMR (CDCl3): δ 1.16 (s, 6H), 2.16 (s, 2H), 2.42 (s, 2H), 5.60 (s, 1H), 6.66
(br., 1H), 7.19-7.25 (m, 2H), 7.86-791 (m, 2H); 13C NMR (CDCl3) δ: 26.7, 32.8, 43.4, 50.4,
100.8, 106.7, 118.6, 120.2, 121.0, 122.1, 133.4, 143.2, 165.1, 198.7; Anal. calcd. for
C15H16N2O: C, 74.97; H, 6.71; N, 11.66. Found: C, 75.14; H, 6.83; N, 11.74.
5,5-Dimethyl-3-(pyridin-2-ylmethylamino)cyclohex-2-enone (Table 3, entry 8)
1
White solid; H NMR (CDCl3): δ 1.14 (s, 6H), 1.92 (s, 2H), 2.19 (s, 2H), 4.35 (s, 2H), 5.20
(s, 1H), 6.17 (br., 1H), 7.22 (m, 2H), 7.68 (m, 1H), 8.55 (m, 1H); 13C NMR (CDCl3): δ 28.3,
32.9, 43.4, 46.8, 50.3, 96.3, 122.0, 122.7, 136.9, 148.8, 154.6, 162.2, 196.9; Anal. calcd. for
C14H18N2O: C, 73.01; H, 7.88; N, 12.16. Found: C, 72.80; H, 7.96; N, 12.29.
3-(Furan-2-ylmethylamino)-5,5-dimethylcyclohex-2-enone (Table 3, entry 9)
1
White solid; H NMR (CDCl3): δ 1.05 (s, 6H), 1.90 (s, 2H), 1.97 (s, 2H), 4.23 (s, 2H), 4.88
(s, 1H), 5.06 (s, 1H), 6.25 (d, 1H, J = 7.7 Hz), 6.31 (m, 1H), 7.34 (d, 1H, J = 5.6 Hz); 13C
NMR (CDCl3): δ 27.3, 31.5, 40.1, 43.3, 50.2, 96.3, 107.8, 110.5, 142.3, 149.8; 165.6, 196.8;
Anal. calcd. for C13H17NO2: C, 71.21; H, 7.81; N, 6.39. Found: C, 71.04; H, 7.70; N, 6.51.
3-(Butylamino)-5,5-dimethylcyclohex-2-enone (Table 3, entry 10)
1
White solid; H NMR (CDCl3): δ 0.87 (t, J = 6.1 Hz, 3H), 1.06 (s, 6H), 1.31 (m, 2H), 1.51
(m, 2H), 2.09 (s, 2H), 2.14 (s, 2H), 3.03 (m, 2H), 4.54 (s, 1H) 5.05 (s, 1H); 13C NMR
(CDCl3): δ 13.9, 19.8, 27.4, 30.9, 34.1, 40.5, 42.1, 49.9, 96.8, 164.3, 197.0; Anal. calcd. For
C12H21NO: C, 73.80; H, 10.84; N, 7.17. Found: C, 73.57; H, 10.68; N, 7.26.
(Z)-4-(3-Oxo-1,3-diphenylprop-1-enylamino)phenyl acetate (Table 3, entry 22)
Pale yellow solid; 1H NMR (CDCl3): δ 2.49 (s, 3H ), 5.28 (s, 1H), 6.77 (d, J = 7.5 Hz, 2H),
7.39-7.51 (m, 8H), 7.97 (d, 2H, J = 7.5 HZ), 8.10 (d, 2H, J = 7.0 Hz), 12.88 (s, 1H); 13C
NMR (CDCl3): δ 26.1, 99.0, 113.8, 121.6, 127.4, 128.9, 129.3, 130.1, 130.8, 131.8, 132.2,
135.5, 139.4, 144.1, 160.0, 190.3, 196.8; Anal. calcd. for C23H19NO3: C, 77.29; H, 5.36; N,
3.92. Found: C, 77.11; H, 5.49; N, 4.01.
Results and Discussion
At first, the reaction of aniline (1 mmol) with dimedone (1 mmol) was examined in the
presence of different amounts of SSA at range of 25-90 ºC under solvent-free conditions
in order to optimize the reaction conditions with respect to amount of the catalyst and

1549
A. HASANINEJAD et al.
temperature (Scheme 1). The results are summarized in Table 1. As it can be seen from
Table 1, the reasonable results were obtained when the reaction was carried out using 0.4 g
SSA at 80 ºC.
Table 1. Effect of amount of SSA and temperature on the reaction of aniline with dimedone
Yielda, %
Amount of SSA, g
Temperature, °C
Time, min
0.1
0.2
0.3
0.4
0.5
0.4
0.4
0.4
0.4
80
50
30
10
5
67
80
79
80
88
80
93
80
5
93
25 (r.t.)
120
20
10
4
Trace
71
60
70
87
90
aIsolated yield.
91
In another study, the reaction was checked in several solvents to recognize the efficiency
of the solvent-free procedure in comparison to solution conditions. For this purpose, a
mixture of aniline (1 mmol), dimedone (1 mmol) and SSA (0.4 g) was stirred in different
solvents (10 mL) at 80 or under reflux conditions (Table 2). As Table 2 indicates, the
solvent-free method afforded the product in higher yield and shorter reaction time.
Table 2. Comparative the reaction between aniline and dimedone using SSA in solution
conditions versus the solvent-free method
Solvent
H2O
Temperature, °C
80
Time, min
Yielda, %
60
60
60
60
60
60
5
27
76
69
66
58
45
93
EtOH
Reflux
Reflux
Reflux
Reflux
Reflux
80
MeOH
CHCl3
CH3CN
THF
Solvent-free
aIsolated yield
To assess the generality and scope of our method, different aromatic and aliphatic amines
were reacted with some β-diketones and β-ketoesters. The results are displayed in Table 3. As it
is shown in Table 3, all reactions proceeded efficiently and the desired products were obtained
in high to excellent yields and in short reaction times. The results showed that the presence of
electron-releasing substituents or halogens on the aromatic ring of aromatic amines had no
significant effect on the reaction results (Table 3, entries 2-5, 12-14, 22 and 26-29); however,
electron-withdrawing substituents slightly decreased the yields (Table 3, entry 6). The
condensation of aliphatic amines, NH4OAc as well as diamines with β-dicarbonyl compounds
was also successfully carried out and the corresponding products were obtained in high to
excellent yields and short reaction times (Table 3, entries 7-10, 15-17, 19, 20, 23 and 30-32).

A Green Solventless Protocol
1550
Table 3. Synthesis of β-enaminones and β-enamino esters using SSA under solvent-free
conditions at 80 °C
Time,
min
Yielda,
%
Entry
1
M.p. °C (Lit.)
Product
O
5
93
184-186(185)48
N
H
O
2
8
86
126-128(129-131)49
N
H
OMe
O
O
O
MeO
AcO
Br
3
4
5
6
3
7
7
5
96
92
93
87
192-194 (195)48
226-228(225-227)17
219-220(219-220)17
181-183
N
H
N
H
N
H
O
NC
N
H
O
7
8
5
6
95
94
127-128(125)48
N
H
O
160-161(162-163)17
N
H
N
O
9
6
8
95
92
148-150
N
H
O
O
10
117-119
N
H
Contd…

1551
A. HASANINEJAD et al.
11
10
6
89
88
93
47-49(47)50
44-46(40.5-41.2)51
66-68(65-67)52
NH
O
MeO
12
13
14
NH
O
Me
8
NH
O
Cl
7
91
60-62(60-62)52
NH
O
NH
O
O
15
16
17
8
83
82
90
Oil(Oil)53
Oil(Oil)53
NH
10
20
NH2
O
35-37(32)30
NH
O
18
15
90
109-111(108)24
NH
O
19
20
15
25
93
88
60-62(59)54
O
HN
NH
O
180-182(180)21
NH
O
21
22
20
28
90
91
101-104(99-101)16
AcO
149-150(149-150)17
NH
O
Contd…

A Green Solventless Protocol
1552
23
24
NH
O
15
30
91
89
102-105(100)55
Oil(Oil)53
NH
O
O
OEt
25
26
30
20
86
91
45-46(42-45)56
NH
OMe
O
MeO
Me
46-48(44.5-45)50
NH
NH
OEt
Oil(Oil)53
O
O
27
28
29
25
25
35
87
90
90
OEt
Me
59-60(57-58)53
NH
OMe
OEt
Cl
57-58(53-54)52
NH
O
NH
O
30
31
32
20
20
85
90
86
Oil(Oil)53
38-40(36-37)53
Oil(Oil)30
OMe
O
NH
OMe
NH2
O
35
OEt
aIsolated yield
The interesting behavior of SSA lies in the fact that it can be reused after simple
washing with EtOAc, thus rendering process more economical. For the reaction of aniline
with dimedone no significant loss of the product yield was observed when the catalyst was
reused after three times recycling (Table 4).
Table 4. The condensation of aniline with dimedone in the presence of recycled SSA
Entry
Cycle
1st use
2nd use
3rd use
4th use
5th use
Time, min
5
Yielda, %
1
2
3
4
5
93
93
92
87
79
5
10
25
30
Conclusion
In summary, we have developed a new efficient method for the synthesis of β-enaminones
and β-enamino esters from amines and β-dicarbonyl compounds. The advantages the
presented methodology are efficiency, generality, high yield, short reaction time, low cost,
cleaner reaction profile, ease of product isolation, simplicity, potential for recycling of the
catalyst and finally agreement with the green chemistry protocols.

1553
A. HASANINEJAD et al.
Acknowledgment
The authors thank Persian Gulf University and Payame Noor University Research Councils
for the financial support of this work.
References
1.
Rappoport Z (Eds), The Chemistry of Enamines, John Wiley & Sons, New York,
1994, Part 1, pp 525-639.
2.
3.
4.
5.
Vohra R K, Renaud J L and Bruneau C, Collect Czech Chem Commun., 2005, 70, 1943.
Stevens C V, Kesteleyn B, Alonso E R and De Kimpe N, Tetrahedron, 2001, 57, 7685.
Elassar A Z A and El-Khair A A, Tetrahedron, 2003, 59, 8463.
Alan C, Spivey A C, Srikaran R, Diaper C M, David J and Turner D, Org Biomol
Chem., 2003, 1638 and the references cited therein.
6.
Michael J P, De Koning C B, Gravestock D, Hosken G D, Howard A S, Jungmann
C M, Krause R W M, Parsons A S, Pelly S C and Stanbury T V, Pure Appl Chem.,
1999, 71, 979-988.
7.
8.
Hassneen H M and Abdallah T A, Molecules, 2003, 8, 333.
Edafiogho I O, Ananthalakshmi K V V and Kombian S B, Bioorg Med Chem., 2006,
14, 5266.
9.
Khurana M, Salama N N, Scott K R, Nemieboka N N, Jr Bauer K S and Eddington N
D, Drug Dispos, 2003, 24, 397.
10. Wang Y F, Izawa T, Kobayashi S and Ohno M, J Am Chem Soc., 1982, 104, 6465.
11. Michael J P, Koning C B, Hosken G D and Stanbury T V, Tetrahedron, 2001, 57,
9635.
12. Edafiogho I O, Alexander M S, Moore J A, Farrar V A and Scott KR, Curr Med
Chem., 1994, 1, 159-175.
13. Boger D L, Ishizaki T, Jr Wysocki J R, Munk S A, Kitos P A and Suntornwat O, J Am
Chem Soc., 1989, 111, 6461.
14. White J D and Ihle D C, Org Lett., 2006, 8, 1081.
15. Edafiogho I O, Kombian S B, Ananthalakshmi K Y V V, Salama N N, Eddington N
D, Wilson T L, Alexander M S, Jackson P L, Hanson C D and Scott K R, J Pharm
Sci., 2007, 96, 2509.
16. Martin D F, Janusonis G A and Martin B B, J Am Chem Soc., 1961, 83, 73.
17. Mohammadizadeh M R, Hasaninejad A, Bahramzadeh M and Khanjarloo Z S, Synth
Commun., 2009, 39, 1152.
18. Valduga C J, Squizani A, Braibante H S and Braibante M E F, Synthesis, 1998, 1019.
19. Bartoli G, Bosco M, Locatelli M, Marcantoni E, Melchiorre P and Sambri L, Synlett,
2004, 239.
20. Arcadi A, Bianchi G, Giuseppe S D and Marinelli F, Green Chem., 2003, 5, 64-67.
21. Khosropour A R, Khodaei M M and Kookhazadeh M, Tetrahedron Lett., 2004, 45, 1725.
22. Khodaei M M, Khosropour A R and Kookhazadeh M, Synlett, 2004, 1980.
23. Yadav J S, Kumar V N, Rao R S, Priyadarshini A D, Rao P P, Reddy B V S and
Nagaiah K, J Mol Catal A: Chem., 2006, 256, 234.
24. Epifano F, Genovese S and Curini M, Tetrahedron Lett., 2007, 48, 2717.
25. Bhosale R S, Suryawanshi P A, Ingle S A, Lokhande M N, More S P, Mane S B,
Bhosale S V and Pawar R P, Synlett, 2006, 933.
26. Das B, Venkateswarlu K, Majhi A, Reddy M R, Reddy K N, Rao Y K, Ravikumar K
and Srihar B, J Mol Catal A: Chem., 2006, 246, 276.
27. Zhang Z H, Li T-S and Li J J, Catal Commun., 2007, 8, 1615.

A Green Solventless Protocol
1554
28. Gogoi S, Bhuyan R and Barua N C, Synth Commun., 2005, 35, 2811.
29. Gholap A R, Chakor N S, Daniel T, Lahoti R J and Srinivasan K V, J Mol Catal A:
Chem., 2006, 245, 37.
30. Lenin R and Raju R M, ARKIVOC, 2007, xiii, 204.
31. Turunen B J and Georg G I, J Am Chem Soc., 2006, 128, 8702.
32. Calle M, Calvo L A, Gonzales-Ortega A and Gonzales-Nogal A, Tetrahedron, 2006,
62, 611.
33. Martins M A P, Frizzo C P, Moreira D N, Rosa F A, Marzari M R B, Zanatta N and
Bonacorso H G, Catal Commun., 2007, 9, 375.
34. Katritzky A R, Hayden A E, Kirichenko K, Pelphrey P and Ji Y, J Org Chem., 2004,
69, 5108.
35. Kang J, Liang F, Sun S-G, Liu Q and Bi X-H, Org Lett., 2006, 8, 2547.
36. Zolfigol M A, Tetrahedron, 2001, 57, 9509.
37. Salehi P, Zolfigol M A, Shirini F and Baghbanzadeh M, Curr Org Chem., 2006, 10,
2171 (Review).
38. Hasaninejad A, Zare A, Shekouhy M, Moosavi-Zare A R, E-J Chem., 2009, 6(S1),
S247.
39. Zare A, Hasaninejad A, Rostami E, Moosavi-Zare A R, Merajoddin M, Arghoon A,
Pishahang N and Shekouhy M, E-J Chem.,2009, 6(S1), S390.
40. Hasaninejad A, Zare A, Jafari F and Moosavi-Zare A R, E J Chem. 2009, 6, 459.
41. Hasaninejad A, Zare A, Zolfigol M A and Shekouhy M, Synth Commun., 2009, 39,
569-579.
42. Zare A, Parhami A, Moosavi-Zare A R, Hasaninejad A, Khalafi-Nezhad A and
Beyzavi M H, Can J Chem., 2009, 87, 416.
43. Zare A, Hasaninejad A, Beyzavi M H, Moosavi Zare A R, Khalafi-Nezhad A, Asadi F,
Baramaki L, Jomhori-Angali S and Ghaleh-Golabi R, Synth Commun., 2009, 39, 139.
44. Khalafi-Nezhad A, Parhami A, Zare A, Moosavi Zare A R, Hasaninejad A and Panahi F,
Synthesis, 2008, 617.
45. Zare A, Hasaninejad A, Beyzavi M H, Parhami A, Moosavi Zare A R, Khalafi-
Nezhad A and Sharghi H, Can J Chem., 2008, 86, 317.
46. Zare A, Hasaninejad A, Khalafi-Nezhad A, Parhami A and Moosavi Zare A R, J Iran
Chem Soc., 2008, 5, 100.
47. Zare A, Hasaninejad A, Shekouhy M and Moosavi Zare A R, Org Prep Proced Int.,
2008, 40, 457.
48. Scott K R, Edafiogho I O, Richardson E L, Farrar V A, Moore J A, Tietz E I, Hinko C N,
Chang H, El-Assadi A and Nicholson J M, J Med Chem., 1993, 36, 1947.
49. Iida H, Yuasa Y and Kibayashi C, J Org Chem., 1980, 45, 2938.
50. Werner W, Tetrahedron, 1971, 27, 1755.
51. Zhou J C, Magn Reson Chem., 1997, 35, 311.
52. Potesil T, J Chromatogr., 1984, 312, 387.
53. Zhang Z-H, Yin L and Wang Y-M, Adv Synth Catal., 2006, 348, 184.
54. Kibayashi C, Yuasa Y and Lida H, J Chem Soc Dalton Trans., 1981, 11, 2212.
55. Coromwell N H, Chem Rev., 1946, 38, 83.
56. Yale H L and Spitzmiller E R, J Heterocycl Chem., 1977, 14, 1419.

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Hindawi Publishing Corporation
Volume 2013
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Volume 2013
International Journal of
Electrochemistry
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Bioinorganic Chemistry
and Applications
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Hindawi Publishing Corporation
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Volume 2013
Volume 2013
Volume 2013
Volume 2013
Journal of
Chemistry
Journal of
International Journal of
Journal of
Chromatography
Research International
Spectroscopy
Spectroscopy
Catalysts
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Volume 2013
Volume 2013
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ISRN
ISRN
ISRN
ISRN
ISRN
Analytical
Chemistry
Inorganic Chemistry
Organic Chemistry
Physical Chemistry
Chromatography
Hindawi Publishing Corporation
Hindawi Publishing Corporation
Hindawi Publishing Corporation
Hindawi Publishing Corporation
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Hindawi Publishing Corporation
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http://www.hindawi.com
Volume 2013
http://www.hindawi.com
Volume 2013
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Volume 2013
Volume 2013