Graphite oxide mediated oxidative aromatization of 1,4-dihydropyridines into pyridine derivatives

Article abstract of DOI:10.1016/j.tetlet.2012.03.026

A new approach utilizing graphite oxide as an oxidizing agent is applied for the oxidative aromatization of 1,4-dihydropyridines. Graphite oxide efficiently aromatized Hantzsch 1,4-dihydropyridines into their corresponding pyridine derivatives in excellen

Full text of DOI:10.1016/j.tetlet.2012.03.026

Tetrahedron Letters 53 (2012) 2473–2475
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Tetrahedron Letters
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Graphite oxide mediated oxidative aromatization of 1,4-dihydropyridines
into pyridine derivatives
Maryam Mirza-Aghayan a, , Rabah Boukherroub b, Mohammad Nemati a, Mahshid Rahimifard a
⇑
a Chemistry and Chemical Engineering Research Center of Iran (CCERCI), PO Box 14335-186, Tehran, Iran
b Institut de Recherche Interdisciplinaire (IRI, USR 3078), Parc de la Haute Borne, 50 Avenue de Halley-BP70478, 59658 Villeneuve d’Ascq, France
a r t i c l e i n f o
a b s t r a c t
Article history:
A new approach utilizing graphite oxide as an oxidizing agent is applied for the oxidative aromatization
of 1,4-dihydropyridines. Graphite oxide efficiently aromatized Hantzsch 1,4-dihydropyridines into their
corresponding pyridine derivatives in excellent yields. The reaction was carried out in toluene at 100 °C.
Ó 2012 Elsevier Ltd. All rights reserved.
Received 3 December 2011
Revised 20 February 2012
Accepted 7 March 2012
Available online 13 March 2012
Keywords:
Graphite oxide
1,4-Dihydropyridine derivatives
Oxidative aromatization
Pyridine derivatives
Due to their low cost and wide variety of reasonably well-
defined physicochemical properties and morphologies, carbon-
based materials are desirable catalytic agents. However, little
systematic attention has been given to their use and behavior as
catalysts. Carbon-based materials catalyze a variety of reactions
in solution.1 Medina et al. reported that carbon samples (carbon
black, activated carbon, non-activated charcoal, and graphite)
catalyzed nitrobenzene reduction with hydrazine.2 Carbon nano-
tubes have been shown to dehydrogenate n-butane,3 while C60
has successfully been used to catalyze the hydrogenation of nitro-
benzene.4 Graphite oxide (GO) and other chemically modified
graphene-based materials (CMGs) have not been explored exten-
sively as catalysts for facilitating synthetically useful transforma-
tions. In a recent patent, Lizhu et al. investigated the reduction of
graphite oxide to graphene using 1,4-dihydropyridines as hydro-
gen donors.5 GO impregnated with palladium nanoparticles dis-
played very high turnover frequencies in Suzuki–Miyaura
coupling reactions.6 More recently, GO was applied for the oxida-
tion of alcohols and alkenes, and the hydration of various alkynes
into their respective aldehydes and ketones in good to excellent
yields. The reactions proceed under relatively mild conditions
and simple filtration was shown to be a convenient and effective
method for catalyst recovery.7
pyridines has attracted much attention, and a number of proce-
dures have been developed.9 Among these, a very convenient ap-
proach which attracted our attention was the oxidative
aromatization of 1,4-dihydropyridines (1,4-DHPs). These com-
pounds generally undergo oxidative metabolism in the liver by
the action of cytochrome P450 to form the corresponding pyridine
derivatives.10 A variety of reagents and methods such as tetrakis-
(pyridine)cobalt(II) dichromate,11 electrochemical catalysis,12
14
peroxydisulfate-Co(II),13 H6PMo9V3O40
,
MnO2,15 silica modified
sulfuric acid/NaNO2,16 and silica chromate17 have been utilized
for this oxidative conversion.
Herein, we report on the use of graphite oxide (GO), a readily
available and inexpensive material, as a mild and efficient agent
for the oxidative aromatization of Hantzsch 1,4-dihydropyridines
(Schemes 1 and 2).
The synthesis of graphite oxide typically involves the oxidation
of graphite using a modified Hummers method.18 The relatively
R
R
N
MeO2C
Me
CO2Me
Me
MeO2C
Me
CO2Me
Me
Graphite oxide
toluene, 100 °C
N
H
The pyridine nucleus is of substantial significance as it is the key
component in a variety of bioactive compounds, both naturally
occurring and synthetic.8 Thus, the synthesis of highly substituted
2a-e
1a-e
R= Ph, p-Me-C6H4, p-Br-C6H4, m-HO-C6H4, p-O2N-C6H4
⇑
Corresponding author. Tel.: +98 21 44580720; fax: +98 21 44580777.
E-mail address: m.mirzaaghayan@ccerci.ac.ir (M. Mirza-Aghayan).
Scheme 1. Graphite oxide mediated oxidative aromatization of symmetrical 1,4-
dihydropyridines.
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.03.026

2474
M. Mirza-Aghayan et al. / Tetrahedron Letters 53 (2012) 2473–2475
Table 2
O
O
R'
R'
Synthesis of pyridine derivatives
CO2Et
Me
CO2Et
Me
Graphite oxide
toluene, 100 °C
Entry R or R0
Producta Yield (%)b
Mp (°C)
Reported
136–13824
N
N
H
1f-i
Found
136
1
2
3
4
5
6
7
8
9
C6H4
2a
93
90
96
92
95
91
94
95
92
2f-i
p-Me-C6H4
p-Br-C6H4
m-HO-C6H4
p-O2N-C6H4
p-Cl-C6H4
p-HO-C6H4
p-MeO-C6H4
2b
137–138 137–13825
2c17
2d
139
136–14017
R'=p-Cl-C6H4, p-HOC6H4, p-MeO-C6H4, m-EtO-p-HO-C6H3
191–192
148
—
2e
14826
—
Scheme 2. Graphite oxide mediated oxidative aromatization of unsymmetrical 1,4-
dihydropyridines.
2f
151–152
134–135
2gc
2h27
—
196–198 15327
p-HO-m-EtO-C6H3 2ic
121–122
—
harsh conditions used in this synthetic protocol introduce a variety
of oxygen-containing functionalities (e.g., alcohols, epoxides, and
carboxylates) into the material. As a result, GO is slightly acidic19
and has long been recognized as having strong oxidizing
properties.20
All products were characterized by 1H NMR and mass spectrometry.28
Isolated yields.
When the 1,4-dihydropyridine was not completely soluble in toluene, one drop
a
b
c
of DMF was added.
The GO used in this work was synthesized according to a mod-
ified Hummers method.21,22 The prepared GO was characterized
using powder XRD, and UV, and FT-IR spectroscopy to establish
its authenticity.23
chloride was added and the mixture was filtered through a sin-
tered funnel. GO is insoluble in methylene chloride and could be
removed by filtration. The dried recycled oxidant was used three
times in consecutive reactions of 1a with only a 20% loss in the
yield, compared to the original experiment, for each run.
In conclusion, we have developed a novel method using graph-
ite oxide, a cheap and easily available material, for the oxidative
aromatization of symmetrical and unsymmetrical 1,4-dihydropyr-
idine derivatives. The reaction is carried out at 100 °C and affords
excellent yields of products in short reaction times. The present
method has many advantages, including simplicity and generality.
Graphite oxide was synthesized from inexpensive graphite using
readily available reagents. Further investigations using graphite
oxide for other chemical transformations are currently in progress.
In a typical experimental procedure, a solution of 1,4-dihydro-
pyridine 1a (1 mmol) in CHCl3 as solvent was heated under reflux
for six hours in the presence of graphite oxide (200 wt %). Under
these conditions, dimethyl 2,6-dimethyl-4-phenylpyridine-3,5-
dicarboxylate (2a) was obtained in 32% yield (entry 1, Table 1). It
should be noted that increasing the oxidant concentration from
200 to 300 wt % had a negligible effect on the yield of the corre-
sponding pyridine 2a in CHCl3 (entry 2, Table 1). Performing the
reaction in the absence of solvent at 100 °C gave the corresponding
pyridine in a high 75% yield (entry 3, Table 1). A high yield was ob-
tained when CHCl3 was replaced by toluene as the solvent. Indeed,
the reaction of 1 equiv of 1,4-dihydropyridine 1a in the presence of
200 wt % GO in toluene at 100 °C gave the corresponding pyridine
2a in 93% yield after three hours (entry 4, Table 1).
In a similar fashion, various symmetrical and unsymmetrical
1,4-dihydropyridines 1a–e and 1f–i reacted smoothly with GO
under similar reaction conditions to give the corresponding sym-
metrical pyridines 2a–e and unsymmetrical pyridine derivatives
2f–i, respectively, in 90–96% yields (Schemes 1 and 2). The results
are summarized in Table 2. Symmetrical and unsymmetrical 1,4-
dihydropyridines containing electron-withdrawing or electron-
donating groups on the 4-aryl substituent gave the corresponding
pyridine derivatives in excellent yields.
References and notes
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The results obtained using GO as the oxidizing agent are compa-
rable to those previously reported using other oxidants, but with
several advantages including short reaction times, high yields,
and avoidance of the use of toxic transition metals. Furthermore,
GO is easily synthesized from inexpensive and readily available
graphite. The utility of this methodology should make this simple
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Table 1
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Effect of the solvent and temperature on the oxidative aromatization of dimethyl 2,6-
dimethyl-4-phenyl-1,4-dihydropyridine-3,5-dicarboxylate (1a)
Entry
GO (wt %)
Solvent
Time (h)
Yielda (%)
1
2
3
4
200
300
200
200
CHCl3 (reflux)
6
6
7
3
32
40
75
93
CHCl3 (reflux)
Solvent-freeb (100 °C)
Toluene (100 °C)
11. Wang, B.; Hu, Y.; Hu, H. Synth. Commun. 1999, 29, 4193.
12. Pragst, F.; Kaltofen, B.; Volke, J.; Kuthan, J. J. Electroanal. Chem. 1981, 119, 301.
13. Anniyappam, M.; Muralidharan, D.; Perumal, P. T. Tetrahedron 2002, 58, 5069.
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Oskooie, H. A. Bioorg. Med. Chem. Lett. 2007, 17, 3305.
a
Isolated yield.
b
1,4-Dihydropyridine 1a was dissolved in CHCl3 and added to GO; the solvent
was evaporated from the mixture which was then heated at 100 °C.
15. Bagley, M. C.; Lubinu, M. C. Synthesis 2006, 1283.

M. Mirza-Aghayan et al. / Tetrahedron Letters 53 (2012) 2473–2475
2475
16. Zolfigol, M. A.; Shirini, F.; Choghamarania, A. G.; Mohammadpoor-Baltork, I.
Green Chem. 2002, 4, 562.
17. (a) Zolfigol, M. A.; Salehi, P.; Choghamarani, A. G.; Safaiee, M.; Shahamirian, M.
Synth. Commun. 2007, 37, 1817; (b) Ghorbani-Choghamarani, A.; Zeinivand, J.
Synth. Commun. 2010, 40, 2457.
18. Marcano, D. C.; Kosynkin, D. V.; Berlin, J. M.; Sinitskii, A.; Sun, Z.; Slesarev, A.;
Alemany, L. B.; Lu, W.; Tour, J. M. ACS Nano 2010, 4, 4806.
19. Szab, T.; Tombcz, E.; Ills, E.; Dkny, I. Carbon 2006, 44, 537.
Dimethyl 4-(3-hydroxyphenyl)-2,6-dimethylpyridine-3,5-dicarboxylate (2d),
Mp: 191–192 °C; 1H NMR (CDCl3, 500 MHz): d = 2.56 (s, 6H, 2CH3), 3.55 (s, 6H,
2OCH3), 6.67 (d, J = 7.6 Hz, 1H, Ar), 6.73 (s, 1H, Ar), 6.83 (d, J = 7.6 Hz, 1H, Ar),
7.17 (t, J = 7.8 Hz, 1H, Ar), 8.75 (br s, 1H, OH); 13C NMR (CDCl3, 125 MHz):
d = 22.86, 52.78, 115.13, 116.48, 120.04, 127.42, 130.11, 137.93, 146.89,
155.95, 156.68, 168.70; MS (EI) (70 eV), m/z (%): 315 (35) [M]+, 284 (20), 252
(100), 224 (42), 196 (24), 59 (24), 29 (22), 15 (18); IR (KBr)
m = 3500, 2953,
1735, 1654, 1558, 1444, 1288, 1031 cmꢀ1; Anal. Calcd for C17H17NO5: C, 64.75;
H, 5.43; N, 4.44. Found: C, 64.54; H, 5.40; N, 4.32.
20. Boehm, H. P.; Clauss, A.; Fischer, G.; Hofmann, U. In Fifth Conference on Carbon;
Pergamon Press: Oxford, 1962; pp 73–80.
Ethyl 4-(4-chlorophenyl)-2-methyl-5-oxo-5,6,7,8-tetrahydroquinoline-3-carboxyl-
ate (2f), Mp: 151–152 °C; 1H NMR (CDCl3, 500 MHz): d = 1.02 (t, J = 7.1 Hz, 3H,
CH3), 2.21 (m, 2H, CH2), 2.60 (s, 3H, CH3), 2.64 (t, J = 6.2 Hz, 2H, CH2), 3.23 (t,
J = 6.2 Hz, 2H, CH2), 4.04 (q, J = 7.1 Hz, 2H, OCH2), 7.10 (d, J = 8.5 Hz, 2H, Ar), 7.37
(d, J = 8.5 Hz, 2H, Ar); 13C NMR (CDCl3, 125 MHz): d = 14.08, 21.77, 23.67, 34.04,
40.43, 61.99, 124.17, 128.39, 129.40, 130.61, 134.21, 136.38, 148.01, 158.61,
165.04, 167.68, 197.43; MS (EI) (70 eV), m/z (%): 343 (10) [M]+, 315 (6), 298 (6),
21. (a) Zhou, X.; Huang, X.; Qi, X.; Wu, S.; Xue, C.; Boey, F. Y. C.; Yan, Q.; Chen, P.;
Zhang, H. J. Phys. Chem. C 2009, 113, 10842; (b) Wang, Z.; Zhou, X.; Zhang, J.;
Boey, F. Y. C.; Zhang, H. J. Phys. Chem. C 2009, 113, 14071; (c) Kovtyukhova, N. I.;
Ollivier, P. J.; Martin, B. R.; Mallouk, T. E.; Chizhik, S. A.; Buzaneva, E. V.;
Gorchinskiy, A. D. Chem. Mater. 1999, 11, 771.
22. Synthesis of graphite oxide using the modified Hummers method21: graphite
(8 g) was added to a mixture of 98% H2SO4 (14 mL), K2S2O8 (4 g), and P2O5 (4 g),
and the mixture was stirred and the solution was kept at 80 °C for 6 h. The
resulting preoxidized product was washed with H2O and dried. CAUTION: The
preoxidized product (8 g) was added to 98% H2SO4 (180 mL), followed by the
slow addition of KMnO4 (24 g) with the temperature kept at <20 °C in order to
avoid overheating and explosion. The solution temperature was increased to
35 °C and maintained for 2 h. Next, H2O (400 mL) was added over 15 min.
Further H2O (1.1 L) was added to dilute the solution, and 30% H2O2 (20 mL) was
injected into the solution to completely react with the excess KMnO4. A brown
solution was obtained which was washed with 1:10 37% HCl: H2O solution
(2 L) in order to remove metal ions and H2O (2 L). Dried graphite oxide was
obtained by centrifugation followed by dehydration on a rotary evaporator
under vacuum.
270 (7), 139 (8), 29 (100), 27 (3); IR (KBr) m = 3425, 3356, 3078, 2887, 1726, 1681,
1544, 1487, 1265, 1219, 1080 cmꢀ1; Anal. Calcd for C19H18ClNO3: C, 66.38; H,
5.28; N, 4.07. Found: C, 65.89; H, 5.12; N, 4.01.
Ethyl
4-(4-hydroxyphenyl)-2-methyl-5-oxo-5,6,7,8-tetrahydroquinoline-3-
carbo-xylate (2g), Mp: 134–135 °C; 1H NMR (CDCl3, 500 MHz): d = 1.04 (t,
J = 7.1 Hz, 3H, CH3), 2.20 (m, 2H, CH2), 2.65 (s, 3H, CH3), 2.67 (t, J = 6.7 Hz, 2H,
CH2), 3.25 (t, J = 6.1 Hz, 2H, CH2), 4.06 (q, J = 7.1 Hz, 2H, OCH2), 6.81 (d, J = 8.5 Hz,
2H, Ar), 7.03 (d, J = 8.5 Hz, 2H, Ar), 8.25 (br s, 1H, OH); 13C NMR (CDCl3, 125 MHz):
d = 14.13, 21.75, 23.36, 33.81, 40.56, 61.92, 115.43, 124.86, 128.74, 129.31,
131.28, 149.79, 157.22, 158.05, 164.77, 168.17; 197.91; MS (EI) (70 eV), m/z (%):
325 (10) [M]+, 296 (3), 280 (5), 77 (5), 43 (72), 29 (100); IR (KBr)
m
= 3091, 3066,
2991, 2947, 1726, 1693, 1602, 1552, 1510, 1442, 1373, 1273, 1224, 1006 cmꢀ1
;
Anal. Calcd for C19H19NO4: C, 70.14; H, 5.89; N, 4.31. Found: C, 69.66; H, 5.70; N,
4.29.
23. (a) Kumar, A. V.; Rao, K. R. Tetrahedron Lett. 2011, 52, 5188; (b) Paredes, J. I.;
Villar-Rodil, S.; Martinez-Alonso, A.; Tascon, J. M. D. Langmuir 2008, 24, 10560.
24. Bocker, R. H.; Guengerich, F. P. J. Med. Chem. 1986, 29, 1596.
25. Zeynizadeh, B.; Dilmaghani, K. A.; Roozijoy, A. J. Chin. Chem. Soc. 2005, 52, 1001.
26. Chavan, S. P.; Kharul, R. K.; Kalkote, U. R.; Shivakumar, I. Synth. Commun. 2003,
33, 1333.
Ethyl 4-(3-ethoxy-4-hydroxyphenyl)-2-methyl-5-oxo-5,6,7,8-tetrahydroquino-
line-3-carboxylate (2i), Mp: 121–122 °C; 1H NMR (CDCl3, 500 MHz): d = 1.03 (t,
J = 7.1 Hz, 3H, CH3), 1.46 (t, J = 6.9 Hz, 3H, CH3), 2.22 (m, 2H, CH2), 2.64 (s, 3H,
CH3), 2.65 (br s, 2H, CH2), 3.24 (t, J = 6.1 Hz, 2H, CH2), 4.04 (q, J = 7.1 Hz, 2H,
OCH2), 4.10 (br s, 2H, OCH2), 6.65 (d, J = 8.0 Hz, 1H, Ar), 6.68 (s, 1H, Ar), 6.94 (d,
J = 8.0 Hz, 1H, Ar), 7.30 (br s, 1H, OH); 13C NMR (CDCl3, 125 MHz): d = 14.18,
15.18, 21.82, 23.54, 34.04, 40.59, 61.90, 64.87, 112.20, 114.33, 121.10, 124.69,
129.47, 131.14, 145.66, 146.01, 149.23, 158.15, 164.83, 168.19, 197.49; MS (EI),
(70 eV) m/z (%): 369 (10) [M]+, 313 (15), 267 (15), 43 (25), 29 (100); IR (KBr)
27. (a) Fang, X.; Liu, Y. C.; Li, C. J. Org. Chem. 2007, 72, 8608; (b) Antaki, H. J. Chem.
Soc. 1963, 4877.
28. Typical procedure for the oxidation of 1,4-dihydropyridines using graphite
oxide: A mixture of symmetrical or unsymmetrical 1,4-dihydropyridine 1a–e
or 1f–i (1 mmol) and GO (200 wt %) was stirred at 100 °C in toluene (2 mL) for
3 h. After completion of the reaction as indicated by TLC, the solvent was
evaporated and the residue dissolved in CH2Cl2 and filtered through a sintered
funnel. The filtrate was purified by recrystallization from EtOH.
m
= 3360, 2985, 2937, 2885, 1730, 1699, 1647, 1598, 1512, 1429, 1269, 1222,
1035 cmꢀ1; Anal. Calcd for C21H23NO5: C, 68.28; H, 6.28; N, 3.79. Found: C, 67.79;
H, 6.06; N, 3.68.