Synthesis of 2,4,6-Tri-substituted pyridine derivatives in aqueous medium via Hantzsch multi-component reaction catalyzed by cerium (IV) ammonium nitrate

Article abstract of DOI:10.1002/jhet.1589

2,4,6-Tri-substituted pyridine derivatives have been efficiently synthesized in excellent yields using catalytic amounts of cerium (IV) ammonium nitrate in aqueous medium via one-pot, multi-component reaction. Condensation of dehydroacetic acid with aldeh

Full text of DOI:10.1002/jhet.1589

Month 2013
Synthesis of 2,4,6-Tri-Substituted Pyridine Derivatives in Aqueous
Medium via Hantzsch Multi-Component Reaction Catalyzed by
Cerium (IV) Ammonium Nitrate
Santhosh Penta and Rajeswar Rao Vedula
Department of Chemistry, National Institute of Technology, Warangal 506 004, India
*
E-mail: vrajesw@yahoo.com
Received October 18, 2011
DOI 10.1002/jhet.1589
Published online in Wiley Online Library (wileyonlinelibrary.com).
R3
R2
R1
O
H
OH
O
OH
O
OH
O
O
R1
R2
Water / 5mol% CAN
N
CH3
NH4OAc
+
+
H3C
O
O
CH3
H3C
O
R3
4
1
3
2
2,4,6-Tri-substituted pyridine derivatives have been efficiently synthesized in excellent yields using catalytic
amounts of cerium (IV) ammonium nitrate in aqueous medium via one-pot, multi-component reaction.
Condensation of dehydroacetic acid with aldehydes and ammonium acetate afforded corresponding tri-substituted
pyridine derivatives in excellent yields by using Hantzsch pyridine synthesis. The structures of all the newly
synthesized compounds were confirmed from their analytical and spectral data.
J. Heterocyclic Chem., 00 00, (2013).
INTRODUCTION
niguldipine undergo redox processes during their metabo-
lism catalyzed by cytochrome P-450 in the liver [9].
Recently, cerium (IV) ammonium nitrate (CAN) is the
most notable one-electron oxidant and has been utilized
extensively for a broad variety of oxidative transformations
in organic chemistry [10–15]. Additionally, many advan-
tages such as excellent solubility in water, inexpensiveness,
eco-friendly nature, uncomplicated handling, and high
reactivity make CAN a potent catalyst in organic syntheses.
Besides this, CAN is able to catalyze various organic
transformations on the basis of the Lewis acidic property.
These facts inspired us to use this catalyst (CAN) for the
synthesis of 2,4,6-tri substituted pyridine derivatives.
A literature survey revealed that there are numerous
routes reported for the synthesis of highly substituted pyr-
idines according to modified Hantzsch pyridine synthesis
[16]. These can be prepared by reaction of aldehyde, 2
moles of b-keto ester and ammonium acetate. However,
these methods suffers more drawbacks such as complex
work-up and purification, lower the overall yields, longer
reaction times, and high boiling solvents, which are a threat
to the environment. Therefore, the development of a new
catalytic system to overcome these shortcomings and fulfill
the criteria of a simple, efficient and environmentally
benign protocol for the synthesis of highly substituted
pyridines at ambient temperature is an important task for
organic chemists.
With regard to green chemistry, development of selective
and atom-efficient transformations of easily available
starting materials into complex functionalized heterocyclic
building blocks become increasingly important to both
pharmaceuticals and organic chemists. In this context,
multi-component reactions (MCRs) involving domino
processes “in which more than three different reactants
directly get converted into their products by one-pot reaction”
[1]. MCRs play an important role in modern organic
chemistry, because they generally exhibit higher atom
economy, selectivity, molecular complexity and diversity as
well as produce fewer by-products compared to classical
multistep synthesis [2]. The first MCR was described in
1850 by Strecker [3] and thereafter many such reactions have
been reported in the literature [4].
Designing of MCRs in water is another attractive area in
chemistry, [5] because water is a cheap, safe, environmen-
tally benign solvent, and isolation of the organic products
can be performed by simple phase separation. The signifi-
cant enhancement in the rate of reaction has been attributed
to hydrophobic packing, solvent polarity, hydration, and
hydrogen bonding [6]. There are beneficial effects of aqueous
solvents on rates and selectivities of important organic
transformations, for example, Diels–Alder reactions, aldol
reactions, and Michael additions [7,8].
Pyridine is one of the most prominent heterocycles and
is widely distributed in many biologically important mole-
cules, it was found in drugs, such as nifedipine and
On the basis of the aforementioned observations and as a
part of our research program in the synthesis of novel hetero-
cyclic systems [17–21], we wish to report in this article the
© 2013 HeteroCorporation

S. Penta and R. R. Vedula
Vol 000
modified Hantzsch condensation of 2,4,6-tri-substituted
pyridine derivatives catalyzed by CAN via multi-component
approach in aqueous medium.
protons. Like this, the remaining spectral data confirms
the newly prepared compounds structures (4a–k).
CONCLUSION
RESULTS AND DISCUSSIONS
We have developed a simple, efficient, and green
method for the synthesis of a variety of 2,4,6-tri-substituted
pyridine derivatives via an improved Hantzsch reaction
catalyzed by small amount of CAN. The reaction condi-
tions are mild, and the reaction gave excellent yields of
products. This method does not involve the use of volatile
organic solvents and thus is an environmentally friendly
process. The biological activity of these compounds is
under investigation.
Reaction of 3-acetyl-4-hydroxy-6-methyl-2H-pyran-2-
one (2 mmol) with 4-nitrobenzaldehyde (1mmol) and am-
monium acetate (1.5 mmol) using catalytic amount of
CAN at ambient temperature in aqueous medium gave
2,4,6-tri-substituted pyridine derivatives in good yields
(Scheme 1). We have carried out the reactions without
any catalyst. In these cases, the 2,4,6-tri-substituted pyri-
dine derivatives were isolated in poor yields (30–40%). Al-
though using CAN (3 mol%) as catalyst, the reaction gave
a yellow product in 90%, yield in 3 h. By changing the
amount of the catalyst from 3 to 5 and 10 mol%, the reac-
tion resulted in the formation of 4a in 95 and 85% yields,
respectively. Thus, the use of just 5 mol% of CAN was
chosen as a quantitative catalyst to push the reaction for-
ward with maximum yield of the product. We then contin-
ued to optimize the model process by detecting the
efficiency of several classic solvents chosen as the medium
for comparison (Table 1). Among the tested solvents, such
as ethanol, acetonitrile, chloroform, and aqueous medium,
the latter gave the best result.
EXPERIMENTAL SECTION
General. All the reagents and solvents were pure, purchased
from commercial sources and were used without further
purification unless otherwise stated. Melting points were
determined in open capillaries with a “Cintex” melting point
apparatus Mumbai, India and were uncorrected. CHNS analysis
was carried out by Carlo Erba EA 1108 automatic elemental
analyzer (Italy). The purity of the compounds was checked using
TLC plates (E. Merck Mumbai, India). IR spectra (KBr) were
recorded on a Bruker WM-4(X) spectrometer (577 models).
1HNMR spectra were recorded on a Bruker WM-400 spectrometer
in d ppm using TMS as standard. Mass spectra (EI-MS)
were determined on Perkin Elmer (SCIEX API-2000, ESI)
at 12.5 eV.
General procedure for the synthesis of compounds 4a–k.
In a typical experimental procedure, dehydroacetic acid
(3-acetyl-4-hydroxy-6-methyl-2H-pyran-2-one) 1 (2 mmol),
aldehyde 2 (1mmol), ammonium acetate 3 (1.5 mmol), and
CAN (0.05 mmol) were taken in a 3 ml of water, the resultant
mixture was refluxed for 3 h. After an appropriate time, the
solid obtained was cooled, filtered, and washed with water.
The structures of newly prepared compounds were con-
firmed from their analytical and spectral data. For example,
the IR spectrum of compound 4a showed three strong ab-
sorption peaks at 3243, 1715, and 1597 cm-1 for OH, lac-
tone carbonyl, and C = N, respectively. The 1H NMR
spectrum of compound 4a showed sharp singlets at d
2.05 and d 2.12 for methyl groups of pyran moiety. Two
singlets observed at d 9.75 and d 9.79 for pyridine ring
Scheme 1. One-pot synthesis of 2,4,6 tri-substituted pyridine derivatives in aqueous medium.
R3
R2
R1
O
H
OH
O
OH
O
OH
O
O
R1
R2
Water / 5mol% CAN
N
CH3
NH4OAc
+
+
H3C
O
O
CH3
H3C
O
R3
4
3
2
1
Compd R1
R2
H
H
H
R3
N(CH3)2
OH
H
H
Compd R1
R2
H
OCH3
H
H
H
H
R3
NO2
OCH3
Br
Cl
CH3
OCH3
g
h
i
H
H
OH
H
4a
b
c
H
H
H
H
H
H
j
NO2
d
e
f
K
2-hydroxy-1-naphthaldehyde
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

2013
With Regard to Green Chemistry, Development of Selective and Atom-Efficient
Table 1
3-(4-(4-Chlorophenyl)-6-(4-hydroxy-6-methyl-2-oxo-2H-pyran-
3-yl)pyridin-2-yl)-4-hydroxy-6-methyl-2H-pyran-2-one (4d).
Color: yellow solid; mp 217–219ꢀC; IR (potassium bromide):
3243 (–OH), 1715 (O-C = O), 1601 (C = N); 1H NMR
(dimethyl sulfoxide d6): d 2.06 (s, 3H, CH3), 2.15 (s, 3H, CH3),
5.77 (s, 1H, pyran), 5.80 (s, 1H, pyran), 7.24 (d, 2H, J = 8.4 Hz,
ArH), 7.61 (d, 2H, J = 7.6 Hz, ArH), 9.72 (s, 1H, pyridine), 9.73
(s, 1H, pyridine), 12.11 (s, 1H, OH), 12.20 (s, 1H, OH). Anal.
calcd. for C23H16ClNO6: C, 63.09; H, 3.68; N, 3.20. Found: C,
63.14; H, 3.61; N, 3.24.
4-Hydroxy-3-(6-(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-
yl)-4-p-tolylpyridin-2-yl)-6-methyl-2H-pyran-2-one (4e).
Color: yellow solid; mp 243–245ꢀC; IR (potassium bromide):
3246 (–OH), 1715 (O-C= O), 1598 (C = N); 1H NMR (dimethyl
sulfoxide d6): d 2.05 (s, 3H, CH3), 2.10 (s, 3H, CH3), 2.24 (s, 3H,
CH3), 5.71 (s, 1H, pyran), 5.79 (s, 1H, pyran), 6.84 (d, 2H, J = 8.8
Hz, ArH), 7.30 (d, 2H, J = 8.8 Hz), 9.71 (s, 1H, pyridine), 9.78
(s, 1H, pyridine), 11.85 (s, 1H, OH), 12.10 (s, 1H, OH). Anal.
calcd. for C24H19NO6: C, 69.06; H, 4.59; N, 3.36. Found: C,
68.94; H, 4.52; N, 3.31.
4-Hydroxy-3-(6-(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-4-
(4-methoxyphenyl)pyridin-2-yl)-6-methyl-2H-pyran-2-one (4f).
Color: yellow solid; mp >300ꢀC; IR (potassium bromide): 3252
(–OH), 1727 (O-C = O), 1596 (C = N); 1H NMR (dimethyl
sulfoxide d6): d 2.06 (s, 3H, CH3), 2.10 (s, 3H, CH3), 3.82 (s, 3H,
OCH3), 5.71 (s, 1H, pyran), 5.79 (s, 1H, pyran), 7.12 (d, 2H,
J = 8.0 Hz, ArH), 7.61 (d, 2H, J = 7.6 Hz, ArH), 9.72 (s, 1H,
pyridine), 9.75 (s, 1H, pyridine), 12.06 (s, 1H, OH), 12.12
(s, 1H, OH). Anal. calcd. for C24H19NO7: C, 66.51; H, 4.42; N,
3.23. Found: C, 66.55; H, 4.38; N, 3.18.
3-(4-(4-(Dimethylamino)phenyl)-6-(4-hydroxy-6-methyl-2-oxo-
2H-pyran-3-yl)pyridin-2-yl)-4-hydroxy-6-methyl-2H-pyran-
2-one (4g). Color: yellow solid; mp 264–266ꢀC; IR (potassium
bromide): 3243 (–OH), 1731 (O-C= O), 1595 (C= N); 1H NMR
(dimethyl sulfoxide d6): d 2.09 (s, 3H, CH3), 2.13 (s, 3H, CH3),
3.04 (s, 6H, CH3), 5.67 (s, 1H, pyran), 5.78 (s, 1H, pyran), 6.79
(d, 2H, J= 8.8 Hz, ArH), 7.68 (d, 2H, J= 8.8 Hz, ArH), 9.67 (s, 1H,
pyridine), 9.72 (s, 1H, pyridine), 12.07 (s, 1H, OH), 12.15 (s, 1H,
OH). 13C NMR (dimethyl sulfoxide d6): 19.1, 42.0, 111.9, 125.9,
126.2, 126.8, 127.0, 127.7, 128.0, 129.6, 130.9, 151.3, 162.1,
183.2. Anal. calcd. for C25H22N2O6: C, 67.26; H, 4.97; N, 6.27.
Found: C, 67.21; H, 4.91; N, 6.20.
4-Hydroxy-3-(6-(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-4-
(4-hydroxyphenyl)pyridin-2-yl)-6-methyl-2H-pyran-2-one (4h).
Color: yellow solid; mp 231–232ꢀC; ir (potassium bromide): 3235
(–OH), 1717 (O-C= O), 1594 (C = N); 1H NMR (dimethyl
sulfoxide d6): d 2.06 (s, 3H, CH3), 2.14 (s, 3H, CH3), 5.77 (s, 1H,
pyran), 5.83 (s, 1H, pyran), 7.14 (d, 2H, J = 8.8 Hz, ArH), 7.52
(d, 2H, J = 8.8 Hz, ArH), 9.58 (s, 1H, pyridine), 9.60 (s, 1H,
pyridine), 12.07 (s, 1H, OH), 12.15 (s, 1H, OH), 12.30 (s, 1H,
OH). Anal. calcd. for C23H17NO7: C, 65.87; H, 4.09; N, 3.34.
Found: C, 65.81; H, 4.12; N, 3.28.
4-Hydroxy-3-(6-(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-4-
(2-hydroxyphenyl)pyridin-2-yl)-6-methyl-2H-pyran-2-one (4i).
Color: orange yellow solid; mp 225–227ꢀC; IR (potassium
bromide): 3212 (–OH), 1721 (O-C = O), 1595 (C = N); 1H NMR
(dimethyl sulfoxide d6): d 1.96 (s, 3H, CH3), 2.04 (s, 3H, CH3),
5.67 (s, 1H, pyran), 5.79 (s, 1H, pyran), 7.31 (t, 1H, J=7.6 Hz,
ArH), 7.49 (d, 1H, J= 8.8 Hz, ArH), 7.61 (d, 1H, J= 8.0 Hz, ArH),
9.72 (s, 1H, pyridine), 9.75 (s, 1H, pyridine), 12.10 (s, 1H, OH),
12.21 (s, 1H, OH), 12.27 (s, 1H, OH). Anal. calcd. for C23H17NO7:
C, 65.87; H, 4.09; N, 3.34. Found: C, 65.81; H, 4.12; N, 3.30.
4a. Reaction of 2-mmole dehydroacetic acid, 1-mmol 4-nitrobenzaldehyde,
and 1.5-mmol ammonium acetate: effect of solvent and temperature and
yields of products in water for various synthesized compounds (4a–4k).
Temperature
(ꢀC)
Time
(min)
Yield
(%)
Entry
Solvent
1
2
3
4
4a
4b
4c
4d
4e
4f
4g
4h
4i
C2H5OH
CH3CN
CHCl3
DMF
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
180
180
180
180
180
180
180
180
180
180
180
180
180
180
180
86
67
53
70
95
86
81
92
90
87
92
87
80
86
83
4j
4k
The crude product was purified by recrystallization from
absolute ethanol.
4-Hydroxy-3-(6-(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-
4-(4-nitrophenyl)pyridin-2-yl)-6-methyl-2H-pyran-2-one(4a).
Color: light yellow solid; mp 210–212ꢀC; IR (potassium bromide):
3243 (–OH), 1715 (O-C = O), 1597 (C = N). 1H NMR (dimethyl
sulfoxide d6): d 2.05 (s, 3H, CH3), 2.12 (s, 3H, CH3), 5.73 (s, 1H,
pyran), 5.82 (s, 1H, pyran), 7.23 (d, 2H, J= 8.4 Hz, ArH), 7.84
(d, 2H, J = 8.4 Hz, ArH), 9.75 (s, 1H, pyridine), 9.79 (s, 1H,
pyridine), 12.06 (s, 1H, OH), 12.14 (s, 1H, OH). 13C NMR
(dimethyl sulfoxide d6): 20.4, 110.9, 130.0, 131.9, 132.0, 132.7,
133.1, 133.5, 133.8, 135.6, 152.5, 166.4, 183.1. ESI-MS 449
[M + H]+; Anal. calcd. for C23H16N2O8: C, 61.61; H, 3.60; N,
6.25. Found: C,61.69; H, 3.51; N, 6.20.
4-Hydroxy-3-(6-(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-
4-(3,4-dimethoxyphenyl) pyridine-2-yl)-6-methyl-2H-pyran-2-
one (4b). Color: orange solid; mp 287–289ꢀC; IR (potassium
bromide): 3220 (–OH), 1721 (O-C = O), 1596 (C= N); 1H NMR
(dimethyl sulfoxide d6): d 2.06 (s, 3H, CH3), 2.09 (s, 3H, CH3),
3.81 (s, 6H, OCH3), 5.67 (s, 1H, pyran), 5.74 (s, 1H, pyran), 7.19
(d, 1H, J = 6.8 Hz, ArH), 7.37–7.41 (m, 1H, ArH), 7.68–7.72
(m, 1H, ArH), 9.73 (s, 1H, pyridine), 9.74 (s, 1H, pyridine), 11.95
(s, 1H, OH), 12.15 (s, 1H, OH). ESI-MS 464 [M+ H]+; Anal.
calcd. for C25H21NO8: C, 64.79; H, 4.57; N, 3.02. Found: C,
64.71; H, 4.51; N, 3.14.
3-(4-(4-Bromophenyl)-6-(4-hydroxy-6-methyl-2-oxo-2H-pyran-
3-yl)pyridin-2-yl)-4-hydroxy-6-methyl-2H-pyran-2-one (4c).
Color: yellow solid; mp 252–254ꢀC; IR (potassium bromide):
3217 (–OH), 1712 (O-C= O), 1598 (C= N); 1H NMR (dimethyl
sulfoxide d6): d 1.92 (s, 3H, CH3), 2.07 (s, 3H, CH3), 5.67 (s, 1H,
pyran), 5.77 (s, 1H, pyran), 7.13 (d, 2H, J = 8.8 Hz, ArH), 7.78
(d, 2H, J = 8.8 Hz, ArH), 9.74 (s, 1H, pyridine), 9.78 (s, 1H,
pyridine), 12.00 (s, 1H, OH), 12.12 (s, 1H, OH). 13C NMR
(dimethyl sulfoxide d6): 19.1, 107.3, 128.0, 128.7, 129.0, 129.2,
130.1, 130.5, 131.2, 131.6, 153.9, 162.1, 192.3. Anal. calcd. for
C23H16BrNO6: C, 57.28; H, 3.34; N, 2.90. Found: C, 57.21; H,
3.38; N, 2.85.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

S. Penta and R. R. Vedula
Vol 000
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4-Hydroxy-3-(6-(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-
4-(3-nitrophenyl)pyridin-2-yl)-6-methyl-2H-pyran-2-one (4j).
Color: orange yellow solid; mp 287–289ꢀC; IR (potassium
bromide): 3224 (–OH), 1713 (O-C = O), 1597 (C= N); 1H NMR
(dimethyl sulfoxide d6): d 2.08 (s, 3H, CH3), 2.11 (s, 3H, CH3),
5.73 (s, 1H, pyran), 5.75 (s, 1H, pyran), 7.38 (d, 1H, J = 8.8 Hz,
ArH), 7.61–7.67 (m, 3H, ArH), 9.72 (s, 1H, pyridine), 9.73
(s, 1H, pyridine). Anal. calcd. for C23H16N2O8: C, 61.61; H, 3.60;
N, 6.25. Found: C, 61.68; H, 3.54; N, 6.21.
4-Hydroxy-3-(6-(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-4-
(2-hydroxynaphthalen-1-yl) pyridine À2-yl)-6-methyl-2H-pyran-
2-one (4k). Color: orange yellow solid; mp 234–236ꢀC; IR
(potassium bromide): 3246 (–OH), 1715 (O-C = O), 1598 (C = N);
1H NMR (dimethyl sulfoxide d6): d 1.90 (s, 3H, CH3), 2.06
(s, 3H, CH3), 5.74 (s, 1H, pyran), 5.81 (s, 1H, pyran), 7.33–7.37
(m, 2H, ArH), 7.43 (d, 1H, J = 8.0 Hz, ArH), 7.52 (d, 2H, J = 8.8
Hz, ArH), 7.70 (d, 1H, J = 7.6 Hz, ArH), 9.81 (s, 1H, pyridine),
9.83 (s, 1H, pyridine), 12.11 (s, 1H, OH), 12.13 (s, 1H, OH),
12.16 (s, 1H, OH). Anal. calcd. for C27H19NO7: C, 69.08; H,
4.08; N, 2.98. Found: C, 69.12; H, 4.12; N, 2.92.
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Acknowledgment. The authors are thankful to the Director,
NIT, Warangal for providing facilities. One of the authors
(SANTHOSH) is thankful to the Director for awarding
Institute Fellowship.
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Journal of Heterocyclic Chemistry
DOI 10.1002/jhet