Three-component one-pot synthesis of 2,4,6-triarylpyridines without catalyst and solvent

Article abstract of DOI:10.1002/jhet.2132

An efficient and green synthesis of 2,4,6-triarylpyridines by a one-pot three-component condensation of aromatic aldehydes, substituted acetophenones, and ammonium acetate without catalyst at 130°C under solvent-free conditions is described. This method offers several advantages such as simple procedure, easy work-up, short reaction time, low cost, environmentally friendly conditions, and moderate to high yields.

Full text of DOI:10.1002/jhet.2132

Month 2014
Three-Component One-Pot Synthesis of 2,4,6-Triarylpyridines without
Catalyst and Solvent
a
a
b
a
*
Min Wang, Zhongyong Yang, Zhiguo Song, and Qinglin Wang
aCollege of Chemistry, Chemical Engineering and Food Safety, Bohai University, Jinzhou 121013, China
bCenter for Science & Technology Experiment, Bohai University, Jinzhou 121013, China
*
E-mail: minwangszg@hotmail.com
Received July 20, 2013
DOI 10.1002/jhet.2132
Published online 00 Month 2014 in Wiley Online Library (wileyonlinelibrary.com).
An efficient and green synthesis of 2,4,6-triarylpyridines by a one-pot three-component condensation of
aromatic aldehydes, substituted acetophenones, and ammonium acetate without catalyst at 130°C under
solvent-free conditions is described. This method offers several advantages such as simple procedure, easy
work-up, short reaction time, low cost, environmentally friendly conditions, and moderate to high yields.
J. Heterocyclic Chem., 00, 00 (2014).
INTRODUCTION
reaction of acetophenones, benzaldehydes, and ammonium
acetate in the presence of various catalysts such as
heteropolyacid [12], supported acids [13,14], solid acids
[15,16], ionic liquids [17,18], phase transfer catalysts
[19,20], and Lewis acids [21,22] at 120°C or under micro-
wave irradiation. However, many of the established methods
are subjected to certain disadvantages including use of costly
and toxic catalysts, acidic media, and organic solvents. To
avoid such drawbacks, development of more simple,
inexpensive, green, and efficient protocols is still in demand.
In this research, we report a simple and green method for
the synthesis of 2,4,6-triarylpyridines in moderate to high
yields by the three-component condensation of various
aromatic aldehydes 1, substituted acetophenones 2 with
ammonium acetate at 130°C (Scheme 1). To the best of
our knowledge, the synthesis of title compounds without cat-
alyst and solvent under conventional heating conditions has
not been reported. Many new products were reported first.
In modern synthetic organic chemistry, multi-component
reactions (MCRs) have been regarded as efficient tools
because MCRs fulfilled the requirements of environmentally
friendly processes by reducing the number of synthetic steps,
decreasing energy and resources consumption, and isolating
no intermediates. The product purity was improved. There-
fore, developing new MCRs and improving existing MCRs
are very significant research areas.
Now, pyridines play a key role in biological and chemical
systems. They were found in biologically active compounds
and natural products such as nicotinamide adenine dinucleo-
tides, vitamin B6, and pyridine alkaloids [1]. Compounds
containing pyridine rings show variable biological activities
such as hypoglycemic activity, hypolipidemic activity,
fungicidal activity, antimicrobial agent, dopamine trans-
porter inhibitors, and anti-inflammatory agents [2–6]. The
pyridine rings also used in agrochemicals such as herbicides
[4]. In addition, because of their π-stacking ability, some
pyridines are used in supramolecular chemistry [7].
RESULTS AND DISCUSSION
Traditionally, 2,4,6-triarylpyridines (Kröhnke-type pyridine)
are synthesized from N-phenacylpyridinium salts with
α,β-unsaturated ketones in the presence of ammonium
acetate [8]. However, pyridinium salts and the unsaturated
ketones have to be synthesized first, so the method is
relative expensive, time consuming, and harmful to the
environment. Since then, some new methods for the
synthesis of 2,4,6-triarylpyridines have been reported,
for example, the reaction of α-ketoketene dithioacetals
with methyl ketone carbanions and ammonium acetate in
hot acetic acid [9], reaction of N-(diphenylphosphiny)-1-
phenylethanimine with aldehydes [10], solvent-free reaction
of chalcones with ammonium acetate [11], three-component
At the onset of our research, we screened different
catalysts and reaction conditions using the model reaction
of benzaldehyde, acetophenone, and ammonium acetate.
The results were summarized in Table 1. It can be seen that
the results in the presence of catalysts were almost the same
as the results in the absence of catalyst (entries 1–7). That is
to say the catalyst did not show distinct catalytic activity on
the reaction. Catalyst is not necessary for this conversion. A
satisfied result was obtained with 1 : 2 : 1.3 molar ratio of
benzaldehyde, acetophenone, and ammonium acetate in the
absence of catalyst at 130°C (entry 7). Further increase or
decrease of the reaction temperature cannot favor the product
© 2014 HeteroCorporation

M. Wang, Z. Yang, Z. Song, and Q. Wang
Vol 000
Scheme 1
reaction time was shortest. No conversion to product was
obtained when the reaction was carried out in water (2mL).
In order to show the generality and scope of this new
protocol, we screened various aromatic aldehydes and
substituted acetophenones, the results are summarized in
Table 2. All reactions proceeded smoothly in the absence
of catalyst. It gave the corresponding 2,4,6-triarylpyridines
in moderate to high yields. Aromatic aldehydes and
ketones carrying either electron-withdrawing group or
electron-donating group were all suitable for use with this
procedure. Compared with other reported methodologies
for the synthesis of 2,4,6-triarylpyridines via one-pot
reaction, the present protocol offers suitable conditions with
respect to reaction time, yield, cost, and environmental
pollution. However, the position of the substituents on the ar-
omatic ring has obvious effects on this conversion. Ortho-
substituted aromatic aldehydes such as 2-chlorobenzaldehyde
and 2-nitrobenzaldehyde failed to give the desired products.
A probable mechanism for the synthesis of highly
substituted pyridines has been proposed in Scheme 2. An
aromatic aldehyde reacted with a substituted acetophenone
Table 1
Screening of different catalysts and reaction temperature for the
condensation.a
Temp.
(°C)
Time
(h)
Yield
(%)
Entry
Catalyst (mol%)
1
2
3
4
5
6
7
8
9
NaHSO4∙H2O (10)
CH3SO3H (5)
Al(NO3)3∙9H2O (10)
H3O40PW12∙xH2O (1)
Fe2(SO4)3∙9H2O (10)
SnCl4∙5H2O (10)
—
130
130
130
130
130
130
130
140
120
110
7.5
6.0
10.0
6.0
7.5
7.5
5.5
5.5
6.0
6.0
54
55
57
75
78
79
75
76
63
44
—
10
aBenzaldehyde, 4 mmol; acetophenone, 8 mmol; and ammonium acetate,
5.2 mmol.
yields (entries 7–10). In addition, the model reaction was also
examined in various solvents at 130°C. The yield of the reac-
tion under solvent-free conditions was the highest, and the
Table 2
Three-component reactions of aromatic aldehydes with substituted acetophenones and ammonium acetate at 130°C.
mp (°C)
Entry
R1
R2
Time (h)
Yield (%)
Found
Reported
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
3p
3q
3r
3s
H
4-Cl
H
H
H
H
H
H
H
4-NO2
4-NO2
4-Cl
5.5
2
6
1
4
2
4
0.7
1
2
5
1.5
1
2.5
6
2
6
6
6
75
81
72
79
82
85
60
86
79
68
76
75
62
69
77
68
74
78
82
134–135
124–126
126–128
117–118
97–98
139–140
264–266
>300
166–167
186–187
269–270
230–232
221–223
193–194
163–164
124–125
128–129
134–135
149–150
130–131 [16]
120–122 [23]
3-NO2
4-CH3
4-OCH3
4-(CH3)2N
4-OH
4-NO2
4-(CH3)2N
H
—
118–118.5 [12]
99–100 [12]
136–138 [23]
—
>300°C [24]
—
—
4-Cl
4-Cl
4-Cl
4-Cl
4-Cl
264–265 [21]
3-NO2
4-CH3
4-OCH3
4-N(CH3)2
H
4-CH3
4-OCH3
4-N(CH3)2
—
—
—
—
4-Cl
4-OCH3
4-OCH3
4-OCH3
4-OCH3
—
—
134–135 [25]
—
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2014
Synthesis of 2,4,6-Triarylpyridines
Scheme 2
C23H16N2O2: C, 78.39; H, 4.58; N, 7.95. Found: C, 78.48; H,
4.52; N, 8.01.
to form a 1,3-diaryl-2-propen-1-one A, which further
underwent in situ Michael addition with substituted
acetophenone to yield an intermediate B. Intermediate B is
then cyclized and dehydrogenated to afford the title product 3.
4-(4-hydroxyphenyl)-2,6-diphenylpyridine (3g). White solid.
IR (KBr): 3197, 1603, 1546, 1519, 1398, 839, 776, 696 cmÀ1
.
1H-NMR (400 MHz, DMSO-d6): δ 9.90 (s, 1H), 8.32 (d, 4H,
J = 7.5 Hz), 8.13 (s, 2H), 7.93 (d, 2H, J = 8.1 Hz), 7.57–7.47
(m, 6H), 6.95 (d, 2H, J = 8.1 Hz). 13C-NMR (100 MHz,
DMSO-d6): δ 159.2, 156.7, 149.8, 139.4, 129.5, 129.1, 128.5,
127.3, 116.3, 116.1. MS (ESI): m/z (%) 324 (M++H, 100).
Anal. Calcd for C23H17NO: C, 85.42; H, 5.30; N, 4.33. Found:
C, 85.51; H, 5.34; N, 4.26.
CONCLUSIONS
In conclusion, a novel and environmentally benign
method for synthesizing 2,4,6-triarylpyridines was achieved
without any catalyst and solvent. The protocol has obvious
environmental benefits. In addition, it simplified the overall
experimental process. Our work makes a valuable contribu-
tion to the synthesis of 2,4,6-triarylpyridines.
4-(4-dimethylaminophenyl)-2,6-bis(4-nitrophenyl)pyridine
(3i).
Reddish brown solid. IR (KBr): 2907, 2361, 1601,
1569, 1522, 1437, 1340, 855, 806 cmÀ1
.
1H-NMR (400MHz,
DMSO-d6): δ 8.37–8.31 (m, 8H), 7.75–7.73 (m, 4H), 6.76 (d, 2H,
J = 8.0Hz), 2.85 (s, 6H). 13C-NMR (100 MHz, DMSO-d6): δ
186.2, 151.1, 148.2, 145.7, 142.2, 130.1, 128.3, 122.6, 120.4,
114.4, 110.5, 43.5. MS (ESI): m/z (%) 441 (M++H, 100). Anal.
Calcd for C25H20N4O4: C, 68.17; H, 4.58; N, 12.72. Found: C,
68.06; H, 4.63; N, 12.78.
2,6-bis(4-chlorophenyl)-4-phenylpyridine (3j). White solid.
IR (KBr): 2361, 1602, 1544, 1492, 1387, 834, 763 cmÀ1. 1H-NMR
(400 MHz, DMSO-d6): δ 8.38 (d, 4H, J = 8.4 Hz), 8.27 (s, 2H), 8.06
(d, 2H, J = 7.3 Hz), 7.61 (d, 4H, J = 8.5 Hz), 7.58–7.53 (m, 3H).
13C-NMR (100 MHz, DMSO-d6): δ 155.7, 150.3, 137.8, 134.6,
129.9, 129.5, 129.2, 127.9, 117.3. MS (ESI): m/z (%) 377 (M++H,
100). Anal. Calcd for C23H15NCl2: C, 73.42; H, 4.02; N, 3.72.
Found: C, 73.53; H, 3.98; N, 3.77.
EXPERIMENTAL
Melting points were determined using an RY-1 micromelting
point apparatus. Infrared spectra were recorded on a Scimitar 2000
series Fourier Transform instrument of VARIAN (Palo Alto, CA).
1H-NMR and 13C-NMR spectra were recorded on an Agilent 400-
MR instrument (Santa Clara, CA) in DMSO-d6 using TMS as an
internal standard. Mass spectra were obtained with an Agilent 1100
series LC/MSD VL ESI instrument (Santa Clara, CA). Elemental
analyses were carried out on an EA 2400II elemental analyzer
(PerkinElmer, Waltham, MA).
General procedure for the synthesis of 2,4,6-triarylpyridines
(3).
A mixture of an aromatic aldehyde 1 (4 mmol), a
4-(3-nitrophenyl)-2,6-bis(4-chlorophenyl)pyridine (3l). White
solid. IR (KBr): 1600, 1525, 1493, 1350, 830, 738 cmÀ1. 1H-NMR
(400 MHz, DMSO-d6): δ 8.86 (s, 1H), 8.52 (d, 1H, J=7.6 Hz),
8.41–8.35 (m, 7H), 7.86 (t, 1H, J= 8.0 Hz), 7.61 (d, 4H,
J=8.3Hz). 13C-NMR (100 MHz, DMSO-d6): δ 154.2, 147.3,
146.4, 137.9, 135.9, 133.1, 132.9, 129.3, 128.2, 127.6, 122.8,
121.0, 116.0. MS (ESI): m/z (%) 422 (M++H, 100). Anal. Calcd
for C23H14N2Cl2O2: C, 65.57; H, 3.35; N, 6.65. Found: C, 65.66;
H, 3.31; N, 6.70.
substituted acetophenone 2 (8 mmol), and ammonium acetate
(5.2 mmol) was magnetically stirred at 130°C in an oil bath and
the reaction was monitored by TLC (ethyl acetate/n-hexane, 1/4).
After completion, the gummy mixture was purified by column
chromatography over silica gel using hexane as eluent to obtain pure
1
product. The pure products were identified by mp, IR, H-NMR,
13C-NMR, MS, and elemental analysis. The characteristic data of
some new 2,4,6-triarylpyridines are given in the succeeding text:
4-(3-nitrophenyl)-2,6-diphenylpyridine (3c).
Yellow solid.
4-(4-methylphenyl)-2,6-bis(4-chlorophenyl)pyridine (3m). White
IR (KBr): 1603, 1526, 1438, 1397, 1350, 775, 740, 690 cmÀ1
.
solid. IR (KBr): 3030, 2361, 1602, 1543, 1491, 831, 811 cmÀ1
.
1H-NMR (400MHz, DMSO-d6): δ 8.84 (s, 1H), 8.51 (d, 1H,
J = 7.5 Hz), 8.38–8.28 (m, 7H), 7.86 (t, 1H, J = 7.9Hz), 7.64–7.49
(m, 6H). 13C-NMR (100 MHz, DMSO-d6): δ 157.1, 149.0, 147.8,
139.9, 138.9, 134.6, 131.0, 129.8, 129.1, 127.5, 124.3, 122.6,
117.3. MS (ESI): m/z (%) 353 (M++H, 100). Anal. Calcd for
1H-NMR (400 MHz, DMSO-d6): δ 8.37 (d, 4H, J = 8.3 Hz),
8.24 (s, 2H), 7.98 (d, 2H, J = 7.8 Hz), 7.61 (d, 4H, J = 8.3 Hz),
7.38 (d, 2H, J = 7.9 Hz), 2.41 (s, 3H). 13C-NMR (100 MHz,
DMSO-d6): δ 155.1, 149.5, 139.1, 137.3, 134.3, 134.0, 129.5,
129.1, 128.6, 127.1, 116.4, 20.7. MS (ESI): m/z (%) 391
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

M. Wang, Z. Yang, Z. Song, and Q. Wang
Vol 000
(M++H, 100). Anal. Calcd for C24H17NCl2: C, 73.85; H, 4.39; N,
REFERENCES AND NOTES
3.59. Found: C, 73.96; H, 4.32; N, 3.62.
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Scriven, E. V. F. Comprehensive Heterocyclic Chemistry II; Pergamon
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[10] Kobayashi, T.; Kakiuchi, H.; Kato, H. Bull Chem Soc Jpn
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Bijanzadeh, H. R. Tetrahedron Lett 2006, 47, 5957.
[12] Heravi, M. M.; Bakhtiari, K.; Daroogheha, Z.; Bamoharram, F. F.
Catal Commun 2007, 8, 1991.
4-(4-methoxyphenyl)-2,6-bis(4-chlorophenyl)pyridine (3n). White
solid. IR (KBr): 2836, 2361, 1602, 1545, 1514, 1491, 825,
578 cmÀ1 1H-NMR (400MHz, DMSO-d6): δ 8.37 (d, 4H,
.
J = 8.0 Hz), 8.21 (s, 2H), 8.05 (d, 2H, J = 8.1 Hz), 7.60 (d, 4H,
J = 8.0 Hz), 7.11 (d, 2H, J = 8.1 Hz), 3.86 (s, 3H). 13C-NMR
(100MHz, DMSO-d6): δ 160.9, 155.6, 149.7, 137.9, 134.5,
129.9, 129.1, 128.8, 116.6, 114.8, 55.8. MS (ESI): m/z (%) 407
(M++H, 100). Anal. Calcd for C24H17NCl2O: C, 70.95; H, 4.22;
N, 3.45. Found: C, 71.07; H, 4.16; N, 3.42.
4-(4-dimethylaminophenyl)-2,6-bis(4-chlorophenyl)pyridine
(3o). Crocus solid. IR (KBr): 2361, 1600, 1534, 1490, 1435,
1
831, 807 cmÀ1. H-NMR (400 MHz, DMSO-d6): δ 8.35 (d, 4H,
J = 7.6 Hz), 8.16 (s, 2H), 7.95 (d, 2H, J = 7.8 Hz), 7.59 (d, 4H,
J = 7.6 Hz), 6.84 (d, 2H, J = 7.9 Hz), 3.01 (s, 6H). 13C-NMR
(100 MHz, DMSO-d6): δ 155.4, 151.6, 150.1, 138.1, 134.3,
129.1, 128.4, 124.3, 115.6, 112.6, 110.0, 40.1. MS (ESI): m/z
(%) 420 (M++H, 100). Anal. Calcd for C25H20N2Cl2: C, 71.61;
H, 4.81; N, 6.68. Found: C, 71.49; H, 4.86; N, 6.73.
2,6-bis(4-methoxyphenyl)-4-phenylpyridine (3p).
White
solid. IR (KBr): 3065, 2833, 1608, 1545, 1512, 833, 773, 583 cmÀ1
.
1H-NMR (400 MHz, DMSO-d6): δ 8.30 (s, 4H), 8.06–8.02 (m, 4H),
7.57–7.53 (m, 3H), 7.11 (s, 4H), 3.84 (s, 6H). 13C-NMR
(100MHz, DMSO-d6): δ 160.1, 155.9, 149.2, 137.9, 131.3,
129.0, 128.1, 127.2, 114.8, 113.9, 55.1. MS (ESI): m/z (%) 368
(M++H, 100). Anal. Calcd for C25H21NO2: C, 81.72; H, 5.76; N,
3.81. Found: C, 81.85; H, 5.66; N, 3.76.
[13] Nagarapu, L.; Aneesa, B.; Peddiraju, R.; Apuri, S. Catal
Commun 2007, 8, 1973.
4-(4-methylphenyl)-2,6-bis(4-methoxyphenyl)pyridine (3q). White
solid. IR (KBr): 2957, 2361, 1608, 1544, 1514, 1425, 833, 814,
[14] Davoodnia, A.; Razavi, B.; Tavakoli-Hoseini, N. E-J Chem
2012, 9, 2037.
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Orient J Chem 2012, 28, 303.
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Khashi, M. Monatsh Chem 2010, 141, 867.
[18] Ingole, P. G.; Jadhav, S. V.; Bajaj, H. C. Int J ChemTech Res
2010, 2, 289.
580 cmÀ1 1H-NMR (400MHz, DMSO-d6): δ 8.28 (d, 4H,
.
J = 8.3 Hz), 8.04 (s, 2H), 7.93 (d, 2H, J = 7.6 Hz), 7.37 (d, 2H,
J = 7.6 Hz), 7.09 (d, 2H, J = 8.3 Hz), 3.85 (s, 6H), 2.40 (s, 3H).
13C-NMR (100 MHz, DMSO-d6): δ 160.6, 156.4, 149.5, 139.2,
135.4, 131.8, 130.0, 128.7, 127.5, 115.0, 114.4, 55.7, 21.3. MS
(ESI): m/z (%) 382 (M++H, 100). Anal. Calcd for C26H23NO2: C,
81.86; H, 6.08; N, 3.67. Found: C, 81.95; H, 6.01; N, 3.72.
4-(4-dimethylaminophenyl)-2,6-bis(4-methoxyphenyl)pyridine
[19] He, Q. P.; Wang, J. Y.; Feng, R. K. Lett Org Chem 2010,
7, 172.
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(3s).
Green-yellow solid. IR (KBr): 2931, 1593, 1514, 1438,
1364, 814, 578 cmÀ1
.
1H-NMR (400MHz, DMSO-d6): δ 8.27
(dd, 4H, J = 8.1, 5.1 Hz), 7.99–7.90 (m, 4H), 7.09 (dd, 4H,
J = 8.2, 5.1 Hz), 6.87–6.85 (m, 2H), 3.85 (d, 6H, J = 5.0 Hz), 3.00
(d, 6H, J = 4.9 Hz). 13C-NMR (100 MHz, DMSO-d6): δ 160.5,
156.2, 151.4, 149.5, 132.1, 128.6, 128.2, 125.0, 114.4, 113.9,
112.7, 55.6, 40.2. MS (ESI): m/z (%) 411 (M++H, 100). Anal.
Calcd for C27H26N2O2: C, 79.00; H, 6.38; N, 6.82. Found: C,
78.87; H, 6.29; N, 6.89.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet