A one-pot three-component synthesis of 4,6-diarylpyrimidin-2(1H)-ones (DAPMs) using atomized sodium in THF under sonic condition

Article abstract of DOI:10.1016/j.ultsonch.2013.12.021

A simple and an efficient procedure for the synthesis of 4,6-diarylpyrimidin-2(1H)-ones using atomized sodium/THF via a one-pot three-component Biginelli-like cyclocondensation of an aldehyde, a methyl ketone and urea under ultrasonic condition is develop

Full text of DOI:10.1016/j.ultsonch.2013.12.021

Ultrasonics Sonochemistry 21 (2014) 1279–1283
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Ultrasonics Sonochemistry
journal homepage: www.elsevier.com/locate/ultson
Short Communication
A one-pot three-component synthesis of 4,6-diarylpyrimidin-2(1H)-ones
(DAPMs) using atomized sodium in THF under sonic condition
⇑
Mohamed Afzal Pasha , Nagashree Shrivatsa
Department of Studies in Chemistry, Central College Campus, Bangalore University, Bengaluru 560 001, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 25 April 2013
Received in revised form 20 December 2013
Accepted 24 December 2013
Available online 3 January 2014
A simple and an efficient procedure for the synthesis of 4,6-diarylpyrimidin-2(1H)-ones using atomized
sodium/THF via a one-pot three-component Biginelli-like cyclocondensation of an aldehyde, a methyl
ketone and urea under ultrasonic condition is developed. The method is mild and inexpensive; yields
are high and the reactions go to completion within 10–15 min.
Ó 2013 Elsevier B.V. All rights reserved.
Keywords:
Atomized sodium
Aldehydes
Methyl ketones
Urea
4,6-Diarylpyrimidin-2(1H)-ones (DAPMs)
Ultrasound
1. Introduction
In recent days multi-component reactions are preferred for the
syntheses of a variety of organic molecules because of ease of exe-
In recent years synthesis of biological active compounds is in
great demand. Pyrimidine nucleus is found in many natural bioac-
tive products possessing multiple biological and medical proper-
ties [1]. Some of these compounds serve as antihypertensive,
antibacterial, and anti-inflammatory agents [2]. The batzelladine
alkaloids containing 3,4-DHPM isolated from marine sources
inhibits the binding of HIV envelope protein gp-120 to human
CD4 cells [3]. Such properties make these pyrimidones highly
important. There are only a few methods reported for the synthesis
of DHPMs, wherein a one-pot cyclocondensation of methyl ketones
with aldehydes and urea instead of 1,3-diketones is reported [4].
Heravi et al. used TMSCl and sulfamic acid as catalysts for the syn-
thesis of 4,6-diarylpyrimidin-2(1H)-ones (DAPMs) [5], Khosropour
et al. used Bi(TFA)3 immobilized on [nbpy]FeCl4 [6], and Cai-hui
used con. HCl in ionic liquid [BMIM][BF4] to promote this reaction
[7]. Other reported methods for the synthesis of DAPMs are from
urea and 1,3-diphenylpropenone or 1,3-diphenylpropynone or
1,3-diphenylpropane-1,3-dione in the presence of NaOEt/Et3N or
cyanouric trichloride/CF3SO3Zn as catalysts [8–11]. The above re-
ported methods suffer from drawbacks such as use of stoichiome-
tric amounts of catalysts, expensive reagents, prolonged reaction
time, and varying yields of the products.
cution, non-isolation of intermediates, short reaction times, and
quantitative yields of the products [12]. In the last decade, sono-
chemistry has gained tremendous popularity in the field of organic
syntheses for the reason that, it is more convenient, high yielding,
reactions go to completion in short durations when compared to
the traditional methods. Also, the number of steps involved are less
and cruder reagents can be used under sonic conditions [13–21].
Richards and Loomis were the first to report the use of ultrasound
in organic syntheses in the year 1927 [22]. In continuation of the
work from our laboratory to develop new methods for the synthe-
sis of various biologically important molecules such as N,N-disub-
stituted ureas/thioureas [23], azines [24], b-acetamido-b-aryl-
propiophenones [25] and aryl-14H-dibenzo[a,j]xanthenes [26],
we are reporting an effective protocol for the synthesis of 4,6-
diarylpyrimidin-2(1H)-ones using atomized sodium in THF via a
one-pot three-component cyclocondensation of methyl ketones
and urea with various substituted aryl aldehydes under ultrasonic
condition. This one-pot route is mild, energy efficient, and inex-
pensive. The yields are high (up to 90%) and the reactions go to
completion within 10–15 min as shown in Scheme 1.
2. Results and discussion
We started our investigations with various catalysts, in various
solvents under different reaction conditions in order to develop a
new method for the synthesis of 4,6-diarylpyrimidin-2(1H)-ones
⇑
Corresponding author. Tel.: +91 8022961337; fax: +91 8022961331.
E-mail address: m_af_pasha@ymail.com (M.A. Pasha).
1350-4177/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ultsonch.2013.12.021

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M.A. Pasha, S. Nagashree / Ultrasonics Sonochemistry 21 (2014) 1279–1283
H2N
NH2
R1
+
+
R
atomized Na
2
H
CH3
O
THF, ))))
R2
R1
N
NH
O
O
10-15 mins
O
1
2
3
4
Scheme 1. Cyclocondensation of benzaldehyde, acetophenone, and urea using atomized sodium in THF under sonic condition.
Table 2
via a one-pot three-component Biginelli-type cyclocondensation
reaction. To standardize the conditions all the reactions were car-
ried out with 4-(N,N-dimethylamino)benzaldehyde, acetophenone
and urea as model substrates. Initially we selected a series of met-
als and conducted the above reaction to get high yield of the de-
sired product with atomized sodium in THF as a solvent under
sonic condition within 10–20 min. It was found that, at silent con-
dition in-order to get the same yield we require to stir for 360–
480 min as shown in Table 1 (entry b). It was also found that, with
commercial LR grade sodium the yield is only 70%, which can be
attributed to the presence of hydroxide/oxide layer on the surface
of the metal, which requires cleaning first and then participation in
the reaction. As the surface area of the atomized sodium is large
the reaction with atomized sodium is fast and gives high yield of
the product under sonic condition. Hence, pre-treatment of the
commercial sodium to get atomized sodium is essential to get
the high yield of the product in short reaction duration. However,
the pre-treatment of commercial sodium with ultrasound for about
10 min followed by the reaction with the substrates did not im-
prove the yield of the reaction, which may be due to the non-atom-
ization of the sodium metal under sonic condition.
Effect of nature of solvent on the synthesis of 4f in the presence of sodium.a
Entry
Solventb
Time (min)
Yield (%)c,d
Silent 25 °C
MW
US
a
b
c
d
e
f
g
h
i
No solvent
Acetone
Acetonitrile
Chloroform
DCE
DCM
Ethanol
Ether
360–480
360–480
360–480
360–480
360–480
360–480
360–480
360–480
360–480
360–480
360–480
360–480
60–80
60–80
60–80
60–80
60–80
60–80
60–80
60–80
60–80
60–80
60–80
60–80
60–80
50–60
50–60
50–60
50–60
50–60
60–80
60–70
30–40
60–80
10–20
50–60
5
10
5
25
25
25
25
10
20
20
90
5
Hexane
Methanol
THF
j
k
l
Xylene
a
4-(N,N-dimethylamino)benzaldehyde (2.0 mmol), acetophenone (2.0 mmol),
urea (3.0 mmol) and atomized sodium (2 mg atom) under sonic condition (35 kHz).
b
5 mL.
Isolated yields.
Compared with authentic sample on TLC.
c
d
In order to verify whether THF is a suitable solvent or not for the
above reaction, the reaction was carried out in various solvents and
under solvent-free condition. The results of these studies are pre-
sented in Table 2; and it was found that, atomized sodium in
THF is ideal in terms of yield and the time of the completion of
Table 3
Optimisation of the amount of sodium required for the synthesis of 4f.
Entry Amount of atomized sodium (mg atom) Time (min) Yield (%)a,b
US
a
b
c
d
e
f
0.0
0.5
1.0
1.5
2.0
2.5
3.0
50
30
20
20
10
10
10
ND
70
75
80c
90
90
90
the reaction. As Imax (maximum cavitation intensity) and TI
max
(the temperature at which Imax is reached) of any solvent has a pro-
found effect in sonochemical reactivity, Imax of THF may be respon-
sible for the increase in the reaction rate when compared to the
other solvents [27]. Hence, the rate of the reaction under sonic con-
dition gets accelerated substantially in THF when compared to
other solvents.
For optimizing the amount of atomized sodium, we worked
with different amounts of atomized sodium required for the reac-
tion and the results of this study are given in Table 3. From this
Table it is clear that, equivalent amounts (2 mg atom) of the metal
is essential for the present reaction.
g
a
b
c
Isolated yields; after silica gel column chromatography.
Compared with authentic sample on TLC; ND: not detected.
4-(N,N-dimethylamino)benzaldehyde (2.0 mmol), acetophenone (2.0 mmol),
and urea (3.0 mmol) in THF (5.0 mL) under sonic condition (35 kHz).
In order to find the minimum amount of THF required to get
maximum yield in short duration, the reaction was carried out in
different volumes of THF and it was found that, the minimum
amount of THF required to get the maximum yield of the product
is 2 mL. The results of this study are presented in the Table 4. From
the data provided in Tables 1–4 it is also clear that, synthesis of
4,6-diarylpyrimidin-2(1H)-one (4f) using atomized sodium/THF
via a three-component one-pot Biginelli-type cyclocondensation
under the influence of ultrasound at 35 kHz is efficient and gives
high yield of the product in short duration.
Table 1
A comparative study on the synthesis of 4f with different metals in THF.a
Entry
Metalb
Time (min)
Silent
Yield (%)c,d
US
In order to find the generality of the use of atomized sodium in
THF for the cyclocondensation of an aldehyde with acetophenone
and urea under sonic condition, different substituted aromatic
aldehydes and methyl ketones were selected and the reactions
were carried out in a sonic bath working at 35 kHz (constant fre-
quency, 80 W) maintained at 25 °C by circulating water. The re-
sults of this study are presented in Table 5. It can be seen that,
the reaction is not influenced by the presence of neither electron
donating nor electron withdrawing substituents on the aromatic
ring of aldehydes and ketones at different positions.
a
b
c
d
e
f
Sodium
360–480
360–480
360–480
360–480
360–480
360–480
30–40
10–20
12–20
12–20
12–20
12–20
70
90
10
15
20
05
Atomized sodium
Aluminium
Zinc
Iron
Copper
a
b
c
5 mL.
2 mg atom.
Isolated yields.
Compared with authentic sample on TLC.
d

M.A. Pasha, S. Nagashree / Ultrasonics Sonochemistry 21 (2014) 1279–1283
1281
Table 4
sonochemical effects in the present heterogeneous reaction. The
phenomenon of acoustic cavitation attributes to the accomplish-
ment of the organic reactions under sonic condition [32]. The pri-
mary chemical reactions are due to the transient state of immense
temperature, pressure and extraordinary heating rates which are
generated due the cavitation bubble collapse [21]. The other effects
are considered to be physical rather than chemical and judged to
be ‘false’ sonochemical effects [33].
Amount of THF required for the synthesis of 4f.
Entry
THF (mL)
Time (min)
US
Yield (%)a,b,c
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
0.5
1.0
1.5
2
2
2
2
2
2
2
2
2
2.5
2.5
5
50
50
50
50
40
35
30
25
20
15
10
08
10
15
10
10
80
80
85
90
90
90
90
90
90
90
90
90
90
90
90
86
3. Experimental
3.1. Materials and methods
All the chemicals used were commercially available reagents.
All the solvents were distilled before use. THF was distilled and
dried over sodium. All the reactions were studied using SIDILU In-
dian make sonic bath working at 35 kHz (constant frequency,
80 W) maintained at 25 °C (by circulating water). The completion
of the reaction was monitored on TLC (eluent: 8–10% ethyl acetate
in light petrol), by comparison with the authentic samples. Melting
points of the obtained products were determined using a Büchi
apparatus. Nuclear magnetic resonance spectra were obtained on
a 400 MHz Bruker AMX spectrometer in DMSO-d6 using TMS as a
standard. GC–Mass spectra were obtained using a Shimadzu GC–
MS QP 5050A instrument equipped with a 30 m length and
0.32 mm dia BP-5 column with the column temperature 80–15–
250 °C. Infrared spectra were recorded using Shimadzu FT-IR-
8400s Spectrophotometer as KBr pellets for solids.
Typical experimental procedure for the synthesis of 4f: A mix-
ture 4-(N,N-dimethylamino)benzaldehyde (0.274 g, 2.0 mmol),
acetophenone (0.24 g, 2.0 mmol), urea (0.18 g, 3.0 mmol), atom-
ized sodium (2.0 mg atom), THF (2 mL) were sonicated in a sonic
bath working at 35 kHz (constant frequency, 80 W) maintained
at 25 °C (by circulating water) for 10 min. At the end of the reac-
tion, liquefied reaction mixture suddenly becomes solid, to which
water was added and shaken for few minutes. This was filtered
through a sintered funnel to afford the crude product, which was
further purified by recrystallization using absolute ethanol.
10
a
b
c
Isolated yields.
Compared with authentic sample on TLC.
4-(N,N-dimethylamino)benzaldehyde (2.0 mmol), acetophenone (2.0 mmol),
atomized sodium (2 mg atom) and urea (3.0 mmol) under sonic condition (35 kHz).
2.1. Effect of ultrasound on the reaction
Sonochemistry is a unique and distinctive chemistry, in which
the physical properties of the medium will have a decisive effect
on the chemical reactivity. The reactions carried out under the
influence of ultrasound are considered to be clean and the method
is green as it involves use of an energy efficient technique [30,31].
The present reaction is an example of a three-phase system: the li-
quid phase (reagents in solvents), solid phase (atomized sodium
and solid substrates), and the gas phase (dissolved gases in the liq-
uids and gases on the inner-surface of the vessel) [31]. When sound
waves pass through liquid medium, they induce vibrational motion
to the medium, the solvent molecules then compress, stretch and
oscillate around their mean position due to time-varying pressure,
at a point when the intensity of the sonic waves is higher enough
to break the intermolecular forces existing between the solvent
molecules it breaks down and a cavity is formed. The process of
generating cavitational bubble is called acoustic cavitation
[30,32]; and the bubble collapse then becomes non-spherical near
the solid surface i.e., near the surface of the solid atomized sodium
and the surface of the vessel, which drags the liquid high-speed
jets near the surface creating shockwaves which can activate the
surface of the metal. The formation of the micro-jets and shock-
waves create the localized erosion responsible for most of the
4. Spectral data
4.1. 4,6-Diphenyl-pyrimidin-2(1H)-one (4a)
m.p. 235 °C; IR (KBr):
m ;
3358, 3159, 2960, 1612, 1502 cmꢀ1 1H
NMR (DMSO, 300 MHz): d 7.1–7.15 (d, 2H, J = 15 Hz, HAr and CH),
7.3–7.6 (m, 7H, J = 90 Hz, HAr), 7.88–7.92 (d, 2H, J = 12 Hz, HAr),
7.99 (s, 1H, NH) ppm; MS (70 eV), m/z: 248 [M+]
Table 5
Three-component cyclocondensation of aldehyde, urea with aromatic ketones by atomized sodium in dry THF under sonic condition (35 kHz constant frequency at 25 °C).
Entry
Ketone
Aldehyde
Product
Time (min)
US
Yield (%)a,b
Melting point (°C)
R1 (1)
R2 (2)
(4)
Found
Reportedc,d
a
b
c
d
e
f
g
h
i
H
H
H
H
H
H
H
4-CH3
4-Cl
4a
4b
4c
4d
4e
4f
4g
4h
4i
10
14
13
13
12
10
10
11
11
10
90
88
86
86
88
90
88
88
87
90
235
288
255–257
258–261
258
292
250–253
310
311
285–289
233–240c
287–290c
258–260c
260–263c
258–260c
290–293d
251–254c
308–310c
312–314c
280–290c
4-OH
4-OCH3
4-N,N-(CH3)2
H
4-Cl
4-Cl
4-Cl
4-NO2
4-OCH3
4-OCH3
j
4-N,N-(CH3)2
4j
a
b
c
Isolated yields.
All the products are known and were characterized by comparison of their spectroscopic and physical data with the authentic samples.
References [28,29].
References [28,29].
d

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M.A. Pasha, S. Nagashree / Ultrasonics Sonochemistry 21 (2014) 1279–1283
4.2. 4-(40-Toluyl)-6-phenyl-pyrimidin-2(1H)-one (4b)
CH3), 3.88 (s, 3H, OCH3), 7.101 (d, 2H, J = 8.86 Hz, HAr), 7.62 (s,
1H, H-5), 7.63 (d, 2H, J = 8.56 Hz, HAr), 8.19 (d, 2H, J = 8.17 Hz,
HAr), 8.23 (d, 2H, J = 8.16 Hz, HAr), 11.97 (br s, 1H, NH) ppm; MS
(70 eV), m/z: 321 [M+]
m.p. 288 °C; IR (KBr):
m 3449, 3099, 2923, 1620, 1513,
1460 cmꢀ1 1H NMR (DMSO, 300 MHz): d 2.39 (s, 3H, CH3), 7.36
;
(d, 2H, J = 7.5 Hz, HAr), 7.53–7.57 (m, 4H, H-5 and HAr), 8.07 (d,
2H, J = 7.6 Hz, HAr), 8.15 (d, 2H, J = 5.75 Hz, HAr) ppm; MS
(70 eV), m/z: 262 [M+].
5. Conclusions
We have developed an efficient synthesis of 4,6-diarylpyrimi-
din-2(1H)-ones by a one-pot three-component cyclocondensation
reaction between an aldehyde, a methyl ketone and urea using
atomized sodium in THF under sonic condition. This new protocol
has advantages such as: (i) the use of cheap, easy to handle and
commercially available sodium metal; (ii) short reaction times
(10–15 min); and (iii) high yields (91–96%).
4.3. 4-(40-Chlorophenyl)-6-phenyl-pyrimidin-2(1H)-one (4c)
m.p. 255–257 °C; IR (KBr):
m 3429, 3230, 3083, 1605, 1549,
1509 cmꢀ1 1H NMR (DMSO, 500 MHz): d 7.59 (d, 2H, J = 7.33 Hz,
;
HAr), 7.60–7.69 (m, 4H, HAr and H-5), 8.16 (d, 2H, J = 7.45 Hz,
HAr), 8.22 (d, 2H, J = 8.32 Hz, HAr) ppm; MS (70 eV), m/z: 282 [M+]
4.4. 4-(40-Hydroxyphenyl)-6-phenyl-pyrimidin-2(1H)-one (4d)
Acknowledgements
m.p. 258–261 °C; IR (KBr):
m 3389, 2922, 1613, 1515,
1450 cmꢀ1 1H NMR (DMSO, 500 MHz): d 6.96–7.04 (m, 3H, NH
;
The authors acknowledge the VGST, Dept. of IT, BT and Science
& Technology, Government of Karnataka for the financial assis-
tance under the CESEM Award Grant No. 24 (2010–2011).
and H-4), 7.52–7.71 (m, 5H, HAr and H-5), 8.05–8.16 (m, 5H,
HAr), 11 (s, 1H, OH) ppm; MS (70 eV), m/z: 264 [M+]
4.5. 4-(40-Methoxyphenyl)-6-phenyl-pyrimidin-2(1H)-one (4e)
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m.p. 258 °C; IR (KBr):
m 3440, 3095, 2930, 1608, 1514,
1458 cmꢀ1 1H NMR (DMSO, 400 MHz): d 3.9 (s, 3H, CH3), 7.2–8.2
;
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(m, 10H, H-5 and HAr), 11.95 (S, 1H, NH) ppm; MS (70 eV), m/z:
278 [M+]
4.6. 4-(40-N,N-Dimethylphenyl)-6-phenyl-pyrimidin-2(1H)-one (4f)
(b) G.C. Rovnyak, S.D. Kimball, B. Beyer, G. Cucinotta, J.D. DiMarco, J.Z.
Gougoutas, A. Hedberg, M.F. Malley, J.P. McCarthy, R. Zhang, S.J. Moreland,
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m.p. 292 °C; IR (KBr):
m ;
3448, 3095, 2925, 1619, 1509 cmꢀ1 1H
NMR (DMSO, 300 MHz): d 3.04 (d, 6H, J = 6.63 Hz, CH3), 6.79–6.81
(d, 2H, J = 6 Hz, HAr), 7.36 (s, 1H, CH), 7.52–7.58 (m, 3H, J = 18 Hz,
HAr), 8.06–8.12 (m, 4H, J = 18 Hz, HAr), 11.89 (br s, 1H, NH) ppm;
MS (70 eV), m/z: 291 [M+]
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4.7. 4-(40-Chlorophenyl)-6-phenyl-pyrimidin-2(1H)-one (4g)
m.p. 250–253 °C; IR (KBr):
m ;
3320, 1608, 1532, 1488 cmꢀ1 1H
NMR (DMSO, 300 MHz): d 7.56 (d, 3H, J = 5.90 Hz, HAr), 7.82 (s,
1H, H-5), 8.17 (d, 2H, J = 6.62 Hz), 8.35 (d, 2H, J = 8.25 Hz, HAr),
8.46 (d, 2H, J = 8.16 Hz, HAr) ppm; MS (70 eV), m/z: 282 [M+]
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(4h)
m.p. 310 °C; IR (KBr):
m 3412, 3192, 2921, 1612, 1548, 1515,
1456, 1348 cmꢀ1 1HNMR (DMSO, 300 MHz): d 6.90–7.83 (m, 9H,
;
H-5 and HAr), 9.98 (s, 1H, NH) ppm; MS (70 eV), m/z: 327 [M+]
4.9. 4-(40-Chlorophenyl)-6-(400-methoxyphenyl)–pyrimidin-2(1H)-one
(4i)
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