Ultrasound assisted dehydrogenation of 2-oxo-1,2,3,4-tetrahydropyrimidine- 5-carboxamides

Article abstract of DOI:10.1016/j.ultsonch.2010.10.006

Dehydrogenation of various 2-oxo-1,2,3,4-tetrahydropyrimidine-5- carboxamides (THPMs) to 2-oxo-1,2-dihydropyrimidine-5-carboxamides (DHPMs) using tetrabutylammonium peroxydisulfate (TBAPS) as an efficient oxidizing agent under thermal and sono-thermal con

Full text of DOI:10.1016/j.ultsonch.2010.10.006

Ultrasonics Sonochemistry 18 (2011) 745–752
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Ultrasonics Sonochemistry
journal homepage: www.elsevier.com/locate/ultsonch
Ultrasound assisted dehydrogenation of 2-oxo-1,2,3,4-tetrahydropyrimidine-
5-carboxamides
⇑
Hamid R. Memarian , Mousa Soleymani
Catalysis Division, Department of Chemistry, Faculty of Science, University of Isfahan, 81746-73441 Isfahan, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 8 June 2010
Received in revised form 6 October 2010
Accepted 11 October 2010
Available online 21 October 2010
Dehydrogenation of various 2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxamides (THPMs) to 2-oxo-1,2-
dihydropyrimidine-5-carboxamides (DHPMs) using tetrabutylammonium peroxydisulfate (TBAPS) as an
efficient oxidizing agent under thermal and sono-thermal conditions has been investigated. In contrast to
the thermal reaction, a decrease of the amount of oxidant and an increase of the rate of reaction are
observed by simultaneously applying heat and ultrasound. The nature of both C-4 and C-5 substituents
on the heterocyclic ring influences the rate of reaction under both conditions. The proposed electron-
transfer-induced dehydrogenation in this study is supported by conductometric studies.
Ó 2010 Elsevier B.V. All rights reserved.
Keywords:
Biginelli compounds
Dehydrogenation
Electron-transfer
1,2,3,4-Tetrahydropyrimidinones
Peroxydisulfates
Sono-thermal
1. Introduction
5-acetyl-2-oxo-1,2,3,4-tetrahydropyrimidines was first reported
by our group to 2-oxo-1,2-dihydropyrimidines through an electron
Dehydrogenation
of
2-oxo-1,2,3,4-tetrahydropyrimidines
transfer mechanism in CHCl3 solution [10,11].
(THPMs), also known as Biginelli compounds, to their correspond-
ing 2-oxo-1,2-dihydropyrimidines (DHPMs) is one of the reactions
which can affect the biological activities of these compounds.
Recent investigations concerning the biological activities of THPMs
indicate that this activity is dependent on the C4 absolute configu-
ration of these compounds [1], which can be easily lost upon
dehydrogenation and conversion to the corresponding 1,2-
dihydropyrimidinones.
In contrast to 1,4-dihydropyridines (DHP) and 1,4-dihydropyr-
imidines, which are easily dehydrogenated to their corresponding
pyridines and pyrimidines by thermal procedures using simple
oxidants such as NaNO2/AcOH, PCC, MnO2, KMnO4, DDQ [2], and
BaMnO4 [3], for both series of compounds or by photochemical
means for the dehydrogenation of 1,4-DHP [4], 2-oxo-1,2,3,4-
tetrahydropyrimidines are resistant to dehydrogenation by
using various oxidizing agents [2]. However, in recent years,
some procedures were reported for the dehydrogenation of 5-
carboethoxy- and 5-acetyl-2-oxo-1,2,3,4-tetrahydropyrimidines,
such as dehydrogenation with nitric acid [5], tert-butyl hydro-
peroxide [6], ceric ammonium nitrate (CAN) [7], and potassium
peroxydisulfate under thermal condition [8], and microwave
irradiation [9]. Photodehydrogenation of 5-carboethoxy- and
Application of tetrabutylammonium peroxydisulfate (TBAPS)
for various organic transformations has been reported, such as
the iodination [12] and bromination [13] of aromatic compounds,
cleavage of N,N-dimethylhydrazones to ketones [14], epoxidation
of electron-deficient olefins [15], synthesis of fused acetals [16],
oxidative diphosphonylation of 1,4-dihydropyridines and
pyridinium salts [17], oxidation of sulfides to sulfoxides [18],
nickel-catalyzed oxidation of primary amines to nitriles [19] and
nickel-catalyzed oxidation of primary alcohols [20].
The application of ultrasound in organic synthesis has been
increasing, because of its advantages such as shorter reaction
times, milder reaction condition, and higher yields in comparison
to the classical methods [21–23]. Since in this technique the reac-
tion is carried out normally at lower temperature relative to the
usually thermal methods, the possibility of occurrence of unde-
sired reactions is reduced and as a result of a cleaner reaction,
the workup is easier. The generation of many cavities and a dra-
matic increase in the temperature and pressure during collapse
of the cavities are the most important effects of ultrasound.
Recently we have reported on the effect of the simultaneous
application of ultrasound and heat in the dehydrogenation of
5-carboethoxy- and 5-acetyl-2-oxo-1,2,3,4-tetrahydropyrimidines
by potassium peroxydisulfate (PPS) in aqueous acetonitrile
[24,25]. The results indicate that by the application of ultrasound
the time of reaction is drastically reduced and in some cases the
⇑
Corresponding author. Tel.: +98 311 793 2707; fax: +98 311 668 9732.
E-mail address: memarian@sci.ui.ac.ir (H.R. Memarian).
1350-4177/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ultsonch.2010.10.006

746
H.R. Memarian, M. Soleymani / Ultrasonics Sonochemistry 18 (2011) 745–752
Table 2
reactions go to completion. The results also indicate that the steric
and the electronic effects of the substituent on 4-position of the
heterocyclic ring and the presence of the acetyl or the carboethoxy
groups on 5-positions influence the rate of reaction under both
conditions.
Due to our interest in investigating the nature of the substituent
on the heterocyclic ring by dehydrogenation reactions of these
compounds, we have synthesized various 2-oxo-1,2,3,4-tetrahy-
dropyrimidine-5-carboxamides [26] and investigated dehydro-
genation of the title compounds by tetrabutylammonium
peroxydisulfate (TBAPS) under thermal and sono-thermal condi-
tions. The following points are the aims of the present work:
Solvent effect on dehydrogenation reaction of 1g by TBAPS under reflux condition.
Entrya
Solvent
Time (min)
Conversion (%)
1
2
3
4
5
EtOH
Cyclohexane
MeCN
THF
MeCN
90
90
5
ꢁ5–10
ꢁ5
100
0
90
120b
0
a
1g:TBAPS (1:1.7).
At room temperature.
b
vents such as acetonitrile, cyclohexane, ethanol and tetrahydrofu-
ran under reflux conditions and also in acetonitrile at room
temperature until maximum consumption of 1g (TLC monitoring,
Table 2). The results presented in Table 2 indicate that acetonitrile
is the best solvent for this conversion.
(1) To determine the effect of the carboxamide group as a less
electron-withdrawing group compared with the acetyl and
the carboethoxy groups on the rate of dehydrogenation
reaction.
Due an increase in the reaction temperature which occurs dur-
ing sonication and also in an attempt to elucidate the effect of sonic
waves on the dehydrogenation of the title compounds by TBAPS,
dehydrogenation of 1g as test substrate is carried out in different
1g:TBAPS ratios in acetonitrile by:
(2) To determine the effect of the nature of the additional sub-
stituent and its position on the phenyl ring located on C-4
on the rate of dehydrogenation reaction.
(3) To determine the effect of sonic waves on the time of reac-
tion and also on the amount of the oxidant used.
(4) To provide a comparison of the above mentioned points
under ultrasound irradiation and under thermal reaction
conditions.
(1) applying only ultrasound irradiation,
(2) applying the ultrasound at 22 °C (simultaneously cooling the
reaction vessel by running cold water during sonication),
and
(3) simultaneously applying heat (74 °C) and ultrasound (i.e.,
sono-thermal) until the maximum consumption of 1g
occurred. The results are summarized in Table 3.
2. Results and discussion
2.1. Solvent effect and optimization of the reactants
In order to find a suitable oxidant for conversion of THPM-
amides to their corresponding DHPM-amides, we have carried
out the experiment with 1g as a model substrate in the presence
of various oxidants such as: KMnO4, K2Cr2O7 and MnO2 (all in ace-
tonitrile/water) under reflux conditions, but the dehydrogenation
failed by using these oxidants. The reaction of 1a, 1g and 1h in
the presence of K2S2O8 (PPS) in CH3CN/H2O (10:2) under thermal
conditions (the same experimental conditions were used for the
dehydrogenation of THPM-esters and ketones [8,25]) resulted in
the formation of the corresponding 2-oxo-1,2-dihydropyrimi-
dine-5-carboxamides 2a, 2g and 2h as the major products, besides
various hitherto unidentified by-products. Since PPS is not soluble
in dry acetonitrile, it seems that the presence of water disturbs the
reaction; therefore we decided to use an organic oxidant based on
peroxydisulfate, namely, tetrabutylammonium peroxydisulfate
(TBAPS), which is readily soluble in many organic solvents, in order
to avoid the use of water.
The results indicate that a ratio of 1:1.2 for 1g:TBAPS is suffi-
cient for total conversion of 1g under sono-thermal conditions.
The interesting points displayed in Tables 2 and 3 are the failure
of the reaction at room temperature or by holding the reaction
temperature at 22 °C during sonication. These indicate the neces-
sity of heating either under ultrasound irradiation or under ther-
mal reaction, because the cleavage of the OꢀO bond in the S2O2ꢀ
8
has a relatively high activation energy of around 130 kJ/mol
[27,28]. It is also the case that by starting the sonication at room
temperature, the temperature of the reaction medium is increased
up to 49 °C after 5 min of sonication and remains at this tempera-
ture even after 20 min of sonication. Under these conditions, there
is 50% conversion of 1g.
The effect of sonication intensity was also studied for the dehy-
drogenation reaction of 1g in dry acetonitrile with TBAPS in the ra-
tio of 1:1.2 at 20%, 40%, 60%, 80% and 100% of the rated power of
the ultrasonic horn (92, 184, 276, 368 and 460 W cmꢀ2, respec-
tively). The results shown in Table 4 indicate that by increasing
the ultrasound intensity, a decrease in the time of reaction was
The reaction of 1g as a model substrate in the presence of var-
ious ratios of 1g:TBAPS in dry acetonitrile was carried out under re-
flux conditions until maximum consumption of THPMs occurred
(as monitored by TLC). The results presented in Table 1 indicate
that total conversion of 1g to 2g was achieved by taking the ratio
of 1:1.7 for 1g:TBAPS.
Table 3
Optimization of the dehydrogenation reaction under sono-thermal conditiona and
ultrasound irradiationb,c in dry acetonitrile.
Since the nature of the solvent influences the rate of reaction,
dehydrogenation of 1g by TBAPS was carried out in various sol-
Entry
1g:TBAPS
Time (min)
Conversion (%)
1
2
3
4
5
6
7
8
1:1
30
10
5
4
3
90
95
Table 1
1:1.1
1:1.2
1:1.3
1:1.5
1:1.7
1:1.2
1:1.2
Optimization of 1g:TBAPS molar ratio for the dehydrogenation reaction in refluxing
dry CH3CN.
100
100
100
100
50
Entry
1g:TBAPS
Time (min)
Conversion (%)
3
1
2
3
4
5
6
1:0.5
1:1
1:1.5
1:1.6
1:1.7
1:2
90
90
15
15
5
30
60
95
95
100
100
20b
20c
0
a
b
c
Bath temperature at 74 °C.
Temperature of solution is increased to 49 °C after 5 min sonication.
Temperature of solution was hold at 22 °C by running cold water.
5

H.R. Memarian, M. Soleymani / Ultrasonics Sonochemistry 18 (2011) 745–752
747
Table 4
The effect of maximum power intensity of ultrasound on the rate of oxidation of 1g by TBAPS in CH3CN at 74 °C.
Max. power density
Time (min)
20% (92 W cmꢀ2
16a
)
40% (184 W cmꢀ2
13a
)
60% (276 W cmꢀ2
10
)
80% (368 W cmꢀ2
8
)
100% (460 W cmꢀ2
)
5
a
The reaction was not completed.
observed. This can be due to the homogeneous distribution of the
reactants throughout the solution, namely, the effective mass
transfer by applying the sonic waves and also creation of the max-
imum cavitation around the probe. All of these effects lead to an
enhancement of the rate constant during sonication. It should be
noted that stirring the solution during sonication did not result
of an increase of the rate of reaction.
In an optimized reaction condition, dehydrogenation of various
THPM-amides 1a–q by TBAPS in dry acetonitrile under thermal
and sono-thermal conditions were carried out until total disap-
pearance of the most of the THPMs studied in this work occurred
(Scheme 1). The results are summarized in Table 5.
The results indicate that simultaneous application of heat and
ultrasound (sono-thermal) in comparison to a thermal reaction
alone leads to an increase in the rate of reaction, the use of a smal-
ler amount of the oxidant, and, in some cases, the completion of
the reaction.
(1) A comparison of the IR spectra of 2a–q with those of 1a–q
showed a decrease in the intensity of the NH vibration with
small shift to lower frequency.
(2) A comparison of the UV data of 2a–q with those of 1a–q
indicates that due to dehydrogenation and elimination of
3- and 4-hydrogens, an imino-diene system is formed which
is cross-conjugated with the 4-aryl substituent. This leads to
a bathochromic shift in the UV spectra of 2a–q.
(3) A comparison of the 1H NMR spectra of 2a–q with those of
1a–q shows the following changes in the spectra: (i) a shift
of the 1-NH and ArNH absorptions to lower field, (ii) the lack
of 3-NH and 4-H resonances and (iii). the shift of 6-CH3 res-
onance to lower field due to the attachment of this group to
the imino-diene system.
2.2. The study of mechanism
The characterization of the products 2a–q was achieved by
comparison of their IR, UV, 1H NMR and MS data with those of
the starting materials 1a–q as following:
The results presented in Table 5 indicate that the nature of both
R1 and R2 groups affects the rate of reaction. Whereas electron-
withdrawing substituent such as nitro group on the R1 (1l and
1m) (especially in the para-position, 1m) reduces the rate of reac-
tion, electron-releasing substituent such as the methoxy group (1n
and 1o) (especially in the para-position, 1o) increases the rate of
reaction. We have proposed earlier a radical mechanism in the
dehydrogenation of 5-carboethoxy- and 5-acetyl-THPMs by potas-
sium peroxydisulfate (PPS) in CH3CN/H2O solution [8,25]. Accord-
ing to this mechanism, homolytic cleavage of PPS in the first step
leads to the formation of potassium sulfate radical, which abstracts
hydrogen from water in the second step to form hydroxyl radical.
Removal of 4-hydrogen by hydroxyl radical in the third step (as the
rate determining step) followed by elimination of a second hydro-
gen atom in the last step completes the reaction for the formation
O
O
R1
R1
H
TBAPS / CH3CN
)))
NH
N
R2HN
R2HN
or
,
O
O
H3C
N
H
H3C
N
H
1a-q
2a-q
Scheme 1.
Table 5
Dehydrogenation of THPMs by TBAPS in dry acetonitrile under refluxa and sono-thermalb condition.
1
R1
R2
2
D
D
,
Time (min)
Yield (%)c
Time (min)
Yield (%)c
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
o-ClC6H4
m-ClC6H4
p-ClC6H4
o-BrC6H4
p-BrC6H4
m-NO2C6H4
p-NO2C6H4
m-MeOC6H4
p-MeOC6H4
p-MeC6H4
MeCHC6H5
C6H5
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
6d
3
5
4
5
5
5
6
3
89
93
86
88
85
88
90
90
89
93
87
81
86
90
93
89
71
5 (3.5)e
4
90
90
90
91
89
88
92
91
92
90
90
84
85
91
93
89
80
C6H5–CH2
p-FC6H4
o-ClC6H4
p-ClC6H4
p-BrC6H4
o-ClC6H4
o-ClC6H4
o-ClC6H4
o-ClC6H4
o-ClC6H4
o-ClC6H4
o-ClC6H4
o-ClC6H4
o-ClC6H4
o-ClC6H4
o-ClC6H4
5
4 (2.5)e
5
5 (3)e
5 (3)a
6
4 (2.5)a
6
5
3
5 (2.5)a
8d
7d
8d
4
8d (5)a
5
2.5
5d
8d
3 (2)a
5
9d
a
b
c
[THPM]/[TBAPS] = 1:1.7.
[THPM]/[TBAPS] = 1:1.2.
Isolated yield.
Dehydrogenations were not completed.
The times given in parenthesis refer to sono-thermal reaction by [THPM]/[TABP] = 1:1.7.
d
e

748
H.R. Memarian, M. Soleymani / Ultrasonics Sonochemistry 18 (2011) 745–752
of 2-oxo-1,2-dihydropyrimidine (DHPM) product. In contrast to
the results obtained for the dehydrogenation of the title com-
pounds (THPM-amides) by PPS in CH3CN/H2O solution as men-
tioned earlier, a complete dehydrogenation of these compounds
was observed by using TBAPS in CH3CN solution. It is noteworthy
that, whereas PPS is not able to oxidize the THPM-esters and ke-
tones in dry acetonitrile [8,24,25], dehydrogenation of 1d and 1g
by PPS in dry acetonitrile has been observed in ꢁ40% and ꢁ20%,
respectively. It should be noted that thermal reaction of 4-(20-chlo-
rophenyl)-substituted 5-carboethoxy-THPM and 4-(20-chloro-
phenyl)-substituted 5-carboxamide-THPMs 1g by TBAPS in
acetonitrile leads to complete consumption of the former and 1g
within 25 and 5 min, respectively. This explains the sensitivity of
carboxamides-THPMs towards oxidation.
It is clear that the first step of the dehydrogenation is the homo-
lytic cleavage of the O–O bond in the peroxydisulfate ion and for-
mation of either potassium sulfate radical or tetrabutylammonium
sulfate radical. If these radicals are responsible for the abstraction
of 4-H, we should expect that due to smaller steric hindrance of
potassium sulfate radical compared with tetrabutylammonium
sulfate radical, this reaction should be faster with the former rad-
ical than with the latter. This suggestion is in contrast to the above
mentioned results. Therefore, another mechanism should be con-
sidered for the dehydrogenation of THPM-5-carboxamides by
TBAPS in dry acetonitrile solution.
study (Scheme 2). Thermal cleavage of the weakest O–O bond in
the TBAPS molecules (path 1) leads to the formation of tetrabutyl-
ammonium sulfate radical (TBASR). An electron-transfer from the
3-N to the TBASR in the second step (path 2) leads to the formation
of 2-oxo-1,2,3,4-tetrahydropyrimidinyl radical cation (THPMÅ+) and
tetabutylammonium sulfate anion (TBASA). Removal of the first
hydrogen as proton from THPMÅ+ by TBASA in the third step (path
3) leads to the formation of 2-oxo-1,2,3-trihydropyrimidinyl radical
(TrHPMÅ) and tetrabutylammonium hydrogen sulfate (TBAHS). The
second electron-transfer (path 4) and the following second proton
removal (path 5) complete the reaction for the formation of 2-oxo-
1,2-dihydropyrimidine (DHPM) product.
In order to get more information about the proposed mecha-
nism in this study as an electron transfer-induced dehydrogena-
tion of THPM-5-carboxamides by TBAPS and also to support our
experimental results obtained by this dehydrogenation reaction,
conductance measurement, as a very sensitive method, were per-
formed. Conductance measurements were carried out for solutions
of 1k and 1m, TBAPS, and their mixtures at five mole ratios (0.5:1,
1:1, 1.5:1, 1.75:1 and 2:1; for TBAPS to 1k or 1m) at 25 °C, 45 °C
and 65 °C in dry acetonitrile solution. The results are summarized
in Table 6.These studies showed that:
(1) By increasing the temperature, the conductivity of TBAPS is
increased, whereas the conductivities of 1k and 1m change
a little (Table 6). This can be due to the temperature effect
and diminished ion pairing in the TBAPS molecule and con-
sequently enhanced ion mobility of this molecule.
According to these results and the results presented in Table 5
and especially the failure of the reaction by carrying out at room
temperature, we propose the following mechanism in the present
.
(Bu4N)2S2O8
TBAPS
1)
2)
2Bu4NOSO3
or
, )))
TBASR
O
O
R1
H
R1
H
.
+
NH
NH
TBASR
R2HN
R2HN
H3C
Bu4NOSO3
TBASA
+
O
O
H3C
O
N
H
N
H
.
THPM+
THPM
R1
O
R1
H
.
.
+
TBASA
-H+
NH
NH
3) R2HN
R2HN
+ Bu4NOSO3H
TBAHS
O
O
H3C
O
N
H
H3C
O
N
H
.
.
THPM+
TrHPM
R1
.
R1
+
NH
TBASR
NH
R2HN
Bu4NOSO3
+
R2HN
4)
TBASA
O
O
H3C
O
N
H
H3C
O
N
H
.
DHPM+
TrHPM
R1
R1
+
TBASA
-H+
NH
N
R2HN
R2HN
5)
+
Bu4NOSO3H
TBAHS
O
O
H3C
N
H
H3C
N
H
DHPM
DHPM+
Scheme 2.

H.R. Memarian, M. Soleymani / Ultrasonics Sonochemistry 18 (2011) 745–752
749
Table 6
Observed conductances (
l
s/cm2) of EDA-complexes 1k and 1m with TBAPS at different mole ratios at 25 °C, 45 °C and 65 °C in dry acetonitrile solutiona.
[THPM]:[TBAPS] 1.0:0 mM
1.0:0.5 mM
1.0:1.0 mM
0.01:1.5 mM
0.01:1.75 mM
45 °C 65 °C
0.01:2.0 mM
25 °C 45 °C 65 °C
25 °C 45 °C 65 °C 25 °C 45 °C 65 °C 25 °C 45 °C 65 °C 25 °C 45 °C 65 °C 25 °C
1k
1
10.2
1.48
1.28
10.9
2.0
1.46
11.9
2.67
178
188
210
210
235
240
236
242
305
300
360
365
393
403
470
476
526
538
461
467
64.60 89.2
549
593
650
644
119.2
497
508
610
630
685
683
1m
1kb
[THPM]:[TBAPS]
0:0.05 mM
178 196
0:1.0 mM
233 261
0:1.5 mM
390 446
0:1.75 mM
0:2.0 mM
495 588
TBAPS
225
333
500
460
525
627
117.7
650
TBAPSb
63.1
87.7
a
Conductances of acetonitrile and ethanol at 25 °C, 45 °C and 65 °C are 0.60, 0.88 and 0.95 l l
s/cm2, and 0.41, 0.66 and 1.03 s/cm2, respectively.
The measurements were carried out in ethanol.
b
(2) The addition of TBAPS to 1k and 1m causes a sharp increase
in the conductances, which is dependent on the applied
temperature.
THPM ring. In almost in all cases studied, total dehydrogenation
was observed.
(3) The conductances of the mixture of 1k or 1m with TBAPS are
more than the sum of the conductivities of the separate
compounds, and the differences increase by increasing the
temperature and the TBAPS/THPMs ratios. These results
clearly indicate that by mixing either 1k or 1m with
TBAPS as the oxidant, the nature of the medium is getting
more polar and the mixtures are more mobile than the indi-
vidual compounds [29]. All these facts indicate that the nat-
ure of the additional substituent on the phenyl ring
influences the electronic behavior of the 2-oxo-1,2,3,4-tetra-
hydropyrimidine ring towards electron donation to the
oxidant.
(4) By increasing the temperature, the cleavage of the O–O bond
in the TBAPS molecule is easier. Diffusion of the tetarbuty-
lammonium sulfate radicals (TBASR) from the solvent cage,
followed by the acceptance of an electron from the THPMs
initiate the dehydrogenation.
4. Experimental
4.1. Materials
THMPs and (TBAPS) were prepared according to the reported
procedure [26,30].
4.2. Equipment
The ultrasonic device used was a UP 400 S instrument from Dr.
Hielscher GmbH. A S3 immersion horn emitting 24 kHz ultrasound
at intensity levels tunable up to a maximum sonic power density of
460 W cmꢀ2 was used. Sonication was carried out at 100% (maxi-
mum amplitude 210 lm). A 3 mm long sonotrode (maximum im-
merse depth of 90 mm) was immersed directly into the reaction
mixture. Melting points were determined on a Stuart Scientific
SMP2 apparatus and are uncorrected. IR spectra were recorded
using KBr discs on a Shimadzu IR-435. 1H NMR spectra were ob-
tained with a Bruker 300 MHz instrument. They are reported as
follows: chemical shifts, [multiplicity, number of protons, assign-
ment and coupling constants J (Hz)]. 13C NMR spectra were re-
corded with a Bruker 75.48 MHz spectrometer. Mass spectra
were obtained on Platform II Mass Spectrometer from Micromass;
EI mode at 70 eV. UV spectra were taken in C2H5OH with Shimadzu
UV-160 spectrometer. The conductance measurements were car-
ried out with a JENWAY 4510 Conductivity Meter. A dip-type cell
with a cell constant of 0.997 cmꢀ1 for the platinum blank was used.
Stock solutions of the 1k and 1m and TBAPS were prepared in ace-
tonitrile. Varying concentrations of TBAPS were added to a fixed
concentration of the related 1k and 1m to prepare the desired
TBAPS to 1k and 1m mole ratios of 0.5:1, 1:1, 1.5:1, 1.75:1 and
2:1 for conductance measurements at 25 °C, 45 °C and 65 °C.
The last suggestion is supported by the results obtained by the
thermal dehydrogenation of 1g in ethanol and acetonitrile solu-
tions and by the comparison of the data obtained by conductomet-
ric measurements in acetonitrile and ethanol solutions. Whereas
the low yield of 2g (ꢁ5–10%) was obtained by dehydrogenation
of 1g in ethanol after 90 min, the reaction is completed after
5 min in dry acetonitrile. This explains that the effective solvation
of TBASR in ethanol compared with acetonitrile hinders the diffu-
sion of these radical species from the solvent cage. Consequently,
the extent of electron transfer from THPMs to TBASR is decreased,
which results in low conductances in ethanol, and therefore a low-
er rate of dehydrogenation should be expected in ethanol than in
acetonitrile. In contrast to ethanol as a polar and protic solvent,
the diffusion of TBASR is more possible by carrying out the reaction
in acetonitrile as a polar and aprotic solvent. Finally, the failure of
the reaction in THF and the low conversion in cyclohexane could be
possibly due to inefficient solubility of the reactants in THF and
cyclohexane.
4.3. General procedure for dehydrogenation of 2-oxo-1,2,3,4-
tetrahydropyrimidine-5-carboxamides
(i) Thermal: Tetrabutylammonium peroxydisulfate (0.51 mmol)
was added to a solution of 2-oxo-1,2,3,4-tetrahydropyrimidines
(0.3 mmol) in 10 ml dry acetonitrile. The reaction mixture was im-
mersed in at 85 °C preheated oil-bath for the times given in Table 5
until maximum progression of THPMs was observed (TLC). Solvent
was evaporated and the crude reaction mixture was extracted with
chloroform (3 ꢂ 15 ml) then with water to remove tetrabutylam-
monium hydrogen sulfate. The organic layer was evaporated and
the residue was isolated by flash column chromatography with
ethyl acetate as the eluent, or PLC for 2q with ethyl acetate as
the eluent.(ii) Sono-thermal: Tetrabutylammonium peroxydisulfate
3. Conclusions
We have described the dehydrogenation of some 2-oxo-1,2,3,4-
tetrahydropyrimidine-5-carboxamides with tetrabutylammonium
peroxydisulfate as an efficient oxidant under thermal and sono-
thermal conditions. By a combination of heat and ultrasound, the
THPM:TBAPS ratio was reduced from 1:1.7 for the thermal reaction
to 1:1.2 for the sono-thermal reaction. The rate of dehydrogenation
was affected by the nature of both C-4 and C-5 substituents on the

750
H.R. Memarian, M. Soleymani / Ultrasonics Sonochemistry 18 (2011) 745–752
(0.072 mmol) was added to a solution of dihydropyrimidinones
(0.06 mmol) in 2 ml dry acetonitrile. The reaction mixture was im-
mersed in at 74 °C in a preheated oil-bath by simultaneous ultra-
sound irradiation for the times given in Table 5 until maximum
progression of the reaction (TLC). The products were isolated as
indicated above.
(%) 339 (M+ 35Cl, 3), 213 (M+ –HNC6H4Cl, 8), 155 (OCNC6H437Cl+,
9), 129 (H2NC6H437Cl+, 10), 128 (HNC6H437Cl+, 10), 127
(H2NC6H435Cl+, 22), 126 (HNC6H435Cl+, 29), 113 (C6H437Cl+, 12),
111 (C6H435Cl+, 9), 103 (Ph-CN+, 6), 77 (Ph+, 55), 76 (C6H4+, 46).
UV (EtOH): kmax (log e): 318 nm (3.87), 254.5 (4.40), 206.0 4.45).
4.3.6. N-(4-Bromophenyl)-6-methyl-2-oxo-4-phenyl-1,2-
4.3.1. N,4-Diphenyl-6-methyl-2-oxo-1,2-dihydropyrimidine-5-
dihydropyrimidine-5-carboxamide (2f)
carboxamide (2a)
Pale yellow solid. Mp: 206–208 °C. IR:
m 3350, 3250 (N–H),
Yellow solid. Mp: 215–217 °C. IR:
m
3250 (N–H), 1680, 1640
1655, 1640 (CO), 1600 cmꢀ1 1H NMR (DMSO-d6): d (ppm) 2.34
.
(CO), 1595 cmꢀ1 1H NMR (DMSO-d6): d 2.35 (s, 3H, CH3), 7.02–
.
(s, 3H, CH3), 7.19–7.86 (several multiplets, 9H, aromatic H), 10.43
(s, 1H, HNAr), 12.27 ppm (br, 1H, 1-NH). 13C NMR (DMSO-d6): d
116.06, 121.81, 128.41, 128.68, 130.87, 132.03, 138.31,
164.80 ppm. MS (70 eV, EI): m/z (%) 385(M+ 81Br, 3), 81 (81Br+,
16), 79 (79Br+, 24), 77 (Ph+, 35), 76 (C6H4+, 7). UV (EtOH): kmax
7.67 (several multiplets, 10H, aromatic H), 10.31 (s, 1H, HNAr),
12.23 ppm (br, 1H, 1-NH). 13C NMR (DMSO-d6): d 115.06, 119.99,
124.40, 128.46, 128.66, 128.76, 129.18, 130.84, 138.95, 164.62
ppm. MS (70 eV, EI): m/z (%) 213 (M+ –HNPh, 7), 119 (PhNCO+,
3), 103 (Ph-CN+, 7), 93 (PhNH2+, 24), 92 (PhNH+, 30), 77 (Ph+, 42).
(log e): 317.0 nm (3.76), 257.5 (4.36), 205.5 (4.39).
UV (EtOH): kmax (log e): 320.0 nm (3.61), 251.0 (4.13), 205.0 (4.31).
4.3.7. N,4-Di(2-chlorophenyl)-6-methyl-2-oxo-1,2-
4.3.2. N-Benzyl-6-methyl-2-oxo-4-phenyl-1,2-dihydropyrimidine-5-
dihydropyrimidine-5-carboxamide (2g)
carboxamide (2b)
Pale yellow solid. Mp: 239–241 °C. IR:
m 3400, 3225 (N–H),
Pale green solid. Mp: 126–128 °C. IR:
m
3200, 3100 (N–H), 1670,
1680, 1650 (CO), 1590 cmꢀ1 1H NMR (DMSO-d6): d 2.45 (s, 3H,
.
1650 (CO), 1615 cmꢀ1. 1H NMR (DMSO-d6): d 2.27 (s, 3H, CH3), 4.23
(d, 2H, CH2, J = 5.8 Hz), 6.95–7.60 (several multiplets, 10H, aro-
matic H), 7.60 (s, 1H, 1-NH), 8.76 ppm (t, 1H, HNAr, J = 5.7 Hz).
13C NMR (DMSO-d6): d 43.03, 114.96, 127.26, 127.73, 127.80,
128.60, 128.67, 130.73, 138.88, 156.51, 165.95 ppm. MS (70 eV,
EI): m/z (%) 319 (M+, 4), 228 (M+ –CH2Ph, 2), 213 (M+ –NHCH2Ph,
CH3), 7.16–7.49 (several multiplets, 8H, aromatic H), 9.89 ppm (s,
1H, HNAr). 13C NMR (DMSO-d6): d 20.36, 115.99, 126.89, 127.09,
127.37, 127.80, 128.01, 129.68, 129.96, 130.44, 130.83, 131.42,
134.88, 136.77, 164.62 ppm. MS (70 eV, EI): m/z (%) 375 (M+
35Cl37Cl, 5), 247 (M+ –HNC6H4Cl, 7), 156 (CONHC6H437Cl+, 9), 155
(OCNC6H437Cl+, 9), 153 (OCNC6H435Cl+, 6), 137 (35ClC6H4CN+, 15),
129 (H2NC6H437Cl+, 4), 127 (H2NC6H435Cl+, 5), 126 (HNC6H435Cl+,
10), 212 (M+ –NH2CH2Ph, 3), 186 (M+ –OCNCH2Ph, 5), 185 (M+
–
CONHCH2Ph, 12), 107 (PhCH2NH2+, 11), 106 (PhCH2NH+, 50), 103
5), 111 (C6H435Cl+, 35), 76 (C6H4+, 27). UV (EtOH): kmax (log
e):
306.0 nm (4.05), 240.0 (4.41), 213.0 (4.62).
(Ph-CN+, 12), 91 (PhCH2+, 100), 77 (Ph+, 85). UV (EtOH): kmax (log
e): 319.0 nm (3.71), 205.5 (4.32).
4.3.8. N-(2-Chlorophenyl)-4-(30-chlorophenyl)-6-methyl-2-oxo-1,2-
4.3.3. N-(4-Flourophenyl)-6-methyl-2-oxo-4-phenyl-1,2-
dihydropyrimidine-5-carboxamide (2h)
dihydropyrimidine-5-carboxamide (2c)
Pale yellow solid. Mp: 260 °C (dec.). IR:
m 3250 (N–H), 1660
Yellow solid. Mp: 195–198 °C. IR:
m
3050 (N–H), 1740, 1680
(CO), 1595 cmꢀ1 1H NMR (DMSO-d6): d 2.42 (s, 3H, CH3), 7.22–
.
(CO), 1590 cmꢀ1 1H NMR (DMSO-d6): d 2.35 (s, 3H, CH3), 7.08–
.
7.68 (several multiplets, 8H, aromatic H), 10.10 (s, 1H, HNAr),
12.35 ppm (br, 1H, 1-NH). 13C NMR (DMSO-d6): d 127.09, 127.22,
127.74, 127.89, 128.02, 128.33, 130.08, 130.62, 130.72, 133.40,
134.44, 164.91 ppm. MS (70 eV, EI): m/z (%) 373 (M+ 35Cl35Cl, 3),
8.19 (several multiplets, 9H, aromatic H), 10.32 (s, 1H, NHAr),
12.17 ppm (br, 1H, 1-NH). 13C NMR (DMSO-d6): d 18.81, 114.79,
121.48, 127.99, 128.02, 128.43, 128.66, 129.11, 129.39, 130.85,
137.90, 137.94, 156.74, 164.83 ppm. MS (70 eV, EI): m/z (%) 323
(M+, 2), 260 (2), 213 (M+ –HNC6H4F, 5), 186 (M+ –OCNC6H4F, 17),
185 (M+ –OCNHC6H4F, 14), 111 (H2NC6H4F+, 11), 110 (HNC6H4F+,
7), 95 (C6H4F+, 26), 77 (Ph+, 35), 76 (C6H4+, 19). UV (EtOH): kmax
247 (M+ 35ClC6H4NH, 4), 139 (37ClC6H4CN+, 5), 137 (35ClC6H4CN+,
–
5), 129 (H2NC6H437Cl+, 5), 128 (HNC6H437Cl+, 30), 127
(H2NC6H435Cl+, 15), 126 (HNC6H435Cl+, 9), 113 (C6H437Cl+, 5), 111
(C6H435Cl+, 25), 76 (C6H4+, 25). UV (EtOH): kmax (log
e): 317.0 nm
(log
e
): 320 nm (3.87), 250 (4.35), 205.5 4.41).
(3.52), 244.0 (4.02), 206.5 (4.31).
4.3.4. N-(2-Chlorophenyl)-6-methyl-2-oxo-4-phenyl-1,2-
4.3.9. N-(2-Chlorophenyl)-4-(40-chlorophenyl)-6-methyl-2-oxo-1,2-
dihydropyrimidine-5-carboxamide (2d)
dihydropyrimidine-5-carboxamide (2i)
Pale yellow solid. Mp: 195–197 °C. IR:
m
3250 (N–H), 1660 (CO),
Pale yellow solid. Mp: 290 °C (dec.). IR:
m 3400, 3250 (N–H),
1600 cmꢀ1. 1H NMR (DMSO-d6): d 2.41 (s, 3H, CH3), 7.18–7.69 (sev-
eral multiplets, 9H, aromatic H), 10.06 (s, 1H, HNAr), 11.74 ppm
(br, 1H, 1-NH). 13C NMR (DMSO-d6): d 18.92, 114.68, 127.07,
127.60, 127.85, 127.94, 128.61, 128.69, 130.02, 130.88, 134.55,
156.67, 165.20 ppm. MS (70 eV, EI): m/z (%) 339 (M+ 35Cl, 3), 213
(M+ –HNC6H4Cl, 13), 129 (H2NC6H437Cl+, 5), 128 (HNC6H437Cl+, 4),
127 (H2NC6H435Cl+, 4), 126 (HNC6H435Cl+, 22), 113 (C6H437Cl+, 4),
111 (C6H435Cl+, 8), 103 (Ph-CN+, 4), 77 (Ph+, 42), 76 (C6H4+, 22).
1650 (CO), 1595 cmꢀ1 1H NMR (DMSO-d6): d 2.41 (s, 3H, CH3),
.
7.19–7.70 (several multiplets, 8H, aromatic H), 10.09 (s, 1H, NHAr),
11.73 ppm (br, 1H, 1-NH). 13C NMR (DMSO-d6): d 127.16, 127.65,
127.83, 127.92, 128.86, 130.05, 130.48, 134.44, 135.76, 156.60,
165.06 ppm. MS (70 eV, EI): m/z (%) 374 (5), 139 (37ClC6H4CN+,
5), 129 (H2NC6H437Cl+, 5), 128 (HNC6H437Cl+, 5), 127
(H2NC6H435Cl+, 12), 126 (HNC6H435Cl+, 8), 113 (C6H437Cl+, 6), 111
(C6H435Cl+, 11), 76 (C6H4+, 28). UV (EtOH): kmax (log
e): 318.0 nm
UV (EtOH): kmax (log
e
): 319.0 nm (4.05), 245.0 (4.48), 210.5 (4.59).
(3.37), 248.5 (3.84), 205.5 (4.09).
4.3.5. N-(4-Chlorophenyl)-6-methyl-2-oxo-4-phenyl-1,2-
4.3.10. N-(2-Chlorophenyl)-4-(20-bromophenyl)-6-methyl-2-oxo-1,2-
dihydropyrimidine-5-carboxamide (2e)
dihydropyrimidine-5-carboxamide (2j)
Yellow solid. Mp: 200–202 °C. IR:
m
3450, 3350 (N–H), 1665
Yellow solid. Mp: 170–172 °C. IR: m 3200 (N–H), 1650 (CO),
(CO), 1600 cmꢀ1 1H NMR (DMSO-d6): d 2.34 (s, 3H, CH3), 7.31–
.
1590 cmꢀ1. 1H NMR (DMSO-d6): d 2.45 (s, 3H, CH3), 7.17–7.45 (sev-
eral multiplets, 8H, aromatic H), 7.66 (s, 1H, 1-NH), 9.95 ppm (brd
s, 1H, HNAr). 13C NMR (DMSO-d6): d 126.94, 127.55, 127.64,
127.85, 128.04, 130.01, 130.18, 131.23, 132.88, 134.65,
163.72 ppm. MS (70 eV, EI): m/z (%) 420 (38), 418 (3), 390 (2),
7.65 (several multiplets, 9H, aromatic H), 10.46 (s, 1H, NHAr),
12.25 ppm (br, 1H, 1-NH). 13C NMR (DMSO-d6): d 18.78, 114.81,
121.46, 127.99, 128.44, 128.66, 128.88, 129.11, 129.39, 130.82,
130.96, 137.22, 137.94, 156.84, 164.87 ppm. MS (70 eV, EI): m/z

H.R. Memarian, M. Soleymani / Ultrasonics Sonochemistry 18 (2011) 745–752
751
389 (M+ –CO, 2), 290 (M+ –ClC6H4NH2, 3), 128 (HNC6H437Cl+, 14),
3), 107 (C6H4OMe+, 3), 76 (C6H4+, 20). UV (EtOH): kmax (log
e):
319.8 nm (4.13), 264.8 (4.10), 212.4 (4.16).
127 (H2NC6H435Cl+, 21), 126 (HNC6H435Cl+, 69), 111 (C6H435Cl+,
15), 81 (81Br+, 7), 76 (C6H4+, 31). UV (EtOH): kmax (log
e):
304.0 nm (3.67), 246.0 (4.01), 207.5 (4.37).
4.3.16. N-(2-Chlorophenyl)-6-methyl-4-(40-methylphenyl)-2-oxo-1,2-
dihydropyrimidine-5-carboxamide (2p)
4.3.11. N-(2-Chlorophenyl)-4-(40-bromophenyl)-6-methyl-2-oxo-1,2-
dihydropyrimidine-5-carboxamide (2k)
Yellow solid. Mp: 205–207 °C. IR:
m 3400, 3300 (N–H), 1660
(CO), 1590 cmꢀ1 1H NMR (DMSO-d6): d 2.34 (s, 3H, 4-CH3), 2.40
.
Pale yellow solid. Mp: 230–232 °C. IR: m 3450, 3240 (N–H), 1655
(s, 3H, pyrimidin-C6-CH3), 7.18–7.88 (several multiplets, 8H, aro-
matic H), 10.09 (s, 1H, HNAr), 12.12 ppm (br, 1H, 1-NH). 13C
NMR (DMSO-d6): d 21.39, 61.22, 127.13, 127.56, 127.87, 127.93,
128.66, 129.24, 130.04, 134.63, 140.79, 165.38 ppm. MS (70 eV,
EI): m/z (%) 353 (M+ 35Cl, 2), 128 (HNC6H437Cl+, 7), 126
(CO), 1615 cmꢀ1. 1H NMR (DMSO-d6): d 2.41 (s, 3H, CH3), 7.19–7.70
(several multiplets, 8H, aromatic H), 10.08 (s, 1H, HNAr),
11.92 ppm (br, 1H, 1-NH). 13C NMR (DMSO-d6): d 18.66, 114.55,
127.15, 127.66, 127.84, 127.91, 128.82, 129.01, 130.05, 130.47,
130.58, 134.43, 135.77, 156.58, 165.04 ppm. MS (70 eV, EI): m/z
(%) 293 (M+ –NHC6H4Cl, 9), 291 (M+ –NHC6H4Cl, 9), 183
(HNC6H435Cl+, 8), 91 (C6H4CH3+, 17). UV (EtOH): kmax (log
e):
306.0 nm (3.90), 248.0 (4.23), 207.5 (4.48).
(
81BrC6H4CN+, 3), 157 (C6H481Br+, 5), 156 (CONHC6H437Cl+, 2), 155
(C6H479Br+, 8), 129 (H2NC6H437Cl+, 28), 128 (HNC6H437Cl+, 19),
127 (H2NC6H435Cl+, 79), 126 (HNC6H435Cl+, 26), 113 (C6H437Cl+,
6), 111 (C6H435Cl+, 9), 81 (81Br+, 6), 79 (79Br+, 5), 76 (C6H4+, 24).
4.3.17. N-(2-Chlorophenyl)-6-methyl-2-oxo-4-(1-phenylethyl)-1,2-
dihydropyrimidine-5-carboxamide (2q)
White solid. Mp: 210–212 °C. IR:
m 3400, 3300 (N–H), 1660
UV (EtOH): kmax (log e): 316.0 nm (4.06), 248.0 (4.51), 211.0 (4.61).
(CO), 1615 cmꢀ1 1H NMR (DMSO-d6): d 1.53 (d, 3H, CH3CHPh,
.
J = 5.55 Hz), 2.32 (s, 3H, pyrimidin-C6-CH3), 4.39 (q, 1H, CHMePh,
J = 6.78 Hz), 7.19–7.61 (several multiplets, 9H, aromatic H), 10.19
(s, 1H, HNAr), 12.01 ppm (s, 1H, 1-NH). 13C NMR (DMSO-d6): d
18.04, 20.70, 43.79, 114.86, 114.92, 127.04, 127.74, 127.85,
128.01, 128.35, 128.43, 128.69, 130.16, 134.64, 142.95, 143.03,
4.3.12. N-(2-Chlorophenyl)-6-methyl-4-(30-nitrophenyl)-2-oxo-1,2-
dihydropyrimidine-5-carboxamide (2l)
Pale yellow solid. Mp: 288–290 °C. IR:
m 3400 (N–H), 1670, 1650
(CO), 1610 cmꢀ1 1H NMR (DMSO-d6): d (ppm) 2.45 (s, 3H, CH3),
.
7.19–8.47 (several multiplets, 8H, aromatic H), 10.13 (s, 1H, HNAr),
12.43 ppm (br, 1H, 1-NH). MS (70 eV, EI): m/z (%) 384 (M+ 35Cl, 7),
193 (35ClC6H4NHCOCCMe+, 3), 156 (CONHC6H437Cl+, 6), 128 (HNC6-
H437Cl+, 9), 127 (H2NC6H435Cl+, 4), 126 (HNC6H435Cl+, 41), 113
(C6H437Cl+, 11), 111 (C6H435Cl+, 37), 76 (C6H4+, 17). UV (EtOH): kmax
156.76, 164.93 ppm. MS (70 eV, EI): m/z (%) 367 (M+ 35Cl, 14),
+
169 (16), 150 (6), 119(16), 114 (3), 100 (12), 97 (4), 77 (C6H5
,
8). UV (EtOH): kmax (log e): 302.0 nm (3.50), 242.0 (3.91), 206.5
(4.26).
(log e): 318.0 nm (3.68), 232.5 (4.34), 208.5 (4.42).
Acknowledgment
4.3.13. N-(2-Chlorophenyl)-4-(40-nitrophenyl)-6-methyl-2-oxo-1,2-
dihydropyrimidine-5-carboxamide (2m)
We are thankful to the Center of Excellence (Chemistry), Re-
search Council and Office of Graduate Studies of the University of
Isfahan for their financial support. We would like to thank also
Dr. A. Kiani for helpful discussion by the conductometric studies.
Yellow solid. Mp: 220–222 °C. IR:
m 3400, 3230 (N–H), 1680,
1655 (CO), 1585 cmꢀ1 1H NMR (DMSO-d6): d 2.36 (s, 3H, CH3),
.
7.18–8.34 (several multiplets, 8H, aromatic H), 10.12 ppm (br,
2H, 1-NH, HNAr). 13C NMR (MHz, DMSO-d6): d 123.91, 127.27,
127.71, 127.82, 127.95, 130.03, 130.15, 134.32, 148.85,
164.65 ppm. MS (70 eV, EI): m/z (%) 385 (2), 153 (OCNC6H435Cl+,
9), 128 (NHC6H437Cl+, 5), 126 (NHC6H435Cl+, 31), 76 (C6H4+, 6).
References
[1] G.C. Rovnyak, S.D. Kimball, B. Beyer, G. Cucinotta, J.D. Dimarco, J. Gougoutas, A.
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blockers and activators: conformational and structural determinants of
dihydropyrimidine calcium channel modulators, J. Med. Chem. 38 (1995)
119–129.
UV (EtOH): kmax (log e): 336.0 nm (3.88), 259.5 (4.32), 209.0 (4.51).
4.3.14. N-(2-Chlorophenyl)-4-(30-methoxyphenyl)-6-methyl-2-oxo-
[2] J.J. Vanden Eynde, N. Audiart, V. Canonne, S. Michel, Y. Van Haverbeke, C.O.
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1967–1978.
1,2-dihydropyrimidine-5-carboxamide (2n)
Pale yellow solid. Mp: 192–194 °C. IR:
m 3200 (N–H), 1650, 1640
(CO), 1600 cmꢀ1 1H NMR (DMSO-d6): d 2.40 (s, 3H, CH3), 3.74 (s,
.
[3] H.R. Memarian, M.M. Sadeghi, A.R. Momeni, Aromatization of Hantzsch 1,4-
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2244.
3H, OCH3), 7.05–7.47 (several multiplets, 8H, aromatic H), 10.03
(s, 1H, HNAr), 12.22 ppm (br, 1H, 1-NH). 13C NMR (DMSO-d6): d
55.64, 55.75, 114.04, 116.55, 120.83, 126.91, 127.57, 127.85,
129.86, 130.05, 134.59, 159.40, 167.17 ppm. MS (70 eV, EI): m/z
(%) 369 (M+ 35Cl, 4), 176 (M+ –ClC6H4NHCOCCMe, 2), 155
(OCNC6H437Cl+, 2), 153 (OCNC6H435Cl+, 2), 128 (HNC6H437Cl+, 10),
126 (HNC6H435Cl+, 4), 111 (C6H435Cl+, 7), 107 (C6H4OMe+, 10). UV
[4] H.R. Memarian, M. Abdoli-Senejani, Ultrasound-assisted photochemical
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dihydropyrimidin-2(1H)-ones mediated by ceric ammonium nitrate,
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[8] H.R. Memarian, A. Farhadi, Potassium peroxydisulfate as an efficient oxidizing
agent for conversion of ethyl 3,4-dihydropyrimidin-2(1H)-one-5-carboxylates
to their corresponding ethyl pyrimidin-2(1H)-one-5-carboxylates, J. Iran.
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[9] H.R. Memarian, H. Sabzyan, A. Farhadi, Microwave-assisted oxidation of 3,4-
dihydropyrimidin-2(1H)-ones, Z. Naturforsch. 64b (2009) 532–540.
[10] H.R. Memarian, A. Farhadi, Light-induced dehydrogenation of 3,4-dihydro-
pyrimidin-2(1H)-ones, Monatsh. Chem. 140 (2009) 1217–1220.
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209 (2010) 95–103.
(EtOH): kmax (log e): 316.0 nm (3.43), 254.0 (3.78), 204.0 (4.08).
4.3.15. N-(2-Chlorophenyl)-4-(40-methoxyphenyl)-6-methyl-2-oxo-
1,2-dihydropyrimidine-5-carboxamide (2o)
Yellow solid. Mp: 278–280 °C. IR:
m 3370, 3300 (N–H), 1670,
1660 (CO), 1580 cmꢀ1 1H NMR (DMSO-d6): d 2.39 (s, 3H, CH3),
.
3.79 (s, 3H, OCH3), 7.00–7.71 (several multiplets, 8H, aromatic
H), 10.08 (s, 1H, HNAr), 12.13 ppm (br, 1H, 1-NH). 13C NMR
(DMSO-d6):
d 55.81, 114.15, 114.27, 127.15, 127.56, 127.89,
130.04, 130.51, 134.62, 156.61, 161.69, 165.55 ppm. MS (70 eV,
EI): m/z (%) 370 (3), 155 (OCNC6H437Cl+, 12), 154 (CONHC6H435Cl+,
10), 153 (OCNC6H435Cl+, 7), 126 (HNC6H435Cl+, 6), 113 (C6H437Cl+,

752
H.R. Memarian, M. Soleymani / Ultrasonics Sonochemistry 18 (2011) 745–752
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