Ultrasound-assisted dehydrogenation of 5-acetyl-3,4-dihydropyrimidin-2(1H)-ones

Article abstract of DOI:10.1016/j.ultsonch.2009.11.014

In this study, various 5-acetyl-3,4-dihydropyrimidin-2(1H)-ones were synthesized and the dehydrogenation of these compounds by potassium peroxydisulfate in aqueous acetonitrile under thermal and sono-thermal conditions were investigated. Whereas the effec

Full text of DOI:10.1016/j.ultsonch.2009.11.014

Ultrasonics Sonochemistry 17 (2010) 579–586
Contents lists available at ScienceDirect
Ultrasonics Sonochemistry
journal homepage: www.elsevier.com/locate/ultsonch
Ultrasound-assisted dehydrogenation of 5-acetyl-3,4-dihydropyrimidin-2(1H)-ones
*
Hamid Reza Memarian , Asadollah Farhadi, Hassan Sabzyan
University of Isfahan, Faculty of Science, Department of Chemistry, Isfahan 81746-73441, Islamic Republic of Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 11 May 2009
Received in revised form 18 November 2009
Accepted 20 November 2009
Available online 26 November 2009
In this study, various 5-acetyl-3,4-dihydropyrimidin-2(1H)-ones were synthesized and the dehydrogena-
tion of these compounds by potassium peroxydisulfate in aqueous acetonitrile under thermal and sono-
thermal conditions were investigated. Whereas the effect of the nature of 4-substituent influences the
rate of reaction, the application of sonic waves decreases drastically the time of thermal reaction.
Ó 2009 Elsevier B.V. All rights reserved.
Keywords:
3,4-Dihydropyrimidin-2(1H)-ones
Dehydrogenation
Pyrimidin-2(1H)-ones
Potassium peroxydisulfate
Ultrasound
1. Introduction
increasing the yields of reactions and in some cases the ratio of
formed products. The mostly important effect of ultrasound by
Azaheterocyclic systems such as six-membered nitrogen-con-
taining compounds, 3,4-dihydropyrimidin-2(1H)-ones are very
interesting in medicinal chemistry because of their application as
antihypertensive agents [1], anti-cancer [2], calcium channel mod-
ulators [3], and also as anti-staphylococcal antibiotics [4]. In partic-
ular, batzelladine alkaloids as pyrimidine derivatives have been
found to be potent HIV gp-120 CD4 inhibitors [5] and MKC-442
is also one of the most important classes of drugs to inhibit the
HIV virus [6].
The dehydrogenation of Hantzsch-type 1,4-dihydropyridines
(DHPs) and 3,4-dihydropyrimidin-2(1H)-ones (DHPMs) have at-
tracted interest in organic chemistry [7–11], but in contrast to
DHPs, where aromatization of them to their corresponding pyri-
dines is typically facile, the oxidation of DHPMs is known to be
nontrivial [12]. However, many oxidizing agents were used for
the oxidation of DHPMs, but the application of these reagents suf-
fer from some disadvantages such as the use of hazardous or
expensive, less easily available oxidants, vigorous reaction condi-
tions, prolonged reaction times, especially low yields and forma-
tion of side products [12–20].
passing its waves through a liquid medium is the generation of
many cavities. This leads to development of high temperatures
and high pressures within the cavities during their collapse. Re-
cently we have reported on the effect of the combination of ultra-
sound and UV-light in the ring opening reaction of
a-epoxyketones
[26] and in the oxidation reaction of 1,4-dihydropyridines [27], the
combination of ultrasound and heat in the oxidation of some ethyl
3,4-dihydropyrimidin-2(1H)-one-5-carboxylates [28] and also the
effect of sonic waves on thiocyanation of aromatic and heteroaro-
matic compounds [29]. In all of these reactions, it was found that
ultrasound accelerates the reactions by comparison the time of
reactions without applying the sonic waves.
Peroxydisulfate ion is known as one of the strongest oxidizing
agents with E0(S2O2ꢀ=SO24ꢀ) = ꢀ2.01 V [30,31] for oxidation of alkyl
8
aryl sulfides to their corresponding sulfoxides [32], oxidation of
1,4-dihydropyridines to the pyridine derivatives [9], free radical
degradation of chitosan [33] and for the preparation of polymer/
silicate nanocomposites [34]. In our recent studies, we have used
potassium peroxydisulfate (PPS) as an efficient oxidant for the
dehydrogenation of various ethyl 3,4-dihydropyrimidin-2(1H)-
one-5-carboxylates under thermal [35] and sono-thermal condi-
tions [28]. The aim of the work was to elucidate the effect of the
nature and the steric hindrance of the substituent on position 4
of the dihydropyrimidinone ring on the rate of reaction. Our
computational studies concerning the optimized structures of var-
ious 5-acetyl and 5-carboethoxy substituted 4-aryl-3,4-dihydro-
pyrimidinones revealed that the polar effects and the steric
hindrances of the substituents located at 4- and 5-positions of
the dihydropyrimidinone ring influence the dihedral angles of both
The effect of ultrasound on different reactions is widely studied
during the last two decades both in cavitation and pre-cavitation
regime [21–25]. The success and advantages of ultrasound-assisted
chemical reactions include shorter reaction times, higher yields
and milder reaction conditions when compared with classical
methods. The effect of ultrasound has mostly been shown by
* 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 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ultsonch.2009.11.014

580
H.R. Memarian et al. / Ultrasonics Sonochemistry 17 (2010) 579–586
Table 1
CO moieties in carboethoxy and the acetyl groups at 5-position and
the dihedral angle of the aromatic rings with respect to dihydro-
pyrimidinone ring [36]. All these points, especially the presence
of the acetyl group instead of the carboethoxy group in position
5 affect the amount of the electron density on the atoms involved
in the oxidation process of these compounds. These observations
prompted us to synthesis various 5-acetyl-4-aryl-3,4-dihydropyr-
imidin-2(1H)-ones and investigated their oxidation by PPS under
thermal and sono-thermal conditions to investigate the following
points on the rate of reaction:
Oxidation of 5-acetyl-6-methyl-4-phenyl-3,4-dihydropyrimidin-2(1H)-one (1a) to 5-
acetyl-6-methyl-4-phenylpyrimidin-2(1H)-one (2a) by K2S2O8 under reflux condition
in various mixture of solvents.
K2S2O8/1a
Solvent
Time (min)a
(2a) Yield (%)
0.5:1
1:1
2:1
1:1
1:1
1:1
1:1
CH3CN/H2O (10:2)
CH3CN/H2O (10:1)
CH3CN/H2O (10:1)
CH3CN/H2O (10:2)
Dry acetonitrile
180
190
180
180
180
180
180d
ꢁ60b
100
100
95c
No reaction
No reaction
ꢁ5b
Absolute ethanol
CH3CN/H2O (10:2)
a
b
c
II The effect of the acetyl group instead of the carboethoxy
group in position 5.
III The effect of the nature of the additional substituent and its
location on the phenyl ring located on C-4.
The times are given after maximum progression of reaction.
Estimated according to TLC observation.
Isolated yield.
d
The reaction is carried out at room temperature.
IIII The effect of ultrasound irradiation on the rate of reaction
and comparison of the obtained results with those obtained
under thermal conditions.
O
R
O
R
H
2. Results and discussion
H
O
K2S2O , CH3CN / H2O
N
H3C
N
H3C
Δ
or
Δ
,
)))
H3C
H3C
N
H
O
N
H
2.1. Solvent effect and optimization of the reactants
2a-l
1a-l
Since the nature of solvent has a great effect on the solubility of
the oxidant which influences the rate of reaction, we first studied
the oxidation of 4-phenyl derivative 1a by PPS in different solvents
such as absolute ethanol, dry acetonitrile, aqueous ethanol or
aqueous acetonitrile (different ratios) under reflux condition
(Scheme 1).
R = a: C6H5, b: 4-CH3C6H4, c: 4-CH3OC6H4, d: 3-CH3OC6H4, e: 2-CH3OC6H4 f: 4-ClC6H4
g: 3-ClC6H4 , h: 2-ClC6H4, i: 4-BrC6H4, j: 2-BrC6H4, k: 4-NO2C6H4, l: 3-NO2C6H4
,
Scheme 2.
According to the data presented in Table 1, a mixture of CH3CN/
H2O (10:2) has been chosen as the best solvent mixture for this
purpose. According to the data presented in Table 1 we found
out that:
Table 2
Oxidation of 1a–l by PPS in aqueous acetonitrile under reflux condition and
simultaneous sonication and heating by stirring the reaction mixture.
Compound
R
Thermal
Sono-thermal
1. Owing to better solubility of the oxidant, the presence of H2O is
necessary for the reaction, since the reaction does not occur in
dry acetonitrile.
Time
Yield
(%)b
Time
Yield
(min)a
(min)a
(%)b
2. The optimized mole ratio of PPS/DHPM (1:1) indicates that the
removal of two hydrogens from 1a depends on the presence of
the equimolar amounts of the oxidant, since the reaction is not
completed by the 0.5:1 ratio of oxidant/DHPM.
1a
1b
1c
1d
1e
1f
1g
1h
1i
C6H5–
180
110
75
110
60
105
120
90
160
85
95
95
90
95
90
90
90
85
90
90
90
90
17
12
12
14
10
14
16
12
15
12
27
40
97
90
90
95
90
95
90
85
90
93
90
90
4-CH3C6H4–
4-CH3OC6H4–
3-CH3OC6H4–
2-CH3OC6H4–
4-ClC6H4–
3-ClC6H4–
2-ClC6H4–
4-BrC6H4–
2-BrC6H4–
4-NO2C6H4–
3-NO2C6H4–
In an optimized reaction conditions various 5-acetyl-3,4-dihy-
dropyrimidin-2(1H)-ones (1a–l) (0.23 mmol) were subjected to
the oxidation reaction in the presence of PPS (0.23 mmol) in
12 ml acetonitrile and water (10:2) under reflux condition and un-
der ultrasound irradiation with simultaneous heating the reaction
mixture at 70 °C (sono-thermal) and stirring the reaction mixture
(Scheme 2). The reaction was followed by TLC until total disap-
pearance of DHPMs. These results are summarized in Table 2.
A comparison of the results presented in Table 2 indicates that:
1j
1k
1l
360
420
a
The times are given after total disappearance of DHPMs (100% conversion by
TLC monitoring).
b
Isolated yields.
1. The combination of ultrasound and heat (sono-thermal)
decreases drastically the time of reaction compared with the
reaction under thermal condition, but the same products were
obtained under both reaction conditions. It should be noted that
stirring the reaction mixture by simultaneous sonication and
heat affects also the shortening the reaction time.
Ph
O
Ph
O
H
2. The performance of heating is necessary for the reaction either
under ultrasound irradiation or under thermal reaction, since
H
H3C
N
K2S2O8 , solvent
H3C
N
the cleavage of O–O bond in the S2O2ꢀ has relatively high acti-
8
Δ
H3C
H3C
vation energy of around 130 kJ/mol [37,38].
O
N
O
N
H
H
Density functional theory (DFT) B3LYP with 6-31++G (d,p) basis
set, as implemented in the G98W software, is used to obtain the
optimized structures of compounds 1a and 2a, including position
of the acetyl group conformation with respect to the C@C bond
2a
1a
Scheme 1.

H.R. Memarian et al. / Ultrasonics Sonochemistry 17 (2010) 579–586
581
pared with 1N–H (1.0091 Å), and the shorter bond-length C2–C3
(1.3567 Å) compared with 1N–C2 (1.4045) indicate that 3N nitro-
gen lone pair is conjugated with 2-CO more strongly than the 1N
nitrogen lone pair. These observations support the assignment of
the chemical shifts for 1-NH and 3-NH in the 1H NMR spectra.
According to the results summarized in Tables 1 and 2, espe-
cially the failure of the reaction by carrying out at room tempera-
ture, we will confirm the proposed mechanism for the
dehydrogenation of 5-carboethoxy-3,4-dihydropyrimidinones by
potassium peroxydisulfate [35] in the present study (Scheme 3).
Thermal decomposition of the weakest O–O bond in potassium
peroxydisulfate yields the sulfate radical anions (path 1), which
should preferably abstract a hydrogen atom from the present
water to give hydroxyl radicals (path 2). The oxidation of DHPMs
is presumed to be initiated by a hydrogen abstraction from 4-posi-
tion by hydroxyl radical to produce hydropyrimidinoyl radical
intermediate and water (path 3). This step is followed by the loss
of another hydrogen atom to generate pyrimidinone product (path
4).
Fig. 1. The B3LYP/6-31++G** optimized structures of 1a (a) and 2a (b).
of the heterocyclic ring. Fig. 1a and b shows the optimized struc-
tures of 1a and 2a, respectively. Interesting results is the shift of
6-CH3 resonances in 2a–l to higher field in the 1H NMR spectra.
This can be explained as follows: a comparison of the dihedral an-
gles of C@C–C@O moiety in 1a (175.0°) and in 2a (122.9°) indicate
that: (i) the electron-withdrawing character of oxygen in 2a is
more efficient than in 1a, therefore the 6-C in 2a is more positive
than in 1a (+0.291 vs. +0.259, as found from NBO charge analysis),
(ii) the anisotropy effect of carbonyl group on the 6-CH3 in 2a due
to smaller dihedral angle. The 1-NH and 3-NH resonances in 1a–l
appear between 7 and 8 and around 9 ppm, respectively, which
indicate that 3-NH is more acidic than 1-NH. This can be supported
by the observation of acylation of 3-N in the presence of n-BuLi as
the base [39] or preparation of N3-acetoxymethyl-3,4-dihydropyri-
midinones [40] and also by our computational studies. As we
showed in Fig. 1a, the greater bond-length 3N–H (1.0099 Å) com-
Following points will support our argument that path 3 is the
rate determining step either in the case of carboethoxy or acetyl
derivatives and the hydroxyl radical is involved as active species
in this step:
A. Due to insolubility of PPS in dry acetonitrile even under
reflux condition, the presence of enough water is necessary
for the reaction, since the reaction did not work in dry
acetonitrile.
B. Although the oxidant is not completely soluble in C2H5OH/
H2O (10:2) under reflux condition in comparison to
CH3CN/H2O (10:2), but there are enough hydrogen sources
(C2H5OH and H2O) for donation hydrogen to sulfate radical
O
S
O
O
S
.
+ -O
+ -
-
+
K
2
S
K
O
O
O
K
O
O
(step1)
(step 2)
O
O
O
O
O
S
.
+ -
.
+ -
S
H2O
K
O
+
O
+
K
O H
O
OH
O
O
O
R
R
O
H
H
H
.
N
H3C
N
H3C
.
(step 3)
+
H2O
+
OH
H3C
N
H
O
H3C
N
H
O
O
R
R
O
H
.
.
N
-
H3C
SO
+
4
H3C
N
-
HSO4
+
(step 4)
H3C
N
H
O
H3C
N
H
O
Scheme 3.

582
H.R. Memarian et al. / Ultrasonics Sonochemistry 17 (2010) 579–586
anion and formation of hydroxyl and ethoxy radicals. The
reason of inefficient reaction in C2H5OH/H2O (10:2) should
be either the competition between hydroxyl radical with
ethoxy radical for removal of 4-H or the solvation of sulfate
radical anion by the polar protic solvent such as ethanol. It
seems that solvation of the sulfate radical anion prevents
the formation of hydroxyl radical, as a more reactive hydro-
gen abstracting species.
C. The observed substituent effect in 4-position on the rate of
reaction indicates that the removal of a hydrogen atom from
the more covalent C–H bond compared with the less cova-
lent N–H bond is more possible; therefore, path 3 is the rate
determining step.
D. The stability of hydropyrimidinoyl radical intermediate
formed in the rate determining step which is simultaneously
a benzylic radical (stabilized by interaction with the aro-
matic ring) or allylic radical (by conjugation with C5@C6
bond) should lower the activation energy of its formation.
This influences the rate of path 3, as the rate determining
step. The presence of the 4-methyl (1b) or 4-methoxy (1c)
substituents as electron-donating species on the phenyl
group attached to dihydropyrimidinone ring should stabilize
the formation of the benzylic radical intermediate rather
than the 4-nitro substituent (1k) as electron-withdrawing
species. These data show also that the electron-donating
substituents such as methyl 1b or methoxy substituents
1c, 1d and 1e decreases the time of oxidation. It is interest-
ing to compare the time of reactions of 1c, 1d and 1e, which
is dependent on the balance of the inductive and the reso-
nance effects of the methoxy group located on 4-, 3- and
2-positions, respectively.
Fig. 2. The optimized structures of 1e and corresponding ester derivative obtained
at the B3LYP/6-31++G (d,p) level of theory.
X
X
.
δ
OH
O
H
H
O
H
H
R
N
.
δ
N
.
R
+
OH
-H2O
N
H
O
H3C
N
H
O
H3C
X
O
E. A comparison of the results obtained in this study (Table 1)
with those obtained by oxidation of 5-carboethoxy deriva-
tives either under thermal [35] or sono-thermal conditions
[28] indicates that the reaction is slower in the case of 5-
acetyl derivatives under both reaction conditions and the
same products were also obtained.
.
H
R
H3C
N
N
O
H
Scheme 4.
The results obtained from ab initio calculation at the B3LYP/6-
31++G** level of theory for the optimized structures of both classes
of compounds can partially explain the observed comparative
behavior of the acetyl-DHPMs vs. the DHPM-esters based on the
following arguments:
All experimental facts obtained by thermal and sono-thermal
reactions of both classes of compounds support our argument that
removal of 4-H by a hydroxyl radical is occurred in the rate deter-
mining step. As is shown in Scheme 4, the interaction of a hydroxyl
radical with 4-H in the transition state leading to a hydropyrimid-
inoyl radical intermediate. In this case, when the aromatic ring is
1. Due to the presence of formal three sp3-centers in these mole-
cules (N1, N3 and C4), the dihydropyrimidinone ring adopts a
boat conformation, flatted at N1 toward an envelope conforma-
tion, with a pseudoaxial orientation of the C4-substituent. The
extent of deviation of C4 atom from planarity depends on the
orientation of the aryl group attached to this atom, especially
on the position of an additional substituent at the phenyl ring
and also on the nature and the size of this substituent.
2. The dihedral angle of the carbonyl function in the ester and the
acetyl groups with respect to the C5–C6 double bond depends
on the type of the substituent on the C4 atom and the extent
of conjugation with C5@C6 bond.
perpendicular to the radical center formed on C-4 (the ring p-orbi-
tal are parallel to the radical p-orbital), the stabilization of the rad-
ical center through conjugation with the aromatic ring is more
possible and simultaneously the steric hindrance for the linear ap-
proach of the hydroxyl radical to 4-H is diminished. This leads to
an increase of the rate of reaction. In this case and as a comparative
example, accomplished oxidations of 1e and the corresponding es-
ter derivative are observed after 60 and 25 min under thermal and
10 and 6 min under sono-thermal conditions, respectively. As a re-
sult, the balances of steric and electronic effects of the additional
substituent on the phenyl ring located on C-4 and also those of
the acetyl and the carboethoxy groups influence the rate of
oxidation.
3. The dihedral angle formed by the C20–C10–C4–N3 bonds
depends on the stereoelectronic effect of the carboethoxy or
acetyl groups located on C5 and also on the location of the
additional substituent on the phenyl ring located on C4. Fig. 2
shows the optimized structures of 1e and the corresponding
ester derivative obtained at the B3LYP/6-31++G (d,p) level of
theory. This figure shows clearly that the orientation of the 2-
methoxy group with respect to dihydropyrimidinone ring is
dependent on the substituent on C5; acetyl or carboethoxy
groups.
2.2. Effect of intensity of sonication and stirring
The important result in the present study was the acceleration
of thermal reaction by applying the sonic waves (sono-thermal)
and stirring the reaction mixture, which is clearly presented in Ta-

H.R. Memarian et al. / Ultrasonics Sonochemistry 17 (2010) 579–586
583
Table 3
The effect of maximum power intensity of ultrasound on the rate of oxidation of 1a by PPS in aqueous CH3CN at 70 °C.
Max. power density (min)
Timea
20% (92 W cmꢀ2
34
)
40% (276 W cmꢀ2
29
)
60% (276 W cmꢀ2
27
)
80% (368 W cmꢀ2
22
)
100% (460 W cmꢀ2
17
)
a
The times are given after total disappearance of DHPMs.
ble 2. This led us also to study the effect of intensity on sono-ther-
mal oxidation. This was studied for the reaction of 1a in CH3CN/
H2O (10:2) solution in the presence of PPS at 20%, 40%, 60%, 80%
and 100% of the rated power of the ultrasonic horn (92, 184, 276,
368 and 460 W cmꢀ2, respectively). The presented data in Table 3
show that by increasing the ultrasound intensity, a decrease in
the time of reaction is observed. This observation can be explained
as follows:
were recorded with a Bruker 300 MHz machine. They are reported
as follows; chemical shifts [multiplicity, coupling constants J (Hz),
number of protons, and assignment]. 13C NMR spectra were re-
corded with a Bruker 75.48 MHz machine. Mass spectra were ob-
tained on Platform II spectrometer from Micromass; EI mode at
70 eV. UV spectra were taken with Shimadzu UV-160
spectrometer.
4.3. General procedure for the oxidation of 5-acetyl-6-methyl-3,4-
(i) The homogeneous distribution of the reactants throughout
the solution, namely, the effective mass transfer by applying
the sonic waves and stirring the solution.
(ii) The increasing of temperature by applying the sonic waves,
since the temperature of solution of 1a with PPS after 3 and
5 min sonication at 100% intensity without using the water-
bath is raised to 47 and 53 °C, respectively, whereas by using
the water-bath at 70 °C, sonication of this solution for 5 min
at 100% intensity causes an increase of temperature to 75–
80 °C.
(iii) The maximum cavitation is normally created around the
probe. It seems, using simultaneous sonic wave and mag-
netic stirrer causes homogenization the reaction solution,
therefore an enhancement of the rate constant of decompo-
sition of PPS compared with the rate constant in the absence
of stirring and sonic waves (thermal).
dihydropyrimidin-2(1H)–ones (1a–l)
(i) Thermal: Potassium peroxydisulfate (61.5 mg, 0.23 mmol)
wasaddedto asolutionof dihydropyrimidinones(0.23 mmol)
in acetonitrile and water (10:2 mL). The reaction mixture was
refluxed for the times given in Table 2. TLC monitoring of the
reaction using n-hexane/ethyl acetate (2:1) as eluent was fol-
lowed until total disappearance of the DHPMs. Solvent was
evaporated and the crude reaction mixture was purified by
column chromatography (2/1 n-hexane/ethyl acetate), then
recrystallized from n-hexane/ethyl acetate.
(ii) Sono-thermal: The same reaction mixture was immersed in
at 70 °C preheated water-bath by simultaneous ultrasound
irradiation and stirring the solution for the times given in
Table 2 until total disappearance of DHPMs was observed
(TLC). Solvent was evaporated and the crude reaction mix-
ture was extracted with 2 ꢂ 10 ml diethyl ether/water mix-
ture, the organic layer was evaporated and the residue was
recrystallized form n-hexane/ethyl acetate. It should be
noted that the reactions were carried out in 5 min sonication
and 2 min relaxation to prevent the splashing of solvent
until total disappearance of DHPMs. The water-bath has
been removed during the relaxation times to prevent the
thermal oxidation and better comparison of the times under
ultrasound irradiation. The physical and spectral data of the
starting material and the products are as following.
3. Conclusion
From the results of the present work, combination of ultra-
sound, heat and stirring accelerate the oxidation of 5-acetyl-3,4-
dihydropyrimidin-2(1H)-ones, compared with reaction without
applying the sonic waves, but in comparison to the oxidation of
5-carbothoxy-3,4-dihydropyrimidin-2(1H)-ones the time of reac-
tion is longer. Easy work-up of the reaction due to complete con-
sumption of DHPMs and short reaction times are the advantages
of this oxidative method.
4.3.1. 5-Acetyl-6-methyl-4-phenyl-3,4-dihydropyrimidin-2(1H)-one
(1a)
4. Experimental
White solid. Mp: 228–230 °C. Ref. Mp [41]: 233–236 °C.
4.3.2. 5-Acetyl-6-methyl-4-(40-methylphenyl)-3,4-dihydropyrimidin-
4.1. Materials
2(1H)-one (1b)
White solid. Mp: 234–236 °C. IR:
(CH3CN): kmax (log
(DMSO-d6): d 2.07 (s, 3H, CH3), 2.25 (s, 3H, CH3CO), 2.27 (s, 3H,
40-CH3), 5.20 (s, 1H, 4-H), 7.12 (br, s, 4H, H-aromatic), 7.76 (s, 1H,
1-NH), 9.13 (s, 1H, 3-NH). EI-MS: m/z (%): 244 (M+, 14), 243
(M+ꢀH, 25), 229 (M+ꢀCH3, 49), 201 (M+ꢀCH3CO, 32), 153
(M+ꢀC7H7, 100), 91 (Ph–CHþ2 , 30).
m
1640, 1590, 1505 cmꢀ1. UV
5-Acetyl-3,4-dihydropyrimidin-2(1H)-ones (1a–l) have been
prepared by adoption of the known procedure [41]. Acetonitrile
was purchased from Merck and distilled before used.
e
) 288.8 (3.80), 241.4 nm (3.41). 1H NMR
4.2. Equipments
The ultrasonic device used was an UP 400 S instrument from Dr.
Hielscher GmbH. A S3 immersion horn emitting 24 kHz ultrasound
at intensity levels tunable up to maximum sonic power density of
460 W cmꢀ2 was used. Sonication was carried out at 100% (maxi-
4.3.3. 5-Acetyl-4-(40-methoxyphenyl)-6-methyl-3,4-
dihydropyrimidin-2(1H)-one (1c)
mum amplitude 210
lm). A 3 mm long sonotrode (maximum im-
White solid. Mp: 182–184 °C. Ref. Mp [41]: 168–170 °C.
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
from KBr discs on a Shimadzu apparatus IR 435. 1H NMR spectra
4.3.4. 5-Acetyl-4-(30-methoxyphenyl)-6-methyl-3,4-
dihydropyrimidin-2(1H)-one (1d)
White solid. Mp: 226–228 °C. Ref. Mp [42]: 228–230 °C.

584
H.R. Memarian et al. / Ultrasonics Sonochemistry 17 (2010) 579–586
4.3.5. 5-Acetyl-4-(20-methoxyphenyl)-6-methyl-3,4-
4.3.12. 5-Acetyl-6-methyl-4-(30-nitrophenyl)-3,4-dihydropyrimidin-
dihydropyrimidin-2(1H)-one (1e)
2(1H)-one (1l)
White solid. Mp: 250–252 °C. IR:
m
1670, 1580, 1430 cmꢀ1. UV
Yellow solid. Mp: 286–288 °C. IR:
(CH3CN): kmax (log
) 282.6 nm (3.98). 1H NMR (DMSO-d6): d 2.19
m
1650, 1585, 1420 cmꢀ1. UV
(CH3CN): kmax (log
e
) 283.6 (4.42), 240.2 nm (3.90). 1H NMR
e
(DMSO-d6): d 2.00 (s, 3H, CH3), 2.28 (s, 3H, CH3CO), 3.81 (s, 3H,
CH3O), 5.56 (s,1H, 4-H), 7.06 (mc, 4H, H-aromatic), 7.33 (s, 1H, 1-
NH), 9.11 (s, 1H, 3-NH). EI-MS: m/z (%): 260 (M+, 61), 259
(M+ꢀH, 80), 245 (M+ꢀCH3,51), 229 (M+ꢀCH3O, 92), 217
(M+ꢀCH3CO, 85),153 (M+ꢀ2-CH3COC6H4, 100).
(s, 3H, CH3), 2.32 (s, 3H, CH3CO), 5.45 (d, J = 3.24 Hz, 1H, 4-H),
7.99 (brd s, 1H, 1-NH), 8.11 (mc, 4H, H-aromatic), 9.34 (s, 1H, 3-
NH). EI-MS: m/z (%): 259 (M+ꢀOH, 5), 258 (M+ꢀH2O, 32), 232
(M+ꢀCH3CO, 7), 228 (M+ꢀHNO2, 27), 153 (3-O2NC6H4–CH@NH+,
100).
4.3.13. 5-Acetyl-6-methyl-4-phenylpyrimidin-2(1H)-one (2a)
4.3.6. 5-Acetyl-4-(40-chlorophenyl)-6-methyl-3,4-dihydropyrimidin-
2(1H)-one (1f)
Pale yellow solid. Mp: 162–163 °C. IR:
UV (CH3CN): kmax (log
) 307.5 (2.32), 249.0 nm (2.52). 1H NMR
m .
1700, 1670, 1590 cmꢀ1
e
White solid. Mp: 249–251 °C. Ref. Mp [43]: 223–225 °C.
(DMSO-d6): d 1.84 (s, 3H, 6-CH3), 2.30 (s, 3H, CH3CO), 7.52 (mc,
5H, H-aromatic), 12.33 (brd s, 1H, NH). 13C NMR (75.48 MHz,
DMSO-d6): d = 18.82, 32.37, 118.33, 128.63, 129.25, 131.32,
155.89, 201.05. EI-MS: m/z (%): 228 (M+, 42), 227(M+ꢀH, 49), 213
(M+ꢀCH3, 100), 185 (M+ꢀCH3CO, 11), 104 (C6H5–C@NH+, 61), 103
(C6H5–CN+, 7), 77 (C6H5+, 44).
4.3.7. 5-Acetyl-4-(30-chlorophenyl)-6-methyl-3,4-dihydropyrimidin-
2(1H)-one (1g)
White solid. Mp: 285–287 °C. IR:
(CH3CN): kmax (log
) 291.4 (3.08), 239.8 nm (2.70). 1H NMR
m
1700, 1615, 1525 cmꢀ1. UV
e
(DMSO-d6): d 2.15 (s, 3H, CH3), 2.30 (s, 3H, CH3CO), 5.27 (d,
J = 3.25 Hz, 1H, 4-H), 7.27 (mc, 4H, H-aromatic), 7.87 (s, 1H,
1-NH), 9.28 (s, 1H, 3-NH). EI-MS: m/z (%): 266 (M+37Cl, 49), 265
(M+37ClꢀH, 64), 264 (M+35Cl, 32), 263 (M+35ClꢀH, 79), 249
(M+35ClꢀCH3, 80), 229 (M+35Clꢀ35Cl, 42), 223 (M+37ClꢀCH3CO,
28), 221 (M+35ClꢀCH3CO, 74), 170 (2-37ClC6H4–CH@NH+, 3), 169
(2-37ClC6H4–C@NH+, 8), 168 (2-35ClC6H4–CH@NH+, 9), 167
(2-35ClC6H4–C@NH+, 9), 153 (M+ꢀ2-ClC6H4, 100).
4.3.14. 5-Acetyl-6-methyl-4-(40-methylphenyl)pyrimidin-2(1H)-one
(2b)
Pale yellow solid. Mp: 219–221 °C. IR:
UV (CH3CN): kmax (log
) 320.0 (sh, 3.48), 259.5 nm (3.70). 1H NMR
m .
1695, 1590, 1510 cmꢀ1
e
(DMSO-d6): d 1.85 (s, 3H, CH3), 2.29 (s, 3H, CH3CO), 2.50 (s, 3H, 40-
CH3), 7.31 (d, J = 7.83 Hz, 2H, 2-H0 and 6-H0), 7.37 (d, J 8.52 Hz, 2H,
3-H0 and 5-H0), 12.26 (brd s, 1H, NH). 13C NMR (75.48 MHz, DMSO-
d6): d = 19.05, 21.41, 32.42, 118.18, 128.67, 129.80, 135.06, 141.33,
156.26, 161.12, 201.29. EI-MS: m/z (%): 242 (M+, 46), 241 (M+ꢀH,
32), 227 (M+ꢀCH3, 100), 199 (M+ꢀCH3CO, 11), 117 (4-CH3C6H4–
C@NH+, 4), 116 (4-CH3C6H4–CN+, 8), 91 (–C6H4–CH3, 37).
4.3.8. 5-Acetyl-4-(20-chlorophenyl)-6-methyl-3,4-dihydropyrimidin-
2(1H)-one (1h)
White solid. Mp: 262–264 °C. IR:
(CH3CN): kmax (log
) 291.0 (3.99), 240.2 nm (3.62). 1H NMR
m
1690, 1615, 1420 cmꢀ1. UV
e
4.3.15. 5-Acetyl-4-(40-methoxyphenyl)-6-methylpyrimidin-2(1H)-one
(DMSO-d6): d 2.05 (s, 3H, CH3), 2.33 (s, 3H, CH3CO), 5.66 (s,1H, 4-
H), 7.36 (mc, 4H, H-aromatic), 7.72 (s, 1H, 1-NH), 9.27 (s, 1H,
3-NH). EI-MS: m/z (%): 266 (M+37Cl, 4), 265 (M+37ClꢀH, 7), 264
(M+35Cl, 10), 263 (M+35ClꢀH, 16), 249 (M+35ClꢀCH3,10), 231
(M+37Clꢀ37Cl, 6), 229 (M+35Clꢀ35Cl, 94), 223 (M+37ClꢀCH3CO, 6),
221 (M+35ClꢀCH3CO, 72), 170 (2-37ClC6H4–CH@NH+, 14), 169
(2-37ClC6H4–C@NH+, 18), 168 (2-35ClC6H4–CH@NH+, 17), 167
(2-35ClC6H4–C@NH+, 8), 153 (M+ꢀ2-ClC6H4, 100).
(2c)
Pale yellow solid. Mp: 189–191 °C. IR:
UV (CH3CN): kmax (log
) 296.5 (3.08), 255.0 nm (3.08). 1H NMR
m .
1670, 1680, 1425 cmꢀ1
e
(DMSO-d6): d 1.87 (s, 3H,6-CH3), 2.28 (s, 3H, CH3CO), 3.82 (s, 3H,
CH3O), 7.06 (d, J = 8.55 Hz, 2H, 2-H0 and 6-H0), 7.45 (d, J = 8.52,
2H, 3-H0 and 5-H0), 12.18 (brd s, 1H, NH). 13C NMR (75.48 MHz,
DMSO-d6): d = 18.83, 32.34, 55.84, 114.67, 117.91, 130.53,
155.97, 161.99, 155.97, 161.99, 201.35. EI-MS: m/z (%): 258 (M+,
84), 257 (M+ꢀH, 40), 243 (M+ꢀCH3, 100), 227 (M+ꢀCH3O, 10),
215 (M+ꢀCH3CO, 11), 200 (M+ꢀCH3CO, –CH3, 18), 134 (4-
CH3OC6H4–CH@NH+, 71), 133 (4-CH3OC6H4–C@NH+, 4), 132 (4-
CH3OC6H4–CN+, 3).
4.3.9. 5-Acetyl-4-(40-bromophenyl)-6-methyl-3,4-dihydropyrimidin-
2(1H)-one (1i)
White solid. Mp: 232–233 °C. IR:
(CH3CN): kmax (log
) 290.8 (4.04), 240.2 nm (3.85). 1H NMR
m
1650, 1580, 1420 cmꢀ1. UV
e
4.3.16. 5-Acetyl-4-(30-methoxyphenyl)-6-methylpyrimidin-2(1H)-one
(2d)
Pale yellow solid. Mp: 163–164 °C. IR:
UV (CH3CN): kmax (log
(DMSO-d6): d 2.12 (s, 3H, CH3), 2.28 (s, 3H, CH3CO), 5.23 (s, 1H,
4-H), 7.18 (d, J = 6.90 Hz, 20- and 60-H), 7.51 (d, J = 6.77 Hz, 30-
and 50-H), 7.88 (s, 1H, 1-NH), 9.23 (s, 1H, 3-NH).
m .
1675, 1595, 1425 cmꢀ1
e
) 303.5 (3.75), 250.0 nm (3.88). 1H NMR
(DMSO-d6): d 1.85 (s, 3H, 6-CH3), 2.28 (s, 3H, CH3CO), 3.80 (s, 3H,
40-CH3O), 6.98 (d, J 7.33 Hz, 2H, 40-H), 7.12 (d, J = 8.20 Hz, 2H, 60-
H), 7.03 (s, 1H, 20-H),7.41 (t, J = 6.67 Hz, J = 7.55 Hz, 1H). 13C NMR
(75.48 MHz, DMSO-d6): d = 30.87, 55.60, 111.79, 119.23, 121.19,
130.54, 132.43, 155.94, 156.40, 198.86. EI-MS: m/z (%): 258 (M+,
3), 257 (M+ꢀH, 2), 243 (M+ꢀCH3, 2), 200 (M+ꢀCH3CO, –CH3, 2),
134 (4-CH3OC6H4–CH@NH+, 14), 133 (4-CH3OC6H4–C@NH+, 7),
132 (4-CH3OC6H4–CN+, 8), 77 (100).
4.3.10. 5-Acetyl-4-(20-bromophenyl)-6-methyl-3,4-dihydropyrimidin-
2(1H)-one (1j)
White solid. Mp: 254–257 °C. IR:
(CH3CN): kmax (log
) 292.2 (3.98), 239.8 nm (3.70). 1H NMR
m
1700, 1620, 1420 cmꢀ1. UV
e
(DMSO-d6): d 2.04 (s, 3H, CH3), 2.33 (s, 3H, CH3CO), 5.62 (d,
J = 2.85 Hz, 1H, 4-H), 7.39 (mc, 4H, H-aromatic), 7.69 (brd s, 1H,
1-NH), 9.28 (s, 1H, 3-NH). EI-MS: m/z (%): 267 (M+81BrꢀCH3CO,
10), 265 (M+79BrꢀCH3CO, 11), 231 (M+81Brꢀ81Br, 2), 229
(M+79Brꢀ79Br, 97), 214 (M+79Brꢀ79Br, –CH3, 13) 168 (2-BrC6H4–
CH@NH+, 5), 153 (M+ꢀ2-BrC6H4, 100).
4.3.17. 5-Acetyl-4-(20-methoxyphenyl)-6-methylpyrimidin-2(1H)-one
(2e)
Pale yellow solid. Mp: 166–167 °C. IR:
UV (CH3CN): kmax (log
) 303.0 (4.15), 258.0 nm (4.15). 1H NMR
m .
1960, 1590, 1550 cmꢀ1
e
4.3.11. 5-Acetyl-6-methyl-4-(40-nitrophenyl)-3,4-dihydropyrimidin-
2(1H)-one (1k)
(DMSO-d6): d 1.87 (s, 3H, CH3), 2.32 (s, 3H, CH3CO), 3.70 (s, 3H,
CH3O), 7.24 (mc, 4H, H-aromatic), 12.12 (brd s, 1H, NH). 13C NMR
(75.48 MHz, DMSO-d6): d = 30.85, 55.58, 111.78, 119.24, 121.18,
Yellow solid. Mp: 229–230 °C (dec.). Ref. Mp [41]: 230 °C (dec.).

H.R. Memarian et al. / Ultrasonics Sonochemistry 17 (2010) 579–586
585
130.54, 132.44, 155.96, 198.82. EI-MS: m/z (%): 258 (M+, 6), 257
(M+ꢀH, 4), 243 (M+ꢀCH3, 13), 227 (M+ꢀCH3O, 100), 215
(M+ꢀCH3CO, 22), 134 (2-CH3OC6H4–CH@NH+, 38), 133 (2-
CH3OC6H4–C@NH+, 10), 132 (2-CH3OC6H4–CN+, 6).
H-aromatic), 7.73 (d, J = 7.82 Hz, 1H, 6-H0), 12.36 (brd s, 1H, NH).
EI-MS: m/z (%): 227 (M+ꢀBr, 100), 185 (2-81BrC6H4CH@NH+, 10),
184 (2-81BrC6H4C@NH+, 26) 183 (4-79BrC6H4CH@NH+, 3), 182
(4-79BrC6H4C@NH+, 6).
4.3.18. 5-Acetyl-4-(40-chlorophenyl)-6-methylpyrimidin-2(1H)-one
4.3.23. 5-Acetyl-6-methyl-4-(40-nitrophenyl)-pyrimidin-2(1H)-one
(2f)
(2k)
m .
1650, 1580, 1420 cmꢀ1
Pale yellow solid. Mp: 265–267 °C. IR:
UV (CH3CN): kmax (log ) 330 (sh, 3.71), 302 (sh, 3.86), 262.0 nm
m .
1665, 1600, 1505 cmꢀ1
Pale yellow solid. Mp: 235–237 °C. IR:
UV (CH3CN): kmax (log
) 313.0 (3.34), 252.0 nm (3.56). 1H NMR
e
e
(4.07). 1H NMR (DMSO-d6): d 2.35 (s, 3H, CH3CO), 1.95 (s, 3H,
CH3), 7.73 (d, J = 8.52 Hz, 2H, 2-H0 and 6-H0), 8.33 (d, J = 8.49, 2H,
3-H0 and 5-H0), 9.27 (s, 1H, NH), 12.48 (brd s, 1H, NH). 13C NMR
(75.48 MHz, DMSO-d6): d = 18.83, 124.33, 130.06, 144.44, 148.98.
EI-MS: m/z (%): 273 (M+, 20), 272 (M+ꢀH, 13), 258 (M+ꢀCH3,
100), 256 (M+ꢀOH, 25), 226 (M+ꢀHNO2, 12).
(DMSO-d6): d 1.90 (s, 3H, CH3), 2.30 (s, 3H, CH3CO), 7.49 (d, J
8.27 Hz, 2H, 3-H0 and 5-H0), 7.58 (d, J = 8.21 Hz, 2H, 2-H0 and 6-
H0),12.21 (brd s, 1H, NH). 13C NMR (75.48 MHz, DMSO-d6):
d = 18.97, 32.53, 118.30, 129.33, 130.51, 136.09, 137.02, 156.35,
161.11, 168.92, 200.99. EI-MS: m/z (%): 264 (M+37Cl, 27), 263
(M+37ClꢀH, 32), 262 (M+35Cl, 78), 261 (M+35ClꢀH, 59), 249
(M+37ClꢀCH3, 69), 247 (M+35ClꢀCH3, 99), 227 (M+ꢀCl, 17), 221
(M+37ClꢀCH3CO, 5), 219 (M+35ClꢀCH3CO, 13), 140 (4-37ClC6-
H4C@NH+, 42), 139 (4-37ClC6H4CN+, 19), 138 (4-35ClC6H4C@NH+,
87), 137 (4-35ClC6H4CN+, 12).
4.3.24. 5-Acetyl-6-methyl-4-(30-nitrophenyl)-pyrimidin-2(1H)-one
(2l)
Pale yellow solid. Mp: 256–258 °C. IR:
UV (CH3CN): kmax (log
m .
1675, 159, 1520 cmꢀ1
e
) 305.0 (3.57), 259.0 nm (3.85). 1H NMR
4.3.19. 5-Acetyl-4-(30-chlorophenyl)-6-methylpyrimidin-2(1H)-one
(DMSO-d6): d 1.97 (s, 3H, CH3), 2.35 (s, 3H, CH3CO), 7.80 (t,
J = 8.80 Hz, 1H, 5-H0), 7.88 (d, J = 7.49 Hz, 1H, 6-H0), 8.29 (s, 1H, 2-
H0), 8.39 (d, J = 7.96 Hz, 1H, 4-H0), 12.48 (brd s, 1H, NH). EI-MS:
m/z (%): 273 (M+, 15), 272 (M+ꢀH, 8), 258 (M+ꢀCH3, 100), 256
(M+ꢀOH, 30), 226 (M+ꢀHNO2, 16).
(2g)
Pale yellow solid. Mp: 196–198 °C. IR:
UV (CH3CN): kmax (log ) 320 (sh, 3.99), 304 (4.03), 259.0 nm (4.18).
m .
1650, 1580, 1430 cmꢀ1
e
1H NMR (DMSO-d6): d 1.90 (s, 3H, CH3), 2.30 (s, 3H, CH3CO), 7.54
(mc, 4H, H-aromatic), 9.27 (s, 1H, NH). 13C NMR (75.48 MHz,
DMSO-d6): d = 19.13, 32.55, 118.37, 127.31, 128.32, 130.89,
131.09, 133.93, 140.37, 156.73, 161.39, 168.58, 200.95. EI-MS: m/
z (%): 264 (M+37Cl, 21), 263 (M+37ClꢀH, 23), 262 (M+35Cl, 58), 261
(M+35ClꢀH, 38), 249 (M+37ClꢀCH3, 45), 247 (M+35ClꢀCH3, 100),
227 (M+ꢀCl, 14), 221 (M+37ClꢀCH3CO, 5), 219 (M+35ClꢀCH3- CO,
9), 140 (3-37ClC6H4C@NH+, 36), 139 (3-37ClC6- H4CN+, 18), 138
(3-35ClC6H4C@NH+, 78), 137 (3-35ClC6H4CN+, 9).
Acknowledgments
We are thankful to the Center of Excellence (Chemistry),
Research Council of the University of Isfahan and Office of
Graduate Studies of the University of Isfahan for their financial
support.
4.3.20. 5-Acetyl-4-(20-chlorophenyl)-6-methylpyrimidin-2(1H)-one
References
(2h)
Pale yellow solid. Mp: 175–176 °C. IR:
UV (CH3CN): kmax (log
) 305.0 (3.34), 259.0 nm (3.45). 1H NMR
m .
1700, 1620, 1430 cmꢀ1
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e
ˇ
(DMSO-d6): d 1.90 (s, 3H, CH3), 2.30 (s, 3H, CH3CO), 7.47 (mc, 4H,
H-aromatic),12.26 (brd s, 1H, NH). 13C NMR (75.48 MHz, DMSO-
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(M+35ClꢀCH3, 5), 227 (M+ꢀCl, 100), 219 (M+35ClꢀCH3CO, 3), 140
(2-37ClC6H4C@NH+, 24), 139 (2-37ClC6H4CN+, 13) 138 (2-35ClC6-
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4.3.21. 5-Acetyl-4-(40-bromophenyl)-6-methylpyrimidin-2(1H)-one
(2i)
Pale yellow solid. Mp: 239–240 °C. IR:
UV (CH3CN): kmax (log ) 332 (sh, 3.36), 304 (sh, 3.48), 252.0 nm
m .
1670, 1620, 1420 cmꢀ1
e
(3.76). 1H NMR (DMSO-d6): d 1.91 (s, 3H, CH3), 2.30 (s, 3H, CH3CO),
7.41 (d, J = 8.18 Hz, 2H, 3-H0 and 5-H0), 7.72 (d, J = 8.12, 2H, 2-H0
and 6-H0), 12.30 (brd s, 1H, NH). 13C NMR (75.48 MHz, DMSO-
d6): d = 19.02, 32.56, 118.30, 124.88, 130.70, 132.24, 137.40,
156.52, 161.20, 168.92, 201.01. EI-MS: m/z (%): 308 (M+81Br, 38),
307 (M+81BrꢀH, 32), 306 (M+79Br, 37), 305 (M+79BrꢀH, 26), 293
(M+81BrꢀCH3, 81), 291 (M+79BrꢀCH3, 83), 265 (M+81Brꢀ CH3CO,
6), 263 (M+79BrꢀCH3CO, 7), 227 (M+ꢀBr, 24), 185
(4-81BrC6H4CH@NH+, 16), 183 (4-79BrC6H4CH@NH+, 61), 182
(4-79BrC6H4C@NH+, 16), 181 (4-79BrC6H4CN+, 45).
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4.3.22. 5-Acetyl-4-(20-bromophenyl)-6-methylpyrimidin-2(1H)-one
(2j)
Pale yellow solid. Mp: 202–204 °C. IR:
UV (CH3CN): kmax (log
) 301.5 (3.89), 264.0 nm (3.86). 1H NMR
(DMSO-d6): d 1.85 (s, 3H, CH3), 2.37 (s, 3H, CH3CO), 7.43 (mc, 3H,
m .
1700, 1615, 1420 cmꢀ1
e

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H.R. Memarian et al. / Ultrasonics Sonochemistry 17 (2010) 579–586
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