Photo-oxidation of 5-acetyl-3,4-dihydropyrimidin-2(1H)-ones

Article abstract of DOI:10.1016/j.jphotochem.2009.10.012

A variety of Biginelli 5-acetyl-3,4-dihydropyrimidin-2(1H)-ones are efficiently oxidized to their corresponding pyrimidin-2(1H)-one derivatives upon UV irradiation under argon atmosphere in chloroform solution. The nature of the additional substituent on the phenyl ring located on C-4 of the heterocyclic ring influences the rate of reaction. An electron-transfer induced photoreaction is proposed based on the formation of HCl and CH₂Cl₂.

Full text of DOI:10.1016/j.jphotochem.2009.10.012

Journal of Photochemistry and Photobiology A: Chemistry 209 (2010) 95–103
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Photo-oxidation of 5-acetyl-3,4-dihydropyrimidin-2(1H)-ones
Hamid Reza Memarian∗, Asadollah Farhadi, Hassan Sabzyan, Mousa Soleymani
Department of Chemistry, Faculty of Science, University of Isfahan, Hezar Jarib Ave., 81746-73441 Isfahan, I.R., Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 11 August 2009
Received in revised form 17 October 2009
Accepted 31 October 2009
Available online 10 November 2009
A variety of Biginelli 5-acetyl-3,4-dihydropyrimidin-2(1H)-ones are efficiently oxidized to their corre-
sponding pyrimidin-2(1H)-one derivatives upon UV irradiation under argon atmosphere in chloroform
solution. The nature of the additional substituent on the phenyl ring located on C-4 of the heterocyclic
ring influences the rate of reaction. An electron-transfer induced photoreaction is proposed based on the
formation of HCl and CH2Cl2.
© 2009 Elsevier B.V. All rights reserved.
Keywords:
Biginelli
Dihydropyrimidinone
Electron transfer
Photochemistry
Pyrimidinone
1. Introduction
of deviation of C-4 of the ring from planarity depends on various
factors such as: (i) the substituent located on C-4; (ii) the type of
3,4-Dihydropyrimidin-2(1H)-ones (DHPMs) are one of impor-
tant classes of heterocyclic compounds. Many of them are known as
biological active natural products and drugs, such as blockers of cal-
cium (Ca2+) channel [1], inhibitors of the HIV virus [2], anti-cancer
[3], antibacterial agents and also as anti-staphylococcal antibiotics
[4]. All these effects are due to the existence of pyrimidine cores
in these compounds. In addition, Itami et al. have reported that
pyrimidine cores with extended ␲-systems exhibit interesting flu-
orescent properties [5]. However, in comparison to photochemical
behavior of 1,4-dihydropyridines [6], surprisingly little is known
about the light sensitivity of 3,4-dihydropyrimidin-2(1H)-ones. It
is important to know that these compounds may easily lose their
biological activities due to some molecular changes upon expos-
ing to the UV light. Recently, we have studied the effect of the
nature of the substituent on 4-position of the heterocyclic ring on
the rate of oxidation of various ethyl 3,4-dihydropyrimidin-2(1H)-
one-5-carboxylates by potassium peroxydisulfate under thermal
conditions [7] or by applying the ultrasound irradiation [8]. In
another work, we have further investigated this effect on the light
sensitivity of these compounds by exposing them to the UV light
[9].
the group present on C-5 (being ester or keto groups); and (iii) the
location of the additional substituent on the phenyl ring located
on C-4. On the other hand, the type of the substituents located on
the C-4 and C-5 atoms influence also the amount of the dihedral
angle of both C-4 and C-5 substituents with respect to the ring
atoms. All these observations are affected by the polar and steric
effects of these substituents [10].
In our recent study, various 5-acetyl-3,4-dihydropyrimidin-
2(1H)-ones were synthesized and the effect of the acetyl and
the carboethoxy groups in position 5 of the dihydropyrimidinone
ring on the rate of oxidation by potassium peroxydisulfate under
microwave irradiation was investigated [11]. The results indicate
that the ester derivatives are oxidized faster than the correspond-
ing acetyl derivatives. In continuation of our work concerning the
light sensitivityofdihydropyrimidinonesespeciallyto elucidatethe
comparative effects of the acetyl and carboethoxy groups on the
rate of photo-oxidation, here the photochemical behavior of these
compounds under oxygen and argon atmospheres are investigated.
2. Results and discussion
The results of the computational studies of 3,4-
dihydropyrimidin-2(1H)-ones indicate that the pyrimidine
cores in these systems are not completely planar and the amount
The important factor in photochemical behavior of organic
compounds is the spin multiplicity (i.e. being singlet or triplet)
of the excited state of the light absorbing compounds involved
in the photoreaction. The lifetime of these species determine the
rate of reaction especially in the triplet excited state, which can be
affected by the triplet oxygen present in the reaction vessel either
as the atmosphere or as a dissolved species during UV irradiation.
∗
Corresponding author. Tel.: +98 311 793 2707; fax: +98 311 668 9732.
E-mail address: memarian@sci.ui.ac.ir (H.R. Memarian).
1010-6030/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jphotochem.2009.10.012

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H.R. Memarian et al. / Journal of Photochemistry and Photobiology A: Chemistry 209 (2010) 95–103
Scheme 1.
Table 2
Therefore, we first carried out irradiation of 4-phenyl substituted
compound 1a, as a model substrate, in the CHCl3 solvent under
oxygen and argon atmospheres. The results of the photoreactions
indicate that irradiation of 1a under oxygen atmosphere resulted
in a complicated reaction because of the formation of the oxidation
product 2a as a major product besides various hitherto uniden-
tified by-products. This is while, a clean reaction was observed
by irradiation under argon atmosphere and a sole product 2a has
been obtained. In continuation, a 3 mM solution of each of the 3,4-
dihydropyrimidinones (1a–1l) in chloroform was irradiated under
argon atmosphere until total disappearance of 1a–1l monitored
by TLC (Scheme 1). The solvent was evaporated and the pure prod-
ucts were obtained by recrystallization from n-hexane/ethyl
acetate solvent mixture. The results are summarized in
Table 1.
Comparison of the UV-absorption [ꢀmax (nm)] peaks of 1a–1l with those of 2a–2l in
acetonitrile solution.
1
ꢀmax (log ε)
2
ꢀmax (log ε)
a
b
c
d
e
f
g
h
i
290.5 (4.10)
288.8 (3.80), 241.4 (3.42)
286.4 (3.82)
a
b
c
d
e
f
g
h
i
307.5 (2.31), 249 (2.52)
320 (3.48, sh), 259.5 (3.70)
296.5 (4.06), 255 (4.06)
303.5 (3.75), 250 (3.88)
303 (4.15), 258 (4.15)
313 (3.35), 252 (3.56)
320 (sh, 3.99), 304 (4.03), 259 (4.18)
305 (3.34), 259 (3.45)
322 (sh, 2.36), 304 (sh, 3.48), 252 (3.76)
301.5 (3.89), 264 (3.86)
330 (sh, 3.71), 302 (sh, 3.86), 262.0 (4.07)
305.0 (3.57), 259.0 (3.85)
284.4 (3.88), 239.6 (3.43)
283.6 (4.42), 240.2 (3.90)
290.6 (4.04), 240 (3.77)
291.4 (3.08), 239.8 (2.68)
291 (3.99), 240.2 (3.62)
290.8 (4.04), 240.2 (3.85)
292.2 (3.98), 239.8 (3.70)
279.2 (4.07)
j
k
l
j
k
l
282.6 (3.98)
The occurrence of the photo-dehydrogenation and characteri-
zation of the photoproducts was confirmed by comparison of the
IR, UV, 1H NMR, 13C NMR and MS data of the photoproducts,
pyrimidin-2(1H)-ones (2a–2l), with those of the starting materials,
3,4-dihydropyrimidin-2(1H)-ones (1a–1l). A comparative study of
the UV data, presented in Table 2, shows bathochromic shift in the
spectra of the products due to the formation of the imino-diene
moiety in the heterocyclic ring system (formed after the elimina-
tion of the 3- and 4-hydrogens).
Comparison of the IR spectra of the products 2a–2l with those
of the corresponding starting materials 1a–1l, presented in Table 3,
shows a small shift of the CO stretching band of the acetyl group
(5-COCH3) to higher frequencies and shifts of the stretching modes
of the 2-C O and C5 C6 double bonds to lower frequencies due to
the extended conjugation.
Table 3
Comparison of the IR spectra (ꢁ/cm−1) of 1a–1l with those of 2a–2l.
1
CH3CO
2-CO
C
C
2
CH3CO
2-CO
C C
a
b
c
d
e
f
g
h
i
1700
1640
1650
1670
1670
1690
1700
1690
1650
1700
1650
1650
1670
1590
1580
1590
1580
1615
1615
1615
1580
1620
1580
1585
1600
1505
1430
1425
1430
1420
1525
1420
1420
1420
1520
1420
a
b
c
d
e
f
g
h
i
1700
1695
1670
1675
1690
1650
1650
1700
1670
1700
1665
1675
1670
1590
1680
1595
1590
1580
1580
1620
1620
1615
1600
1590
1590
1510
1425
1425
1550
1420
1430
1430
1420
1420
1505
1520
j
k
l
j
k
l
Analysis of the 1H NMR spectra of the products shows a shift
of the 1-NH line to lower fields, lack of 3-NH and 4-H lines due
to being eliminated upon oxidation, and a shift of the 6-CH3 reso-
nance to higher fields as compared to those of the starting materials
Table 1
Completion times and yields of the photo-oxidation of 5-acetyl-3,4-
dihydropyrimidinones (1a–1l) under argon atmosphere.
Table 4
1
R
2
Time (h)a
Yield (%)b
Structurally relevant 1H NMR chemical shifts (ı values) of 1a–1l compounds in
comparison with those of 2a–2l.
a
b
c
d
e
f
g
h
i
C6H5–
a
b
c
d
e
f
g
h
i
18
14
8
13
7.15
9.5
13
8
13
10
12
13.5
95
90
90
87
92
90
85
95
83
90
90
85
4-CH3C6H4–
4-CH3OC6H4–
3-CH3OC6H4–
2-CH3OC6H4–
4-ClC6H4–
3-ClC6H4–
2-ClC6H4–
4-BrC6H4–
2-BrC6H4–
4-NO2C6H4–
3-NO2C6H4–
1
6-CH3
1-NH
3-NH
4-H
Ref.
2
6-CH3
1-NH
a
b
c
d
e
f
g
h
i
2.10
2.07
2.06
2.07
2.00
2.10
2.15
2.05
2.12
2.04
2.18
2.19
7.81
7.76
7.80
7.80
7.33
7.80
7.87
7.72
7.88
7.69
7.98
7.99
9.16
9.13
9.16
9.11
9.11
9.20
9.28
9.27
9.23
9.28
9.34
9.34
5.26
5.20
5.20
5.22
5.56
5.20
5.27
5.66
5.23
5.62
5.39
5.45
This work
–
[19]
[20]
This work
[21]
This work
–
a
b
c
d
e
f
g
h
i
1.84
1.85
1.87
1.85
1.87
1.90
1.90
1.90
1.91
1.85
1.95
1.97
12.33
12.26
12.18
12.12
12. 21
9.27
12.26
12.30
12.36
12.48
12.48
j
k
l
j
k
l
–
–
j
k
l
j
k
l
a
The times are given after total disappearance of DHPMs (100% conversion
[19]
This work
according to TLC observation).
b
Isolated yields.

H.R. Memarian et al. / Journal of Photochemistry and Photobiology A: Chemistry 209 (2010) 95–103
97
Scheme 2.
(Table 4). No significant changes have been observed for the protons
of the acetyl group.
dominant resonance effects of the methoxy group and chlorine
atom over their inductive effects. On the contrary, the electron-
withdrawing character of the nitro group (affecting as both the
inductive and the resonance effects) in 4- and 3-positions (1k, 1l)
and the inductive effect of the methoxy group and chlorine atom
in 3-position, i.e. the “wrong” position (1d, 1g) increases the time
of reaction.
It can be seen from the data presented in Table 1 that
the nature of the additional substituent on the phenyl ring
located on C-4 position influences the rate of photo-oxidation of
the 3,4-dihydropyrimidinone ring. As is expected, the efficient
electron-donating substituents such as methoxy group or chlorine
atom in 2- and 4-positions on the phenyl ring, as in 1e, 1c, 1h and
1f, decrease the time of reaction. This is due to the result of the
According to the results summarized in Table 1 and the results
obtained from our earlier study [9], our proposed mechanism is
Scheme 3.

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H.R. Memarian et al. / Journal of Photochemistry and Photobiology A: Chemistry 209 (2010) 95–103
Table 5
Photo-oxidation of 5-carboethoxy-3,4-dihydropyrimidin-2(1H)-ones (3a–3j) in
CHCl3 under argon atmosphere.
3
R
4
Time (h)a
Yield (%)b
a
b
c
d
e
f
g
h
i
C6H5–
a
b
c
d
e
f
g
h
i
26
7.5
93
95
94
92
96
92
92
96
95
92
4-CH3C6H4–
4-CH3OC6H4–
3-CH3OC6H4–
2-CH3OC6H4–
3-ClC6H4–
9.15
12.5
11.5
20
13.5
16
2-ClC6H4–
2-BrC6H4–
4-NO2C6H4–
PhCH2CH2–
28.45
20.5
j
j
a
The times are given after total disappearance of 3a–3j (100% conversion accord-
ing to TLC observation).
b
Isolated yields after recrystallization.
Fig. 1. Boat conformation of dihydropyrimidinone ring showing the pseudoaxial
orientation of the C-4 aryl group.
confirmed, which is a light-induced electron-transfer reaction for
the dehydrogenation of dihydropyrimidin-2(1H)-ones by irradia-
tion in chloroform solution (Scheme 2). Since, the reaction is not
occurred in the absence of light (ꢀ ≥ 280 nm), a comparison of the
UV-absorption spectra of dihydropyrimidinones (1a–1l) and chlo-
roform (solvent) indicate that only these compounds are selectively
excited. Therefore, UV irradiation of dihydropyrimidinone (PM-
H2) leads to the generation of their excited state (PM-H∗2), which
CBrCl3 solvents [14,15], unsymmetrical 1,4-dihydropyridines [6]
and 3,4-dihydropyrimidin-2(1H)-ones in CHCl3 solvent [9].
A comparison of the rate of photo-oxidation of 5-carboethoxy-
3,4-dihydropyrimidin-2(1H)-ones (3a–3j) (Scheme 3 and Table 5)
[9] with those of 5-acetyl-3,4-dihydropyrimidin-2(1H)-ones
(1a–1l) (Table 1) obtained in the present study explains that the
reaction is faster in almost all the corresponding acetyl derivatives
1a–1l.
Computational study on the geometries of some dihydropy-
rimidinones carried out at the B3LYP/6-31++G** level of theory
indicates that the six-membered heterocyclic ring adopt a boat con-
formation, flatted at N1 towards an envelope conformation, with
a pseudoaxial orientation of the C4-substituent, i.e. in all 1a–1l the
4-substitution adopts the up orientation with respect to the hete-
rocyclic ring boat plane (Figs. 1 and 2). This orientation corresponds
to the antagonist activity of these compounds. The same structural
trends had already been observed for the 1,4-dihydropyridines
[16]. Therefore, similar activities are expected for dihydropyrmidi-
nones and 1,4-dihydropyridines.
•+
•−
donates an electron to chloroform to form PM-H2 and CHCl3
species. Elimination of HCl from both intermediates leads to the
formation of a radical pair, namely the hydropyrimidinoyl (PM-
H•), and the dichloromethyl (•CHCl2) radicals. The final step of
the reaction is the hydrogen abstraction by •CHCl2 radical from
hydropyrimidinoyl radical (PM-H•), which leads to the forma-
tion of the pyrimidinone compound (PM) and dichloromethane.
This proposed mechanism is supported by the formation of
dichloromethane during the reaction, which has been confirmed by
GC-analysis of the reaction mixture and the acidity of the solution
after irradiation. The proposed mechanism in the present work is
also supported by a comparison of the oxidation potential of DHPMs
considered in this study with the oxidation potential of CHCl3.
Electrochemical reduction of chloroform in acetonitrile has been
studied [12]. The reported reduction potential at various metal elec-
trodes in water–acetonitrile mixture vs. Fe/Fe+ is between −2.58
and −2.88 V. We have measured the oxidation potential for some
compounds considered in our study in acetonitrile vs. Fe/Fe+. The
obtained values 1a, Eox = 1.668 V; 1c, Eox = 1.665 V; 1h, Eox = 1.456 V
and 1k, Eox = 1.660 V. Under our experimental condition for cyclic
voltammetric studies, we did not observe any peak between 0
and 2 V for the oxidation of chloroform. This indicate that chlo-
roform is not able to reduce the DHPMs. Other studies have also
supported the electron-transfer induced mechanism by photo-
oxidation of symmetrical 1,4-dihydropyridines in CCl4 [13] and
The natural bond order (NBO) atomic charges [17,18] for the
N1, H1, N3, H3 atoms of 5-acetyl-3,4-dihydropyrimidin-2(1H)-
ones (1a–1l) and 5-carboethoxy-3,4-dihydropyrimidin-2(1H)-ones
(3a–3j) show that the electron density on N3 is greater than that on
N1 in both series of compounds (Table 6). These data support our
suggestion that N3 atom in the excited DHPM definitely donat•e−s
•+
an electron to CHCl3 under the formation of PM-H2 and CHCl3
species.
The results of oxidation of various 5-acetyl-3,4-dihydropy-
rimidin-2(1H)-ones (1a–1l) and 5-carboethoxy-3,4-dihydrop-
yrimidin-2(1H)-ones (3a–3j) by potassium peroxydisulfate (PPS)
Table 6
NBO atomic charges calculated for 5-acetyl-3,4-dihydropyrimidin-2(1H)-ones (1a–1l) and 5-carboethoxy-3,4-dihydropyrimidin-2(1H)-ones (3a–3j) using the B3LYP/6-
31++G(p,d) method.
1
R
N1
N3
H5
3
R
N1
N3
H5
a
b
c
d
e
f
g
h
i
C6H5–
−0.655
−0.656
−0.656
−0.198
−0.643
−0.655
−0.655
−0.285
−0.655
−0.647
−0.655
−0.655
−0.663
−0.663
−0.663
−0.380
−0.663
−0.664
−0.665
−0.425
−0.664
−0.662
−0.666
−0.666
0.281
0.280
0.278
0.255
0.274
0.283
0.283
0.240
0.283
0.267
0.286
a
b
c
d
e
f
g
h
j
C6H5–
−0.654
−0.655
−0.250
−0.225
−0.653
−0.655
−0.322
−0.323
−0.273
−0.663
−0.665
−0.382
−0.396
−0.672
−0.665
−0.407
−0.450
−0.347
0.274
0.274
0.232
0.238
0.293
0.283
0.234
0.237
0.248
4-CH3C6H4–
4-CH3OC6H4–
3-CH3OC6H4–
2-CH3OC6H4–
4-ClC6H4–
3-ClC6H4–
2-ClC6H4–
4-BrC6H4–
2-BrC6H4–
4-NO2C6H4–
3-NO2C6H4–
4-CH3C6H4–
4-CH3OC6H4–
3-CH3OC6H4–
2-CH3OC6H4–
3-ClC6H4–
2-ClC6H4–
2-BrC6H4–
4-NO2C6H4–
j
k
l
0278

H.R. Memarian et al. / Journal of Photochemistry and Photobiology A: Chemistry 209 (2010) 95–103
99
Fig. 2. Front side presentation (left) and boat conformation (right) of 1a, 1d and 1e.

100
H.R. Memarian et al. / Journal of Photochemistry and Photobiology A: Chemistry 209 (2010) 95–103
under microwave irradiation in water indicate that the ester deriva-
tives (3a–3j) are oxidized faster than the corresponding acetyl
derivatives (1a–1l) [11]. According to the proposed mechanism
(presented as supplementary materials), thermal cleavage of the
weakest O–O bond in PPS leads to the formation of potassium sul-
fate radicals, which abstract hydrogen from water to form hydroxyl
radicals. Removal of 4-H by the hydroxyl radical in the rate deter-
mining step, followed by the elimination of the second hydrogen
(3N–H), completes the reaction towards the formation of pyrim-
idinones. The results obtained from ab initio calculations at the
B3LYP/6-31++G** level of theory for the optimized structures of
these compounds can partially explain the observed comparative
behavior of the two classes of compounds in oxidation reaction
by PPS. Based on the results of these computations: (i) the dihy-
dropyrimidinone ring adopts a boat conformation, flattened at
N1 towards an envelope conformation, with a pseudoaxial ori-
entation of the C4-substituent, (ii) the extent of deviation from
planarity around C-4 depends on the orientation of the phenyl
group attached to this atom, especially on the position of an addi-
tional substituent at the phenyl ring, and (iii) the dihedral angle
of the ester carbonyl group or the acetyl moiety with respect to
the C5 C6 bond depends on the type of the substituent on the
C-4 atom. All these points explain that the electronic and steric
factors influence the removal of 4-H by a hydroxyl radical in the
rate determining step. The interesting result in the present work
is the comparative behavior of the two classes of compounds after
UV-light excitation. A comparison of the reaction times of photo-
oxidation of corresponding 5-carboethoxy derivatives and 5-acetyl
derivatives (with the same 4-aryl substituent) indicates that almost
all 5-acetyl derivatives are photo-oxidized faster, which is in con-
trast to the results obtained by MW-reaction. These opposite trends
explicitly show that the mechanisms for the thermal and photo-
chemical reactions are totally different: “Free radical oxidation by
in situ formed hydroxyl radical in the thermal reaction” vs. “light-
induced electron-transfer oxidation”. The faster photo-oxidation
reaction observed for the acetyl compounds as compared to the
photo-oxidation reaction of the corresponding ester compounds
can be attributed to better light absorption of 1a–1l compared to
3a–3j, especially above 280 nm by comparison of their UV spectra
(Table 2 and the supplementary data). Since the presence of the
more excited DHPMs (PM*-H2 in Scheme 2) leads to an increase
were obtained on Platform II Mass Spectrometer from Micromass;
EI mode at 70 eV. UV spectra (in CH3CN) were taken with Shi-
madzu UV-160 spectrometer.The cyclic voltammetric experiments
were performed on Potentiostat Galvanostat (SAMA 500). The elec-
trochemical studies were conducted by using acetonitrile solution
containing tertbutylammonium perchlorate. A three electrode sys-
tem with a silver electrode, a platinum foil and a platinum disk as
the reference, counter and working electrodes, respectively, was
used.
A solution of 3,4-dihydropyrimidinones (0.03 mmol) in 10 ml
of distilled chloroform (c = 3 mM) was irradiated with a 400 W
high pressure mercury lamp in a Pyrex tube while bubbling argon
through the solution at ambient temperature. The reaction was
followed by thin layer chromatography (TLC) until total disap-
pearance of dihydropyrimidinones. The solvent was evaporated at
room temperature under reduced pressure and the products were
recrystallized from n-hexane/ethyl acetate solvent mixture. The
photoproducts 2a–2l were identified with the melting points, IR,
1H NMR, MS and the UV spectra which are reported below.
4.1. 5-Acetyl-6-methyl-4-phenyl-3,4-dihydropyrimidin-2(1H)-one
(1a)
White solid. Mp: 228–230 ◦C (Lit. [20] 233–236 ◦C). IR: ꢁ 1700,
1670, 1600 cm−1. UV (CH3CN): ꢀmax (log ε) 290.5 nm (4.10). 1H
NMR (300 MHz, DMSO-d6): ı 2.10 (s, 3H, CH3), 2.28 (s, 3H, CH3CO),
5.26 (d, J = 3.32 Hz, 1H, 4-H), 7.29 (mc, 5H, H-aromatic), 7.81 (s, 1H,
1-NH), 9.16 (s, 1H, 3-NH).
4.2. 5-Acetyl-6-methyl-4-(4ꢀ-methylphenyl)-3,4-dihydropyrimidin-
2(1H)-one (1b)
White solid. Mp: 234–236 ◦C. IR: ꢁ 1640, 1590, 1505 cm−1. UV
(CH3CN): ꢀmax (log ε) 241.4 nm (3.41) and 288.8 (3.80). 1H NMR
(300 MHz, DMSO-d6): ı 2.07 (s, 3H, CH3), 2.25 (s, 3H, CH3CO),
2.27 (s, 3H, 4ꢀ-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−CH2+, 30).
•+
in the electron transfer to CHCl3 under formation of PM-H2 and
4.3. 5-Acetyl-4-(4ꢀ-methoxyphenyl)-6-methyl-3,4-dihydropyrimidin-
2(1H)-one (1c)
CHCl3•− species, an increase of the rate of photo-oxidation of 1a–1l
is therefore expected.
White solid. Mp: 182–184 ◦C (Lit. [20] 168–170 ◦C). IR: ꢁ 1650,
1580, 1430 cm−1. UV (CH3CN): ꢀmax (log ε) 286.4 nm (3.82).
3. Conclusion
In conclusion, this work describes electron-transfer induced
photo-oxidation of various 5-acetyl-3,4-dihydropyrimidin-2(1H)-
ones to their corresponding pyrimidinones in chloroform solution.
The atmosphere of the reaction mixture (being oxygen or argon)
plays an important role in the rate of reaction and also in the
number, types, and mole ratios of the products. The nature of 4-
substituent is a determining factor in the completion time of the
reaction.
4.4. 5-Acetyl-4-(3ꢀ-methoxyphenyl)-6-methyl-3,4-dihydropyrimidin-
2(1H)-one (1d)
White solid. Mp: 226–228 ◦C (Lit. [21] 228–230 ◦C). IR: ꢁ 1670,
1590, 1425 cm−1. UV (CH3CN): ꢀmax (log ε) 239.6 nm (3.43) and
284.4 (3.88).
4.5. 5-Acetyl-4-(2ꢀ-methoxyphenyl)-6-methyl-3,4-dihydropyrimidin-
2(1H)-one (1e)
4. Experimental
White solid. Mp: 250–252 ◦C. IR: ꢁ 1670, 1580, 1430 cm−1. UV
(CH3CN): ꢀmax (log ε) 240.2 nm (3.90) and 283.6 (4.42). 1H NMR
(300 MHz, DMSO-d6): ı 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 (s, M+,
61), 259 (M+−H, 80), 245 (M+−CH3, 51), 229 (M+−CH3O, 92), 217
(M+−CH3CO, 85), 153 (M+−2-CH3COC6H4, 100).
The acetyl derivatives 1a–1l were prepared by adoption of the
known procedure [19]. Melting points were determined on a Stu-
art Scientific SMP2 apparatus and are uncorrected. IR spectra were
recorded using KBr discs on a Shimadzu IR-435. 1H NMR spec-
tra were obtained with a Bruker 300 MHz instrument. They are
reported as follows: chemical shifts [multiplicity, coupling con-
stants J (Hz), number of protons, and assignment]. Mass spectra

H.R. Memarian et al. / Journal of Photochemistry and Photobiology A: Chemistry 209 (2010) 95–103
101
4.6. 5-Acetyl-4-(4ꢀ-chlorophenyl)–6-methyl-3,4-dihydropyrimidin-
2(1H)-one (1f)
4.12. 5-Acetyl-6-methyl-4-(3ꢀ-nitrophenyl)-3,4-dihydropyrimidin-
2(1H)-one (1l)
White solid. Mp: 249–251 ◦C (Lit. [22] 223–225 ◦C). IR: ꢁ 1690,
1615, 1420 cm−1. UV (CH3CN): ꢀmax (log ε) 240.0 nm (3.77) and
290.6 (4.04).
Yellow solid. Mp: 286–288 ◦C. IR: ꢁ 1650, 1585, 1420 cm−1. UV
(CH3CN): ꢀmax (log ε) 282.6 nm (3.98). 1H NMR (300 MHz, DMSO-
d6): ı 2.19 (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).
4.7. 5-Acetyl-4-(3ꢀ-chlorophenyl)-6-methyl-3,4-dihydropyrimidin-
2(1H)-one (1g)
White solid. Mp: 285–287 ◦C. IR: ꢁ 1700, 1615, 1525 cm−1
.
4.13. 5-Acetyl-6-methyl-4-phenylpyrimidin-2(1H)-one (2a)
UV (CH3CN): ꢀmax (log ε) 291.4 nm (3.08), 239.8 (2.68). 1H NMR
(300 MHz, DMSO-d6): ı 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+37Cl–H, 64), 264 (M+35Cl, 32), 263 (M+35Cl–H, 79), 249
(M+35Cl–CH3, 80), 229 (M+35Cl–35Cl, 42), 223 (M+37Cl–CH3CO,
28), 221 (M+35Cl–CH3CO, 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).
Pale yellow solid. Mp: 162–163 ◦C. IR: ꢁ 1700, 1670, 1590 cm−1
.
UV (CH3CN): ꢀmax (log ε) 307.5 nm (2.31), 249 (2.52). 1H NMR
(300 MHz, DMSO-d6): ı 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): ı = 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).
4.8. 5-Acetyl-4-(2ꢀ-chlorophenyl)-6-methyl-3,4-dihydropyrimidin-
4.14. 5-Acetyl-6-methyl-4-(4’-methylphenyl)pyrimidine-2(1H)-
one (2b)
2(1H)-one (1h)
Pale yellow solid. Mp: 219–221 ◦C. IR: ꢁ 1695, 1590, 1510 cm−1
.
White solid. Mp: 262–264 ◦C. IR: ꢁ 1690, 1615, 1420 cm−1
.
UV (CH3CN): ꢀmax (log ε) 296.5 nm (4.06), 255 (4.06). 1H NMR
(300 MHz, DMSO-d6): ı 1.85 (s, 3H, CH3), 2.29 (s, 3H, CH3CO),
2.50 (s, 3H, 4ꢀ-CH3), 7.31 (d, J = 7.83 Hz, 2H, 2-Hꢀ and 6-Hꢀ), 7.37
(d, J = 8.52 Hz, 2H, 3-Hꢀ and 5-Hꢀ), 12.26 (brd s, 1H, NH). 13C NMR
(75.48 MHz, DMSO-d6): ı = 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).
UV (CH3CN): ꢀmax (log ε) 291 nm (3.99), 240.2 (3.62). 1H NMR
(300 MHz, DMSO-d6): ı 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+37Cl–H,
7), 264 (M+35Cl, 10), 263 (M+35Cl–H, 16), 249 (M+35Cl–CH3, 10),
231 (M+37Cl–37Cl, 6), 229 (M+35Cl–35Cl, 94), 223 (M+37Cl–CH3CO,
6), 221 (M+35Cl–CH3CO, 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).
4.15. 5-Acetyl-4-(4ꢀ-methoxyphenyl)-6-methylpyrimidin-2(1H)-
one (2c)
4.9. 5-Acetyl-4-(4ꢀ-bromophenyl)-6-methyl-3,4-dihydropyrimidin-
2(1H)-one (1i)
Pale yellow solid. Mp: 189–191 ◦C. IR: ꢁ 1670, 1680, 1425 cm−1
.
White solid. Mp: 232–233 ◦C. IR: ꢁ 1650, 1580, 1420 cm−1
.
UV (CH3CN): ꢀmax (log ε) 296.5 nm (4.06), 255 (4.06). 1H NMR
(300 MHz, DMSO-d6): ı 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-Hꢀ and 6-Hꢀ), 7.45
(d, J = 8.52 Hz, 2H, 3-Hꢀ and 5-Hꢀ), 12.18 (brd s, 1H, NH). 13C NMR
(75.48 MHz, DMSO-d6): ı = 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).
UV (CH3CN): ꢀmax (log ε) 290.8 nm (4.04), 240.2 (3.85). 1H NMR
(300 MHz, DMSO-d6): ı 2.12 (s, 3H, CH3), 2.28 (s, 3H, CH3CO), 5.23
(s, 1H, 4-H), 7.18 (d, J = 6.90 Hz, 2ꢀ- and 6ꢀ-H), 7.51 (d, J = 6.77 Hz, 3ꢀ-
and 5ꢀ-H), 7.88 (s, 1H, 1-NH), 9.23 (s, 1H, 3-NH).
4.10. 5-Acetyl-4-(2ꢀ-bromophenyl)-6-methyl-3,4-dihydropyrimidin-
2(1H)-one (1j)
White solid. Mp: 254–257 ◦C. IR: ꢁ 1700, 1620, 1420 cm−1
.
UV (CH3CN): ꢀmax (log ε) 292.2 nm (3.98), 239.8 (3.70). 1H NMR
(300 MHz, DMSO-d6): ı 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+81Br–CH3CO, 10),
265 (M+79Br–CH3CO, 11), 231 (M+81Br–81Br, 2), 229 (M+79Br–79Br,
97), 214 (M+79Br–79Br, –CH3, 13) 168 (2-BrC6H4–CH NH+, 5), 153
(M+−2-BrC6H4, 100).
4.16. 5-Acetyl-4-(3ꢀ-methoxyphenyl)-6-methylpyrimidin-2(1H)-
one (2d)
Pale yellow solid. Mp: 163–164 ◦C. IR: ꢁ 1675, 1595, 1425 cm−1
.
UV (CH3CN): ꢀmax (log ε) 303.5 nm (3.75), 250 (3.88). 1H NMR
(300 MHz, DMSO-d6): ı 1.85 (s, 3H, 6-CH3), 2.28 (s, 3H, CH3CO), 3.80
(s, 3H, 4ꢀ-CH3O), 6.98 (d, J = 7.33 Hz, 2H, 4ꢀ-H), 7.12 (d, J = 8.20 Hz,
2H, 6ꢀ-H), 7.03 (s, 1H, 2ꢀ-H), 7.41 (t, J = 6.67 Hz, J = 7.55 Hz, 1H).
13C-NMR (75.48 MHz, DMSO-d6): ı = 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).
4.11. 5-Acetyl-6-methyl-4-(4ꢀ-nitrophenyl)-3,4-dihydropyrimidin-
2(1H)-one (1k)
Yellow solid. Mp: 229–230 ◦C (dec.) (Lit. [20] 230 ◦C (dec.). IR: ꢁ
1650, 1580, 1520 cm−1. UV (CH3CN): ꢀmax (log ε) 279.2 nm (4.07).

102
H.R. Memarian et al. / Journal of Photochemistry and Photobiology A: Chemistry 209 (2010) 95–103
4.17. 5-Acetyl-4-(2ꢀ-methoxyphenyl)-6-methylpyrimidin-2(1H)-
one (2e)
132.24, 137.40, 156.52, 161.20, 168.92, 201.01. EI-MS: m/z (%):
308 (M+81Br, 38), 307 (M+81Br–H, 32), 306 (M+79Br, 37), 305
(M+79Br–H, 26), 293 (M+81Br–CH3, 81), 291 (M+79Br–CH3, 83), 265
(M+81Br–CH3CO, 6), 263 (M+79Br–CH3CO, 7), 227 (M+−Br, 24), 185
(4-81BrC6H4CH NH+, 16), 183 (4-79BrC6H4CH NH+, 61), 182 (4-
79BrC6H4C NH+, 16), 181 (4-79BrC6H4CN+, 45).
Pale yellow solid. Mp: 166–167 ◦C. IR: ꢁ 1960, 1590, 1550 cm−1
.
UV (CH3CN): ꢀmax (log ε) 303 nm (4.15), 258 (4.15). 1H NMR
(300 MHz, DMSO-d6): ı 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): ı = 30.85, 55.58, 111.78,
119.24, 121.18, 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).
4.22. 5-Acetyl-4-(2ꢀ-bromophenyl)-6-methylpyrimidin-2(1H)-
one (2j)
Pale yellow solid. Mp: 202–204 ◦C. IR: ꢁ 1700, 1615, 1420 cm−1
.
UV (CH3CN): ꢀmax (log ε) 301.5 nm (3.89), 264 (3.86). 1H NMR
(300 MHz, DMSO-d6): ı 1.85 (s, 3H, CH3), 2.37 (s, 3H, CH3CO), 7.43
(mc, 3H, H-aromatic), 7.73 (d, J = 7.82 Hz, 1H, 6-Hꢀ), 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).
4.18. 5-Acetyl-4-(4ꢀ-chlorophenyl)-6-methylpyrimidin-2(1H)-
one (2f)
Pale yellow solid. Mp: 235–237 ◦C. IR:
ꢁ 1650, 1580,
1420 cm−1. UV (CH3CN): ꢀmax (log ε) 313 nm (3.35), 252 (3.56).
1H NMR (300 MHz, DMSO-d6): ı 1.90 (s, 3H, CH3), 2.30 (s,
3H, CH3CO), 7.49 (d, J 8.27 Hz, 2H, 3-Hꢀ and 5-Hꢀ), 7.58 (d,
J = 8.21 Hz, 2H, 2-Hꢀ and 6-Hꢀ), 12.21 (brd s, 1H, NH).). 13C NMR
(75.48 MHz, DMSO-d6): ı = 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+37Cl–H, 32), 262 (M+35Cl, 78), 261
(M+35Cl–H, 59), 249 (M+37Cl–CH3, 69), 247 (M+35Cl–CH3, 99), 227
(M+−Cl, 17), 221 (M+37Cl–CH3CO, 5), 219 (M+35Cl–CH3CO, 13),
140 (4-37ClC6H4C NH+, 42), 139 (4-37ClC6H4CN+, 19), 138 (4-
35ClC6H4C NH+, 87), 137 (4-35ClC6H4CN+, 12).
4.23. 5-Acetyl-6-methyl-4-(4’-nitrophenyl)pyrimidine-2(1H)-
one (2k)
Pale yellow solid. Mp: 265–267 ◦C. IR: ꢁ 1665, 1600, 1505 cm−1
.
UV (CH3CN): ꢀmax (log ε) 330 nm (sh, 3.71), 302 (sh, 3.86), 262.0
(4.07). 1H NMR (300 MHz, DMSO-d6): ı 1.95 (s, 3H, CH3), 2.35 (s, 3H,
CH3CO), 7.73 (d, J = 8.52 Hz, 2H, 2-Hꢀ and 6-Hꢀ), 8.33 (d, J = 8.49 Hz,
2H, 3-Hꢀ and 5-Hꢀ), 9.27 (s, 1H, NH), 12.48 (brd s, 1H, NH). 13C NMR
(75.48 MHz, DMSO-d6): ı = 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).
4.19. 5-Acetyl-4-(3ꢀ-chlorophenyl)-6-methylpyrimidin-2(1H)-
one (2g)
4.24. 5-Acetyl-6-methyl-4-(3’-nitrophenyl)pyrimidine-2(1H)-
one (2l)
Pale yellow solid. Mp: 196–198 ◦C. IR: ꢁ 1650, 1580, 1430 cm−1
.
Pale yellow solid. Mp: 256-258 ◦C. IR: ꢁ 1675, 159, 1520 cm−1
.
UV (CH3CN): ꢀmax (log ε) 320 nm (sh, 3.99), 304 (4.03), 259 (4.18).
1H NMR (300 MHz, DMSO-d6): ı 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): ı = 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+37Cl–H, 23), 262 (M+35Cl,
58), 261 (M+35Cl–H, 38), 249 (M+37Cl–CH3, 45), 247 (M+35Cl–CH3,
100), 227 (M+−Cl, 14), 221 (M+37Cl–CH3CO, 5), 219 (M+35Cl–CH3CO,
9), 140 (3-37ClC6H4C NH+, 36), 139 (3-37ClC6H4CN+, 18), 138 (3-
35ClC6H4C NH+, 78), 137 (3-35ClC6H4CN+, 9).
UV (CH3CN): ꢀmax (log ε) 305.0 nm (3.57), 259.0 (3.85). 1H NMR
(300 MHz, DMSO-d6): ı 1.97 (s, 3H, CH3), 2.35 (s, 3H, CH3CO), 7.80
(t, J = 8.80 Hz, 1H, 5-Hꢀ), 7.88 (d, J = 7.49 Hz, 1H, 6-Hꢀ), 8.29 (s, 1H,
2-Hꢀ), 8.39 (d, J = 7.96 Hz, 1H, 4-Hꢀ), 12.48 (brd s, 1H, NH). 13C-NMR
(75.48 MHz, DMSO-d6): ı = 32.68, 123.37, 125.69, 130.96, 134.92,
148.28. EI-MS: m/z (%): 273 (M+, 15), 272 (M+−H, 8), 258 (M+−CH3,
100), 256 (M+−OH, 30), 226 (M+−HNO2, 16).
Acknowledgements
4.20. 5-Acetyl-4-(2ꢀ-chlorophenyl)-6-methylpyrimidin-2(1H)-
one (2h)
We are thankful to the Center of Excellence (Chemistry),
Research Council and Office of Graduate Studies of the University
of Isfahan for their financial support.
Pale yellow solid. Mp: 175–176 ◦C. IR: ꢁ 1700, 1620, 1430 cm−1
.
UV (CH3CN): ꢀmax (log ε) 305 nm (3.34), 259 (3.45). 1H NMR
(300 MHz, DMSO-d6): ı 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-d6): ı = 20.23, 31.50, 119.22, 127.88, 130.06,
130.54, 131.00, 131.61, 137.32, 156.67, 163.00, 198.89. EI-MS: m/z
(%): 247 (M+35Cl–CH3, 5), 227 (M+−Cl, 100), 219 (M+35Cl–CH3CO,
3), 140 (2-37ClC6H4C NH+, 24), 139 (2-37ClC6H4CN+, 13) 138 (2-
35ClC6H4C NH+, 47), 137 (2-35ClC6H4CN+, 8).
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jphotochem.2009.10.012.
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4.21. 5-Acetyl-4-(4ꢀ-bromophenyl)-6-methylpyrimidin-2(1H)-
one (2i)
Pale yellow solid. Mp: 239–240 ◦C. IR: ꢁ 1670, 1620, 1420 cm−1
.
UV (CH3CN): ꢀmax (log ε) 322 nm (sh, 2.36), 304 (sh, 3.48), 252
(3.76). 1H NMR (300 MHz, DMSO-d6): ı 1.91 (s, 3H, CH3), 2.30
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