Light induced oxidation of 2,3-dihydroquinazolin-4(1H)-ones

Article abstract of DOI:10.1016/j.jphotochem.2013.07.008

Light induced oxidation of various of 2-substituted 2,3-dihydroquinazolin- 4(1H)-ones (DHQZs) results smoothly the formation of quinazolin-4(3H)-ones (QZs) product. The electronic nature of the substituent on the 2-position and also the nature of solvent

Full text of DOI:10.1016/j.jphotochem.2013.07.008

Accepted Manuscript
Title: Light induced oxidation of
2,3-dihydroquinazolin-4(1H)-ones
Author: Hamid R. Memarian Saeid Ebrahimi
PII:
S1010-6030(13)00320-1
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.jphotochem.2013.07.008
JPC 9476
To appear in:
Journal of Photochemistry and Photobiology A: Chemistry
Received date:
Revised date:
Accepted date:
28-4-2013
18-7-2013
21-7-2013
Please cite this article as: H.R. Memarian, S. Ebrahimi, Light induced oxidation of
,3-dihydroquinazolin-4(1H)-ones, Journal of Photochemistry and Photobiology A:
2
Chemistry (2013), http://dx.doi.org/10.1016/j.jphotochem.2013.07.008
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1
Light induced oxidation of 2,3-dihydroquinazolin-4(1H)-ones
Hamid R. Memarian* and Saeid Ebrahimi
Department of Chemistry, University of Isfahan, Isfahan 81746-73441, I.R. Iran.
ABSTRACT
Light induced oxidation of various of 2-substituted 2,3-dihydroquinazolin-4(1H)-ones
DHQZs) results smoothly the formation of quinazolin-4(3H)-ones (QZs) product. The
(
electronic nature of the substituent on the 2-position and also the nature of solvent affect the
rate of reaction, which supports the proposed mechanism based on the electron-transfer
induced photo-oxidation. Analysis of the computational results obtained at the DFT-
B3LYP/6-31++G** level of theory supports the mechanism in which the first electron
removal occurs preferably from the N1 atom of the heterocyclic ring. In contrast to the
solution photochemistry, no changes have been observed by irradiation in the solid state.
Keywords: 2,3-Dihydroquinazolin-4(1H)-one; Electron transfer; Photo-oxidation;
Quinazolin-4(3H)-one.
_
_____________
*
Corresponding author: Fax: +311 668 9732, Phone: +98 311 793 2707.
E-mail address: memarian@sci.ui.ac.ir (H. R. Memarian),
1
. Introduction
2
,3-Dihydroquinazolin-4(1H)-ones (DHQZs) and the corresponding oxidation products,
quinazolin-4(3H)-ones (QZs) are interested to the medicinal chemists due to their various
biological activities such as antibacterial, anticonvulsant, anticancer, antifungal, anti-
inflammatory, antitumor agents [1-6]. Various works are devoted to the synthesis of
Page 1 of 24

2
quinazolin-4(3H)-ones either by oxidation of 2,3-dihydroquinazolin-4(1H)-ones using
suitable oxidizing agents [7,8] or by various condensation procedures [9-13]. Since many
pharmaceutical compounds may lose or increase their biological activities due to some
molecular changes upon exposure to the UV light, therefore, the knowledge on the light
sensitivity of these drugs is important. Surprisingly little is known about photochemical
behavior of the title compound.
Our previous studies concerning the light sensitivity of heterocyclic compounds with
pharmaceutical activities, namely 1,4-dihydropyridines [14] and 2-oxo-1,2,3,4-
tetrahydropyrimidines [15] (Scheme 1), indicate that the electronic nature and the steric
hindrance of the substituent on the C4-saturated carbon atom of the heterocyclic ring affects
the rate of photo-oxidation (or photo-dehydrogenation). In continuation to these works, we
were interested to investigate the electronic nature of the substituent on the 2-position of the
heterocyclic ring in 2,3-dihydroquinazolin-4(1H)-ones on the readiness of photo-oxidation.
Scheme 1
2
. Results and Discussion
To elucidate the effect of the nature of solvent on the readiness of the photo-oxidation of
DHQZs, irradiation of compound 1a as test substance in acetonitrile, chloroform and ethanol
was followed by UV spectroscopy. The UV reaction spectra show a hypsochromic shift and
also a decrease in the absorption of 1a at longer wavelength due to oxidation of the
heterocyclic ring and formation of 2a. The reaction spectra presented in Figure 1 show some
isosbestic points which indicate of a clean reaction and smooth conversion of 1a to 2a. A
comparison of the slope in the extinction vs. time diagrams (ET-diagrams) [16] at 360 nm in
all three solvents shown in Fig. 1 indicate a comparative fast reaction in CHCl with those in
3
Page 2 of 24

3
acetonitrile and ethanol. It should be noted that in contrast to the solution photochemistry, no
changes have been observed by irradiation in the solid state.
Figure 1
Based on these results, a solution of 0.05 mmol (1a-1m) in 50 mL air saturated CHCl3
was irradiated until maximum progression of the reaction (Scheme 2). Most of products were
precipitated on irradiation and due to screening effect, the reactions were interrupted. The
results are summarized in Table 1.
Scheme 2
Table 1
1
13
IR, UV, H NMR, C NMR and MS data gave useful information on the structural
assignment of the photoproducts, quinazolin-4(3H)-ones (2a-2k, 2m) and quinazolin-4(1H)-
ones (3k, 3l), due to the photo-oxidation of the corresponding 2,3-dihydroquinazolin-4(1H)-
ones (1a-1m). A comparison of the UV data, presented in Table 2, shows hypsochromic shift
and also hyperchromic effect in the spectra of the products due to oxidation of the
heterocyclic ring upon removal of two hydrogens and formation of a quasi-aromatic
heterocyclic ring system.
Table 2
A comparison of the IR spectra showed a decrease in the intensity of the NH vibration
and small shift of the CO stretching to higher frequency upon removal of two hydrogens from
N1 and C2 atoms, formation of C=N double bond and reduced conjugation of N3 lone pair
with the 4–CO group due to cross conjugation with the imine moiety.
Page 3 of 24

4
1
Analysis of the H NMR spectra of the products shows a shift of 3–NH to lower field, a
lack of 1–NH and 2–H due to being eliminated upon oxidation, and low field shift of the
aromatic protons. It should be noted that in the case of the photoproduct 2k the formation of
quinazolin-4(1H)-ones (3k) is also observed which is proved by different chemical shifts and
H/D exchange of both 3H (at 12.72 ppm) and 1H (at 3.62 ppm) peaks. Due to the observed
sharp melting point for the photoproduct obtained by the irradiation of 1k, we assumed that
the compounds 2k and 3k are tautomeric mixtures, which are present in the solution. The
results of computational studies indicate that quinazolin-4(3H)-ones are energetically more
stable than the corresponding quinazolin-4(1H)-ones [18]. In the case of 3l, the observed
broad singlet at 4.56 ppm for the NH proton indicate that only 2-(4-Pyridyl)quinazolin-
4
(1H)-one (3l) is formed.
The data shown in Table 1 indicate that the electronic nature of 2-substitution plays an
important role on the progress of the photo-oxidation. It is expected that the balance of the
positive resonance (+M) and the negative inductive (–I) effects of the electron-donating
substituents such as methoxy group or halogen atoms increases the electron density on the
aromatic ring, which displays on the reduced irradiation times. While the presence of the
electron-withdrawing nitro group (–M and –I) causes a decrease on the electron density on
the aromatic ring and retarded the reaction. The observed electronic effect of the substituent
and also the effective role of CHCl as solvent in the reaction support our previous proposed
3
mechanism as Electron-transfer Induced Photo-oxidation of organic compounds. It should be
noted that as a control experiment, irradiations of 1a as representative under oxygen and
argon atmospheres are carried out. The reaction spectra and the corresponding extinction time
diagrams presented as supporting material shown that the rate of reaction is not significantly
affected by the presence of oxygen or argon atmosphere, therefore, the role of oxygen as an
electron-acceptor species is ruled out. According to the proposed mechanism and due to the
Page 4 of 24

5
failure of reaction in the absence of UV exposure, excited 2,3-dihydroquinazolin-4(1H)-ones
*
+
–
(
DHQZ ) donates an electron to chloroform with formation of DHQZ· and CHCl · species
3
in the first electron transfer step. Elimination of HCl from both intermediates in the next step
leads to the formation of a radical pair, namely hydroquinazolinyl (HQZ·) and
dichloromethyl (·CHCl ) radicals. The second electron transfer step and followed proton
2
removal complete the reaction under formation of the quinazolin-4(3H)-ones, QZ (3H) and/or
quinazolin-4(1H)-ones QZ (1H), and dichloromethane. The formation of dichloromethane
during the reaction, which has been proved by GC-analysis of the reaction mixture and by
testing for acidity of the solution after irradiation (due to formation of HCl), support the
proposed electron transfer mechanism for this conversion, in which chloroform is involved in
the reaction as an electron acceptor species (Scheme 3). We have measured the oxidation
+
potential for some compounds considered in the present study in chloroform vs. Fe/Fe . The
obtained values are 1a, E = 1.131 V; 1c, E = 1.146 V and 1f, E = 1.410 V. Under our
ox
ox
ox
experimental condition for cyclic voltammetric studies, we did not observe any peak between
and 2 V for the oxidation of chloroform. The ΔG values for the reaction (in kJ/mol) can be
0
calculated from the simplified Rehm-Weller Equation [19].
ΔG = 96.5 (E – E ) – E
s
ox
red
Where E and E are the singlet energy and the oxidation potential of DHQZs, respectively,
s
ox
and Ered is the reduction potential of chloroform. The calculated ΔGs for 1a, 1c and 1f, –
0.71, –17.86, and –0.05 kJ/mol, respectively, indicate that the electron-transfer process is
5
exothermic. Other studies have also proposed this mechanism for the photo-oxidation of
symmetrical 1,4-dihydropyridines in CCl [20] and CBrCl solutions [21, 22], unsymmetrical
4
3
1
,4-dihydropyridines [14], and 2-oxo-1,2,3,4-tetrahydropyrimidines [15] in CHCl solution.
3
Page 5 of 24

6
The slower reaction in acetonitrile relative to chloroform can be explained by comparison of
the reduction potentials of both solvents. The reduction potentials of acetonitrile and
+
chloroform are reported −3.1 V and −1.77 V (vs. Fc / Fc, Ferrocene), respectively [23, 24].
Ethanol seems also to be a very poor electron acceptor solvent due to failure of d-orbital on
its oxygen or carbon-atoms. The calculated ΔG for 1a in acetonitrile, as representative,
+
75.22 kJ/mol (E = 1.106 V) indicates of an endothermic reaction in this solvent, which
ox
supports of a slower reaction compared to that in chloroform solution. Therefore, according
to the proposed mechanism, the electron-transfer from excited DHQZs (DHQZ*) to CHCl3
should occur faster than that to CH CN and C H OH.
3
2
5
The important point in the present study is indicating the suitable position in the
molecule for donation of an electron to CHCl . These positions in the heterocyclic ring are
3
+
+
either the lone pair on the N1 or N3 atoms under formation of DHQZ(N1)· and DHQZ(N3)·
intermediates after the first electron removal. The results of the computational studies, using
the DFT B3LYP method with the 6-31++G** basis set, on these compounds can partially
help us in this regard. A comparison of the NBO (Natural bond orbital) spin densities in the
+
DHQZ· radical cation (Table 3), obtained after the first electron removal from excited 2,3-
*
dihydroquinazolin-4(1H)-ones (DHQZ ) indicates that the N1 atom in the heterocyclic ring
preferably donates this electron and as expected the spin density on the N3 atom remains
unchanged. Following points support the suggestion that the first electron removal should be
occurred from N1 atom rather than N3 atom:
1
.
After electron removal from either N1 or N3 atoms, the radical cation species formed
+
on the N1 atom in DHQZ(N1)· as azabenzyl radical cation is stabilized via delocalization
of the radical center over the adjacent aromatic ring, whereas the radical cation species
+
formed on the N3 atom in DHQZ(N3)· is destabilized because of the presence of adjacent
electron-withdrawing carbonyl group. The change of the observed spin densities on the C4a,
Page 6 of 24

7
C6 and C8 atoms of the condensed benzene ring (Table 3) is the evident on the radical
+
delocalization in DHQZ(N1)· species.
2
.
Possible delocalization of the nitrogen lone pair on the N3 atom toward the electron-
withdrawing oxygen atom of the carbonyl group (amide moiety) in DHQZ decreases the
electron-donor ability of this atom to any electron-acceptor species present in the medium.
3
.
As usual by any electron-transfer process (ET), back electron transfer process (BET)
is also possible especially for unstable radical cation species. Therefore, BET process is
+
expected being faster for DHQZ(N3)· intermediate (dashed line) than those for
+
DHQZ(N1)· intermediate (solid line).
Scheme 3
Table 3
+
The first proton detachment from both possible DHQZ· radical cation species leads to
the formation of hydroquinazolinyl radical (HQZ·) as simultaneously benzylic radical and
also donor-substituted radical (dative radical). This radical center is stabilized either via
delocalization over the aromatic ring located on the C2 position and also by interaction with
the nitrogen lone pairs on the N1 or N3 atoms. The stability of the benzylic radical is affected
by coplanarity of the aromatic ring with the radical center
The interesting result is a comparison of the irradiation time for over 95% conversion of
2
-methoxy (1b) and 4-methoxy compounds (1c), 25 and 45 minutes, respectively. This can be
explained by the following suggestions:
Delocalization of the oxygen lone pair of the methoxy group on the right position of
the aromatic ring (2 or 4-positions) increases the electron density on the C-aromatic ring
C10) attached to the C2 of the heterocyclic ring. Therefore, the aryl ring acts as an
1
.
(
Page 7 of 24

8
electron-pushing group via the σ-bond towards the N1 atom. This increases the electron
density on the N1 atom and displays on the reducing of the irradiation time.
3
2
2
.
This delocalization requires rehybridization of the oxygen atom (from sp to sp ) and
planarity of this group with the aromatic ring. Due to steric hindrance of 2-methoxy group
with the heterocyclic ring, there is only one possible way for 2-CH O group to contribute
3
increasing the ring’s electron density (upward orientation of the group), whereas 4-CH O
3
group has two possible ways for this contribution. Therefore, it is expected that 4-CH O
3
group increases the electron density of the aromatic ring effectively than 2-CH O group.
3
The measured oxidation potentials for 1b and 1c, 1.171 V and 1.146 V, respectively,
support this suggestion. Thus, the shorter irradiation time should be expected for the former
case, which is not observed in the present study.
3.
In the case of 2-CH O group, possible intramolecular interaction between the oxygen
3
atom and the hydrogen of the N1–H moiety decreases the electron donating character of this
group on the 2-position. Based on this suggestion, a shorter irradiation time should be
expected for compound 1c with 4-CH O group, which is not observed.
3
Plausible explanation for the observed irradiation times is considering an alternative or
possible site for the electron-transfer process in this study. Analysis of the NBO spin
densities indicate that in the case of the electron-donating substituent on the C2-position (2-
or 4-methoxyphenyl group), the aromatic ring competes with the N1–atom in the electron
donation process to CHCl . Back electron-transfer (BET) process is possible for both cases.
3
·+
In contrast to N1H intermediate, in which the proton detachment from this species under
formation of hydroquinazolinyl radical (HQZ·) is possible, the radical cation formed on the
methoxyphenyl group should only accept an electron and returning back to the neutral
molecule DHQZ. As mentioned above, the methoxy group on the 4-position compared to
this group on the 2-position increases more the electron density on the phenyl ring, which
Page 8 of 24

9
can compete with the N1–atom in the first electron transfer step, therefore, irradiation time
for compound 1b with the methoxy group on the 2-position is shorter than compound 1c
with this group on the 4-position.
3
. Conclusion
The present work describes electron-transfer induced photo-oxidation of 2-substituted
,3-dihydroquinazolin-4(1H)-ones to their corresponding quinazolin-4(3H)-ones in
2
chloroform as an efficient electron-acceptor species. In two cases the formation of
quinazolin-4(1H)-ones is also observed. The nature of 2-substitution is a determining factor
in the completion time of the reaction.
4
. Experimental
2
-Substituted 2,3-dihydroquinazolin-4(1H)-ones were synthesized by adoption of the
known procedure [25]. Melting points were determined on a Stuart Scientific SMP2
apparatus and are not corrected. IR spectra were recorded from KBr-discs on a Jasco FT/IR-
1
13
6
300 spectrometer. The H and C NMR spectra (DMSO-d ) were recorded on Bruker
6
1
Avance III 400 spectrometers at 400 and 100.62 MHz. The H NMR spectra are reported as
follows: chemical shifts, [multiplicity, number of protons, coupling constants J (Hz), and
assignment]. Mass spectra were obtained on Platform II Mass Spectrometer from Micromass;
EI mode at 70 eV. UV spectra were taken with Shimadzu UV-160 spectrometer. All
irradiations were performed using a 400 W high-pressure Hg-vapor lamp from NARVA. The
cyclic voltammetry (CV) measurements were performed using SAMA 500
Potentio/Galvanostat. All electrochemical experiments were carried out in a conventional
three electrode system at room temperature. A silver electrode, a large area Pt plate (99.99%),
Page 9 of 24

1
0
and a glass carbon electrode (GCE) were used as reference, counter and working electrodes,
respectively.
General procedure for the irradiation of 2-substituted 2,3-dihydroquinazolin-4(1H)-ones.
A solution of 0.05 mmol (1a-m) in 50 mL air saturated CHCl was irradiated. The
3
progress of reaction was followed until maximum progression of the reaction (the
corresponding irradiation times are given in Table 2). The solvent was evaporated and the
product was isolated by recrystallization from appropriate solvent to afford the corresponding
quinazolin-4(3H)-ones.
Physical and spectroscopic data of some new 2,3-dihydroquinazolin-4(1H)-ones and new
quinazolin-4(3H)-ones.
4
.1. 2-(2-Pyridyl)-2,3-dihydroquinazolin-4(1H)-one (1j)
M. p. 191-193˚C, recrystallized from ethanol, 38 %. IR (KBr): ν = 3293, 3189, 3079, 2923,
-1 1
1
665, 1613, 1513, 1130, 754, 685 cm . H NMR (400 MHz, DMSO-d ): δ = 5.71 (m , 1H,
6 c
N1–H), 6.66 ( m , 1H, C –H), 6.75 (m , 1H, aromatic H), 7.23 (m , 2H, aromatic H), 7.35
c
2
c
c
(
m , 1H, pyridine H), 7.50 (m , 1H, pyridyl H), 7.61 (m , 1H, pyridyl H), 7.83 (m , 1H,
c c c c
1
3
pyridyl H), 8.36 (s, 1H, CONH), 8.55 ppm (m , 1H, pyridyl H). C NMR (100 MHz, DMSO-
c
d ): δ = 67.22 (C ), 114.39, 114.85, 116.99, 120.47, 123.42, 127.21, 133.27, 137.04, 147.32,
6
2
+
+
1
1
7
3
48.94, 160.23, 163.29 ppm. MS (EI, 70 eV): m/z (%) = 225 (M , 17), 181 (M –CONH ,
2
+
+
+
+
8), 104 (C H CO , 69), 147 (M –C H N, 100), 120 (C H CONH , 72), 92 (C H NH , 26),
6
4
5
4
6
4
2
6
4
2
+
+
8 (C H N , 96), 43 (CONH , 86). UV (CHCl ): λ (log ε) = 340.0 nm (sh, 3.52), 325 (sh,
5
4
3
max
.63), 330 (sh, 3.59), 305 (sh, 3.65), 255 (4.07).
4
.2. 2-(3-Pyridyl)-2,3-dihydroquinazolin-4(1H)-one (1k)
Page 10 of 24

1
1
M. p. 225-227˚C, recrystallized from ethyl acetate, 44 %. IR (KBr): ν = 3445, 3262, 3064,
-
1 1
2
1
844, 1658, 1615, 1521, 1130, 754, 713 cm . H NMR (400 MHz, DMSO-d ): δ = 5.86 (s,
6
H, N1–H), 6.71 (m , 1H, aromatic H), 6.76 (m , 1H, aromatic H), 7.17 (s, 1H, C –H), 7.27
c
c
2
(
m , 1H, aromatic H), 7.44 (m ,1H, pyridyl H), 7.63 (m , 1H, aromatic H), 7.9 (m , 1H,
c c c c
pyridyl H), 8.38 (s, 1H, CONH), 8.56 (m , 1H, J = 1.6 Hz, pyridyl H), 8.67 ppm (m , 1H,
c
c
13
pyridyl H). C NMR (100 MHz, DMSO-d ): δ = 64.63 (C ), 114.52, 115.00, 117.46, 123.50,
6
2
1
27.36, 133.43, 134.60, 136.78, 147.67, 148.35, 149.65, 163.53 ppm.MS (EI, 70 eV): m/z
+
+
+
+
(
(
(
%) = 225 (M , 5), 147 (M –C H N, 73), 120 (C H CONH , 31), 92 (C H NH , 35), 78
5 4 6 4 2 6 4 2
+
+
+
C H N , 40), 57 (CONHCH , 95), 43 (CONH , 100). UV (CHCl ): λ (log ε) = 332.2 nm
5
4
2
3
max
3.64), 247.4 (4.09).
4
.3. 2-(4-Pyridyl)-2,3-dihydroquinazolin-4(1H)-one (1l)
M. p. 162-164˚C, recrystallized from ethyl acetate, 50 %. IR (KBr): ν = 3286, 3171, 3028,
-1 1
2
921, 1658, 1611, 1512, 1160, 744, 691cm . H NMR (400 MHz, DMSO-d ): δ = 5.8 (s, 1H,
6
N1–H), 6.7 (m , 1H, aromatic H), 6.79 (m , 1H, aromatic H), 7.27 (m , 1H, aromatic H), 7.33
c
c
c
(
s, 1H, C –H), 7.46 (m , 2H, pyridyl H), 7.61 (m , 1H, aromatic H), 8.52 (s, 1H, CONH), 8.58
2 c c
13
ppm (m , 2H, pyridyl H). C NMR (100 MHz, DMSO-d ): δ = 64.73 (C ), 114.48, 114.52,
c
6
2
1
14.96, 117.39, 117.43, 121.54, 127.34, 133.49, 147.23, 149.72, 150.58, 163.27 ppm. MS
+
+
+
+
(
EI, 70 eV): m/z (%) = 225 (M , 5), 197 (M –CO, 5), 181 (M –CONH ), 147 (M –C H N,
2 5 4
+
+
+
1
00), 120 (C H CONH , 85), 119 (C H CONH , 89), 104 (C H NHCH , 58), 92
6
4
2
6
4
6
4
+
+
+
(
C H NH , 97), 78 (C H N , 89), 43 (CONH ,47 ). UV (CHCl ): λ (log ε) = 340 nm (sh,
6
4
2
5
4
3
max
3
.27), 300 (sh, 3.58), 280 (sh, 3.93), 260 (4.04).
4
.4. 2-(5-Methyl-2-furyl)-2,3-dihydroquinazolin-4(1H)-one (1m)
Page 11 of 24

1
2
M. p. 182-184˚C, recrystallized from ethanol, 55 %. IR (KBr): ν = 3287, 3189, 3069, 2923,
-1 1
2
861, 1645, 1611, 1514, 1124, 1010, 772, 757 cm . H NMR (400 MHz, DMSO-d ): δ = 2.22
6
(
s, 3H, CH ), 5.69 (s, 1H, N1–H), 5.99 (m , 1H, furyl H), 6.13 (m , 1H, furyl H), 6.67 (m ,
3 c c c
1
6
1
1
H, aromatic H), 6.67 (m , 1H, aromatic H), 7.17 (s, 1H, C –H), 7.24(m , 1H, aromatic H),
c 2 c
1
3
.61 (m , 1H, aromatic H), 8.34 ppm (s, 1H,.CONH). C NMR (100 MHz, DMSO-d ): δ =
c
6
3.29 (CH ), 60.26 (C ), 106.29, 108.09, 114.45, 114.90, 117.12, 127.22, 133.19, 147.14,
3
2
+
+
51.39, 152.50, 163.25 ppm. MS (EI, 70 eV): m/z (%) = 228 (M , 19), 213 (M –CH , 5), 185
3
+
+
+
+
(
CONH , 9), 147 (M –5-methyl-2-furyl, 24), 120 (C H CONH , 100), 108 (M –
6 4 2
+
+
+
C H CONH , 14), 92 (C H NH , 72), 81 (5-methyl-2-furyl , 28), 43(CONH , 86). UV
6
4
2
6
4
2
(
CHCl ): λ (log ε) = 329.8 nm (3.34), 245 (3.82).
3 max
4
.5. 2-(2-Nitrophenyl)quinazolin-4(3H)-one (2c)
M. p. 229-230˚C, recrystallized from ethanol. IR (KBr): ν = 3435, 2919, 1663, 1604, 1526,
-1 1
1
463, 1352, 1111, 776, 716 cm . H NMR (400 MHz, DMSO-d ): δ = 7.59 (m , 1H, aromatic
6 c
H), 7.67 (m , 1H, aromatic H), 7.89 (m , 4H, aromatic H), 8.21(m , 1H, aromatic H), 12.84
c
c
c
13
ppm (s, 1H, CONH). C NMR (100 MHz, DMSO-d ): δ = 121.13, 124.50, 125.85, 127.10,
6
1
27.31, 129.12, 131.46, 131.52, 133.90, 134.64, 147.42, 148.47, 151.62, 161.45 ppm. MS
+
+
+
+
(
EI, 70 eV): m/z (%) = 267 (M , 21), 221 (M –NO , 6), 191 (M –C H , 3), 163 (M –
2 6 4
+
+
+
C H CO, 4), 145 (M –C H NO , 2), 135 (2-NO C H CH , 41), 119 (M –2-NO C H CN,
6
4
6
4
2
2
6
4
2
6
4
+
+
+
+
+
1
4
00), 104 (C H CO , 25), 92 (C H NH , 42), 90 (C H N , 98), 76 (C H , 95), 43 (CONH ,
6 4 6 4 2 6 4 6 4
9). UV (CHCl ): λ (log ε) = 306.2 nm (4.34), 295 (sh, 4.28), 248.2 (4.06).
3
max
4
.6. 2-(4-Fluorophenyl)quinazolin-4(3H)-one (2i)
M. p. 279-280˚C, recrystallized from n-hexane/ethyl acetate. IR (KBr): ν = 3172, 2958, 1675,
-1 1
1
608, 1484, 1236, 841, 765 cm . H NMR (400 MHz, DMSO-d ): δ = 7.41(m , 2H, aromatic
6 c
Page 12 of 24

1
3
H), 7.54(m , 1H, aromatic H), 7.85(m , 2H, aromatic H), 8.16 (m , 1H, aromatic H), 8.26 (m ,
c
c
c
c
1
3
2
1
H, aromatic H), 12.59 (s, 1H, CONH) ppm. C NMR (100 MHz, DMSO-d ): δ = 115.51,
6
15.73, 125.82, 126.61, 127.45, 130.31, 130.40, 134.64, 162.82, 165.26 ppm. MS (EI, 70
+
+
+
+
+
eV): m/z (%) = 240 (M , 22), 212 (M –CO, 2), 149 (M –C H NH , 42), 145 (M –C H F,
6
4
6
4
+
+
+
+
1
7
2
0), 136 (M –C H CO, 2), 122 (4-FC H CNH , 33), 119 (C H CONH , 100), 95 (C H F ,
6 4 6 4 6 4 6 4
+
+
0), 76 (C H , 10), 57 (90), 43 (CONH , 68). UV (CHCl ): λ (log ε) = 325 nm (sh, 3.69),
6
4
3
max
92.8 (3.93), 245.2 (4.04).
4
.7. 2-(2-Pyridyl)quinazolin-4(3H)-one (2j)
M.p. 165-166˚C, recrystallized from ethanol. IR (KBr): ν = 3250, 3967, 1667, 1602, 1563,
-
1
1
1
7
136, 803, 776 cm . H NMR (400 MHz, DMSO-d ): δ = 7.58 (m , 1H, aromatic H),
6 c
.67 (m , 1H, aromatic H), 7.82 (m , 1H, aromatic H), 8.89 (m , 1H, pyridyl H), 8.09 (m , 1H,
c
c
c
c
pyridyl H), 8.20 (m , 1H, aromatic H), 8.47 (m , 1H, pyridyl H), 8.75 (m , 1H, pyridyl H),
c
c
c
1
3
1
1
1.83 ppm (s, 1H, CONH). C NMR (100 MHz, DMSO-d ): δ = 122.14, 126.08, 126.57,
6
27.25, 127.69, 134.68, 137.98, 148.41, 148.65, 148.97, 149.90, 160.68, 206.45 ppm. MS
+
+
+
+
(
EI, 70 eV): m/z (%) = 223 (M , 25), 195 (M –CO, 25), 119 (M –PyCN, 100), 105 (PyCN ,
+
+
+
+
3
8), 90 (C H N , 54), 78 (C H N , 57), 76 (C H , 23), 43(CONH , 43). UV (CHCl ): λ
6 5 6 5 6 4 3 max
(log ε) = 340 nm (sh, 3.57), 325.4 (3.85), 307.4 (3.92), 243.8 (3.87).
4
.8. 2-(3-Pyridyl)quinazolin-4(3H)-one (2k)/ 2-(3-Pyridyl)quinazolin-4(1H)-one (3k)
M.p. 273-274 ˚C, recrystallized from ethanol. IR (KBr): ν = 3436, 3039, 1677, 1605, 1563,
-
1 1
1
1
152, 768, 710 cm . H NMR (400 MHz, DMSO-d ): δ = 3.62 (brd s, N1–H, 3k), 7.57 (m ,
6 c
H, aromatic H), 7.62 (m , 1H , aromatic H), 7.78 (m , 1H , aromatic H), 7.87 (m , 1H,
c
c
c
pyridyl H), 8.18 (m , 1H, aromatic H), 8.53 (m , 1H, pyridyl H), 8.78 (m , 1H, pyridyl H),
c
c
c
1
3
9
.31 ppm (m , 1H, pyridyl H), 12,72 (brd s, N –H, 1k). C NMR (100 MHz, DMSO-d ): δ =
c 3 6
Page 13 of 24

1
4
1
1
21.10, 123.62, 125.86, 126.97, 127.49, 128.77, 134.69, 135.69, 148.41, 148.47, 150.61,
+
+
51.51, 162.04 ppm. MS (EI, 70 eV): m/z (%) =223 (M , 5), 119 (M –PyCN, 29), 90
+
+
+
+
+
(
C H N , 14), 78 (C H N , 18), 76 (C H , 15), 57 (CONHCH , 67), 43 (CONH , 100). UV
6 5 6 5 6 4 2
(
CHCl ): λ (log ε) = 303.6 nm (4.23), 295 (sh, 4.21), 245.8 (4.17).
3
max
4
.9. 2-(4-Pyridyl)quinazolin-4(1H)-one (3l)
M.p. 274-275 ˚C, recrystallized from ethyl acetate. IR (KBr): ν = 3434, 3028, 1678, 1598,
-1 1
1
553, 1149, 830, 771 cm . H NMR (400 MHz, DMSO-d ): δ = 4.56 (brd s, N1–H), 7.63
6
(
m , 1H, aromatic H), 7.83 (m , 1H, aromatic H), 7.92 (m , 1H, aromatic H), 8.21 (m , 1H,
c c c c
1
3
aromatic H), 8.38 (m , 2H, pyridyl H), 8.95 (m , 2H, pyridyl H). C NMR (100 MHz,
c
c
DMSO-d ): δ = 121.57, 122.99, 125.96, 127.85, 127.89, 134.90, 143.13, 147.26, 147.97,
6
+
+
+
1
49.60, 161.88 ppm. MS (EI, 70 eV): m/z (%) =223 (M , 12), 195 (M –CO, 12), 119 (M –
+
+
+
+
PyCN,79), 105 (PyCN , 28), 92 (C H NH , 38), 90 (C H N , 48), 78 (C H N , 40),76
6
4
2
6
5
6
5
+
+
+
(
C H , 37), 57 (CONHCH , 57), 43 (CONH ,100). UV (C H OH): λ (log ε) = 350 nm
6 4 2 2 5 max
(3.19), 305 (sh, 4.04), 295 (4.09), 275 (sh, 4.08), 235 (4.12).
4
.10. 2-(5-Methyl-2-furyl)quinazolin-4(3H)-one (2m)
M.p. 191-192 ˚C, recrystallized from ethanol. IR (KBr): ν = 3447, 3058, 1673, 1600, 1562,
-1 1
1
149, 909, 772 cm . H NMR (400 MHz, DMSO-d ): δ = 2.09 (s, 3H, CH ), 6.38 (m , 1H,
6 3 c
furyl H), 7.48 (m , 1H, aromatic H), 7.56 (m , 1H, furyl H), 7.69 (m , 1H, aromatic H), 7.80
c
c
c
1
3
(
m , 1H, aromatic H), 8.11 (m , 1H, aromatic H), 12.37 ppm (s, 1H, CONH). C NMR (100
c
c
MHz, DMSO-d ): δ = 13.54, 108.94, 115.86, 120.92, 125.87, 126.16, 127.04, 134.57, 144.38,
6
+
+
+
1
56.16, 161.57 ppm. MS (EI, 70 eV): m/z (%) = 226 (M , 23), 211 (M –CH , 9), 197 (M –
3
+
+
+
CO, 13), 145 (M –5-Methyl-2-furyl, 12), 90 (C H N , 55), 81 (5-Methyl-2-furyl , 21), 43
6
5
+
(
CONH , 100). UV (CHCl ): λ (log ε) = 335 nm (sh, 3.67), 313.8 (3.84), 244 (3.70).
3 max
Page 14 of 24

1
5
Acknowledgement
We are thankful to the Research Council and Office and Office of Graduate Studies of
the University of Isfahan for their financial support.
References
[
[
[
1] N. B. Patel, J. C. Patel, Synthesis and antimicrobial activities of 2-azetidinyl-4-
quinazolinone derivatives of diclofenac analogue, Med. Chem. Res. 20 (2011) 511-
5
21.
2] N. D. Amnerkar, K. P. DandBhusari, Synthesis, anticonvulsant activity and 3D-
QSAR study of some prop-2-eneamido and 1-acetyl-pyrazolin derivatives of
aminobenzothiazole, Eur. J. Med. Chem. 45 (2010) 149-159.
3] A. Kamal, E. V. Bharathi, J. S. Reddy, M. J. Ramaiah, D. Dastagiri, M. K. Reddy, A.
Viswanath, T. L. Reddy, T. B. Shaik, S.N.C.V.L. Pushpavalli, M. P. Bhadra,
Synthesis and biological evaluation of 3,5-diaryl isoxazoline/isoxazole linked 2,3-
dihydroquinazolinone hybrids as anticancer agents, Eur. J. Med. Chem. 46 (2011)
6
91-703.
[
[
[
4]
H. Wu, X.L. Xie, G. Liu, Parallel Solution phase synthesis of 3,6,7−4(3H)-
quinazolinones and evaluation of their antitumor activities against human cancer, J.
Comb. Chem. 12 (2010) 346-355.
5] A.M. Farghaly, R. Soliman, M. A. Khalil, A. A. Bekhit, A. el-Din, A. Bekhit,
Thioglycolic acid and pyrazole derivatives of 4(3H)-quinazolinone: synthesis and
antimicrobial evaluation, Boll. Chem. Farm. 141 (2002) 372-378.
6] L. Racane, M. Kralj, L. Suman, R. Stojkovic,V. Tralic-Kulenovic, G. Karminski-
Zamola, Novel amidino substituted 2-phenylbenzothiazoles: Synthesis, antitumor
evaluation in vitro and acute toxicity testing in vivo, Bioorg. Med. Chem. 18 (2010)
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1
6
1
038-1044.
7] M. Bakavoli, O. Sabzevari, M. Rahimizadeh, Microwave activated synthesis of
-aryl-quinazolin-4(3H)-ones, Chin. Chem. Lett. 18 (2007) 1466–1468.
[
2
[
8] A. Davoodnia, S. Allameh, A. R. Fakhari, N. Tavakoli-Hoseini, Highly efficient
solvent-free synthesis of quinazolin-4(3H)-ones and 2,3-dihydroquinazolin-4(1H)-
ones using tetrabutylammonium bromide as novel ionic liquid catalyst, Chin. Chem.
Lett. 21 (2010) 550–553.
[9]
M. Dabiri, P. Salehi, A. A. Mohammadi, M. Baghbanzadeh, One‐pot synthesis of
mono‐ and disubstituted (3H)‐quinazolin‐4‐ones in dry media under microwave
irradiation, Synth. Commun. 35 (2005) 279–287.
[
10] X. Xu, P. Lu, Y. Zhang, Facile synthesis of 2-substituted-quinazolin-4-(3H)-ones
promoted by SmI , Synth. Commun. 31 (2001) 323–327.
2
[
11] N. Montazeria, K. Rad-Moghadam, A convenient synthesis of substituted quinazolin-
4
-(3H)-ones under microwave and solvent-free conditions, Phosphorus, Sulfur, and
Silicon. 179 (2004) 2533–2536.
[
12] D. Shi, L. Rong, J. Wang, Q. Zhuang, X. Wang, H. Hu, Facile synthesis of
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1
7
substituted quinazolin‐4‐(3H)‐ones using low‐valence titanium reagent, Synth.
Commun. 34 (2004) 1759–1765.
[
13] R. J. Abdel-Jalil, W. Voelter,M. Saeed, A novel method for the synthesis of 4(3H)-
quinazolinones, Tetrahedron Lett. 45 (2004) 3475–3476.
[
14] H. R. Memarian, M. Abdoli-Senejani, D. Döpp, Photoinduced aromatization of
unsymmetrically substituted 1,4-dihydropyridines, J. Chin. Chem. Soc. 54 (2007)
1
31-139 and references cited therein.
[15] H. R. Memarian, M. Soleymani, H. Sabzyan, Light-induced dehydrogenation of 2-
oxo-1,2,3,4-tetrahydropyrimidine-5-carboxamides, J. Iran. Chem. Soc. 9 (2012) 805-
8
13 and references cited therein.
16] The absolute term ”extinction” is a German word and has now been replaced with
absorbance”, but the phrase ”Extinction time” is still using.
[
”
[17] M. Bakavoli, A. Shiri, Z. Ebrahimpour, M. Rahimizadeh, Clean heterocyclic synthesis
in water: I /KI catalyzed one-pot synthesis of quinazolin-4(3H)-ones, Chin. Chem.
2
Lett. 19 (2008) 1403–1406.
[
18] S. M. Bakalova, A. Gil Santos, I. Timcheva, J. Kaneti, I. L. Filipova, G. M.
Dobrikov, V. D. Dimitrov, Electronic absorption and emission spectra and
computational studies of some 2-aryl, 2-styryl, and 2-(40-aryl)butadienyl quinazolin-
4
-ones, J. Mol. Struct. (Theochem) 710 (2004) 229–234.
[19] D. Rehm, A. Weller, Kinetics of fluorescence quenching by electron and H-atom
Page 17 of 24

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8
transfer. Isr. J. Chem. 8 (1970) 259–271.
[
20] M.-Z. Jin, L. Yang, L.-M. Wu, Y.-C. Liu, Z.-L. Liu, Novel photoinduced
aromatization of Hantzsch 1,4-dihydropyridines, Chem. Commun. (1998) 2451-
2
452.
[
21] J. L. Kurz, R. Hutton, F. H. Westheimer,The photochemical reduction of
bromotrichloromethane by derivatives of 1, 4-dihydropyridine, J. Am. Chem. Soc.83
(1961) 584-588.
[
[
[
22] M. Julliard, M. Chanon, Photoelectron-transfer catalysis: its connections with thermal
and electrochemical analogs, Chem. Rev.83 (1983) 425-506.
23] K. Izutsu, Electrochemistry in Nonaqueous Solutions, Wiley-VCH Verlag GmbH &
Co. KGaA. 8 (2002) 224.
24] A. J. Włodarczyk, P. P. Roman´czyk, Redox and catalytic properties of alkoxides
based on tris(3,5-dimethylpyrazolyl)borato tungsten nitrosyls, Inorg. Chim. Acta. 363
(2010) 813-816.
[
25] M. Abdollahi-Alibeik, E. Shabani, Synthesis of 2,3-dihydroquinazolin-4(1H)-ones
catalyzed by zirconium (IV) chloride as a mild and efficient catalyst, Chin. Chem.
Lett. 22 (2011) 1163–1166.
Page 18 of 24

2
2
Table 1
Light induced dehydrogenation of 2,3-dihydroquinazolin-4(1H)-ones.
o
o
R
C
2-CH
4- CH
2-NO
3- NO
4- NO
4-BrC
4-ClC
4-FC
Product Time (min) Yield (%) M.p. ( C)
M.p. ( C, [17])
235–237
208-210
248-249
This work
351-353
363-364
315-316
305-307
This work
-
1
1
1
1
1
1
1
1
1
1
1
1
1
a
b
c
d
e
f
g
h
i
H
6
5
2a
2b
2c
2d
2e
35
25
40
50
40
45
50
40
38
80
45
30
20
90
90
90
70
40
50
90
80
65
90
75
60
40
232-234
189-191
241-243
229-230
>350
OC
OC
H
H
6 4
3
6
4
3
a
a
a
C H
2 6 4
C
C
H
H
2
6
4
4
>350
2
6
2f
H
6
2g
2h
2i
2j
2k,3k
3l
310-311
305-307
259-261
165-166
273-274
274-275
191-192
4
H
6 4
H
4
6
j
k
l
2-Pyridyl
3- Pyridyl
4- Pyridyl
a
a
a
-
-
-
m
5-Methyl-2-furyl 2m
a
The irradiations were stopped due to precipitation of products and caused screening effect.
Table 2
Comparison of the UV-absorption [λmax (nm)] peaks of 1a-1m with those of 2a-2m in
chloroform solution.
λmax (log ε)
λmax (log ε)
1
1
1
1
a
b
c
331.2 (3.39), 245.2 (3.81)
2a
296.8 (4.12), 244.2 (4.19)
332.4 (3.32), 280 (sh, 3.39), 250.4 (3.63) 2b
315 (sh, 4.04), 299.4 (4.11), 250.8 (3.92)
306.2 (4.34), 295 (sh, 4.28) , 248.2 (4.06)
310 (sh, 4.02), 303.6 (4.06), 265 (sh, 4.25), 250.4
350 (3.23), 273.4 (3.87), 245 (3.80)
331 (3.70), 249.8 (4.20)
2c
d
2d
(4.26)
1
1
e
f
327 (3.61), 254.8 (4.06),
328.2 (3.53), 256.0 (4.22)
2e
2f
310 (sh, 2.49), 294 (3.98), 256 (4.00)
350 (sh, 4.10), 339 (3.26), 315 (3.25), 300.5 (4.26),
253 (4.42)
1
1
1
1
g
h
i
329.4 (3.39), 249.2 (3.71)
328.4 (3.45), 249.4 (3.73)
331.8 (3.40), 244.0 (3.78)
340 (sh, 3.52), 325 (3.63), 330 (sh,
2g
2h
2i
315 (sh, 4.03), 295.8 (4.13) , 255.4 (4.08)
303.6 (4.17), 295 (sh, 4.15), 248.6 (4.18)
325 (sh, 3.69), 292.8 (3.93), 245.2 (4.04)
340 (sh, 3.57), 325.4 (3.85), 307.4 (3.92), 295 (sh,
3.81), 243.8 (3.87)
j
2j
3
.59), 305 (sh, 3.65), 255 (4.07)
1
1
1
k
l
332.2 (3.64), 247.4 (4.09)
2k, 303.6 (4.23), 295 (sh, 4.21), 245.8 (4.17)
3
3l
k
I
340 (sh, 3.27), 300 (sh, 3.58), 280 (sh,
350 (3.19), 305 (sh, 4.04), 295 (4.09), 275 (sh, 4.08),
235 (4.12)
3
.93), 260 (4.04)
m
329.8 (3.34), 245 (3.82).
2m 335 (sh, 3.67), 313.8 (3.84), 244 (3.70)
I
The UV spectra was taken in ethanol.
Page 19 of 24

2
3
Table 3
+
NBO Spin densities on the DHQZ, radical cation (DHQZ· ) and radical (HQZ·) obtained by
using B3LYP/6-31++G** level of theory
1
N1
C2
N3
C4
C4a
C5
C6
C7
C8
C8a
0.195
0.229
0.192
0.178
0.229
0.187
0.195
0.215
0.193
0.199
0.231
0.183
0.179
0.236
0.183
0.180
0.235
0.189
0.194
0.229
0.192
0.194
0.230
0.192
0.194
0.230
0.192
0.191
0.229
0.195
0.183
0.231
0.186
0.183
0.234
0.191
0.182
0.211
0.193
O9
a
-0.649
-0.432
-0.582
-0.677
-0.440
-0.580
-0.649
-0.454
-0.587
-0.651
-0.427
-0.560
-0.671
-0.439
-0.577
-0.670
-0.438
-0.570
-0.650
-0.437
-0.581
-0.650
-0.435
-0.582
-0.650
-0.435
-0.582
-0.673
-0.429
-0.572
-0.668
-0.439
-0.567
-0.667
-0.436
-0.575
-0.668
-0.431
-0.584
0.127
0.120
0.383
0.117
0.123
0.368
0.129
0.125
0.374
0.124
0.114
0.472
0.116
0.121
0.400
0.114
0.118
0.426
0.127
0.120
0.387
0.127
0.120
0.386
0.128
0.120
0.356
0.107
0.107
0.362
0.117
0.119
0.367
0.115
0.118
0.393
0.083
0.091
0.329
-0.681
-0.659
-0.625
-0.680
-0.656
-0.627
-0.680
-0.666
-0.627
-0.688
-0.662
-0.618
-0.694
-0.662
-0.625
-0.694
-0.663
-0.622
-0.682
-0.662
-0.626
-0.682
-0.661
-0.626
-0.682
-0.661
-0.625
-0.686
-0.660
-0.622
-0.688
-0.660
-0.625
-0.692
-0.661
-0.624
-0.683
-0.668
-0.627
0.680
0.662
0.670
0.676
0.671
0.673
0.680
0.664
0.669
0.684
0.660
0.677
0.680
0.663
0.673
0.680
0.663
0.675
0.681
0.663
0.672
0.681
0.663
0.671
0.680
0.662
0.670
0.677
0.666
0.672
0.679
0.663
0.671
0.680
0.663
0.672
0.678
0.665
0.670
-0.199
-0.107
-0.189
-0.187
-0.105
-0.192
-0.199
-0.121
-0.189
-0.203
-0.113
-0.182
-0.192
-0.109
-0.187
-0.193
-0.109
-0.186
-0.199
-0.110
-0.189
-0.199
-0.109
-0.189
-0.199
-0.108
-0.189
-0.197
-0.111
-0.192
-0.194
-0.110
-0.188
-0.195
-0.109
-0.188
-0.193
-0.132
-0.193
-0.166
-0.168
-0.168
-0.175
-0.174
-0.169
-0.166
-0.166
-0.169
-0.165
-0.166
-0.169
-0.170
-0.165
-0.165
-0.169
-0.165
-0.163
-0.165
-0.167
-0.166
-0.165
-0.167
-0.166
-0.165
-0.167
-0.167
-0.171
-0.167
-0.168
-0.170
-0.166
-0.166
-0.169
-0.166
-0.165
-0.171
-0.160
-0.168
-0.272
-0.104
-0.269
-0.258
-0.123
-0.273
-0.273
-0.132
-0.272
-0.272
-0.105
-0.244
-0.256
-0.096
-0.260
-0.256
-0.096
-0.254
-0.271
-0.106
-0.266
-0.271
-0.104
-0.266
-0.271
-0.102
-0.268
-0.265
-0.109
-0.267
-0.260
-0.103
-0.265
-0.260
-0.098
-0.263
-0.260
-0.138
-0.274
-0.198
-0.199
-0.193
-0.207
-0.202
-0.200
-0.198
-0.198
-0.193
-0.194
-0.201
-0.197
-0.200
-0.197
-0.196
-0.200
-0.197
-0.188
-0.196
-0.199
-0.191
-0.196
-0.199
-0.191
-0.196
-0.199
-0.192
-0.202
-0.200
-0.192
-0.201
-0.197
-0.191
-0.200
-0.198
-0.191
-0.202
-0.198
-0.193
-0.281
-0.198
-0.281
-0.256
-0.205
-0.267
-0.282
-0.210
-0.283
-0.277
-0.190
-0.233
-0.258
-0.196
-0.262
-0.259
-0.196
-0.270
-0.280
-0.199
-0.279
-0.281
-0.198
-0.279
-0.281
-0.197
-0.280
-0.263
-0.193
-0.274
-0.262
-0.198
-0.279
-0.262
-0.196
-0.275
-0.260
-0.209
-0.283
-0.625
-0.432
-0.615
-0.632
-0.569
-0.620
-0.627
-0.567
-0.621
-0.622
-0.560
-0.596
-0.615
-0.549
-0.602
-0.616
-0.549
-0.596
-0.622
-0.555
-0.612
-0.622
-0.555
-0.613
-0.622
-0.554
-0.615
-0.627
-0.558
-0.614
-0.620
-0.552
-0.610
-0.619
-0.551
-0.613
-0.624
-0.561
-0.619
+
•
a
a
•
b
b
b
c
+
•
•
+
•
c
c
•
O
9
4
d
d
d
e
+
•
•
5
8
4
a
6
7
NH
3
+•
e
e
f
f
f
•
Ar
2
8
a
N
H
1
+•
H
•
g
g
g
+
•
•
h
h
h
i
i
i
+
•
•
+
•
•
j
j
j
+
•
•
k
+
•
k
•
k
l
+
•
l
l
•
m
m
m
+
•
•
Page 20 of 24

Photo- oxidation of 2-substituted 2,3-dihydroquinazolin-4(1H)-ones results in the
formation of quinazolin-4(3H)-ones.
The electronic nature of the substituent on the 2-position and also the nature of solvent
affect the rate of reaction.
An electron-transfer induced mechanism is proposed for this study.
Analysis of the computational results obtained at the DFT-B3LYP/6-31++G** level of
theory supports this mechanism.
Page 21 of 24

O
O
O
H
Ar
H
R'
H
O
R
R
R
N
CH3
N
H
CH3
H
3
C
N
H
R = Alkyl, Aryl, Hetrocycle
R' = CH , OC H
R = CH
3
, OCH
3
,OC
2
H
5
, NHAr
3
2
5
Scheme 1. The structures of 1,4-dihydropyridines and 2-oxo-1,2,3,4-tetrahydropyrimidines
O
N
O
N
O
N
H
H
N
N
N
hv  280 nm
Ar
H
+
CHCl3
Ar
Ar
H
a - m
H
3k ,3l
1
2a - k, 2m
Ar: a = C H , b = 2-CH OC H , c = 4-CH OC H , d = 2-NO C H , e = 3-NO C H , f = 4-NO C H , g = 4-BrC H ,
6
5
3
6
4
3
6
4
2
6
4
2
6
4
2
6
4
6
4
h = 4-ClC H , i = 4-FC H , j = 2-Pyridyl, k = 3-Pyridyl, l = 4-Pyridyl, m = 5-Methyl-2-furyl
6
4
6 4
Scheme 2. Photo-oxidation of 2,3-dihydroquinazolin-4(1H)-ones
Page 22 of 24

O
O
*
H
H
N
N
hv
Ar
Ar
N
H
N
H
H
H
DHQZ
*
DHQZ
O
CHCl3
O
H
BET
BET
.
N
.
H
+
CHCl
N
3
- e (N3)
+
Ar
- e (N
1
)
.
.
+
1. ET
Ar
+ CHCl
3
N
H
N
H
H
H
.
+
1
DHQZ(N )
.
+
-
HCl
O
DHQZ (N3)
H
N
CHCl2
+
N
Ar
H
HQZ
O
O
N
-
CH Cl
2
2
H
N
N
2
. ET
N
H
Ar
Ar
and/or
QZ(3H)
QZ(1H)
Scheme 3. Electron-transfer induced photo-oxidation of 2,3-dihydroquinazolin-4(1H)-ones
Page 23 of 24

Fig. 1. Reaction spectra of photo-oxidation of 1a in chloroform, acetonitrile and ethanol
solutions and the corresponding extinction time (ET) diagrams at 360 nm. Corresponding time
intervals are CH CN (5 min), C H OH (5 min) and CHCl (30 sec).
3 2 5 3
Page 24 of 24