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

Article abstract of DOI:10.1515/znb-2016-0260

A series of 2-substituted 2,3-dihydroquinazolin- 4(1H)-ones were oxidized to quinazolin-4(3H)-ones using tetrabutylammonium peroxydisulfate. The rate and the outcome of the reaction are dependent on the type and nature of 2-substitution. An electron transfer mechanism is proposed for this study, which is supported by the retention or elimination of 2-substitution during the oxidation process.

Full text of DOI:10.1515/znb-2016-0260

Z. Naturforsch. 2017; aop
Hamid Reza Memarian* and Saeideh Ghahremani
Electron transfer-induced oxidation of
2
,3-dihydroquinazolin-4(1H)-ones
DOI 10.1515/znb-2016-0260
peroxydisulfate ion in organic synthesis has been widely
investigated [15]. Tetrabutylammonium peroxydisul-
fate (TBAPS) belongs to this family and its applications
for various organic transformations have been reported
Received December 4, 2016; accepted February 15, 2017
Abstract: A series of 2-substituted 2,3-dihydroquinazolin-
4
(1H)-ones were oxidized to quinazolin-4(3H)-ones using
[
(
16, 17]. We have earlier used potassium peroxydisulfate
K S O , PPS) as an efficient oxidizing agent for the oxi-
tetrabutylammonium peroxydisulfate. The rate and the
outcome of the reaction are dependent on the type and
nature of 2-substitution. An electron transfer mechanism
is proposed for this study, which is supported by the reten-
tion or elimination of 2-substitution during the oxidation
process.
2
2
8
dation of a series of 1,4-dihydropyridines [18] and various
-oxo-1,2,3,4-tetrahyropyrimidines under different reac-
2
tion conditions in acetonitrile/water solution [19–21]. In
further studies, we investigated the oxidation of 2-oxo-
1,2,3,4-tetrahyropyrimidine-5-carboxamides using TBAPS
Keywords: dihydroquinazolines; oxidation; peroxydisul- under thermal and sono-thermal conditions [22]. The
fates; quinazolines.
results of these oxidative studies revealed that the oxida-
tion of the heterocyclic compounds considered in these
works by PPS occurred by the hydrogen abstraction from
the C-4 position of the heterocyclic ring via in situ formed
hydroxyl radical [19], whereas by using TBAPS an electron
transfer-induced mechanism is proposed for the oxidative
reaction (Scheme 1) [22].
1
Introduction
Quinazolin-4-ones are a class of heterocyclic compounds
having a fused benzene and pyrimidine rings with the
carbonyl group as a part of the heterocyclic ring. 2,3-Dihy-
droquinazolin-4(1H)-ones (DHQZs) and their dehydrogen-
ated derivatives, namely, quinazolin-4(3H)-ones (QZs),
belong to this family. These compounds exhibit a wide
range of pharmaceutical and biological activities such as
anticancer [1], antibacterial [2, 3], antimalarial [4], anti-
hypertensive [5], antifungal [6] and anticonvulsant [7].
Thermal oxidation of DHQZs to their corresponding QZs
In continuation to this work, we were interested in
using TBAPS for the oxidation of various DHQZs to eluci-
date the effect of the electronic nature of 2-substitution on
the rate of reaction and also possible confirmation of the
earlier reported reaction mechanism using a suitable sub-
stituent on the C-2 position of the heterocyclic ring.
has been reported using KMnO [8] and tetrabutylammo-
nium bromide/CuCl [9], but the results of many studies
4
2
Results and discussion
2
concerning the synthesis of these heterocyclic compounds
revealed that QZs are prepared as final reaction prod-
ucts during the synthesis of DHQZs. For the latter case,
gallium(III) triflate [10], molecular iodine [11], thiamine
hydrochloride [12] and bismuth trinitrate [13] have been
used for this transformation.
The peroxydisulfate ion is one of the strongest oxi-
dizing agents known in aqueous solution with a redox
potential of −2.01 V [14]. The oxidative application of
In order to obtain the optimized oxidation condition, the
reaction of 1a as a model substrate in the presence of
various ratios of 1a:TBAPS in dry acetonitrile was carried
out at 70°C until total disappearance of 1a occurred (as
monitored by thin-layer chromatography). The results
presented in Table 1 indicate that total conversion of 1a to
2
a was achieved by taking the ratio of 1:1.5 for 1a:TBAPS.
In optimized reaction conditions, the oxidation of
2
-substituted DHQZs (1a–k) by TBAPS in dry acetonitrile
under thermal conditions was carried out until total dis-
appearance of DHQZs (Scheme 2). The results are summa-
rized in Table 2.
*
Corresponding author: Hamid Reza Memarian, Department of
Chemistry, University of Isfahan, 81746-73441 Isfahan, I.R. Iran,
e-mail: memarian@sci.ui.ac.ir
The characterization of the products 2a–k and 3 was
1
achieved by the comparison of their IR, H NMR and UV
Saeideh Ghahremani: Department of Chemistry, University of
Isfahan, 81746-73441 Isfahan, I.R. Iran
data with those of the starting materials 1a–k as follows:
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ꢀH.R. Memarian and S. Ghahremani: Oxidation of 2,3-dihydroquinazolin-4(1H)-ones
O
Ar
C
R
N
K2S2O8
H3C
N
H
O
CH3CN/H2O, ∆
O
Ar
H
C
H
R = CH3, OC2H5
R
N
O
C
Ar
H3C
N
O
H
N
(
n-Bu4)2S2O8
CH3CN, ∆
Ar'HN
R = CH3, OC2H5, NHAr'
H C
3
N
H
O
Scheme 1:ꢁThermal oxidation of 2-oxo-1,3,4-tetrahydropyrimidines.
1.
A comparison of the IR spectra of the products with
those of the starting materials showed a decrease in
peaks of the phenylethyl group are observed upon the
oxidative dealkylation process.
the intensity of the NH vibration with a small shift to 3. A comparison of the UV spectra showed a hypsoch-
lower frequency. Due to the oxidation of the hetero-
cyclic ring and diminished delocalization of the lone
pair on the N-3 atom (cross conjugation), the carbonyl
stretching is shifted to higher frequency.
romic shift in the UV spectra of 2a–k due to the oxi-
dation of the heterocyclic ring and formation of a
semi-aromatic benzo-condensed pyrimidinone ring,
which displays in the observed hyperchromic effect
(increased absorption intensity) in the aromatic
region. In the case of compound 3, which is formed
by the oxidative dealkylation process, the absorption
intensity is lower than the corresponding substituted
compound 2k. The UV spectra of the latter observa-
tions are presented in Fig. 1.
1
2
.
A comparison of the H NMR spectra of 2a–k with
those of 1a–k showed the lack of the 1-NH and 2-CH
resonances and a simultaneous shift of the 3-NH
resonance to a lower field due to aromatization of
the heterocyclic ring. But in the case of compound 3,
the lack of the 1-NH resonance and the characteristic
The results presented in Table 2 indicate that the type of
the substituent located on the C-2 position of the hetero-
cyclic ring, especially the nature of the additional sub-
stituent on the phenyl ring, affects the rate and outcome
of the reaction. Whereas electron-releasing substituents
Table 1:ꢁOptimization of the 1a: TBAPS molar ratio for the oxidation
reaction in refluxing dry acetonitrile.
Entry
ꢀa:TBAPS
Time (min)
9ꢄa
ꢃ
ꢅ
ꢇ
ꢉ
ꢃ:ꢃ
ꢃ:ꢃ.ꢆ
ꢃ:ꢃ.ꢈ
ꢃ:ꢅ
ꢇꢄ such as methoxy, dimethylamino or methyl groups facili-
ꢅꢆ
ꢃꢆ
tate the oxidation process, electron-withdrawing substit-
uents such as nitro group increase the time of reaction.
aThe reaction is not completed.
Interesting results are obtained by the location of the
O
O
O
NH
(Bu N) S O
NH
4
2
2
8
NH
+
CH3CN / ∆
N
H
R
N
R
N
H
2
a−k
1
a−k
3
Scheme 2:ꢁOxidation of 2,3-dihydroquinazolin-4(1H)-ones by tetrabutylammonium peroxydisulfate.
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H.R. Memarian and S. Ghahremani: Oxidation of 2,3-dihydroquinazolin-4(1H)-onesꢁꢂꢁꢁꢁꢁ3
Table 2:ꢁOxidation of DHQZs (1a–k) by TBAPS under thermal condi-
a
tions to QZs (2a–k) and 3.
Comp.
R
Product
R
Time (min)b
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
a
b
c
d
e
f
g
h
i
j
k
C H -
ꢂa
ꢂb
ꢂc
ꢂd
ꢂe
ꢂf
ꢂg
ꢂh
ꢂi
C H -
ꢇꢄ
ꢉꢄ
ꢉꢆ
ꢆꢄ
ꢅꢆ
ꢅꢄ
ꢅꢄ
ꢉꢄ
ꢅꢆ
ꢉꢆ
ꢅꢄ
ꢊ
ꢆ
ꢊ
ꢆ
ꢉ-NO C H -
ꢉ-NO C H -
ꢅ
ꢊ
ꢉ
ꢅ ꢊ ꢉ
ꢇ-NO C H -
ꢇ-NO C H -
ꢅ ꢊ ꢉ
ꢅ
ꢊ
ꢉ
ꢅ-NO C H -
ꢅ-NO C H -
ꢅ
ꢊ
ꢉ
ꢅ ꢊ ꢉ
ꢉ-CH OC H -
ꢉ-CH OC H -
ꢇ ꢊ ꢉ
ꢇ
ꢊ
ꢉ
ꢇ-CH OC H -
ꢇ-CH OC H -
ꢇ
ꢊ
ꢉ
ꢇ ꢊ ꢉ
ꢅ-CH OC H -
ꢅ-CH OC H -
ꢇ ꢊ ꢉ
ꢇ
ꢊ
ꢉ
ꢉ-ClC H -
ꢉ-ClC H -
ꢊ
ꢉ
ꢊ ꢉ
ꢉ-CH C H -
ꢉ-CH C H -
ꢇ ꢊ ꢉ
ꢇ
ꢊ
ꢉ
ꢉ-(CH ) NC H - ꢂj
ꢉ-(CH ) NC H -
ꢇ
ꢅ
ꢊ
ꢉ
ꢇ ꢅ ꢊ ꢉ
Ph(CH )CH-
ꢂk
ꢃ
Ph(CH )CH-
ꢇ
ꢇ
H
Fig. 1:ꢁComparison of the UV spectra of 1k with those of the cor-
responding non-dealkylated and dealkylated oxidation products, 2k
and 3, respectively in chloroform.
a
0
.115 mmol DHQZs, 0.172 mmol TBAPS in 2.5 mL dry CH CN at 70°C.
3
b
Times are given after total disappearance of DHQZs.
secondary alkyl group at the C-2 position (1k). In this case, first electron removal is stabilized by delocalization of the
non-dealkylated 2k and dealkylated 3 compounds are radical center over the condensed benzene ring. In contrast
observed. These observations are explained as follows.
to this, the radical cation formed on the N-3 atom is desta-
Recently, we have reported the oxidation of various sub- bilized by the attachment of this atom to the 4-CO group.
stituted 2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxamides Both these arguments are also supported by the results
[
22] by TBAPS and also photo-oxidation of DHQZs (the title obtained in our earlier study [23]. The occurrence of the
+
compounds) in chloroform solution by exposure to the UV positive charge on the N-1 atom in the DHQZ(N1)
˙
species
light [23]. The results of these studies support the mecha- forces the molecule to eject a proton, as a competitive way
nism based on the electron transfer-induced oxidation of to the back electron transfer process (BET), resulting in the
organic compounds, which starts by the electron transfer formation of stable benzylic and also donor substituted
from the molecule either in the ground state (thermal oxi- radical, namely, hydroquinazolinyl radical (HQZR˙). In the
dation, first study) or in the excited state (photo-oxidation, case of 2k, containing a simultaneous secondary alkyl and
latter case) to the suitable electron acceptor species present benzylic group on the 2-position, exclusion of this group as
in the reaction vessel. Based on the proposed mechanism in a stable benzylic cation under the formation of hydroquina-
the first study (Scheme 3), the application of heat causes the zolinyl radical HQZR(H)˙ is also possible. Further electron
homolytic cleavage of the weakest O–O bond in the peroxy- removal and proton detachment from both HQZR(R)˙ and
disulfate ion and formation of tetrabutylammonium sulfate HQZR(H)˙ species accomplish these processes under the
radical (TBASR). Since TBASR is so voluminous to abstract formation of the reaction products (QZs) 2a–k and 3. The
the hydrogen atom from the C-2 position in the heterocyclic expulsion of the benzylic and secondary alkyl substituents
ring of DHQZs and starting the oxidative process, an electron in the latter proposal is supported by the result obtained
transfer process is occurred from a suitable electron-donor on the elimination of the tert-butyl group upon oxidative
position in the molecule to TBASR. Two potential electron- photo-elimination of 2-tert-butyl substituted DHQZ [24] and
donor positions, N-1 and N-3 atoms, are available for dona- also on the thermal oxidation of 1,4-dihydropyridines [25].
tion of an electron to the TBASR species under formation
+
of 2,3-dihydroquinazolin-4(1H)-one radical cation (DHQZ )
˙
3
−
and tetrabutylammonium sulfate anion (Bu NOSO ,
4
TBASA). It seems that the electron pair on the N-1 atom is 3 Conclusion
more readily transferred to the electron-acceptor species
rather than the electron pair on the N-3 atom. The reasons Various 2-substituted DHQZs were synthesized and thermal
of this suggestion and preferred electron donation from N-1 oxidation of these compounds to QZs was studied using
atom are that (i) the electron pair on the N-3 atom is delocal- TBAPS. An electron transfer mechanism is proposed for
ized towards the 4-CO group as a part of the amide group, this oxidative reaction. The rate and outcome of the reac-
and (ii) the radical cation formed on the N-1 atom after the tion are dependent on the nature and type of 2-substitution.
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ꢀH.R. Memarian and S. Ghahremani: Oxidation of 2,3-dihydroquinazolin-4(1H)-ones
O
H
N
∆
(
Bu N) S O
2 Bu NOSO3
R
H
4
2
2
8
4
TBAPS
N
TBASR
H
ET
DHQZ
O
H
N
R
N
H
Bu NOSO
4
3
H
DHQZ
TBASA
O
O
H
H
H
N
R+
H+
N
N
H
N
H
R
e
H+
HQZR(H)
HQZR(R)
O
O
H
H
N
N
N
H
N
R
QZ(H)
QZ(R)
Scheme 3:ꢁThe mechanism of oxidation of 2-substituted DHQZs using (Bu N) S O .
4
2
2
8
the mixture was extracted with chloroform/water. The
4
Experimental section
organic layer was dried over MgSO . After evaporation of
4
solvent, the residue was recrystallized from ethanol. The
physical and spectroscopic data of the new compounds
are reported below.
Melting points were determined on a Stuart Scientific
SMP2 apparatus and are not corrected. IR spectra were
recorded from KBr disks on a Jasco FT/IR-6300 spectrome-
ter. The H and C NMR spectra ([D ]DMSO) were recorded
on Bruker Avance III 400 spectrometers at 400.13 and
1
13
6
4
.1.1 2-(3-Methoxyphenyl)-2,3-dihydroquinazolin-4(1H)-
1
00.62 MHz. UV spectra were taken in CHCl with a Shi-
3
one (1f)
madzu UV-160 spectrometer.
M.p. 150–153°C, recrystallized from n-hexane-ethyl
acetate. – IR: νꢀ=ꢀ3292, 3192, 1646, 1611, 1490, 1255, 775,
−1
1
4
.1 General procedure for the oxidation of
DHQZs by TBAPS
748 cm . – H NMR (400.13 MHz, [D ]DMSO): δꢀ=ꢀ3.75 (s, 3
6
H, OCH ), 5.72 (s, 1 H, C2-H), 6.67 (m, 1 H, aromatic H), 6.75
3
(
d, Jꢀ=ꢀ8.4 Hz, 1 H, aromatic H), 6.91 (dd, Jꢀ=ꢀ8.4 Hz, 2 Hz, 1
A mixture of 2-substituted DHQZs (1a–k, 1 mmol), H, aromatic H), 7.06 (m, 2 H, aromatic H), 7.13 (s, 1 H, N1-H),
Bu N) S O (1.5 mmol) in 2.5 mL dry acetonitrile was 7.23–7.32 (m, 2 H, aromatic H), 7.61 (d, Jꢀ=ꢀ7.2 Hz, 1 H, aro-
(
4
2
2
8
1
3
stirred at 70°C for some specific times (Table 2). After com- matic H), 8.31 ppm (s, 1 H, CONH). – C NMR (100.62 MHz,
pletion of the reaction, the solvent was evaporated and [D ]DMSO): δꢀ=ꢀ55.05 (OCH ), 66.17 (C-2), 112.52, 113.64,
6
3
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H.R. Memarian and S. Ghahremani: Oxidation of 2,3-dihydroquinazolin-4(1H)-onesꢁꢂꢁꢁꢁꢁ5
1
14.34, 114.94, 117.08, 118.89, 127.29, 129.39, 133.27, 143.28, 4.1.5 Quinazolin-4(3H)-one or 4-Hydroxyquinazoline (3)
147.76, 159.17, 163.52 ppm. – UV (CHCl ): λmax(log ε)ꢀ=ꢀ332 nm
3
(
3.97).
M.p. 211–215°C, recrystallized from n-hexane-ethyl acetate.
IR: νꢀ=ꢀ3203, 3130, 2929, 1697, 1659, 1609, 1468, 1325, 1172,
–
−1
1
9
17 cm . – H NMR (400.13 MHz, [D ]DMSO): δꢀ=ꢀ7. 5 1–7. 5 5
6
4
.1.2 2-(2-Phenylethyl)-2,3-dihydroquinazolin-4(1H)-
(m, 1 H, aromatic H), 7.66–7.69 (m, 1 H, aromatic H), 7.80–
7.85 (m, 1 H, aromatic H), 8.10–8.14 (m, 2 H, C2-H and aro-
one (1k)
1
3
matic H), 12.25 ppm (s, 1 H, CONH). – C NMR (100.62 MHz,
M.p. 170–173°C, recrystallized from ethanol. – IR: νꢀ=ꢀ3317, [D ]DMSO): δꢀ=ꢀ122.58, 125.79, 126.73, 127.21, 134.31, 145.34,
3
7
Jꢀ=ꢀ7.2 Hz, 3 H, CH ), 3.04 (m, 1 H, C*H), 4.80 (m, 1 H, C2-H),
6
=
6
228, 3060, 3031, 1644, 1610, 1508, 1486, 1393, 1153, 757, 148.73 ppm. – UV (CHCl ): λmax(log ε)ꢀ=ꢀ313 nm (3.93).
3
−1
1
00 cm . – H NMR (400.13 MHz, [D ]DMSO): δꢀ=ꢀ1.26 (d,
6
3
.58 (m, 1 H, aromatic H), 6.69 (s, 1 H, N1-H), 6.74 (d, J
8.4 Hz, 1 H, aromatic H), 7.17–7.21 (m, 2 H, aromatic H),
5
Supplementary information
7
.24–7.30 (m, 4 H, aromatic H), 7.49 (dd, Jꢀ=ꢀ7.6 Hz, 1.2 Hz,
1
13
IR, H NMR, C NMR and UV spectra of 1f, 1k, 2f, 2k and 3
1
H, aromatic H), 7.65 ppm (d, Jꢀ=ꢀ2.4 Hz, 1 H, CONH).
are given as supporting information available online (DOI:
0.1515/znb-2016-0260).
1
3
–
C NMR (100.62 MHz, [D ]DMSO): δꢀ=ꢀ15.83 (CH ), 44.51,
6
3
1
6
8.63 (C-2), 114.08, 114.67, 116.46, 126.38, 127.07, 128.03,
28.46, 133.03, 141.43, 147.49, 163.14 ppm. – UV (CHCl ):
1
3
Acknowledgments: We are thankful to the Research Coun-
cil and Office of Graduate Studies of the University of Isfa-
han for their financial support.
λmax(log ε)ꢀ=ꢀ354 nm (sh, 3.61), 334 (3.91).
4.1.3 2-(3-Methoxyphenyl)-quinazolin-4(3H)-one (2f)
M.p. 204–206°C, recrystallized from ethanol. – IR: νꢀ=ꢀ3038,
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1
2
882, 1673, 1608, 1584, 1473, 1222, 1044, 854, 768 cm . – H
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6
3
7
.17 (qd, Jꢀ=ꢀ2.6 Hz, 0.8 Hz, 1 H, aromatic H), 7.45–7.49 (m,
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m, 1 H, aromatic H), 7.79–7.81 (m, 2 H, aromatic H), 7.83–
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20.09, 125.82, 126.62, 127.51, 129.73, 134.61, 159.32 ppm. –
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3
[
[
[
[
[
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4
.1.4 2-(2-Phenylethyl)-quinazolin-4(3H)-one (2k)
M.p. 217–220°C, recrystallized from n-hexane-ethyl
acetate. – IR: νꢀ=ꢀ2987, 2850, 1677, 1610, 1465, 1339, 1246, [14] K.-C. Huang, R. A. Couttenye, G. E. Hoag, Chemosphere 2002,
−1
1
49, 413.
8
78, 769 cm . – H NMR (400.13 MHz, [D ]DMSO): δꢀ=ꢀ1.61
6
[
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15] T. Itahara, Y. Fujii, M. Tada, J. Org. Chem. 1988, 53, 3421 and
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(
d, Jꢀ=ꢀ6.8 Hz, 3 H, CH ), 4.12 (q, Jꢀ=ꢀ6.8 Hz, 1 H, benzylic
3
H), 7.21–7.25 (m, 1 H, aromatic H), 7.28–7.34 (m, 3 H, aro-
matic H), 7.39–7.41 (m, 1 H, aromatic H), 7.46–7.50 (m, 1 H,
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3
367.
(
1
m, 1 H, aromatic H), 8.07 (d, Jꢀ=ꢀ8 Hz, 1 H, aromatic H),
2.26 ppm (s, 1 H, CONH). – 1 C NMR (100.62 MHz, [D6]
3
[18] H. R. Memarian, I. Mohammadpoor-Baltork, M. M. Sadeghi, Z.
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DMSO): δꢀ=ꢀ19.28, 46.15, 125.66, 125.99, 126.24, 126.86,
27.15, 127.38, 128.24, 128.47, 134.38 ppm. – UV (CHCl ):
[
1ꢋ] H. R. Memarian, A. Farhadi, J. Iran. Chem. Soc. 2009, 6, 638.
1
3
[20] H. R. Memarian, H. Sabzyan, A. Farhadi, Z. Naturforsch. 2009,
64b, 532.
λmax(log ε)ꢀ=ꢀ316 nm (4.08), 309 (4.07).
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ꢁꢁꢁꢂ
6ꢀ ꢀH.R. Memarian and S. Ghahremani: Oxidation of 2,3-dihydroquinazolin-4(1H)-ones
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[
21] H. R. Memarian, A. Farhadi, H. Sabzyan, Ultrasonics Sonochem. [25] H. R. Memarian, M. M. Sadeghi, A. R. Momeni, Synth. Commun.
2
010, 17, 57ꢋ.
22] H. R. Memarian, M. Soleymani, Ultrasonics Sonochem. 2011,
8, 745.
23] H. R. Memarian, S. Ebrahimi, J. Photochem. Photobiol. A: Chem.
2001, 31, 2241 and references cited therein.
1
2013, 271, 8.
Supplemental Material: The online version of this article
(DOI: 10.1515/znb-2016-0260) offers supplementary material,
available to authorized users.
24] F. A. Cabrera-Rivera, C. Ortíz-Nava, J. Escalante, J. M. Hernán-
dez-Pérez, M. Hô, Synlett 2012, 23, 1057.
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Z. Naturforsch.ꢀ
ꢀ2017 | Volume x | Issue x(b)
Graphical synopsis
Hamid Reza Memarian and Saeideh
Ghahremani
Electron transfer-induced oxidation
of 2,3-dihydroquinazolin-4(1H)-ones
DOI 10.1515/znb-2016-0260
Z. Naturforsch. 2017; x(x)b: xxx–xxx
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