SbCl3 as effective catalyst for the preparation of 2,3-Dihydroquinazolin-4(1H)-ones, spectroscopic investigation and DFT study

Article abstract of DOI:10.1016/j.jpcs.2017.03.008

A simple and efficient method has been developed for the synthesis of Quinazolines using SbCl₃ as a heterogeneous catalysis at room temperature. This method provides a good pathway for the synthesis of 2,3-Dihydroquinazolin-4(1H)-ones derivatives in the terms of excellent yields and short reaction times. Also we studied theoretically and experimentally on 2-phenyl-2,3-dihydroquinazolin-4(1H)-one (PDQ). Using density functional theory (DFT), the tautomerism of PDQ was also studied. Thermal stability of PDQ was studied by thermo gravimetric analysis (TGA). The spectroscopic results and theoretical calculations indicate that the strength of intramolecular hydrogen bonding (IHB) of PDQ is stronger than that in 2-methyl-4-quinolinol (2MQ). The absorption spectra of the PDQ in solvents with different polarity were obtained and the results show that PDQ exists in both keto-amine and enol-imine forms in THF, while it has keto-amine form in other solvents. Theoretical results show that the conductance of the two tautomers (keto-amine and enol-imine) varies greatly, which offers that the potential usage of this molecule is as a molecular device.

Full text of DOI:10.1016/j.jpcs.2017.03.008

Author’s Accepted Manuscript
SbCl as effective catalyst for the preparation of
3
2,3-Dihydroquinazolin-4(1H)-ones, spectroscopic
investigation and DFT study
Seied Ali Pourmousavi, Ayoob Kanaani, Hamid
Reza Fatahi, Fatemeh Ghorbani, Davood Ajloo
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PII:
S0022-3697(16)30855-1
http://dx.doi.org/10.1016/j.jpcs.2017.03.008
PCS8006
DOI:
Reference:
To appear in:
Journal of Physical and Chemistry of Solids
Received date: 9 October 2016
Revised date: 22 January 2017
Accepted date: 9 March 2017
Cite this article as: Seied Ali Pourmousavi, Ayoob Kanaani, Hamid Reza Fatahi,
Fatemeh Ghorbani and Davood Ajloo, SbCl as effective catalyst for the
3
preparation of 2,3-Dihydroquinazolin-4(1H)-ones, spectroscopic investigation
and DFT study, Journal of Physical and Chemistry of Solids
http://dx.doi.org/10.1016/j.jpcs.2017.03.008
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SbCl3 as effective catalyst for the preparation of 2,3-
Dihydroquinazolin-4(1H)-ones, spectroscopic investigation and
DFT study
Seied Ali Pourmousavia,b*, Ayoob Kanaania, Hamid Reza Fatahia, Fatemeh Ghorbania,
Davood Ajlooa,b
aSchool of Chemistry, Damghan University, Damghan, 36715-364, Iran
bInstitute of Biological Science, Damghan University, Damghan, 36716-41167, Iran
*Corresponding author. Tel.: +98-233-522-0097; fax: +98-233-522-0095; e-mail: pourmousavi@du.ac.ir.
Abstract
A simple and efficient method has been developed for the synthesis of Quinazolines using
SbCl3 as a heterogeneous catalysis at room temperature. This method provides a good
pathway for the synthesis of 2,3-Dihydroquinazolin-4(1H)-ones derivatives in the terms of
excellent yields and short reaction times. Also we studied theoretically and experimentally on
2-phenyl-2,3-dihydroquinazolin-4(1H)-one (PDQ). Using density functional theory (DFT),
the tautomerism of PDQ was also studied. Thermal stability of PDQ was studied by thermo
gravimetric analysis (TGA). The spectroscopic results and theoretical calculations indicate
that the strength of intramolecular hydrogen bonding (IHB) of PDQ is stronger than that in 2-
methyl-4-quinolinol (2MQ). The absorption spectra of the PDQ in solvents with different
polarity were obtained and the results show that PDQ exists in both keto-amine and enol-
imine forms in THF, while it has keto-amine form in other solvents. Theoretical results show
that the conductance of the two tautomers (keto-amine and enol-imine) varies greatly, which
offers that the potential usage of this molecule is as a molecular device.
Keywords: 2-Aminobenzamide; 2,3-Dihydroquinazolin-4(1H)-ones; Catalyst; DFT
1.Introduction
The heterocyclic fused rings quinazolines have attracted a huge consideration because of
their expanded applications in the field of pharmaceutical chemistry.[1-4] Many substituted
quinazoline derivatives possess a wide range of bioactivities such as antimalarial,[5]
anticancer,[6] antimicrobial,[7] antifungal,[8] antiviral,[9] antihypertensive,[10] anti-
inflammatory,[11] anti-diabetes,[12] muscle relaxant,[13] antitubercular,[14] anti-

obesity,[15] anticonvulsant,[16] antiproliferative,[17] anti-oxidant,[18] and many other ones.
Quinazolines compounds are used in preparation of various functional materials for the
synthetic chemistry and also present in molecules of various drugs (Fig. S1).
Several synthetic routes have been widely used for the preparation of quinazoline
derivatives. These compounds have been synthesized in the presence of a variety of
homogeneous or heterogeneous catalysts such as molecular iodine (I2),[19] cyanuric
chloride,[20] morpholinoethanesulfonic acid,[21] silica supported polyphosphoric acid
(SiO2-PPA),[22] NH4Cl,[23] tetrabutylammonium bromide (TBAB),[24] p-sulfonic acid
calix[4]arene,[25]
[Al(H2PO4)3],[26]
Fe3O4
β-cyclodextrin-SO3H,[27]
nanoparticles,[29] [bmim]HSO4,[30]
[PYC4SO3H][HSO4]/A300SiO2,[28]
Sc(OTf)3,[31] cellulose-SO3H,[32] β-cyclodextrin,[33] ZrCl4,[34] Amberlyst-15,[35]
H3PW12O40,[36] Heteropoly Acids [37] or by electrochemical reactions.
These reported methods produce good results in many instances. However, some of them
suffer from one or more drawbacks, including complex steps, prolonged reaction times, low
yields and tedious work-up procedure and using expensive catalysts. Therefore, these
compounds develop more efficient, rapid and simple procedures to prepare the similar
skeleton compounds.
The use of antimony trichloride (SbCl3) as catalyst has received considerable attention in
organic synthesis, because it is cheap and easy to handle. SbCl3 has shown a profound
catalytic activity. As a Lewis acid, it has been used in organic synthesis such as Friedel-
Crafts acylations,[38] reductions with NaBH4 [39] and in the synthesis of some
heterocycles.[40] To the best of our knowledge, there has been no such a report in the
literature for the synthesis of quinazoline derivatives with SbCl3 as a catalyst.
In continuation of our ongoing program to develop the new methodologies in organic
synthesis, here we wish to report the extremely convenient and practical synthesis of 2,3-
dihydroquinazolin-4(1H)-on derivatives via the simple and efficient condensation reaction of
2-aminobenzamide and aldehydes in the presence of a catalytic amount of SbCl3 in MeOH.
Also, the tautomeric stability, optimized geometry, vibrational spectra, electronic
absorption spectra, statistical thermodynamic parameters, molecular electrostatic potential,
frontier molecular orbitals (FMOs), nonlinear optical properties, thermal stability and the
electron transport properties based on the molecular switch of the 2-phenyl-2,3-
dihydroquinazolin-4(1H)-one (PDQ), have been studied.

2.Experimental section:
2.1.General
The mid-IR spectrum was obtained using KBr pellets on a Perkin-Elmer RXI Fourier
Transform spectrophotometer. The ultraviolet absorption spectra were examined in the range
of 200–500 nm using Perkin-Elmer lambda 25 recording spectrophotometer equipped with a
10 mm quartz cell. The NMR Spectra were prepared at the ambient temperatures on Brucker
AVANCE DRX-400 MHz spectrometer. Thermal analysis of TGA and DTG were performed
on a Perkin–Elmer model under nitrogen at a heating rate of 10 °C/min for the temperature
range of 100-800°C.
2.2.General procedure for the synthesis of quinazoline derivatives (1-16)
To a solution of 2-aminobezamide (1 mmol) and aldehyde or ketone (1 mmol) in MeOH
(3 mL), SbCl3 (0.03 gr) was added. The mixture was stirred at room temperature. After
completion of the reaction, as indicated by TLC (ethyl acetate: n-hexane 1:1), the product
was precipitated by addition of 9 mL of water. Then the precipitate was filtered off and
washed with extra water. Finally the crude product was purified by recrystallization from
EtOH and water to afford the corresponding 2,3-dihydroquinazolin-4-(1H)-ones.
2.3.Spectral data
2,3-dihydro-2- phenyl quinazolin-4(1H)-one (3a): 1H NMR (400 MHz, DMSO): δ 5.75 (s, 1H),
6.67 (t, 1H), 6.76 (d, J= 8 Hz, 1H), 7.11 (s, 1H), 7.24 (t, 1H), 7.34-7.39 (m, 3H), 7.49 (d, J= 8 Hz ,
2H), 7.61 (d, J= 6.4 Hz), 8.29 (s, 1H, br).
1
2,3-dihydro-2-(4-methoxy phenyl) quinazolin-4(1H)-one (3f): H NMR (400 MHz, CDC13):
δ 3.84 (s, 3H), 4.39 (s, 1H, br ), 5.70 (s, 1H), 5.86-7.54 (m, 8H), 7.95 (s, 1H, br).
1
2,3-dihydro-2-(3,4- dimethoxy phenyl) quinazolin-4(1H)-one (3h): H NMR (400 MHz,
DMSO): δ 3.74 (s, 3H), 3.75 (s, 3H ), 5.69 (s, 1H), 6.67 (t, 1H), 6.75 (dd, J= 8 Hz, 1H), 6.93-6.98 (m,
2H), 7.01 (s, 1H, br), 7.24 (m, 1H), 7.60 (dd, J= 8 Hz), 8.16 (s, 1H).
1
2,3-dihydro-2-(3,4,5-trimethoxy phenyl) quinazolin-4(1H)-one (3i): H NMR (400 MHz,
DMSO): δ 3.64 (s, 3H), 6.67-6.71 (m, J= 8 Hz, 1H), 6.76 (dd, J= 8 Hz, 1H), 6.84 (s, 2H), 7.04 (s, 1H,
br), 7.26 (m, J= 8 Hz , 1H), 7.62 ( s, J= 7.8 Hz ,1H), 8.21 (s, 1H). 13C NMR (400 MHz, DMSO):

56.34, 60.34, 67.34, 104.86, 104.86, 114.89, 115.48, 117, 127.82, 133.75, 137.03, 137.03, 137.03,
137.97, 148.50, 153.18, 164.16.
3.Computational details
Quantum calculation chemistry has been quite successful in providing theoretical background
of popular qualitative chemical concepts [41]. Quantum chemical calculations help chemist to
calculate the structural and physicochemical properties of the molecule. With the encouraging
experimental data of 2,3-dihydro-2-arylquinazolin-4(1H)-ones 3, our attention was focused
on calculations for investigation of the physicochemical properties of 3a such as
conformational studies, optimized geometry, vibrational analysis, intermolecular hydrogen
bonding, molecular electrostatic potential (MEP) surface, UV–Vis spectra, electronic
properties, Thermal analysis, transition state, current−voltage characteristics of linear switch.
The entire calculations for the PDQ have been done with a hybrid functional B3LYP at 6-
311++G(d,p) basis set. We used, a higher computation level, such as B3LYP/6-
311++G(2d,p), which allow a rationalization of these observations. All calculations were
performed using Gaussian 03W program package [42] with the default convergence criteria
without any constraint on the geometry.[43] The molecular structure of PDQ in the ground
state was optimized. For all calculations in this study, optimized structural parameters were
used. The vibrational frequencies were calculated and scaled down by the suitable scaling
factor.[43] The vibrational wavenumber assignments were carried out by combining the
results from the GaussView [44] and VEDA4 programs.[45] The Lorentzian function has
been utilized for deconvolution of IR spectrum. Electronic excitations of PDQ were
calculated using TD-DFT.[46] The polarizable continuum model (PCM) was used for
solution phase calculations.[47] AIM 2000 software was applied to obtain the AIM
computations.[48] The transition state (TS) structure of tautomeric reaction was obtained
using the QST3 method.
The transport properties of the molecular junction were calculated using the TranSIESTA
package [49] which is based on the combination of DFT with the nonequilibrium Green’s
function (NEGF) technique. In the lateral dimension, a 6×6 supercell was used, large enough
to remove interactions between periodic images. Based on the experimental results, it is
accepted that hydrogen atoms are not attached to metal surfaces.[50] According to this, the
two hydrogen atoms which are to be connected to the metal surface were replaced with sulfur
atoms, and the remaining portion was placed between two parallel Au(111) planes, which
have a face-cantered cubic (FCC).

4. Results and Discussion
4.1. Synthesis of 2,3-dihydro-2-arylquinazolin-4(1H)-ones
A preliminary experiment was performed to determine the suitable reaction conditions.
The reaction of 2-aminobezamide and 4-Methyl benzaldehyde in the presence of SbCl3 was
investigated. The best result was obtained in the presence of 0.03 gr SbCl3 at room
temperature in MeOH (Table 1).
The yield of 3b was low at r.t. in the absence of SbCl3 (10%, Table 1, entry 6), and was
much greater in the presence of various quantities of the catalyst, reaching to a maximum of
100% yield with 0.03 gr SbCl3 (Table 1, entries 3). Different solvents were also tested (Table
1, entries 7-14), and MeOH appeared to be the best medium for this transformation (Scheme).
These optimized conditions were applied to the conversion of various kinds of aryl
aldehydes or ketones into the 2,3-dihydro-2-arylquinazolin-4(1H)-ones. All of reactions that
are done using aldehydes containing electron-withdrawing or electron-donating groups,
proceeded smoothly within a few mins, giving 3a-p (Table 2). The products were synthesized
1
13
in good to excellent yields and characterized by H-NMR, C-NMR, as well as by their
physical constants. To further evaluate the overall utility of the current methodology, we
compared our results with those obtained using other techniques previously reported for the
synthesis of 2,3-dihydro-2-arylquinazolin-4(1H)-ones. As shown in Table 3, our both
methods clearly reduce the required reaction time and generate higher yields of the products.
4.2.Conformational studies and optimized geometry
All optimization calculations for PDQ were performed by aid of OPT=Very Tight and
INT=Ultrafine options. DFT calculations were performed for three tautomers of PDQ (Fig.
1). The calculated relative energies in gas and solution phases are presented in Table S1. The
keto-amine (I) tautomer form is more stable than the enol-imine (II) and Enol-amine (III)
tautomers by 11.30 and 34.38 kcal/mol in gas phase, which these amounts increase with
increasing the polarity of solvent. According to Table S1, the keto-amine and the enol-imine
forms have the highest and lowest dipole moment amounts, respectively.
The calculated IR spectra for different I-III configurations of PDQ at B3LYP-/6-
311++G(2d,p) level of theory are shown in Figs. S2, S3. The stretching and bending modes
of C=O, which were observed experimentally, do not detected in calculated IR spectra at
configurations II and III. Also, there is a peak in the high-frequency region, which is not seen

in the experimental results. This peak is assigned to the stretching vibration of OH. In these
configurations (II, III), the observed bands corresponding to δO-H, υC=N and υC–O
vibrations, have not seen in the experimental spectrum. These results confirmed that our PDQ
is stable at the keto-amine form.
Geometric optimization of PDQ was performed using DFT/B3LYP method with 6-
311++G(2d,p) basis set (Fig. 2). The selected torsion angles, bond angles and bond lengths
are listed in Table 4. The results are compared with another similar system in which the
crystal structure was solved.[51]
Because of the hydrogen bonding formation, dimerization of PDQ considerably reduces
the energy about -50.26 kJ/mol (at the B3LYP/6-311++G(d,p). The energy difference
between dimer and keto forms suggests that there is a hydrogen bond in the dimeric form
(Fig. S4). The O...H distance in hydrogen bonded dimer is found to be 1.770 Å. The N–H and
C=O distances involved in hydrogen bonds are lengthened by 0.025 and 0.022 Å respectively
upon dimerization.
The bond lengths of C3–N15=1.389 Å, C10–N16=1.361 Å, C13–N16=1.461 Å and C13–
N15=1.463 Å are shorter than the normal C–N single bond length of about 1.48 Å, which this
shortening indicates a resonance in this part of the molecule.[52] For PDQ, it is found that the
carbon-carbon bond lengths in the benzene ring are between generic C=C double (1.34 Å)
and C–C single (1.54 Å) bonds lengths. The greater bond length of C3–C4 (1.409Å) is a result
of delocalization of electron density with adjacent quinazoline ring. The calculated value of
C=O bond length (1.243 Å) in PDQ dimer reported in Table 4 is in good agreement with
experimental data.
The ortho and mono substituted phenyl rings are designated as rings I and II, respectively.
For PDQ, the dihedral angles are C5–C4–C10–N16= -175.5º and C10–N16–C13–C18= -166.1º.
This shows that the phenyl ring I and the quinazoline moiety of PDQ are in tilted situation.
Also, the dihedral angles C13–C18–C20–C23, C18–C13–N15–C3, and C18–C13–N16–C10 are -
179.5º, 172.2º and -176.1º, respectively, which indicate the phenyl ring II and the quinazoline
moiety are not in the same plane.
None of three bond angles around C10 atom are equal to 120º. It is seen that the angle C4–
C10–O17 (122.1º) is considerably greater than the angle N16–C10–C4 (115.6º), which can be
explained because of a decline in the repulsion among the lone pairs existing in N16 and O17
atoms.

4.3.Vibrational analysis
The PDQ molecule contains 29 atoms, which has 81 normal modes of fundamental
vibrations. The experimental and calculated FT-IR spectra of PDQ in the region of 4000–400
cm-1 are shown in Fig. 3 (a) and (b), respectively. In order to clarify the observation of these
bands, the band deconvolution technique is used in the IR spectrum. The deconvoluted IR
spectrum of PDQ is demonstrated in Fig. S5. The value of the correlation coefficient provides
good linearity between the calculated and experimental wavenumbers (R2=0.9973) and is
shown in Fig. S6 in Supplementary.
In PDQ, the calculated C=O stretching vibration is at 1726 cm-1 and a strong band is
observed in IR spectrum at 1671 cm-1 (Table 5). The dominant in-plane C=O bending
vibration in the case of PDQ is calculated at 599 cm-1 in complete consistency with Rastogi et
al.[53]
In this study, the theoretical calculation presents that the values of the scaled frequencies
at 3438 and 3423 cm-1 are assigned to N–H stretching vibrations. The PED corresponding to
these vibrations are pure modes with a contribution of 100 %. These bands are observed at
3301 and 3178 cm-1 in FT-IR spectrum as a medium band.
In the present study, the frequencies observed in the FT-IR spectrum at 1587, 1439, 1427,
1362 cm-1 are assigned to N–H in-plane bending vibrations. Considering the N–H out-of-
plane bending vibrations, medium to week FT-IR bands are assigned at 641, 600 and 565 cm-
1. These assignments are in agreement with the literature.[54]
Tanak et al.[55] assigned C–N stretching absorption in the region of 1339–1151 cm-1 for
aromatic amines. In the present work, the bands observed in the region of 1284–1134 cm-1 in
FT-IR spectrum are assigned to C–N stretching vibrations. These modes are not pure but
contain significant contributions from other modes.
For ortho substituted benzene, the υPh modes are expected to be in the range of 1620–
1260 cm-1 and for mono substituted benzene these modes are seen in the region of 1285–1610
cm-1.[56] For ring Ph I, the υPh modes are observed at 1660, 1587, 1510, 1327 cm-1
experimentally and at 1642, 1612, 1520, 1342 cm-1 theoretically and for ring Ph II, are
observed at 1649, 1613, 1301 cm-1 experimentally and at 1638, 1621, 1310 cm-1 theoretically.
The ring breathing mode of PDQ is assigned at 1075 cm-1 for ring Ph I and at 1035 cm-1 for
ring Ph II by PED calculations. The bands occurring at 922, 852, 727 and 664 cm-1 in infrared
are assigned to CCC in-plane bending modes of PDQ. The bands are assigned to CCC out-of-
plane bending vibrations are observed at 529, 508 and 490 cm-1 in PDQ.

The C–H stretching vibrations are calculated at 3056–3016 cm-1. These vibrations are in
good agreement with the experimental values. For example, the experimental value is
appeared at 3035 cm-1 and the calculated one is obtained at 3045 cm-1. As can be seen from
the Potential Energy Distribution (PED) column shown in Table 5, these modes are pure. The
in-plane and out of plane C–H bending vibrations emerge in the range 1000–1300 cm-1 and
750–1000 cm-1, respectively. As an example, the emergence of C–H out of plane bending
vibration (or wagging) modes started from 985 cm-1 and distributed up to 699 cm-1, whereas
these are predicted in the region of 987–712 cm-1.
4.4.Intermolecular hydrogen bonding
Some optimized geometrical parameters, AIM results and the spectroscopic properties
related to the hydrogen bond strength for PDQ and 2-methyl-4-quinolinol (2MQ) [57] are
listed in Table 6. By comparing these properties, the following trend in hydrogen bond
strength is concluded: PDQ > 2MQ
According to Table 6, the values of O…N and O…H distances decrease, while the NHO
bond angle and N-H bond length in PDQ increase compared to 2MQ. This is in agreement
with the AIM results (see Table 6). The electron density at bond critical point (ρBCP) in PDQ
is greater than that of in 2MQ. Thus, it is evidence showing that IHB in PDQ is stronger than
2MQ. The values of the hydrogen bond energy (EHB) for PDQ (13.54) and 2MQ (7.08), are
calculated and reported in Table 6, which is in agreement with the above trend for IHB
strength. This is confirmed by studying the IR frequencies of PDQ. PDQ, compared to 2MQ,
has smaller N16-H14 stretching frequency (3438 cm-1) and bigger out-of-plane bending
frequency (571 cm-1).
4.5.Molecular electrostatic potential (MEP) surface
To predict reactive sites for electrophilic and nucleophilic attacks for PDQ, the MEP at
B3LYP/6-311++G(2d,p) method is calculated. The red and yellow1 (negative) and the blue
(positive) areas of MEP are linked to electrophilic and nucleophilic reactivity. It can be
concluded from Figure 4 that the negative territory of the compound is concentrated around
the carbonyl O17 atom. The maximum value of negative electrostatic potential for this
electrophilic site calculated at B3LYP/6-311++G(2d,p) is about -22.410 a.u with point charge
1 For interpretation of colour in Fig. 4, the reader is referred to the web version of this article.

-0.618 e. For the feasible nucleopilic reaction, the maximum positive regions are located on
hydrogen atoms bonded to N atoms. These sites give information about the regions in which
the compound can have intermolecular interactions.
4.6.UV–Vis spectra and electronic properties
Gauss-Sum 2.2 program [58] is used to calculate group contributions to the molecular
orbitals (HOMO and LUMO) and provide the density of the states (DOS), as shown in Fig.
S7. DOS plot shows population analysis per orbital and indicates an easy outlook of the
makeup of the molecular orbitals in a certain energy range. The energy gap between HOMO
and LUMO characterizes the molecular chemical stability, softness, hardness and chemical
reactivity of the molecule. [59] For PDQ, the energy difference between HOMO and LUMO
is 4.6856 eV (see Fig. 5).
Experimental UV–vis spectra of PDQ in five organic solvents with different polarities
(CH2Cl2, C2H5OH, THF, CH3OH and CH3CN) are shown in Fig. 6. The experimental
spectrum shows three bands at 330, 261 and 219 nm (in CH3CN).
The absorption spectra of this compound is characterized by intense absorption peaks
near 200–250 nm and the less intense ones around 290–400 nm. The band in the region 290–
400 nm is due to π–π* transition attributed to the conjugated quinoline ring of the molecule in
analogy with the assignment for π-styrylquinolines [60], whereas the lowest energy band
which is largely of charge transfer character is due to the aryl group. The band observed in
205 nm unacceptable, because it is less than UV cutoff for THF solvent.
However, a new absorption band at 368 nm is observed in the spectrum of PDQ in THF
(Fig. 6), which is not present in the case of the other solvents. The enol-imine form becomes
important in the solution and is stabilized by the less polar solvent. The electron donating
phenyl group stabilizes zwitter ionic form and eases the formation of enol-imine form with
resonance. In addition, the formation of enol-imine form can be related to the polarity of
solvent. According to Table S1, the enol-imine form has the lowest dipole moment amount.
Among the solvents used in this work, THF has the lowest polarity amount. This property
causes both keto-amine and enol-imine forms to be stable in the solvent.
In addition, the first 10 spin-allowed singlet–singlet excitations for both keto-amine and
enol-imine forms are calculated by TD-DFT approach. For both keto-amine and enol-imine
forms of PDQ, wavelength (λ), oscillator strength (f) and major contributions of calculated
transitions are given in Table 7. There is good agreement between theoretical and

experimental results. For keto form the charge transfer band at λcal. 239 nm results mainly
(46%) due to an electronic transition from HOMO to LUMO+4. smaller contributions (20%,
12%) to these states are attributed to electronic transition from HOMO-2 to LUMO and
HOMO-1 to LUMO. The HOMO and LUMO are mainly localized on the 2,3-
Dihydroquinazolin-4(1H)-one and the whole molecule, respectively (see Figure 5). The bands
calculated at. 270 and 324 nm are due to one electronic transitions from HOMO to LUMO+1
(96%) and from HOMO to LUMO (97%), respectively. Also, the major contributions from
enol form are listed in table 7.
4.7.Thermal analysis
Thermal analysis of PDQ is carried out using the Perkin–Elmer model and simultaneous
thermo gravimetric/differential thermal (TG/DT) analyzer. The sample is scanned in the
temperature range of 100–800 °C at a rate of 10 °C/min. The TG/DT curve is shown in Fig.
7. The major weight loss (80%) take occurs between 270 °C and 378 °C. In the differential
thermal gravimetry (DTG) curve, one peak is identified at temperature of 324 °C, indicating
that the weight loss caused by thermal decomposition occurs in one step, presumably due to
the decomposition of functional groups and carbonization (Fig. 7). This TGA and DTG show
that PDQ compound is chemically stable up to 324 °C.
4.8. Transition state and kinetic
The transition state (TS) structure of tautomer equilibrium (I↔II) gained to use QST3
method and optimized structure is shown in Fig. S8. The imaginary frequency that
characterizes the TS is mainly associated with the hydrogen transfer from O17 to the N16.
Intrinsic reaction coordinate (IRC) calculations are accomplished to confirm that the
transition state structures connect the reactant and product during the reaction (Fig. S9).
Frequency calculations provide thermodynamic parameters to approximate activation
parameters; the results are given in Table S2.
The first order rate constant k(T) is calculated using the transition state theory (TST).[61]
In order to evaluate the effect of temperature on the reaction rate, reaction rate constants (k)
are calculated in the temperature range of 250–450 K. The value of activation energy is
obtained from the plot of calculated (–logk) vs. 1000/T.
is obtained from the slope of
E
a
plot and the data are presented in Table S3. By increasing the temperature, the rate constant

increased too. When the temperature changed from 250 K to 450 K, k increased
approximately 1015 times.
One way to obtain the most stable tautomer is to calculate the tautomeric equilibrium
constant, Keq, which is readily calculated from the Gibb’s free energy via Keq=e-ΔG/RT.[62]
The ΔG value at the B3LYP/6-311++G(d,p) level is predicted to be 49.208 kJ/mol between
keto-amine and enol-imine tautomers of PDQ. The computed Keq is 2.703 ×10-9 at 298.15 K
for keto-amine ↔ enol-imine tautomerization. This result demonstrates that the direction of
equilibrium is in favor of the keto-amine tautomeric form.
4.9.Current−Voltage Characteristics of Linear Switches
The structural optimization is accomplished in the SIESTA package[49] with the
maximum force of 0.02 eV/Å, and core electrons are modeled using Troullier-Martins[63]
soft norm-conserving pseudo potentials. The Perdew–Burke–Ernzerhof (PBE) exchange–
correlation functional is adopted for the generated gradient approximation (GGA).[64] The
Au atoms are described as a single-ξ plus single polarization (SZP) basis set while for the
other atoms a double-ξ plus single polarization (DZP) basis set is used. The current through
the device is computed using the Landauer–Büttiker formula in the TranSIESTA
package.[49]
As illustrated in Fig. S10, the whole device is divided into three regions, the right
electrode, the central scattering region, and the left electrode. Fig. 8 shows the calculated I–V
characteristics of the system with two forms (keto-amine, enol-imine) at a bias up to 2 V. The
switching action can be obviously seen in Fig. 8; the current of keto-amine form is greater
than that of enol-imine form at the same bias. It can be predicted that there is a switch from
the on (low resistance) state to the off (high resistance) state when the keto-amine form is
changed to the enol-imine form.
5. Conclusion
In summary, we have developed an efficient methodology for the synthesis of a variety of
2,3-dihydro-2-arylquinazolin-4(1H)-one derivatives in excellent yields. This approach is very
simple from the experimental point of view and would permit easy access to large families of
quinazolin-4(1H)-ones. Our work is clean, efficient and mild with short reaction times and
easy purification. Minimized amount of waste for each organic transformation and economic
availability of the catalyst are the other noticeable features of this method. Also, this paper

presents a combined experimental and theoretical study on 2-phenyl-2,3-dihydroquinazolin-
4(1H)-one (PDQ). FT-IR spectra analysis showed that the vibrational frequencies are in nice
agreement with the experimental values. PDQ compound is chemically stable up to 324 °C.
The experimental (IR) and theoretical (AIM and geometrical parameters) results confirmed
that the hydrogen bond in PDQ is stronger than that in 2MQ. UV-vis spectra of PDQ were
recorded in different organic solvents in order to peruse the dependence of tautomerism on
solvent types. The results showed that PDQ exists in both keto-amine and enol-imine forms
in THF, while it has only keto-amine form in C2H5OH, CH2Cl2, CH3OH and CH3CN. The
computed tautomeric equilibrium constant was 2.703 ×10-9 at 298.15 K for keto-amine ↔
enol-imine tautomerization. Our results showed that the conductance of two isomers varies
greatly, which offers that the potential usage of this molecule is as a molecular switch.
Acknowledgments
Authors are grateful to the Damghan University for financial support.
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Table 1: Optimization of reaction conditionsa
Entry
SbCl3 )gr(
Solvent
Time (min)
Yield )%(
70
90
100
100
90
10
53
92
94
30
60
86
82
93
1
2
3
4
5
6
7
8
9
10
11
12
13
14
0/01
0/02
0/03
0/05
0/01
---
0/03
0/03
0/03
0/03
0/03
0/03
0/03
0/03
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
---
80
40
3
3
3
1440
120
5
50
115
65
90
50
5
DMF
CH3CN
n-Hexane
DCM
Ethyl Acetate
H2O
EtOH
a Reaction conditions: 2-aminobezamide (1 mmol), 4-Methyl benzaldehyde (1 mmol), solvent (3 mL),
room temperature.
a
Table 2 Synthesis of 2,3-dihydro-2-arylquinazolin-4(1H)-ones promoted by Sbcl3
Entry
Aldehyde or ketone
Product
Time (min) Yield (%)b
1
5
3
95
97
92
96
3a
2a
2b
2c
2d
2
3
4
3b
8
3c
10
3d

5
6
8
8
92
98
2e
2f
3e
3f
7
8
14
7
94
96
2g
3g
3h
2h
9
18
97
2i
2j
3i
10
11
12
5
90
88
93
3j
30
60
3k
2k
2l
3l
13
45
98
2m
3m

14
15
16
30
15
11
98
94
97
2n
2o
3n
3o
2p
3p
a
Reaction conditions: 2-aminobezamide (1 mmol), aldehyde or ketone (1 mmol), solvent (3 mL),
room temperature
b Isolated yields
Table 3 Comparison results of SbCl3 with recently reported catalyst in the synthesis of 2,3-
Dihydroquinazolin-4(1H)-ones.
O
O
O
NH2
NH2
H
NH
H
Ph
N
H
Entry
1
Catalyst
TBAB
Conditionsa
Time
5 min
Yieldb %
94
Solvent-free 100 °C
2
3
4
9
ZrCl4
H3PW12O40
Al/Al2O3 NPs
SbCl3
EtOH r.t.
H2O r.t.
45 min
38 min
15 min
5 min
91
92
88
90
Solvent-free 115 °C
MeOH r.t.
a
Reaction conditions: 2-aminobezamide (1 mmol), benzaldehyde (1 mmol) and catalyst under
different conditions
b Isolated yields

Table 4 Optimized geometrical parameters of PDQ at B3LYP/6-311++G(2d,p) level.
Parametersa
Bond lengths (Å)
C2-C3
Monomer Dimer Exp.b
Parametersa
Monomer Dimer Exp.b
1.400
1.406
1.395
1.393
1.011
1.485
1.221
1.379
1.403
1.409
1.397
1.389
1.011
1.485
1.243
1.361
1.406 N16-C13
1.460
1.104
1.460
1.514
1.393
1.397
1.011
---
1.461
1.105
1.463
1.461
1.395
1.398
1.036
2.871
1.770
1.461
C3-C4
1.406 C13-H29
1.397 C13-N15
1.383 C13-C18
0.878 C18-C19
1.478 C18-C20
1.247 RN—H
1.349 RO…N
RH…O
C4-C5
1.458
1.545
1.392
1.400
0.878
2.846
1.970
C3-N15
N15-H7
C4-C10
C10-O17
C10-N16
---
Bond angles (°)
A(2,3,4)
119.2
121.6
119.9
119.9
116.4
114.7
123.9
121.7
114.3
119.2
122.1
120.0
119.4
116.9
115.5
122.1
122.3
115.6
122.4 A(14,16,13)
122.4 A(10,16,14)
120.1 A(10,16,13)
119.1 A(15,13,16)
117.5 A(15,13,18)
118.4 A(15,13,29)
122.4 A(16,13,18)
121.9 A(13,18,19)
115.7 A(N–H…O)
117.1
114.6
121.7
106.9
111.2
110.0
111.2
120.1
---
118.0
116.4
122.0
107.6
110.6
109.8
111.6
120.1
175.2
115.1
119.9
121.9
106.8
111.4
A(2,3,15)
A(3,4,5)
A(3,4,10)
A(3,15,13)
A(3,15,7)
A(4,10,17)
A(16,10,17)
A(4,10,16)
Dihedral angles (°)
D(2,3,15,13)
D(2,3,4,10)
D(3,4,10,17)
D(3,4,10,16)
D(4,3,15,13)
D(4,10,16,13)
D(5,4,10,16)
110.9
119.0
174.4
153.1
176.4
-171.8
5.4
153.2
175.6
155.4 D(17,10,16,13)
171.9 D(10,16,13,15)
-161.1
-48.8
-165.7 −165.4
-44.5
172.2
−45.85
-169.1 −166.3 D(3,15,13,18)
172.8
-170.4
-179.8
51.3
167.0
8.5
-29.7
16.7
11.1
− 6. 8 D(13,18,20,23)
17.0 D(16,13,15,3)
D(10,16,13,18)
-166.1 −163. 4
-29.6
21.6
179.5
50.1
-179.9
50.0
-177.8
-175.5 -174.3 D(16,13,18,19)
D(15,13,18,20)
-117.8
-56.9
-120.1
-59.4
127.9
−53. 8
a For atom numbering from Fig. 2.
bRef.[51]

Table 5 Experimental (FT-IR wavenumbers (in cm-1)) and theoretical (scaled wavenumbers (in cm-1))
of PDQ at B3LYP/6-311++G(d,p) and B3LYP/6-311++G(2d,p) level of theory.
B3LYP/6-311++G(d,p
B3LYP/6-311++G(2d,p)
Freq I.IR
AR
Freq
I.IR
AR
IR (Neat)
Vibrational assignments (PED)
3601
3590
3199
3193
3187
3177
3173
3156
2904
37
16
10
7
96
95
3438
3423
3056
3051
3045
3035
3032
3016
2774
37
15
10
7
94
93
3301(31)
3178(20)
3131(17)
3057(16)
3035(13)
2936(10)
2902(9,sh)
2850(7)
υN16H14(100)
υN15H7(100)
210
286
99
204
294
89
υsCHI(96)
υsCHII(96)
18
15
12
7
17
14
11
7
υaCHII(99)
102
114
57
101
115
56
υaCHII(100)
υaCHI(95)
υaCHI(93)
78
105
76
103
2804(7)
υC13H29(100)
1813(2)
Overtone/combination
Overtone/combination
Overtone/combination
Overtone/combination
υC=O(77)
1884(3)
1910(4)
1950(4)
1741 536
1650 168
55
47
45
11
12
6
1726 510
1642 155
55
46
45
11
12
5
1671(57)
1660(40)
1649(63)
1613(64)
υCCI(38), δCHI(15), υaC4-C10=O17(11)
υCCII(48), δCHI(21)
υCCII(40)
1644
1628
1620
0
0
4
1638
1621
1612
1520
0
0
4
1587(12,sh) υaCCI(34), δN15H7(12)
1523 153
1514 197
61
1510(45)
1484(37)
1454(18)
1439(25)
1424(9,sh)
1384(22)
1362(16)
1327(14)
1301(29)
1284(8)
δCHI( 4), υaCCI(14), δNH(14)
2
1509 254
2
δCHI( ), νC3-N15(1 ), υaCCI(11)
δCHI(4 ), δC13H29(15)
1491
1469
1436
1393
23
46
71
11
3
1490
1466
1430
1390
23
61
67
13
2
18
10
5
19
9
δNH( 8), δCHI(18), υsNCN(10)
δNH( 8), δC13H29( 5), υaC4C10N16(10)
δCHII(43), δC13H29(21)
δNH(1 ), δCHI(14), δC13H29(14)
υaCCI(36)
4
1373 167
10
8
1369 170
9
1349
1316
1306
1279
1248
1198
1183
1181
1167
1149
1114
10
25
62
4
1342
1310
1299
1275
1242
1196
1180
1178
1161
1143
1112
27
23
62
5
19
1
1
υaCCII( 1), δC13H29(13)
δC13H29(1 ), υaC4C10N16(15), δNH(14)
δCHI( ), υC3N15(16), δC13H29(10)
υCN(34), δC13H29(14)
15
25
33
5
15
20
35
5
1257(7)
2
2
1239(6)
5
5
1206(3)
δCHII(95)
0
3
0
3
1169(15)
1158(6)
δCHII(68), υaCCII(19)
14
27
34
1
8
13
30
31
1
8
δCHI(64)
2
2
1149(16)
1134(9)
νaC10-N16-C13(31), δCHI(26)
νaN-C-N(50), δCHI(11)
δCCCI(35), δCHI(13)
7
8
6
6
1119(3)

1105
1055
1048
1018
1012
996
991
975
942
913
870
853
803
790
782
767
744
714
707
660
618
3
7
0
39
10
40
16
0
1101
1051
1045
1018
1006
987
981
966
938
913
866
851
798
790
780
762
743
712
705
660
621
3
6
0
40
8
1095(2)
1075(3)
1035(5)
1027(8)
1003(4)
985(3)
νaCCCI(38), δCHI(38)
Ring breathing I(64)
Ring breathing II(82)
Trigonal bending II(85)
νsNCN(57)
13
1
12
0
46
14
0
9
8
0
0
γCHI(79)
0
0
0
0
969(2)
γCHII(89)
1
0
1
0
950(3)
γCHI(80)
5
0
5
0
940(3)
γCHI(78)
6
6
5
6
922(6)
δCCCI(24), δCCCII(14), δNCN(11)
γCHI(70)
4
0
5
1
911(7)
2
3
2
3
852(4,sh)
811(28)
793(3)
δCCCI(1 ), δCCCII(15), νC13-C18(10)
γC4C10O17(45), γCHI(13)
δNCN(35)
2
0
2
0
53
32
54
3
14
1
58
27
50
3
11
2
772(4,sh)
747(57,sh)
727(57)
699(37)
685(18)
664(34)
641(25)
γCHII(44), γCCCII(12)
γCHI(73), γCCCII(11)
δCCCI( 5), δC3C4C10(11), δNCN(10)
γCHII(59)
2
2
9
9
45
29
2
0
45
30
2
0
1
1
γC4C10N16(34), γCCCII(28)
δCCCII(18), δCCCI(13)
γNH( 0), δO=C-N(16)
δO=C-N(16), γNH(1 ),
δC10N16C13(10)
5
5
31
3
39
5
598
2
7
599
3
7
621(3,sh)
571
551
540
498
481
449
47
124
24
19
2
2
1
1
2
2
6
571
556
539
497
479
449
45
132
11
16
3
2
1
1
2
2
6
600(10)
565(7)
γNH(50)
γNH(53)
529(16)
508(10)
490(19)
461(3)
γCCC3N15(10)
δNCN(15), γCCCII(10)
γNH(30), γCCCII(11)
δCN15C( 5), γNH(13)
5
3
Freq, vibrational wavenumber; I.IR, IR intensities in kM/mol; AR., Raman scattering activities in
A**4/AM; experimental relative intensities are given in parenthesis; sh, sholder; s, symmetric; a,
asymmetric υ, stretching; δ, in-plane bending; γ, out-of-plane bending.

Table 6 Comparing several properties related to the hydrogen bond strength (O…H–N) for PDQ and
2MQ (All calculated at the B3LYP/6-311++G(2d,p) level).
PDQ
2MQ d
Geometrical resultsa
RO…N
2.871
1.036
1.770
175.2
2.887
1.027
1.864
174.1
RN–H
O…H
θ N–H…O
AIM resultsb
ρBCP
0.0484
0.0279
-0.0076
13.5384
0.0309
0.0228
-0.0001
7.0837
∇2ρBCP
HBCP
H-bond energy
Spectroscopic resultsc
νNH
3438 (3301)
571 (600)
3610 (3426)
437 (435)
γNH
a
R is the intramolecular O…N, N–H, O…H distances in Å, θ: the hydrogen bond angle N-H…O in
degree.
b
The units of AIM results are: ρBCP (e au-3), ∇2ρBCP (e au-5), HBCP (hartree au-3) and H-bond energy
(kcal/mol).
c
ν and γ are stretching and out-of-plane bending modes frequencies, respectively, in cm-1.
(Experimental values are given in parenthesis).
d Data source: Ref.[57]

O
O
O
SbCl3 (0.03 gr)
MeOH, r.t.
NH2
NH2
NH
R1
R1
R2
2a-p
N
H
R2
3a-p
1
Scheme. Synthesis of 2,3-Dihydroquinazolin-4(1H)-ones catalyst by SbCl3
Fig. 1. Tautomeric forms for (PDQ); I: keto-amine, II: enol-imine, and III: enol-amine.
Fig. 2. The theoretical optimized geometric structure with atoms numbering of PDQ.
Fig. 3. Comparison of observed and calculated IR spectra of PDQ (a) observed; (b) calculated
with B3LYP/6-31++G(2d,p).
Fig. 4. Molecular electrostatic potential map (MEP) of PDQ.
Fig. 5. The atomic orbital compositions of the frontier molecular orbital for PDQ.
Fig. 6. UV-Vis absorption spectra of PDQ in different solvents.
Fig. 7. TG and DTG curves of PDQ.
Fig. 8. Calculated current−voltage (I−V) characteristics for OFF and ON state structures of
PDQ.

O
OH
OH
N
NH
N
NH
H
H
H
N
H
N
H
Fig. 1
2
Fig. 2

(a)
(b)
400
800
1200
1600
2000
3000
3500
4000
Wavenumber (cm-1)
Fig. 3