Synthesis of diarylpyrimidinones (DAPMs) using large pore zeolites

Article abstract of DOI:10.1016/j.molcata.2011.12.019

A series of diarylpyrymidin-2(1H)-one (DAPM) belongs to one of the important class of therapeutic and pharmacological active hetrocycles, were synthesized through the multicomponent reactions (MCRs) of aldehydes, ketone and urea, followed by the heterogen

Full text of DOI:10.1016/j.molcata.2011.12.019

Journal of Molecular Catalysis A: Chemical 355 (2012) 210–215
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Synthesis of diarylpyrimidinones (DAPMs) using large pore zeolites
Sunil R. Mistry, Kalpana C. Maheria∗
Applied Chemistry Department, S. V. National Institute of Technology, Surat 395 007, Gujarat, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 October 2011
Received in revised form 1 December 2011
Accepted 15 December 2011
Available online 23 December 2011
A series of diarylpyrymidin-2(1H)-one (DAPM) belongs to one of the important class of therapeutic and
pharmacological active hetrocycles, were synthesized through the multicomponent reactions (MCRs) of
aldehydes, ketone and urea, followed by the heterogeneous catalysis. The synthetic utility of this method
is well demonstrated by avoiding expensive reagent TMSCl, using large pore zeolites (H-MOR, HY and H-
BEA) as potential solid acid catalyst. Key role of textural properties such as surface acidity, hydrophobicity
and porosity on catalytic activity of the zeolites on the synthesis of DAPMs has also been described.
© 2011 Elsevier B.V. All rights reserved.
Keywords:
Zeolite
Heterogeneous catalyst
DAPM
MCRs
1. Introduction
(a nontelomeric) endogenous reverse transcriptase [5]. The syn-
theses of these heterocycles have recently received a great deal of
Concurrent research in organic synthesis focuses on economy. In
fact, the efficiency of a synthetic sequence is more than ever corrob-
orated with its conciseness and sustainability issues, as witnessed
by the remarkable efforts currently aimed at the development
of multiple bond forming and catalytic chemical processes. The
efficiency of a chemical synthesis can be measured not only by
parameters such as selectivity and overall yield, of course, but also
by its raw material, time, human resources, and energy require-
ments, as well as the toxicity and hazard of the chemicals and
the protocols involved. It is thus now recognized that the step
count is one of the most important criteria when evaluating the
efficiency of a synthesis [1]. In this context Multicomponent reac-
tions (MCRs) have emerged as powerful and bond-forming efficient
tools in organic, combinatorial, and medicinal chemistry. The MCRs
strategy offers significant advantages over conventional multistep
synthesis due to its flexible, convergent, and atom economic nature.
In a true sense, MCRs represent environmentally friendly processes
by reducing the number of steps, energy consumption, and waste
production. These features make MCRs well-suited for the easy con-
struction of diversified arrays of, e.g., valuable heterocyclic scaffolds
[2].
consideration for the innovation of improved protocols towards
milder reaction conditions, clean and high yielding approaches.
Many procedures have been reported for the preparation of these
heterocycles [6] but only few methods exist for the synthesis
of pyrimidin-2(1H)-ones [7–9]. Thus the development of facile
synthetic methods towards pyrimidin-2(1H)-ones, constitutes an
active area of investigation in organic synthesis.
The uses of acidic zeolites in different areas of the organic chem-
istry have now grabbed significant levels, not only for the possibility
to perform environmentally benign synthesis, but also for the good
yields [10]. Further, zeolites are broadly used in the synthesis
of specialty and fine chemicals [11]. Moreover, excellent reviews
have been devoted to a large number of zeolite-catalyzed organic
reactions [12,13]. In continuation of our work [14,15] on zeolite cat-
alyzed multicomponent reactions (ZCMCRs), we herein report the
synthesis of 4,6-diarylpyrimidinones (DAPMs) using various acidic
zeolites as novel heterogeneous “E” catalyst (Eco-friendly, Efficient
and Economic) (Scheme 1). To the best of our knowledge, no reports
are available on the synthesis of DAPMs using zeolite as catalyst.
Owing to the wide range of pharmaceutical and therapeutic
properties of pyrimidinones (PMs) such as antitumor action in the
treatment of B16 melanoma and P388 leukemia [3,4] or antago-
nize cell proliferation and induce cell differentiation by inhibiting
2. Experimental
2.1. Catalyst preparation and characterization
The zeolites Na-Beta (BEA(12); Si/Al = 12), H-Mordenite (H-
MOR(11); Si/Al = 11), Na-Y (Si/Al = 2.43), Na-ZSM-5 (Si/Al = 15)
zeolites were obtained from Sud-Chemie India Pvt. Ltd., India. The
H-form of zeolite were prepared by ion exchange of the Na-form
∗
Corresponding author.
E-mail address: maheria@gmail.com (K.C. Maheria).
1381-1169/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2011.12.019

S.R. Mistry, K.C. Maheria / Journal of Molecular Catalysis A: Chemical 355 (2012) 210–215
211
X
O
CHO
N
NH
Zeolite
H3C
+
Toluene, Reflux
X
4a
1a
2
+
X = O or S
H2N
NH2
3
Scheme 1. Zeolite catalyzed synthesis of DAPM.
Table 1
Physiochemical properties of various zeolites.
Catalysts
Si/Al
Pore structure
SBET (m2/g)
Ammonia uptake (mmol/g)
Weak
Strong
Total
0.76 × 0.64
0.55 × 0.55
0.65 × 0.70
0.74 × 0.74
0.53 × 0.56
H-BEA
12
680
0.89
0.70
1.60
H-MOR
H-Y
H-ZSM-5
11
2.43
15
412
480
320
2.02
2.30
1.95
2.39
–
1.40
4.41
2.30
3.35
samples with aqueous solution of NH4NO3 (1 M), followed by dry-
ing and calcination at 823 K.
(125 MHz, DMSO-d6): 58.6, 126.4, 126.6, 127.4, 129.4, 132.7, 156.6,
157.9; ESI/MS: 284. 1 (M+2).
The phase purity and crystallinity of the zeolites were analyzed
by XRD (D8 Advanced Brucker AXS, Germany) with Cu K␣ radi-
ation and nickel filter. Surface area measurement (BET method)
was carried out on Micromeritics Gemini at −196 ◦C using nitro-
gen adsorption isotherms. Acidity of zeolites were determined on
Micromeritics Chemisorb 2720, by a temperature programmed
desorption (TPD) of ammonia. Ammonia was chemisorbed at 120 ◦C
and then desorption was carried out up to 700 ◦C at heating rate of
10 ◦C/min. The solvents were distilled before use. All reagent used
were of analytical grade.
4-(2-Chlorophenyl)-6-phenyl-pyrimidin-2(1H)-thione (1h).
Mp. 200–205 ◦C; FTIR (KBr) ꢀmax = 3427, 3233, 3081, 1608, 1549,
1509, 1090, 754 cm−1 1H NMR (DMSO, 400 MHz): ı 8.19 (s, 1H),
;
7.72 (m, 2H), 7.56–7.40 (m, 6H), 7.23–7.19 (m, 1H) ppm; 13C NMR
(125 MHz, DMSO-d6): 58.2, 126.5, 127.3, 129.4, 132.8, 134.5, 158.6,
160.1; ESI/MS: 300 (M+2).
4-(4-Chlorophenyl)-6-phenyl-pyrimidin-2(1H)-thione (1i).
Mp. 220–230 ◦C; FTIR (KBr) ꢀmax = 3429, 3231, 3080, 1600, 1550,
1506, 1092, 767 cm−1 1H NMR (DMSO, 400 MHz): ı 9.36 (s, 1H,
;
NH), 7.72 (m, 2H), 7.56–7.40 (m, 6H), 7.23–7.19 (m, 1H) ppm; 13C
NMR (125 MHz, DMSO-d6): 58.8, 115.1, 127.2, 132.9, 156.5, 157.8,
159.9; ESI/MS: 300(M+2).
2.2. Typical procedure for the synthesis of DAPM
3. Results and discussion
All zeolites were activated, by heating at higher temperature of
773–823 K for 3–4 h, before loading into the reactor.
Zeolites are crystalline, highly ordered, microporous alumi-
nosilicates with intracrystalline channels and cages of molecular
dimensions. They have received an increasing attention because of
their tunable acidity, the variety of structures and pore dimensions
and excellent thermal stability which makes them economically
and environmentally feasible [11]. Moreover, zeolite Y exhibits the
FAU (faujasite) structure. It has a 3-dimensional pore structure,
All the reactions were carried out in a round bottom flask
attached to a condenser and equipped with a magnetic stirrer
under heating in an oil bath. In a typical reaction, to a solution of
ketone (1.2 mol) and urea (1.5 mol) in toluene, appropriate amount
of aldehyde (1 mol) and zeolite (5 wt.%) were added. The reaction
mixture was refluxed for 20–30 min and 60–70 min with zeolite
H-BEA and H-Y, respectively. After completion of the reaction
indicated by TLC, the spent catalysts were collected by filtra-
tion and then washed with ethanol. Crude product was recovered
by evaporating the solvent under reduced pressure. This product
was purified by recrystallization with ethanol to afford pure 4,6-
diphenyl-pyrimidin-2(1H)-one having melting point 232–235 ◦C
(reported, 233–240 ◦C) in 82% yield with zeolite H-BEA and 85%
yield with H-Y.
˚
characterized by supercages of approximately 12 A in diameter,
˚
which are linked through windows about 8 A in diameter composed
of rings of 12 linked tetrahedra (12-rings). These cages and pores
permit access to quite large molecules, making this structure useful
in catalytic applications (Fig. 1) [21].
Zeolites with different topologies as solid acid catalysts were
used to elucidate the role of the zeolite channel system on their
activity and selectivity on the synthesis of DAPM (Table 1). Table 2
shows the effect of various structural features such as, geometry
(pore structure and dimension), acidity and Si/Al ratio of zeolites
on the synthesis of DAPM. H-BEA and H-Y with 3-dimensional 12-
membered ring (large pore) showed the high yield of 82% and 85%
respectively (runs 1 and 3, Table 2) in considerably shorten reac-
tion time as compared to other zeolites indicating that higher acid
strength of the acid centre. Thus, the preferential order to yield
DAPM was found to be: H-Y > H-BEA > H-MOR > H-ZSM-5.
The desire product, 4,6-diphenyl-pyrimidin-2(1H)-one (4a) was
characterized by comparison of their physical data with those of
known compound [16–20] and the spectral data of novel DAPM
(entries 1g–1i) are given below.
4-(2-Chlorophenyl)-6-phenyl-pyrimidin-2(1H)-one (1g). Mp.
205–210 ◦C; FTIR (KBr) ꢀmax = 3429, 3230, 3083, 1605, 1549,
754 cm−1 1H NMR (DMSO, 400 MHz): ı 7.71 (m, 2H), 7.54–7.31
;
(m, 6H), 7.30 (dd, 1H, J = 7.5), 7.24–7.19 (m, 1H) ppm.; 13C NMR

212
S.R. Mistry, K.C. Maheria / Journal of Molecular Catalysis A: Chemical 355 (2012) 210–215
Fig. 1. (a) Faujasite structure of zeolite Y, illustrating the aluminosilicate framework with Lewis and Bronsted acidic form of zeolite.
3.1. Effect of geometry and surface acidity
less polar zeolite should favor the desorption of adsorbed polar
product. Hence, it is concluded that low to moderate acidity along
with higher surface area and higher Si/Al ratio of zeolite BEA are
prime factors for higher catalytic activity towards the synthesis of
DAPMs.
According to our recent investigation on ZCMCR of Biginelli reac-
tion [15], the low activity of zeolite ZSM-5, is probably ascribed
to the diffusional limitation of the pores towards bulkier reactant
molecules and geometrical constraints for the formation of inter-
mediates inside the pores. Whereas, MOR exhibits largest number
of acid sites compare to other zeolites (Table 1) but it seems that
the unidirectional channels system causes either inherent diffu-
sional limitations or pore blocking owing to strong adsorption of
the reactant or products. Further, existence of strong acid sites in
ZSM-5 and MOR does not favor the reaction due to the possibility of
denseness of the active sites. Moreover, BEA zeolite possesses com-
paratively lower strong acid sites than other zeolite and the surface
area of BEA zeolites is higher than other zeolites. Whereas, zeolite
H-Y consists of supercages (Fig. 1) of pore structure and contain
higher weak Lewis acid sites (Al). The most unexpected observa-
tion was the low activity shown by H-Y and H-MOR with respect
to the reaction time (60–70 and 35–40 min respectively) compared
to H-BEA (Table 2). It should be noted in this case that, there is no
geometrical constraints for the diffusion of reactant through the
pores but the strong adsorption of reactants and/or products in the
pores of the catalyst that poisons or block the active sites and chan-
nels. The higher activity of H-BEA may also ascribed to higher Si/Al
ratio compared to rest of the zeolites consequently leads to higher
hydrophobicity. Moreover, it is noteworthy that, with increasing
framework Si/Al ratio, the catalyst becomes more hydrophobic, the
concentration of acid sites (both, Bronsted and Lewis) decreases
and strength of remaining sites increases [22]. According to the
results and conclusions presented above, we could expect that the
3.2. Synthesis of substituted DAPMs
In order to optimize the catalyst concentration, the reaction of
acetophenone, urea and benzaldehyde, was carried out with var-
ied amount of H-BEA and H-Y (1, 3, 5 up to 10 wt.%) in toluene as a
solvent. The best result was obtained by carrying out the reaction
with 1.2:1.5:1 molar ratio of acetophenone, urea and benzalde-
hyde using 5 wt.% of zeolites H-BEA and H-Y under reflux condition
(Fig. 2).
Using the optimized reaction conditions, the performance and
efficiency of these procedures were explored for the synthesis
of a wide range of substituted DAPMs. The results are summa-
rized in Table 3. It is observed that, aromatic aldehydes with both
electron withdrawing and electron-donating substituents reacted
efficiently with urea and acetophenone in the presence of catalytic
Table 2
Synthesis of DAPM using different zeolites.a
Catalysts
Time (min)
Yield (%)b
H-BEA
H-MOR
H-Y
20–30
35–40
60–70
60–80
82
60
85
25
H-ZSM-5
a
Reaction conditions: aldehyde (1 mmol), acetophenone (1.2 mmol), urea
(1.5 mmol), catalyst (5 wt%) under toluene reflux.
b
Isolated yields.
Fig. 2. Optimization of catalyst concentration.

S.R. Mistry, K.C. Maheria / Journal of Molecular Catalysis A: Chemical 355 (2012) 210–215
213
Table 3
Zeolites catalyzed synthesis of 4,6 diaryl pyrimidin-2(1H)-ones under reflux conditions.a
Entry
Aldehydes
X
H-BEA
H-Y
Time (min)
Yield (%)b
Time (min)
Yield (%)b,c
Yield (%)
1a
1b
1c
1d
1e
1f
1g
1h
1i
C6H5CHO
O
O
O
O
O
O
O
S
20–30
20–30
20–30
20–30
20–30
20–30
20–30
20–30
20–30
50–60
50–60
–
82
76
76
79
85
83
81
75
80
–
60–70
60–70
60–70
60–70
60–70
60–70
60–70
60–70
60–70
60–70
60–70
–
85
78
71
76
88
85
84
79
83
–
–
–
–
–
–
–
–
–
4-Br-C6H4CHO
4-HO-C6H4CHO
4-MeO-C6H4CHO
4-Cl-C6H4 CHO
4-Me-C6H4CHO
2-Cl-C6H4CHO
2-Cl-C6H4CHO
4-Cl-C6H4CHO
CH3CHO
S
–
–
–
1j
1k
1l
O
O
O
O
CH3CH CHCHO
C6H5CHO
C6H5CHO
–
–
–
–
–
–
75d,e
–
1i
50–60
20–30
Bold values represents the polar reactants.
a
Reaction conditions: aldehyde (1 mmol), acetophenone (1.2 mmol), urea (1.5 mmol), catalyst (5 wt%) under toluene reflux.
Isolated yields.
All known products (except 1g–1i) have been reported previously in the literature and were characterized by comparison of Mp, IR and NMR spectra with authentic
b
c
samples [16–20].
d
Reaction was carried in the presence of TMSCl as a catalyst in DMF/CH3CN at 90 ◦C according to reported method [23].
Isolated yields in the presence of TMSCl catalyst.
e
amount of H-BEA and H-Y (5 wt.%) under reflux condition to give the
corresponding DAPMs in moderate to high (70–88%) yields without
the formation of any side products. Moreover, as could be expected,
less polar zeolite H-BEA found to be more efficient with respect to
the shorten reaction time and when subjected more polar substrate
involved in the reaction (Table 3, entries 1c and 1d) compare to the
zeolite H-Y. The scope of the reaction was also investigated with
aliphatic aldehydes and ˛,ˇ-unsaturated aldehydes. In our prelim-
inary attempts with aliphatic aldehydes such as acetaldehyde and
crotonaldehyde (Table 3, entries 1j and 1k) the reaction failed to
yield the corresponding DAPM. Moreover, reaction in the absence
of zeolite catalyst did not give corresponding DAPM (Table 3, entry
1i). The overall 15–20% less yield revels that there is still scope of
development of zeolite catalyst with regards to restricted pore size
of zeolite which limiting the application of zeolite towards bulkier
organic molecule. The XRD patterns of zeolite before and after the
reaction revealed that the zeolite retained its crystallinity through-
out. Thus, the catalyst can be reused. Further, the catalysts were
recycled for five runs without significant loss of activity (Fig. 3).
Recently, Lewis acids such as sulphamic acid, bismuth(III) triflu-
oroacetate and heteropolyacids along with trimethylsilyl chloride
(TMSCl) have been reported as an efficient catalysts for the syn-
thesis of DAPM [16–19]. Scheme 2 shows the merit of the present
work in comparison with the above mentioned reported methods.
Additionally, it shows that use of TMSCl is essential for this reaction
and absence of either one, failed to give the reaction. In this context,
we could not found any reasonable explanation about the role of
TMSCl in this transformation. In order to ensure the Lewis acidity
characteristic of TMSCl, we attempted the synthesis of DAPM using
exclusively TMSCl as a catalyst according to the method reported by
Wang et al. and afforded 75% yield of corresponding DAPM (Table 3,
entry 1i). TMSCl has also been reported as Lewis acid catalyst for
many MCRs for the preparation of other heterocyclic compounds
[23,24]. Therefore, we assume that the Lewis acidity of the zeolite
catalyst in the present study is the main driving force for the desired
conversion. The efficiency of zeolite towards this transformation
can be explained by the various physiochemical parameters such
as both zeolites (H-BEA and H-Y) possess large porosity and higher
surface area. The results revealed that zeolite can act as an effec-
tive catalyst with respect to acidity profile, reaction times, yields
and the obtained products as well as elimination of expensive and
toxic reagent TMSCl.
On the basis of our above preliminary results, the mechanism of
zeolite catalyzed synthesis of DAPM is shown in Scheme 3. More-
over, we have not found any suggested mechanism for this reaction
in the literature except proposed by Heravi et al. [16]. To ensure
Fig. 3. (a) Reusability of catalyst (b) XRD pattern of zeolite H-BEA fresh (black, lower) and after four run (red, upper). (For interpretation of the references to color in this
figure legend, the reader is referred to the web version of this article)

214
S.R. Mistry, K.C. Maheria / Journal of Molecular Catalysis A: Chemical 355 (2012) 210–215
O
40 min, 91%
O
NH SO H/
TMSCl
2 3
CHO
O
N
NH
15 min, 95 %
+
TMSCl
HPAs/
2.15 h, 70%
Bi(TFA)3-
+
/
TMSCl
[nbpy]FeCl4
DAPM
H2N
NH2
Zeolite
20-30 min, 85%
Scheme 2. Comparison of present catalytic system with reported catalyst.
H
H
H
H
O
OH
O
HO
H
O
O
Al
O
Si
Si
Ar
Zeolite
Ar
H
Ar
Ar'
Ar'
Ar'
H-Zeolite
H
O
O
O
-H
H2C
H2C
H3C
Ar'
O
H
H
O
H2N
OH
O
OH
O
N
H2N
NH2
O
H2C
Ar
Ar
Ar
Ar'
Ar'
Imine intermediate
O
H-Zeolite
N
NH
Ar and Ar' = C6 H5
-H2O
Ar
Ar'
DAPM
Scheme 3. Plausible mechanism of zeolite catalyzed synthesis of DAPM.
formation of ˇ-hydroxy ketone in the mechanism, the reaction of p-
chlorobenzaldehyde with acetophenone was carried out separately
in the presence of zeolite H-BEA and obtained product 3-(4-
chlorophenyl)-3-hydroxy-1-phenylpropan-1-one was confirmed
by comparison of their physical data with those of known com-
pound [25] (Mp: 97–99 ◦C, Reported: 99.4–100.4 ◦C) On further
reaction of ˇ-hydroxy ketone with urea yielded desired DAPM. We
have been currently exploring the involvement of nature of acidity
(Lewis and Bronsted) in the mechanism aspect of DAPM formation
using zeolite.
cleaner green technology over the reported Lewis acid catalysts
used for the synthesis of DAPMs by eliminating the use of toxic
TMSCl. It has been found that the presence of strong acid sites in
zeolite does not favor the reaction. Zeolite H-BEA and H-Y showed
higher catalytic activity compared to the other zeolites for ZCMCRs
under study. Moreover, H-BEA has been found to be more efficient
as compared to H-Y with respect to shorter reaction time. This can
be attributed to the higher surface area and Si/Al ratio of zeolite
H-BEA.
4. Conclusion
Acknowledgements
The synthesis of biological active DAPM over various large pore
zeolites (H-Y, H-MOR and H-BEA) was studied. Zeolite presents
The authors are thankful to the Director, SVNIT, Surat, for pro-
viding research and financial assistance. The authors would also like

S.R. Mistry, K.C. Maheria / Journal of Molecular Catalysis A: Chemical 355 (2012) 210–215
215
to thank Sud-Chemie India Pvt. Ltd., India, for the gift of samples of
zeolites.
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