An efficient, one-pot synthesis of pyrido[2,3-d:6,5-d′]dipyrimidines using SBA-15-supported sulfonic acid nanocatalyst under solvent-free conditions

Article abstract of DOI:10.1007/s13738-015-0604-1

Abstract An acidic nanocatalyst SBA-15-SO₃H with a high surface area and high acid content was readily synthesized, characterized, and effectively used in the synthesis of some new and known pyrido[2,3-d:6,5-d′]dipyrimidine derivatives by conde

Full text of DOI:10.1007/s13738-015-0604-1

J IRAN CHEM SOC
DOI 10.1007/s13738-015-0604-1
ORIGINAL PAPER
An efficient, one‑pot synthesis of pyrido[2,3‑d:6,5‑d′]dipyrimidines
using SBA‑15‑supported sulfonic acid nanocatalyst
under solvent‑free conditions
Shahnaz Rostamizadeh · Leili Tahershamsi ·
Negar Zekri
Received: 5 December 2014 / Accepted: 5 February 2015
© Iranian Chemical Society 2015
Abstract An acidic nanocatalyst SBA-15-SO3H with a
high surface area and high acid content was readily synthe-
sized, characterized, and effectively used in the synthesis
of some new and known pyrido[2,3-d:6,5-d′]dipyrimidine
derivatives by condensation reaction of 6-aminouracil and
different aldehydes under solvent-free conditions. The cat-
alyst was reused for 6 runs without significant loss of its
activity. Short reaction times, high yield of the products,
solvent-free conditions, and use of a robust and reusable
catalyst are worthwhile advantages of the present method.
drawbacks, such as long reaction times, use of toxic sol-
vent, tedious work-up, low yield of products, and use of
microwave irradiation.
Due to the importance of dipyrimidines and to overcome
the drawbacks of the reported methods, there is a still need
to develop a new route to synthesize these compounds.
Designing nanocatalysts is an interesting area in organic
synthesis due to their high surface area, stability, durabil-
ity, activity as well as their reusability. SBA-15 (Santa Bar-
bara Amorphous-15) mesoporous nanocatalyst, with high
surface area, well ordered hexagonal arrays of cylindrical
channels, fine pore size distributions, high thermal stabil-
ity, large pore size, thick silica walls, and appreciable num-
ber of silanol groups at the surface of its channels, is an
interesting candidate for the support in catalytic reactions
[16–18]. This efficient support can be modified to extend
its physical and chemical properties. Acidifying the SBA-
15 can boost its acid character in order to use it as an effi-
cient, heterogeneous, and reusable catalyst in acid-cata-
lyzed reactions.
In continuation of our interest toward the synthesis
and application of new catalytic systems for the synthesis
of heterocyclic compounds [19–25], we wish to report a
simple and green method for the synthesis of pyrido[2,3-
d:6,5-d′]dipyrimidine derivatives by the use of sulfonic
acid-modified SBA-15 (SBA-15-SO3H) as a new catalyst
(Scheme 1).
Keywords Nanocatalyst · SBA-15-SO3H · Pyrido[2,3-
d:6,5-d′]dipyrimidine · Solvent-free
Introduction
Dipyrimidines are useful heterocyclic compounds with a
broad range of biological, medicinal, and pharmacological
properties, such as antitumor [1], antibacterial [2], antifun-
gal [3], antiviral [4], and anti-oxidant [5]. In spite of the
wide variety applications of dipyrimidines, only few meth-
ods have been reported for the preparation of these com-
pounds. Dipyrimidines are generally synthesized by the
reaction of active methylene carbons with 5-dimethylami-
nomethylene-6-imino-1,3-dimethyluracil (the Vilsmeier
intermediate) [6–12]. Reaction of barbituric acid with alde-
hydes and aminouracil derivatives also gave fused dipyri-
midines [13–15]. All of the aforementioned methods for
the preparation of dipyrimidines suffer from one or more
Experimental
All chemicals were purchased from Sigma-Aldrich and
Merck companies. X-ray powder diffraction (XRD) was
implemented on a Philips X’Pert diffractometer using
CuKα radiation. The prepared catalyst pore structure
S. Rostamizadeh (*) · L. Tahershamsi · N. Zekri
Department of Chemistry, Faculty of Science, K. N. Toosi
University of Technology, P.O Box 15875-4416, Tehran, Iran
e-mail: shrostamizadeh@yahoo.com
1 3

J IRAN CHEM SOC
Scheme 1 SBA-15-SO3H as
a novel acid catalyst for the
preparation of pyrido[2,3-d:6,5-
d′]dipyrimidine derivatives
Scheme 2 Modification of
SBA-15 with chlorosulfonic
acid
H
OSO3
H
O
H
OSO3
OH
H
OSO3
H
O
l
H
C SO3
H
O
H
OSO3
r
t
2C 2
,
H
C
l
H
O
H
O
OSO3H
OSO3H
H
O
OSO3H
was verified by the nitrogen sorption isotherm ([5.0.0.3]
Belsorp, BEL Japan, Inc.) and also Micrometrics Tristar
ΙΙ 3020. Transmission electron micrographs (TEM) were
recorded on a Philips EM-208 instrument on an accel-
erating voltage of 100 kV. The morphology of the cata-
lyst was determined by scanning the electron microscope
model VEGA\\ TESCAN-XMU instrument with an
accelerating voltage of 20 kV. Melting points were deter-
mined using melting point IA 8103 apparatus; IR spec-
tra were recorded on an ABB Bomem model FTLA200-
added dropwise to 1 g of SBA-15 in 20 mL dichlorometh-
ane and stirred for 60 min at room temperature. Then the
reaction mixture was filtered and washed with dichlo-
romethane (20 mL) and dried in a vacuum oven to obtain
SBA-15-SO3H (Scheme 2).
General procedure for the synthesis
of pyrido[2,3‑d:6,5‑d′]dipyrimidine derivatives in the
presence of SBA‑15‑SO3H under solvent‑free conditions
1
100 instrument. H and 13C NMR spectra were measured
on a Bruker DRX-300 spectrometer at 300 and 75 MHz,
respectively. Mass spectra were measured on a Shimadzu
QP 1100 EX mass spectrometer with 70-eV ionization
potential. The number of acid sites on SBA-15-SO3H was
determined by acid–base titration. The thermal analysis
(C, H, N) was carried out using Carlo ERBA Model EA
1108 analyzer.
In a reaction vessel, a mixture of 6-aminouracil (2 mmol),
aldehyde (1 mmol), and SBA-15-SO3H (0.05 g) was heated
at 120 °C under solvent-free conditions for a specified time
(completion of the reaction was monitored by TLC). After
completion of the reaction, hot DMF (5 mL) was added and
the catalyst was separated by simple filtration. Then water
(15 mL) was added to the filtrate to give the solid product.
Spectral data of some compounds
Preparation of SBA‑15‑SO3H
5‑(4‑Nitrophenyl)‑9,10‑dihydropyrido[2,3‑d:6,5‑d′]
dipyrimidine‑2,4,6,8(1H,3H,5H,7H)‑tetraone (Table 3,
compound 3b)
SBA-15 was prepared according to the common method
reported in the literature [26].
IR (KBr, cm−1): 3336, 3150, 1719, 1668. 1HNMR
(300 MHz, DMSO) δ (ppm): 10.78 (s, NH), 10.36 (s, NH),
8.97 (s, NH), 8.10 (d, J = 9 Hz, 2H-Ar) 7.94 (s, 2NH),
7.43 (d, J = 9 Hz, 2H-Ar), 4.83 (s, 1H). Anal.Calcd for
C15H10N6O6: C, 37.66; H, 2.09; N, 13.39. Found: C, 37.84;
H, 2.25, N, 13.48.
Modification of SBA‑15
For modification of the Support (SBA-15), chlorosulfonic
acid (ClSO3H) was used as an acidic source which is inno-
vative for modifying SBA-15; 9 mmol of ClSO3H was
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J IRAN CHEM SOC
Fig. 1 The IR spectra of a
SBA-15; b SBA-15-SO3H
40000
30000
20000
10000
0
5‑(4‑Chlorophenyl)‑9,10‑dihydropyrido[2,3‑d:6,5‑d′]
dipyrimidine‑2,4,6,8(1H,3H,5H,7H)‑tetraone (Table 3,
compound 3c)
IR (KBr, cm−1): 3325, 3148, 1720, 1667. 1HNMR
(300 MHz, DMSO) δ (ppm): 10.51 (s, 2NH), 10.32 (s,
2NH), 7.15 (d, J = 6 Hz, 2H-Ar), 7.06 (d, J = 6 Hz,
2H-Ar), 6.70 (s, NH), 5.27 (s, 1H). 13CNMR (75 MHz,
DMSO) δ (ppm): 165.32, 154. 29, 149.75, 138.68, 129.49,
128.56, 127.53, 85.72, 32.14. MS (m/z): 360 (M++1).
Anal.Calcd for C15H10N5O4 Cl: C, 50.07; H, 2.78; N,
19.47. Found: C, 50.12; H, 2.85, N, 19.53.
0
2
4
6
8
10
Posiꢀon [°2θ] (Copper (Cu))
Fig. 2 The XRD pattern of SBA-15-SO3H in low angle region of
1.0° (2θ) to 10.0° (2θ)
5‑(2,4‑Dichlorophenyl)‑9,10‑dihydropyrido[2,3‑d:6,5‑d′]
dipyrimidine‑2,4,6,8 (1H,3H,5H,7H)‑ tetraone (Table 3,
compound 3d)
4H-Ar), 6.70 (s, NH), 5.18 (s, 1H). 13CNMR (75 MHz,
DMSO) δ (ppm): 169.70, 165.76, 153.60, 149.70, 135.65,
133.22, 127.93, 127.61, 124.00, 84.83, 35.50. Anal.Calcd
for C15H10N5O4 Br: C, 44.56; H, 2.47; N, 17.33. Found:
C, 45.02; H, 2.53, N, 17.42.
IR (KBr, cm−1): 3465, 3327, 3168, 1716, 1634.1HNMR
(300 MHz, DMSO) δ (ppm): 10.26 (s, 2NH), 10.19
(s, 2NH), 7.36 (s, H–Ar), 7.29 (d, J = 9 Hz, H–Ar),
7.25 (d, J = 9 Hz, H–Ar), 6.45 (s, NH), 5.23 (s, 1H).
13CNMR (75 MHz, DMSO) δ (ppm): 162.36, 153.96,
149.84, 149.70, 137.87, 133.23, 130.64, 130.45,
128.70, 85.00, 35.82. Anal.Calcd for C15H9N5O4 Cl2:
C, 45.68; H, 2.28; N, 17.77. Found: C, 45.70; H, 2.30,
N, 17.79.
5‑(3‑Nitrophenyl)‑9,10‑dihydropyrido[2,3‑d:6,5‑d′]
dipyrimidine‑2,4,6,8(1H,3H,5H,7H)‑tetraone (Table 3,
compound 3f)
IR (KBr, cm−1): 3354, 3153, 1711, 1632. 1HNMR
(300 MHz, DMSO) δ (ppm): 10.62 (s, 2NH), 10.44 (s,
2NH), 7.74 (m, 4H-Ar), 6.73 (s, NH), 5.38 (s, 1H).13CNMR
(75 MHz, DMSO) δ (ppm): 165.46, 154.50, 149.81, 147.82,
142.44, 133.89, 129.23, 121.30, 120.39, 85.19, 32.63. Anal.
Calcd for C15H10N6O6: C, 37.66; H, 2.09; N, 13.39. Found:
C, 37.70; H, 2.11, N, 13.48.
5‑(2‑Bromophenyl)‑9,10‑dihydropyrido[2,3‑d:6,5‑d′]
dipyrimidine‑2,4,6,8(1H,3H,5H,7H)‑tetraone (Table 3,
compound 3e)
IR (KBr, cm−1): 3336, 3168, 1712, 1635. 1HNMR (300 MHz,
DMSO) δ (ppm): 10.45 (s, 2NH), 10.21 (s, 2NH), 7.07 (m,
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J IRAN CHEM SOC
Fig. 3 The SEM images of SBA-15 and SBA-15-SO3H (a, b), TEM images of SBA-15-SO3H (c, d)
Table 1 Surface area, pore volume, and average pore size of SBA-
5‑(4‑Acetamidophenyl)‑9,10‑dihydropyrido[2,3‑d:6,5‑d′]
dipyrimidine‑2,4,6,8(1H,3H,5H,7H)‑tetraone (Table 3,
compound 3h)
15-SO3H
Adsorbent
BET surface
area (m2/g)
BJH desorption BJH desorption
cumulative vol- average pore
ume of pores
width (nm)
IR (KBr, cm−1): 3339, 3169, 1737, 1638. 1HNMR
(300 MHz, DMSO) δ (ppm): 10.48 (s, 2NH), 10.28 (s,
2NH), 7.93 (s, NH), 7.36 (d, J = 9 Hz, 2H-Ar), 6.95 (d,
J = 9 Hz, 2H-Ar,) 6.69 (s, NH), 5.23 (s, 1H), 1.73 (s, 3H,
(cm3/g)
SBA-15
798
0.73
0.41
4.47
5.18
SBA-15-SO3H 318
13
CH3). CNMR (75 MHz, DMSO) δ (ppm): 23.90, 35.80,
84.85, 118.63, 126.72, 133.95, 136.42, 149.79, 162.33,
167.91, 169.72.; MS (m/z): 382(M+). Anal.Calcd for
C17H14N6O5: C, 53.40; H, 3.66; N, 21.99. Found: C, 53.50;
H, 3.80, N, 22.01.
5‑(4‑Methylphenyl)‑9,10‑dihydropyrido[2,3‑d:6,5‑d′]
dipyrimidine‑2,4,6,8(1H,3H,5H,7H)‑tetraone (Table 3,
compound 3g)
IR (KBr, cm−1): 3389, 3255, 1732, 1514. 1HNMR
(300 MHz, DMSO) δ (ppm): 10.49 (s, 2NH), 10.29 (s,
2NH), 6.98 (d, J = 9 Hz, 2H-Ar), 6.93 (d, J = 9 Hz,
2H-Ar), 6.69 (s, NH), 5.25 (s, 1H), 2.21 (s, 3H, CH3).13
CNMR (75 MHz, DMSO) δ (ppm): 165.42, 162.37,
154.25, 149.84, 136.31, 128.32, 126.51, 86.22, 32.12,
20.54. Anal.Calcd for C16H13N5O4: C, 56.64; H, 39.23; N,
20.65. Found: C, 56.70; H, 39.28, N, 20.67.
5‑(5‑Bromo‑2‑hydroxyphenyl)‑9,10‑dihydropyrido[2,3‑
d:6,5‑d′]dipyrimidine‑2,4,6,8(1H,3H,5H,7H)‑tetraone
(Table 3, compound 3j)
IR (KBr, cm−1): 3400, 3289, 3177, 1730. 1HNMR
(300 MHz, DMSO) δ (ppm): 11.73 (s, NH), 10.89 (s, NH),
10.03 (s, NH), 10.01 (s, NH), 7.13 (m, 3H-Ar), 6.47 (s,
NH), 4.78 (s, 1H).13 CNMR (75 MHz, DMSO) δ (ppm):
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J IRAN CHEM SOC
500
400
300
200
100
0
Fig. 4 N2 adsorption–desorp-
tion isotherm and BJH of SBA-
15-SO3H (a, b)
(a) 300
(b)
200
100
0
ADS
DES
0
0.5
1
1
10
100
P/P0
rp/nm
Table 2 Optimization of the
reaction conditions
Entry
Catalyst (g)
Solvent
Temperature (°C) Time (min)
Yield (%)
1
–
Solvent free
Solvent free
Solvent free
Solvent free
EtOH
120
60
60
Trace
85
2
0.02
0.05
0.1
120
3
120
10
96
4
120
10
95
5
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
Reflux
Reflux
Reflux
Reflux
100
120
120
120
120
60
70
6
CH3CN
65
7
DMF
75
8
H2O
50
9
Solvent free
Solvent free
Solvent free
Solvent free
65
10
11
12
110
60
90
120
10
96
130
10
96
163.31, 154.43, 151.57, 150.18, 149. 62, 148.86, 130.88,
130.16, 127.53, 89.33, 26.70. MS (m/z):421 (M++2). Anal.
Calcd for C15H10N5O4Br: C, 42.96; H, 2.39; N, 16.71.
Found: C, 43.15; H, 2.58, N, 16.89.
the intensity of the OH band in SBA-15-SO3H con-
firms that the modification of SBA-15 has been occurred.
The existence of strong peaks at 1175 and 1286 cm−1 is
related to the symmetrical and unsymmetrical stretching
S=O bonds in SBA-15-SO3H. A peak at 580 cm−1 can be
assigned to S–O bond in the synthesized catalyst. In both
spectra (Fig. 1a, b), a peak appeared at 1071 cm−1 which
is due to the Si–O stretching vibration [27]. The concentra-
tion of acidic groups in the SBA-15 determined by acid–
base titration showed that the amount of H+ in the catalyst
is 3.45 mmol g−1.
The XRD pattern of SBA-15-SO3H (Fig. 2) shows a
peak at 1.05° (2θ) and one small peak at 9.80° (2θ) which
completely confirms the mesoporous structure of the cata-
lyst. The SEM images of SBA-15 (Fig. 3a, b) show spheri-
cal morphology before and after the modification of the
catalyst with different sizes of spheres. They indicate that
the surface of SBA-15 is covered with sulfonic groups after
modification (Fig. 3b). It can be concluded that its spherical
morphology remains unchanged during the surface modifi-
cation. Figure 3b shows uniformity in particles. This figure
also shows nanoparticles with the size about 50 nm. The
TEM images (Fig. 3c, d) show the hexagonal arrangement
of the functionalized catalyst.
5‑(4‑Hydroxyphenyl)‑9,10‑dihydropyrido[2,3‑d:6,5‑d′]
dipyrimidine‑2,4,6,8(1H,3H,5H,7H)‑tetraone (Table 3,
compound 3i)
1
IR (KBr, cm−1): 3171, 1712, 1628. HNMR (300 MHz,
DMSO) δ (ppm) : 10.45 (s, 2NH), 10.23 (s, 2NH), 8.98
(s, OH), 6.81 (d, J = 9 Hz, 2H-Ar), 6.68 (s, NH), 6.57
(d, J = 9 Hz, 2H-Ar), 5.19 (s, 1H).13CNMR (75 MHz,
DMSO) δ (ppm): 165.78, 154.71, 153.64, 149.79, 129.17,
127.42, 114.49, 84.85, 35.81. Anal.Calcd for C15H11N5O6:
C, 50.42; H, 3.08; N 19.60. Found: C, 50.55, H, 3.15; N,
19.70.
Catalyst characterization
In the IR spectra (Fig. 1a, b), the bands appearing at 3427
and 3397 cm−1 are due to the stretching of the OH groups.
In comparison with the IR spectra of SBA-15, increasing
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J IRAN CHEM SOC
Table 3 Synthesis of pyrido[2,3-d:6,5-d′]dipyrimidine derivatives (3) from reaction of 6-aminouracil (1) and aldehydes (2) in the presence of
SBA-15-SO3H as catalyst
Entry
1
Aldehyde 2(a–l)
Producta 3(a–l)
Time (min)
30
Yieldb (%)
96
Mp (°C)/Ref.
295/[14]
3a
3a
2
3
4
15
10
15
95
96
85
230/[14]
300/[14]
>300/[14]
3b
3b
3c
3c
3d
3d
5
60
73
>300
3e
3e
6
30
98
250/[14]
3f
3f
1 3

J IRAN CHEM SOC
Table 3 continued
Entry
7
Aldehyde 2(a–l)
Producta 3(a–l)
Time (min)
45
Yieldb (%)
88
Mp (°C)/Ref.
>300/[14]
3g
3g
8
60
77
>300
3h
3h
9
30
90
>300
3i
3i
10
11
15
30
92
85
>300
3j
3j
>300/[14]
3k
3k
12
30
90
228/[28]
3l
3l
a
Reaction conditions: T = 120º C, 6-aminouracil (2 mmol), aldehyde (1 mmol), and SBA-15-SO3H (0.05 g)
Isolated yields; all the synthesized compounds were known except 3e, 3h, 3i, 3j and their physical and spectral data agree with the reported values
b
1 3

J IRAN CHEM SOC
Scheme 3 Plausible mechanism for the synthesis of pyrido[2,3-d:6,5-d′]dipyrimidine derivatives
According to Table 2, the best result was obtained
when 0.05 g of SBA-15-SO3H was used (Table 2, entry
3). Increasing the amount of the catalyst did not have any
effect on the product yield and the reaction time (Table 2,
entry 4). It should be mentioned that when the reaction pro-
ceeded in the absence of the catalyst, only a trace amount
of the product was obtained (Table 2, entry 1). The perfor-
mance of the SBA-15-SO3H in various solvents (EtOH,
CH3CN, DMF and H2O) was also investigated (Table 2,
entries 5–8). The results demonstrate that solvent-free con-
dition was the best choice (Table 2, entry 3). In order to
determine the optimum temperature for this reaction, the
condensation reaction was carried out under solvent-free
conditions at 100 to 130 °C using SBA-15-SO3H as cat-
alyst. At 100 °C, the yield of the reaction was 65 % and
increased to 96 % at 120 °C (Table 2, entries 9 and 11).
There was no significant change in the yield and reaction
time at higher temperature (Table 2, entry 12).
After optimization of the reaction conditions, a series
of pyrido[2,3-d:6,5-d′]dipyrimidine derivatives were syn-
thesized by the condensation of 6-aminouracil (1) and dif-
ferent aldehydes (2a–l) under optimized reaction condi-
tions (Table 3). All the reactions were completed within
10–60 min. As Table 3 shows, the aldehydes with electron
withdrawing substituents afford the desired product in
shorter reaction times and higher yields (Table 3, entries
2, 3 and 6). In the case of 2-bromobenzaldehyde, the steric
hindrance resulted in the low yield of the product (Table 3,
entry 5). A plausible mechanism for the formation of the
pyrido[2,3-d:6,5-d′]dipyrimidine derivatives is shown in
Scheme 3. First, acidic sites on the surface of the catalyst
activate the aldehyde (2). In the second step, nucleophilic
Fig. 5 Reusability of the catalyst
BET studies of the catalyst show that the surface area
and pore volume decreased after modification of SBA-
15 with ClSO3H (Table 1). BJH analysis shows pore vol-
ume and pore area distribution in the mesoporous range
(Fig. 4b).
Catalytic activity of SBA‑15‑SO3H
The catalytic activity of SBA-15-SO3H was investigated
during the synthesis of pyrido[2,3-d:6,5-d′]dipyrimidine
derivatives. The reaction between 6-aminouracil (1) and
4-chlorobenzaldehyde (2) (Scheme 1) was chosen as a
model reaction to find the best condition for the prepa-
ration of pyrido[2,3-d:6,5-d′]dipyrimidine derivatives.
The results of optimization studies are summarized in
Table 2.
1 3

J IRAN CHEM SOC
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hyde (2), and consequently water elimination produces the
intermediate (4). In the next step, nucleophilic attack of the
other 6-aminouracil molecule (1) to intermediate (4) leads
to the production of the intermediate (5). NH2 activation in
the intermediate (6) by SBA-15-SO3H helps in the elimina-
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The reusability of the catalyst was investigated using
6-aminouracil and 4-nitrobenzaldehyde as model sub-
strates. After completion of the reaction, the decanted cata-
lyst was washed with dichloromethane and dried in an oven
at 60 °C for 2 h. Then it was subjected to another reac-
tion with identical substrates. As can be seen in Fig. 5, the
recovered catalyst can be used for at least 6 runs without
significant loss of its activity.
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