Nano-basic silica as an efficient catalyst for the multi-component preparation of pyrano[2,3-d]pyrimidine derivatives

Article abstract of DOI:10.1515/mgmc-2016-0034

A high-yield protocol is explored for the synthesis of pyrano[2,3-d]pyrimidines through the multi-component reaction of aromatic aldehydes, 1,3-Dimethylbarbituric acid, and malononitrile using nano-basic silica as an efficient catalyst. The method tolerat

Full text of DOI:10.1515/mgmc-2016-0034

Main Group Met. Chem. 2016; aop
NNaafisnehosa-dbataShseiikchasn-iSlhiacmasabaadsi aandnMaejifdfGihcaisehanngt* catalyst for the
multi-component preparation of pyrano[2,3-d]
pyrimidine derivatives
DOI 10.1515/mgmc-2016-0034
1971; Pershin et al., 1972; Regnier et al., 1972; Suguira et al.,
1973; Heber et al., 1993; Furuya and Ohtaki, 1994; Hirota
et al., 1994; Musstazza et al., 2001).
Received August 9, 2016; accepted October 27, 2016
Abstract: Ahigh-yieldprotocolisexploredforthesynthesis
of pyrano[2,3-d]pyrimidines through the multi-component
reaction of aromatic aldehydes, 1,3-Dimethylbarbituric
acid, and malononitrile using nano-basic silica as an
efficient catalyst. The method tolerates various electron-
donating and electron-withdrawing groups on the aro-
matic ring. Nano-basic silica was characterized by field
emission scanning electron microscope (FE-SEM) N2
adsorption-desorption isotherm, dynamic light scattering
(DLS), and X-ray powder diffraction (XRD) techniques. The
particles of nano-basic silica have uniform spheres with
sizes that are <ꢀ100 nm. XRD pattern shows that nano-
basic silica is amorphous. The specific surface area and
pore volume distribution of nano-basic silica are 663 m2g−1
and 0.634 cm3g−1, respectively.
Therefore, great research attention has been devoted
to the synthesis of such compounds, and at present, the
multi-component reaction of aromatic aldehydes, barbi-
turic acids, and malononitrile under different conditions
is the simplest and newest approach for their synthesis.
Many different bases have been found to be viable cat-
alysts for this reaction (Devi et al., 2003; Bagley et al.,
2004; Seeliger et al., 2007; Elinson et al., 2011; Azari-
far et al., 2012; Khurana and Vij, 2013; Elinson et al.,
2014; Khazaei et al., 2015). Despite these procedures,
the established method for the reaction systems based
on the uses of homogeneous catalysts are often plagued
by many inherent problems, including corrosion, diffi-
culties related to catalyst recycling, and generation of
waste. Thus, the use of heterogeneous catalysts remains
Keywords: 1,3-dimethylbarbituric acid; multi-component in demand.
reaction; nano-basic silica; pyrano[2,3-d]pyrimidines.
In continuation of our reports on the synthesis of het-
erocyclic compounds (Ghashang, 2012a,b, 2016; Dehbashi
et al., 2013; Shafiee et al., 2013; Ghashang et al., 2014,
2015a,b, 2016a,b; Shafiee et al., 2014; Momayezan et al.,
2015; Baziar and Ghashang, 2016; Taghrir et al., 2016;
Zare et al., 2016), we were encouraged to examine the effi-
ciency of a nano-basic silica as a green, environmentally
friendly catalyst in preparation of pyrano[2,3-d]pyrimi-
dines (Scheme 1).
Introduction
Over the years uracil and its fused derivatives, e.g.
pyrano[2,3-dpyrimidines, have gained considerable inter-
est, because they are a class of natural and synthetic
compounds possessing a great variety of biological and
pharmaceutical activities. Thus, the discovery of such
compounds in both natural products as well as via syn-
thetic procedures has received significant challenges.
Various pyrano[2,3d]pyrimidine derivatives that have
been found so far show interesting anti-tumor, hepatopro-
tective, anti-bronchitis, and anti-AIDS activities (Metolcsy,
Results and discussion
We investigated the morphological evolution of the cata-
lyst using the field emission scanning electron microscope
(FE-SEM) image of the sample. As shown in Figure 1, the
particles of nano-basic silica are relatively homogeneous
in size and shape; they are uniform spheres with sizes of
<ꢀ100 nm.
Dynamic light scattering (DLS) was used to deter-
mine the particle size distributions of the nanoparti-
cles of nano-basic silica dispersed in ethanol (1 gl−1 was
sonicated in 20 ml of ethanol for 2 h). According to the
*Corresponding author: Majid Ghashang, Department of Chemistry,
Faculty of Sciences, Najafabad Branch, Islamic Azad University,
P.O. Box 517, Najafabad, Esfahan, Iran,
e-mail: ghashangmajid@gmail.com
Nafisehsadat Sheikhan-Shamsabadi: Department of Chemistry,
Faculty of Sciences, Najafabad Branch, Islamic Azad University, P.O.
Box 517, Najafabad, Esfahan, Iran
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ꢀN. Sheikhan-Shamsabadi and M. Ghashang: Nano-basic silica as an efficient catalyst
2ꢀ
DLS-measurement, the size distribution of the nano-
particles is almost less than 100 nm, with an average of
88 nm (Figure 2). Figure 3 shows the X-ray powder diffrac-
tion (XRD) pattern of nano-basic silica. The XRD pattern
shows a hump at 2θ ranging from 20–30, thus indicating
the amorphous state of the nano-particles.
Using the Brunauer–Emmett–Teller (BET) method, we
investigated the nitrogen adsorption/desorption isotherm
to determine the specific surface area and pore volume
400
100
0
20
30
40
50
60
70
80
Position (2θ°)
H
C
3
O
Figure 3:ꢁXRD pattern of nano-basic silica.
N
O
NH2
CN
O
Nano-basic silica
Solvent-free
H
3C
N
+ Ar-CHO + CH2(CN)2
N
H3C
N
O
O
Ar
O
70
60
50
40
30
CH3
Scheme 1:ꢁPreparation of pyrano[2,3-d]pyrimidines using nano-
basic silica.
20
10
0
0.0
0.2
0.4
0.6
0.8
1.0
P/P0
Figure 4:ꢁNitrogen adsorption/desorption isotherm of nano-basic
silica at 77K.
distribution at 663 m2g−1 and 0.634 cm3g−1, respectively.
The isotherm of nano-basic silica was classified as type IV
with hysteresis loops of H1 type (Figure 4), indicating the
mesoporous nature of the sample.
Figure 1:ꢁFE-SEM micrograph of nano-basic silica.
100
80
60
40
20
0
The catalytic activity of the as-prepared nano-basic
silica was examined by the condensation reaction of
aromatic aldehydes, 1,3-dimethylbarbituric acid, and
malononitrile to afford pyrano[2,3-d]pyrimidines.
First, to optimize the reaction conditions, the conden-
sations of benzaldehyde, 1,3-dimethylbarbituric acid,
and malononitrile were examined in different polar and
non-polar solvents as well as a solvent-free condition at
reflux or at 90°C (Table 1). The reaction yields no product
at room temperature, in the absence of a catalyst and
also in non-polar solvents, such as hexane, CH2Cl2,
and Et2O. The main reason for these results is that the
temperature has an essential role in the progress of the
reaction. Using polar solvents, such as EtOH, EtOAc,
0
20
40
60
80
100
120
140
Size (nm)
Figure 2:ꢁParticle size distribution of nano-basic silica.
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N. Sheikhan-Shamsabadi and M. Ghashang: Nano-basic silica as an efficient catalystꢀ
ꢀ3
Table 1:ꢁOptimization of the reaction conditions.
and CH3CN, can lead to poor yields. Finally, we observed
that solvent-free, thermal heating to 90°C is the optimal
choice to generate an excellent product yield (89%) in
2 h. Increasing the catalyst amounts do not improve the
product yield. Thus, the optimum condition is a solvent-
free and thermal condition (90°C) using 25 mol% of the
catalyst.
The proposed reaction mechanism of the three-
component reaction of aromatic aldehydes, 1,3-dimeth-
ylbarbituric acid and malononitrile catalyzed by
nano-basic silica is shown in Scheme 2. At the beginning
of the reaction, two active methylene groups (a CH2 group
in 1,3-dimethylbarbituric acid and malononitrile) reacted
with basic silica to form carbanions A and E. Carbanion
A quickly attaches to the carbonyl group of aromatic
Entryꢁ
Catalyst amountꢁ Solventꢁ Temperatureꢁ
(mol%) (5 ml) (°C)
Time (h)/
Yield (%)a
1
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
25ꢃ Hexane ꢃ Reflux
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
2/0
2/32
2/61
2/66
2/0
2
25ꢃ EtOAc
25ꢃ EtOH
25ꢃ H2O
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
Reflux
Reflux
Reflux
Reflux
Reflux
90
3
4
5
25ꢃ Et2O
25ꢃ CH2Cl2
6
2/0
7
25ꢃ
10ꢃ
50ꢃ
75ꢃ
25ꢃ
–ꢃ
–
–
–
–
–
–
1.1/92
2/78
1/88
0.8/85
2/0
8
90
9
90
10
11
12
90
r.t.
90
2/0
aIsolated yield.
Nano-basic silica
N
Ar
O
O
Ar-CHO
N
H
H
NC
CN
OH
H
N
B
N
A
+
OH
Ar
OH
CN
O
N
H
3C
NC
N
O
O
C
O
O
CH3
O
N
H
3C
D
N
C
N
CN
O
Ar
O
E
H
CH3
CH3
CH3
N
O
O
N
O
O
CN
CN
1,3-H shift
CN
CN
N
N
H
3C
H
3C
Ar
O
Ar
O
Cyclization
CH3
N
NH2
CN
O
O
N
H
3C
O
Ar
Scheme 2:ꢁProposed reaction mechanism.
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ꢀN. Sheikhan-Shamsabadi and M. Ghashang: Nano-basic silica as an efficient catalyst
4ꢀ
aldehyde, resulting in B and C intermediates. The formed aromatic aldehydes bearing electron-withdrawing groups
intermediate C eliminates one molecule of water to (e.g. nitro and halide), showed better reactivity and the
form benzylidene malononitrile D (generally known as reactions were completed in shorter time. On the one
Knoevenagel condensation of benzaldehyde with malon- hand, the presence of electron-withdrawing groups, such
onitrile). The condensation of E with D and the continuing as nitro, has a powerful deactivating effect on the posi-
reaction progress via an intramolecular cyclization leads tive carbon of aldehydes. Thus, it decreased the activa-
to the formation of the desired products.
tion energy of the carbanion addition to a carbonyl group
Subsequently, the scope of the reaction for different (Scheme 2) and increased the rate of the reaction. On the
aldehydes was studied using the optimized reaction con- other hand, electron-withdrawing groups decreased the
ditions (see Table 2). Both aldehydes with various sub- energy of the LUMO orbital, and the nucleophilic addi-
stituents participated smoothly in the reaction, providing tion of carbanion D to benzylidene malononitrile D is
the desired products in high to excellent yields. However, faster when compared with that of electron-donating
Table 2:ꢁPreparation of pyrano[2,3-d]pyrimidines using nano-basic silica as catalyst (25 mol%).
Entry
Aldehyde
CHO
Time (h)
Yield (%)a
M.p. [°C] (Lit. M.p.)
References
1
1.1
92
218–220 (219–222)
Elinson et al., 2014
CHO
2
3
1.4
0.9
75
206–208 (202–203)
210–212 (206)
Elinson et al., 2014
Khazaei et al., 2015
CHO
89
Cl
CHO
4
0.6
93
207–209 (204)
Khazaei et al., 2015
NO2
CHO
5
6
7
8
1.2
1
79
89
96
73
210–212 (211–212)
231–233 (235)
Khazaei et al., 2015
Khazaei et al., 2015
Elinson et al., 2014
Khazaei et al., 2015
Cl
Cl
CHO
Br
CHO
0.9
1
228–230 (229–232)
246–248 (247–248)
F
CHO
Cl
CHO
Cl
9
1.5
77
69
241–243 (238–239)
263–265 (–)
Azarifar et al., 2012
CHO
10
2
–
OMe
MeO
OMe
aIsolated yield; all products were characterized by NMR analysis.
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N. Sheikhan-Shamsabadi and M. Ghashang: Nano-basic silica as an efficient catalystꢀ
ꢀ5
until water was completely evaporated. The resulting precipitate
was washed with water several times and dried in an oven at 100°C
for 1 h.
groups. Moreover, compared to those at the para posi-
tion, aldehydes substituted at the ortho position, such as
2-chloro and 2,4-dichloro (Table 2, Entries 5,9), produced
a good yield but converted to the product in longer reac-
tion times. This can be attributed to the steric hindrance
of ortho position.
General procedure for the synthesis of pyrano[2,3-d]
pyrimidine derivatives
A mixture of aldehydes (1 mmol), 1,3-dimethylbarbituric acid
(1 mmol), malononitrile (1 mmol), and nano-basic silica (25 mol%)
was heated in 90°C for the appropriate time. The progress of the
reaction was monitored by TLC. Upon completion of the reaction,
the reaction mixture was dissolved in hot ethanol. The catalyst was
removed by simple filtration. The solvent was concentrated, and the
crude products were purified by crystallization from EtOH. The spec-
tral data of selected compounds are given below.
Conclusion
Nano-basic silica was prepared from the reaction of NaOH
with nano-silica and then characterized by FE-SEM, DLS,
XRD, and BET techniques. The results show that the parti-
cles are homogeneous in size and shape, with an average
size of 88 nm. The sample has specific surface area and
pore volume distribution of 663 m2g−1 and 0.634 cm3g−1,
respectively. Using the prepared nano-basic silica as cata-
lyst, a number of pyrano[2,3-d]pyrimidines were synthe-
sized in high yields through the multi-component reaction
of 1,3-dimethylbarbituric acid, aromatic aldehydes, and
malononitrile. The study provides a procedure with the
advantage of operational simplicity and a satisfactory
substrate scope.
7-amino-1,3-dimethyl-2,4-dioxo-5-phenyl-1,3,4,5-tetrahy-
dro-2H-pyrano[2,3-d]pyrimidine-6-carbonitrile
(Table
2,
Entry 1):ꢁ1H-NMR (400 MHz, DMSO-d6): δꢀ=ꢀ3.04 (s, 3H, CH3), 3.34 (s,
3H, CH3), 4.63 (s, 1H, CH), 7.14–7.30 (m, 7H) ppm; Elemental analysis:
Found: C, 61.85; H, 4.48; N, 17.98%; C16H14N4O3; requires: C, 61.93; H,
4.55; N, 18.06%.
7-amino-1,3-dimethyl-2,4-dioxo-5-(p-tolyl)-1,3,4,5-tetrahy-
dro-2H-pyrano[2,3-d]pyrimidine-6-carbonitrile
(Table
2,
Entry 2):ꢁ1H-NMR (400 MHz, DMSO-d6): δꢀ=ꢀ2.27 (s, 3H, CH3), 3.04
(s, 3H, CH3), 3.35 (s, 3H, CH3), 4.61 (s, 1H, CH), 7.08 (d, Jꢀ=ꢀ7.9, 2H),
7.18 (d, Jꢀ=ꢀ7.9, 2H), 7.27 (s, 2H, NH2) ppm; 13C-NMR (100 MHz, DMSO-
d6): δꢀ=ꢀ21.4, 29.3, 31.2, 39.6, 62.5, 119.4, 127.0, 127.5, 129.3, 138.6, 145.2,
152.4, 158.8, 161.6, 162.5 ppm; Elemental analysis: Found: C, 62.90;
H, 4.93; N, 17.22% C17H16N4O3; requires: C, 62.95; H, 4.97; N, 17.27%.
Experimental section
All reagents were purchased from Merck Company (Mumbai,
India) and used without further purification. FE-SEM images were
obtained on HITACHI S-4160, Japan. N2 adsorption measurements
of the catalyst were carried out using micro metrics adsorption
equipment (Quantachrome instrument, Model Nova 2000, USA), N2
(99.99%) as the analysis gas and the catalyst samples were slowly
heated to 120°C for 3 h under nitrogen atmospheric. The total pore
volume was obtained from the maximum amount of nitrogen gas
adsorbed at partial pressure P/P0ꢀ=ꢀ0.999. DLS measurement was
done using a Zetasizer Nano ZS instrument (Zetasizer Nano ZS,
Model ZEN3600, Malvern Instruments, Malvern, UK). The NMR
spectra were recorded on a Bruker Avance DPX 400 MHz instrument
(Bruker BioSpin, Fällanden, Switzerland). The spectra were meas-
ured in DMSO-d6 relative to TMS (0.00 ppm). Elemental analyses
(C, H, N) were carried out on a Perkin-Elmer 2400 analyzer (Perkin
Elmer, Norwalk, CT, USA). Melting points were determined in open
capillaries with a BUCHI 510 melting point apparatus (Mount Holly,
NJ, USA). TLC was performed on silica gel Polygram SIL G/UV 254
plates (Merck, Darmstadt, Germany).
7-amino-5-(4-chlorophenyl)-1,3-dimethyl-2,4-dioxo-1,3,4,5-
tetrahydro-2H-pyrano[2,3-d]pyrimidine-6-carbonitrile (Table 2,
1
Entry 3):ꢀ H-NMR (400 MHz, DMSO-d6): δꢀ=ꢀ3.04 (s, 3H, CH3), 3.35
(s, 3H, CH3), 4.75 (s, 1H, CH), 7.23–7.37 (m, 6H) Elemental analysis:
Found: C, 55.64; H, 3.71; N, 16.16% C16H13ClN4O3; requires: C, 55.74; H,
3.80; N, 16.25%.
7-amino-1,3-dimethyl-5-(3-nitrophenyl)-2,4-dioxo-1,3,4,5-tet-
rahydro-2H-pyrano[2,3-d]pyrimidine-6-carbonitrile (Table 2,
product 4):ꢁ1H-NMR (400 MHz, DMSO-d6): δꢀ=ꢀ3.05 (s, 3H, CH3), 3.37
(s, 3H, CH3), 5.07 (s, 1H, CH), 7.33 (s, 2H, NH2), 7.63–7.96 (m, 3H), 8.11
(d, Jꢀ=ꢀ7.7 Hz, 1H) ppm; Elemental analysis: Found: C, 54.06; H, 3.63;
N, 19.66% C16H13N5O5; requires: C, 54.09; H, 3.69; N, 19.71%.
7-amino-5-(2,4-dichlorophenyl)-1,3-dimethyl-2,4-dioxo-1,3,4,5-
tetrahydro-2H-pyrano[2,3-d]pyrimidine-6-carbonitrile (Table 2,
Entry 5):ꢁ1H-NMR (400 MHz, DMSO-d6): δꢀ=ꢀ3.04 (s, 3H, CH3), 3.35 (s,
3H, CH3), 4.87 (s, 1H, CH), 7.17–7.61 (m, 5H) Elemental analysis: Found:
C, 50.59; H, 3.14; N, 14.64% C16H12Cl2N4O3; requires: C, 50.68; H, 3.19;
N, 14.78%.
7-amino-5-(4-bromophenyl)-1,3-dimethyl-2,4-dioxo-1,3,4,5-tet-
rahydro-2H-pyrano[2,3-d]pyrimidine-6-carbonitrile (Table 2,
Entry 6):ꢁ1H-NMR (400 MHz, DMSO-d6): δꢀ=ꢀ3.03 (s, 3H, CH3), 3.34
(s, 3H, CH3), 4.34 (s, 1H, CH), 7.20–7.48 (m, 6H) Elemental analysis:
Found: C, 49.29; H, 3.25; N, 14.27% C16H13BrN4O3; requires: C, 49.38;
H, 3.37; N, 14.40%.
Preparation of basic silica nanopowders
To a suspension of silica nanopowders (10 g, 30–50 nm) in pure
water (100 mL), 5 g of NaOH was added under vigorous magnetic stir-
ring. The mixture was continuously stirred at a temperature of 100°C
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6ꢀ
7-amino-5-(4-fluorophenyl)-1,3-dimethyl-2,4-dioxo-1,3,4,5-
tetrahydro-2H-pyrano[2,3-d]pyrimidine-6-carbonitrile (Table 2,
midines using microwave heating in the solid state. Tetrahedron
Lett. 2003, 44, 8307–8310.
Entry 7):ꢁ1H-NMR (400 MHz, DMSO-d6): δꢀ=ꢀ3.02 (s, 3H, CH3), 3.34 Elinson, M. N.; Ilovaisky, A. I.; Merkulova, V. M.; Nikishin, G. I.;
(s, 3H, CH3), 4.26 (s, 1H, CH), 7.08–7.23 (m, 6H) Elemental analysis:
Found: C, 58.63; H, 4.08; N, 17.12% C16H13FN4O3; requires: C, 58.54; H,
3.99; N, 17.07%.
Zaimovskaya, T. A. Electrocatalytic multicomponent assem-
bling of aldehydes, N-alkyl barbiturates and malononitrile: an
efficient approach to pyrano[2,3-d]pyrimidines. Mendeleev.
Commun. 2011, 21, 122–124.
7-amino-5-(3-chlorophenyl)-1,3-dimethyl-2,4-dioxo-1,3,4,5- Elinson, M. N.; Ryzhkov, F. V.; Merkulova, V. M.; Ilovaisky, A. I.;
tetrahydro-2H-pyrano[2,3-d]pyrimidine-6-carbonitrile (Table 2,
Entry 8):ꢁ1H-NMR (400 MHz, DMSO-d6): δꢀ=ꢀ3.04 (s, 3H, CH3), 3.35 (s,
3H, CH3), 4.71 (s, 1H, CH), 7.19–7.36 (m, 6H) ppm; Elemental analysis:
Found: C, 55.68; H, 3.87; N, 16.17%; C16H13ClN4O3; requires: C, 55.74; H,
3.80; N, 16.25%.
Nikishin, G. I. Solvent-free multi-component assembling of
aldehydes, N,N′-dialkyl barbiturates and malononitrile: fast
and efficient approach to pyrano[2,3-d]pyrimidines. Heterocycl.
Commun. 2014, 20, 281–284.
Furuya, S.; Ohtaki, T. Pyridopyrimidine derivatives, their production
and use. Eur. Pat. Appl. 1994, EP 608565.
7-amino-5-(2-chlorophenyl)-1,3-dimethyl-2,4-dioxo-1,3,4,5- Ghashang, M. ZnAl2O4–Bi2O3 composite nano-powder as an efficient
tetrahydro-2H-pyrano[2,3-d]pyrimidine-6-carbonitrile (Table 2,
Entry 9):ꢁ1H-NMR (400 MHz, DMSO-d6): δꢀ=ꢀ3.04 (s, 3H, CH3), 3.34 (s,
3H, CH3), 4.73 (s, 1H, CH), 7.21–7.30 (m, 5H), 7.39 (d, Jꢀ=ꢀ7.7 Hz, 1H) ppm;
catalyst for the multi-component, one-pot, aqueous media
preparation of novel 4H-chromene-3-carbonitriles. Res. Chem.
Intermed. 2016, 42, 4191–4205.
13C-NMR (100 MHz, DMSO-d6): δꢀ=ꢀ27.6, 29.3, 33.4, 57.3, 88.0, 118.7, 127.7, Ghashang, M. Zinc hydrogen sulfate promoted multi-component
128.6, 129.7, 132.1, 136.0, 141.2, 150.0, 151.2, 157.9, 160.8 ppm; Elemental
analysis: Found: C, 55.89; H, 3.95; N, 16.21%; C16H13ClN4O3; requires:
C, 55.74; H, 3.80; N, 16.25%.
preparation of highly functionalized piperidines. Lett. Org.
Chem. 2012a, 9, 497–502.
Ghashang, M. Preparation and application of barium sulfate nano-
particles in the synthesis of 2, 4, 5-triaryl and N-aryl (alkyl)-2, 4,
5-triaryl imidazoles. Curr. Org. Synth. 2012b, 9, 727–732.
7-amino-1,3-dimethyl-2,4-dioxo-5-(3,4,5-trimethoxyphenyl)-
1,3,4,5-tetrahydro-2H-pyrano[2,3-d]pyrimidine-6-carbonitrile Ghashang, M.; Mansoor, S. S.; Aswin, K. Thiourea dioxide: an
1
(Table 2, Entry 10):ꢀ H-NMR (400 MHz, DMSO-d6): δꢀ=ꢀ3.04 (s, 3H,
CH3), 3.34 (s, 3H, CH3), 3.83 (s, 6H, OCH3), 3.84 (s, 3H, OCH3), 4.27 (s,
1H, CH), 6.45 (s, 2H), 7.31 (s, 2H, NH2) ppm; 13C-NMR (100 MHz, DMSO-
efficient and reusable organocatalyst for the rapid one-pot syn-
thesis of pyrano [4,3-b] pyran derivatives in water. Chin. J. Catal.
2014, 35, 127–133.
d6): δꢀ=ꢀ27.9, 29.6, 33.7, 56.1, 57.5, 58.1, 88.3, 106.1, 119.1, 136.2, 136.5, Ghashang, M.; Jabbarzare, S.; Tavakoli, H.; Banisadeghi, H.;
150.2, 151.5, 158.2, 160.3. 161.4 ppm; Elemental analysis: Found: C,
57.23; H, 5.24; N, 13.89%; C19H20N4O6; requires: C, 57.00; H, 5.04; N,
13.99%.
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Acknowledgments: The authors are indebted to the
Islamic Azad University, Najafabad Branch, for the finan-
cial support provided for this research.
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