G Model
CCLET-2675; No. of Pages 4
2
D. Rajguru et al. / Chinese Chemical Letters xxx (2013) xxx–xxx
NH2
d
23.27, 30.49, 55.87, 101.64, 111.55, 112.90, 116.17, 118.86,
CN
122.44, 124.11, 150.92, 151.67, 152.05, 153.94, 158.71, 159.50.
OH
O
CN
2.2.3. 2-Amino-4-(furan-2-yl)-7-methyl-5-oxo-4H,5H-pyrano[4,3-
b]pyran-3-carbonitrile (4i, C14H10N2O4)
.
H6P2W18O62 18H2O (1 mol%)
Ar
+
+
ArCHO
Water/ reflux
O
Pink crystals; yield: 95%; Mp 223–225 8C (223–224 8C) [29]; IR
CN
O
O
O
(KBr, cmÀ1):
n
3208, 3085, 2195, 1620, 1384, 1258, 1139, 1013,
1 (a-l)
2
3
4 (a-l)
980, 754; 1H NMR (400 MHz, DMSO-d6):
d
2.25 (s, 3H, CH3), 4.47 (s,
1H, CH), 6.10 (s, 1H, 55CH), 6.16 (d, 1H, ArH, J = 3.1 Hz); 6.30 (dd,
1H, ArH, Ja = 1.8, Jb = 1.2 Hz); 6.97 (s, 2H, NH2), 7.37 (d, 1H, ArH,
Scheme 1. H6P2W18O62Á18H2O catalyzed synthesis of 2-amino-4-aryl-3-cyano-5-
oxo-4H,5H-pyrano[4,3-b]pyrans in water.
J = 1.0 Hz); 13C NMR (100 MHz, DMSO-d6):
d 19.43, 29.88, 55.36,
97.95, 98.40, 105.90, 110.17, 118.89, 141.55, 154.12, 158.58,
Based on the previous studies on the use of heteropolyacids as
catalysts, and in a continuation of our endeavors for the develop-
ment of simple and highly expedient methods for the synthesis of
polyfunctionalized heterocycles of biological importance [29], we
examined the possibility of using H6P2W18O62Á18H2O, a Wells-
Dawson type heteropolyacid, as a catalyst for the one-pot synthesis
of pyrano[4,3-b]pyran derivatives by condensing aromatic alde-
hydes, malononitrile and 4-hydroxy-6-methylpyran-2-one in water
under reflux (Scheme 1).
158.75, 161.13, 162.36. MS (m/z): 270.0 (M+).
2.2.4. 2-Amino-7-methyl-5-oxo-4-(thiophen-2-yl)-4H,5H-
pyrano[4,3-b]pyran-3-carbonitrile (4j, C14H10N2O3S)
Colorless crystals; yield: 92%; Mp 242–244 8C (242–244 8C)
[29]; IR (KBr, cmÀ1):
n
3081, 2857, 2196, 1717, 1614, 1375, 1254,
1189, 1044, 777; 1H NMR (400 MHz, DMSO-d6):
d
2.23 (s, 3H, CH3),
4.66 (s, 1H, CH), 6.13 (s, 1H, 55CH), 6.91 (dd, 1H, ArH, Ja = 3.5 Hz,
Jb = 1.5 Hz); 6.97 (d, 1H, ArH, J = 2.9 Hz); 7.13 (s, 2H, NH2), 7.25 (d,
1H, ArH, J = 3.9 Hz); 13C NMR (100 MHz, DMSO-d6):
d 19.40, 31.26,
2. Experimental
57.81, 97.94, 100.89, 119.03, 124.44, 124.63, 126.61, 147.78,
157.72, 158.44, 161.22, 162.57. MS (m/z): 286.1 (M+).
All the chemicals were purchased from Merck and Sigma–
Aldrich and used without further purification. Melting points were
determined in open glass capillaries and are uncorrected. IR
spectra were recorded on a Perkin Elmer-1430 spectrophotometer
using potassium bromide discs. 1H NMR and 13C NMR spectra were
obtained at 400 MHz with a Bruker WM-400 spectrometer using
DMSO-d6 as solvent and TMS as an internal standard. MS spectra
were measured at Micromass ZMD ESI (70 eV) system.
2.2.5. 2-Amino-7-methyl-4-(5-methyl-thiophen-2-yl)-5-oxo-4H,5H-
pyrano[4,3-b]pyran-3-carbonitrile (4k, C15H12N2O3S)
Brown crystals; yield: 93%; Mp 176–177 8C (175–177 8C) [29];
IR (KBr, cmÀ1):
n
3471, 3363, 3119, 2923, 2211, 1639, 1549, 1296,
1039, 743; 1H NMR (400 MHz, DMSO-d6):
d
2.24 (s, 3H, CH3), 2.39
(s, 3H, CH3), 4.57 (s, 1H, 55CH), 6.04 (s, 1H, 55CH), 6.55 (d, 1H, ArH,
J = 1.6 Hz), 6.74 (d, 1H, ArH, J = 3.3 Hz), 6.84 (s, 2H, NH2); 13C NMR
(100 MHz, DMSO-d6):
d 14.97, 19.44, 31.30, 58.19, 97.89, 101.02,
2.1. General procedure for the synthesis of 2-amino-4-aryl-5-oxo-4H,
5H-pyrano[4,3-b]pyran-3-carbonitriles
118.97, 124.29, 124.47, 138.17, 140.64, 157.51, 158.28, 161.30,
162.10. MS (m/z): 301.1 (M++1).
A mixture of 4-hydroxy-6-methylpyran-2-one (1 mmol), aro-
matic aldehyde (1 mmol), malononitrile (1.2 mmol) and
H6P2W18O62Á18H2O (1 mol%) in 20 mL of water was stirred under
reflux for appropriate time. After completion of the reaction as
monitored by TLC, the reaction mixture was cooled to room
temperature. The solid product was collected by filtration, washed
with aqueous ethanol (1:1) and recrystallized from ethanol to yield
the pure product. All products were characterized by their spectral
and physical data.
2.2.6. 2-Amino-4-(5-chlorothiophen-2-yl)-7-methyl-5-oxo-4H,5H-
pyrano[4,3-b]pyran-3-carbonitrile (4l, C14H9ClN2O3S)
Yellow crystals; yield: 89%; Mp 226–227 8C (228–229 8C) [29];
IR (KBr, cmÀ1):
n
3322, 3191, 3112, 2196, 1671, 1606, 1514, 1344,
1262, 1037, 732; 1H NMR (400 MHz, DMSO-d6):
d
2.22 (s, 3H, CH3),
4.24 (s, 1H, CH), 6.13 (s, 1H,55CH), 6.84 (d, 1H, ArH, J = 2.7 Hz), 6.93
(s, 2H, NH2), 7.11 (d, 1H, ArH, J = 1.5 Hz); 13C NMR (100 MHz,
DMSO-d6):
d 19.35, 35.47, 58.28, 97.89, 101.18, 119.19, 123.95,
128.44, 133.26, 135.34, 159.97, 161.28, 162.07, 164.28. MS (m/z):
320.0 (M+).
2.2. Characterization data for the representative compounds
3. Results and discussion
2.2.1. 2-Amino-7-methyl-5-oxo-4-phenyl-4H,5H-pyrano[4,3-b]pyran
-3-carbonitrile (4a, C16H12N2O3)
We report herein a green approach for the synthesis of
pyrano[4,3-b]pyrans catalyzed by H6P2W18O62Á18H2O in water
under reflux. In our initial study, the reaction of 4-hydroxy-6-
methylpyran-2-one, benzaldehyde and malononitrile was used as
a model reaction to optimize the reaction conditions. The model
reaction was carried out in the presence of a variety of catalysts
and solvents under different conditions. The results obtained are
summarized in Table 1 and determined that the best results in
terms of reaction time, cost and yield were obtained with 1 mol% of
H6P2W18O62Á18H2O as catalyst in water under reflux. Higher
loading of the catalyst did not improve the product yield to a great
extent (Table 1, entry 9). The product formation was also observed
under reaction conditions at room temperature. However, the yield
was unsatisfactory (62%) and the reaction was incomplete even
after 4 h (Table 1, entry 8). Thus, refluxing all the components in
presence of 1 mol% of H6P2W18O62Á18H2O in water proved to be
the optimum conditions for this reaction.
Yellow crystals; yield: 92%; Mp 234–236 8C (236–238 8C) [22];
IR (KBr, cmÀ1):
n
3458, 3260, 3131, 3088, 2293, 1649, 1555, 1342,
1053, 790; 1H NMR (400 MHz, DMSO-d6):
d
2.56 (s, 3H, CH3), 4.76
(s, 1H, CH), 6.43 (s, 1H, 55CH), 7.20–7.22 (dd, 2H, ArH, Ja = 3.9 Hz,
Jb = 1 Hz), 7.27 (s, 2H, NH2), 7.42 (d, 1H, ArH, J = 3.5 Hz), 7.63–7.65
(dd, 2H, ArH, Ja = 4.2 Hz, Jb = 0.9 Hz); 13C NMR (100 MHz, DMSO-
d6):
d 23.15, 31.94, 57.84, 103.97, 116.22, 118.94, 122.51, 124.27,
124.58, 124.67, 127.72, 140.90, 152.95, 153.84, 158.40, 159.49.
2.2.2. 2-Amino-4-(4-methoxyphenyl)-7-methyl-5-oxo-4H,5H-
pyrano[4,3-b]pyran-3-carbonitrile (4h, C17H14N2O4)
Yellow crystals; yield: 86%; Mp 202–205 8C (205–207 8C) [22];
IR (KBr, cmÀ1):
n
3472, 3365, 2925, 2212, 1637, 1540, 1296, 1039,
824; 1H NMR (400 MHz, DMSO-d6):
d
2.57 (s, 3H, CH3), 3.76 (s, 3H,
OCH3), 5.13 (s, 1H, CH), 6.35 (s, 1H, 55CH), 6.65–6.66 (m, 2H, ArH);
7.41 (m, 2H, ArH), 7.57 (s, 2H, NH2); 13C NMR (100 MHz, DMSO-d6):
Please cite this article in press as: D. Rajguru, et al., H6P2W18O62Á18H2O: A green and reusable catalyst for one-pot synthesis of