A simple and facile solventless procedure for the cyclization of 2′-amino- and 2′-hydroxy-chalcones using silica-supported sodium hydrogen sulphate as heterogenous catalyst

Article abstract of DOI:10.1139/V06-133

A simple environmentally friendly method for the cyclization of 2′-amino- and 2′-hydroxy-chalcones under solventless conditions using silica-supported sodium hydrogen sulphate has been reported.

Full text of DOI:10.1139/V06-133

1079
A simple and facile solventless procedure for the
cyclization of 2′-amino- and 2′-hydroxy-chalcones
using silica-supported sodium hydrogen sulphate
as heterogenous catalyst
K. Hemanth Kumar and P. T. Perumal
Abstract: A simple environmentally friendly method for the cyclization of 2′-amino- and 2′-hydroxy-chalcones under
solventless conditions using silica-supported sodium hydrogen sulphate has been reported.
Key words: 2′-aminochalcones, 2′-hydroxychalcones, silica gel, sodium hydrogen sulphate, quinolones and flavanones.
Résumé : On a mis au point une méthode simple et écologique de cyclisation des 2′-amino- et 2′-hydroxychalcones
dans des conditions sans solvant en présence de sulfate acide de sodium déposé sur de la silice qui agit comme catalyseur.
Mots clés : 2′-aminochalcones, 2′-hydroxychalcones, gel de silice, sulfate acide de sodium, quinoléones, flavones.
[Traduit par la Rédaction] Kumar and Perumal 1083
Introduction
Scheme 1.
Substituted tetrahydroquinolones and flavanones display
various pharmacological activities (1, 2) and can be prepared
(3, 4) by acid or base catalyzed reactions. Many of these
procedures involve the use of corrosive reagents such as
orthophosphoric acid, acetic acid, or strong alkali. Further-
more, many of them are of limited synthetic scope because
of lower yields, extended reaction time, and the amount of
catalyst or solvent used. In recent years, there has been in-
creasing interest in solid-supported reagents coupled with
microwave irradiation owing to the benefits of enhanced re-
action rates, improved yields, cleaner reaction profiles, greater
selectivity, and operational simplicity (5).
O
O
NaHSO4-SiO2
2 min
MW
N
H
NH2
R
R
R = H, Me, Cl, OMe
Scheme 2.
O
O
In continuation of our studies on the synthesis of
heterocyclic compounds with medicinal potential from 2′-
aminochalcones (6) and 2′-hydroxychalcones (7), we report
an efficient and simple method for the synthesis of tetra-
hydroquinolones and flavanones through the cyclization of
the corresponding chalcones using silica-supported sodium
hydrogen sulphate under solventless conditions. The catalyst
NaHSO4-SiO2 can be easily prepared (8), safely handled and
removed from the reaction mixture, is inexpensive, and
works under heterogeneous conditions.
NaHSO4-SiO2
MW 3 min
Ph
N
H
NH2
N Ph
N
N
N
R
R
R = Cl, H, OMe, OEt
Results and discussion
2′-Aminochalcone was uniformly mixed with silica gel
(finer than 200 mesh), preimpregnated with NaHSO4, trans-
ferred into a glass vial, and irradiated by microwaves until
(2 min) the reaction was complete (TLC). The reaction mix-
ture was directly charged on a small silica gel column and
eluted with a mixture of ethyl acetate – hexane (1:9) to af-
ford the product 2-aryltetrahydro-4-quinolone in excellent
yield (Scheme 1). To extend the scope of the reaction, a
wide range of substituted and structurally diverse 2′-
aminochalcones were subjected to similar conditions
(Scheme 2). The reactions proceeded in a similar fashion
Received 12 May 2006. Accepted 23 August 2006. Published
on the NRC Research Press Web site at http://canjchem.nrc.ca
on 20 October 2006.
K.H. Kumar and P.T. Perumal.1 Organic chemistry
Division, Central Leather Research Institute, Adyar, Chennai
600 020, India.
1Corresponding author (e-mail: ptperumal@hotmail.com).
Can. J. Chem. 84: 1079–1083 (2006)
doi:10.1139/V06-133
© 2006 NRC Canada

1080
Can. J. Chem. Vol. 84, 2006
Table 1. NaHSO4-SiO2 catalyzed cyclization of 2′-aminochalcones under solventless conditions.
Microwave
time (yield)a
Conventional heating
time (yield)
'
Product
Entry
2-Aminochalcone
O
O
2 h (72)
2 min (95)
1
N
H
NH2
O
O
2
3
2 h (68)
2 min (90)
NH2
O
N
H
O
2 h (70)
2 min (88)
NH2
O
N
H
Cl
Cl
O
4
5
2 h (75)
2 min (96)
NH2
O
N
H
OMe
OMe
Ph
O
4 h (70)
3 min (86)
NH2
N
H
N
N
Ph
N
N
Cl
Cl
O
O
4 h (65)
3 min (80)
6
NH2
N
H
Ph
N
Ph
N
N
N
O
O
7
4 h (74)
3 min (92)
NH2
N
H
N
Ph
N
Ph
N
N
MeO
O
MeO
O
4 h (70)
3 min (87)
8
NH2
N
H
N
Ph
N
Ph
N
N
EtO
EtO
aMicrowave irradiation was carried out at 650 W (BPL, India).
and substituted tetrahydro-4-quinolones were obtained in
good yields (Table 1). The reaction rates and yields were
dramatically enhanced by microwave irradiation.
Flavanones form a large and important group of naturally
occurring secondary metabolites and are important interme-
diates for the synthesis of biologically active flavones and
isoflavones (9). The conventional methods for the
cyclization of 2′-hydroxychalcones involve prolonged time
and the use of corrosive reagents such as sulphuric acid, hy-
drochloric acid, and strong alkalis (10), furnishing
flavanones in not more than 50% yields. Hence, we at-
tempted to synthesize flavanones by using NaHSO4 on silica
gel under solvent-free conditions as a mild catalyst for the
cyclization of 2′-hydroxychalcones (Scheme 3), which fur-
© 2006 NRC Canada

Kumar and Perumal
Table 2. NaHSO4-SiO2 catalyzed cyclization of 2′-hydroxychalcones under solventless conditions.
1081
Microwave
time (yield)a
Conventional heating
time (yield)
Entry
Product
2'-Hydroxychalcone
O
O
1
6 min (75)
6 h (60)
OH
O
O
O
6 min (70)
6 h (60)
2
OH
O
O
O
3
8 min (72)
7 h (55)
OH
O
O
O
Cl
Cl
Cl
Cl
8 min (68)
7 h (52)
4
O
OH
O
O
O
5 h (62)
6 min (75)
5
OH
OMe
OMe
aMicrowave irradiation was carried out at 650 W (BPL, India).
Scheme 3.
dures for the synthesis of tetrahydroquinolones and
flavanones.
O
O
NaHSO4-SiO2
Experimental
MW 6–8 min
O
R
OH
R
2′-Amino- and 2′-hydroxy-chalcones were prepared using
appropriate aldehyde and corresponding o-substituted aceto-
phenones by earlier reported procedures (11, 12). 2-Amino-
and 2-hydroxy-acetophenones (Sigma-Aldrich) were used as
purchased. Sodium hydrogen sulphate and aromatic alde-
hydes were obtained from E-Merck (India) Ltd. Melting
points were determined in capillary tubes and are uncor-
rected. Analytical TLC was performed on precoated plastic
sheets of silica gel G/UV-254 of 0.2 mm thickness
(Macherey-Nagel, Germany). FT-IR spectra were taken as
KBr pellets on a PerkinElmer Spectrum RXI FT-IR spectro-
R = H, 4-Me, 4- and 2-Cl, 4-OMe
nished the flavanones in good yields (Table 2). Here too, the
use of microwave irradiation significantly enhanced the re-
action rates as well as the yields.
Conclusion
1
photometer. H NMR (500 MHz) and 13C NMR (125 MHz)
In conclusion, the present procedure catalyzed by
NaHSO4 impregnated with silica gel provides an efficient
and rapid synthesis of tetrahydroquinolones and flavanones
by the cyclization of the corresponding 2′-aminochalcones
and 2′-hydroxychalcones. The notable advantages of this
procedure are (i) operational simplicity, (ii) fast and clean
reaction, (iii) high yield, and (iv) safe and inexpensive cata-
lyst. We believe that this procedure will provide a better
scope and a more practical alternative to the existing proce-
spectra were recorded in CDCl3 solution with TMS as an in-
ternal standard. Column chromatography was performed on
silica gel (60–120 mesh, SRL, India).
Cyclization of 2′-amino- or 2′-hydroxy-chalcones under
microwave irradiation — Typical procedure A
The chalcone (1 mmol) was added to 2 g of silica gel
(100–200 mesh activated by heating for 8 h at 150 °C before
© 2006 NRC Canada

1082
Can. J. Chem. Vol. 84, 2006
use) impregnated with sodium hydrogen sulphate (2 g). The
whole mixture was stirred for 5 min for uniform mixing and
was then transferred to a glass tube and inserted in an alu-
mina bath (100 g, 60 GF254, Fisher Scientific bath 6.8 cm
diameter) inside the microwave oven. The compound was ir-
radiated in a domestic microwave oven (BPL, India) at
650 W for the appropriate time. On completion, the reaction
mixture was directly charged on a small silica gel column
and eluted with a mixture of ethyl acetate – hexane (1:9 for
quinolones, 2:8 for flavanones) to afford the corresponding
products in high yields. The results are summarized in Ta-
bles 1 and 2.
193.2. MS m/z: 257 (M+). Anal. calcd. for C15H12NOCl: C
69.91, H 4.69, N 5.43; found: C 69.82, H 4.60, N 5.35.
2-(4-Methoxyphenyl)-2,3-dihydroquinolin-4(1H)-one
(Table 1, entry 4)
Pale yellow solid, mp 147 °C (lit. value (3c) 146 to
147 °C). IR (cm–1) νmax: 3332, 1632, 1596, 1529, 1226,
1
1113. H NMR δ: 2.85 (m, 2H), 3.81 (s, 3H, OCH3), 4.50
(br s, NH, 1H), 4.70 (dd, J = 3.4, 13.7 Hz, 1H, H-2), 6.68–
7.37 (m, 7H), 7.86 (dd, J = 1.15, 7.98 Hz, 1H, H-5). 13C
NMR δ: 44.6, 55.5, 58.0, 114.4, 116.0, 118.5, 119.1, 127.7,
127.9, 133.1, 135.5, 151.7, 159.7, 193.7. MS m/z: 253 (M+).
Anal. calcd. for C16H15NO2: C 75.87, H 5.97, N 5.53; found:
C 75.82, H 5.90, N 5.48.
Cyclization of 2′-amino- or 2′-hydroxy-chalcones by
conventional means — Typical procedure B
2-[3-(4-Chlorophenyl)-1-phenyl-1H-pyrazol-4-yl]-2,3-
dihydroquinolin-4(1H)-one (Table 1, entry 5)
The chalcone (1 mmol) was added to 2 g of silica gel
(100–200 mesh activated by heating for 8 h at 150 °C before
use) impregnated with sodium hydrogen sulphate (2 g). The
whole mixture was stirred for 5 min for uniform mixing and
was then transferred to a 100 mL RB flask and kept in a wa-
ter bath for the appropriate time. On completion, the reac-
tion mixture was directly charged on a small silica gel
column and eluted with a mixture of ethyl acetate – hexane
(1:9 for quinolones, 2:8 for flavanones) to afford the corre-
sponding products in high yields. The results are summa-
rized in Tables 1 and 2.
Pale white solid, mp 190–192 °C. IR (cm–1) νmax: 3344,
1
1656, 1585, 1534, 1219, 1140. H NMR δ: 2.84–2.91 (m,
2H), 4.60 (s, br s, NH, 1H), 4.92–4.95 (m, 1H), 6.65 (d, J =
8.4 Hz, 1H, H-8), 6.77–6.8 (m, 1H, H-7), 7.28–7.87 (m,
10H), 7,85–7.87 (dd, J = 1.5, 7.65 Hz, 1H, H-5), 8.05 (s, 1
H, pyrazole-CH). 13C NMR δ: 45.6, 49.3, 116.1, 118.9,
119.2, 119.3, 121.8, 126.7, 127.1, 127.7, 129.2, 129.5,
129.6, 131.3, 134.6, 135.6, 139.7, 150.0, 151.5, 193.1. MS
m/z: 400 (M+). Anal. calcd. for C24H18ClN3O: C 72.09, H
4.54, N 10.51; found: C 72.01, H 4.48, N 10.45.
2-(1,3-Diphenyl-1H-pyrazol-4-yl)-2,3-dihydro-quinolin-
4(1H)-one (Table 1, entry 6)
Spectral data
Pale white solid, mp 128 to 129 °C. IR (cm–1) νmax: 3346,
2-Phenyl-2,3-dihydroquinolin-4(1H)-one (Table 1, entry 1)
Pale yellow solid, mp 149 to 150 °C (lit. value (3c) 148–
150 °C). IR (cm–1) νmax: 3303, 1650, 1605, 1480, 1308,
1
1645, 1595, 1523, 1205, 1133. H NMR δ: 2.86–2.94 (m,
2H, H-3), 4.59 (s, br s, NH, 1H), 4.94–4.97 (m, 1H), 6.65 (d,
J = 8.4 Hz, 1H, H-8), 6.81 (t, 1H, J = 7.65 Hz, H-7), 7.29–
7.47 (m, 7H), 7.58 (d, J = 8.4 Hz, 2H), 7.69 (d, J = 7.65 Hz,
2H) 7.86 (d, J = 6.8 Hz, 1H, H-5), 8.0 (s, 1H, pyrazole-CH).
13C NMR δ: 45.6, 49.3, 116.1, 118.9, 119.1, 119.3, 121.8,
122.8, 126.7, 127.1, 127.7, 129.6, 129.8, 131.8, 132.1,
135.6, 139.7, 150.0, 151.2, 193.2. MS m/z: 365 (M+). Anal.
calcd. for C24H19N3O: C 78.88, H 5.24, N 11.50; found: C
78.80, H 5.18, N 11.42.
1
1152. H NMR δ: 2.85 (m, 2H), 4.60 (br s, NH, 1H), 4.74
(dd, J = 3.14, 13.2 Hz, 1H, H-2), 6.70–7.50 (m, 8H), 7.86
(dd, J = 1.72, 8.05 Hz, 1H, H-5). 13C NMR δ: 46.5, 58.2,
116.1, 118.4, 119.2, 126.8, 127.6, 128.6, 129.1, 135.5,
141.1, 151.7, 193.4. MS m/z: 223 (M+). Anal. calcd. for
C15H13NO: C 80.69, H 5.87, N 6.27; found: C 80.60, H
5.73, N 6.12.
2-(4-Methylphenyl)-2,3-dihydroquinolin-4(1H)-one
(Table 1, entry 2)
2-[3-(4-Methoxyphenyl)-1-phenyl-1H-pyrazol-4-yl]-2,3-
dihydroquinolin-4(1H)-one (Table 1, entry 7)
Pale yellow solid, mp 148 to 149 °C (lit. value (3b)
Pale white solid, mp 175–177 °C. IR (cm–1) νmax: 3330,
149 °C). IR (cm–1) νmax: 3318, 1660, 1602, 1580, 1298,
1
1642, 1577, 1509, 1234, 1116. H NMR δ: 2.89–2.91 (m,
1
1142. H NMR δ: 2.36 (s, 3H, CH3), 2.84 (m, 2H), 4.67
2H), 3.83 (s, 3H, OCH3), 4.61 (s, br s, NH, 1H), 4.94–4.96
(m, 1H), 6.62 (d, J = 8.05 Hz, 1H, H-8), 6.76 (m, 1H, H-7),
6.95–7.7 (m, 10H), 7.85 (d, J = 8.0 Hz, 1H, H-5), 8.04 (s,
1H, pyrazole-CH). 13C NMR δ: 45.0, 49.3, 56.5, 114.0,
114.8, 115.8, 118.3, 119.1, 120.3, 124.9, 126.0, 126.4,
127.3, 128.5, 129.4, 134.4, 138.9, 152.3, 154.3, 159.1,
193.2. MS m/z: 395 (M+). Anal. calcd. for C25H21N3O2: C
75.93, H 5.35, N 10.63; found: C 75.82, H 5.30, N 10.58.
(br s, NH, 1H), 4.70 (dd, J = 3.8, 11.9 Hz, 1H, H-2), 6.69–
7.48 (m, 7H), 7.84 (dd, J = 1.14, 8.02 Hz, 1H, H-5). 13C
NMR δ: 21.4, 46.5, 58.3, 116.1, 118.4, 119.0, 126.6, 127.7,
129.8, 129.1, 135.5, 138.2, 151.1, 193.6. MS m/z: 237 (M+).
Anal. calcd. for C16H15NO: C 80.98, H 6.37, N 5.90; found:
C 80.92, H 6.31, N 5.86.
2-(4-Chlorophenyl)-2,3-dihydroquinolin-4(1H)-one
(Table 1, entry 3)
2-[3-(4-Ethoxyphenyl)-1-phenyl-1H-pyrazol-4-yl]-2,3-
dihydroquinolin-4(1H)-one (Table 1, entry 8)
Pale yellow solid, mp 168 °C (lit. value (3c) 167 to
168 °C). IR (cm–1) νmax: 3325, 1625, 1608, 1540, 1238,
Pale white solid, mp 178 to 179 °C. IR (cm–1) νmax: 3349,
1658, 1569, 1519, 1227, 1136. 1H NMR δ: 1.41 (t, J =
6.9 Hz, 3H), 2.8–2.84 (m, 2H, H-3), 4.0 (q, J = 6.9,
13.75 Hz, 2H) 4.64 (s, br s, NH, 1H), 4.94–4.97 (m, 1H),
6.62 (d, J = 8.45 Hz, 1H, H-8), 6.76–7.86 (m, 11H), 7.84 (d,
1
1152. H NMR δ: 2.90 (m, 2H), 4.54 (br s, NH, 1H,), 4.81
(dd, J = 4.0, 13.7 Hz, 1H, H-2), 6.72–7.39 (m, 7H), 7.86 (d,
J = 8.0 Hz, 1H, H-5). 13C NMR δ: 46.3, 57.3, 116.1, 118.1,
119.1, 127.4, 128.2, 129.2, 134.3, 135.6, 139.6, 151.9,
© 2006 NRC Canada

Kumar and Perumal
1083
J = 7.65 Hz, 1H, H-5), 8.03 (s, 1H, pyrazole-CH). 13C NMR
δ: 14.9, 45.6, 49.3, 63.6, 114.5, 114.9, 116.1, 118.7, 119.0,
121.5, 125.1, 126.4, 126.7, 127.7, 129.5, 130.6, 135.5,
139.8, 151.0, 151.3, 159.3, 193.4. MS m/z: 409 (M+). Anal.
calcd. for C26H23N3O2: C 76.26, H 5.66, N 10.26; found: C
76.19, H 5.58, N 10.18.
89 °C) IR (cm–1) νmax: 1689, 1588, 1513, 1443, 1243, 1123.
1H NMR δ: 2.86–3.0 (m, 2H), 3.8 (s, 3H), 5.39 (dd, J = 2.8,
13.70 Hz, 1H, H-2), 6.96 (d, J = 8.0 Hz, 1H), 7.01–7.05 (m,
2H), 7.39 (d, J = 8.6 Hz, 2H), 7.36 (d, J = 8 Hz, 2H), 7.91
(dd, J = 1.7, 8.0 Hz, 1H, H-5). 13C NMR δ: 44.5, 55.5, 77.4,
114.3, 118.2, 121.0, 121.6, 127.1, 130.9, 136.3, 160.1,
161.7, 192.3. MS m/z: 254 (M+). Anal. calcd. for C16H14O3:
C 75.57, H 5.55; found: C 75.50, H 5.48.
2-Phenyl-2,3-dihydro-4H-chromen-4-one (Table 2, entry 1)
Pale white solid, mp 75 to 76 °C (lit. value (10a) 78 to
77 °C). IR (cm–1) νmax: 1691, 1606, 1517, 1464, 1223, 1174.
1H NMR δ: 2.84–3.12 (m, 2H), 5.46 (dd, J = 2.85, 13.15 Hz,
1H, H-2), 7.04–7.07 (m, 2H), 7.37–7.52 (m, 6H), 7.90 (dd,
J = 1.75, 8.05 Hz, 1H, H-5). 13C NMR δ: 44.8, 77.4, 118.2,
121.0, 121.7, 126.3, 127.2, 128.9, 135.0, 136.3, 138.8,
161.7, 192.1. MS m/z: 224 (M+). Anal. calcd. for C15H12O2:
C 80.34, H 5.39; found: C 80.27, H 5.32.
Acknowledgement
One of the authors, KHK expresses gratitude to the Coun-
cil of Scientific and Industrial Research (CSIR, New Delhi,
India) for financial support.
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2-(4-Methylphenyl)-2,3-dihydro-4H-chromen-4-one
(Table 2, entry 2)
Pale white solid, mp 82 to 83 °C (lit. value (10a) 83 to
84 °C). IR (cm–1) νmax: 1696, 1595, 1520, 1459, 1225, 1162.
1H NMR δ: 2.38 (s, 3H), 2.89–3.12 (m, 2H), 5.43 (dd, J =
1.95, 13.75 Hz, 1H, H-2), 7.03–7.06 (m, 2H), 7.23 (d, J =
8 Hz, 2H), 7.36 (d, J = 8 Hz, 2H), 7.48 (m, 1H, H-6), 7.92
(dd, J = 1.7, 8.55 Hz, 1H, H-5). 13C NMR δ: 21.3, 44.7,
77.4, 118.3, 121.0, 121.6, 126.3, 127.1, 129.6, 135.8, 136.3,
138.8, 161.7, 192.3. MS m/z: 238 (M+). Anal. calcd. for
C16H14O2: C 80.65, H 5.92; found: C 80.58, H 5.84.
2-(4-Chlorophenyl)-2,3-dihydro-4H-chromen-4-one
(Table 2, entry 3)
Pale white solid, mp 95 to 96 °C (lit. value (4) 94 to
95 °C). IR (cm–1) νmax: 1692, 1575, 1519, 1464, 1256, 1162.
1H NMR δ: 2.84–3.05 (m, 2H), 5.43–5.46 (m, 1H), 7.03–
7.06 (m, 2H), 7.38–7.52 (m, 5H), 7.90 (dd, J = 1.55,
7.65 Hz, 1H, H-5). 13C NMR δ: 44.7, 77.4, 118.2, 121.0,
121.9, 127.2, 127.6, 128.3, 129.1, 136.4, 137.4, 161.4,
191.6. MS m/z: 258 (M+). Anal. calcd. for C15H11ClO2: C
69.64, H 4.29; found: C 69.59, H 4.21.
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2-(3-Chlorophenyl)-2,3-dihydro-4H-chromen-4-one
(Table 2, entry 4)
Pale white solid, mp 98 to 99 °C (lit. value (4) 99 to
100 °C). IR (cm–1) νmax: 1697, 1568, 1523, 1454, 1297,
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1
1145. H NMR δ: 2.83–3.15 (m, 2H), 5.44–5.47 (m, 1H, H-
2), 7.1–7.3 (m, 2H), 7.36–7.58 (m, 5H), 7.90 (dd, J = 1.65,
8.45 Hz, 1H, H-5). 13C NMR δ: 45.3, 76.4, 118.1, 119.4,
120.8, 121.9, 124.7, 127.0, 127.8, 128.0, 129.6, 136.4,
136.9, 160.4, 193.1. MS m/z: 258 (M+). Anal. calcd. for
C15H11ClO2: C 69.64, H 4.29; found: C 69.57, H 4.22.
2-(4-Methoxyphenyl)-2,3-dihydro-4H-chromen-4-one
(Table 2, entry 5)
Pale white solid, mp 87 to 88 °C (lit. value (4) 88 to
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