Antimony trichloride: An efficient and mild catalyst for cyclization of 2-aminochalcones to the corresponding 2-aryl-2,3-dihydroquinolin-4(1H)-ones

Article abstract of DOI:10.1080/00397910902985523

Antimony trichloride is an efficient catalyst for the cyclization of 2-amino chalcones to the corresponding 2-aryl-2,3-dihydroquinolin-4(1H)-ones under mild reaction conditions and in almost quantitative yields. Copyright Taylor & Francis Group, LLC.

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Antimony Trichloride: An Efficient
and Mild Catalyst for Cyclization of 2-
Aminochalcones to the Corresponding 2-
Aryl-2,3-Dihydroquinolin-4(1H)-ones
R. N. Bhattacharya a , Pradip Kundu a & Gourhari Maiti a
a Department of Chemistry, Jadavpur University, Jadavpur, Kolkata,
India
Version of record first published: 03 Feb 2010.
To cite this article: R. N. Bhattacharya , Pradip Kundu & Gourhari Maiti (2010): Antimony Trichloride:
An Efficient and Mild Catalyst for Cyclization of 2-Aminochalcones to the Corresponding 2-Aryl-2,3-
Dihydroquinolin-4(1H)-ones, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 40:4, 476-481
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Synthetic Communications1, 40: 476–481, 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910902985523
ANTIMONY TRICHLORIDE: AN EFFICIENT AND
MILD CATALYST FOR CYCLIZATION OF
2-AMINOCHALCONES TO THE CORRESPONDING
2-ARYL-2,3-DIHYDROQUINOLIN-4(1H)-ONES
R. N. Bhattacharya, Pradip Kundu, and Gourhari Maiti
Department of Chemistry, Jadavpur University, Jadavpur, Kolkata, India
Antimony trichloride is an efficient catalyst for the cyclization of 2-amino chalcones to the
corresponding 2-aryl-2,3-dihydroquinolin-4(1H)-ones under mild reaction conditions and in
almost quantitative yields.
Keywords: 2-Aminochalcones; 2-aryl-2,3-dihydroquinolin-4(1H)-ones; antimony trichloride; intramol-
ecular aza-Michael
INTRODUCTION
2-Aryl-2,3-dihydroquinolin-4-(1H)-ones bearing substituents on the aromatic
rings exhibit various pharmacological activities.[1] They are also valuable precursors[2]
for the synthesis of medicinally important compounds[3] that are eventually not
readily accessible.[3,4] These compounds reportedly had been prepared from the
corresponding 2-aminochalcones bearing substituents in the aromatic rings by an
intramolecular aza-Michael reaction catalyzed by either an acid or base[5] and also
by microwave-assisted reaction on solid support such as clay, silica gel, or neutral
alumina. Most of the existing procedures involve the use of corrosive reagents such as
orthophosphoric acid, acetic acid, or strong alkalis. Moreover, many of them are of
limited synthetic scope because of their poor yields, long reaction times, and need for
large amount of catalyst, specialized solvents,[6] or either microwave irradiation with
solid support[7] or high temperature on solid support.[8] Therefore, the development of
new methods that lead to a convenient procedure and better yield are still desirable.
In continuation of our effort in exploring antimony trichloride (SbCl3)[9] as a
mild and efficient catalyst, we report herein an efficient method for the synthesis
of 2-aryl-2,3-dihydroquinolin-4(1H)-ones through the cyclization of 2-aminochal-
cones using SbCl3 in acetonitrile at 55ꢀC. The salient features of this methodology
include quantitative conversion, operational simplicity, inexpensive catalyst, ease
of isolation of product, clean reaction, and mild conditions. To our knowledge, there
is no report of this catalyst for such type of intramolecular aza-Michael reactions.
Received January 23, 2009.
Address correspondence to Gourhari Maiti, Department of Chemistry, Jadavpur University,
Jadavpur, Kolkata 700 032, India. E-mail: ghmaiti123@yahoo.co.in
476

AZA-MICHAEL REACTION OF 2-AMINOCHALCONES
477
RESULTS AND DISCUSSION
By using very simple experimental procedures, a wide range of substituted and
structurally diverse 2-aminochalcones were subjected to cyclization reaction. We
carried out the aza-Michael reaction of 2-aminochalcones in the presence of SbCl3
(10–30 mol%) at 55ꢀC in dry acetonitrile to furnish the corresponding 2,3-dihydro-
quinolin-4(1H)-ones in a quantitative yield (Scheme 1). Thus, a series of 2-amino-
chalcones bearing substituents with various stereoelectronic effects were subjected
to SbCl3-catalyzed cyclization reaction, and the results are summarized in Table 1.
The structures of the products were established from their spectral analysis [infrared
1
(IR), H, 13C NMR, and high-resoultion mass spectrometry (HRMS)] and also by
comparison with the literature values.[7b] A few other solvents such as dichloro-
methane (DCM), ethanol, and tetrahydrofuran (THF) were also tested but they
required longer reaction times and gave poorer yields compared to acetonitrile.
The reaction was also carried out at room temperature, which required a longer
reaction time (48 h) but resulted in almost quantitative cyclization without formation
of any side product (Table 1, entry 3). Increasing the temperature from 55ꢀC to
refluxing condition has a negligible effect on the reaction rate. An electron-donating
group in the aromatic ring increases the rate, whereas an electron-withdrawing
group decreases the rate of the reaction. Moreover, in the case of synthesis of
2-(40-nitrophenyl)-2,3-dihydroquinolin-4(1H)-one derivative, the corresponding
2-(40-nitrophenyl) aminochalcone did not undergo cyclization to a considerable
extent after heating at 55ꢀC for 24 h with 30 mol% catalyst loading, but 50% conver-
sion was noted after it was left for 7 days at room temperature. It is known that silica
gel or neutral alumina coated with p-toluenesulphonic acid catalyzes the reaction
with relatively poor yield, whereas basic alumina spoils the substrate. Microwave
irradiation of montmorillonite K-10 as solid support[7a] and InCl3 on silica gel[7b]
gave good yields of the products, but the catalyst systems are reported to be less
efficient under conventional thermal conditions. Although SiO2-TaBr5 at high tem-
perature (140ꢀC)[8a] gave good yields of products, TaBr5 alone in solution gave the
product in poor yield (30–40%), even after a prolonged reaction time. Very recently,
CeCl3 ꢁ 7H2O ꢁ NaI on either silica gel or alumina support[8b] has been reported to
afford good yield of products, whereas CeCl3 ꢁ 7H2O ꢁ NaI in refluxing DCM gave
only 20–25% of desired products after 3 days. Hence, the present study unequivo-
cally has proved that antimony trichloride acts as a better catalyst in the solution
phase for the intramolecular aza-Michael reaction.
With these encouraging results in hand, we also performed the aza-Michael
reaction with 10 mol% SbCl3 on silica gel support (60–120 mesh) under solvent-free
Scheme 1.

478
R. N. BHATTACHARYA, P. KUNDU, AND G. MAITI
Table 1. Antimony trichloride–catalyzed efficient synthesis of 2,3-dihydroquinolin-4(1H)-onesa
Entry
Substrate
Productb
Catalyst (mol %)
Time
Yieldc
1
30
3.0
99
2
3
4
10
10
10
3.0
99
99
90
1.0
0.75
5
6
10
10
1.0
91
97
1.25
7
8
9
10
30
30
1.25
5.0
98
97
98
3.5
(Continued )

AZA-MICHAEL REACTION OF 2-AMINOCHALCONES
479
Table 1. Continued
Entry
10
Substrate
Productb
Catalyst (mol %)
Time
10.0
Yieldc
30
97
11
30
3.0
96
aAll reactions were carried out using SbCl3 in acetonitrile at 55ꢀC (method A).
bAll products were characterized by mp, IR, NMR, and HRMS data and are agreement with the
literature values.
cYield refers to pure isolated products.
conditions (method B) in four cases [Table 1, entries 1 (97%), 3 (96%), 10 (98%), and
11 (96%)], and it was found that the reaction was completed within 10 min on
conventional heating at 100ꢀC in almost quantitative yield. In the case of
2-(40-nitrophenyl) aminochalcone, the reaction was completed within 2.5 h at
100ꢀC in 95% yield. It can be interpreted that the rate of the reaction is very much
dependent on the electronic nature of the aromatic ring substituents.
In conclusion, we have developed a mild and efficient methodology for the
synthesis of 2-aryl-2,3-dihydroquinolin-4(1H)-ones both in solution phase and under
solventless conventional heating condition on solid silica-gel support. Antimony tri-
chloride was found to be the better catalyst in terms of cost, handling, remarkable
operational simplicity, and ease of product isolation.
EXPERIMENTAL
Representative Procedure (Method A)
Solid antimony trichloride (68 mg, 0.3 mmol) was added to a stirred solution of
2-amino chalcone, 1i (303 mg, 1.0 mmol), in acetonitrile (1.0 mL). The reaction
mixture was heated at 50–55ꢀC for 3.5 h (completion was monitored by thin-layer
chromatography (TLC). The reaction mixture was decomposed with 5 mL water
and extracted with DCM (2 ꢂ 15 mL), washed with brine solution (5 mL), and dried
over anhydrous Na2SO4. Volatiles were removed, and the crude residue was purified
by short-column chromatography using 10% ethyl acetate–petroleum ether as eluent
to afford 2i solid (297 mg, 98%).
1
Spectral data of 2i. Mp 126ꢀC; H NMR (300 MHz, CDCl3) d 2.74 (dd,
J ¼ 12.6, 16.3 Hz, 1H), 2.95 (dd, J ¼ 3.9, 16.3 Hz, 1H), 4.58 (s, 1H), 5.20 (dd, J ¼ 3.9,
12.5 Hz, 1H), 6.74 (d, J ¼ 8.2 Hz, 1H), 6.80 (t, J ¼ 7.7 Hz, 1H), 7.19 (dt, J ¼ 1.5,
7.7 Hz, 1H), 7.32–7.39 (m, 2H), 7.58 (d, J ¼ 8.0 Hz, 1H), 7.68 (dd, J ¼ 1.3, 7.8 Hz,

480
R. N. BHATTACHARYA, P. KUNDU, AND G. MAITI
1H), 7.88 (d, J ¼ 7.9 Hz, 1H); 13C NMR (75 MHz, CDCl3) d 44.2, 56.8, 116.1, 118.7,
119.1, 122.9, 127.6, 127.7, 128.2, 129.7, 133.3, 135.5, 139.9, 151.5, 192.8. HRMS calcd.
for [C15H12NBrO þ Naþ] 323.9999; found 324.0032.
1
Spectral data of 2k. Mp 92ꢀC, H NMR (300 MHz, CDCl3) d 2.92 (dd,
J ¼ 5.4, 16.1 Hz, 1H), 3.00 (dd, J ¼ 9.8, 16.3 Hz, 1H), 4.79–4.84 (m, 2H), 6.25 (d,
J ¼ 3.2 Hz, 1H), 6.32 (m, 1H), 6.70 (d, J ¼ 8.3 Hz, 1H), 6.76 (t, J ¼ 5.9 Hz, 1H),
7.31 (dt, J ¼ 1.5, 7.3 Hz, 1H), 7.37 (s, 1H), 7.84 (dd, J ¼ 1.2, 7.9 Hz, 1H); 13C
NMR (75 MHz, CDCl3) d 441.9, 50.7, 106.8, 110.3, 116.0, 118.5, 119.1, 127.3,
135.4, 142.4, 150.4, 153.3, 192.6. HRMS calcd. for [C13H11NO2 þ Naþ] 236.0687;
found 236.0685.
Representative Procedure (Method B)
A solution of 2-aminochalcone (1j) (121 mg, 0.5 mmol) in 0.5 mL of acetonitrile
was added to silica gel impregnated with SbCl3 (12 mg, 0.05 mmol) [prepared by
adding a solution of SbCl3 in acetonitrile (1 mL) to silica gel (200 mg, 60–120 mesh)],
followed by evaporation of the solvent in vacuum. The dry reaction mixture was
heated at 100ꢀC for 10 min, and on completion, the reaction mixture was directly
charged onto a small silica-gel column (10% ethyl acetate–petroleum ether) to afford
the pure product 2j (118 mg, 98%).
1
Spectral data of 2j. Mp 134ꢀC; H NMR (300MHz, CDCl3): d 2.67–2.85
(m, 2H), 4.64 (s, 1H), 4.70 (dd, J ¼ 4.3, 13.2Hz, 1H), 6.74 (d, J ¼ 8.5 Hz, 1H), 6.79
(d, J ¼ 8.5 Hz, 1H), 7.06 (t, J ¼ 8.6 Hz, 2H), 7.34 (dt, J ¼ 1.4, 7.7 Hz, 1H), 7.41 (dd,
J ¼ 5.4, 8.6 Hz, 2H), 7.84 (d, J ¼ 7.9 Hz, 1H); 13C NMR (75 MHz, CDCl3): d 46.5,
57.8, 115.9 (d, J ¼ 22Hz), 116.0, 118.6, 119.0, 127.6, 128.3 (d, J ¼ 8 Hz), 135.5, 136.8
(d, J ¼ 3 Hz), 151.5, 162.8 (d, J ¼ 262 Hz), 193.1.
ACKNOWLEDGMENTS
One of the authors, P. K., thanks Jadavpur University, Kolkata, and the
government of West Bengal for awarding the senior research fellowship.
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