Domino Knoevenagel condensation, Michael addition, and cyclization using ionic liquid, 2-hydroxyethylammonium formate, as a recoverable catalyst

Article abstract of DOI:10.1016/j.molliq.2010.11.010

The Knoevenagel condensation reaction of aromatic aldehydes with malononitrile or dimedone was investigated. Also, the three-component and one-pot synthesis of 2-amino-5-oxo-4-aryl-4,5-dihydropyrano[3,2-cchromene-3- carbonitrile derivatives by condensing

Full text of DOI:10.1016/j.molliq.2010.11.010

Journal of Molecular Liquids 158 (2011) 145–150
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Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Domino Knoevenagel condensation, Michael addition, and cyclization using ionic
liquid, 2-hydroxyethylammonium formate, as a recoverable catalyst
H.R. Shaterian ⁎, M. Arman, F. Rigi
Department of Chemistry, Faculty of Sciences, University of Sistan and Baluchestan PO Box 98135-674, Zahedan, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
The Knoevenagel condensation reaction of aromatic aldehydes with malononitrile or dimedone was
investigated. Also, the three-component and one-pot synthesis of 2-amino-5-oxo-4-aryl-4,5-dihydropyrano
Received 11 November 2010
Received in revised form 18 November 2010
Accepted 19 November 2010
Available online 26 November 2010
[3,2-c]chromene-3-carbonitrile derivatives by condensing 4-hydroxycoumarin, aldehydes and malononitriles
using a catalytic amount of 2-hydroxyethylammonium formate as an effective ionic liquid without using any
additional co-catalyst under solvent-free conditions at room temperature is reported. Furthermore, the
domino Knoevenagel condensation, conjugate addition, and cyclization for the preparation of tetrahydro-
benzo[b]pyran, and spirooxindole derivatives in high atomic efficiency take place in excellent yields.
© 2010 Elsevier B.V. All rights reserved.
Keywords:
Benzylidenemalononitriles
2
-Benzylidene-5,5-dimethylcyclohexane-1,3-
diones
-Amino-5-oxo-4-aryl-4,5-dihydropyrano
3,2-c]chromene-3-carbonitrile
2
[
Tetrahydrobenzo[b]pyran
Ionic liquid
Spirooxindole
1
. Introduction
Low melting point salts consisting of ions, which are often
was synthesized for the first time by Bicak and showed heat stability
up to 150 °C [11].
classified as ionic liquids exist in the liquid state at ambient
temperatures and have received a significant attention from research
groups and industry for a range of novel applications [1]. Ionic liquids
show several properties such as good solvents (green and environ-
mentally benign solvent) for a large variety of organic as well as
inorganic substances, polar, non-volatile, non-flammable, immiscible
with many commonly used solvents, low vapor pressure (stable in
high vacuum), no toxic, low melting point (liquid below 100 °C),
thermal stability, and recyclability [2]. There has been an increasing
interest in exploiting the potential of ionic liquids as a reaction
medium to develop green methodologies; allowing reuse of the
catalysts or reagents [3]. This properties and applications prompted us
to initiate a systematic exploration on the preparation of organic
compounds with the help of ionic liquids [4–6]. In continuation to our
research on application of catalysts in several organic transformations
2. Experimental
All reagents were purchased from Merck and Aldrich and used
without further purification. All yields refer to isolated products after
purification. Products were characterized by comparison with
authentic samples and by spectroscopy data (IR, 1H NMR spectra).
The NMR spectra were recorded on a Bruker Avance DPX 500 MHz
6
instrument. The spectra were measured in DMSO-d relative to TMS
(0.00 ppm). Elemental analyses for C, H, and N were performed using
a Heraeus CHN–O-Rapid analyzer. FT-IR spectra were recorded on a
JASCO FT-IR 460 plus spectrophotometer. Mass spectra were recorded
on an Agilent technologies 5973 network mass selective detector
(MSD) operating at an ionization potential of 70 eV. TLC was
performed on silica-gel Poly Gram SIL G/UV 254 plates.
[
7–10], we herein report some applications of 2-hydroxyethylammo-
2.1. Preparation of benzilidenemalononitriles and
2-benzylidene-5,5-dimethylcyclohexane-1,3-diones
+
−
3 2 2
nium formate, [H N –CH –CH –OH][HCOO ], as a recoverable ionic
liquid. The ionic liquid showed weak basic character and was used as a
green catalyst for the preparation of several organic compounds. It
A mixture of an aromatic aldehyde (1 mmol), malononitrile
(
1 mmol) or dimedone (1 mmol), and ionic liquid (0.27 mmol), was
stirred at room temperature under solvent-free condition for
appropriate time (Table 1). After completion of the reaction which
was monitored by TLC, the mixture was washed with water and the
solid product was purified by recrystallization from ethanol.
⁎
Corresponding author. Tel.: +98 541 2446565; fax: +98 541 2431067.
E-mail address: hrshaterian@chem.usb.ac.ir (H.R. Shaterian).
0167-7322/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molliq.2010.11.010

146
H.R. Shaterian et al. / Journal of Molecular Liquids 158 (2011) 145–150
+
Table 1
1252, 1062, and 763; MS (EI, 70 eV) m/z (%)=334 (M , 22), 267 (13),
Knoevenagel condensation for different substituted benzaldehydes with malononitrile
or dimedone in the presence of ionic liquid under ambient conditions.
2
39 (100), 121 (21), and 92 (8).; Anal. Calcd for: C19
8.26; H, 3.32; N, 8.38%. Found: C, 68.35; H, 3.30; N, 8.40%.
2-Amino-5-oxo-4-o-tolyl-4,5-dihydropyrano[3,2-c]chromene-3-
2 3
H11FN O : C,
6
Entry Substrate
Product Time Yield m.p (Lit.m.p 0C) [ref]
a
(min) (%)
1
carbonitrile (Table 3, Entry 13): H NMR (DMSO-d
(s, 3H, CH ), 4.73 (s, 1H, CH), 6.90–7.20 (m, 4H, Ar), 7.34 (s, 2H, NH
.41 (d, J=8.3 Hz, 1H, Ar), 7.46 (t, J=7.6 Hz, 1H, Ar), 7.66–7.73 (m,
H, Ar), 7.89 (d, J=7.8 Hz, 1H, Ar) ppm; 13C NMR (DMSO-d
6
, 500 MHz): δ 2.48
1
1a
1a
b1
91
82–83 (82–85) [19]
160–161 (160) [19]
3
2
),
7
1
1
1
1
1
7
6
,
25 MHz): δ 19.0, 57.9, 104.5, 122.8, 116.4, 119.1, 122.3, 124.6,
26.6, 123.6, 126.7, 127.8, 130.0, 132.7, 135.2, 142.2, 152.0, 153.4,
57.7, 159.5 ppm; IR (KBr, cm ): 3400, 3283, 3179, 2202, 1709,
675, 1637, 1603, 1490, 1457, 1377, 1171, 1059, 957, 753; MS (EI,
0 eV) m/z (%)=330 (M , 18), 249 (24), 240 (17), 239 (100), 121
2
3
4
83
−1
1a
1a
6
3
79
66
140–141 (141–143)
+
[
26]
(
21).; Anal. Calcd for: C20
C, 72.80; H, 4.30; N, 8.50%.
-Amino-5-oxo-4-(2,5-dimethoxyphenyl)-4,5-dihydropyrano
14 2 3
H N O : C, 72.72; H, 4.27; N, 8.48%. Found:
2
4
5
103–105 (100–102)
26]
1
[
[3,2-c]chromene-3-carbonitrile (Table 3, Entry 14): H NMR (DMSO-
, 500 MHz): δ 3.63 (s, 3H, CH ), 3.64 (s, 3H, CH ), 4.64 (s, 1H, CH),
.66 (d, J=2.3 Hz, 1H, Ar), 6.75–6.79 (m, 1H, Ar), 6.90 (d, J=8.8 Hz,
H, Ar), 7.25 (s, 2H, NH ), 7.41–7.49 (m, 2H, Ar), 7.67 (t, J=7.7 Hz, 1H,
d
6
3
3
6
1
2
13
1a
2
75
132–133 (132–133)
19]
Ar), 7.89 (d, J=7.7 Hz, 1H, Ar) ppm; C NMR (DMSO-d
, 125 MHz): δ
5.2, 56.4, 56.8, 103.1, 112.2, 112.9, 113.1, 115.7, 116.4, 119.2, 122.2,
24.5,125, 131.9, 132.6, 151.5, 152.0, 153.1, 153.9, 158.5, and
6
[
5
1
1
1
3
1
−1
59.4 ppm; IR (KBr, cm ): 3403, 3322, 3192, 2195, 1708, 1672,
605, 1501, 1380, 1224, 1054, 959, and 620; MS (EI, 70 eV) m/z (%)=
76 (M , 23), 361 (14), 345 (42), 279 (100), 239 (26), 215 (13), and
21 (24).; Anal. Calcd for: C21H N O : C, 67.82; H, 4.28; N, 7.44%.
16 2 5
Found: C, 67.92; H, 4.36; N, 7.55%.
-Amino-5-oxo-4-phenethyl-4,5-dihydropyrano[3,2-c] chro-
mene-3-carbonitrile (Table 3, Entry 15): H NMR (DMSO-d
00 MHz): δ 1.81–1.87 (m, 1H,), 2.09–2.16 (m, 1H,), 2.45–2.52 (m,
1H,), 2.54–2.62 (m, 1H), 3.50–3.6 (m, 1H,), 7.00 (t, J=8.1, 1H, Ar),
.08 (d, J=7.0 Hz, 2H, Ar), 7.13 (t, J=7.5 Hz, 2H, Ar), 7.34–7.45 (m,
H, NH and Ar), 7.62–7.67 (m, 1H, Ar), 7.76 (dd, J=5.9, 1.2 Hz, 1H,
6
7
8
9
1a
1a
1a
2a
1
4
82
61
96
58
93–95 (80–82) [19]
+
155–157 (160–162)
[
23]
2
1
6
,
5
3
113–114 (111–115)
19]
[
7
4
2
45
138–140 (127–129)
24]
13
Ar) ppm; C NMR (DMSO-d
6
, 125 MHz): δ 30.4, 30.7, 54.8, 103.7,
[
1
1
3
12.9, 116.3, 119.5, 122.1, 124.3, 125.5, 127.93 (2 C), 128.1, 132.5,
−1
41.2, 152.0, 154.0, 159.4, and 159.8 ppm; IR (KBr, cm ): 3382, 3315,
189, 2198, 1694, 1671, 1608, 1396, 1315, 1179, 1211, 1112, and 759;
MS (EI, 70 eV) m/z (%)=344 (M , 7), 240 (20), 239 (100), 187 (8),
10
2a
30
63
123–125 (108–110)
22]
+
[
1
4
16 2 3
38 (21), 91 (10), 43 (17).; Anal. Calcd for: C21H N O : C, 73.24; H,
.68; N, 8.13%. Found: C, 73.28; H, 4.70; N, 8.20%.
a
Yields refer to isolated a pure products. The known products were characterized and
their physical properties (M.p, 1H NMR, C NMR and IR) with authentic samples
13
2.3. Preparation of tetrahydrobenzo[b]pyrans
[
19,22–26] were compared.
A mixture of an aromatic aldehyde (1 mmol), malononitrile
1.2 mmol), dimedone (1 mmol) and ionic liquid (0.27 mmol), was
(
2
.2. Preparation of 2-amino-5-oxo-4-aryl-4,5-dihydropyrano[3,2-c]
stirred at room temperature under solvent-free condition for
appropriate time (Table 4). After completion of the reaction which
was monitored by TLC, the mixture was washed with water and the
solid product was purified by recrystallization from ethanol.
chromene-3-carbonitrile
A mixture of an aromatic aldehyde (1 mmol), malononitrile
(
(
1.2 mmol), 4-hdroxycoumarine (1 mmol) and ionic liquid
0.27 mmol), was stirred at room temperature under solvent-free
2.4. Preparation of spirooxindole derivatives
condition for appropriate time (Table 3). After completion of the
reaction which was monitored by TLC, the mixture was washed with
water and the solid was product purified by recrystallization from
ethanol. All of the desired product(s) were characterized by
comparison of their physical data with those of known compounds
and characterization data for novel products are given below.
A mixture of isatin (1 mmol), malononitrile (1 mmol), dimedone
or 4-hydroxycoumarin (1 mmol) and ionic liquid (0.27 mmol), was
stirred at room temperature under solvent-free condition for
appropriate time. After completion of the reaction which was
monitored by TLC, the mixture was washed with water and the
solid product was purified by recrystallization from ethanol.
2
-Amino-5-oxo-4-(3-flourophenyl)-4,5-dihydropyrano[3,2-c]
1
6
chromene-3-carbonitrile (Table 3, Entry 12): H NMR (DMSO-d ,
5
00 MHz): δ 4.50 (s, 1H, CH), 7.01–7.14 (m, 3H, Ar), 7.31–7.41 (m, 5H,
3. Results and discussion
2
NH and Ar), 7.63–6.69 (m, 1H, Ar), 7.87 (dd, J=7.9, 1.2 Hz, 1H, Ar)
1
3
ppm; C NMR (DMSO-d
6
, 125 MHz): δ 57.5, 103.2, 112.9, 113.8,
13.9, 114.4, 114.5, 116.4, 119.0, 122.5, 123.7, 124.5, 130.3, 130.3,
32.8, 146.1, 146.2, 152.1, 153.6, 157.9, 159.5, 161.2, and 163.1 ppm;
The Knoevenagel condensation is a very useful reaction and
generates double bonds from a carbonyl compound and an active
methylene compound in the presence of a catalytic amount of weak
base [12–17]. Recently, the Knoevenagel condensation of carbonyl
1
1
−1
IR (KBr, cm ): 3375, 3315, 3191, 2195, 1711, 1675, 1619, 1489, 1370,

H.R. Shaterian et al. / Journal of Molecular Liquids 158 (2011) 145–150
147
didn't progress after 24 h and starting materials were intact using
ionic liquid.
To show the merit of the present work in comparison with the
reported results in the literature, we compared the results of 2-
hydroxyethylammonium formate with MgO [26], Ni-nanoparticles
[22], Ti-TUD-1[25], and porous calcium [23] in the synthesis of
benzylidenemalononitriles. As shown in Table 2, the ionic liquid can
act as suitable catalyst with respect to reaction times and yields of the
products.
Scheme 1. The Knoevenagel condensation for preparation of benzilidenemalononitriles
Next, as part of our program aimed at developing useful new
synthesis methods based on the use of mentioned ionic liquid as a
catalyst, we have studied the three-component one-pot synthesis of
and 2-benzylidene-5,5-dimethylcyclohexane-1,3-diones.
2
-amino-4-aryl-5-oxo-4,5-dihydropyrano[3,2-c]chromene-3-carbo-
nitrile derivatives [27–33] by condensing 4-hydroxycoumarin, alde-
hydes and malononitriles using catalytic amount of 2-
Table 2
Comparison results of 2-hydroxyethylammonium formate with MgO [26], Ni-
nanoparticles [22], Ti-TUD-1 [25] and porous calcium [23] in the synthesis of
benzylidenemalononitriles from benzaldehyde and malononitrile.
a
hydroxyethylammonium formate at room temperature. Furthermore,
the three-component reaction of dimedone, aldehydes, and maloni-
trile for preparation of tetrahydrobenzo[b] pyrans [34–37] was
investigated (Scheme 2).
Entry Catalyst
Conditions
Time Yield (%)
(min)
1
2
MgO
Ni-
nanoparticles
Ti-TUD-1
2
H O, EtOH as solvent at r.t
7
19
94
98
EtOH as solvent at r.t
Subsequently, a series of differently substituted 2-amino-4-aryl-5-
oxo-4,5-dihydropyrano[3,2-c]chromene-3-carbonitrile and tetrahydro-
benzo[b]pyrans derivatives was prepared successfully under solvent-
free neat conditions. These results are listed in Tables 3 and 4. The results
clearly indicate that reactions can tolerate a wide range of differently
substituted aldehydes. The reactions were complete within 2–15 min
and excellent yields of products were obtained by both methods.
However, in case of aliphatic aldehydes, reactions were not completed
under solvent-free conditions and desired products were obtained in
low yields.
The proposed mechanism for the reaction using ionic liquid as
catalyst is also described in Scheme 3. According to literature report
[27–33], ionic liquid with weak base character [11] is an effective
catalyst for the readily in-situ formation of Knoevenagel product from
activated aryl aldehyde and carboanion of malononitrile. Afterward,
enamine is formed from 2-hydroxyethylammonium formate and 4-
hydroxycoumarin, which then reacts with protonated Knoevenagel
product (formic acid formed and acts as protonated source) via 1,4-
conjugted addition, followed by cyclization to give desired cyclic
product after hydrolysis (Scheme 3). In this mechanism cation and
anion of IL are catalytically act and reformed to prepare 2-
hydroxyethylammonium formate in each cycles.
In continuation to this research, a simple and an efficient one-pot
synthetic approach was used for the preparation of biologically
interesting spirooxindole derivatives [38,39] in high yields by means
of three-component reactions of isatin, malononitrile, and dimedone
or 4-hydroxycoumarin catalyzed by mentioned ionic liquid as catalyst
under mild solvent-free and ambient conditions (Scheme 4).
We suggested a mechanism according to the literature [38,39], the
formation of spirooxindole can be explained by a formation of
isatylidene malononitrile via a domino Knoevenagel condensation of
isatin and malononitrile. Then, similar to Scheme 3, Michael addition
3
4
5
EtOH as solvent at r.t
30
2
91
87
Porous calcium CH
2
Cl
2
as solvent under MW
Ionic liquid Solvent-free at r.t
b1
91 (present work)
compounds with rhodanine to afford arylalkylidene rhodanines in the
presence of 2-hydroxyethylammonium formate was reported [18].
First report, the Knoevenagel condensation reaction of aromatic
aldehydes with malononitrile or dimedone produces benzilidenema-
lononitriles [19–26] and 2-benzylidene-5,5-dimethylcyclohexane-
1
,3-diones [22,24] respectively in the presence of 0.029 g
(
(
0.27 mmol) of ionic liquid as catalyst at ambient conditions
Scheme 1).
The efficiency and versatility of the ionic liquid as catalyst for the
Knoevenagel condensation for different substituted benzaldehydes
using malononitrile or dimedone were investigated (Table 1). Using
catalytic amount of the ionic liquid as catalyst, different substituted
benzaldehydes got readily condensed with malononitrile to give
corresponding product at short reaction times (b6 min) with
excellent yield. The substrates when condensed with dimedone
using similar amount of ionic liquid as catalyst gave desired
condensed products consumed at longer times (30, 45 min). This
may be attributed to the fact that the abstraction of proton from the
active methylene group of malononitrile is easier compared to
dimedone (Table 1, Entries 9, 10). All two Knoevenagel condensation
reactions produced the dehydrated products without any side
reactions such as self condensation, Cannizaro products or hydrated
products of Knoevenagel adducts. The reaction of aliphatic aldehydes
with malononitrile yielded a mixture of hydrated and dehydrated
products, while the reaction of dimedone with aliphatic aldehydes
Scheme 2. The one-pot synthesis of 2-amino-5-oxo-4-aryl-4,5-dihydropyrano[3,2-c]chromene-3-carbonitrile and tetrahydrobenzo[b]pyran.

148
H.R. Shaterian et al. / Journal of Molecular Liquids 158 (2011) 145–150
Table 3
Table 4
Preparation of a series of differently substituted 2-amino-4-aryl-5-oxo-4,5-dihydro-
pyrano[3,2-c]chromene-3-carbonitrile in the presence of 2-hydroxy ethylammonium
formate as catalyst from aryl aldehyde, malononitrile and hydroxycoumarine 4- at
ambient conditions.
Preparation of a series of differently substituted tetrahydrobenzo[b]pyrans in the
presence of 2-hydroxy ethylammonium formate as catalyst from aryl aldehyde,
malononitrile and dimedone at ambient conditions.
0
Entry Substrate
Product Time
Yield m.p(Lit.m.p C)
0
(min) (%)a
Entry Substrate
product Time Yield m.p(Lit.m.p C) [ref]
[ref]
a
(min) (%)
1
2b
5
70
227–229
1
1b
15
73
255–256 (257–258)
27]
(226–228) [34]
[
2
3
2b
2b
2
4
70
86
195–196
(197–199) [34]
2
3
4
5
1b
1b
1b
1b
13
5
89
75
67
74
261–262 (261–262)
27]
[
169–171
(175–176) [34]
280–283 (280–282)
28]
[
4
2b
3
57
208–211
201–205) [34]
(
8
245–247 (255–257)
28]
[
5
6
7
8
2b
2b
2b
2b
6
79
85
43
87
203–206
202–203) [34]
(
6
261–262 (258–260)
28]
[
3
212–215
209–211) [34]
(
6
7
1b
12
79
244–245 (247–248)
32]
6
174–177
(198–200) [35]
[
10
113–115
(115–117) [36]
1b
1b
20
12
62
73
254–255 (254–255)
33]
[
a
Yields refer to isolated pure products. The known products were characterized and
their physical properties (M.p, H NMR, C NMR and IR) with authentic samples [34–
7] were compared.
1
13
3
8
9
273–274 (266–268)
33]
[
of dimedone or 4-hydroxycoumarin with isatylidene malononitrile
followed by cyclization in the presence of ionic liquid as catalyst
produce desired spirooxindole (Scheme 5).
1b
1b
1b
7
60
70
71
261–262 (260–262)
28]
[
We also investigated the recycling of the catalyst under solvent-
free conditions using a model reaction of 4-chlorobenzaldehde,
malononitrile and 4-hydroxycoumarin (Table 3, entry 2). After
completion of the reaction, water was added and the precipitated
mixture was filtered off for separation of crude products. After
washing solid products with water completely, the water containing
ionic liquid (IL is soluble in water) was evaporated under reduce
pressure and ionic liquid was recovered and reused. The recovered
catalyst was reused for at least five runs without any loss of its
activities (Fig. 1).
1
1
0
1
15
10
258–259 (260–262)
33]
[
222–224 (247–249)
29]
[
1
2
3
1b
1b
10
7
40
65
241–242b
260–261b
4
. Conclusions
1
In summary, we have successfully developed a simple, facile and
efficient method for the synthesis of benzylidenmalononitrile, 2-
benzylidene-5,5-dimethylcyclohexane-1,3-dione, 2-amino-4-aryl-5-
Table 3 (continued)
1
1
4
5
1b
1b
6
7
68
98
230–233b
179–182b
0
Entry Substrate
product Time Yield m.p(Lit.m.p C) [ref]
a
(min) (%)
Notes to Table 3:
a
Yields refer to isolated pure products. The known products were characterized and
1
13
their physical properties (M.p, H NMR, C NMR and IR) with authentic samples [27–
3
b
0,32,33] were compared. Four new unknown products was synthesized.

H.R. Shaterian et al. / Journal of Molecular Liquids 158 (2011) 145–150
149
Scheme 3. The proposed mechanism for one-pot synthesis of 2-amino-5-oxo-4-aryl-4,5-dihydropyrano[3,2-c]chromene-3-carbonitrile.
oxo-4,5-dihydropyrano[3,2-c]chromene-3-carbonitrile, tetrahydro-
benzo[b] pyran, spirooxindole using a catalytic amount of 2-
hydroxyethylammonium formate as an inexpensive and available
ionic liquid under solvent-free and ambient conditions. The recov-
ered ionic liquid was reused for 5 cycles. The method offered several
advantages such as high yields, broader substrate scope, an easy and
Scheme 4. Preparation of spirooxindole derivatives.

150
H.R. Shaterian et al. / Journal of Molecular Liquids 158 (2011) 145–150
Scheme 5. The proposed mechanism for one-pot synthesis of spirooxindoles.
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8100
99
98
97
9
6
95
96
1
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9
1
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6
5
4
3
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0
0
0
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0
0
0
0
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[
[
Reaction Yield (%)
Catalyst Yield (%)
[
[
[
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1
2
3
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Numbera of runs
Fig. 1. The recycling of the catalyst under solvent-free conditions using a model reaction
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Acknowledgment
We are thankful to the University of Sistan and Baluchestan
Research Council for the partial support of this research.
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