Synthesis of pyranopyrazoles, benzopyrans, amino-2-chromenes and dihydropyrano[c]chromenes using ionic liquid with dual Br?nsted acidic and Lewis basic sites

Article abstract of DOI:10.1515/chempap-2015-0066

An efficient ionic liquid with both Br?nsted acidic and Lewis basic sites, namely 1,4-dimethyl-1- (4-sulphobutyl)piperazinium hydrogen sulphate (IL1), was synthesised and characterised. IL1 is a "green", homogeneous and reusable catalyst for: i) the synth

Full text of DOI:10.1515/chempap-2015-0066

Chemical Papers 69 (4) 586–595 (2015)
DOI: 10.1515/chempap-2015-0066
ORIGINAL PAPER
Synthesis of pyranopyrazoles, benzopyrans, amino-2-chromenes
and dihydropyrano[ ]chromenes using ionic liquid
with dual Brønsted acidic and Lewis basic sites
Davood Habibi*, Atefeh Shamsian, Davood Nematollahi
Department of Organic Chemistry, Faculty of Chemistry, Bu-Ali Sina University, Hamedan, 6517838683 Iran
Received 1 April 2014; Revised 15 August 2014; Accepted 21 August 2014
An efficient ionic liquid with both Brønsted acidic and Lewis basic sites, namely 1,4-dimethyl-1-
(4-sulphobutyl)piperazinium hydrogen sulphate (IL1), was synthesised and characterised. IL1 is a
“green”, homogeneous and reusable catalyst for: i) the synthesis of pyranopyrazoles (Va–Vj) and
benzopyrans (VIa–VIj and VIIa–VIIf) at ambient temperature under solvent-free conditions and ii)
the synthesis of amino-2-chromenes (VIIIa–VIIIi and IXa–IXi) and dihyropyrano[c]chromenes (Xa–
Xi) at 80◦C under solvent-free conditions. The reactions were rapid with excellent product yields.
In addition, the double Brønsted acid, 1,4-dimethyl-1,4-bis(4-sulphobutyl)piperazinium hydrogen
sulphate (IL2), was prepared to evaluate the cooperation efficiency of their Brønsted acidic and
Lewis basic sites as compared with the double Brønsted acidic sites in IL1.
c
ꢀ 2014 Institute of Chemistry, Slovak Academy of Sciences
Keywords: ionic liquid, synthesis, pyranopyrazoles, benzopyrans, amino-2-chromenes, dihydropy-
rano[c]chromenes
Introduction
problems (Cole et al., 2002). They have a high cat-
alytic activity and are non-volatile, non-corrosive and
can be used as dual solvents and catalysts (Firouz-
abadi et al., 2006; Kamal & Chouhan, 2004; Sugimura
et al., 2007; Wu et al., 2004). Also, the base catalysts
can be used in different organic syntheses (Bartók et
al., 1999; Niknam et al., 2013; Yokoi et al., 2012), and
different basic ILs have recently been prepared (Davis,
2004).
In addition, modern syntheses need to be rapid
and efficient, in order to avoid toxic solvents and te-
dious procedures (Banerjee & Sereda, 2009; Baner-
jee et al., 2011). Multi-component reactions (MCRs)
are, therefore, ideally suited for this purpose and have
been shown to be valuable methods in organic and
medicinal chemistry (Bräse et al., 2002; Ganem, 2009).
Hence, the development of MCRs in the presence of
ILs would be most beneficial, both economically and
environmentally.
Ionic liquids (ILs) have received increased atten-
tion as “green” solvents and environmentally friendly
catalysts. ILs possess remarkable properties; they are
non-flammable, non-corrosive and are liquid at am-
bient temperature with low vapour pressure (Dupont
et al., 2002; Sheldon, 2001; Welton, 1999). ILs suc-
cessfully have been used as dual solvent-catalysts in
many reactions since they possess the advantages of
both solid and liquid acids such as stability in water
and air, easy separation and reusability (Gupta et al.,
2007).
More specifically, research efforts into ILs have
been directed towards Brønsted acidic ILs. Some re-
cent work focuses on chloride ILs as strong acids
in various organic reactions. However, further devel-
opments are required to decrease the sensitivity of
the catalysts to water. The functionalised sulphoalkyl
groups have been used effectively and have attracted
increased attention with a view to overcoming these
Furthermore, many biological systems have the
pyranopyrazole structure and many methods for their
*Corresponding author, e-mail: davood.habibi@gmail.com
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D. Habibi et al./Chemical Papers 69 (4) 586–595 (2015)
587
Fig. 1. Synthesis of two novel ionic liquids. Reaction conditions: i) 1,4-butane sultone (II) (1 mmol), solvent-free, ambient tem-
perature, 10 h; ii) II (excess), toluene, reflux, 60 h; iii) H2SO4, 80◦C.
syntheses have been reported (Bonsignore et al.,
1993). Benzopyran derivatives are found in a variety
of important biological products such as pheromones,
antibiotics and antimicrobial agents (Al-Haiza et al.,
2003; Darbarwar & Sundaramurthy, 1982). A variety
of methods including the use of microwave (Al’-Assar
et al., 2002), [bmim]OH (Ranu et al., 2008), DMF
(Singh et al., 1996), acetic acid (Wang et al., 2003),
and (S)-proline (Balalaie et al., 2006) have been used
in the syntheses of benzopyrans.
Due to the distinctive properties of 2-amino-2-
chromenes and dihydropyrano[c]chromenes, which can
be used in spasmolytic, diuretic, anticancer, anti-
coagulant and anti-HIV treatments, they have at-
tracted a great deal of research. They have also been
shown to act as cognitive enhancers for the treatment
of neurodegenerative diseases including Parkinson’s
disease, Down’s syndrome, schizophrenia, Alzheimer’s
disease and AIDS-associated dementia (Hafez et al.,
1987; Konkoy et al., 2000). Recently, several catalysts
such as KF/Al2O3 (Ballini et al., 2000), basic alu-
mina (Maggi et al., 2004), tetrabutylammonium bro-
mide (TBAB) (Khurana & Kumar, 2009) potassium
phthalimide (Kiyani & Ghorbani, 2014) and sodium
dodecyl sulphate (Mehrabi & Abusaidi, 2010) were
applied to synthesise chromene derivatives. However,
some of these procedures have been limited by the use
of toxic organic solvents, expensive catalysts and te-
dious workup.
Experimental
All chemicals purchased from the Aldrich and
Merck chemical companies were of high-grade quality
and used without further purification. Melting points
were taken in open capillary tubes using a BUCHI 510
melting point apparatus and are uncorrected. NMR
spectra were recorded in DMSO-d6 using Bruker AM
400, Bruker AM 300 and Jeol FT 90 MHz spectrom-
eters. FTIR spectra (KBr discs or Nujol techniques)
were recorded on a Perkin–Elmer 781 spectrometer.
Mass spectra (70 eV) were obtained using a Shimadzu
GC-MS-QP 1100 EX instrument.
General procedures for synthesis of IL1 and
IL2
1,4-Dimethylpiperazine (I) (10.0 mmol, 1.4 mL)
was added to 1,4-butane sultone (II) (10.0 mmol,
1.0 mL) and the mixture was stirred under solvent-free
conditions at ambient temperature for 10 h. The white
solid zwitterion Z1 (formed early in the reaction) was
filtered, washed with diethyl ether (3 × 5 mL) to re-
move any impurities and dried under diminished pres-
sure at 110◦C (yield 95 %). Sulphuric acid was added
to Z1 (mole ratio of 1 : 1) and the mixture was stirred
at 80◦C for 6 h to form IL1 (yield of 92 %). The IL1
so obtained was then washed with ether (3 × 5 mL)
to remove the non-ionic residues and dried under di-
minished pressure at 110◦C.
Analogously, I (10.0 mmol, 1.4 mL) was added to
II (50.0 mmol, 5 mL) in toluene (5 mL) and the mix-
ture was heated under reflux for 60 h. The white solid
zwitterion Z2 was filtered, washed with diethyl ether
(3 × 5 mL) to remove any impurities and dried under
diminished pressure at 110◦C (yield of 92 %).
In continuation of our researches into the syn-
thesis of different oxygen- and nitrogen-containing
heterocycles (Habibi et al., 2007, 2013; Habibi &
Shamsian, 2013), this paper describes the synthe-
sis of novel and efficient ionic liquids IL1 and IL2
(Fig. 1) for the production of different pyranopyra-
zoles, benzopyrans, amino-2-chromenes and dihyro-
pyrano[c]chromenes.
Sulphuric acid was added to Z2 (mole ratio of 2 : 1)
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588
D. Habibi et al./Chemical Papers 69 (4) 586–595 (2015)
Table 1. Optimisation of reaction conditions for preparation of Z1, Z2, IL1 and IL2
Entry
I/II ratio
Conditions
Zwitterion/yielda/%
Ionic liquid/yielda/%
1
2
3
4
5
6
1 : 1
1 : 1
1 : 1
1 : 5
1 : 5
1 : 5
Solvent-free, r.t., 5 h
Solvent-free, r.t., 10 h
Solvent-free, r.t., 10 h
Solvent-free, r.t., 10 h
Toluene, reflux, 24 h
Toluene, reflux, 60 h
Z1/70
Z1/95
Z1/95
Z1/95
Z1/96
Z2/92
–
IL1/92
–
–
–
IL2/90
a) Isolated yields; r.t. refers to ambient temperature.
and the mixture was stirred at 80◦C for 8 h. The IL2
thus obtained (yield of 90 %) was then washed repeat-
edly with diethyl ether (3 × 5 mL) to remove non-
ionic residues and dried under diminished pressure at
110◦C.
General procedure for synthesis of pyranopy-
razoles and benzopyrans
Fig. 2. Possible formation of IL1 and IL1ꢀ.
To a mixture of aldehyde (1.0 mmol), malononi-
trile (1.0 mmol) and 3-methyl-1-phenyl-2-pyrazolin-5-
one/dimedone/1,3-cyclohexane-dione (1.0 mmol), IL1
(0.03 mmol, 0.01 g) was added as catalyst and the
reaction carried out at ambient temperature under
solvent-free conditions for a certain time. The contents
of the flask solidified, the solid was washed with H2O
(2 × 5 mL), filtered and the crude products purified
by recrystallisation from ethanol/water (ϕr = 7 : 3).
All products were characterised by comparing their
physical and spectral data with those of known com-
pounds.
Fig. 3. Structure of acidic catalysts III and IV.
zwitterion Z2 would be produced with a mole ratio of
1 : 2; however, the ring conformational flexibility of
Z1 which related to the pyramidal properties of the
piperazine cycle, apparently inhibited its attack to II ,
hence more sultone molecules were required. Even at
a 1 : 5 mole ratio, Z2 was not formed at ambient tem-
perature, but it was eventually formed by changing
the conditions to a 1 : 5 mole ratio in refluxed toluene
(entry 6). Compounds IL1 and IL2 were synthesised
from purified Z1 and Z2, respectively, by the addition
of the appropriate amount of sulphuric acid at 80◦C
(Table 1).
General procedure for synthesis of chromenes
The reaction of aldehyde (1 mmol), malononitrile
(1 mmol), α- or β-naphthol or 4-hydroxycoumarin
(1 mmol) and IL1 (0.03 mmol, 0.01 g) was performed
at 80◦C under solvent-free conditions for a certain
time (monitored by TLC) until the contents of the
flask solidified. The reaction mixture was cooled to
ambient temperature, the solid was washed with H2O
(2 × 5 mL), filtered and the crude product was recrys-
tallised from ethanol/water (ϕr = 7 : 3).
During the protonation stage of Z1 with sulphuric
acid, the equilibrium would have occurred for IL1
and both IL1 and IL1ꢀ could theoretically be formed
(Fig. 2).
The catalyst-containing aqueous filtrate was reused
in subsequent runs without further purification.
Results and discussion
To investigate whether the protonated nitrogen
could catalyse the reaction or the SO3H group, two
acidic catalysts were synthesised. Sulphuric acid or p-
toluenesulphonic acid (PTSA) (2 mmol) were added
to I (1 mmol) to prepare III and IV (Fig. 3). The
1H NMR spectrum of I showed two peaks at δ 1.57
(6H, 2 × CH3) and δ 1.72 (8H, 4 × CH2) while the 1H
NMR spectrum of the new compound III showed three
peaks at δ: 2.48 (6H, 2 × CH3), 3.13 (8H, 4 × CH2)
and 8.63 (2H, NH). The signals at δ 1.57–2.48 and δ
1,4-Dimethylpiperazine (I ) and 1,4-butane sultone
(II ) were used under different conditions in order to
synthesise IL1 and IL2 (Fig. 1). In the first step, the
reaction conditions were optimised for the prepara-
tion of zwitterions, Z1 and Z2 (Table 1). For Z1, the
optimal conditions were found to be the 1 : 1 mole
ratio of I and II under solvent-free conditions and
ambient temperature (entry 2). It was expected that
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D. Habibi et al./Chemical Papers 69 (4) 586–595 (2015)
Table 2. Effect of different amounts of catalyst on two sets of reactions
Reaction conditions Aa
589
Reaction conditions Bb
Entry
Catalyst/mole %
Time/min
Yieldc/%
TFd/min−1
Time/min
Yieldc/%
TFd/min−1
1
2
3
4
5
6
7
IL1/3
IL1/4
IL1/5
IL2/3
III/5
4
4
4
96
95
94
92
76
78
–
8
6
5
5
5
94
95
93
92
68
70
–
6.3
4.7
3.7
6.0
0.7
0.7
–
4.7
5.2
1.7
1.7
–
6
5
15
15
30
20
20
30
IV/5
No catalyst
a) 4-Chlorobenzaldehyde (1.0 mmol), malononitrile (1.0 mmol), dimedone (1.0 mmol), ambient temperature, solvent-free; b) 4-
chlorobenzaldehyde (1.0 mmol), malononitrile (1.0 mmol), β-naphthol (1.0 mmol), 80◦C, solvent-free; c) isolated yields; d) TF =
turnover frequency.
Table 3. Spectral data of zwitterions and ionic liquids
Compound
Spectral data
Z1
IR (KBr), ν˜/cm−1: 898, 1039 (SO3), 1179 (C—N)
1H NMR (400 MHz, D2O), δ: 1.82–1.88 (m, 2H, CH2), 1.94–2.02 (m, 2H, CH2), 2.39 (s, 3H, NCH3), 2.82–2.92 (m,
4H, Hpiperazinium), 3.00 (t, J = 7.6 Hz, 2H, NCH2), 3.14 (s, 3H, NCH3), 3.45–3.50 (m, 6H, SCH2 and Hpiperazinium
13C NMR (100 MHz, D2O), δ: 20.18, 21.38, 44.00, 46.98, 47.53, 50.30, 59.75, 63.92
MS (70 eV), m/z (Ir/%): 250 (M+, 5), 173 (100), 157 (12), 127 (25), 114 (14)
)
IL1
Z2
IR (Nujol), ν˜/cm−1: 901, 1040, (SO3), 1182 (C—N(, 3100–3500 (br, O—H)
1H NMR (400 MHz, D2O), δ: 1.72–1.78 (m, 2H, CH2), 1.84–1.92 (m, 2H, CH2), 2.29 (s, 3H, NCH3), 2.74–2.80 (m,
4H, Hpiperazinium), 2.90 (t, J = 7.6 Hz, 2H, NCH2), 3.04 (s, 3H, NCH3), 3.35–3.39 (m, 6H, SCH2 and Hpiperazinium
13C NMR (100 MHz, D2O): δ: 19.82, 21.03, 43.64, 46.61, 47.18, 49.93, 53.60, 59.40, 63.56
MS (70 eV), m/z (Ir/%): 348 (M+, 5), 251 (25), 170 (12), 157 (8), 129 (22), 114 (100)
IR (KBr), ν˜/cm−1: 898, 1041 (SO3), 1179 (C—N)
1H NMR (400 MHz, D2O), δ: 1.81–1.90 (m, 4H, CH2), 1.89–2.09 (m, 4H, CH2), 3.01 (t, J = 7.6 Hz, 4H, NCH2),
)
3.35 and 3.36 (6H, 2 × NCH3), 3.65–3.70 (m, 4H, SCH2), 3.93–4.02 (m, 8H, Hpiperazinium
)
13C NMR (100 MHz, D2O), δ: 20.16, 20.91, 45.33, 49.81, 53.85, 67.33
MS (70 eV), m/z (Ir/%): 386 (M+, 5), 228 (20), 187 (10), 114 (12), 55 (100)
IL2
IR (Nujol), ν˜/cm−1: 905, 1050 (SO3), 1200 (C—N), 2680–3550 (br, O—H)
1H NMR (400 MHz, D2O), δ: 1.72-1.80 (m, 4H, CH2), 1.91-1.95 (m, 4H, CH2), 2.91 (t, J = 7.6 Hz, 4H, NCH2),
3.25 and 3.26 (6H, 2 × NCH3), 3.55–3.60 (m, 4H, SCH2), 3.83–3.92 (m, 8H, Hpiperazinium
)
13C NMR (100 MHz, D2O), δ: 20.05, 20.83, 46.32, 49.76, 53.82, 66.01
1.72–3.13 as well as the new peak at δ 8.63 indicated
the formation of III . In addition, the H NMR spec-
Structure confirmation of ionic liquids
1
trum of IV (δ: 2.22 (s, 3H, NCH3), 2.83 (s, 3H, CH3),
3.43 (s, 4H, 2 × CH2), 7.15 (d, 2H, Haryl) and 7.52 (d,
2H, Haryl) confirms its formation.
The structures of compounds Z1, Z2, IL1, and IL2
were confirmed by IR, NMR and mass spectra (Ta-
ble 3). The presence of the SO3H group was indicated
by the broad peaks at 3500–3100 cm−1 and 3550–
2680 cm−1 in the IR spectra of IL1 and IL2. In addi-
tion, the peaks at 1040 cm−1 for IL1 and 1050 cm−1
for IL2 corresponded to the vibrational modes of the
O—SO2 bonds. The 1H NMR spectra showed two sep-
arated singlets of NCH3 at δ 2.29 and δ 3.04 for IL1
and a split singlet at δ 3.25 and δ 3.26 for IL2.
As can be seen from the diagrams of thermal
gravimetric analysis (TGA) and differential thermal
gravimetry (DTG) of IL1 and IL2 (Figs. 4 and 5),
both ionic liquids show high thermal stability with
thermal decomposition of above 270◦C.
Unfortunately, catalysts III and IV were not ca-
pable of promoting the synthesis of two different sets
of pyran derivatives and the yields were appropriately
low (Table 2). Accordingly, it was concluded that the
protonated nitrogen could not promote the reactions,
apparently for the following two reasons: i) the con-
jugate acid of a strong base is a weak acid and ii)
the steric hindrance of the tertiary amine apparently
prevents the acidic proton from catalysing the reac-
tions. It was noted that the prepared ionic liquids with
the long sulphonated alkyl chain were more active in
catalysing the reactions.
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590
D. Habibi et al./Chemical Papers 69 (4) 586–595 (2015)
at ambient temperature, in contrast with preparation
of the zwitterion Z2, as an intermediate for IL2 which
requires higher concentrations of II as well as reflux
conditions. In addition, the use of III and IV resulted
in long reaction times and low yields (Table 2, entries
5 and 6). As shown in entry 7, in the absence of the
catalyst, the yield was very low.
The catalytic efficiency can be described by the
turnover frequency (TF) (Jiménez-González & Con-
stable, 2011), hence the TF of all the catalysts were
calculated (Table 2). IL1 had the highest TF, indicat-
ing a greater efficiency than the other catalysts.
Four different categories of oxygen- and nitrogen-
containing heterocycles were synthesised in the pres-
ence of IL1 (Fig. 6): i) pyranopyrazoles were synthe-
sised by the reaction of different aldehydes (RCHO),
malononitrile and 3-methyl-1-phenyl-2-pyrazolin-5-
one (V ) at ambient temperature and under solvent-
free conditions; ii) benzopyrans were synthesised by
the reaction of different aldehydes (RCHO), mal-
ononitrile and dimedone (VI) or 1,3-cyclohexanedione
(VII ) at ambient temperature and solvent-free con-
ditions; iii) amino-4H-chromenes were synthesised by
the reaction of different aldehydes (RCHO), malonon-
itrile and α-naphthol (VIII ) or β-naphthol (IX ) at
80◦C and under solvent-free conditions; iv) dihyropy-
rano[c]chromenes were synthesised by the reaction
of different aldehydes (RCHO), malononitrile and 4-
hydroxycoumarin (X ) at 80◦C and under solvent-free
conditions.
Fig. 4. TGA/DTG diagram (TGA curve – solid line; DTG
curve – dashed line) of IL1.
The experimental procedure was highly efficient,
convenient, rapid and tolerated a variety of functional
groups under different reaction conditions. As shown
by the synthesis of pyranopyrazoles (Va–Vj) and ben-
zopyrans (VIa–VIj and VIIa–VIIf), the aromatic alde-
hydes carrying either electron-donating or electron-
withdrawing substituents reacted efficiently affording
excellent yields (Table 4).
Fig. 5. TGA/DTG diagram (TGA curve – solid line; DTG
curve – dashed line) of IL2.
Efficiency and applications of ionic liquids
Two sets of model reactions were selected to op-
timise the reaction conditions (Table 2): reaction of
4-chlorobenzaldehyde (1.0 mmol) and malononitrile
(1.0 mmol) with dimedone (1.0 mmol) at ambient tem-
perature and under solvent-free conditions (reaction
conditions A) and reaction of 4-chlorobenzaldehyde
(1.0 mmol) and malononitrile (1.0 mmol) with β-
naphthol (1 mmol) at 80◦C under solvent-free con-
ditions (reaction conditions B). According to Table 2,
IL1 is an effective catalyst for the synthesis of pyra-
nopyrazoles, benzopyrans and amino-2-chromenes.
The best yield was obtained with 0.03 mmol of IL1
(entry 1) and increasing the amount of the catalyst
had no significant effect on the yield or time (entries
2 and 3). Also, the model reactions were carried out
with IL2 (entry 4); although the results were accept-
able with high yields, it was decided to restrict the
study to the use of IL1 since preparation of the zwitte-
rion Z1, which is an intermediate for IL1, requires less
time and lower concentrations of II and is synthesised
All the synthesised compounds are known and were
characterised by comparing their melting points and
spectral data with authentic samples.
In addition, amino-2-chromenes (VIIIa–VIIIi,
IXa–IXi) and 3,4-dihydropyrano[c]chromenes (Xa–Xi)
were efficiently synthesised in the presence of IL1 (Ta-
ble 5).
All the synthesised compounds are known and were
characterised by comparing their melting points and
spectral data with authentic samples.
Tables 4 and 5 show that the reactions were more
rapid with aromatic aldehydes bearing the electron-
withdrawing groups such as nitro or halogen, while
the reactions were slower with those containing the
electron-donating groups such as methyl or methoxy.
Electron-withdrawing groups decrease the electron
density on the carbon of the carbonyl group, facili-
tating the nucleophilic attack, while the converse is
true for the electron-donating groups.
The main advantages of this protocol are the sim-
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D. Habibi et al./Chemical Papers 69 (4) 586–595 (2015)
591
Fig. 6. Synthesis of various pyran and chromene derivatives. Reaction conditions: i) IL1 (3 mole %), solvent-free, ambient tem-
perature; ii) IL1 (3 mole %), solvent-free, 80◦C.
Table 4. Synthesis of pyranopyrazoles (Va–Vj) and benzopyrans (VIa–VIj and VIIa–VIIf) from aldehyde RCHO, malononirile and
cyclic ketone V or VI or VII in the presence of IL1 (see Fig. 6)
Entry
R
Ketone
Producta
Time/min
Yieldb/%
1
2
C6H5
4-Cl-C6H4
V
V
Va
Vb
10
8
90
92, 92, 90, 89c
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
4-F-C6H4
2,4-Cl2-C6H3
3-Cl-C6H4
3-NO2-C6H4
2-Naphthyl
4-Ph-C6H4
4-(O=CH)-C6H4
3-EtO-4-HO-C6H3
C6H5
4-Me-C6H4
2-Cl-C6H4
4-Cl-C6H4
4-MeO-C6H4
4-F-C6H4
2,4-Cl2-C6H3
3-NO2-C6H4
2-NO2-C6H4
1-Naphthyl
2,4-Cl2-C6H3
4-MeO-C6H4
3-NO2-C6H4
4-Me-C6H4
4-Cl-C6H4
V
V
V
V
V
V
V
V
VI
VI
VI
VI
VI
VI
VI
VI
VI
VI
VII
VII
VII
VII
VII
VII
Vc
Vd
Ve
Vf
Vg
Vh
Vi
Vj
VIa
VIb
VIc
VId
VIe
VIf
VIg
VIh
VIi
VIj
VIIa
VIIb
VIIc
VIId
VIIe
VIIf
12
8
90
93
90
92
90
89
90
88
13
10
15
15
20
15
5
10
4
4
10
7
3
2
5
96
88
93
96, 96, 95, 93c
89
90
96
92
90
88
92
85
10
5
7
4
5
90
87
93, 91, 90, 89c
88
3
5
2-Cl-C6H4
a) See Fig. 6; b) isolated yiels; c) isolated yields from recovered IL1 used in four successive runs.
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D. Habibi et al./Chemical Papers 69 (4) 586–595 (2015)
Table 5. Synthesis of amino-2-chromenes (VIIIa–VIIIi, IXa–IXi) and dihydropyrano[c]chromenes (Xa–Xi) from aldehyde RCHO,
malononitrile and aromatic hydroxy compounds (ArOH) VIII or IX or X in the presence of IL1 (see Fig. 6)
Entry
R
ArOH
Producta
Time/min
Yieldb/%
1
2
3
4
5
6
7
8
C6H5
2-Furyl
VIII
VIII
VIII
VIII
VIII
VIII
VIII
VIII
VIII
IX
IX
IX
IX
IX
IX
IX
IX
IX
X
X
X
X
X
X
X
X
VIIIa
VIIIb
VIIIc
VIIId
VIIIe
VIIIf
VIIIg
VIIIh
VIIIi
IXa
IXb
IXc
IXd
IXe
IXf
IXg
IXh
IXi
Xa
Xb
Xd
Xe
Xf
Xg
3
9
13
2
7
4
2
2
8
4
12
10
3
4
8
5
3
2
6
94
91
82
4-HO-C6H4
4-Cl-C6H4
4-MeO-C6H4
2-Cl-C6H4
2,4-Cl2-C6H3
3-NO2-C6H4
4-Me-C6H4
C6H5
94, 94, 92, 90c
89
90
94
95
87
95
88
86
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
2-Furyl
4-Me-C6H4
4-Cl-C6H4
2-Cl-C6H4
4-MeO-C6H4
4-F-C6H4
2,4-Cl2-C6H3
3-NO2-C6H4
C6H5
4-Cl-C6H4
4-Br-C6H4
3-NO2-C6H4
4-NO2-C6H4
4-MeO-C6H4
3,4-(MeO)2-C6H3
4-Me2N-C6H4
94, 93, 91, 89c
95
88
90
94
93
94
5
6
5
6
8
15
15
95, 93, 91,89c
91
94
90
88
84
88
Xh
Xi
a) See Fig. 6; b) isolated yields; c) isolated yields from recovered IL1 used in four successive runs.
Table 6. Spectral data of selected pyranopyrazoles, benzopyrans and chromenes
Compound
Spectral data
Vd
IR (KBr), ν˜/cm−1: 1529, 1660, 2198, 3322, 3456
1H NMR (400 MHz, DMSO-d6), δ: 1.78 (s, 3H, CH3), 5.10 (s, 1H, H-4), 7.32–7.8 (m, 10H, ArH and NH2)
13C NMR (100 MHz, DMSO-d6), δ: 12.5, 34.9, 56.0, 97.7, 120.9, 120.1, 126.8, 129.0, 129.8, 130.6, 132.2, 137.8, 143.5,
144.6, 145.2, 160.2, 160.5
VIc
VIIb
VIIIi
IR (KBr), ν˜/cm−1: 1606, 1637, 1676, 2190, 3185, 3382
1H NMR (400 MHz, DMSO-d6), δ: 0.95 (s, 3H, CH3), 1.02 (s, 3H, CH3), 2.18 (d, J = 16.4 Hz, 2H, CH2), 2.50 (s,
2H, CH2), 4.21 (s, 1H, H-4), 7.04–7.32 (m, 6H, ArH and NH2)
13C NMR (100 MHz, DMSO-d6), δ: 27.3, 28.8, 32.2, 35.4, 50.4, 58.6, 113.1, 115.4, 115.5, 120.2, 129.4, 129.5, 141.4,
159.1, 160.1, 162.1, 195.4
IR (KBr), ν˜/cm−1: 750, 770, 840, 1026, 1245, 1368, 1450, 1510, 1600, 1700, 2220, 3320, 3460
1H NMR (400 MHz, DMSO-d6), δ: 1.93–1.96 (m, 2H, H-7), 2.26–2.30 (m, 2H, H-8), 2.58–2.62 (m, 2H, H-6), 3.74
(s, 3H, OCH3), 4.20 (s, 1H, H-4), 6.82 (d, 2H, J = 8.0 Hz, ArH), 6.98 (s, 2H, NH2), 7.06 (d, 2H, J = 8.0 Hz, ArH)
13C NMR (100 MHz, DMSO-d6), δ: 20.7, 27.5, 33.9, 37.3, 60.2, 114.4, 119.2, 127.3, 128.2, 130.5, 130.4, 133.5, 141.1,
157.6, 164.5, 196.1
IR (KBr), ν˜/cm−1: 1379, 1507, 1605, 1677, 2194, 3322, 3416
1H NMR (400 MHz, DMSO-d6), δ: 2.61(s, 3H, CH3), 4.88 (s, 1H, CH), 7.01 (s, 2H, NH2), 7.07 (d, J = 8.7 Hz, 1H,
ArH), 7.17–7.32 (m, 5H, ArH), 7.42–7.53 (m, 2H, ArH), 7.89 (d, J = 7.2 Hz, 1H, ArH), 8.26 (d, J = 8.1 Hz, 1H,
ArH)
13C NMR (100 MHz, DMSO-d6), δ: 32.3, 54.4, 57.9, 112.2, 116.3, 117.8, 120.9, 121.5, 125.3, 127.6, 128.4, 128.9,
129.0, 129.6, 130.1, 131.4, 134.9, 147.5, 159.1, 160.7
IXi
Xb
IR (KBr), ν˜/cm−1: 1302, 1529, 1590, 1659, 2191, 3356, 3464
1H NMR (400 MHz, DMSO-d6), δ: 5.6 (s, 1H, CH), 7.1 (s, 2H, NH2), 7.4–7.7 (m, 5H, ArH), 7.34 (d, J = 8.7 Hz,
1H, ArH), 7.42–7.47 (m, 3H, ArH), 8.09 (s, 1H, ArH)
13C NMR (100 MHz, DMSO-d6), δ: 37.8, 57.4, 115.2, 117.4, 120.4, 121.9, 122.3, 123.9, 125.6, 127.8, 129.0, 130.4,
130.5, 130.9, 131.3, 134.7, 147.7, 148.4, 148.5, 160.5
IR (KBr), ν˜/cm−1: 1379, 1507, 1605, 1677, 1716, 2194, 3292, 3378
1H NMR (400 MHz, DMSO-d6), δ: 5.1 (s, 1H, H-4), 7.01–8.03 (m, 12H, ArH and NH2)
13C NMR (100 MHz, DMSO-d6), δ: 36.3, 57.9, 103.8, 112.9, 115.0, 116.6, 119.1, 123.0, 130.0, 133.0, 139.5, 152.1,
153.4, 157.9, 159.5, 160.2, 162.2
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Table 7. Comparison of 4H-benzo[b]pyrans synthesis catalysed by IL1 with methods reported in the literature
Entry Catalysts and conditionsa
Time/min Yieldsb/% TN TF/min−1 Reference
1
[PhCH2Me2N+ CH2CH2NMe2]Cl−
(5 mole %), solvent free, 60◦C
30
76
15
0.5
Chen et al. (2009)
2
3
4
5
6
[TETA]TFA (5 mole %), EtOH/H2O, reflux
[ADPPY]OH (10 mole %), H2O, r.t.
SB-DABCO (6 mole %), EtOH, r.t.
[TEBSA]HSO4 (5 mole %), solvent-free, 90◦C
IL1 (3 mole %), solvent-free, r.t.
20
15
35
60
4
85
95
96
89
96
17
9.5
16
18
32
0.9
0.6
0.45
0.3
8
Zheng and Li (2011)
Salvi et al. (2011)
Hasaninejad et al. (2011)
Fang et al. (2010)
present work
a) Reactants: dimedone, benzaldehyde, malononitrile in a mole ratio of 1 : 1 : 1; b) isolated yields; r.t. means ambient temperature.
Table 8. Comparison of dihydropyrano[c]chromenes synthesis catalysed by IL1 with methods reported in the literature
Entry Catalysts and conditionsa
Time/min Yieldb/% TN TF/min−1 Reference
1
2
CuO nanoparticle (15 mole %), H2O, reflux
H6[P2W18O62] · 18H2O (1 mole %),
EtOH/H2O, reflux
6
30
93
89
6.3
89
1.05
3
Mehrabi and Kazemi-Mireki (2011)
Heravi et al. (2008)
3
4
TBAB (10 mole %), water/neat
IL1 (3 mole %), solvent-free, 80◦C
45
6
91
94
9.1
31
0.2
5.2
Khurana and Kumar (2009)
present work
a) Reactants: 4-hydroxycoumarin, benzaldehyde, malononitrile in a mole ratio of 1 : 1 : 1; b) isolated yields.
ple procedure and purification of the product, since
IL1, but not the products, is fully miscible with wa-
ter. After product separation, the catalyst was readily
recovered by the removal of water.
The reusability of IL1 was investigated in four dif-
ferent reaction categories. The catalyst was recovered
from the aqueous medium, dried under vacuum and
reused in four successive runs, (Table 4, entries 2, 14
and 25) and (Table 5, entries 4, 13 and 20), showing
the capacity of the applied catalyst without significant
loss of activity.
In general, a slight decrease in the activity of the
catalyst is common and has been reported in several
studies (Fang, et al., 2006; Han, et al., 2012; Liu, et
al., 2013; Luo, et al., 2014; Wang, et al., 2008). In the
current work, although there is no clear explanation
for the slight loss of activity, it might be due to the
ion exchanges.
sic sites. IL1 was used effectively for one-pot three-
component condensations of aldehydes, malononi-
trile and cyclic ketones to synthesise pyranopyra-
zoles and benzopyrans at ambient temperature and
for the synthesis of amino-2-chromenes and 3,4-
dihyropyrano[c]chromenes via the reaction of aldehy-
des, malononitrile and α-naphthol/β-naphthol or 4-
hydroxycoumarin under solvent-free conditions. The
reactions are clean, the catalyst is readily synthesised
and reusable and the products are easily separated.
In addition, several acidic catalysts such as IL2,
III, and IV were synthesised, with IL2 exhibiting an
efficiency comparable to IL1 because of its double
Brønsted acidic sites.
These methods not only afford excellent yields in
very short reaction times, but also avoid the problems
associated with catalysts including high cost, difficulty
in handling, and poor safety and pollution.
Selected spectroscopic data for several known
products are given in Table 6.
Acknowledgements. The authors wish to express their grat-
itude for the financial support afforded by the Bu-Ali Sina Uni-
versity, Hamedan 6517838683 Iran.
In addition, the turnover number (TN) and turn-
over frequency (TF) values of the present catalyst
were compared with those of the catalysts reported
as used in the reaction of 4H-benzo[b]pyrans (Ta-
ble 7) and dihydropyrano[c]chromenes (Table 8). The
TN and TF values showed IL1 to be a more ef-
fective catalyst than those reported in the litera-
ture.
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