Ionic liquid triethylamine-bonded sulfonic acid {[Et3N-SO 3H]Cl} as a novel, highly efficient and homogeneous catalyst for the synthesis of β-acetamido ketones, 1,8-dioxo-octahydroxanthenes and 14-aryl-14H-dibenzo[a,j]xanthenes

Article abstract of DOI:10.1016/j.molliq.2011.12.012

In this work, the efficiency, generality and applicability of novel Br?nsted acidic ionic liquid triethylamine-bonded sulfonic acid {[Et ₃N-SO₃H]Cl, N,N-diethyl-N-sulfoethanammonium chloride} as homogeneous and green catalyst for org

Full text of DOI:10.1016/j.molliq.2011.12.012

Journal of Molecular Liquids 167 (2012) 69–77
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Ionic liquid triethylamine-bonded sulfonic acid {[Et3N–SO3H]Cl} as a novel, highly
efficient and homogeneous catalyst for the synthesis of β-acetamido ketones,
1,8-dioxo-octahydroxanthenes and 14-aryl-14H-dibenzo[a,j]xanthenes
b,
a
b,
Abdolkarim Zare a, , Ahmad Reza Moosavi-Zare , Maria Merajoddin , Mohammad Ali Zolfigol
,
⁎
⁎
⁎
Tahereh Hekmat-Zadeh a, Alireza Hasaninejad c, Ardeshir Khazaei b, Mohammad Mokhlesi b,
Vahid Khakyzadeh b, Fatemeh Derakhshan-Panah b, Mohammad Hassan Beyzavi d, Esmael Rostami a,
Azam Arghoon a, Razieh Roohandeh a
a
Department of Chemistry, Payame Noor University, PO BOX 19395-3697 Tehran, Iran
b
Faculty of Chemistry, Bu-Ali Sina University, Hamedan, 6517838683, Iran
c
Department of Chemistry, Faculty of Sciences, Persian Gulf University, Bushehr 75169, Iran
Institut für Chemie und Biochemie, Freie Universität Berlin, Takustr. 3, 14195 Berlin, Germany
d
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 15 October 2011
Received in revised form 11 December 2011
Accepted 27 December 2011
Available online 12 January 2012
In this work, the efficiency, generality and applicability of novel Brønsted acidic ionic liquid triethylamine-
bonded sulfonic acid {[Et3N–SO3H]Cl, N,N-diethyl-N-sulfoethanammonium chloride} as homogeneous and
green catalyst for organic transformations under various conditions are studied. Herein, the following one-
pot multi-component reactions in the presence of {[Et3N–SO3H]Cl are investigated: (i) the synthesis of β-
acetamido ketones from acetophenones, aldehydes, acetonitrile and acetyl chloride in solution and under
extremely mild conditions (room temperature), (ii) the preparation of 1,8-dioxo-octahydroxanthenes
from dimedone (5,5-dimethyl-1,3-cyclohexanedione) (2 equiv.) and aldehydes (1 equiv.) under solvent-free
conditions at moderate temperature (80 °C), and (iii) the synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes from
β-naphthol (2 equiv.) and aldehydes (1 equiv.) in harsh conditions (120 °C) in the absence of solvent. High
yields, relatively short reaction times, efficiency, generality, clean process, simple methodology, low cost, easy
work-up, ease of preparation and regeneration of the catalyst and green conditions (in the synthesis of
the xanthene derivatives) are advantages of the application of [Et3N–SO3H]Cl as catalyst in the above organic
reactions. This work is the first report of the ionic liquid.
Keywords:
Brønsted acidic ionic liquid
β-Acetamido ketone
1,8-Dioxo-octahydroxanthene
14-Aryl-14H-dibenzo[a,j]xanthene
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
solid acids and traditional mineral liquid acids like sulfuric acid and
hydrochloric acid to catalyze chemical transformations [17–23]. Along
Ionic liquids (ILs) are defined as pure compounds, consisting only of
cations and anions (i.e., salts), which melt at or below 100 °C [1–3].
These salts have attracted rising interest in the last decades for chemists
because of their unique properties such as high thermal and chemical
stability, non-flammability, non-volatility, wide liquid-state tempera-
ture range, large electrochemical window and favorable salvation be-
havior [3,4]. This increased interest led to an exponential growth of
papers reporting on various aspects of ILs, including synthesis of a vast
number of new ILs, and their application in synthetic transformations
(as solvent, catalyst and reagent) [1–15], electrochemistry [3,16], spec-
troscopy and extraction and separation processes [3]. Among the differ-
ent kinds of ionic liquids, Brønsted acidic ones have designed to replace
this line, more recently, we have synthesized some Brønsted acidic
ionic liquids in which a SO3H group has bonded with a positive nitrogen
(N+) in organic compound, and successfully applied them as catalysts
and regents in organic transformations [17–20]. In continuation of our
studies on the preparation of acidic ILs, and their applications as catalyst
and reagent in organic transformations [17–20], we have synthesized
Brønsted acidic ionic liquid triethylamine-bonded sulfonic acid {[Et3N–
SO3H]Cl, N,N-diethyl-N-sulfoethanammonium chloride} (Fig. 1) as a
new, homogeneous and green catalyst, from the simple reaction of
triethylamine with chlorosulfonic acid. According to the high efficacy
of our previous acidic ILs to catalyze organic reactions [17–20], we
predict that our new catalyst, [Et3N–SO3H]Cl, can also promote dif-
ferent organic transformations. Moreover, a lot of ILs do not solve
in organic solvents; [Et3N–SO3H]Cl solves in most of organic sol-
vents. This matter is an important factor to catalyze reactions suc-
cessfully in organic media. Herein, we have found that the one-pot
multi-component synthesis of β-acetamido ketones, 1,8-dioxo-
⁎
Corresponding authors. Fax: +98 771 5559489.
E-mail addresses: abdolkarimzare@yahoo.com (A. Zare), moosavizare@yahoo.com
(A.R. Moosavi-Zare), mzolfigol@yahoo.com (M.A. Zolfigol).
0167-7322/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molliq.2011.12.012

70
A. Zare et al. / Journal of Molecular Liquids 167 (2012) 69–77
+
N
Cl
SO3H
[Et3N-SO3H]Cl
Fig. 1. The structure of triethylamine-bonded sulfonic acid {[Et3N–SO3H]Cl}.
octahydroxanthenes and 14-aryl-14H-dibenzo[a,j]xanthenes can be
efficiently performed in the presence of this novel catalyst.
Multi-component reactions (MCRs) have drawn great interest
enjoying an outstanding status in modern organic synthesis and me-
dicinal chemistry because they are one-pot processes bringing to-
gether three or more components and show high atom economy
and high selectivity [17,24–29]. Moreover, MCRs offer the advantage
of simplicity and synthetic efficiency over conventional chemical re-
actions [17,24–29].
Fig. 2. The solvent-free reaction between β-naphthol and benzaldehyde using 15 mol%
of [Et3N–SO3H]Cl, NEt3, ClSO3H or [Et3N–H]Cl at 120 °C.
β-Acetamido ketones are of importance as they have been used as
the precursor of 1,3-amino alcohols [30], β-amino acids [31], and γ-
lactams [32], as well as various bioactive molecules such as antibiotic
nikkomycins or neopolyoxines [33,34]. These compounds have been
also applied as aglucosidase inhibitors [35]. Thus, the synthesis of β-
acetamido ketones has attracted much attention in organic synthesis.
The one-pot multi-component condensation of acetophenones with ar-
omatic aldehydes, acetonitrile and acetyl chloride has been used as the
most common synthetic route towards β-acetamido ketones [35–46].
Some catalysts have been utilized for this transformation, such as
La(OTf)3 [35], CoCl2 [36], Zr(HSO4)4 [37], ZnO nanoparticles [38], hetero-
poly acids [39], silica sulfuric acid [40], Sc(OTf)3 [41], 1-chloromethyl-4-
diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) [68], KAl(SO4)2·12-
H2O [69], nano-TiO2 [70], Yb(OTf)3 [71], Sc[N(SO2C8F17)2]3 [72], InCl3
[73], TaCl5 [74], and HClO4-SiO2 [75].
Although some catalysts for the synthesis of β-acetamido ketones,
1,8-dioxo-octahydroxanthenes and 14-aryl-14H-dibenzo[a,j]xanthenes
are known, newer catalysts continue to attract attention for their differ-
ence with the others, novelty and effectiveness. Furthermore, most of
the reported methods for the synthesis of the title compounds are asso-
ciated with one or more of the following drawbacks: (i) low yields, (ii)
long reaction times, (iii) the use of large amount of catalyst, and (iv) the
use of expensive, non-available or toxic catalysts, (v) tedious work-up
procedure, (vi) performances under certain special conditions, and
(vii) poor agreement with the green chemistry protocols.
Having the above subjects in mind, and also in continuation of on-
going program to prepare Brønsted acidic ILs and apply them as cat-
alysts in organic synthesis [17–20], we, in this paper, introduce
ionic liquid triethylamine-bonded sulfonic acid {[Et3N–SO3H]Cl} as a
novel, highly efficient, homogeneous, regenerable and green catalyst
for organic reactions. Herein, we report the first applications of this
interesting catalyst for some on-pot multi-component organic trans-
formations including: (i) the synthesis of β-acetamido ketones by
the reaction of acetophenones with aldehydes, acetonitrile and acetyl
chloride, (ii) the preparation of 1,8-dioxo-octahydroxanthenes via
the condensation of 2 equiv. of dimedone with 1 equiv. of aldehydes,
and (iii) the synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes by the
reaction between 2 equiv. of β-naphthol and 1 equiv. of aldehydes.
Interestingly, our protocols have none of the above-mentioned disad-
vantages at all.
fluoro-1,4-diazoniabicyclo[2.2.2]octane-bis(tetrafluoroborate)
[42],
polyaniline-supported salts [43], CeCl3•7H2O [44], ZrOCl2•8H2O [45],
and AlCl3 [46].
There has been significant attention in recent years in the synthesis
of xanthenes and their related derivatives such as 1,8-dioxo-octahy-
droxanthens and 14-aryl-14H-dibenzo[a,j]xanthenes due to their useful
spectroscopic properties and applications in industry as dyes in laser
technology [47], and as pH sensitive fluorescent materials for visualiza-
tion of biomolecules [48]. Moreover, xanthene based compounds exhibit
extensive activities in biological and pharmaceutical aspects such as
anti-inflammatory [49], antiviral [50], antibacterial [51], antitumor
[52], and neuropharmacological [53], and they have been applied
in photodynamic therapy (PDT) [54]. Xanthene derivatives have
been also utilized as inflexible carbon skeletons for the assembly of
chiral bidentate phosphine ligands with potential applications in cata-
lytic processes [55,56]. The usual method for the synthesis of 1,8-
dioxo-octahydroxanthenes involves the one-pot multi-component con-
densation between dimedone (5,5-dimethyl-1,3-cyclohexanedione) (2
equiv.) and aldehydes (1 equiv.), by utilizing a number of catalysts, e. g.
amberlyst-15 [57], NaHSO4-SiO2 [58], SbCl3/SiO2 [58], silica-supported
2. Experimental
H14[NaP5W30O110] nanoparticles [59], SiO2-R-SO3H [60], H3PW12O40
2.1. General
supported MCM-41 [61], DABCO-bromine [62], cyanuric chloride [63],
TMSCl [64], and ZrO(OTf)2 [65]. The best and most interesting protocol
for the synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes is the one-pot
multi-component reaction of β-naphthol (2 equiv.) with aldehydes
(1 equiv.) in the presence of some catalysts, such as ZrO(OTf)2 [65], het-
eropolyacids [66], Dowex-50 W [67], 1-(chloromethyl)-4-fluoro-1,4-
All chemicals were purchased from Merck or Fluka Chemical Com-
panies. Acetonitrile and dichloromethane were dried, distilled and
stored over molecular sieves. All known compounds were identified
by comparison of their melting points and spectral data with those
reported in the literature. Progress of the reactions was monitored by
thin layer chromatography (TLC) using silica gel SIL G/UV 254 plates.
CH2Cl2
+
R
N
+
N
R
R N
ClSO3H
Cl
SO3H
+
2
+
ClSO3H
+
R3NHCl
R N SO3
R
R
[Et3N-SO3H]Cl
Scheme 2. The preparation of R3N+–SO3− by the reaction of tertiary amines (2 equiv.)
Scheme 1. The synthesis of [Et3N–SO3H]Cl.
with chlorosulfonic acid (1 equiv.).

A. Zare et al. / Journal of Molecular Liquids 167 (2012) 69–77
71
R = Me
+
Cl
N
N
Me
SO3H
ClSO3H
[Msim]Cl
N
N
R
R = H
+
Cl
N
N
HO3S
SO3H
[Dsim]Cl
Scheme 3. The nucleophilic reaction of 1-methylimidazole or imidazole with chlorosulfonic acid.
The melting points were recorded on a Büchi B-545 apparatus in open
capillary tubes. The 1H NMR (300, 400 or 500 MHz) and 13C NMR (75,
100 or 125 MHz) were run on a Bruker Avance DPX, FT-NMR spectrom-
eters. Mass spectra were obtained with Shimadzu GC-MS-QP 1100 EX
model.
magnetically, and after solidification of the reaction mixture with a
small rod, at 120 °C. After completion of the reaction, as monitored
with TLC, the reaction mixture was cooled to room temperature,
H2O (5 mL) was added to it, stirred for 3 min, and filtered. Then, the
solid residue was recrystallized from EtOH (95%) to give the pure
product.
2.2. Procedure for the preparation of ionic liquid [Et3N–SO3H]Cl
3. Results and discussion
A solution of triethylamine (0.50 g, 5 mmol) in CH2Cl2 (40 mL)
was added dropwise to a stirring solution of chlorosulfonic acid
(0.58 g, 5 mmol) in dry CH2Cl2 (40 mL) over a period of 10 min at
10 °C. Afterward, the reaction mixture was allowed to heat to room
temperature (accompanied with stirring), and stirred for another
4 h. The solvent was evaporated, and the liquid residue was triturated
with t-butylmethyl ether (3×10 mL) and dried under powerful vacu-
um at 90 °C to give [Et3N–SO3H]Cl as a viscous pale yellow oil in 93%
yield.
3.1. Studies to confirm the structure of triethylamine-bonded sulfonic ac-
id {[Et3N–SO3H]Cl}
To prepare ionic liquid triethylamine-bonded sulfonic acid
(Scheme 1), firstly, triethylamine (in dry CH2Cl2) was added drop-
wise to a stirring solution of chlorosulfonic acid in dry CH2Cl2 over a
period of 10 min at room temperature, and the resulting mixture
was stirred at room temperature for 3 h. Afterward, the solvent was
evaporated, and the liquid residue was triturated with dry t-
butylmethyl ether (three times) and dried under vacuum to give
[Et3N–SO3H]Cl as a viscous pale yellow oil in about 90% purity; we
could not be separated [Et3N–SO3H]Cl from the by-product. We
thought that the by-product was [Et3N–H][ClSO3] which formed be-
sides the catalyst in about 10% by the acid–base reaction between
triethylamine and chlorosulfonic acid; the small peak observed in
11.75 ppm of 1H NMR spectra of the catalyst is related to the acidic
hydrogen of [Et3N–H][ClSO3]. In another procedure, chlorosulfonic
acid (in dry CH2Cl2) was added dropwise to a stirring solution of
triethylamine in dry CH2Cl2 over a period of 10 min at room temper-
ature, and the resulting mixture was stirred at room temperature for
3 h. In these conditions, [Et3N–H][ClSO3] was also produced, accom-
panied with [Et3N–SO3H]Cl, more than the previous method. Increas-
ing the reaction times in both procedures did not improve the results.
In order to synthesize [Et3N–SO3H]Cl purely, in the next step, triethy-
lamine (in dry CH2Cl2) was added dropwise to a stirring solution of
chlorosulfonic acid (in dry CH2Cl2) over a period of 10 min at 10 °C,
and the resulting mixture was stirred at room temperature for 4 h.
Then, the solvent was evaporated, and the liquid residue was triturat-
ed with dry t-butylmethyl ether (three times) and dried under pow-
erful vacuum to afford pure [Et3N–SO3H]Cl as a viscous pale yellow
oil. In this procedure, the by-product {[Et3N–H][ClSO3]} was not
obtained (the peak related to the acidic hydrogen of the by-product
(11.75 ppm) was not observed in the 1H NMR spectra of the catalyst).
The complete explanations on the identification of the structure of
the catalyst are given below:
2.3. General procedure for the synthesis of β-acetamido ketone deriva-
tives 1a–o
To a mixture of compounds consisting of acetophenone (1 mmol),
aldehyde (1 mmol), acetonitrile (3 mL) and acetyl chloride (0.3 mL) in
a 10 mL round-bottomed flask was added [Et3N–SO3H]Cl (0.033 g,
0.15 mmol), and the resulting mixture was stirred at room temperature.
After completion of the reaction, as monitored by TLC, crushed ice
(10 mL) was added to the reaction mixture and stirred thoroughly. On
solidification, the crude product (solid) was filtered, dried, and purified
by short column chromatography on silica gel eluted with EtOAc/n-hex-
ane (1/4).
Note: For the synthesis of tris(β-acetamido ketone) 1p, the
amounts of p-bromoacetophenone, tris(aldehyde), acetonitrile, acetyl
chloride and [Et3N–SO3H]Cl were 3.3 mmol, 1 mmol, 9 mL, 0.9 mL
and 0.25 mmol, respectively.
2.4. General procedure for the synthesis of 1,8-dioxo-octahydroxanthene
derivatives 2a–n
To
a mixture of dimedone (0.28 g, 2 mmol) and aldehyde
(1 mmol) in a test tube, [Et3N–SO3H]Cl (0.055 g, 0.25 mmol) was
added. The resulting mixture was firstly stirred magnetically, and
after solidification of the reaction mixture with a small rod at 80 °C,
and the reaction progress was monitored by TLC. After completion
of the reaction, the mixture was cooled to room temperature, H2O
(5 mL) was added to it, stirred for 3 min and filtered. The solid resi-
due was recrystallized from EtOH (95%) to give the pure product.
The structure of [Et3N–SO3H]Cl was identified by 1H and 13C NMR
and mass spectra. The corresponding spectral data have been
reported in Section 2. Here, we study 1H NMR data of [Et3N–SO3H]
Cl. The important peak of 1H NMR spectra of [Et3N–SO3H]Cl is related
to the acidic hydrogen (SO3H) which was observed in 7.43 ppm. To
confirm that this peak (7.43) is really related to the hydrogen of
SO3H in [Et3N–SO3H]Cl, not the hydrogen of ClSO3H (its unreacted
starting material) or another possible product formed from the
2.5. General procedure for the synthesis of 14-aryl-14H-dibenzo[a,j]xan-
thenes 3a–j
A mixture of β-naphthol (0.42 g, 2 mmol), aldehyde (1 mmol) and
[Et3N–SO3H]Cl (0.033 g, 0.15 mmol) in a test tube, was firstly stirred

72
A. Zare et al. / Journal of Molecular Liquids 167 (2012) 69–77
Fig. 4. Effect of different amounts of [Et3N–SO3H]Cl on the reaction of acetophenone
with benzaldehyde, acetonitrile and acetyl chloride at room temperature.
reaction of NEt3 with ClSO3H {i.e. [Et3N–H][ClSO3]}, we also run 1H
NMR spectra of ClSO3H as well as [Et3N–H]Cl in CDCl3 {the acidic hy-
drogens of [Et3N–H][ClSO3] and [Et3N–H]Cl are same. There was no
[Et3N–H][ClSO3] in the Chemical Companies catalogs. Thus, we used
[Et3N–H]Cl instead of [Et3N–H][ClSO3]}. In these spectra, the peaks
of the acidic hydrogens of [Et3N–SO3H]Cl, ClSO3H and [Et3N–H]Cl
were observed in 7.43, 10.75 and 11.59 ppm, respectively. The differ-
ence between the peaks of the acidic hydrogens in the compounds
confirmed that the peak observed in 7.43 ppm of the 1H NMR spectra
of [Et3N–SO3H]Cl is correctly related to the hydrogen of the SO3H
group of this compound.
In another study, to prove that [Et3N–SO3H]Cl was correctly syn-
thesized, and this is responsible of the catalytic results, as a model,
the condensation of β-naphthol with benzaldehyde, leading to 14-
aryl-14H-dibenzo[a,j]xanthenes 3a, was examined in the presence
of 15 mol% of the starting materials used for the preparation of the
catalyst (i.e. NEt3 and ClSO3H) as well as the possible product formed
by the reaction of NEt3 with ClSO3H {this possible product is [Et3N–H]
[ClSO3]; however, there was not this compound in the Chemical Com-
panies catalogs. Moreover, the acidic hydrogen of the cation of [Et3N–
H][ClSO3] can catalyze the reaction, not its anion. Thus, we used
[Et3N–H]Cl instead of it} at 120 °C under solvent-free conditions.
The results are presented in Fig. 2. As Fig. 2 indicates, [Et3N–SO3H]Cl
efficiently catalyzed the reaction; NEt3 could not catalyze the reac-
tion; and ClSO3H as well as [Et3N–H]Cl and also catalyst-free condi-
tions gave low yields of the product in long reaction times (when
ClSO3H was used as catalyst, by-products were produced besides
the main product; however, in the case of [Et3N–H]Cl, a large amount
of the starting materials remained). It should be mentioned that be-
cause of the low boiling point of NEt3, the reaction was carried out
at 85 °C when this catalyst was applied. The model reaction was
also checked using 15 mol% of the impure catalyst formed by the
above-mentioned procedure {[Et3N–SO3H]Cl accompanied with
about 10% of [Et3N–H][ClSO3]}, at 120 °C in the absence of solvent in
Fig. 3. The thermogravimetry (TG), derivative thermogravimetry (DTG) and differen-
tial thermal analysis (DTA) diagrams of [Et3N–SO3H]Cl.
O
O
O
O
NH
O
[Et3N-SO3H]Cl (15 mol%)
Cl
r.t., 50-130 min
+
+
CH3CN +
R'
H
R
CH3
H3C
R'
R
R = Phenyl, Aryl,
R' = Phenyl, Aryl, Naphthyl
1a-o
84-95%
Scheme 4. The synthesis of β-acetamido ketones from acetophenones, arylaldehydes, acetonitrile and acetyl chloride using [Et3N–SO3H]Cl.

A. Zare et al. / Journal of Molecular Liquids 167 (2012) 69–77
73
Table 1
Moreover, it is well known that tertiary amine–sulfur trioxide
(R3N+–SO3−) produces by the dropwise addition of chlorosulfonic
acid (1 equiv.) to tertiary amines (2 equiv.) dissolved in dichloroethane
at low temperature (Scheme 2) [76,77]. In these conditions, in each
time, there are excess amount of Et3N besides ClSO3H in the reaction
mixture; thus, 1 equiv. of tertiary amine (as a nucleophile) attacks to
the sulfur of ClSO3H to give [R3N–SO3H]Cl, and another 1 equiv. of
amine acts as a base and abstracts the acidic hydrogen of [R3N–SO3H]
Cl to afford R3N+-SO3− and R3NHCl. In the synthesis of [Et3N–SO3H]Cl,
we add 1 equiv. of triethylamine dropwise to 1 equiv. of chlorosulfonic
acid at low temperature. In these conditions, in each time, there are ex-
cess amount of ClSO3H besides Et3N in the reaction mixture; thus, when
NEt3 reacts with ClSO3H, and [Et3N–SO3H]Cl forms, there is no base in
the reaction media to abstract the acidic hydrogen of the compound
to afford Et3N+-SO3− and Et3NHCl. Also, according to the literature
[76,77], in the reaction of tertiary amines with chlorosulfonic acid at
low temperature, the reaction route is the nucleophilic substitution
(substitution of Cl of ClSO3H by the nitrogen of tertiary amine), not
the acid–base reaction (abstraction of the hydrogen of ClSO3H by
tertiary amine to give [R3N–H][ClSO3]. The solvent-free reaction of
β-naphthol with benzaldehyde was also examined using 15 mol%
of Et3N+–SO3− at 120 °C in which the product was obtained in 27%
within 240 min. Considering this subject as well as the above proce-
dures for the preparation of R3N+–SO3− and [Et3N–SO3H]Cl, it is logical
that our procedure must give [Et3N–SO3H]Cl, not [R3N–H][ClSO3] or
Et3N+–SO3−. The peak with integral 1, observed in 7.43 ppm of the 1H
NMR spectra of the catalyst, also confirmed existence a SO3H group in
the catalyst, and consequently its structure {[Et3N–SO3H]Cl}.
Furthermore, more recently, we [17–20] and also Ghaffari Khaligh
[21] showed that when 1-methylimidazole (1 equiv.) or imidazole
(2 equiv.) is reacted with chlorosulfonic acid (1 equiv.), the nitrogen
atoms of 1-methylimidazole or imidazole act as nucleophile (not base),
and attack to the sulfur of ClSO3H to give 3-methyl-1-sulfonic acid
imidazolium chloride {[Msim]Cl} or 1,3-disulfonic acid imidazolium
chloride {[Dsim]Cl}, correspondingly (Scheme 3). This subject also con-
firmed that the reaction of triethylamine (1 equiv.) with chlorosulfonic
acid (1 equiv.) afforded [Et3N–SO3H]Cl, not [Et3N–H][ClSO3].
Thermal gravimetric analysis (TGA) of [Et3N–SO3H]Cl was also
studied. The corresponding diagrams are shown in Fig. 3. The thermo-
gravimetry (TG), derivative thermogravimetry (DTG) and differential
thermal analysis (DTA) diagrams of the catalyst showed weight losses
in one step, and decomposition after about 290 °C.
The triethylamine-bonded sulfonic acid catalyzed synthesis of β-acetamido ketones via
the reaction of acetophenones with aldehydes, acetonitrile and acetyl chloride at room
temperature.
Aldehyde
Product
Time
(min)
Yielda
(%)
M.p. °C (Lit.)
O
70
90
60
60
95
93
92
91
100–102
(104–106)
[37]
CHO
NH
O
O
(1a)
O
O
77–79
(74–76) [45]
CHO
CHO
CHO
NH
NO2
(1b)
126–128
(130–132)
[45]
NH
O
O
OMe
(1c)
O
102–104
(98–101) [43]
NH
Br
(1d)
O
130
84
185–188
(187–188)
[37]
O2
N
N
CHO
NH
O
O
O2
N
N
NO2
(1e)
O
120
75
87
86
162–163
(162–163)
[46]
O2
CHO
CHO
NH
O2
Br
(1f)
O
104–106
(104–105)
[46]
OHC
MeO
NH
O
OHC
Br
(1g)
O
60
91
124–127
(124–127)
[46]
CHO
NH
O
MeO
Me
Cl
OMe
(1h)
O
50
117–119
(118–119)
[46]
Me
Cl
CHO
CHO
NH
O
Me
(1i)
O
120
75
87
89
114–116
(116–118)
[39]
NH
O
NO2
(1j)
O
130–132
(130–132)
[46]
To explore the generality and applicability of the new catalyst, we
studied its efficiency to catalyze three types of organic transformations
under different conditions and temperatures, including the preparation
of β-acetamido ketones in extremely mild (room temperature) and
solution conditions, the synthesis of 1,8-dioxo-octahydroxanthenes
under relatively mild (80 °C) and solvent-free conditions, and the
preparation of 14-aryl-14H-dibenzo[a,j]xanthenes under harsh (120 °C)
and solvent-free conditions. Interestingly, [Et3N–SO3H]Cl efficiently
catalyzed the above reactions under the mentioned conditions to give
the desired products in high to excellent yields and in relatively short
reaction times.
Cl
CHO
CHO
NH
O
Cl
Me
(1k)
O
110
80
87
90
164–165
(165–166)
[46]
NH
O
NO2
OMe
Me
(1l)
CHO
CHO
CHO
O
O
O
108–110
(108–110)
[46]
NH
O
O
(1m)
90
90
85
88
110–112
(112–114)
[46]
NH
3.2. Study of the efficiency of triehylamine-bonded sulfonic acid in the
synthesis of β-acetamido ketones 1a–p
(1n)
139–141
(138–140)
[46]
Initially, as a model, the condensation of acetophenone (1 mmol)
with benzaldehyde (1 mmol), acetonitrile (3 mL) and acetyl chloride
(0.3 mL) was examined in the presence of different molar ratios of
[Et3N–SO3H]Cl at room temperature (Scheme 4). The results are sum-
marized in Fig. 4. As Fig. 4 indicates, 15 mol% of the catalyst was suffi-
cient to catalyze the reaction efficiently; in this case, the corresponding
product was obtained in 95% yield within 70 min (Fig. 4, entry 5). No im-
provement in the reaction results was observed by increasing the
amount of [Et3N–SO3H]Cl (Fig. 4, entry 6).
NH
O
Br
(1o)
a
Isolated yield.
which the product was obtained in lower yield and longer reaction
time with respect to the pure catalyst. These results also confirmed
that the catalyst has been correctly synthesized, and its structure is
[Et3N–SO3H]Cl, not [Et3N–H][ClSO3].

74
A. Zare et al. / Journal of Molecular Liquids 167 (2012) 69–77
O
HN
O
O
OHC
O
O
Br
O
[Et3N-SO3H]Cl (25 mol%)
O
HN
O
O
+
CHO
CH3CN, CH3COCl, r.t.
200 min
Br
O
O
O
CHO
N
Br
H
O
Br
1p
74%
Scheme 5. The synthesis of complex compound 1p using [Et3N–SO3H]Cl.
O
Ar
O
O
[Et3N-SO3H]Cl (25 mol%)
+
Ar-CHO
2
Solvent-free, 80 °C
30-60 min
O
O
2a-n
85-97%
Scheme 6. The condensation of dimedone with aldehydes leading to 1,8-dioxo-octahydroxanthenes using [Et3N–SO3H]Cl.
To assess the efficiency and the scope of [Et3N–SO3H]Cl in the prepa-
and shorter reaction time were obtained when the reaction was carried
our using 25 mol% of the catalyst at 80 °C (Fig. 5, entry 3). Increment the
amount of [Et3N–SO3H]Cl or the reaction time did not improve the yield
(Fig. 5, entries 4 and 7).
After optimization of the reaction conditions, dimedone was reacted
with different aldehydes (including aromatic aldehydes possessing
electron-withdrawing substituents, electron-donating substituents and
halogens on their aromatic ring as well as cinnamaldehyde). The results
are reported in Table 2. As it is shown in Table 2, triethylamine-bonded
sulfonic acid efficiently catalyzed the reactions to furnish the respective
1,8-dioxo-octahydroxanthenes in high to excellent yields (85–97%) and
ration of β-acetamido ketones, different acetophenones were reacted
with structurally and electronically diverse arylaldehydes, acetonitrile
and acetyl chloride under the optimal reaction conditions; the respective
results are displayed in Table 1. As it can be seen in Table 1, our new cat-
alyst was general and efficient; both acetophenone derivatives and arylal-
dehydes bearing electron-withdrawing substituents, electron-releasing
substituents and halogens on the aromatic ring gave the desired
β-acetamido ketones in high to excellent yields (84–95%) and in
relatively short reaction times (50–130 min) (Table 1, compounds
1a–k). [Et3N–SO3H]Cl also catalyzed the reaction efficiently when
2-naphthaldehyde instead of benzaldehyde or its derivatives was
applied; in these cases, the products were obtained in 85–90%
yields after 80–110 min (Table 1, compounds 1l–o).
Interestingly, the condensation of p-bromoacetophenone (3.3 mmol)
with a tris(aldehyde) (1 mmol), acetonitrile (9 mL) and acetyl chloride
(0.9 mL) in the presence of [Et3N–SO3H]Cl (25 mol%) at room tempera-
ture afforded tris(β-acetamido ketone) 1p in 74% yield within 200 min
(Scheme 5).
3.3. Study of the efficacy of [Et3N–SO3H]Cl in the synthesis of 1,8-
dioxo-octahydroxanthenes 2a–n
Considering the high importance of xanthene derivatives [47–56], in
the next step, we examined the efficiency of ionic liquid [Et3N–SO3H]Cl
in the synthesis of 1,8-dioxo-octahydroxanthenes. To obtain the opti-
mized reaction conditions for the synthesis of this class of compounds,
the solvent-free reaction of dimedone (2 mmol) with benzaldehyde
(1 mmol) was selected as a model reaction (Scheme 6), and effect of dif-
ferent molar ratios of [Et3N–SO3H]Cl and temperature on the reaction
was studied (Fig. 5). As it is clear from Fig. 5, higher yield of the product
Fig. 5. The solvent-free reaction of dimedone (2 mmol) with benzaldehyde (1 mmol)
using different molar ratios of [Et3N–SO3H]Cl at range of 60–85 °C.

A. Zare et al. / Journal of Molecular Liquids 167 (2012) 69–77
Table 2 (continued)
75
Table 2
The condensation of dimedone and aldehydes leading to 1,8-dioxo-octahydrox-
anthenes using [Et3N–SO3H]Cl at 80 °C in the absence of solvent.
Aldehyde
Product
Time (min) Yielda (%) M.p. °C (Lit.)
Br
O
40
91
242–244
Br
CHO
Aldehyde
Product
Time (min) Yielda (%) M.p. °C (Lit.)
(240–242) [64]
60
97
199–201
O
O
CHO
(201–203) [64]
O
O
(2m)
O
60
85
172–174
(177–178) [60]
(2a)
NO2
CHO
35
97
224–226
O2
N
CHO
(228–230) [59]
O
O
O
O
O
O
(2n)
O
a
(2b)
Isolated yield.
NO2
O
40
40
97
89
164–166
(168–170) [60]
O2
N
CHO
in short reaction times (30–60). Thus, the novel catalyst was general and
effective in the preparation of 1,8-dioxo-octahydroxanthene derivatives.
O
(2c)
CN
220–222
(217–218) [58]
3.4. Study of the efficiency of the catalyst in the preparation of 14-aryl-
14H-dibenzo[a,j]xanthenes 3a–j
NC
CHO
O
O
After the successful application of [Et3N–SO3H]Cl in the synthesis of
β-acetamido ketones and 1,8-dioxo-octahydroxanthenes, we decided
to test its efficacy in the preparation of 14-aryl-14H-dibenzo[a,j]xan-
thenes from β-naphthol and aldehydes (Scheme 7). For this purpose,
as a model, the condensation of β-naphthol (2 mmol) with benzalde-
hyde (1 mmol) was examined using different amounts of the catalyst
at range of 100–130 °C under solvent-free conditions (Fig. 6). As Fig. 6
shows, the best results were obtained when the reaction was performed
in the presence of 15 mol% of [Et3N–SO3H]Cl at 120 °C (Fig. 6, entry 3).
Moreover, when the reaction was carried out using the catalyst amount
more than 15 mol% or at temperature higher that 120 °C, the results
were not considerably modified (Fig. 6, entries 4 and 7).
Under the optimized reaction conditions, β-naphthol was con-
densed with different aromatic aldehydes (including aldehydes bearing
electron-withdrawing substituents, electron-releasing substituents and
halogens on their aromatic ring); the corresponding results are summa-
rized in Table 3. As it can be seen in Table 3, [Et3N–SO3H]Cl was highly
efficient and general in the synthesis of 14-aryl-14H-dibenzo[a,j]
xanthenes; all reactions proceeded efficiently and the desired prod-
ucts were produced in high yields (92–97%) and short reaction times
(15–40 min).
O
(2d)
OMe
55
90
243–245
(248–250) [59]
MeO
CHO
O
O
O
O
(2e)
MeO
OMe
O
55
45
92
93
161–163
(161–162) [58]
CHO
O
(2f)
OMe
178–180
(175–176) [58]
MeO
MeO
OMe
O
CHO
O
O
(2g)
Me
50
60
40
40
93
85
93
95
216–218
(219–221) [64]
Me
CHO
O
O
Considering the high effectiveness of our novel catalyst {[Et3N–
SO3H]Cl} in the synthesis of β-acetamido ketones 1,8-dioxo-
octahydroxanthenes and 14-aryl-14H-dibenzo[a,j]xanthenes as im-
portant organic compounds, we anticipate that it can be applied as a
highly efficient catalyst in organic reactions which need the use of acidic
catalysts to speed up.
O
(2h)
OH
CHO
250–252
Br
OH
O
O
Br
Cl
O
(2i)
3.5. Regenerating and reusing the catalyst (Scheme 8)
Cl
229–231
(230–232) [64]
CHO
As previously shown, triethylamine-bonded sulfonic acid was highly
efficient and general for the synthesis of three important classes of bio-
logically interesting organic compounds including β-acetamido ketones
1,8-dioxo-octahydroxanthenes and 14-aryl-14H-dibenzo[a,j]xanthenes.
To raise the catalyst worth, recoverability (or regenerability) and reus-
ability of it was studied. For this purpose, the reaction of β-naphthol
with benzaldehyde using [Et3N–SO3H]Cl was carried out several times,
and the reaction mixtures were combined. Afterward, H2O was added
to the combined reaction mixtures, stirred for 3 min, and filtered (the
catalyst is soluble in H2O; however, the reaction mixture is not soluble
in H2O). The H2O of the filtrate (containing the catalyst) was evaporated,
and the liquid residue was triturated with t-butylmethyl ether (3 times)
and dried under powerful vacuum at 90 °C; in this case, a viscous pale
yellow oil was obtained. To confirm that the viscous oil is pure [Et3N–
O
O
O
O
(2j)
Cl
Cl
O
186–187
(183–185) [58]
CHO
O
(2k)
Cl
O
O
30
92
223–225
(226–227) [58]
Cl
CHO
O
(2l)

76
A. Zare et al. / Journal of Molecular Liquids 167 (2012) 69–77
Ar
O
OH
[Et3N-SO3H]Cl (15 mol%)
Ar-CHO
2
+
Solvent-free, 120 °C
15-40 min
3a-j
92-97%
Scheme 7. The reaction of β-naphthol with arylaldehydes to produce 14-aryl-14H-dibenzo[a,j]xanthenes using [Et3N–SO3H]Cl.
Table 3
The [Et3N–SO3H]Cl-promoted synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes from
β-naphthol and aromatic aldehydes under solvent-free conditions at 120 °C.
SO3H]Cl, we run 1H NMR spectrum of it. The spectrum showed that the
recovered catalyst is not pure; we thought that few amount of [Et3N–
SO3H]Cl hydrolyzes by H2O to give [Et3NH]Cl and H2SO4. Thus, we de-
cided to regenerate the catalyst. For this purpose, after the addition of
H2O to the reaction mixture, stirring and filtration, the filtrate (containing
the catalyst) was basified by NaOH; in these conditions, [Et3N–SO3H]Cl
was completely converted to Et3N and Na2SO4. Then, the solution was
extracted with CH2Cl2, washed with H2O and dried over Na2SO4. The re-
covered NEt3 in CH2Cl2 was reacted with chlorosulfonic acid according
to the mentioned procedure to give [Et3N–SO3H]Cl. The catalytic activity
of the reproduced catalyst was the same as the first one. The regenerate
and reuse cycle of [Et3N–SO3H]Cl is summarized in Scheme 8.
Aldehyde
Product
Time (min) Yielda (%) M.p. °C (Lit.)
30
96
186–188
(184–185) [70]
CHO
O
(3a)
NO2
25
97
312–314
(311–312) [68]
O2
N
CHO
O
(3b)
O2N
NO2
30
30
97
95
215–217
(213) [68]
4. Conclusions
CHO
In summary, we have introduced Brønsted acidic ionic liquid [Et3N–
SO3H]Cl as a novel, highly efficient, general, homogeneous and green
catalyst for organic transformations. For example, in this work, the
synthesis of β-acetamido ketones, 1,8-dioxo-octahydroxanthenes
and 14-aryl-14H-dibenzo[a,j]xanthenes efficiently catalyzed by this
ionic liquid. The promising points for the presented protocols are effi-
ciency, generality, high yields, short reaction times, cleaner reaction
profile, simplicity, low cost, ease of preparation and regeneration of
the catalyst, and compliance with the green chemistry protocols (in
the case of the xanthene derivatives).
O
(3c)
212–214
(214–215) [70]
NO2
CHO
NO2
O
(3d)
OMe
30
40
20
92
95
97
200–202
(203–205) [69]
MeO
CHO
Acknowledgements
O
(3e)
Me
225–227
(227–229) [70]
The authors thank Payame Noor University Research Council for
the financial support of this work.
Me
CHO
Appendix A. Supplementary data
O
(3f)
Cl
284–286
(289–290) [69]
Supplementary data to this article can be found online at doi:10.
1016/j.molliq.2011.12.012.
Cl
CHO
O
(3g)
Cl
Cl
20
20
94
95
207–209
(209–211) [70]
CHO
O
(3h)
Cl
209–211
(214–216) [70]
CHO
Cl
O
(3i)
Br
15
96
186–188
Br
(190–191) [70]
CHO
O
(3j)
Fig. 6. Effect of amount of the catalyst and temperature on the condensation of β-naphthol
(2 mmol) with benzaldehyde (1 mmol) under solvent-free conditions.
a
Isolated yield.

A. Zare et al. / Journal of Molecular Liquids 167 (2012) 69–77
77
[32] I.N. Rao, E.N. Prabhakaran, S.K. Das, J. Iqbal, Journal of Organic Chemistry 68
(2003) 4079–4082.
[33] K. Kobinata, M. Uramoto, M. Nishii, H. Kusakabe, G. Nakamura, K. Isono, Agricul-
tural and Biological Chemistry 44 (1980) 1709–1711.
[34] U. Daehn, H. Hagenmaier, H. Hoehne, W.A. Koenig, G. Wolf, H. Zaehner, Archives
of Microbiology 107 (1976) 249–256.
+
N
Cl
SO3H
[35] A.K. Tiwari, R.M. Kumbhare, S.B. Agawane, A.Z. Ali, K.V. Kumar, Bioorganic &
Medicinal Chemistry Letters 18 (2008) 4130–4132.
[Et3N-SO3H]Cl
[36] E.N. Prabhakaran, J. Iqbal, Journal of Organic Chemistry 64 (1999) 3339–3341.
[37] A.R. Momeni, M. Sadeghi, Appl. Catal. A: Gen. 357 (2009) 100–105.
[38] Z. Mirjafary, H. Saeidian, A. Sadeghi, F. Matloubi Moghaddam, Catalysis Communica-
tions 9 (2008) 299–306.
i and ii
[39] M.M. Heravi, L. Ranjbar, F. Derikvand, F.F. Bamoharram, J. Mol. Catal. A: Chem. 271
(2007) 28–31.
[40] M.M. Khodaei, A.R. Khosropour, P. Fattahpour, Tetrahedron Letters 46 (2005)
2105–2108.
N
[41] G. Pandey, R.P. Singh, A. Garg, V.K. Singh, Tetrahedron Letters 46 (2005) 2137–2140.
[42] V.S. Shinu, B. Sheeja, E. Purushothaman, D. Bahulayan, Tetrahedron Letters 50
(2009) 4838–4843.
ClSO3H
[43] M.R. Nabid, S.J. Tabatabaei Rezaei, Appl. Catal. A: Gen. 366 (2009) 108–113.
[44] A.T. Khan, L.H. Choudhury, T. Parvin, A.M. Asif, Tetrahedron Letters 47 (2006)
8137–8141.
i) The synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes
[45] R. Ghosh, S. Maiti, A. Chakraborty, S. Chakraborty, A.K. Mukherjee, Tetrahedron 62
(2006) 4059–4064.
ii) Addition of NaOH solution
[46] M.A. Zolfigol, A. Khazaei, M. Mokhlesi, A. Zare, M. Safaiee, F. Derakhshan-Panah,
H. Keypour, A.A. Dehghani-Firouzabadi, M. Merajoddin, Chin. J. Chem. (in press),
doi:10.1002/cjoc.2011.
Scheme 8. The regenerate and reuse cycle of [Et3N–SO3H]Cl.
[47] S.M. Menchen, S.C. Benson, J.Y.L. Lam, W. Zhen, D. Sun, B.B. Rosenblum, S.H. Khan,
M. Taing, Chemical Abstracts 139 (2003) 54287f.
References
[48] R.J. Sarma, J.B. Baruah, Dyes and Pigments 64 (2005) 91–92.
[49] J.P. Poupelin, G. Saint-Ruf, O. Foussard-Blanpin, G. Narcisse, G. Uchida-Ernouf, R.
Lacroix, Journal of Medicinal Chemistry 13 (1978) 67–71.
[50] J.M. Jamison, K. Krabill, A. Hatwalkar, E. Jamison, C. Tsai, Cell Biology International
Reports 14 (1990) 1075–1084.
[51] Y.F. Qiao, T. Okazaki, T. Ando, K. Mizoue, K. Kondo, T. Eguchi, K. Kakinuma, Journal
of Antibiotics 51 (1998) 282–287.
[52] G.W. Rewcastle, G.J. Atwell, L. Zhuang, B.C. Baguley, W.A. Denny, Journal of Medicinal
Chemistry 34 (1991) 217–222.
[53] C. Kaiser, A.M. Pavloff, E. Garvey, P.J. Fowler, D.H. Tedeschi, C.L. Zirkle, Journal of
Medicinal Chemistry 15 (1972) 665–673.
[54] R.M. Ion, A. Planner, K. Wiktorowicz, D. Frackowiak, Acta Biochimica Polonica 45
(1998) 833–845.
[1] P. Wasserscheid, W. Keim, Angewandte Chemie, International Edition 39 (2000)
3772–3789.
[2] S. Chowdhury, R.S. Mohan, J.L. Scott, Tetrahedron 63 (2007) 2363–2389.
[3] J. Pavlinac, M. Zupan, K.K. Laali, S. Stavber, Tetrahedron 65 (2009) 5625–5662.
[4] H. Olivier-Bourbigou, L. Magna, D. Morvan, Appl. Catal. A: Gen. 373 (2010) 1–56.
[5] P. Wasserscheid, T. Welton, Ionic Liquids in Synthesis, Wiley-VCH, Weinheim,
2008.
[6] R.D. Rogers, K.R. Seddon, Ionic Liquids: Industrial Applications to Green Chemistry,
American Chemical Society, Washington, DC, 2002.
[7] Y.J. Kim, R.S. Varma, Tetrahedron Letters 46 (2005) 1467–1469.
[8] N. Iranpoor, H. Firouzabadi, R. Azadi, European Journal of Organic Chemistry
(2007) 2197–2201.
[9] J. Pavlinac, M. Zupan, S. Stavber, Molecules 14 (2009) 2394–2409.
[10] A. Hasaninejad, A. Zare, M. Shekouhy, J. Ameri Rad, Journal of Combinatorial
Chemistry 12 (2010) 844–849.
[11] A. Zare, A.R. Moosavi-Zare, A. Hasaninejad, A. Parhami, A. Khalafi-Nezhad, M.H.
Beyzavi, Synthetic Communications 39 (2009) 3156–3165.
[12] A. Zare, A. Parhami, A.R. Moosavi-Zare, A. Hasaninejad, A. Khalafi-Nezhad, M.H.
Beyzavi, Canadian Journal of Chemistry 87 (2009) 416–421.
[13] E. Öchsner, M.J. Schneider, C. Meyer, M. Haumann, P. Wasserscheid, Appl. Catal. A:
Gen. 399 (2011) 35–41.
[14] A. Zare, A. Hasaninejad, A.R. Moosavi Zare, A. Parhami, H. Sharghi, A. Khalafi-Nezhad,
Canadian Journal of Chemistry 85 (2007) 438–444.
[15] M. Eichmann, W. Keim, M. Haumann, B.U. Melcher, P. Wasserscheid, J. Mol. Catal.
A: Chem. 314 (2009) 42–48.
[16] P. Hapiot, C. Lagrost, Chemical Reviews 108 (2008) 2238–2264.
[17] M.A. Zolfigol, A. Khazaei, A.R. Moosavi-Zare, A. Zare, V. Khakyzadeh, Appl. Catal.
A: Gen. 400 (2011) 70–81.
[18] M.A. Zolfigol, A. Khazaei, A.R. Moosavi-Zare, A. Zare, Journal of the Iranian Chemical
Society 7 (2010) 646–651.
[19] M.A. Zolfigol, A. Khazaei, A.R. Moosavi-Zare, A. Zare, Organic Preparations and
Procedures International 42 (2010) 95–102.
[20] A. Khazaei, M.A. Zolfigol, A.R. Moosavi-Zare, A. Zare, Science Production In Iran 17
(2010) 31–36.
[55] Y. Hamada, F. Matsuura, M. Oku, K. Hatano, T. Shioiri, Tetrahedron Letters 38
(1997) 8961–8964.
[56] G. Malaise, L. Barloy, J.A. Osborn, Tetrahedron Letters 42 (2001) 7417–7419.
[57] B. Das, P. Thirupathi, I. Mahender, V.S. Reddy, Y.K. Rao, J. Mol. Catal. A: Chem. 247
(2006) 233–239.
[58] Z.-H. Zhang, Y.-H. Liu, Catalysis Communications 9 (2008) 1715–1719.
[59] A. Javid, M.M. Heravi, F.F. Bamoharram, E-Journal of Chemistry 8 (2011) 910–916.
[60] G.H. Mahdavinia, M.A. Bigdeli, Y. Saeidi Hayeniaz, Chinese Chemical Letters 20
(2009) 539–541.
[61] G. Karthikeyan, A. Pandurangan, J. Mol. Catal. A: Chem. 311 (2009) 36–45.
[62] M. Bigdeli, Chinese Chemical Letters 21 (2010) 1180–1182.
[63] Z.-H. Zhang, X.-Y. Tao, Australian Journal of Chemistry 61 (2008) 77–79.
[64] S. Kantevari, R. Bantu, L. Nagarapu, ARKIVOC xvi (2006) 136–148.
[65] I. Mohammadpoor-Baltork, M. Moghadam, V. Mirkhani, S. Tangestaninejad, H.R.
Tavakoli, Chinese Chemical Letters 22 (2011) 9–12.
[66] M. Mohammadpour Amini, M. Seyyedhamzeh, A. Bazgir, Applied Catalysis A:
General 323 (2007) 242–245.
[67] G. Imani Shakibaei, P. Mirzaei, A. Bazgir, Applied Catalysis A: General 325 (2007)
188–192.
[68] P.S. Kumar, B.S. Kumar, B. Rajitha, P.N. Reddy, N. Sreenivasulu, Y.T. Reddy, ARKIVOC
xii (2006) 46–50.
[69] M. Dabiri, M. Baghbanzadeh, M. Shakouri Nikcheh, E. Arzroomchilar, Bioorganic &
Medicinal Chemistry Letters 18 (2008) 436–438.
[21] H.R. Shaterian, M. Ranjbar, Journal of Molecular Liquids 160 (2011) 40–49.
[22] H.R. Shaterian, M. Ranjbar, K. Azizi, Journal of Molecular Liquids 162 (2011)
95–99.
[23] H.R. Shaterian, M. Arman, F. Rigi, Journal of Molecular Liquids 158 (2011)
145–150.
[70] B.F. Mirjalili, A. Bamoniri, A. Akbari, N. Taghavinia, Journal of the Iranian Chemical
Society 8 (2011) S129–S134.
[71] W. Su, D. Yang, C. Jin, B. Zhang, Tetrahedron Letters 49 (2008) 3391–3394.
[72] M. Hong, C. Cai, Journal of Fluorine Chemistry 130 (2009) 989–992.
[73] R. Kumar, G. Chandra Nandi, R.K. Verma, M.S. Singh, Tetrahedron Letters 51 (51)
(2010) 442–445.
[24] J. Zhu, H. Bienayme, Multicomponent Reactions, Wiley-VCH, Weinheim, Germany,
2005.
[25] V. Polshettiwar, R.S. Varma, Pure and Applied Chemistry 80 (2008) 777–790.
[26] A. Hasaninejad, A. Zare, M. Shekouhy, Tetrahedron 67 (2011) 390–400.
[27] S. Stavber, Molecules 16 (2011) 6432–6464.
[28] A. Hasaninejad, M. Shekouhy, N. Golzar, A. Zare, M.M. Doroodmand, Appl. Catal.
A: Gen. 402 (2011) 11–22.
[74] A.K. Bhattacharya, K.C. Rana, M. Mujahid, I. Sehar, A.K. Saxena, Bioorganic & Medicinal
Chemistry Letters 19 (2009) 5590–5593.
[75] M.A. Bigdeli, M.M. Heravi, G.H. Mahdavinia, Journal of Molecular Catalysis A:
Chemical 275 (2007) 25–29.
[76] Ajinomoto Co Inc, Chemical Abstracts 101 (1984) 210548.
[77] N. Sakota, S. Nomura, S. Ito, Chemical Abstracts 114 (1991) 22873.
[29] A. Khazaei, M.A. Zolfigol, A.R. Moosavi-Zare, A. Zare, A. Parhami, A. Khalafi-Nezhad,
Appl. Catal. A: Gen. 386 (2010) 179–187.
[30] D. Enders, M. Moser, G. Geibel, M.C. Laufer, Synthesis (2004) 2040–2046.
[31] M. Mukhopadhyay, B. Bhatia, J. Iqbal, Tetrahedron Letters 38 (1997) 1083–1086.