Bi-SO3H functionalized ionic liquid based on DABCO as a mild and efficient catalyst for the synthesis of 1,8-dioxo-octahydro-xanthene and 5-arylmethylene-pyrimidine-2,4,6-trione derivatives

Article abstract of DOI:10.1007/s11164-014-1905-1

1,8-Dioxo-octahydro-xanthenes are easily prepared via the condensation of aldehydes with 1,3-cyclohexadione and/or dimedone using N-sulfonated DABCO as a new and efficient catalyst. This reagent is also efficiently able to catalyze the condensation of aldehydes with barbituric acid leading to 5-arylmethylene-pyrimidine-2,4,6-triones. The structure of the products was characterized by their IR, ¹H NMR, and ¹³C NMR spectroscopy. The present methodology offers several advantages such as ease of preparation and handling of the catalyst, high yields, simple and green procedure, low cost, short reaction times, easy work-up, and preformation of the reaction in the absence of solvent or in water as a green solvent.

Full text of DOI:10.1007/s11164-014-1905-1

Res Chem Intermed
DOI 10.1007/s11164-014-1905-1
Bi-SO3H functionalized ionic liquid based on DABCO
as a mild and efficient catalyst for the synthesis of 1,8-
dioxo-octahydro-xanthene and 5-arylmethylene-
pyrimidine-2,4,6-trione derivatives
•
Farhad Shirini
Mohaddeseh Safarpoor Nikoo Langarudi
•
•
Mohadeseh Seddighi Omid Goli Jolodar
Received: 15 November 2014 / Accepted: 18 December 2014
Ó Springer Science+Business Media Dordrecht 2015
Abstract 1,8-Dioxo-octahydro-xanthenes are easily prepared via the condensation
of aldehydes with 1,3-cyclohexadione and/or dimedone using N-sulfonated DABCO
as a new and efficient catalyst. This reagent is also efficiently able to catalyze the
condensation of aldehydes with barbituric acid leading to 5-arylmethylene-pyr-
imidine-2,4,6-triones. The structure of the products was characterized by their IR,
1H NMR, and 13C NMR spectroscopy. The present methodology offers several
advantages such as ease of preparation and handling of the catalyst, high yields,
simple and green procedure, low cost, short reaction times, easy work-up, and
preformation of the reaction in the absence of solvent or in water as a green solvent.
Keywords N-sulfonated DABCO {[DABCO](SO3H)2(Cl)2} ꢀ Solvent-free
conditions ꢀ 5-Arylmethylene-pyrimidine-2,4,6-trione ꢀ 1,8-Dioxo-octahydro-
xanthene ꢀ Aldehyde ꢀ Barbituric acid
Introduction
In recent years, ionic liquids have received recognition as green media in organic
synthesis due to their favorable properties, such as good solvating capability, wide
liquid range, negligible vapor pressure, tunable polarity, high thermal stability, and
ease of recyclability [1–3]. Although ionic liquids were initially introduced as an
alternative green reaction medium, today they have marched far beyond this border,
showing their significant role in controlling the reaction as catalysts [4–6]. So, the
development and application of so-called ‘‘task-specific’’ ionic liquids are desirable.
In addition, the synthesis of task-specific ionic liquids, which have a functional
group in their framework, may expand the application of ionic liquids in organic
F. Shirini (&) ꢀ M. S. N. Langarudi ꢀ M. Seddighi ꢀ O. G. Jolodar
Department of Chemistry, College of Science, University of Guilan, 41335 Rasht, Iran
e-mail: shirini@guilan.ac.ir
123

F. Shirini et al.
chemistry [7–9]. Recently, ionic liquids have been successfully used in multi-
component reactions [8–12].
Xanthenes are an important class of organic compounds that find use as dyes,
fluorescent materials for visualization of biomolecules, and in laser technologies
due to their useful spectroscopic properties [13–15].
Xanthenes have also received significant attention from many pharmaceutical and
organic chemists essentially because of the broad spectrum of their biological and
pharmaceutical properties such as their antiviral [16], antibacterial [17], antinocicep-
tive [18], and anti-inflammatory activities [19], as well as their efficiency in
photodynamic therapy [20].
Barbituric acids and their derivatives have been widely used as sedative,
hypnotic, anesthetic, anticonvulsant, antiosteoporosis, as well as antitumor agents.
Arylidene barbituric acids as well as their 2-thio analogues are useful intermediates
in the synthesis of heterocyclic compounds, benzyl barbituric derivatives [21],
oxadiazaflavines [22], and unsymmetrical disulphides [23]. Additionally, some of
them have been recently studied as non-linear optical materials and dyes.
There are several reports in the literature for the synthesis of 1,8-dioxo-
octahydroxanthene and 5-arylidene barbituric acids derivatives; these include use of
[Hbim]BF4 [24], [bmim]HSO4 [25], p-dodecylbenzenesulphonic acid [26], p-
toluenesulfonic acid [27], [TMPSA]HSO4 [28], [Hmim]TFA [29], N-sulfonic acid
poly(4-vinylpyridinium) chloride (NSPVPC) [30], succinimide-N-sulfonic acid
(SuSA) [31], 1,3-dibromo-5,5-dimethylhydantoin (DBH), benzyltriphenylphospho-
nium tribromide (BTPTB) [32] (for the synthesis 1,8-dioxo-octahydro-xanthene),
nickel nanoparticles [33], sodium p-toluene sulfonate (NaPTSA) [34], basic alumina
[35], IR lamp [36] and Ce1MgxZr1-xO2 (CMZO) [37] (for the preparation of
5-arylidene barbituric acids derivatives). However, many of these methods tolerate
many disadvantages such as low yields, long reaction times, harsh reaction
conditions, tedious work-up, and requirement of excess amounts of reagents or
catalysts. Therefore, it is important to find more convenient methods for the
synthesis of these types of compounds.
Experimental
Materials
All chemicals were purchased from Merck, Aldrich, and Fluka Chemical
Companies and used without further purification. All the products were separated
and characterized by their physical constant and comparison with authentic samples.
The purity determination of the substrates and reaction monitoring were accom-
panied by TLC using silica gel SIL G/UV 254 plates.
Characterization techniques
Melting points were recorded on a Bu¨chi B-545 apparatus in open capillary tubes. The
FT-IR spectra were recorded a Perkin-Elmer spectrum BX series spectrophotometer.
123

Bi-SO3H functionalized ionic liquid based on DABCO
In all the cases, the 1H NMR and 13C NMR spectra were recorded with BrukerAvance
400-MHz instrument. All chemical shifts are quoted in parts per million (ppm) relative
to TMS using deuterated solvent.
Catalyst preparation [DABCO](SO3H)2(Cl)2 [38]
A round-bottomed flask (100 ml) was charged with a solution of 1,4-diazabicy-
clo[2]octane, DABCO (0.56 g, 5 mmol) in dry CH2Cl2 (50 ml), and then
chlorosulfonic acid (1.21 g, 10.4 mmol) was added dropwise over a period of
10 min at room temperature. After the addition was completed, the reaction mixture
was left 1 h. In this period of time, a white solid was produced. Afterward, the
CH2Cl2 was decanted. The residue was triturated with dry diethyl ether and dried
under vacuum to give [DABCO](SO3H)2(Cl)2 as a very viscous colorless oil at
98 % yield.
Spectral data of [DABCO](SO3H)2Cl2: 1HNMR (400 MHz, DMSO-d6): d (ppm)
3.58 (s, 6H), 7.72 (s, 1H); 13CNMR (100 MHz, DMSO-d6): d (ppm) 43.2; MS:
m/z = 345 (M?). IR (KBr, cm-1) mmax: 3,500-2,800 (broad), 1,179, 881, 850.
Hammett acidity
An efficient method for evaluating the acidity of a Brønsted acidic ionic liquid is the
Hammett acidity. The Hammett function is defined as:
À
Á
H0 ¼ pKðIÞaq þ log ½Iꢁs=½IHþꢁs
where the pK (I)aq is the pKa value of aqueous solution of indicator, [IH?]s and [I]s
are the molar concentrations of protonated and unprotonated forms of the indicator
in the solvent, respectively. According to Lambert–Beer’s Law, the value of [I]s/
[IH?]s can be determined and calculated through UV–visible spectrum.
For this reason, 4-nitroaniline (pK(I)aq = 0.99) as the basic indicator and CCl4
as the solvent were chosen. As can be seen in Fig. 1, the maximal absorbance of the
unprotonated form of the indicator was observed at 328 nm in CCl4. When
2.5
2
1.5
1
0.5
0
0
100
200
300
400
500
600
-0.5
Wavelenghth
Fig. 1 Diagram of the Hammett acidity for [DABCO](HSO3)2(Cl)2
123

F. Shirini et al.
[DABCO](HSO3)2(Cl)2 as the ionic liquid catalyst was added to the indicator
solution, the absorbance of the unprotonated form of the indicator decreased, which
indicated that the indicator was partially in the form of [IH?]. These results, which
are listed in Table 1, show the acidity strength of [DABCO](HSO3)2(Cl)2.
General procedure for the preparation of 5-arylmethylene-pyrimidine-2,4,6-
trione derivatives
A mixture of the aldehyde (1 mmol), barbituric acid (1 mmol) and [DABCO](SO3-
H)2Cl2 (0.025 mmol, 0.009 g) in water (4 ml) was heated in an oil bath (70 °C).
After completion of the reaction, as monitored by TLC, using n-hexane:EtOAc (1:4)
as the eluent, the crude product was filtered off, washed with water, and
recrystallized from ethanol to give a pure compound. The spectral data of the new
compounds are as follow:
5,50-(1,4-Phenylenebis(methanylylidene))bis(pyrimidine-2,4,6(1H,3H,5H)-
trione) (Table 4, entry 15)
M.p. [ 300 °C; FT-IR(KBr) m = 3,495, 3,202, 3,085, 1,749, 1,685, 1,584, 808;
1HNMR (400 MHz, DMSO-d6) (d, ppm) = 8.05 (s, 4H), 8.29 (s, 2H, HC = C),
11.30 (NH, s, 2H), 11.45 (NH, s, 2H); 13CNMR (400 MHz, DMSO-d6) (d,
ppm) = 120.9, 129.0, 132.3, 136.1, 150.6, 153.4, 161.9, 163.6.
5,50-(1,3-Phenylenebis(methanylylidene))bis(pyrimidine-2,4,6(1H,3H,5H)-
trione) (Table 4, entry 16)
M.p. [ 300 °C; FT-IR(KBr) m = 3,457, 3,201, 3,074, 1,757, 1,682, 1,571, 800, 682;
1HNMR (400 MHz, DMSO-d6) (d, ppm) = 7.55 (t, J = 7.6, 1H), 8.20 (dd,
J1 = 7.8, J2 = 1.6, 2H), 8.29 (s, 2H, HC=C), 8.49 (s, 1H), 11.29 (NH, s, 2H), 11.44
(NH, s, 2H); 13CNMR (400 MHz, DMSO-d6) (d, ppm) = 120.3, 128.0, 132.9,
135.9, 137.6, 150.6, 153.9, 161.9, 163.6.
5-(2-Nitrobenzylidene)pyrimidine-2,4,6(1H,3H,5H)-trione (Table 4, entry 17)
M.p. 276–278 °C; FT-IR(KBr) m = 3,325, 3,197, 3,091, 1,735, 168, 1,572, 1,513,
1,345, 733; 1HNMR (400 MHz, DMSO-d6) (d, ppm) = 7.58 (d, J = 7.6, 1H), 7.68
(dt, J1 = 8, J2 = 0.8, 1H), 7.79 (dt, J1 = 7.6, J2 = 1.2, 1H), 8.24 (dd, J1 = 8,
Table 1 Calculation of the Hammett acidity function (H0) for [DABCO](HSO3)2(Cl)2
Entry
Catalyst
Amax
[I]s %
[IH?]s %
H0
1
2
–
2.2261
1.5784
100
0
–
[DABCO](HSO3)2(Cl)2
70.9
29.1
1.37
Condition for UV–visible spectrum measurement: solvent: CCl4, indicator: 4-nitroaniline (pK
(I)aq = 0.99), 1.44 9 10-4 mol/l (10 ml); Catalyst: [DABCO](HSO3)2(Cl)2 (10 mg), 25 °C
123

Bi-SO3H functionalized ionic liquid based on DABCO
J2 = 1.2, 1H), 8.61 (s, 1H, HC=C), 11.26 (NH, s, 1H), 11.51(NH, s, 1H); 13CNMR
(400 MHz, DMSO-d6) (d, ppm) = 120.9, 124.5, 130.6, 130.8, 132.1, 134.2, 146.7,
150.7, 152.9, 161.6, 162.8.
General procedure for the preparation of 1,8-dioxo-octahydro-xanthene
derivatives
A mixture of dimedone and/or 1,3-cyclohexadione (2 mmol), aldehyde (1 mmol)
and [DABCO](SO3H)2Cl2 (34 mg, 0.1 mmol) was stirred in an oil bath (80 °C)
under solvent-free conditions. After completion of the reaction, as monitored by
TLC, using n-hexane:EtOAc (5:1) as the eluent, water was added to separate the
catalyst and the crude product was separated and recrystallized by EtOH (4 ml) to
give the pure product.
Results and discussion
N-Sulfonic acids are efficient and important catalysts that could be easily prepared
by simple reaction of N-substituted compounds with chlorosulfonic acid under mild
conditions. In recent years, our research group prepared and introduced several
types of these kinds of reagents of which saccharin sulfonic acid (SaSA) [39–42],
melamine trisulfonic acid (MTSA) [43–46], succinimide sulfonic acid (SuSA) [31,
47, 48], and N-sulfonic acid poly(4-vinylpyridinium) chloride (NSPVPC) [30, 49,
50] are examples. Our obtained results showed that these reagents are useful
catalysts that have been successfully utilized in all of the investigated reactions.
Table 2 The effect of temperature, amount of the catalyst, and solvent on the synthesis of 5-aryl-
methylene-pyrimidine-2,4,6-trione derivative of 4-chlorobenzaldehyde and barbituric acid
Entry
Catalyst (%)
Solvent
Temp.
Time (min)
Yield (%)
1
10
20
30
10
20
30
10
10
10
10
5
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
Solvent free
H2O
r.t.
90
90
90
60
60
60
60
100
10
4
20
2
r.t.
20
3
r.t.
10
4
Reflux
Reflux
Reflux
100 °C
r.t.
25
5
20
6
20
7
50
8
100 (20)a
100 (42)a
100 (73)a
100 (90)a
100 (91)a
9
H2O
Reflux
70 °C
70 °C
70 °C
10
11
12
a
H2O
H2O
4
2.5
H2O
4
Isolated yield
123

F. Shirini et al.
Based on these studies, we were interested to investigate the applicability of N-
sulfonated DABCO ([DABCO](SO3H)2Cl2) as a newly reported N-sulfonic acid
[38] in the promotion of the synthesis of 5-arylmethylene-pyrimidine-2,4,6-trione
and 1,8-dioxo-octahydro-xanthene derivatives. Our investigations showed that this
reagent is efficiently able to catalyze the requested reactions under solvent-free
conditions and in water, respectively.
In order to optimize the reaction conditions for each of the above-mentioned
reactions, the condensation of 4-chlorobenzaldehyde (1 mmol) with barbituric acid
(1 mmol) and/or 1,3-cyclohexadione was studied in the presence of [DABCO](SO3-
H)2Cl2, and the results are tabulated in Tables 2 and 3. On the basis of these results,
the optimized conditions are selected as shown in Schemes 1 and 2.
After optimization of the reaction conditions and in order to study the efficiency
of [DABCO](SO3H)2Cl2 in the preparation of 5-arylmethylene-pyrimidine-2,4,6-
trione derivatives, various aromatic aldehydes were reacted with barbituric acid
under the optimal reaction conditions to furnish the corresponding products in high
yields and in short reaction times. The obtained results for the preparation of a
variety type of 5-arylmethylene-pyrimidine-2,4,6-trione derivatives are summarized
in Table 4. It seems that the presence of electron-withdrawing functional groups on
the aromatic ring of the aldehyde increases the reaction time slightly.
To investigate the recyclability of the catalyst in the synthesis of 5-arylmethy-
lene-pyrimidine-2,4,6-trione derivatives, the reaction between 4-chlorobenzalde-
hyde and barbituric acid under optimized reaction conditions was studied again.
When the reaction was completed, the catalyst was separated by filtration and dried
under vacuum at 70 °C. The recovered catalyst was washed with diethyl ether,
dried, and reused for the same reaction. This procedure was repeated for six runs,
and each time the product was obtained by the recovered catalyst without much
change in the reaction time and yield. The results are shown in Fig. 2.
After successful synthesis of a series of 5-arylmethylene-pyrimidine-2,4,6-trione
derivatives, the efficiency of the same catalyst in the synthesis of 1,8-dioxo-
Table 3 The effect of
Entry Catalyst (%) Temp. Solvent Time (min) Yield (%)
temperature, amount of the
catalyst, and solvent on the
1
10
10
10
10
10
10
30
20
10
5
r.t.
Reflux H2O
r.t. EtOH
Reflux EtOH
r.t.
Reflux MeCN 60
H2O
60
90
60
60
80
100 (40)a
synthesis of 1,8-dioxo-
2
octahydro-xanthene derivative
of 4-chlorobenzaldehyde and
1,3-cyclohexadione
3
50
4
50
5
MeCN 60
60
6
80
7
80 °C
80 °C
80 °C
80 °C
100 °C
–
–
–
–
–
3
4
100 (74)a
100 (70)a
100 (90)a
100(80)a
100 (80)a
8
9
4
10
11
10
4
10
a
Isolated yield
123

Bi-SO3H functionalized ionic liquid based on DABCO
O
O
H
N
[DABCO](SO3H)2(Cl)2 (0.025 mmol, 9 mg)
H2O, 70 oC
O
O
ArCHO
+
HN
NH
Ar
NH
O
O
Scheme 1 [DABCO](SO3H)2Cl2 catalyzed the synthesis of 5-arylmethylene pyrimidine-2,4,6-trione
derivatives
O
Ar
O
O
O
2
O
[DABCO](SO3H)2(Cl)2 (0.1 mmol, 34 mg)
Solvent free, 80 oC
R
R
+
ArCHO
R
R
R
R
R = H, CH3
R = H, CH3
Scheme 2 [DABCO](SO3H)2Cl2 catalyzed the synthesis of 1,8-dioxo-octahydro-xanthene derivatives
octahydro-xanthene derivatives via the reaction of 1,3- cyclohexanedione and/or
5,5-dimethyl-1,3-cyclohexadione (dimedone) with aromatic aldehydes was studied
under the selected conditions (Scheme 2). The results showed that this conversion
also occurred with excellent yields in very short times (Table 5).
The recycling process was also performed for 1,8- dioxo-octahydroxanthene
derivatives. This process was repeated for four runs and the results are presented in
Fig. 3. This figure shows a small decrease in the efficiency of the catalyst after four
runs.
In order to show the merit of this method, the efficiency of [DABCO](SO3-
H)2Cl2 with other catalysts in the synthesis of 5-(4-chlorobenzylidene)pyrim-
idine-2,4,6(1H,3H,5H)-trione (Table 4, entry 2) and 3,3,6,6-tetramethyl-9-(4-
chlorophenyl)-1,8-dioxo-octahydroxanthene (Table 5, entry 14), is compared in
Tables 6, 7, respectively. On the basis of these comparisons, we can say that
the present method is more efficient in decreasing of the reaction times,
increasing of the products yield and/or in modulation of the reaction
conditions.
In a plausible mechanism, at first, the aldehyde is activated by the proton from
[DABCO](SO3H)2Cl2. Next, the carbonyl carbon is attacked by the nucleophilic
cyclohexanedione derivatives or barbituric acid to form the related Knoevenagel
products (1) or (2), respectively. The subsequent addition of (1) to cyclohexane
derivatives, gives the acyclic adduct intermediate, which undergoes intramolecular
cyclization with participation of two hydroxyl groups to afford the xanthene
derivatives. The Knoevenagel product at the barbituric acid (2) is not able to
continue the reaction leading to 5-arylmethylene-pyrimidine-2,4,6-trione deriva-
tives (Scheme 3).
123

F. Shirini et al.
Table 4 Preparation of 5-arylmethylene-pyrimidine-2,4,6-trione derivatives using [DABCO](SO3H)2Cl2
as the catalyst
Entry Aldehyde
Time (min) Yield (%)a Mp °C
Picture
Found
Rep. [ref.]
256 [33]
1
C6H5CHO
4
4
2
5
3
5
2
4
5
5
7
84
91
92
88
96
85
85
84
87
93
85
255–256
298–300
278–279
228–230
[300
2
4-ClC6H4CHO
298.5 [33]
3
4-NMe2C6H4CHO
3-NO2C6H4CHO
4-OHC6H4CHO
2-MeOC6H4CHO
C6H5CH = CHCHO
4-BrC6H4CHO
2-ClC6H4CHO
281–282 [37]
231–233 [51]
[300 [33]
4
5
6
265–267
270–273
292–293
261–263
297–300
270–272
268–269 [35]
268 [33]
7
8
292–293 [33]
268 [34]
9
10
11
4-MeOC6H4CHO
4-NO2C6H4CHO
306–308 [37]
272–274 [51]
123

Bi-SO3H functionalized ionic liquid based on DABCO
Table 4 continued
Entry Aldehyde
Time (min) Yield (%)a Mp °C
Picture
Found
Rep. [ref.]
– [37]
12
13
14
3-MeC6H4CHO
3
2
8
86
95
92
213–215
2-OHC6H4CHO
2-Naphtaldehyde
249–250
249–250 [51]
266 (dec) 266 (dec) [33]
15
16
17
a
4-CHOC6H4CHO
3-CHOC6H4CHO
2-NO2C6H4CHO
1
2
7
91
92
88
[300
–
–
–
[300
276–278
Isolated yield
Fig. 2 Reusability of the catalyst in the synthesis of 5-arylmethylene-pyrimidine-2,4,6-trione derivative
of 4-chlorobenzaldehyde
123

F. Shirini et al.
Table 5 Preparation of 1,8-dioxo-octahydro-xanthene derivatives using [DABCO](SO3H)2Cl2 as the
catalyst
Entry Aldehyde
R
Time (min) Yield (%)a Mp °C
Picture
Found
Rep. [ref.]
1
C6H5CHO
H
3
4
85
90
83
85
92
80
87
83
85
81
92
197–200 201–203 [56]
282–285 282–285 [32]
250–252 250–252 [32]
284–285 284–285 [52]
276–278 281–283 [32]
245–246 245–246 [52]
255–257 262–264 [52]
280–282 285–287 [32]
236–239 238–240 [32]
204–207 200–202 [32]
195–197 192–196 [32]
2
4-ClC6H4CHO
2-ClC6H4CHO
4-BrC6H4CHO
3-BrC6H4CHO
4-OHC6H4CHO
4-NO2C6H4CHO
3-NO2C6H4CHO
2-NO2C6H4CHO
4-MeOC6H4CHO
2-MeOC6H4CHO
H
H
H
H
H
H
H
H
H
H
3
7
4
7
5
6
6
24
18
20
24
9
7
8
9
10
11
15
123

Bi-SO3H functionalized ionic liquid based on DABCO
Table 5 continued
Entry Aldehyde
R
Time (min) Yield (%)a Mp °C
Picture
Found
Rep. [ref.]
12
13
14
15
16
17
18
19
20
21
22
23
2-Naphtaldehyde
H
17
3
85
89
90
90
90
93
91
83
87
93
92
86
192–195 197–198 [32]
200–202 206–208 [32]
230–232 225–228 [53]
220–224 228–230 [55]
247–249 246–248 [53]
225–228 220–223 [32]
160–164 168–170 [54]
245–247 251–252 [30]
250–252 243–245 [55]
203–207 209–210 [30]
189–191 194–196 [55]
217–220 226–228 [53]
C6H5CHO
Me
Me
Me
Me
4-ClC6H4CHO
2-ClC6H4CHO
4-OHC6H4CHO
4-NO2C6H4CHO
3-NO2C6H4CHO
2-NO2C6H4CHO
4-MeOC6H4CHO
2-MeOC6H4CHO
2-Naphtaldehyde
6
9
7
Me 22
Me 25
Me 25
Me 10
Me
Me
6
7
4-NMe2C6H4CHO Me 28
123

F. Shirini et al.
Picture
Table 5 continued
Entry Aldehyde
R
Time (min) Yield (%)a Mp °C
Found
Rep. [ref.]
24
1,4-(CHO)2C6H4
Me 20
87
[300
[300 [32]
a
Isolated yield
Fig. 3 Reusability of the catalyst in the synthesis of 1,8-dioxo-octahydro-xanthene derivative of
4-chlorobenzaldehyde
Table 6 Compared performance of various catalysts with [DABCO](SO3H)2Cl2 in the synthesis of 5-(4-
chlorobenzylidene)pyrimidine-2,4,6(1H,3H,5H)-trione (Table 3, entry 2)
Entry
Catalyst/conditions
Time (min)
Yield (%)
Ref.
1
2
3
4
5
6
7
PVP-Ni nanoparticles/ethylene glycol 50 °C
Non-catalyst/infrared irradiation
NaPTSA/r.t.
5
45
4
93
62
92
92
94
83
91
[33]
[36]
[34]
Basic alumina/MW (at 700 W)
CMZO/MW (at 450 W)
3
[35]
3
[37]
Chlorosulfonic acid (1.5 mmol, water, r.t.)
[DABCO](SO3H)2Cl2/water 70 °C
35
4
–
This work
Conclusions
In summary, we have introduced a novel and efficient method for the synthesis of
5-arylmethylene-pyrimidine-2,4,6-trione and 1,8-dioxo-octahydro-xanthene derivatives
in the presence of a catalytic amount of [DABCO](SO3H)2Cl2 as an acidic ionic liquid.
123

Bi-SO3H functionalized ionic liquid based on DABCO
Table 7 Compared performance of various catalysts with [DABCO](SO3H)2Cl2 in the synthesis of
3,3,6,6-Tetramethyl-9-(4-chlorophenyl)-1,8- dioxo-octahydroxanthene (Table 4, entry 14)
Entry Catalyst/conditions
Time (min) Yield (%) Ref.
1
2
3
4
5
6
7
8
9
[bmim] HSO4/80 °C
[Hmim] TFA/80 °C
3.5 (h)
2.5 (h)
18
95
93
92
98
92
90
90
–
[25]
[29]
SuSA/solvent free 80 °C
NSPVPC/solvent free 100 °C
[TMPSA] HSO4/in water 100 °C
BTPTB/solvent free 100 °C
DBH/solvent free 100 °C
[31]
3
[30]
1 (h)
10
[28]
[32]
4
[32]
Chlorosulfonic acid (1.5 mmol, solvent-free, r.t.) 60
Mixture of product
This work
[DABCO](SO3H)2Cl2/80 °C
6
90
H from [DABCO](SO3H)2(Cl)2
H
+δ
O
O
[DABCO](SO3H)2(Cl)2
+
Ar
Ar
H
O
O
O
OH
NH
HO
O
O
O
Or
HN
HN NH
R
R
R
R
O
O
R = H, CH3
R
H
N
O
O
O
R
Ar
Ar
NH
O
OH
OH
O
-H2O
-H2O
O
Ar
O
O
Ar
O
O
H
N
R
O
O
O
(b)
(a)
HN
NH
R
R
R
Ar
NH
Ar
O
N
H
N
H
O
OH
HO
R
R
(2)
(1)
O
O
-H2O
Ar
O
O
R
R
O
R
R
R = H, CH3
Scheme 3 Proposed mechanism for the synthesis of 5-arylmethylene-pyrimidine-2,4,6-trione and 1,8-
dioxo-octahydro-xanthene derivatives in the presence of [DABCO](SO3H)2Cl2
This method has several advantages such as ease of preparation and handling of the
catalyst, simplicity and easy work-up, high reaction rates, excellent yields, and eco-
friendly procedure. In addition, simplicity of the preparation of this catalyst is valuable
point for the presented method.
123

F. Shirini et al.
Acknowledgments The authors are thankful to the University of Guilan Research Council for the
partial support of this work.
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