Preparation of a new DABCO-based ionic liquid [H2-DABCO][H2PO4]2} and its application in the synthesis of tetrahydrobenzo[b]pyran and pyrano[2,3-d]pyrimidinone derivatives

Article abstract of DOI:10.1016/j.molliq.2017.03.063

A new acidic ionic liquid, 1,4-diazabicyclo[2.2.2]octane-1,4-diium dihydrogen phosphate {[H₂-DABCO][H₂PO₄]₂}, was prepared in a quick and straightforward process and characterized by using different methods such as FT-IR, NMR and Mass analysis. Then it was used as a reusable and new catalyst to promote the synthesis of tetrahydrobenzo[b]pyran and pyrano[2,3-d]pyrimidinone derivatives as important biologically active compounds that they are used in pharmaceutical industry. This adequate procedure possess some advantages like producing target compounds in high yields, short reaction times, simple work-up procedure and use of chief and easily preparable catalyst.

Full text of DOI:10.1016/j.molliq.2017.03.063

Accepted Manuscript
Preparation of
a
new DABCO-based ionic liquid
[H2-DABCO][H2PO4]2} and its application in the synthesis of
tetrahydrobenzo[b]pyran
derivatives
and
pyrano[2,3-d]pyrimidinone
Farhad Shirini, Mohaddeseh Safarpoor Nikoo Langarudi, Nader
Daneshvar
PII:
DOI:
Reference:
S0167-7322(16)34155-1
doi: 10.1016/j.molliq.2017.03.063
MOLLIQ 7098
To appear in:
Journal of Molecular Liquids
Received date:
Revised date:
Accepted date:
21 December 2016
16 March 2017
17 March 2017
Please cite this article as: Farhad Shirini, Mohaddeseh Safarpoor Nikoo Langarudi, Nader
Daneshvar , Preparation of a new DABCO-based ionic liquid [H2-DABCO][H2PO4]2}
and its application in the synthesis of tetrahydrobenzo[b]pyran and
pyrano[2,3-d]pyrimidinone derivatives. The address for the corresponding author was
captured as affiliation for all authors. Please check if appropriate. Molliq(2017), doi:
10.1016/j.molliq.2017.03.063
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ACCEPTED MANUSCRIPT
Preparation of a new DABCO-based ionic liquid [H2-
DABCO][H2PO4]2} and its application in the synthesis of
tetrahydrobenzo[b]pyran and pyrano[2,3-d]pyrimidinone
derivatives
Farhad Shirini,a,b* Mohaddeseh Safarpoor Nikoo Langarudia, Nader Daneshvarb
a Department of Chemistry, College of Sciences, Guilan University, Rasht, 41335-19141, Iran
b Department of Chemistry,College of Science, University of Guilan, University Campus 2, Rasht, Iran
Abstract— A new acidic ionic liquid, 1,4-diazabicyclo[2.2.2]octane-1,4-diium dihydrogen phosphate {[H2-DABCO][H2PO4]2}, was
prepared in a quick and straightforward process and characterized by using different methods such as FT-IR, NMR and Mass analysis.
Then it was used as a reusable and new catalyst to promote the synthesis of tetrahydrobenzo[b]pyran and pyrano[2,3-d]pyrimidinone
derivatives as important biologically active compounds that they are used in pharmaceutical industry. This adequate procedure possess
some advantages like producing target compounds in high yields, short reaction times, simple work-up procedure and use of chief and
easily preparable catalyst.
Keywords: DABCO, ionicliquids, tetrahydrobenzo[b]pyrans, pyrano[2,3-d]pyrimidinones.
1. Introduction
In recent years, organocatalysts have been paid much attention because of their specific and characteristic properties. These
reagents are often based on nontoxic organic compounds originating from biological materials and they can be Lewis bases, Lewis
acids, Brønsted bases, and Brønsted acids. 1,4-Diazabicyclo[2.2.2]octane (DABCO) is a small diazabicyclic molecule with weak
alkalescence and medium‐hindrance that is used as an organocatalyst in the synthesis of many biological compounds [1-4] and
recently, it has been used in the preparation of some DABCO-based ionic liquids like [DABCO(C4H8SO3H)2][HSO4]2 [5],
[DABCO](SO3H)2(Cl)2 [6, 7], [DABCO-PDO][OAc] [8, 9], and [DABCO](SO3H)2(HSO4)2 [10]. These reagents were able to
promote some organic transformations such as oxathioacetalization [5], Knoevenagel condensation [8], and Aza-Michael addition
[9], and the synthesis of dihydropyrimidinones [6], 1,8-dioxo-octahydro-xanthene and 5-arylmethylenepyrimidine-2,4,6-trione
derivatives [7], 2H-indazolo[2,1-b]phthalazine-1,6,11(13H)-triones [10] and pyrano[2,3-d]-pyrimidinones [11].
Tetrahydrobenzo[b]pyran derivatives belong to an important class of heterocyclic compounds having important pharmaceutical
and biological activities. Some drugs which possess antianaphylactin, anticoagulant, anticancer, diuretic, and spasmolitic properties
[12, 13] are a part of tetrahydrobenzo[b]pyran derivatives. Also, they can be used as cognition-enhancing drugs for the treatment of
neurodegenerative disease, including Alzheimer’s disease, Huntington’s disease, Parkinson’s disease, Down’s syndrome and
schizophrenia [14, 15]. On the other hand, pyrano[2,3-d]-pyrimidinones are regular structural subunits in some important natural
products, including carbohydrates, alkaloids, polyether antibiotics, pheromones, and iridoids (Fig. 1) [16, 17].
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Also, some derivatives of pyrano[2,3-d]-pyrimidinones have been reported having different biological activities, especially
antipyretic, anti-inflammatory, and gastroprotective properties [18]. Due to these biological activities and properties, recently, the
synthesis of tetrahydrobenzo[b]pyrans and pyrano[2,3-d]-pyrimidinones have attracted considerable attention and several synthetic
methods have been reported to obtain more potentially biological derivatives of these compounds using catalysts such as N-
methylimidazole [19], tetrabutylammonium bromide [20], trisodium citrate [21], p-dodecylbenzenesulfonic acid [22], poly(4-
vinylpyridine) [23], potassium phthalimide-N-oxyl [24], [cmmim]Br and [cmmim][BF4] [25], choline chloride (ChCl) [26], starch
solution [27], (diacetoxyiodo)benzene (DIB) [28] (for the synthesis of tetrahydrobenzo[b]pyrans), diammonium hydrogen
phosphate [29], L-proline [30], KAl(SO4)2.12H2O (alum) [31], tetrabutylammonium bromide [32], DABCO [33], sulfonic acid
nanoporous silica (SBA-Pr-SO3H) [34], Al-HMS-20 [35], Nano‑ sawdust‑ OSO3H [36], succinimidinium hydrogensulfate
([H‑ Suc]HSO4) [37] and ZnO-supported copper oxide [38] (for the synthesis of pyrano[2,3-d]-pyrimidinones). Despite undeniable
advantages of these methods, most of them suffer from some disadvantages like harsh reaction conditions [25, 34], difficulties in
the preparation of the catalyst [36, 38], long reaction times [26, 28, and 35] and need to use of excess amounts of reagents or
catalysts [19, 20, 22, 29, and 31].
In order to adjust these problems and in continuation of our research group efforts to introduce new ionic liquids for the
promotion of some organic reactions [7, 10, 37, and 39-44], in this study, a new ionic liquid called 1,4-diazabicyclo[2.2.2]octane-
1,4-diium dihydrogen phosphate {[H2-DABCO][H2PO4]2} is prepared and applied for the synthesis of tetrahydrobenzo[b]pyrans
and pyrano[2,3-d]-pyrimidinones.
2. Experimental
2.1. Materials
Several materials, most of which are aldehyde, were used in this procedure. All of aldehydes, dimedone, malononitrile, and
barbituric acid were purchased from Merck chemical company (Munich) and were used without further purification. The purity of
them were monitored by thin layer chromatography (TLC). DABCO (CAS: 280-57-9, MW: 112.17 g/gmol, assay ≥ 99% w/w %)
and phosphoric acid (CAS: 7664-38-2, MW: 98.00 g/gmol, concentration ≥ 85 w/w %) were purchased from Sigma-Aldrich
(Mumbai). Both assay and concentration were reported by company and were not examined more. All solvents were prepared from
Merck (Munich) and were kept sealed in airtight bottles as well to minimize the absorption of atmosphere moisturize. Moreover,
they had gotten distilled before being used.
2.2. Characterization techniques
Products were characterized by their physical constants, comparison with authentic samples and IR and NMR spectroscopy. The
purity determination of the substrate and reaction monitoring were accomplished by TLC on silics-gel polygram SILG / UV 254
plates. Melting points were measured by electrothermal IA9100 melting point apparatus in capillary tubes. The starting temperature
of the approximate melting range was input via the keyboard and the melting point range was spotted visually. FT-IR spectra were
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recorded on a Perkin-Elmer spectrum BX series and KBr pellets were used for solid samples. Mass spectra were obtained on
1
Agilent Technologies 5975C spectrometer via mass selective detector (MSD) operating at an ionization potential of 70 eV. H
NMR and 13C NMR spectra were determined on Bruker AV-400 using TMS (0.00 ppm) as internal standard and DMSO-d6 as
solvent.
2.3. Preparation of 1,4-diazabicyclo[2.2.2]octane-1,4-diium dihydrogen phosphate {[H2-DABCO][H2PO4]2}
A mixture of 1,4-Diazabicyclo[2.2.2]octane (DABCO) (0.909 g, 8.1 mmol) in dry dichloromethane (50 mL) was charged into a
100 mL round-bottomed flask and was stirred in an ice-bath for 1 min. Then, a stoichiometric amount of phosphoric acid (85 w/w
%, 1 mL, 1.84 g) was added drop wise to this mixture during a period of 25 min. After the addition, the flask was immersed in a
recirculating heated water-bath and fitted with a reflux condenser for 24 h. After all, the obtained ionic liquid was washed with
diethyl ether repeatedly (3 × 15) to remove non-ionic residues and then dried under vacuum to give [H2-DABCO][H2PO4]2 as a
white solid in 97% yield (2.417 g) (Fig.2). As shown in Fig. 3, this method was repeated in 4 runs for being sure about its accuracy.
The purity of product was determined by melting point, Mass, FT-IR, 1H NMR and 13C NMR.
Spectral data for [H2-DABCO][H2PO4]2 :White solid; M.P. 98 °C; MS: m/e = 308(M+); FT-IR (KBr, cm-1) 휐max: 3421, 2823,
1
2380, 1638, 1115, 1053, 961; H NMR (400 MHz, DMSO-d6): 훿 (ppm) 3.54 (s, 6H), 6.70 (s, 1H, NH), 10.90 (s, 1H, H2PO4); 13C
NMR (100 MHz, DMSO-d6): 훿 (ppm) 43.4.
2.4. General procedure for the synthesis of tetrahydrobenzo[b]pyran derivatives
To prepare tetrahydrobenzo[b]pyran derivatives, an equimolar mixture of an aromatic aldehyde (1 mmol), malanonitrile (1
mmol), and dimedone (1.0 mmol), and [H2-DABCO][H2PO4]2 (0.16 mmol, 0.050 g) was dissolved in 3 mL aqueous ethanol (1:2) and
was stirred under reflux conditions in appropriate times. The reaction progress was followed by TLC (n-hexane : etheylacetate;
8:2). After completion of the reaction, the mixture was cooled to room temperature and the obtained residue was filtered and
washed with cold distilled water (2 mL). At last, the solid products were recrystallized from warm ethanol to give the pure
product.
2.5. General procedure for the synthesis of pyrano[2,3-d]-pyrimidinone derivatives
[H2-DABCO][H2PO4]2 (0.065 mmol, 0.020 g) was added to a mixture of the aromatic aldehyde (1 mmol), malononitrile (1
o
mmol) and barbituric or thiobarbituric acid (1 mmol) in water (3 mL). Then the mixture was heated at 75 C while was monitored
by TLC (n-hexane : etheylacetate; 1:9). After completion of the reaction, the mixture was cooled to room temperature and the solid
product was filtered, washed with cold distilled water (2 mL) and was recrystallized from warm ethanol if necessary.
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3. Results and discussion
As we have mentioned previously in continuation of our studies on the synthesis of new DABCO based ionic liquids [7, 10, and
45], DABCO was utilized to prepare another cheap and efficient ionic liquid by adding phosphoric acid as a commercially
accessible mineral (inorganic) acid that has been used widely in food industry and fertilizers [46].
3.1. Characterization of the catalyst
3.1.1. FT-IR analysis
The infrared spectra of DABCO and [H2-DABCO][H2PO4]2 are shown in Fig. 4. The IR spectrum of [H2-DABCO][H2PO4]2
shows a broad peak at 3421 cm−1 that can be related to the stretching vibrations of NH groups. The OH starching vibrations of the
phosphoric acid moiety are shown at 2623, 2380, 1638 cm-1. The absorption at 1115 cm−1 is ascribed to P=O stretching vibrations
and the peaks at 1053 and 961 cm−1 are assigned to asymmetric and symmetric stretching of P-O, respectively.
3.1.2. Mass spectroscopy
The mass spectrum of the prepared ionic liquid is demonstrated in Fig. 5. It gave the correct molecular ion peak (M+) at m/e =
308 with relative intensity of 9.89. Other ion peaks at m/e = 112 (69.23) (M+-2(H2PO4)), m/e = 98 (51.64) (H3PO4), m/e = 79
(25.27) (PO3), m/e = 63 (PO2) (35.16), m/e = 47 (20.87) (PO) and the base peak at m/e = 43 (100) (NH(CH2)2) were observed as
well.
3.1.3. NMR spectroscopy
1
-
The H NMR spectrum of [H2-DABCO][H2PO4]2 show the broad acidic hydrogen peak at 10.90 ppm corresponded to H2PO4
and another sharp acidic hydrogen peak at 6.70 ppm which is related to N-H and a singlet peak at 3.54 that is related to aliphatic
CH2 (Fig. 6).
In the 13C NMR spectrum, we expected one peak corresponded to the aliphatic carbons of DABCO. This is verified by
appearing one peak at 43.49 ppm (Fig. 7).
3.2. Catalytic activity
After identification of the prepared ionic liquid, the potential of [H2-DABCO][H2PO4]2 to promote the synthesis of
tetrahydrobenzo[b]pyran and pyrano[2,3-d]-pyrimidinone derivatives is investigated. To prepare these compounds in a more
efficient way with minimum amount of the catalyst, the reaction of 4-chlorobenzaldehyde 1b (1.0 mmol), malononitrile 2 (1.0
mmol), and dimedone 3 (1.0 mmol) or barbituric acid 5 (1.0 mmol) was selected as a model system. The obtained results were
tabulated in Tables 1 and 2.
Only a trace amount of the desired products were obtained when aprotic solvents like dichloromethane and acetonitrile were
used at room temperature and under reflux conditions (Tables 1 and 2, entries 1-4). Although the use of protic solvents under
thermal conditions improved the yield of the desired products but the reaction yields were trace in the absence of the catalyst under
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the same conditions (Tables 1 and 2, entry 13). The best conditions are selected on the basis of these results and represented in
Schemes 1 and 2.
In order to generalize the best conditions, different derivatives of tetrahydrobenzo[b]pyran (4a-q) and pyrano[2,3-d]-
pyrimidinone (7a-l and 8a-e) were prepared and the results were summarized in Table 3. After ending the reaction, although the
conversation yields in all reactions were 100%, a small amount of products wasted through work up process and isolated yields got
less than conversation yields.
A comparison of the catalytic efficiency of [H2-DABCO][H2PO4]2 in the synthesis of 2-amino-4-(4-chlorophenyl)-7,7-dimethyl-
5-oxo-5,6,7,8-tetrahydro-4H-chromene-3-carbonitrile 4b (entry 2, Table 3) and 7-amino-5-(4-bromophenyl)-2,4-dioxo-1,3,4,5-
tetrahydro-2H-pyrano[2,3-d]pyrimidine-6-carbonitrile 7d (entry 21, Table 3) as model reactions with the selected catalysts is
presented in Table 4. As shown in Table 4, our presented methods are better than some of the previously reported methods in terms
of the catalyst amount, reaction time and turnover frequency (TOF). The turnover frequency TOF quantifies the specific activity of
a catalytic center for a special reaction under defined reaction conditions by the number of molecular reactions or catalytic cycles
occurring at the center per unit time. This method ascendancy are due to the small amount of catalyst that it affected directly on
increasing TOF. On the other hand, it is obvious that in this procedure avoided to use excess amount of substrate unlike some
previous methods (Table 4, entries 3, 6, and 7).
According to the above obtained results, the proposed mechanism can be described like Scheme 3. . The carbonyl group of the
aldehyde could be activated by hydrogen bonding with Brønsted acidic ionic liquid to lower the energy of the transition state. Then
the reaction could occur from 2 routes (route 1 and 2). In route 1, Knoevenagel condensation between the activated aldehyde a and
malononitrile 2 was took place to form intermediate d. On the other hand, it could happen between activated aldehyde a and β-
diketone 3 in rout 2 so intermediate e was constructed. Both routes associated together in intermediate f which was achieved by a
nucleophilic addition (it accomplished between intermediate d and activated β-diketone c in route 1 or intermediate e and activated
malononitrile b in route 2). Finally, the products 4, 7 or 8 were obtained by an intramolecular cyclization in intermediate f and then,
tautomerization in intermediate g.
3.3. Reusability of the catalyst
The reusability of the catalyst was investigated in the synthesis of 2-amino-4-(4-chlorophenyl)-7,7-dimethyl-5-oxo-5,6,7,8-
tetrahydro-4H-chromene-3-carbonitrile 4b (entry 2, Table 3) and 7-amino-5-(4-chlorophenyl)-2,4-dioxo-1,3,4,5-tetrahydro-2H-
pyrano[2,3-d]pyrimidine-6-carbonitrile 7b (entry 19, Table 3) under both the best reactions conditions. After completion of the
o
reactions, the mixtures were filtered and the solvents were evaporated under vacuum up to 70 C to attain the recovered catalyst. It
was washed with diethyl ether, dried and used again for the same reaction. This procedure was repeated 4 times for both reactions
and each time the product was obtained by the recovered catalysts with the least change in the reaction time and yield. The results
are shown in Figs. 8 and 9.
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4. Conclusion
In conclusion, [H2-DABCO][H2PO4]2 as a new Brønsted acidic ionic liquids is successfully synthesized and utilized as an
effective catalyst for the preparation of tetrahydrobenzo[b]pyran 4 and pyrano[2,3-d]-pyrimidinone (7 and 8) derivatives under mild
conditions. Our procedure is simple, needs no special apparatus, reagents or chemicals, and the formed compounds can be filtered
and purified just by simple recrystallization. This synthesis is also economical due to use of affordable reagent and avoid any
hazardous and expensive organic solvents.
Acknowledgments
We are thankful to the Research Council of University of Guilan for the partial support of this research.
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Fig.1. Pyran moiety in structure of iridoids
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Fig. 2 Preparation of [H2-DABCO][H2PO4]2
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Fig. 3 The obtained yields due to the synthesis of [H2-DABCO][H2PO4]2 in 4 runs.
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200
180
160
140
120
100
80
60
40
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber cm-1
Fig. 4 The FT-IR spectra of DABCO and [H2-DABCO][H2PO4]2
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Fig. 5 The mass spectra of [H2-DABCO][H2PO4]2
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Hydrogens of CH
Hydrogens of N-H
-
Hydrogens of H2PO4
Fig. 6 The 1H NMR spectra of [H2-DABCO][H2PO4]2
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Carbons of CH
Fig. 7 The 13C NMR spectra of [H2-DABCO][H2PO4]2
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Fig. 8 Reusability of [H2-DABCO][H2PO4]2 in the synthesis of 2-amino-4-(4-chlorophenyl)-7,7-dimethyl-5-oxo-5,6,7,8-
tetrahydro-4H-chromene-3-carbonitrile 4b
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Fig. 9 Reusability of [H2-DABCO][H2PO4]2 in the synthesis of 7-amino-5-(4-chlorophenyl)-2,4-dioxo-1,3,4,5-tetrahydro-2H-pyrano[2,3-
d]pyrimidine-6-carbonitrile 7b
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Scheme 1 Synthesis of tetrahydrobenzo[b]pyran derivatives catalyzed by [H2-DABCO][H2PO4]2 in aqueous ethanol (1:2) under
reflux conditions
17

ACCEPTED MANUSCRIPT
Scheme 2 Synthesis of pyrano[2,3-d]-pyrimidinone derivatives catalyzed by [H2-DABCO][H2PO4]2 in water under thermal
conditions
18

ACCEPTED MANUSCRIPT
Scheme 3 Plausible mechanism for the preparation of tetrahydrobenzo[b]pyran 4 and pyrano[2,3-d]-pyrimidinone (7 and 8)
derivatives
19

ACCEPTED MANUSCRIPT
Table 1. Optimization of the amount of the catalyst, temperature and solvent in the synthesis of tetrahydrobenzo[b]pyran derivative
of 4-chlorobenzaldehyde
Entry
1
2
3
4
5
6
7
Amount of catalyst (mol %)
Solvent
CH2Cl2
CH2Cl2
CH3CN
CH3CN
H2O
H2O
C2H5OH
C2H5OH
C2H5OH : H2O (2:1)
C2H5OH : H2O (2:1)
---
Temp. (oC)
r.t.
Reflux
r.t.
Reflux
r.t.
Reflux
r.t.
Reflux
Reflux
Reflux
80
100
Reflux
Time (min) Conversation yield (%)
0.0065
0.016
0.0097
0.016
0.012
0.019
0.012
0.016
0.016
0.019
0.012
0.016
---
120
120
120
120
12
Trace
Trace
Trace
Trace
Not completed
Not completed
Not completed
100(70)a
100(95)
100(93)
100(80)
100(80)
Trace
120
120
100
15
8
9
10
11
12
13
15
45
40
120
---
C2H5OH : H2O (2:1)
a isolated yields
20

ACCEPTED MANUSCRIPT
Table 2. Optimization of the amount of the catalyst, temperature and solvent in the synthesis of pyrano[2,3-d]-pyrimidinone
derivative of 4-chlorobenzaldehyde
Entry Amount of catalyst (mol %)
Solvent
CH2Cl2
CH2Cl2
CH3CN
CH3CN
C2H5OH
C2H5OH
---
H2O
H2O
H2O
H2O
Temp. (oC)
r.t.
Reflux
r.t.
Reflux
r.t.
Reflux
100
r.t.
Reflux
r.t.
Reflux
75
75
Time (min)
120
120
120
120
120
120
120
30
18
15
10
10
Conversation yield (%)
Trace
Trace
Trace
Trace
1
2
0.0049
0.0065
3
0.0049
4
0.0097
5
0.0049
Trace
6
0.0065
Not completed
Not completed
100(80)a
100(80)
100(90)
100(90)
7
0.0065
8
0.0049
9
0.0049
10
11
12
13
0.0065
0.0065
0.0065
H2O
H2O
100(95)
Trace
---
120
a isolated yields
21

ACCEPTED MANUSCRIPT
Table 3. Preparation of tetrahydrobenzo[b]pyran and pyrano[2,3-d]-pyrimidinone derivatives by using [H2-DABCO][H2PO4]2 as
the catalyst
M.P. (oC)
Yield
Entry Aldehyde
Product
Time (min)
Ref.
(%)a
Found
Reported
1
2
C6H5CHO
4a
4b
12
90
225-228
228-230
[27]
4-ClC6H4CHO
15
95
208-210
210-212
[27]
3
4
3-ClC6H4CHO
2-ClC6H4CHO
4c
4d
18
18
90
93
230-233
213-215
235-237
218-220
[20]
[20]
5
6
7
4-BrC6H4CHO
4-FC6H4CHO
4e
4f
20
10
15
95
90
89
199-201
171-174
176-179
203-205
176-178
177-178
[32]
[20]
[32]
4-NO2C6H4CHO
4g
8
9
3-NO2C6H4CHO
2-NO2C6H4CHO
4h
4i
20
17
85
90
202-205
213-217
208-210
215-217
[20]
[20]
22

ACCEPTED MANUSCRIPT
10
11
12
13
4-OHC6H4CHO
4-MeOC6H4CHO
2-MeOC6H4CHO
4-MeC6H4CHO
4j
4k
4l
25
27
35
85
87
85
90
210-214
200-204
198-203
211-214
214-215
199-201
198-200
214-216
[19]
[20]
[23]
[22]
4m 30
14
15
4-NMe2C6H4CHO
2-Naphthaldehyde
4n
4o
40
45
85
92
199-203
262-265
198-200
266-268
[20]
[25]
16
Cinnamaldehyde
4p
35
90
200-203
205-207
[20]
17
18
4-CNC6H4CHO
4q
7a
20
10
95
90
220-223
219-222
224-226
221-224
[25]
[35]
C6H5CHO
23

ACCEPTED MANUSCRIPT
19
20
21
4-ClC6H4CHO
2-ClC6H4CHO
4-BrC6H4CHO
7b
7c
7d
10
12
8
95
90
95
238-240
209-214
227-230
242-243
212-214
230-231
[35]
[36]
[29]
22
23
4-FC6H4CHO
7e
7f
8
93
85
264-266
237-239
268-270
238-240
[38]
[38]
4-NO2C6H4CHO
22
24
25
3-NO2C6H4CHO
2-NO2C6H4CHO
7g
7h
25
20
85
80
261-264
249-251
267-269
253-256
[37]
[37]
26
27
4-OHC6H4CHO
3-OHC6H4CHO
7i
7j
30
27
90
85
>300
>300
[35]
[38]
158-160
160-162
24

ACCEPTED MANUSCRIPT
28
29
4-MeOC6H4CHO
4-CHOC6H4CHO
7k
25
10
87
90
276-279
272-274
335-337
[36]
[38]
7l
>300
30
31
C6H5CHO
8a
8b
15
17
85
90
220-224
>300
224-225
>300
[35]
[35]
4-ClC6H4CHO
32
33
3-ClC6H4CHO
4-BrC6H4CHO
8c
8d
20
22
90
85
233-235
234-237
[36]
[29]
235(dec.)b
236(dec.)
34
4-NO2C6H4CHO
8e
30
83
233-235
235-236
[29]
a Isolated yields
b Decomposition
25

ACCEPTED MANUSCRIPT
Table 4. Catalytic activity and reaction conditions comparison of [H2-DABCO][H2PO4]2 with other reported catalysts
Time Yield
(min) (%)
TOF
(s-1)
Entry Product
Catalyst
Amount
(0.2 mol)
(0.1 mol)
Condition
Ref.
[19]
[20]
C2H5OH /
r.t.
C2H5OH /
reflux
1
2
N-Methylimidazole
60
30
95
95
0.13
0.53
Tetrabutylammonium
bromide
H2O :
(0.05
mol)
C2H5OH
(1:1) /
reflux
Trisodium citrate
5
93
69
89
6.2
[21]
[22]
[28]
3
p-Dodecylbenzenesulfonic
(4×10-4
mol)
H2O / reflux 240
H2O:
C2H5OH
(1:1) /
reflux
H2O:
C2H5OH
(1:2) /
11.98
0.99
acid a
(0.05
mol)
4
5
(Diacetoxyiodo)benzene
30
(1.6×10-4
mol)
This
work
[H2-DABCO][H2PO4]2
15
95
659.7
reflux
H2O :
(0.1 mol) C2H5OH
(1:1) / r.t.
Diammonium hydrogen
phosphateb
6
7
120
81
75
0.11
0.27
[29]
[30]
H2O :
(0.05
L-Prolineb
C2H5OH
mol)
90
40
(1:1) / r.t.
8
9
KAl(SO4)2.12H2O (alum)
Tetrabutylammonium
bromide
(0.1 mol) H2O/ 80 oC
91
95
0.37
0.53
[31]
[32]
(0.1 mol) H2O / reflux 30
(5×10-5
10
11
12
[DABCO](SO3H)2(Cl)2
[DABCO](SO3H)2(HSO4)2
[H2-DABCO][H2PO4]2
H2O / reflux 10
mol)
90
87
95
3000
[11]
[11]
(2×10-5
H2O / reflux
5
14500
3044.9
mol)
(6.5×10-5
mol)
This
work
H2O / 75 oC
8
a Aldehyde (1 mol), Dimedone (1 mol) and malononitrile (1.1 mol) were used in this method.
b In this method, ratio of aldehyde (mmol): barbituric acid (mmol): malononitrile (mmol): is 1:1:1.2.
26

ACCEPTED MANUSCRIPT
Highlights:

Introduction of a simple method for the preparation of tetrahydrobenzo[b]pyran and pyrano[2,3-
d]pyrimidinone derivatives.


Preparation of a green, reusable and eco-friendly catalyst.
Easy, simple and high yeilding multi-component reactions.
27