Task-specific ionic liquid as the recyclable catalyst for the rapid and green synthesis of dihydropyrano[3,2-c]chromene derivatives

Article abstract of DOI:10.1080/00397911.2010.519594

A task-specific ionic liquid, [H3N+-CH2-CH2-OH][CH3COO-], was successfully applied as an efficient and reusable catalyst for the one-pot domino to approach to dihydropyrano[3,2-c]chromene derivatives with atom economy in a condensation reaction of 4-hydro

Full text of DOI:10.1080/00397911.2010.519594

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Task-Specific Ionic Liquid as the
Recyclable Catalyst for the Rapid and
Green Synthesis of Dihydropyrano[3,2-
c]chromene Derivatives
Hamid Reza Shaterian a & Moones Honarmand a
a Department of Chemistry, Faculty of Sciences, University of Sistan
and Baluchestan, Zahedan, Iran
Accepted author version posted online: 30 Jun 2011.Version of
record first published: 08 Jun 2011.
To cite this article: Hamid Reza Shaterian & Moones Honarmand (2011): Task-Specific Ionic Liquid
as the Recyclable Catalyst for the Rapid and Green Synthesis of Dihydropyrano[3,2-c]chromene
Derivatives, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 41:23, 3573-3581
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Synthetic Communications1, 41: 3573–3581, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.519594
TASK-SPECIFIC IONIC LIQUID AS THE RECYCLABLE
CATALYST FOR THE RAPID AND GREEN SYNTHESIS
OF DIHYDROPYRANO[3,2-c]CHROMENE DERIVATIVES
Hamid Reza Shaterian and Moones Honarmand
Department of Chemistry, Faculty of Sciences, University of Sistan and
Baluchestan, Zahedan, Iran
GRAPHICAL ABSTRACT
Abstract A task-specific ionic liquid, [H3Nþ–CH2–CH2–OH][CH3COOꢀ], was success-
fully applied as an efficient and reusable catalyst for the one-pot domino to approach to
dihydropyrano[3,2-c]chromene derivatives with atom economy in a condensation reaction
of 4-hydroxycoumarin, aldehydes, and malononitrile in a combinatorial fashion. The reac-
tion gave excellent yields within short reaction times at room temperature under solvent-free
grinding conditions. The products and ionic liquid could be conveniently separated from the
reaction mixture, indicating that the whole process was performed as a green chemical
transformation.
Keywords Dihydropyrano[3,2-c]chromene; ionic liquid; multicomponent reaction;
recyclable catalyst; solvent-free
INTRODUCTION
Multicomponent[1] (MCR) and domino reaction[2] offer significant advantages
compared to the classical step-by-step formation of individual bonds because of their
greater synthetic efficiency. The resulting reduced number of synthetic and purifi-
cation steps for a given target molecule increases the attractiveness and practicality
of the process. As a special benefit, often MCRs also enhance structural diversity in
an unprecedented way. Because of the wide variation of the starting materials, vari-
ous opportunities arise for the synthesis of compound libraries. Recently, research
in academia and industry has increasingly emphasized the use of MCRs as well as
domino reaction sequences for a broad range of products.[3]
Received July 19, 2010.
Address correspondence to Hamid Reza Shaterian, Department of Chemistry, Faculty of Sciences,
University of Sistan and Baluchestan, P.O. Box 98135-674, Zahedan, Iran. E-mail: hrshaterian@
chem.usb.ac.irm
3573

3574
H. R. SHATERIAN AND M. HONARMAND
Scheme 1. Three-component synthesis of 2-amino-5-oxo-4,5-dihydropyrano[3,2-c]chromene-3-carboni-
trile derivatives.
Ionic liquids (ILs), when used for replacing classical organic solvents, offer a
new, cost-effective, and environmentally benign approach toward modern chemical
green processes.[4] ILs have been considered ecofriendly alternatives to volatile organic
media because of their negligible vapor pressure and nonflammable nature.[5]
Additionally, the incorporation of functional groups can render a particular capability
to the ionic liquids, enhancing their function, which may lead to increased reusability
stability of ILs compared with unfunctionalized counterparts. Moreover, specific func-
tional groups can also be incorporated for task-specific purposes.[6] The implemen-
tation of task-specific ILs further enhances the versatility of ILs for the cases where
both reagent and medium are coupled.[7] Task-specific room-temperature ILs (TSILs)
have emerged as a powerful alternative to conventional molecular organic solvents or
catalysts because of their particular properties, such as low vapor pressure, thermal
stability, wide liquid range, and ease of recovery and reuse.[8]
Pyrano[3,2-c]chromene derivatives are important heterocycles with a wide
range of biological properties[9] such as spasmolytic, diuretic, anticoagulant, antican-
cer, and antianaphylactic activities.[10] In addition, 2-aminochromene derivatives
exhibit a wide spectrum of biological activities including antihypertensive and
anti-ischemic behavior.[11] Also, a number of 2-amino-4H-pyrans are useful as
photoactive materials.[12] 2-Amino-4-aryl-5-oxo-4H,5H-pyrano[3,2-c]chromene-3-
carbonitriles have already been prepared in the presence of organic bases such as pip-
eridine or pyridine in a large volume of organic solvents such as absolute ethanol
under thermal conditions.[13] These compounds have also been prepared in the pres-
ence of diammonium hydrogen phosphate, (NH4)2HPO4 (DAHP), in aqueous etha-
nol[14] and a saturated solution of potassium carbonate in water under microwave
irradiation.[15] Some of the reported procedures require long reaction times, multi-
step reactions, expensive and toxic reagents, complex synthetic workup pathways,
modest yields, and nonreusable catalyst.[16]
In continuation of our research on the synthesis and new applications of hom-
ogenous and heterogeneous catalysts in organic chemistry,[17] here we use the RTIL
2-hydroxyethanaminium acetate (HEAA), [H3Nþ–CH2–CH2–OH][CH3COOꢀ], as
an efficient and reusable catalyst for the one-pot synthesis of 2-amino-5-oxo-
4,5-dihydropyrano[3,2-c]chromene-3-carbonitrile derivatives by three-component
condensation of 4-hydroxycoumarin, aldehydes, and malononitrile at room tempera-
ture under solvent-free grinding conditions (Scheme 1).
RESULTS AND DISCUSSION
We characterize the ionic liquid[18,19] by NMR and infrared (IR) spectroscopy
for the first time. We interpret the results as follows: 1H NMR (DMSO-d6, 500 Hz): d

DIHYDROPYRANO[3,2-c]CHROMENE
3575
1.70 (s, 3H, CH3–COO), 2.77 (t, J ¼ 5.38 Hz, 2H, –O–CH2–), 3.53 (t, J ¼ 5.38 Hz,
2H, –CH2–N), 7.1–7.8 (broad singlet, 4H, ꢀNHþ3 ; ꢀOH) ppm. The Fourier trans-
form (FT)–IR spectrum showed a broad band in the 3600–2400 cmꢀ1 range, which
exhibits zwitterionic quaternary ammonium carboxylate character. The OH stretch-
ing vibration is embedded in this band. The broad band centered at 1567 cmꢀ1 is a
combined band of the carbonyl stretching and N–H plane-bending vibrations. A
literature survey confirms this interpretation of [H3Nþ–CH2–CH2–OH][HCOOꢀ].[20]
To optimize the amount of catalyst, the reaction of benzaldehyde (3 equiv),
malononitrile (3 equiv), and 4-hydroxycoumarin (3 equiv) under grinding conditions
was selected as a model. The best result was obtained by carrying out the reaction
using six drops (0.120 g) of 2-hydroxyethanaminium acetate (HEAA) at room
temperature.
Using these optimized reaction conditions, the scope and efficiency of the
reaction were explored for the synthesis of a wide variety of 2-amino-5-oxo-
4,5-dihydropyrano[3,2-c]chromene-3-carbonitriles using various aldehydes, 4-hydro-
xycoumarin, and malononitrile in excellent yields and short reaction times. The
results are summarized in Table 1.
As shown in Table 1, the direct three-component reactions performed well with
aliphatic aldehydes (entry 13), heterocyclic 2-pyridinecarbaldehyde (entry 16), and a
variety of aryl aldehydes including those bearing electron-withdrawing and
electron-donating groups such as OMe, OH, Cl, F, and NO2. The desired products
were obtained in good to excellent yields in short reaction times. We also have
prepared five new analogs of this class of compound (Table 1, Entries 13–17).
Table 1. Synthesis of dihydropyrano[3,2-c]chromen derivatives in the presence of 2-hydroxyethanami-
nium acetate (HEAA)
Entry
Aldehyde(s)
Time (min)
Yield (%)a
Mp (ꢁC)
Lit. Mp
[Ref]
1
2
Benzaldehyde
8
6
93
83
92
93
94
90
94
72
83
90
74
71
95
94
75
70
93
255–256
263–264
243–244
263–264
261–262
261–262
263–264
259–260
258–259
229–230
282–283
255–256
187–188b
243–244b
264–265b
246–247b
247–248b
256–258
266–268
247–248
263–265
262–264
258–260
260–262
261–262
254–255
226–228
280–282
257–259
[14]
[21]
[22]
[14]
[14]
[14]
[21]
[22]
[23]
[24]
[14]
[14]
2-Chlorobenzaldehyde
3-Chlorobenzaldehyde
4-Chlorobenzaldehyde
3-Nitrobenzaldehyde
3
7
4
10
8
5
6
4-Nitrobenzaldehyde
8
7
4-Fluorobenzaldehyde
4-Hydroxybenzaldehyde
4-Methylbenzaldehyde
4-Methoxybenzaldehyde
2,3-Dichlorobenzaldehyde
2,4-Dichlorobenzaldehyde
3-Phenylpropanal
13
8
8
9
8
10
11
12
13
14
15
16
17
8
11
14
11
8
3-Fluorobenzaldehyde
2-Methylbenzaldehyde
Pyridine-2-carboxaldehyde
2,5-Dimethoxybenzaldehyde
9
10
8
aYields refer to the isolated pure products. All of the desired product(s) were characterized by compari-
son of their physical and spectroscopic data with those of known compounds.[14,23–25]
bThe spectral patterns of the new products showed similar peaks and fragmentations according to
analogous compounds reported in the literature.

3576
H. R. SHATERIAN AND M. HONARMAND
Scheme 2. The suggested mechanism for the preparation of 2-amino-5-oxo-4,5-dihydropyrano[3,2-c]-
chromene-3-carbonitrile derivatives.
The suggested mechanism of the HEAA-catalyzed transformations is shown in
Scheme 2. As reported in the literature,[18] the Knoevenagel coupling of aldehydes
with malononitrile gave intermediate (I). Then, the subsequent 1,4-conjugate
addition of 4-hydroxycoumarin to the intermediate (I) followed by cyclization
affords the corresponding products.[24,25]
The reusability of the catalyst was tested in the synthesis of 2-amino-5-oxo-
4-phenyl-4,5-dihydropyrano[3,2-c]chromene-3-carbonitrile from the reaction of ben-
zaldehyde, malononitrile, and 4-hydroxycoumarin, as shown in Fig. 1. The catalyst
was recovered after each run, dried, and used for the subsequent run to check its
activities. The catalyst was tested for four runs. The catalyst displayed good reusa-
bility. In addition, the IR of the reused TSIL was compared with that of the new
synthesized IL, and the difference was small. The reason for the decreasing yields
Figure 1. Investigation on the reusability of 2-hydroxyethanaminium acetate (HEAA) as the catalyst.

DIHYDROPYRANO[3,2-c]CHROMENE
3577
Table 2. Comparison of results of 2-hydroxyethanaminium acetate (HEAA) with other catalysts reported
in the literature
Entry
Conditions
Time
Yield (%)
1
2
HEAA (0.04 g), solvent-free, rt
6–14 min
4 h
3 h
70–95; present work
81–95
72–88
DAHP (10 mol%), H2O=EtOH (1:1), rt
(S)-Proline (10 mol%), H2O=EtOH (1:1), reflux
H6[P2W18O62] ꢂ 18H2O (1 mol%), H2O EtOH (1:1), reflux
TBAB (10 mol%), H2O, reflux
TBAB (10 mol%), solvent-free, 120 ꢁC
KF-Al2O3 (0.125 g), EtOH, 80 ꢁC
3
4
30–85 min
45–60 min
40 min
4–7 h
86–90
84–93
75–89
80–90
5
6
7
Piperidine (0.5 ml), EtOH, D
TEBA (0.07 g), H2O, 90 ꢁC
30 min
7–18 h
70–90
85–96
could be that in the course of removing water from the TSIL by heating, a little of
the catalyst decomposed.
To demonstrate the merit of the present work in comparison with previously
reported results, we compared results of diammonium hydrogen phosphate and
(S)-proline,[14] H6[P2W18O62] ꢂ 18H2O,[24] tetrabutylammonium bromide,[25] KF-Al2-
O3,[22] piperidine,[23] and triethylbenzylammonium chloride[21] in the synthesis of
2-amino-5-oxo-4,5-dihydropyrano[3,2-c]chromene-3-carbonitriles derivatives. As
shown in Table 2, HEAA can act as an effective catalyst with respect to reaction
times, yield, and the obtained products.
CONCLUSION
In summary, an efficient protocol for the one-pot preparation of 2-amino-5-
oxo-4,5-dihydropyrano[3,2-c]chromene-3-carbonitriles excellent yields and short
reaction times from the three-component condensation reaction of 4-hydroxycou-
marin, aldehydes, and malononitrile using a TSIL HEAA, as an efficient and reusa-
ble catalyst at room temperature under grinding conditions was described. Five
new desired products were synthesized and characterized for the first time. The
safe catalytic system offers several advantages, including operational simplicity,
environmental friendliness, and green chemical transformation.
EXPERIMENTAL
All reagents were purchased from Merck and Aldrich and used without further
purification. All yields refer to isolated products after purification. Products were
characterized by comparison of spectroscopic data (IR, 1H NMR spectra) and melt-
ing points with those of authentic samples. The NMR spectra were recorded on a
Bruker Avance DPX 500-MHz instrument. The spectra were measured in dimethyl-
sulfoxide (DMSO-d6) relative to tetramethylsilane (TMS, 0.00 ppm). IR spectra were
recorded on a Jasco FT-IR 460 plus spectrophotometer. Mass spectra were recorded
on an Agilent technologies 5973 network mass selective detector (MSD) operating at
an ionization potential of 70 eV. Elemental analyses for C, H, and N were performed
using a Heraeus CHN-O-Rapid analyzer. Melting points were determined in open

3578
H. R. SHATERIAN AND M. HONARMAND
capillaries with a Buchi 510 melting-point apparatus. Thin-layer chromatography
(TLC) was performed on silica gel polygram SIL G=UV 254 plates.
General Procedure for the Synthesis of 2-Amino-5-oxo-
4,5-dihydropyrano[3,2-c]chromene-3-carbonitriles
A mixture of aldehydes (3 mmol), malononitrile (3 mmol), and 4-hydroxycou-
marin (3 mmol) in the presence of six drops (0.120 g) of 2-hydroxyethanaminium
acetate (HEAA) were pulverized in a mortar at room temperature for the appropri-
ate time (Table 1). The reaction was monitored by TLC. After completion of the
reaction, water was added, and the precipitated mixture was filtered off for separ-
ation of crude products. The IL is soluble in water, and after washing the solid pro-
ducts with water completely, the water was evaporated under reduced pressure and
the IL was recovered and reused (Fig. 1). For further purification, the solid product
was recrystallized by aqueous ethanol give the pure products. All of the desired
product(s) were characterized by comparison of their physical data with those of
known compounds.[14,21–23] Spectral data for five novel compounds are given.
Selected Data
2-Amino-4-(phenethyl)-3-cyano-4H,5H-pyrano[3,2-c]chromene-5-one
(Table 1, Entry 13). 1H NMR (DMSO-d6, 500 Hz): d 1.81–1.88 (m, 1H, CH2),
2.08–2.17 (m, 1H, CH2), 2.44–2.62 (m, 2H, CH2), 3.50 (t, J ¼ 4.3 Hz, 1H, CH),
7.00 (t, J ¼ 8.1, 1H, Ar), 7.08 (d, J ¼ 7.0 Hz, 2H, Ar), 7.13 (t, J ¼ 7.5 Hz, 3H, Ar),
7.34–7.45 (m, 4H, NH2 & Ar), 7.62–7.67 (m, 1H, Ar), 7.76 (dd, J ¼ 5.9, 1.2 Hz,
1H, Ar) ppm; 13C NMR (DMSO-d6, 125 Hz): d 30.3, 30.7, 34.6, 54.8, 103.7,
112.9, 116.3, 119.5, 122.1, 124.3, 125.5, 127.9, 128.1, 132.5, 141.2, 152.0, 154.0,
159.4, 159.8 ppm; IR (KBr, cmꢀ1): 3382, 3315, 3189, 2198, 1694, 1671, 1608, 1396,
1315, 1179, 1211, 1112, 759; MS (EI, 70 eV) m=z (%) ¼ 344 (Mþ, 7), 240 (20), 239
(100), 187 (8), 138 (21), 91 (10), 43 (17). Anal. calcd for C21H16N2O3: C, 73.24; H,
4.68; N, 8.13%. Found: C, 73.28; H, 4.70; N, 8.20%.
2-Amino-4-(3-flourophenyl)-3-cyano-4H,5H-pyrano[3,2-c]chromene-5-
one (Table 1, Entry 14). 1H NMR (DMSO-d6, 500 Hz): d 4.50 (s, 1H, CH),
7.01–7.14 (m, 3H, Ar), 7.31–7.41 (m, 5H, NH2 & Ar), 7.63–6.69 (m, 1H, Ar), 7.87
(dd, J ¼ 7.9, 1.2 Hz, 1H, Ar) ppm; 13C NMR (DMSO-d6, 125 Hz): d 36.6, 57.5,
103.2, 112.9, 113.8, 113.9, 114.4, 114.5, 116.4, 119.0, 122.5, 123.7, 124.5, 130.3,
130.3, 132.8, 146.1, 146.2, 152.1, 153.6, 157.9, 159.5, 161.2, 163.1 ppm; IR (KBr,
cmꢀ1): 3375, 3315, 3191, 2195, 1711, 1675, 1619, 1489, 1370, 1252, 1062, 763; MS
(EI, 70 eV) m=z (%) ¼ 334 (Mþ, 22), 267 (13), 239 (100), 121 (21), 92 (8). Anal. calcd.
for C19H11FN2O3: C, 68.26; H, 3.32; N, 8.38%. Found: C, 68.35; H, 3.30; N, 8.40%.
2-Amino-4-(2-methylphenyl)-3-cyano-4H,5H-pyrano[3,2-c]chromene-5-
one (Table 1, Entry 15). 1H NMR (DMSO-d6, 500 Hz): d 2.48 (s, 3H, CH3), 4.73
(s, 1H, CH), 6.90–7.20 (m, 4H, Ar), 7.34 (s, 2H, NH2), 7.41 (d, J ¼ 8.3 Hz, 1H, Ar),
7.46 (t, J ¼ 7.6 Hz, 1H, Ar), 7.66–7.73 (m, 1H, Ar), 7.89 (d, J ¼ 7.8 Hz, 1H, Ar) ppm;
13C NMR (DMSO-d6, 125 Hz): d 19.0, 32.4, 57.9, 104.5, 122.8, 116.4, 119.1, 122.3,
124.6, 126.6, 126.7, 127.8, 130.0, 132.7, 135.2, 142.2, 152.0, 153.4, 157.7,

DIHYDROPYRANO[3,2-c]CHROMENE
3579
159.5 ppm; IR (KBr, cmꢀ1): 3400, 3283, 3179, 2202, 1709, 1675, 1637, 1603, 1490,
1457, 1377, 1171, 1059, 957, 753; MS (EI, 70 eV) m=z (%) ¼ 330 (Mþ, 18), 249
(24), 240 (17), 239 (100), 121 (21). Anal. calcd. for C20H14N2O3: C, 72.72; H, 4.27;
N, 8.48%. Found: C, 72.80; H, 4.30; N, 8.50%.
2-Amino-4-(pyridin-2-yl)-3-cyano-4H,5H-pyrano[3,2-c]chromene-5-one
(Table 1, Entry 16). 1H NMR (DMSO-d6, 500 Hz): d 4.61 (s, 1H, CH), 6.26 (d,
J ¼ 3.0 Hz, 1H, Ar), 6.32–6.39 (m, 1H, Ar), 7.42–7.50 (m, 5H, NH2 & Ar), 7.52 (s,
1H, Ar), 7.69 (t, J ¼ 7.5 Hz, 1H, Ar), 7.85 (d, J ¼ 7.7 Hz, 1H, Ar) ppm; 13C NMR
(DMSO-d6, 125 Hz): d 30.6, 55.3, 101.5, 106.4, 110.6, 112.8, 116.6, 118.9, 122.3,
124.6, 133.0, 142.3, 144.5, 152.1, 153.8, 154.1, 158.7, 159.3 ppm; IR (KBr, cmꢀ1):
3368, 3282, 3169, 2201, 1704, 1672, 1604, 1376, 1268, 1171, 1111, 1056, 957, 757;
MS (EI, 70 eV) m=z (%) ¼ 317 (Mþ, 0.2), 306 (60), 278 (100), 239 (54), 158 (41),
121 (67), 92 (13), 63 (11). Anal. calcd. for C18H11N3O3: C, 68.14; H, 3.49; N,
13.24%. Found: C, 68.20; H, 3.54; N, 13.35%.
2-Amino-4-(2,5-dimethoxyphenyl)-3-cyano-4H,5H-pyrano[3,2-c]chromene-
5-one (Table 1, Entry 17). 1H NMR (DMSO-d6, 500 Hz): d 3.63 (s, 3H, CH3), 3.64
(s, 3H, CH3), 4.64 (s, 1H, CH), 6.66 (d, J ¼ 2.3 Hz, 1H, Ar), 6.75-6.79 (m, 1H, Ar),
6.90 (d, J ¼ 8.8 Hz, 1H, Ar), 7.25 (s, 2H, NH2), 7.41-7.49 (m, 2H, Ar), 7.67 (t,
J ¼ 7.7 Hz, 1H, Ar), 7.89 (d, J ¼ 7.7 Hz, 1H, Ar) ppm; 13C NMR (DMSO-d6,
125 Hz): d 32.6, 55.2, 56.4, 56.8, 103.1, 112.2, 112.9, 113.1, 115.7, 116.4, 119.2,
122.2, 124.5, 131.9, 132.6, 151.5, 152.0, 153.1, 153.9, 158.5, 159.4 ppm; IR (KBr,
cmꢀ1): 3403, 3322, 3192, 2195, 1708, 1672, 1605, 1501, 1380, 1224, 1054, 959, 620;
MS (EI, 70 eV) m=z (%) ¼ 376 (Mþ, 23), 361 (14), 345 (42), 279 (100), 239 (26),
215 (13), 121 (24). Anal. calcd. for C21H16N2O5: C, 67.82; H, 4.28; N, 7.44%. Found:
C, 67.92; H, 4.36; N, 7.55%.
ACKNOWLEDGMENT
We are thankful to the University of Sistan and Baluchestan Research Council
for the partial support of this research.
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