Synthesis of a SO3H-bearing carbonaceous solid catalyst, PEG-SAC: Application for the easy access to a diversified library of pyran derivatives

Article abstract of DOI:10.1039/c3ra42352b

A SO₃H-bearing carbonaceous solid catalyst (PEG-SAC) has been synthesized through sulfonation followed by a hydrothermal carbonization method from renewable resources like polyethylene glycol. The biodegradable catalyst was characterized by XRD

Full text of DOI:10.1039/c3ra42352b

RSC Advances
View Article Online
View Journal | View Issue
COMMUNICATION
Synthesis of a SO3H-bearing carbonaceous solid
catalyst, PEG–SAC: application for the easy access to a
Cite this: RSC Advances, 2013, 3, 14254
diversified library of pyran derivatives3
Sanjay Paul,a Sirshendu Ghosh,b Pranabes Bhattacharyyaa and Asish R. Das*a
Received 14th May 2013,
Accepted 25th June 2013
DOI: 10.1039/c3ra42352b
www.rsc.org/advances
A SO3H-bearing carbonaceous solid catalyst (PEG–SAC) has been
synthesized through sulfonation followed by a hydrothermal
carbonization method from renewable resources like polyethy-
lene glycol. The biodegradable catalyst was characterized by XRD,
TEM, FT-IR and EDX. The surface area and pore diameter of the
catalyst were determined from a nitrogen adsorption–desorption
isotherm experiment. A highly convergent, efficient and practical
PEG–SAC catalyzed heteroannulation protocol for the synthesis of
a library of diversified pyran fused heterocyclic scaffolds has been
demonstrated. This synthesis was established to follow the
group-assistant-purification (GAP) chemistry process, which can
avoid traditional chromatography. A recrystallization purification
appeared to be a very good alternative to the traditional classical
methods, demonstrating that a carbon-based catalyst is very
effective in producing pyran fused heterocyclic molecules. The
aqueous reaction medium, easy recovery of the catalyst and high
yield of the products make the protocol attractive, sustainable
and economic.
catalysts are reusable and offer a simplified separation process,
their use prolongs the reaction time due to their very low activity.7
At the present, mesoporous materials have attracted a great
deal of attention in organic synthesis owing to their high surface-
to-volume ratio leading to a large number of active sites.
Mesoporous carbon materials consisting of small polycyclic
aromatic carbon sheets with a high density of sulfonic acid sites
are promising solid acid catalysts.8,9 Solid acids have many
advantages such as ease of handling, fewer reactor and plant
corrosion problems, and environmentally safe disposal.10 Besides,
a major emerging and challenging area of heterogeneous catalysis
is that of environmental pollution control, with tightening
legislation on the release of waste and toxic emissions having
serious implications for the chemical industry. In addition, there
is a lot of current research and general interest in heterogeneous
systems because of their importance in industry and in technology
development.11 These SO3H-bearing amorphous carbon materials
can be readily prepared by partial carbonization of organic
compounds (glucose, starch, and cellulose), followed by sulfona-
tion in fuming H2SO4.12
Herein, we have demonstrated a two step synthesis of SO3H-
bearing carbonaceous solids by hydrothermal carbonization using
polyethylene glycol as the carbon precursor, in a reversed mode
from previously reported methods. In this protocol, the SO3H
groups are first introduced into the carbon precursor polyethylene
glycol using chlorosulphonic acid (Fig. 1, A). The mesoporous
carbonaceous solid acid was then obtained through the incom-
plete carbonization of the SO3H functionalized polyethylene glycol
(Fig. 1, B) at a high temperature.
Introduction
A wide variety of homogeneous Brønsted acids (H2SO4, p-toluene-
sulfonic acid, HCl and H3PO4) have been used for the synthesis of
important chemicals, including pharmaceuticals, agrochemicals,
and fragrances.1–3 These acidic catalysts are economical and
efficient, but have serious drawbacks associated with product
isolation, equipment corrosion, solvent recycling, and reusability
of the catalyst. Heterogeneous acid catalysts like zeolites,
transition-metal ions, and strong acid cation exchange resins
have also been used to serve this purpose.4–6 Although these
aDepartment of Chemistry, University of Calcutta, Kolkata-700009, India.
E-mail: ardchem@caluniv.ac.in; ardas66@rediffmail.com; Fax: +913323519754;
Tel: +913323501014 Tel: +919433120265
bDepartment of Materials Science, Indian Association for the Cultivation of Science,
Kolkata, 700032, India
Electronic supplementary information (ESI) available. CCDC 818608. For ESI and
3
Fig. 1 Synthesis of the solid acid catalyst PEG–SAC.
crystallographic data in CIF or other electronic formats see DOI: 10.1039/c3ra42352b
14254 | RSC Adv., 2013, 3, 14254–14262
This journal is ß The Royal Society of Chemistry 2013

View Article Online
RSC Advances
Communication
It is well known that pyrans are important core units in a
number of natural products13 and photochromic materials.14
These pyran derivatives show antihyperglycemic and antidyslipi-
demic,15 cytotoxic,16 molluscicidal,17 antiinflammatory,18 and
antifungal activities.19 These compounds also exhibit a wide
spectrum of biological activities,20 including anticancer21 and
antimalarial,22 and are also widely employed in cosmetics,
pigments,23 and potential biodegradable agrochemicals.24
Various catalytic systems such as hexadecyltrimethyl ammonium
bromide
(HMTAB),25a
triethylbenzylammonium
chloride
(TEBA),25b rare earth perfluorooctanoate (RE(PFO)3),25c (S)-pro-
line,25d amino functionalized ionic liquids,25e MgO,25f SiO2
nanoparticles,25g silica bonded n-propyl-4-aza-1-azoniabicy-
clo[2.2.2]octane chloride (SB-DABCO),25h H14[NaP5W30O110],26a
Na2HPO4,26b [bmim]OH,26c CAN26d and Na2CO326e have been used
for the synthesis of 4H-pyrans so far. But most of the reported
procedures for the synthesis of pyran derivatives suffer from
drawbacks such as low yields of the products, long reaction times,
the use of hazardous and often expensive catalysts, the use of
volatile and hazardous organic solvents, harsh reaction conditions,
tedious work-ups, and no compliance with green chemistry
protocols. Consequently, the development of efficient, inexpensive
and environmentally benign methods for the synthesis of this
heterocyclic scaffold is still in demand.
SO3H-bearing amorphous carbon materials can function as
stable and highly active solid acid catalyst for various acid-
catalyzed reactions with hydrophilic reactants, such as esterifica-
tion, transesterification, and hydrolysis reactions.8,9,12 In continua-
tion of our research program dedicated to the design and
synthesis of novel heterocyclic systems,27 here we wish to disclose
a PEG derived SO3H-bearing amorphous carbon material catalyst
in a general, rapid, high yielding, green synthetic protocol for a
variety of pyran derivatives.
Fig. 3 FT-IR spectrum of the catalyst.
to amorphous carbon and it also consists of a weak diffraction
peak C(101) at 2h = 35–50u due to the axis of the graphite structure
of the carbonaceous material. Hence, the XRD pattern indicates
amorphous carbon composed of aromatic carbon sheets oriented
in a random manner (Fig. 1). The FT-IR spectrum of the PEG–SAC
catalyst is shown in Fig. 3. The strong peak at around 1710 cm21
and the weak peak at around 1117 cm21 can be typically assigned
to the stretching modes of the SO3H groups, which are regarded as
the ‘‘active sites’’ of this catalyst.28
HR-TEM microscopy (Fig. 4) was used to study the morphology
of the surface of the solid acid catalyst PEG–SAC synthesized from
PEG-6000 by the hydrothermal method. The HR-TEM images
show amorphous carbon and that the carbonaceous material
PEG–SAC has a sponge-like morphology.
Three independent methods – EDX, acid–base back titration,
and elemental analysis – for the quantification of the acid content
in the catalyst have been applied giving similar results. Elemental
analysis of the as-synthesized PEG–SAC catalyst was performed by
energy dispersive X-ray analysis (EDX) equipped onto TEM. The
Results and discussions
The carbon based solid acid was prepared by the hydrothermal
treatment of PEG–OSO3H. The mesoporous carbonaceous PEG
derived solid acid catalyst was denoted as PEG–SAC. Fig. 2 shows
the XRD pattern of the PEG–SAC catalyst. The XRD pattern
exhibits a broad C(002) diffraction peak (2h = 10–30u) attributable
quantitative EDX analysis in Fig. 5 and Table S1 (ESI ) clearly show
3
that C, O and S are the main elemental components of the
catalyst. The acid–base titration of the prepared catalyst was
performed using a 0.03 M NaOH solution with a 50 ml dispersed
solution of the catalyst in water (50 ml water was stirred with 1 g of
the catalyst for 30 min at rt). From the acid–base back titration it
was observed that the acid density (–SO3H) was 1.52 mmol g21
while the elemental analysis (EDX) revealed that the S content of
the catalyst was 1.48 mmol g21
.
Fig. 4 HR-TEM images (a and b) of the catalyst.
Fig. 2 XRD pattern of solid acid catalyst PEG–SAC.
This journal is ß The Royal Society of Chemistry 2013
RSC Adv., 2013, 3, 14254–14262 | 14255

View Article Online
Communication
RSC Advances
Scheme 1 Synthesis of benzo[f]chromene derivatives.
because of their broad spectrum of biological and pharmaceutical
activities. Chromene derivatives containing coumarin nuclei are
components of numerous natural products28 and, in view of the
immense importance of the chromene derivatives, in recent years
efforts have been made in developing new methodologies for the
synthesis of these compounds. A number of methods have been
reported for the synthesis of benzo[f]chromene and dihydropyr-
ano[3,2-c]chromene. However, there are only two reports in the
literature for the synthesis of dihydropyrano[2,3-c]chromene
derivatives from 3-hydroxycoumarin and the condensed product
of malononitrile and aldehyde. Notably, no reports are available in
the literature for the application of this type of carbon based solid
acid catalysts in the synthesis of organic molecules to date. We
advocated the use of the carbon based solid acid catalyst for the
synthesis of a diversified library of pyran derivatives and,
gratifyingly, the catalyst efficiently catalyzed the three-component
coupling reaction for the synthesis of all chromene derivatives.
Pyran derivatives are generally synthesized via the one-pot
three-component condensation reaction between a carbonyl
compound, a carbonyl compound possessing a reactive a-methy-
lene group and an alkylmalonate. Our initial study focused on the
development of the optimal reaction conditions for this transfor-
mation, which included solvent screening and the influence of the
catalyst weight. Initially, the reaction between 3-nitrobenzalde-
hyde, b-naphthol and malononitrile (Scheme 1) was investigated
in different solvents at 70 uC in the presence of 80 mg PEG–SAC.
Various solvents like toluene, acetonitrile, DMF, DMSO, ethanol,
and water were screened to test the efficiency of the catalyst and
the results are summarized in Table 1. The results clearly
indicated the superiority of water over the other solvents. This
phenomenon can be attributed to the high ionization of the
sulphonic acid group functionalized catalyst to provide H+ ions in
the aqueous medium.
Fig. 5 Energy dispersive X-ray analysis (EDX) of the catalyst.
The surface area and pore diameter of the catalyst were
determined by nitrogen adsorption. Fig.
6 shows the N2
adsorption–desorption isotherms by plotting the adsorbed volume
as a function of the gas pressure (P) normalized by the adsorptive
saturation pressure at 77 K (Po). The measured BET (Brunauer,
Emmett and Teller) surface area and NLDFT (Non-Local Density
Functional Theory) pore diameter of the PEG–SAC catalyst were
480 m2 g21 and 6.1 nm respectively. According to the International
Union of Pure and Applied Chemistry (IUPAC), the hysteresis loop
in Fig. 6 indicates the existence of mesoporous structures in the
PEG–SAC catalyst. The carbonaceous material PEG–SAC is
insoluble in most of the organic solvents (ethanol, DMF,
methanol, toluene, DCM, DMSO) including water. Hence, the
synthesized carbonaceous material can be used as a heteroge-
neous catalyst in a wide range of solvents.
Pyranochromenes and their derivatives have engrossed con-
siderable attention from synthetic and medicinal chemists
To find the optimized amount of solid acid catalyst, as shown
in (Fig. 7), the reaction was carried out by varying the amount of
Table 1 Influence of solvent on the synthesis of the benzo[f]chromene
derivative
Entry
Solvent
Time
Yield (%)a
1
2
3
4
5
6
Toluene
Acetonitrile
DMF
DMSO
Ethanol
H2O
1 h
1 h
1 h
1 h
30 min
16 min
49
52
67
69
70
92
Fig. 6 Nitrogen adsorption–desorption isotherms and the pore size distribution
a
Isolated yield of the pure product.
(inset) of the as-prepared PEG–SAC catalyst.
14256 | RSC Adv., 2013, 3, 14254–14262
This journal is ß The Royal Society of Chemistry 2013

View Article Online
RSC Advances
Communication
much higher catalytic activity in aqueous media than the
amphoteric nano ZnO. Table 2 (entries 1–12) clearly shows the
superior catalytic activity of the PEG–SAC catalyst. The products
were isolated, purified by recrystallization and characterized by
their melting point, 1H and 13C NMR, IR spectroscopy and HR-MS.
The X-ray crystal structure of 2c, shown in Fig. 9, further
confirmed the product identity. The results obtained with various
substrates are summarized in Table 2.
A mechanistic rationale for the reaction applying our carbon
based solid acid catalyst, portraying the probable sequence of
events, is given in Scheme 2. The reaction presumably proceeds in
three steps: a Knoevenagel condensation, a Michael addition, and
then an intramolecular cyclization as presented in Scheme 2. The
Knoevenagel adduct formed from the acid catalyzed condensation
of aldehydes and malononitrile subsequently undergoes the solid
acid catalyzed Michael reaction with carbonyl compounds
possessing a reactive a-methylene group (4-hydroxycoumarin,
b-naphthol, 3-hydroxycoumarin, dimedone and cyclohexane-1,3-
dione) that after cyclization affords the pyran annulated hetero-
cyclic systems. The high surface area of the catalyst not only
reduces the reaction time but also enhances the yield of the
chromene derivative due to its very large number of reaction sites.
The catalyst shows the most remarkable activity during the
formation of the pyrano[2,3-c]chromene derivative, as it stabilizes
the 1,2-dicarbonyl intermediate efficiently.
Fig. 7 Weight effect of the catalyst in the three-component coupling of
3-nitrobenzaldehyde, malononitrile and 1-naphthol.
the catalyst on the model reaction. The conversion of the
benzo[f]chromene derivative increased linearly with the catalyst
weight up to 80 mg and became almost steady when the amount
of catalyst was further increased beyond this. Therefore, 80 mg of
the catalyst (0.13 equivalent protons) is sufficient to catalyze the
reaction leading to the expected heterocyclic molecules in excellent
yield.
To assess the capability and efficiency of our catalyst with
respect to the reported catalysts for the preparation of benzo[f]-
chromene, the results have been tabulated in Table 3. In
comparison with other catalysts employed for the synthesis of
benzo[f]chromene from 4-methoxybenzaldehyde, 2-naphthol and
malononitrile, PEG–SAC shows a much higher catalytic activity in
terms of very short reaction times and mild conditions (Table 3).
A heterogeneous catalyst is more interesting when it can be
easily recovered and re-used. For this purpose, the reusability of
the catalyst was tested for the reaction of 3-nitrobenzaldehdye,
malononitrile and b-naphthol at 70 uC. After completion of the
reaction, water was removed under reduced pressure from the
reaction mixture and acetone was added to it for the dissolution of
the crude product. The catalyst was filtered, washed with acetone
and dried under vacuum at 100 uC for 12 h. As shown in Fig. 10,
the catalyst was recovered in excellent yield (90–95%) after each
new reaction. This recycled catalyst was used for the synthesis of
pyran derivatives applying the developed protocol. The catalyst was
found to be reusable for at least 5 cycles without considerable loss
of activity (run 1: 95% yield; run 5: 92% yield of the product).
Furthermore, the loading amount of the five times used catalyst
was determined by elemental analysis, and it was found that 1.31
mmol g21 of SO3H was still grafted onto the surface of the catalyst
compared to 1.48 mmol g21 for the fresh catalyst. These results
indicate that the catalyst is very stable and can endure these
reaction conditions.
Under the optimized reaction conditions, various aromatic
aldehydes and carbonyl compounds possessing
a reactive
a-methylene group (4-hydroxycoumarin, b-naphthol, 3-hydroxy-
coumarin, dimedone and cyclohexane-1,3-dione) were screened.
Indeed, there is no difference in reactivity between 4-hydroxycou-
marin, b-naphthol, dimedone or cyclohexane-1,3-dione, and the
corresponding pyran (Table 2) derivatives were formed within very
short reaction times (10–20 min), although 3-hydroxycoumarin
took longer times (1.5–2 h) for the formation of the dihydropyr-
ano[2,3-c]chromene derivative (Table 2, entries 1–12).
Since 4-hydroxycoumarin is the enol tautomer of a 1,3-
dicarbonyl compound, in the presence of an acid or base it can
act as a nucleophile and easily form chromene[3,2-c] derivatives.
But 3-hydroxycoumarin may be considered as the enol tautomer of
a 1,2-dicarbonyl compound (Fig. 8). During the formation of the
pyran derivative, 3-hydroxycoumarin passes through this very
unstable cyclic 1,2-dicarbonyl intermediate (Michael reaction step)
and hence it is a very poor Michael donor under acidic or basic
conditions, the formation of chromene[2,3-c] derivatives from it is
rather difficult and therefore the rate of the reaction is relatively
sluggish. Following these results, as summarized in Table 2, a
variety of aromatic aldehydes with electron-donating and electron-
withdrawing substituents were converted to 4H-pyrans in excellent
yields. Besides, our methodology has been applied successfully in
acid and base sensitive materials such as heteroaromatic
aldehydes, and the corresponding 4H-pyrans were obtained in
excellent yields without any by-product. In our previous work,27a
we have reported nano crystalline ZnO as an efficient catalyst for
the synthesis of dihydropyrano[2,3-c]chromene derivatives in
water, but PEG–SAC is a more effective catalyst compared to
ZnO for this synthesis. As PEG–SAC is a Brønsted acid, it shows a
Conclusions
In summary, we have developed a green, sustainable and
economic protocol for the one-pot three-component synthesis of
This journal is ß The Royal Society of Chemistry 2013
RSC Adv., 2013, 3, 14254–14262 | 14257

View Article Online
Communication
RSC Advances
Table 2 Scope of hydroxy compounds and aldehydes for pyran derivative synthesis
Entry
1
Hydroxy compound
Ar–CHO
Time
2.0 h
Producta
Yield (%)b
90
Reference
2a
27a
2
3
4
5
6
2.0 h
1.5 h
1.5 h
1.5 h
1.5 h
2b
2c
2d
2e
2f
87
95
93
92
94
27a
27a
27a
27a
27a
7
2.0 h
1.5 h
2.0 h
2.0 h
2g
2h
2i
90
92
90
83
27a
27a
27a
27a
8
9
10
2j
11
12
1.5 h
2.0 h
2k
2l
91
85
—
—
14258 | RSC Adv., 2013, 3, 14254–14262
This journal is ß The Royal Society of Chemistry 2013

View Article Online
RSC Advances
Communication
Table 2 (Continued)
Entry
13
Hydroxy compound
Ar–CHO
Time
Producta
Yield (%)b
91
Reference
15 min
3a
27e
14
15
16
17
18
10 min
15 min
14 min
14 min
14 min
3b
3c
3d
3e
3f
95
89
88
85
86
27e
27e
27e
27e
27e
19
20
21
15 min
16 min
16 min
3g
4a
4b
84
90
92
27e
26a
26a
22
12 min
4c
95
26a
23
24
25
26
27
15 min
10 min
15 min
12 min
12 min
5a
5b
5c
5d
5e
93
89
96
95
95
26f
26f
26f
26f
26f
This journal is ß The Royal Society of Chemistry 2013
RSC Adv., 2013, 3, 14254–14262 | 14259

View Article Online
Communication
RSC Advances
Table 2 (Continued)
Entry
28
Hydroxy compound
Ar–CHO
Time
Producta
Yield (%)b
92
Reference
16 min
6a
26f
29
30
31
16 min
14 min
14 min
6b
6c
6d
90
95
95
26f
26f
26f
a
b
Products were characterized by 1H NMR, 13C NMR, IR, and HR-MS data. Isolated yield of the pure product.
Fig. 8 3-Hydroxycoumarin and the 1,2-dicarbonyl intermediate.
a combinatorial library of diversified pyran fused heterocyclic
molecules with the aid of a SO3H-bearing carbonaceous solid
catalyst (PEG–SAC) developed by us for the first time. The highly
active, stable solid acid catalyst was prepared by carbonization of
PEG–SO3H at 200 uC. The catalysts are composed of polycyclic
aromatic carbons with SO3H groups. The very high surface area
and acid density of the catalyst will surely grab the attention of the
Scheme 2 A plausible mechanism for the PEG–SAC catalyzed three-component
biological and pharmaceutical industries as a very good replace-
ment for the homogeneous acid catalysts used in the synthesis of
organic molecules in the future.
coupling reaction for the synthesis of pyran derivatives.
Table 3 Comparison of different catalysts for the one-pot three-component
reaction of 4-methoxy-benzaldehyde, 2-naphthol and malononitrile
Entry Catalyst
T/uC Time
Yield (%) Reference
1
2
3
4
5
H
14[NaP5W30O110
]
100
120
100
120
70
3 h
1 h
92
88
26a
26b
26c
26d
Na2HPO4
[bmim]OH
CAN
100 min 80
30 min
20 min
89
90
PEG–SAC
This work
Experimental
Preparation of the solid acid catalyst from polyethylene glycol
At 0 uC, chlorosulfonic acid (10 mmol) was added to a solution of
PEG-6000 (1 mmol) in CH2Cl2 (10 ml), and the resulting solution
Fig. 9 X-ray crystal structure of 2c (CCDC 818608).
14260 | RSC Adv., 2013, 3, 14254–14262
This journal is ß The Royal Society of Chemistry 2013

View Article Online
RSC Advances
Communication
1H NMR (300 MHz, DMSO-d6; Me4Si): d 5.34 (s, 1H, CH), 7.18–
8.29 (m, 10H, Ar, NH2); 13C NMR (75 MHz, DMSO-d6; Me4Si): d
37.1, 56.1, 116.3, 119.0, 122.1, 124.7, 125.3, 130.3, 133.9, 134.6,
144.9, 148.1, 150.2, 153.9, 159.2; HRMS calcd. for C19H11N3O5 ([M
+ H]+): 361.0699; found: 361.0692.
Acknowledgements
We gratefully acknowledge the financial support from U.G.C
and Calcutta University. S.P. thanks U.G.C, New Delhi, India
for the grant of Senior Research fellowship. S. G. thanks CSIR,
New Delhi, India for the grant of his Senior Research
fellowship.
Fig. 10 Reusability study and recovery of the catalyst.
References
1 Y. R. Leshkov, J. N. Chheda and J. A. Dumesic, Science, 2006,
312, 1933.
2 (a) M. Bicker, J. Hirth and H. Vogel, Green Chem., 2003, 5, 280;
(b) Y. R. Leshkov, C. J. Barrett, Z. Y. Liu and J. A. Dumesic,
Nature, 2007, 447, 982.
was stirred at room temperature overnight. Then, the solution was
concentrated under vacuum, and ether was added to it. The
resulting precipitate was filtered and washed with ether three
times to afford PEG–OSO3H as a gummy solid.
The carbon based solid acid was prepared by hydrothermal
treatment of PEG–OSO3H. Carbon and SO3H precursor PEG–
OSO3H (6 g) were heated at 200 uC in a 100 ml Teflon
hydrothermal reactor, the conditions were maintained for 6 h at
the autogenous pressure and then, on cooling to room
temperature, a black amorphous solid was formed. The mesopor-
ous carbonaceous PEG derived solid acid catalyst was denoted as
PEG–SAC.
3 J. N. Chheda, Y. Roman-Leshkov and J. A. Dumesic, Green
Chem., 2007, 9, 342.
4 V. V. Ordomsky, J. van der Schaaf, J. C. Schouten and T.
A. Nijhuis, J. Catal., 2012, 287, 68.
5 (a) Z. H. Zhang, B. Liu and Z. B. Zhao, Carbohydr. Polym., 2012, 88,
891; (b) Y. Yang, C. W. Hu and M. M. Abu-Omar, Green Chem.,
2012, 14, 509; (c) B. R. Caes and R. T. Raines, ChemSusChem,
2011, 4, 353; (d) B. Kim, J. Jeong, D. Lee, S. Kim, H. J. Yoon, Y.
S. Lee and J. K. Cho, Green Chem., 2011, 13, 1503.
6 X. H. Qi, M. Watanabe, T. M. Aida and R. L. Smith, Green
Chem., 2008, 10, 799.
General procedure for the synthesis of 4H-pyran derivatives
A mixture of an aldehyde (1.1 mmol), malononitrile (1.1 mmol), a
carbonyl compound possessing a reactive a-methylene group (1.0
mmol), and PEG–SAC (0.080 g) in water (5 ml) was stirred at 70 uC
for a required period of time (TLC). After completion of the
reaction, water was removed under reduced pressure from the
reaction mixture and acetone was added to it for the dissolution of
the crude product. The acetone solution was filtered to remove the
catalyst. A solid was obtained upon concentration of the acetone
solution of the crude product extract. The product thus was
collected by filtration, washed with chilled aqueous ethanol and
finally recrystallized from ethanol to get the pure product.
7 (a) C. Carlini, M. Giuttari, A. M. R. Galletti, G. Sbrana, T. Armaroli
and G. Busca, Appl. Catal., A, 1999, 183, 295; (b) C. Carlini,
P. Patrono, A. M. R. Galletti and G. Sbrana, Appl. Catal., A, 2004,
275, 111.
8 M. Hara, T. Yoshida, A. Takagaki, T. Takata, J. N. Kondo,
K. Domen and S. Hayashi, Angew. Chem., Int. Ed., 2004, 43, 2955.
9 M. Toda, A. Takagaki, M. Okamura, J. N. Kondo, K. Domen,
S. Hayashi and M. Hara, Nature, 2005, 438, 178.
10 (a) A. Corma, Curr. Opin. Solid State Mater. Sci., 1997, 2, 63; (b)
G. Busca, Catal. Today, 1998, 41, 191; (c) A. Corma and
H. Garcia, Catal. Today, 1997, 38, 257; (d) S. K. Sikdar and S.
G. Howell, J. Clean. Prod., 1998, 6, 253.
11 (a) R. A. Sheldon and R. S. Downing, Appl. Catal., A, 1999, 189,
163; (b) Ch. Ramesh, J. Banerjee, R. Pal and B. Das, Adv. Synth.
Catal., 2003, 345, 557.
Selected spectral data
3-Amino-1-(4-chloro-phenyl)-5-oxo-1,5-dihydro-pyrano[2,3-
12 (a) M. Okamura, A. Takagaki, M. Toda, J. N. Kondo, T. Tatsumi,
K. Domen, M. Hara and S. Hayashi, Chem. Mater., 2006, 18,
3039; (b) K. Fukuhara, K. Nakajima, M. Kitano, H. Kato,
S. Hayashi and M. Hara, Chem-SusChem, 2011, 4, 778; (c)
M. Hara, ChemSusChem, 2009, 2, 129.
13 (a) Y. Tang, J. Oppenheimer, Z. Song, L. You, X. Zhang and R.
P. Hsung, Tetrahedron, 2006, 62, 10785; (b) T. C. McKee, R.
W. Fuller, C. D. Covington, J. H. Cardellina, R. J. Gulakowski, B.
L. Krepps, J. B. McMahon and M. R. Boyd, J. Nat. Prod., 1996,
59, 754; (c) T. C. McKee, C. D. Covington, R. W. Fuller, H.
R. Bokesch, S. Young, J. H. Cardellina, M. R. Kadushin, D.
D. Soejarto, P. F. Stevens, G. M. Cragg and M. R. Boyd, J. Nat.
Prod., 1998, 61, 1252; (d) E. J. Jung, B. H. Park and Y. R. Lee,
Green Chem., 2010, 12, 2003.
c]chromene-2-carbonitrile (2k)
Characteristics: Yellow crystalline solid; mp: 218 uC; IR (KBr): 2191,
1
1729, 1650, 1594 cm21; H NMR (300 MHz, DMSO-d6; Me4Si): d
4.84 (s, 1H, CH), 6.68 (s, 2H, NH2) 7.05–7.65 (m, 8H, Ar); 13C NMR
(75 MHz, DMSO-d6): d 37.6, 57.2, 116.2, 116.4, 118.8, 124.4, 125.9,
128.8, 130.0, 132.7, 133.9, 140.6, 150.1, 153.8, 158.7; HR-MS calcd.
for C19H11ClN2O3 ([M + H]+): 350.0458; found: 350.0451.
3-Amino-1-(3-nitro-phenyl)-5-oxo-1,5-dihydro-pyrano[2,3-
c]chromene-2-carbonitrile (2l)
Characteristics: Yellow crystalline solid; mp: 237 uC; IR (KBr): 2190,
1720, 1658, 1592, 1401 cm21
.
This journal is ß The Royal Society of Chemistry 2013
RSC Adv., 2013, 3, 14254–14262 | 14261

View Article Online
Communication
RSC Advances
14 (a) S. Kumar, D. Hernandez, B. Hoa, Y. Lee, J. S. Yang and
A. McCurdy, Org. Lett., 2008, 10, 3761; (b) M. Rawat,
V. Prutyanov and W. D. Wulff, J. Am. Chem. Soc., 2006, 128,
11044; (c) O. A. Fedorova, F. Maure, A. V. Chebunkova, Y.
P. Strokach, T. M. Valova, L. G. Kuzmina, J. A. K. Howard,
M. Wenzel, K. Gloe, V. Lokshin and A. Samat, J. Phys. Org.
Chem., 2007, 20, 469; (d) S. Delbaer, J.-C. Micheau and
G. Vermeersch, J. Org. Chem., 2003, 68, 8968.
15 A. Kumar, R. A. Maurya, S. A. Sharma, P. Ahmad, A. B. Singh,
G. Bhatia and A. K. Srivastava, Bioorg. Med. Chem. Lett., 2009,
19, 6447.
16 T. Raj, R. K. Bhatia, A. Kapur, M. Sharma, A. K. Saxena and M.
P. S. Ishar, Eur. J. Med. Chem., 2010, 45, 790.
17 F. M. Abdelrazek, P. Metz and E. K. Farrag, Arch. Pharm., 2004,
337, 482.
18 T. Symeonidis, K. C. Fylaktakidou, D. J. Hadjipavlou-Litina and
K. E. Litinas, Eur. J. Med. Chem., 2009, 44, 5012.
19 T. Raj, R. K. Bhatia, R. K. Sharma, V. Gupta, D. Sharma and M.
P. S. Ishara, Eur. J. Med. Chem., 2009, 44, 3209.
20 (a) M. M. Khafagy, A. H. F. A. El-Wahas, F. A. Eid and A. M. El-
Agrody, Farmaco, 2002, 57, 715; (b) W. P. Smith, L. S. Sollis, D.
P. Howes, C. P. Cherry, D. I. Starkey and N. K. Cobley, J. Med.
Chem., 1998, 41, 787; (c) A. G. Martinez and L. J. Marco, Bioorg.
Med. Chem. Lett., 1997, 7, 3165; (d) K. Hiramoto, A. Nasuhara,
K. Michiloshi, T. Kato and K. Kikugawa, Mutat. Res., Genet.
Toxicol. Environ. Mutagen., 1997, 395, 47.
21 (a) C. J. Li and Y. L. Li, U.S. Patent Appl. Publ. U.S. 2005222246
A1 20, 051, 006, 2005; (b) M. Ough, A. Lewis, E. A. Bey, J. Gao, J.
M. Ritchie, W. Bornmann, D. A. Boothman, L. W. Oberley and
J. J. Cullen, Cancer Biol. Ther., 2005, 4, 95.
22 (a) V. F. De Andrade-Neto, M. O. F. Goulart, J. F. Da Silva Filho,
M. J. Da Silva, M. D. C. F. R. Pinto, A. V. Pinto, M. G. Zalis, L.
H. Carvalho and A. U. Krettli, Bioorg. Med. Chem. Lett., 2004, 14,
1145; (b) P. S. Elisa, E. B. Ana, A. G. Ravelo, D. J. Yapu and A.
G. Turba, Chem. Biodiversity, 2005, 2, 264.
23 G. P. Ellis, A. Weissberger and E. C. Taylor, John Wiley: New
York, NY, 1977, 11, Chapter 11.
24 E. A. Hafez, M. H. Elnagdi, A. G. A. Elagemey and F. M. A. A. El-
Taweel, Heterocycles, 1987, 26, 903.
25 (a) T. S. Jin, A. Q. Wang, X. Wang, J. S. Zhang and T. S. Li,
Synlett, 2004, 871; (b) D. Q. Shi, S. Zhang, Q. Y. Zhuang, S. J. Tu
and H. W. Hu, Chin. J. Org. Chem., 2003, 23, 877; (c) L. M. Wang,
J. H. Shao, H. Tian, Y. H. Wang and B. Liu, J. Fluorine Chem.,
2006, 127, 97; (d) S. Balalaie, M. Bararjanian, A. M. Amani and
B. Movassagh, Synlett, 2006, 263; (e) Y. Peng and G. Song, Catal.
Commun., 2007, 8, 111; (f) D. Kumar, V. B. Reddy, Sh. Sharadb,
U. Dube and S. Kapur, Eur. J. Med. Chem., 2009, 44, 3805; (g)
S. Banerjee, A. Horn, H. Khatri and G. Sered, Tetrahedron Lett.,
2011, 52, 1878; (h) A. Hasaninejada, M. Shekouhy, N. Golzar,
A. Zare and M. M. Doroodmand, Appl. Catal., A, 2011, 402, 11.
26 (a) M. M. Heravi, K. Bakhtiari, V. Zadsirjan, F. F. Bamoharramb
and O. M. Heravi, Bioorg. Med. Chem. Lett., 2007, 17, 4262; (b) X.-
Y. Meng, H.-J. Wang, C.-P. Wang and Z.-H. Zhang, Synth.
Commun., 2011, 41, 3477; (c) K. Gong, H.-L. Wang, D. Fang and
Z.-L. Liu, Catal. Commun., 2008, 9, 650; (d) A.-Q. Zhang,
M. Zhang, H.-H. Chen, J. Chen and H.-Y. Chen, Synth.
Commun., 2007, 37, 231; (e) A. Kumar, S. Sharma, R.
A. Maurya and J. Sarkar, J. Comb. Chem., 2010, 12, 20; (f)
G. Zhang, Y. Zhang, J. Yan, R. Chen, S. Wang, Y. Ma and
R. Wang, J. Org. Chem., 2012, 77, 878.
27 (a) S. Paul, P. Bhattacharyya and A. R. Das, Tetrahedron Lett.,
2011, 52, 4636; (b) S. Paul and A. R. Das, Tetrahedron Lett., 2012,
53, 2206; (c) S. Paul and A. R. Das, Catal. Sci. Technol., 2012, 2,
1130; (d) P. P. Ghosh, G. Pal, S. Paul and A. R. Das, Green Chem.,
2012, 14, 2691; (e) P. P. Ghosh and A. R. Das, J. Org. Chem.,
2013, 78, 6170.
28 M. Rueping, E. Sugiono and E. Merino, Chem. Eur. J., 2008, 14,
6329.
14262 | RSC Adv., 2013, 3, 14254–14262
This journal is ß The Royal Society of Chemistry 2013