Novel one-pot synthesis of 4H-chromene derivatives using amino functionalized silica gel catalyst

Article abstract of DOI:10.1016/j.cclet.2013.12.016

A simple, efficient, and environmentally benign method for the synthesis of 4H-chromene derivatives was developed using well ordered and recoverable amino functionalized silica gel as a base catalyst. The 4H-chromene derivatives were obtained in short tim

Full text of DOI:10.1016/j.cclet.2013.12.016

Chinese Chemical Letters 25 (2014) 455–458
Contents lists available at ScienceDirect
Chinese Chemical Letters
journal homepage: www.elsevier.com/locate/cclet
Original article
Novel one-pot synthesis of 4H-chromene derivatives using amino
functionalized silica gel catalyst
Vijaykumar M. Joshi a, Rupali L. Magar b, Prashant B. Throat c, Sunil U. Tekale b,
Bhagavan R. Patil d, Mangal P. Kale b, Rajendra P. Pawar b,
*
a Department of Chemistry, Karmveer Ramraoji Aher Arts, Science and Commerce College, Deola 423 105, MS, India
b Department of Chemistry, Deogiri College, Aurangabad 431 005, MS, India
c Department of Chemistry, Dnyanopasak College, Parbhani 431 401, MS, India
d Department of Chemistry, Sharda Mahavidyalaya, Parbhani 431 401, MS, India
A R T I C L E I N F O
A B S T R A C T
Article history:
A simple, efficient, and environmentally benign method for the synthesis of 4H-chromene derivatives
was developed using well ordered and recoverable amino functionalized silica gel as a base catalyst. The
4H-chromene derivatives were obtained in short time and excellent yield (87%–96%) by three
component reaction of aldehydes, malononitrile and cyclic 1,3-diketones in water at 70 8C.
ß 2013 Rajendra P. Pawar. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights
reserved.
Received 27 July 2013
Received in revised form 25 November 2013
Accepted 29 November 2013
Available online 25 December 2013
Keywords:
Aldehydes
4H-Chromenes
Amino functionalized silica gel
1. Introduction
catalysts offers several advantages in process development,
particularly the separation of products from catalyst, and recycling
Base-catalyzed condensation and addition reactions such as the
Aldol, Knoevenagel and Michael reactions are well reported in the
literature for the production of drugs, fragrances, and chemical
intermediates [1–4]. The use of novel environmentally friendly
solid catalysts for the synthesis of biologically potent heterocyclic
compounds has become one of the most active areas of research.
Heterogeneous catalysts, particularly the solid-base catalysts
synthesized by the functionalization of several solid-state materi-
als are capable of catalyzing various C–C coupling reactions [5,6].
Recently, mesoporous silica (OMS) and related materials have
become popular as catalysts and adsorbents and have found
extensive applications as containers for cluster/nanowire growth,
etc. [7]. These materials have several advantages such as tunable
pore diameter and high surface area, for which they have emerged
as effective heterogeneous catalysts in organic synthesis [8].
Aminopropyl functionalized mesoporous silica materials are
reported to be effective base catalysts for Knoevenagel condensa-
tion [9], Aldol condensation [10], Michael addition [9], epoxidation
reactions [11], and Claisen–Schmidt condensations [12]. Further-
more, the development of biomimetic catalysts is also well
reported in the literature [13]. The use of such heterogeneous
of catalyst in reactor. Solid acidic and basic catalysts are
alternatives for clean technologies and sustainable chemistry for
different processes.
Tetrahydrochromene moiety is an important class of benzo-
pyran derivatives found in many natural products [14]. More
specifically, 2-amino-4H-chromene-3-carbonitrile derivatives
possess many biological activities such as anticancer, anticoagu-
lant, antibacterial, and fungicidal properties [15]. These com-
pounds find extensive applications in different fields, such as
cosmetics, pigments, and agrochemicals [16]. Polyfunctionalized
4H-pyrans constitute the essential part of several natural
products [17] and are also known as potential calcium channel
antagonists [18]. As a result of widespread applications, the
synthesis of these compounds has attracted a lot of interest. From
the literature survey, numerous methods have been reported for
the synthesis of tetrahydrochromene derivatives by one pot three
component condensation of aldehyde, malononitrile and 1,3-
dicarbonyl compounds using acidic or basic catalysts. Mola et al.
documented borax catalyzed three component coupling of tetra-
hydrochromene in refluxing ethanol [19]. Silica-bonded
N-propylpiperazine sodium n-propionate was employed as a
recyclable catalyst for the synthesis of tetrahydrochromene
derivatives [20]. Nano-ZnO catalyzed synthesis of dihydropyr-
ano[2,3-c]chromenes can be accomplished in aqueous medium [21].
The other methods used for the synthesis of these compounds
*
Corresponding author.
E-mail address: rppawar@yahoo.com (R.P. Pawar).
1001-8417/$ – see front matter ß 2013 Rajendra P. Pawar. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
http://dx.doi.org/10.1016/j.cclet.2013.12.016

456
V.M. Joshi et al. / Chinese Chemical Letters 25 (2014) 455–458
O
O
R
O
CN
NH
O
CN
Aminopropylated sillica gel
+
+
o
R
H
Water, 70 C, 45-120 min
O
CN
3
2
4(a-n)
1(a-n)
2
Scheme 1. Synthesis of 2-amino-5-oxo-4-phenyl-5,6-dihydro-4H-benzo[H]chromene-3-carbonitrile derivatives.
involve basic catalysts such as piperidine [22], morpholine, pyridine
[23], triethylamine [24] and sodium bromide [25]. The reported
methods still have drawbacks such as long reaction time, high
reaction temperature and use of toxic organic solvents. Therefore,
development of a simpler synthesis method for chromene deriva-
tives becomes essential. In the present study we report the synthesis
of 2-amino-5-oxo-4-phenyl-5,6-dihydro-4H-benzo[H]chromene-
3-carbonitrile derivatives by the reaction of aldehyde (1a) with
5,5-dimethylcyclohexane-1,3-dione (2) and malononitrile (3) at
70 8C using aminopropylated SiO2 (AP-SiO2) as a polyamine
heterogeneous base catalyst (Scheme 1).
product, ethyl acetate was added and the solid catalyst was filtered
off. The organic layer was evaporated to obtain the solid product.
The obtained product was purified by recrystallization using ethyl
acetate to get the desired compound 4a–n. All compounds were
characterized by comparing their spectral data with those reported
in literature [15,26–27]. Spectral data for representative and newly
synthesized compounds is listed below.
2-Amino-7,7-dimethyl-5-oxo-4-phenyl-5,6,7,8-tetrahydro-
4H-chromene-3-carbonitrile (4a): White solid, mp 235–237 8C, 1H
NMR (300 MHz, CDCl3):
d 7.79–7.89 (m, 2H), 7.41–7.50 (m, 1H),
6.88–7.04 (m, 2H), 6.57 (brs, 2H, NH), 4.29 (s, 1H), 2.58 (s, 2H), 2.26
(m, 1H), 2.01 (m, 1H), 1.23 (s, 3H), 0.84 (s, 3H); 13C NMR (75 MHz,
2. Experimental
CDCl3): d201.2, 162.3, 155.8, 145.6, 128.7, 127.5, 119.2, 112.1, 57.6,
49.9, 40.3, 39.9, 36.1, 27.4; GC–MS: m/z 294 (M+); Elem. Anal.
Calcd. for C18H18N2O2: C, 73.45; H, 6.16; N, 9.52; O, 10.87; found: C,
73.43; H, 6.18; N, 9.54; O, 10.90.
All solvents were used as commercial grade without further
purification. Silica gel coated aluminium sheets (Merck made)
were used for thin layer chromatography to monitor progress of
reactions. The column chromatography was done over silica gel
(80–120 mesh). Melting points were determined in an open
capillary tube and are uncorrected. 1H NMR and 13C NMR spectra
were recorded on a Bruker 300 MHz spectrometer in CDCl3 solvent.
Mass spectra were taken on Polaris-Q Thermoscientific GC–MS.
Silica gel supported polyamine catalyst was prepared by a known
literature process [27].
2-Amino-7,7-dimethyl-5-oxo-4-(3,4,5-trimethoxyphenyl)-
5,6,7,8-tetrahydro-4H-chromene-3-carbonitrile (4f): Yellow
solid, mp 247–249 8C, 1H NMR (300 MHz, CDCl3):
d 7.29–7.41
(m, 2H), 6.71 (brs, 2H, NH), 4.22 (s, 1H), 3.73 (s, 9H), 2.51 (s, 2H),
2.23 (m, 1H), 2.17 (m, 1H), 1.10 (s, 3H), 0.92 (s, 3H); 13C NMR
(75 MHz, CDCl3):
d 201.1, 160.0, 157.8, 132.0, 129.6, 129.0,
119.1, 107.2, 106.4, 60.3, 59.3, 57.1, 50.0, 38.0, 32.3, 28.9;
GC–MS m/z 384 (M+); Elem. Anal. Calcd. for C21H24N2O5: C,
65.61; H, 6.29; N, 7.29; O, 20.81; found: C, 65.63; H, 6.26; N,
7.31; O, 20.83.
2.1. General procedure for the synthesis of 4H-chromene derivatives
2-Amino-7,7-dimethyl-5-oxo-4-(2,3-dichlorophenyl)-5,6,7,8-
tetrahydro-4H-chromene-3-carbonitrile (4i): White solid, mp
The mixture of aromatic aldehyde (1 mmol), 5,5-dimethylcy-
clohexane-1,3-dione 2 (1 mmol), and malononitrile 3 (1 mmol)
was taken in water. To this mixture 10 mol% of solid aminopro-
pylated SiO2 catalyst was added. The reaction mixture was stirred
at 70 8C for the appropriate time (as shown in Table 1) and the
progress of reaction was monitored by thin layer chromatography.
After completion of reaction as indicated by TLC, the reaction
mixture was cooled at room temperature. The solvent was
removed under vacuum to obtain the crude product. To the crude
225–227 8C, 1H NMR (300 MHz, CDCl3):
d 7.17–7.21 (m, 1H),
7.40–7.47 (m, 1H), 7.82–7.90 (m, 1H), 6.72 (brs, 2H, NH), 4.24 (s,
1H), 2.61 (s, 2H), 2.28 (m, 1H), 2.06 (m, 1H), 0.94 (s, 3H), 0.74 (s,
3H); 13C NMR (75 MHz, CDCl3):
d 200.7, 159.8, 154.0, 140.1, 131.3,
130.2, 130.0, 119.2, 113.2, 67.6, 60.0, 44.3, 41.2, 32.1, 28.6; GC–MS:
m/z 363 (M+); Elem. Anal. Calcd. for C18H16Cl2N2O2: C, 59.52; H,
4.44; Cl, 19.52; N, 7.71; O, 8.81; found: C, 59.53; H, 4.43; Cl, 19.55;
N, 7.69; O, 8.83.
Table 1
Synthesis of 4H-benzo[b]pyran derivatives using aminopropylated silica gel catalyst.
Entry
R
Product
Time (min)
Yield (%)a
Mp (8C)
Obs
Lit
1
2
Ph
4a
4b
4c
4d
4e
4f
90
60
93
94
96
89
95
96
92
89
88
90
92
89
87
90
235–237
208–210
223–225
199–200
200–202
247–249
213–214
201–203
225–227
152–154
209–211
210–212
187–189
201–203
234–236 [20]
209–210 [15]
224–226 [21]
197–199 [25]
201–203 [26]
–
4-Me-C6H4
4-OH-C6H4
4-Br-C6H4
3
120
90
4
5
4-OMe-C6H4
3,4,5-OMe-C6H2
4-Cl-C6H4
120
150
90
6
7
4g
4h
4i
215–216 [25]
200–202 [25]
–
8
2-Cl-C6H4
90
9
2,3-Cl-C6H3
4-NO2-C6H4
3-NO2-C6H4
4-F-C6H4
90
10
11
12
13
14
4j
45
151–153 [20]
210–212 [20]
208–210 [25]
–
4k
4l
60
60
3-Pyridine carbaldehyde
Furfuraldehyde
4m
4n
90
90
198–200 [26]
a
Isolated yield.

V.M. Joshi et al. / Chinese Chemical Letters 25 (2014) 455–458
457
2-Amino-7,7-dimethyl-5-oxo-4-(pyridin-3-yl)-5,6,7,8-tetrahy-
dro-4H-chromene-3-carbonitrile (4m): Brownish solid; mp 187–
189 8C, 1H NMR (300 MHz, CDCl3):
7.17–7.21 (m, 1H), 7.40–7.47
d
(m, 1H), 7.82–7.90 (m, 1H), 6.72 (brs, 2H, NH), 4.24 (s, 1H), 2.61 (s,
2H), 2.28 (m, 1H), 2.06 (m, 1H), 0.94 (s, 3H), 0.74 (s, 3H); 13C NMR
(75 MHz, CDCl3):
d 200.0, 161.3, 154.0, 153.6, 142.8, 135.1, 129.9,
122.8, 119.1, 114.1, 59.9, 53.5, 38.1, 37.5, 31.3, 30.7; GC–MS: m/z
295 (M+); Elem. Anal. Calcd. for C17H17N3O2: C, 69.14; H, 5.80; N,
14.23; O, 10.83; found: C, 69.15; H, 5.77; N, 14.25; O, 10.81.
2.2. Synthesis of solid aminopropylated SiO2
Silica gel was synthesized under acidic conditions. A known
weight of sodium silicate solution (23.31 SiO2%; 7.48 Na2O%) was
diluted with deionized water. 12% (w/v) SiO2 was added to 5.1 mol/L
H2SO4 solution under stirring with a peristaltic pump over
12.5 min at room temperature to adjust the SiO2 concentration
to 8% (w/v), aged for 2 h, and then kept at 100 8C for 12 h in a
closed Simax glass bottle. The gel obtained was washed until it
was sulfate free (BaCl2 test), dried at 100 8C in an oven, and
further calcined at 600 8C for 6 h. Samples were cooled under
vacuum and stored in a capped bottle over P2O5 in a desiccator.
Surface functionalization of the silica gel was carried out by
suspending the gel in a solution of 3-aminopropyltrimethox-
ysilane in dry toluene (solid:liquid, 10:100, w/v) and refluxed at
boiling temperature for 24 h. Samples were filtered, washed
with isopropanol thoroughly, and dried at 100 8C for overnight.
Two different functionalized silica samples were prepared with
APTMS using different APTMS: silica ratios (w/w), viz. 0.1
(0.56 mmol/g), which were designated as GN1. The synthesized
material was characterized by powder X-ray diffraction and 29Si
solid state NMR analysis.
Fig. 2. 29Si MAS NMR spectra of silica gel and aminopropyl functionalized silica gels.
attributed to silicon in the siloxane binding environment
without hydroxyl groups Q4[(SiO)4Si], isolated silanol groups
Q3[(SiO)3Si–OH], and geminal silanol groups Q2[(SiO)2–Si–
(OH)2] of the silica gel.
3. Results and discussion
The presence of several free NH2 groups in the catalyst (such as
GN3) [28] may lead to the formation of excess hydrogen bonding
with acidic hydrogens of substrates such as phenols and hence may
require prolonged time for completion of reaction. In the case of
the GN 1 catalyst the probability of such interactions is less due to
the presence of a single NH2 group. Hence, it catalyzes the reaction
more efficiently in a short time to afford the corresponding
products in high yields.
Powder X-ray diffraction: Powder X-ray diffraction (PXRD)
patterns of functionalized silica showed the hexagonal structure of
GN1; a typical mesoporous structure with three sharp peaks
corresponding to the (1 0 0), (1 1 0), and (2 0 0) planes (Fig. 1). It
has been seen that the value of d1 0 0 and a0 remained almost
constant with the standard deviation of 0.35, indicating that the
surface modification did not result in structural properties of GN1.
29Si NMR spectra: The 29Si NMR spectra of silica gel samples
treated at different temperatures and functionalized silica gels are
Preliminary efforts were mainly focused on the evaluation of
different molar ratios of the catalyst AP-SiO2. Initially, the reaction
was carried out using 5 mol% of the catalyst in ethanol; the product
4a was obtained in lower than 52% yield within 12 h. When the
reaction was carried out using 10 mol% of catalyst, the reaction was
completed in 5.5 h and the yield obtained of product 4a was 64%.
Further increase in catalyst concentration did not show any
significant effect on reaction time and yield of 4a. The reaction
proceeds well in the presence of 10 mol% of the catalyst in ethanol
at room temperature but require longer time for completion. As the
temperature of reaction was raised slowly (Table 2); it was found
that the reaction proceeds giving excellent yield at 70 8C
temperature within 1.5 h. Further increase in reaction temperature
to 80 8C showed similar results without change in yield or reaction
time, and thus the optimized reaction conditions involve the use of
10 mol% of the catalyst at 70 8C with a 1.5 h reaction time.
Under the optimized reaction conditions, the ability of catalyst
was explored in multicomponent reaction. Both electron-rich and
electron deficient aryl aldehydes afforded 4H-chromene deriva-
tives in 73%–98% yield in relatively short reaction times.
Comparatively, the rate of reaction of electron-deficient aryl
aldehyde was faster than the electron-rich aryl aldehyde. 4H-
Chromene derivatives formed were obtained in pure form by
shown in Fig. 2. The three peaks at
d
À112, À102 and À92 can be
Table 2
Effect of temperature on synthesis of 4a.
Entry
Temperature (8C)
Time (h)
Yield (%)a
1
2
3
4
5
r.t.
50
60
70
80
4.5
3.0
2.0
1.5
1.5
69
78
86
93
92
a
Fig. 1. PXRD patterns of silica gel G and aminopropylated silica gel.
Isolated yield.

458
V.M. Joshi et al. / Chinese Chemical Letters 25 (2014) 455–458
References
100
80
60
40
20
0
92
92
90
88
84
[1] G.J. Kelly, F. King, F. Kett, Waste elimination in condensation reactions of indus-
trial importance, Green Chem. 4 (2002) 392–399.
[2] J. Weitkamp, M. Hunger, U. Rymsa, Base catalysis on microporous and mesopor-
ous materials: recent progress and perspectives, Microporous Mesoporous Mater.
48 (2001) 255–270.
[3] R.A. Sheldon, Atom efficiency and catalysis in organic synthesis, Pure Appl. Chem.
72 (2000) 1233–1246.
[4] A. Zapf, M. Beller, Fine chemical synthesis with homogeneous palladium cata-
lysts: examples, status and trends, Top. Catal. 19 (2002) 101–109.
[5] B.M. Choudary, M.L. Kantam, P. Sreekanth, et al., Knoevenagel and Aldol con-
densations catalysed by a new diamino-functionalised mesoporous material, J.
Mol. Catal. A 142 (1999) 361–365.
[6] Y. Kubota, Y. Nishizaki, H. Ikeya, et al., Organic silicate hybrid catalysts based on
various defined structures for Knoevenagel condensation, Microporous Mesopor-
ous Mater. 70 (2004) 135–149.
1
2
3
4
5
Runs
[7] Y. Wan, D. Zhao, On the controllable soft-templating approach to mesoporous
silicates, Chem. Rev. 107 (2007) 2821–2860.
[8] Q.Q. Wang, D.F. Shantz, Ordered mesoporous silica-based inorganic nanocompo-
sites, J. Solid State Chem. 181 (2008) 1659–1669.
Fig. 3. Reusability of solid aminopropylated SiO2 as a catalyst for the synthesis of 4a.
[9] X.G. Wang, K.S.K. Lin, J.C.C. Chan, S.F. Cheng, Direct synthesis and catalytic
applications of ordered large pore aminopropyl-functionalized SBA-15 mesopor-
ous materials, J. Phys. Chem. B 109 (2005) 1763–1769.
[10] Y. Kubota, K. Goto, S. Miyata, et al., Enhanced effect of mesoporous silica on base-
catalyzed Aldol reaction, Chem. Lett. 32 (2003) 234–235.
[11] A.C. Blanc, D.J. Macquarrie, S. Valle, et al., The preparation and use of novel
immobilised guanidine catalysts in base-catalysed epoxidation and condensation
reactions, Green Chem. 2 (2000) 283–288.
[12] X.G. Wang, Y.H. Tseng, J.C.C. Chan, S.F. Cheng, Catalytic applications of amino-
propylated mesoporous silica prepared by a template-free route in flavanones, J.
Catal. 233 (2005) 266–275.
[13] M. Luechinger, A. Kienhofer, G.D. Pirngruber, Immobilized complexes of metals
with amino acid ligands – a first step toward the development of new biomimetic
catalysts, Chem. Mater. 18 (2006) 1330–1336.
[14] D. Lu, Y. Li, Y. Gong, Organocatalytic asymmetric tandem Michael addition-
hemiacetalization: a route to chiral dihydrocoumarins, chromanes, and 4H-
chromenes, J. Org. Chem. 75 (2010) 6900–6907.
[15] W. Kemnitzer, J. Drewe, S. Jiang, et al., Discovery of 4-aryl-4H-chromenes as a new
series of apoptosis inducers using a cell and caspase-based high throughput
screening assay. 4. Structure–activity relationships of N-alkyl substituted pyrrole
fused at the 7,8-positions, J. Med. Chem. 51 (2008) 417–423.
[16] E.C. Witte, P. Neubert, A. Roesch, 7-(Piperazinyl propoxy)-2H-1-benzopyran-2-
ones, Ger. Offen DE, 3427985, Chem. Abstr. 104 (1986) 224915f.
[17] J. Kuthan, Pyrans, thiopyrans, and selenopyrans, Adv. Heterocycl. Chem. 34 (1983)
145–157.
recrystallization process. In order to extend the scope of amino
propylated silica gel catalyzed multicomponent reactions, it was
also successfully applied to aromatic heterocyclic aldehydes
(Table 1).
After performing the condensation of C–H activated ketones
with aromatic aldehydes and alkylmalonates for the synthesis of
2-amino-7,7-dimethyl-5-oxo-4-phenyl-5,6,7,8-tetrahydro-4H-
chromene-3-carbonitrile derivatives under present conditions,
ethyl acetate was added to the reaction mixture. The catalyst
was separated by
a simple filtration from the resulting
heterogeneous mixture, washed with water 3–4 times, dried,
and reused for consecutive runs under the same reaction
conditions. The average isolated yield of 4a for five consecutive
runs was 89%, which clearly demonstrates the practical
reusability of this catalyst (Fig. 3). Structure of the recovered
catalyst was also studied with XRD analysis. The powder XRD
pattern of the recovered catalyst was similar to that of the fresh
catalyst indicating that the recovered catalyst remains unaf-
fected in its structure.
[18] M. Suarez, E. Salfran, Y. Verdecia, et al., X-ray and theoretical structural study of
novel 5,6,7,8-tetrahydrobenzo-4H-pyrans, Tetrahedron 58 (2002) 953–960.
[19] A. Molla, E. Hossain, S. Hussain, Multicomponent domino reactions: borax cata-
lyzed synthesis of highly functionalised pyran-annulated heterocycles, RSC Adv. 3
(2013) 21517–21523.
4. Conclusion
[20] K. Niknam, A. Jamali, Silica-bonded N-propylpiperazine sodium n-propionate as
recyclable basic catalyst for synthesis of 3,4-dihydropyrano[c]chromene deriva-
tives and biscoumarins, Chin. J. Catal. 33 (2012) 1840–1849.
[21] S. Paul, P. Bhattacharyya, A.R. Das, One-pot synthesis of dihydropyrano[2,3-
c]chromenes via a three component coupling of aromatic aldehydes, malononi-
trile, and 3-hydroxycoumarin catalyzed by nano-structured ZnO in water: a green
protocol, Tetrahedron Lett. 52 (2011) 4636–4641.
[22] N. Martin, C. Pascual, C. Seoane, J.L. Soto, The use of some activated nitriles in
heterocyclic syntheses, Heterocycles 26 (1987) 2811–2816.
[23] A.F. Harb, A.M. Hesien, S.A. Metwally, M.H. Elnagdi, The reaction of ethyl 6-amino-
5-cyano-4-aryl-2-methyl-4H-pyran-3-carboxylate with nucleophilic reagents,
Ann. Chem. (1989) 585–590.
In summary, we synthesized silica gel supported amino
functionalized heterogeneous solid aminopropylated SiO2 as a
base catalyst. After structural characterization, its capability in
organic transformations was investigated to synthesize 2-amino-
7,7-dimethyl-5-oxo-4-phenyl-5,6,7,8-tetrahydro-4H-chromene-
3-carbonitrile 4a. The catalyst was found to catalyze the reaction
under mild reaction conditions. The solid catalyst aminopropy-
lated SiO2 was efficient for the synthesis of 4a and showed
excellent stability and activity. The scope of the catalyst was
further explored to catalyze the synthesis of 4H-chromene
derivatives using different aromatic and heterocyclic aldehydes.
The reactions proceeded well on all kind of aldehydes giving
excellent yield of products in shorter reaction time. Finally, silica
supported amine catalyst can be recovered by simple filtration
procedure and reused without much loss in its activity.
[24] S.E. Zayed, E.I. Abou-Elmaged, S.A. Metwally, M.H. Elnagdi, Reactions of six-
membered heterocyclic b-enaminonitriles with electrophilic reagents, Chem.
Commun. 56 (1991) 2175–2182.
[25] I. Devi, P.J. Bhuyan, Sodium bromide catalysed one-pot synthesis of tetrahydro-
benzo[b]pyrans via
a three-component cyclocondensation under microwave
irradiation and solvent free conditions, Tetrahedron Lett. 45 (2004) 8625–
8627.
[26] X.S. Wang, D.Q. Shi, S.J. Tu, C.S. Yao, A convenient synthesis of 5-oxo-5,6,7,8-
tetrahydro-4H-benzo-[b]-pyran derivatives catalyzed by KF-alumina, Syn. Com-
mun. 33 (2003) 119–126.
Acknowledgments
[27] V. Manu, H.M. Mody, H.C. Bajaj, R.V. Jasra, Adsorption of Cu2+ on amino functio-
nalized silica gel with different loading, Ind. Eng. Chem. Res. 48 (2009) 8954–8960.
[28] R.L. Magar, P.B. Thorat, V.B. Jadhav, et al., Silica gel supported polyamine: a
versatile catalyst for one pot synthesis of 2-amino-4H-chromene derivatives, J.
Mol. Catal. A: Chem. 374–375 (2013) 118–124.
The authors are thankful to the Principal, DSM College, Parbhani
and Principal, Deogiri College, Aurangabad for encouragement
during the process of carrying out this work.