Silica bonded n-propyl-4-aza-1-azoniabicyclo[2.2.2]octane chloride (SB-DABCO): A highly efficient, reusable and new heterogeneous catalyst for the synthesis of 4H-benzo[b]pyran derivatives

Article abstract of DOI:10.1016/j.apcata.2011.04.012

The reaction of 3-chloropropyl silica with diazabicyclo[2.2.2]octane in dry acetone affords silica bonded n-propyl-4-aza-1-azoniabicyclo[2.2.2]octane chloride (SB-DABCO) as a new basic catalyst. The catalyst is used for the efficient synthesis of 4H-benzo

Full text of DOI:10.1016/j.apcata.2011.04.012

Applied Catalysis A: General 402 (2011) 11–22
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Silica bonded n-propyl-4-aza-1-azoniabicyclo[2.2.2]octane chloride (SB-DABCO):
A highly efficient, reusable and new heterogeneous catalyst for the synthesis of
4H-benzo[b]pyran derivatives
Alireza Hasaninejada,∗, Mohsen Shekouhya, Nooshin Golzara,
Abdolkarim Zareb, Mohammad Mahdi Doroodmandc
a Department of Chemistry, Faculty of Sciences, Persian Gulf University, Bushehr 75169, Iran
b Department of Chemistry, Payame Noor University (PNU), Iran
c Department of Chemistry, College of Science, Shiraz University, Shiraz 71454, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction of 3-chloropropyl silica with diazabicyclo[2.2.2]octane in dry acetone affords silica bonded
n-propyl-4-aza-1-azoniabicyclo[2.2.2]octane chloride (SB-DABCO) as a new basic catalyst. The catalyst
is used for the efficient synthesis of 4H-benzo[b]pyran derivatives via one-pot three-component reaction
of cyclic ketones/1,3-diketones with aromatic aldehydes and alkylmalonates.
Received 1 October 2010
Received in revised form 20 March 2011
Accepted 11 April 2011
Available online 16 April 2011
© 2011 Elsevier B.V. All rights reserved.
Keywords:
Silica bonded n-propyl-4-aza-1-
azoniabicyclo[2.2.2]octane chloride
(SB-DABCO)
4H-Benzo[b]pyran
Silica supported catalyst
Alkylmalonate
5,5-dimethylcyclohexane-1,3-dione
1. Introduction
base catalysts have not been extensively studied [8]. The potential
use of microporous and mesoporous base catalysts in fine chemi-
Base-catalyzed condensation and addition reactions are indus-
trially important in the production of drugs, fragrances and
chemical intermediates [1]. One of the most important classes
of these reactions is C–C coupling reactions, such as Aldol and
Knoevenagel condensations as well as Michael reactions [2–4].
Conventionally, almost stoichiometric amounts of homogeneous
bases are used for such purposes [5,6,1]. In such systems, several
difficult issues arise, of which we may address to the isolation
of the products, the corrosive nature of the reaction mixture
and formation of large amounts of waste materials. Therefore,
improved synthesis routes in terms of product purity, yield, and
minimal waste formation are highly desirable. Moreover, replace-
ment of liquid acids and bases with the corresponding cleaner solid
alternatives, possessing desirable characteristics such as being non-
stoichiometric, non-corrosive and reusable, is necessary in view of
environmentally benign. Solid acid catalysts have been extensively
studied and applied in numerous reactions so far [7]; however, solid
cal production is enormous [9]. These heterogeneous catalysts are
known to suppress side reactions, which include self-condensation
and oligomerization, resulting in better selectivity and product
yield. This means cost and energy savings for the downstream sep-
aration and purification of the product. It also avoids the complex
neutralization and separation steps needed to recover the homo-
geneous base catalysts from the reaction mixture. The recovered
solid catalysts can be readily regenerated for further use.
1,4-Diazabicyclo[2.2.2]octane (DABCO), a cage-like compound,
is a small diazabicyclic molecule with weak alkalescency and
medium-hindrance [10]. DABCO has been applied as an inex-
pensive, eco-friendly, high reactive and non-toxic base catalyst
for various organic transformations, including ring opening of
aziridines with amines or thiols [11], oxidative deprotection
of (tetrahydropyranyl) ethers and silyl ethers [12], conversion
of tetrahydropyranyl ethers into acetates [13], regioselective
nucleophilic aromatic substitution reaction [14], synthesis of
isoxazolines [15], synthesis of N-arylphthalimides [16], syn-
thesis of industrially important polyurethane foams [17], and
Baylis–Hillman reactions [18]. Nevertheless, in many of these cases,
DABCO has not been recovered, and eliminated as a residue.
∗
Corresponding author. Fax: +98 771 4145494.
E-mail address: ahassaninejad@yahoo.com (A. Hasaninejad).
0926-860X/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2011.04.012

12
A. Hasaninejad et al. / Applied Catalysis A: General 402 (2011) 11–22
Because of the diversity in pharmacological activities, the
2.2. Basicity measurements
synthesis of compounds having benzopyran rings has attracted
great interest since many years [19]. The pyran pharmacophore
is an important core structure of many natural products show-
ing antibacterial, antitumor, antiallergic, antibiotic, hypolipidemic,
and immunomodulating activities [20]. Substituted 2-amino-
4H-pyrans have a special importance among the 6-membered
oxygen-containing heterocycles as they have been used as anti-
cancer and antimicrobial agents [21], and photoactive materials
[22]. 2-Amino-4H-pyran derivatives have been also utilized in syn-
thesis of blood anticoagulant warfarin [23] and tacrine analogs
(cholinesterase inhibitors) [24]. Some catalysts such as hexade-
cyltrimethyl ammonium bromide (HMTAB) [25], triethylbenzy-
lammonium chloride (TEBA) [26], rare earth perfluorooctanoate
(RE(PFO)3) [27], (S)-proline [28], and amino functionalized ionic
liquids [29] have been used for the synthesis of 4H-benzo[b]pyrans
so far. However, most of these methods suffer from some draw-
backs such as low yields, long reaction times, harsh reaction
conditions, tedious work-up procedures and application of expen-
sive catalysts. Moreover, in most of the reported methods, catalysts
are not recyclable. Therefore, development of an efficient, one-pot,
chemoselective procedure for the synthesis of benzo[b]pyrranes is
of considerable interest.
As part of our research program to develop selective, effi-
cient and green methods and catalysts in organic synthesis [30],
we report here the preparation of silica bonded n-propyl-4-
aza-1-azoniabicyclo[2.2.2]octane chloride (SB-DABCO), as a novel
heterogeneous and recyclable catalyst, from the reaction of 3-
chloropropyl silica (SilprCl) with DABCO (Scheme 1), and its
successful application in the synthesis of 4H-benzo[b]pyran
derivatives via the one-pot three-component condensation of
cyclic ketones/1,3-diketones with aromatic aldehydes and alkyl-
malonates (Scheme 2).
The basicity measurements of silica bonded n-propyl
chloride
(SiPrCl)
and
silica
bonded
n-propyl-4-aza-1-
azoniabicyclo[2.2.2]octane chloride (SB-DABCO) were analyzed
by temperature programmed desorption (TPD) of CO2 with TGA
method. About 0.5 g of the sample was packed in a quartz tube
and the initial flushing was carried out with dry nitrogen for 3 h.
Afterward, CO2 was passed over the catalyst bed; by this process,
CO2 was adsorbed by the catalyst. After adsorption, the system
was evacuated to remove the physisorbed CO2, and again CO2
was passed through the system. The adsorption and evacuation
processes were repeated five times for saturating the samples. The
extent of CO2 adsorbed over each sample was measured by TGA
in a homemade system. Nitrogen, as purge gas, was passed during
desorption of CO2. The TGA study was conducted at a heating rate
of 10 ◦C min−1 up to 400 ◦C.
2.3. Preparation of silica bonded n-propyl chloride
Silica (25.0 g) was first immersed in hydrochloric acid for
24 h, and washed with deionized water, and dried under vac-
uum at 120 ◦C for 8 h. The activated silica (25.0 g) was suspended
in dry toluene (300 mL), and then an excess amount of 3-
chloropropyltrimethoxysilane (25.0 mL), and triethylamine (as a
catalyst, 2.5 mL) was added. The suspension was mechanically
stirred and refluxed for 48 h. Afterward, the reaction mixture was
cooled to room temperature, transferred to a vacuum glass filter,
and washed with toluene, ethanol–water mixture, deionized water
in turn and finally with methanol. The resulting solid was dried
under vacuum at 60 ◦C for 4 h to give silica bonded n-propyl chloride
[38].
2.4. Preparation of silica bonded
n-propyl-4-aza-1-azoniabicyclo[2.2.2]octane chloride
(SB-DABCO)
2. Experimental
2.1. Chemicals and apparatus
3-Chloropropyl silica (1 g) and DABCO (0.56 g, 5 mmol) were
added in a 50 mL round-bottomed flask contained dry acetone
(30 mL) connected to a reflux condenser, and refluxed for 36 h.
Afterward, the reaction mixture was cooled to room temperature,
transferred to a vacuum glass filter, and washed with acetone,
ethanol, and methanol in turn. The resulting solid was dried under
vacuum at 50 ◦C for 4 h to give SB-DABCO as a white powder
(1.127 g).
All known compounds were identified by comparison of their
melting points and 1H NMR data with those reported in the
literature. FT-IR spectra were recorded with a Jasco FT-IR, model
460 at 4 cm−1 resolution. Self-supported disks of the materials
were prepared having a diameter of 2.5 cm, weighing ca. 100 mg,
with a disk thickness sufficiently thin to allow the measurements
by the transmission technique. The 1H NMR (500 MHz) and 13C
NMR (125 MHz) were run on a Bruker Avance DPX-250, FT-NMR
spectrometer. Microanalyzis was performed on a Perkin-Elmer
240-B microanalyzer. Melting points were recorded on a Stuart
Scientific Apparatus SMP3 (UK) in open capillary tubes. All chem-
icals were purchased from Merck or Fluka Chemical Companies.
The chemicals purity include silica gel: 60 (0.040–0.063 mm);
toluene: 99.9%; 3-chloropropyltrimethoxysilane: 98%; triethy-
lamine: 99%; ethanol: 99.5%; 1,4-diazabicyclo[2.2.2]octane:
98%; ethyl acetate: 99.8%; dimedone: 99%; benzaldehyde:
2.5. General procedure for the preparation of 4H-benzo[b]pyran
derivatives
Ketone (1 mmol), malononirile (1 mmol) and aldehyde (1 mmol)
were added in a 25 mL round-bottomed flask contained SB-DABCO
(0.06 g, 6 mol%) and ethanol (5 mL), and the resulting mixture was
stirred at room temperature (method A). After completion of the
reaction (as monitored by TLC), the ethanol was evaporated. EtOAc
(15 mL) was added to the mixture, stirred for 5 min and filtered to
separate the catalyst. Then, the solvent of the filtrate was evapo-
rated and the crude product was purified by recrystallization from
hot ethanol. The recycled catalyst was washed by EtOAc and ace-
tone, dried and reused.
99%;
4-chlorobenzaldehyde:
98%;
2-chlorobenzaldehyde:
99%; 4-ethoxybenzaldehyde: 99%; 4-nitrobenzaldehyde: 98%;
4-iso-propylbenzaldehyde: 98%; 2-naphthylaldehyde: 97%;
4-methylbenzaldehyde: 97%; 3-phenoxybenzaldehyde: 99%;
2-oxo-2-phenylacetaldehyde: 98%; 2-thienylcarbaldehyde: 98%;
4-cyanobenzaldehyde: 99%; 4-hydroxybenzaldehyde: 98%; 4-
(trifluoromethyl)benzaldehyde: 98%; Malononitrile: 98%; ethyl
2-cyanoacetate: 99%; methyl 2-cyanoacetate: 99%; cyclohexane-
1,3-dione: 98% and 3-methyl-1-phenyl-1H-pyrazol-5(4H)-one:
98%.
Note: When alkylcyanoacetates were applied instead of mal-
ononirile, the reactions were carried out in EtOH/H2O (1/1) under
reflux conditions (method B).

A. Hasaninejad et al. / Applied Catalysis A: General 402 (2011) 11–22
13
Scheme 1. The preparation of silica bonded n-propyl-4-aza-1-azoniabicyclo[2.2.2]octane chloride (SB-DABCO).
6.93 (s, 2H), 7.03 (d, J = 8.5 Hz, 2H). 13C NMR (DMSO-d6, 125 MHz):
ı 15.5, 27.9, 29.2, 32.9, 35.6, 50.8, 59.4, 63.7, 113.9, 114.9, 120.6,
129.0, 137.5, 158.0, 159.3, 162.9, 196.5.
2.6. Selected spectral data of the products
2.6.1. 2-Amino-4-(phenyl)-5,6,7,8-tetrahydro-7,7-dimethyl-5-
oxo-4H-chromene-3-carbonitrile (compound
6a)
1H NMR (CDCl3, 500 MHz): ı 0.96 (s, 3H), 1.03 (s, 3H), 2.12–2.15
(m, 2H), 2.39 (m, 2H), 4.29 (s, 1H), 5.15 (s, 2H), 7.11 (t, J = 9.0 Hz,
1H), 7.14 (d, J = 3.5 Hz, 2H), 7.19 (t, J = 9.0 Hz, 2H). 13C NMR (CDCl3,
125 MHz): ı 27.9, 29.2, 32.5, 36.0, 51.0, 62.3, 114.3, 119.6, 127.3,
127.8, 128.8, 144.0, 158.4, 162.1, 196.3.
2.6.4. 2-Amino-4-(4-nitrophenyl)-5,6,7,8-tetrahydro-7,7-
dimethyl-5-oxo-4H-chromene-3-carbonitrile (compound
6d)
1H NMR (CDCl3, 500 MHz): ı 0.99 (s, 3H), 1.08 (s, 3H), 2.16–2.20
(m, 2H), 2.44 (m, 2H), 4.32 (s, 1H), 5.32 (s, 2H), 7.38 (d, J = 4.25 Hz,
2H), 7.11 (d, J = 4.15 Hz, 2H). 13C NMR (CDCl3, 125 MHz): ı 27.9, 29.2,
32.5, 36.2, 50.9, 62.1, 113.3, 119.0, 124.2, 129.0, 147.3, 151.3, 158.7,
162.8, 196.2.
2.6.2. 2-Amino-4-(4-chlorophenyl)-5,6,7,8-tetrahydro-7,7-
dimethyl-5-oxo-4H-chromene-3-carbonitrile (compound
6b)
1H NMR (CDCl3, 500 MHz): ı 0.98 (s, 3H), 1.07 (s, 3H), 2.13-2.22
(m, 2H), 2.40 (m, 2H), 4.32 (s, 1H), 5.20 (s, 2H), 7.13 (d, J = 4.25 Hz,
1H), 7.20 (d, J = 3.5 Hz, 2H).13C NMR (CDCl3, 125 MHz): ı 27.9, 29.2,
32.5, 35.6, 51.0, 62.1, 114.0, 119.3, 129.0, 129.4, 133.0, 142.5, 158.4,
162.2, 196.2.
2.6.5. 2-Amino-5,6,7,8-tetrahydro-7,7-dimethyl-4-(naphthalen-
7-yl)-5-oxo-4H-chromene-3-carbonitrile (compound
6e)
1H NMR (DMSO-d6, 500 MHz): ı 0.92 (s, 3H), 1.01 (s, 3H), 1.87-
1.92 (m, 1H), 1.94–1.97 (m, 1H), 2.61-2.69 (m, 2H), 4.39 (s, 1H),
7.06 (s, 2H), 7.32–7.34 (d, J = 10 Hz, 1H), 7.44–7.50 (m, 2H), 7.69 (s,
1H), 7.83–7.86 (m, 2H), 7.89 (d, J = 8.0 Hz, 1H). 13C NMR (DMSO-
d6, 125 MHz): ı 20.6, 21.4, 23.3, 27.4, 36.6, 37.2, 58.9, 114.4, 120.6,
126.4, 126.5, 126.5, 126.9, 128.2, 128.5, 128.9, 132.8, 133.7, 143.0,
159.3, 165.4, 196.7.
2.6.3. 2-Amino-4-(4-ethoxyphenyl)-5,6,7,8-tetrahydro-7,7-
dimethyl-5-oxo-4H-chromene-3-carbonitrile (compound
6c)
1H NMR (DMSO-d6, 500 MHz): ı 0.94 (s, 3H), 1.02 (s, 3H), 1.29 (t,
J = 6.75 Hz, 3H), 2.09 (d, J = 16.0 Hz, 1H), 2.23 (d, J =16.0 Hz, 1H), 2.45-
2.53 (m, 2H), 3.96-3.97 (m, 2H), 4.11 (s, 1H), 6.81(d, J = 8.5 Hz, 2H),
Scheme 2. The synthesis of 4H-benzo[b]pyran derivatives in the presence of SB-DABCO.

14
A. Hasaninejad et al. / Applied Catalysis A: General 402 (2011) 11–22
2.6.6. 2-Amino-5,6,7,8-tetrahydro-7,7-dimethyl-5-oxo-4-(3-
phenoxyphenyl)-4H-chromene-3-carbonitrile (compound
6f)
2.6.12. Methyl 2-amino-4-(4-chlorophenyl)-5,6,7,8-tetrahydro-
7,7-dimethyl-5-oxo-4H-chromene-3-carboxylate (compound
6l)
1H NMR (DMSO-d6, 500 MHz): ı 0.91 (s, 3H), 1.02 (s, 3H), 2.10
(d, J = 16.0 Hz, 1H), 2.26 (d, J = 16.0 Hz, 1H), 2.41–2.53 (m, 2H), 4.17
(s, 1H), 6.75 (s, 1H), 6.80 (d, J = 8.0 Hz, 1H), 6.92 (d, J = 8.0 Hz, 1H),
6.92–7.01 (m, 4H), 7.13 (t, J = 7.2 Hz, 1H), 7.29 (t, J = 7.7 Hz, 1H), 7.37
(t, J = 8.0 Hz, 2H). 13C NMR (DMSO-d6, 125 MHz): ı 27.5, 29.3, 32.5,
36.2, 50.8, 58.8, 113.2, 117.4, 118.0, 119.4, 120.4, 123.0, 124.3, 130.8,
130.8, 147.8, 157.2, 157.5, 159.3, 163.5, 196.4.
1H NMR (CDCl3, 500 MHz): ı 0.98 (s, 3H), 1.12 (s, 3H), 2.18 (d,
J = 8.1 Hz, 1H), 2.26 (d, J = 8.1 Hz, 1H), 2.40–2.48 (m, 2H), 3.62 (s,
3H), 4.70 (s, 1H), 6.23 (s, 2H), 7.19–7.23 (m,4H). 13C NMR (CDCl3,
125 MHz): ı 27.7, 29.5, 32.6, 33.6, 41.1, 51.1, 51.4, 80.5, 116.9, 128.4,
129.8, 132.1, 144.7, 158.9, 161.9,169.7, 196.6.
2.6.13. 2-Amino-5,6,7,8-tetrahydro-5-oxo-4(4-chlorophenyl)-
4H-chromene-3-carbonitrile (compound
6 m)
2.6.7. 2-Amino-5,6,7,8-tetrahydro-7,7-dimethyl-5-oxo-4-
(thiophen-2-yl)-4H-chromene-3-carbonitrile (compound
6 g)
1H NMR (CDCl3, 500 MHz): ı 1.84–1.88 (m, 1H), 1.92–1.97
(m, 1H), 2.21–2.29 (m, 5H) 2.57-2.61 (m, 2H), 4.15 (s, 1H), 6.95
(s, 2H), 7.04 (d, J = 8.0 Hz, 2H), 7.07 (d, J = 8.0 Hz, 2H). 13C NMR
(DMSO/CDCl3, 125 MHz): ı 20.5, 27.3, 33.8, 37.1, 60.3, 114.1, 119.4,
127.4, 128.5, 130.3, 130.5, 133.5, 140.9, 158.6, 164.6,196.2.
1H NMR (DMSO-d6, 500 MHz): ı 0.97 (s, 3H), 1.06 (s, 3H), 2.14 (d,
J = 16.0 Hz, 1H), 2.29 (d, J = 16.0 Hz, 1H), 2.42 (d, J = 16.0 Hz, 1H), 2.52
(d, J = 16.0 Hz, 1H), 4.53 (s, 1H), 6.85 (d, J = 3.5 Hz, 1H), 6.89–6.91 (m,
1H), 7.10 (s, 2H), 7.30-7.31 (m, 1H). 13C NMR (DMSO-d6, 125 MHz):
ı 27.3, 29.5, 31.2, 32.6, 50.7, 58.9, 113.8, 120.4, 124.8, 125.2, 127.6,
150.1, 159.7, 163.3, 196.3.
2.6.14. 2-Amino-5,6,7,8-tetrahydro-5-oxo-4(4-nitrophenyl)-4H-
chromene-3-carbonitrile (compound
6n)
1H NMR (CDCl3, 500 MHz): ı 2.21–2.26 (m, 1H), 2.27–2.32 (m,
1H), 2.41–2.52 (m, 2H), 2.61–2.69 (m, 2H), 4.57 (s, 1H), 4.69 (s, 2H),
7.46 (d, J = 4.4 Hz, 2H), 8.19(d, J = 4.4 Hz, 2H).
2.6.8. 2-Amino-4-benzoyl-7,7-dimethyl-5-oxo-5,6,7,8-
tetrahydro-4H-chromene-3-carbonitrile (compound
6 h)
1H NMR (DMSO-d6, 500 MHz): ı 1.05 (s, 3H), 1.07 (s, 3H), 2.12
(d, J = 16.0 Hz, 1H), 2.34 (d, J = 16.0 Hz, 1H), 2.41 (d, J = 17.5 Hz, 1H),
2.61 (d, J =17.5 Hz, 1H), 4.98 (s, 1H), 7.23 (s, 2H), 7.55 (t, J = 7.75 Hz,
2H), 7.68 (t, J = 7.5 Hz, 1H), 8.05 (d, J = 7.5 Hz, 2H). 13C NMR (DMSO-
d6, 125 MHz): ı 27.2, 29.5, 33.2, 36.7, 50.4, 53.0, 111.5, 119.9, 129.5,
129.7, 134.4, 136.6, 160.9, 164.8, 196.8, 199.4.
2.6.15. 2-Amino-5,6,7,8-tetrahydro-5-oxo-4-p-tolyl-4H-
chromene-3-carbonitrile (compound
6o)
1H NMR (DMSO-d6, 500 MHz): ı 1.84–1.88 (m, 1H), 1.92–1.97
(m, 1H), 2.21–2.29 (m, 5H) 2.57–2.61 (m, 2H), 4.15 (s, 1H), 6.95 (s,
2H), 7.04 (d, J = 8.0 Hz, 2H), 7.07 (d, J = 8.0 Hz, 2H). 13C NMR (DMSO-
d6, 125 MHz): ı 20.6, 21.4, 27.3, 35.9, 37.2, 59.2, 114.8, 120.6, 127.9,
129.7, 136.4, 142.7, 159.3, 165.1, 196.6.
2.6.9. Ethyl 2-amino-4-(4-trifluoromethylphenyl)-5,6,7,8-
tetrahydro-7,7-dimethyl-5-oxo-4H-chromene-3-carboxylate
(compound 6i)
2.6.16. 2-Amino-5,6,7,8-tetrahydro-4-(naphthalen-7-yl)-5-oxo-
4H-chromene-3-carbonitrile (compound
6p)
1H NMR (DMSO-d6, 500 MHz): ı 0.88 (s, 3H), 1.03 (s, 3H), 1.06
(t, J = 7.0 Hz, 3H), 2.06 (d, J = 8.0 Hz, 1H), 2.26 (d, J = 8.0 Hz, 1H), 2.47
(d, J = 8.8 Hz, 1H), 2.56 (d, J = 8.75 Hz, 1H), 3.91–3.95 (m, 2H), 4.56 (s,
1H NMR (DMSO-d6, 500 MHz): ı 1.87–1.92 (m, 1H), 1.94–1.97
(m, 1H), 2.21–2.26 (m, 1H), 2.27–2.32 (m, 1H), 2.61–2.69 (m, 2H),
4.39 (s, 1H), 7.06 (s, 2H), 7.32–7.34 (d, J = 8.5 Hz, 1H), 7.44–7.50 (m,
2H), 7.69 (s, 1H), 7.83–7.86 (m, 2H), 7.89 (d, J = 8.0 Hz, 1H). 13C NMR
(DMSO-d6, 125 MHz): ı 20.6, 27.4, 36.6, 37.2, 58.9, 114.4, 120.6,
126.4, 126.5, 126.5, 126.9, 128.2, 128.5, 128.9, 132.8, 133.7, 143.0,
159.3, 165.4, 196.7.
1H), 7.35 (d, J = 4.0 Hz, 2H), 7.57 (d, J = 4.0 Hz, 2H), 7.63 (s, 2H). 13
NMR (DMSO-d6, 125 MHz): ı 15.0, 27.4, 29.4, 32.7, 34.5, 50.7, 59.7,
77.8, 115.6, 125.5, 129.5, 151.9, 160.0, 163.4, 168.6, 196.7.
C
2.6.10. Ethyl 2-amino-5,6,7,8-tetrahydro-7,7-dimethyl-4-
(naphthalen-7-yl)-5-oxo-4H-chromene-3-carboxylate
(compound 6j)
2.6.17. 2-Amino-5,6,7,8-tetrahydro-4-(2-chlorophenyl)-5-oxo-
4H-chromene-3-carbonitrile (compound
1H NMR (DMSO-d6, 500 MHz): ı 0.88 (s, 3H), 1.03 (s, 3H), 1.07 (t,
J = 7.5 Hz, 3H), 2.03 (d, J = 16.0 Hz, 1H), 2.26 (d, J = 16.0 Hz, 1H), 2.50
(d, J = 14.5 Hz, 1H), 2.57 (d, J = 17.5 Hz, 1H), 3.87-3.98 (m, 2H), 4.67
(s, 1H), 7.30 (d, J = 8.5 Hz, 1H), 7.39–7.45 (m, 2H), 7.59 (s, 2H), 7.63
(s, 1H), 7.75 (d, J = 8.5 Hz, 1H), 7.78–7.83 (m, 2H). 13C NMR (DMSO-
d6,125 MHz): ı 15.0, 27.2, 29.5, 32.7, 34.4, 50.8, 59.6, 78.5, 116.1,
126.1, 126.7, 126.9, 127.3, 128.1, 128.1, 128.3, 132.5, 133.5, 144.5,
159.9, 163.1, 168.8, 196.7.
6q)
1H NMR (DMSO-d6, 500 MHz): 1.89–1.98 (m, 2H), 2.19–2.49
(m, 2H), 2.59–2.62 (m, 2H), 4.70 (s, 1H), 6.99 (s, 2H), 7.19 (t,
J = 7.5 Hz, 2H), 7.25(t, J = 7.15 Hz, 1H), 7.35(d, J = 7.7 Hz, 1H). 13C NMR
(DMSO/CDCl3, 125 MHz): ı 20.5, 27.3, 33.8, 37.1, 60.3, 114.1, 119.4,
127.4, 128.5, 130.3, 130.5, 133.5, 140.9, 158.6, 164.6,196.2.
2.6.18. methyl 2-amino-4-(4-ethoxyphenyl)-5-oxo-5,6,7,8-
tetrahydro-4H-chromene-3-carboxylate (compound
6 s)
2.6.11. Methyl 2-amino-4-(4-cyanophenyl)-5,6,7,8-tetrahydro-
7,7-dimethyl-5-oxo-4H-chromene-3-carboxylate (compound
6k)
M.P. = 149–150 ◦C. 1H NMR (DMSO-d6, 500 MHz): ı 1.27 (m, 3H),
1.79 (m, 1H), 1.92 (m, 1H), 2.23–2.25 (m, 2H), 2.49–2.58 (m, 2H),
3.49 (s, 3H), 3.92 (m, 2H), 4.49 (s, 1H), 6.73 (m, 2H), 7.02 (m, 2H),
7.50 (s, 2H). 13C NMR (DMSO-d6, 125 MHz): ı 15.5, 20.7, 27.1, 32.9,
37.2, 51.3, 63.6, 78.7, 114.5, 118.0, 129.2, 139.3, 157.5, 160.1, 164.5,
169.2, 196.8. Anal. Calcd for C19H21NO5: C, 66.46; H, 6.16; N, 4.08.
Found: C, 66.51; H, 6.23; N, 4.1
1H NMR (DMSO-d6, 500 MHz): ı 0.86 (s, 3H), 1.02 (s, 3H), 2.06
(d, J = 16.0 Hz, 1H), 2.26 (d, J = 16.0 Hz, 1H), 2.45–2.57 (m, 2H), 3.48
(s, 3H), 4.55 (s, 1H), 7.32 (d, J = 8.0 Hz, 2H), 7.66-7.68 (m, 4H). 13C
NMR (DMSO-d6, 125 MHz): ı 27.3, 29.4, 32.7, 34.7, 50.7, 51.4, 77.3,
109.5, 115.4, 119.7, 129.5, 132.7, 152.7, 160.1, 163.5, 168.8, 196.6.

A. Hasaninejad et al. / Applied Catalysis A: General 402 (2011) 11–22
15
Fig. 1. IR spectra of DABCO (a), silica bonded n-propylchloride (b) and silica bonded n-propyl-4-aza-1-azoniabicyclo[2.2.2]octane chloride (SB-DABCO) (c).
2.6.19. 6-Amino-4-(4-cyanophenyl)-1,4-dihydro-3-methyl-1-
phenylpyrano[2,3-c]pyrazole-5-carbonitrile (compound
6t)
(DMSO-d6, 125 MHz): ı 27.0, 29.5, 32.7, 33.2, 50.7, 51.3, 78.5, 116.8,
127.6, 144.5, 160.3, 163.0, 169.1, 196.6.
1H NMR (DMSO-d6, 500 MHz): 1.77 (s, 3H), 4.83 (s, 1H),
7.30–7.33 (m, 3H), 7.47–7.50 (m, 4H), 7.78 (d, J = 8.5 Hz, 2H), 7.82
(d, J = 8.0 Hz, 2H). 13C NMR (DMSO-d6, 125 MHz): ı 13.4, 37.5, 57.9,
98.5, 110.8, 119.6, 120.6, 120.9, 127.1, 129.8, 130.1, 133.5, 138.3,
144.9, 145.9, 150.0, 160.5.
2.6.25. 4,4ꢀ-(1,4-phenylene)bis(2-amino-5-oxo-5,6,7,8-
tetrahydro-4H-chromene-3-carbonitrile) (compound
8b)
M.p. = 304 ◦C (dec.) 1H NMR (DMSO-d6, 500 MHz): 1.94 (m, 4H),
2.28 (m, 4H), 2.60 (m, 4H), 4.14 (s, 2H), 6.95 (s, 4H), 7.05 (s, 4H).
13C NMR (DMSO-d6, 125 MHz): ı 20.5, 27.3, 35.7, 37.1, 59.0, 59.1,
114.7, 120.7, 127.9, 143.7, 159.4, 159.5, 165.4, 165.5, 196.8.
2.6.20. 6-Amino-4-(4-(trifluoromethyl)phenyl)-1,4-dihydro-3-
methyl-1-phenylpyrano[2,3-c]pyrazole-5-carbonitrile (compound
6u)
2.6.26. 4,4ꢀ-(1,4-phenylene)bis(6-amino-3-methyl-1-phenyl-1,4-
dihydropyrano[2,3-c]pyrazole-5-carbonitrile) (compound
8c)
1H NMR (DMSO-d6, 500 MHz): 1.78 (s, 3H), 4.84 (s, 1H),
7.31–7.34 (m, 3H), 7.48–7.51 (m, 4H), 7.72 (d, J = 7.5 Hz, 2H), 7.78
(d, J = 7.5 Hz, 2H). 13C NMR (DMSO-d6, 125 MHz): ı 13.4, 37.3, 58.2,
98.7, 120.6, 120.9, 126.4, 127.1, 129.5, 130.2, 138.3, 144.8, 146.0,
149.1, 160.5.
M.p. = 296 ◦C (dec.) 1H NMR (DMSO-d6, 500 MHz): 2.19 (s, 6H),
4.72 (s, 2H), 7.21–7.22 (m, 4H), 7.37–7.47 (m, 6H), 7.60–7.62 (m,
4H), 7.69–7.79 (m, 4H). 13C NMR (DMSO-d6, 125 MHz): ı 12.7, 22.4,
58.3, 118.8, 119.7, 120.1, 127.1, 128.3, 129.0, 129.4, 132.3, 138.1,
148.6, 177.1.
2.6.21. 6-Amino-1,4-dihydro-3-methyl-1-phenyl-4-(thiophen-2-
yl)pyrano[2,3-c]pyrazole-5-carbonitrile (compound
6 v)
1H NMR (DMSO-d6, 500 MHz): 1.92 (s, 3H), 5.08 (s, 1H), 6.97 (m,
1H), 7.07 (d, J = 3.0 Hz, 1H), 7.27 (s, 2H), 7.32 (t, J = 7.5 Hz, 1H), 7.43
3. Results and discussions
(d, J = 5.0 Hz, 1H), 7.49 (t, J = 8.0 Hz, 2H), 7.77 (d, J = 8.0 Hz, 2H). 13
C
At first, SB-DABCO was prepared form the reaction of 3-
chloropropyl silica and DABCO as shown in Scheme 1. The catalyst
structure was demonstrated with IR spectroscopy. The FT-IR spec-
tra of the DABCO (a), silica bonded n-propylchloride (b), and silica
bonded n-propyl-4-aza-1-azoniabicyclo[2.2.2]octane chloride (c)
samples are presented in Fig. 1. The pure DABCO shows a charac-
teristic broad absorbance at 1000–1100 cm−1 (C–N stretching), and
at 1480 cm−1 for CH2 bending. In the spectrum of silica bonded n-
propyl chloride, absorbances at 1460 and 1210 cm−1 were observed
which indicate the presence of CH2 bending and Si–C stretching,
respectively. There are four characteristic peaks in the spectrum
of SB-DABCO. The C–N+ stretching at 1615 cm−1, CH2 bending at
1480 cm−1, Si–C stretching at 1210 cm−1, and Si–O stretching at
1110–1090 cm−1 as a broad bond. Compared with the spectrum of
silica bonded n-propyl chloride, SB-DABCO exhibits the character-
istic band at 1615 cm−1 due to the fact that C–N+ group appeared
after the reaction of silica bonded n-propyl chloride with DABCO.
These results prove that the DABCO was successfully linked to silica
bonded n-propyl chloride to give SB-DABCO.
For more investigation about the structure of the catalyst, the
amount of carbon dioxide, produced by the oxidation of the catalyst
during the thermogravimetric (TG) analysis, was determined using
a carbon dioxide sensor. The spectroscopic results are shown in
Fig. 2.
As it can be seen in Fig. 2, the ratio of carbon atoms presented in
silica bonded n-propyl chloride structure (B) relative to that exist
in silica bonded n-propyl-4-aza-1-azoniabicyclo[2.2.2]octane chlo-
ride structure (A) was evaluated to one third. This ratio is partially
NMR (DMSO-d6, 125 MHz): ı 13.3, 32.8, 59.4, 99.5, 120.6, 120.8,
125.8, 126.3, 127.1, 127.5, 130.2, 138.2, 144.3, 146.2, 149.6, 160.0.
2.6.22. 6-Amino-4-(4-(hydroxy)phenyl)-1,4-dihydro-3-methyl-
1-phenylpyrano[2,3-c]pyrazole-5-carbonitrile (compound
6w)
1H NMR (CDCl3, 500 MHz): 1.78 (s, 3H), 4.55 (s, 1H), 6.71 (d,
J = 4.0 Hz, 2H), 7.03 (d, J = 4.0 Hz, 2H), 7.11 (s, 2H), 7.30 (t, J = 7.0 Hz,
1H),7.48 (t, J = 7.4 Hz, 2H). 7.77 (d, J = 4.0 Hz, 2H). 13C NMR (DMSO-
d6, 125 MHz): ı 13.4, 36.9, 59.7, 99.9, 116.1, 120.8, 120.9, 126.9,
129.6, 130.2, 134.8, 138.5, 144.6, 146.2, 157.2, 160.1.
2.6.23. 6-Amino-1,4-dihydro-4-(4-isopropylphenyl)-3-methyl-1-
phenylpyrano[2,3-c]pyrazole-5-carbonitrile (compound
6x)
1H NMR (DMSO-d6, 500 MHz): 1.19 (d, J = 8.3 Hz, 6H), 1.79 (s,
3H), 2.86 (m, 1H), 4.63 (s, 1H), 7.16–7.71 (m, 11H). 13C NMR (DMSO-
d6, 125 MHz): ı 13.3, 32.8, 59.4, 99.5, 120.6, 120.8, 125.8, 126.3,
127.1, 127.5, 130.2, 138.2, 144.3, 146.2, 149.6, 160.0.
2.6.24. Dimethyl 4,4ꢀ-(1,4-phenylene)bis(2-amino-7,7-dimethyl-
5-oxo-5,6,7,8-tetrahydro-4H-chromene-3-carboxylate)
(compound 8a)
M.p. = 226–288 ◦C. 1H NMR (DMSO-d6, 500 MHz): 0.81 (s, 6H),
1.00 (s, 6H), 2.05 (d, J = 16.0 Hz, 2H), 2.22 (d, J = 16.5 Hz, 2H), 2.4–2.5
(m, 4H), 3.47 (s, 6H), 4.45 (s, 2H), 6.93 (s, 4H), 7.5 (s, 4H). 13C NMR

16
A. Hasaninejad et al. / Applied Catalysis A: General 402 (2011) 11–22
O
O
CHO
CN
SB-DABCO
CN
CN
(5)
+
O
+
O
NH2
(6a)
(3a)
(4a)
Scheme 3. The reaction of benzaldehyde (3a) with 5,5-dimethylcyclohexane-1,3-
dione (4a) and malononitrile (5) leading to compound 6a using SB-DABCO.
ature and amount of CO2 desorbed are considered as indexes of
base strength and total number of base sites, respectively. It is
observed that only one major weight losses occurred over SiPrCl
at range of 230–250 ◦C. Moreover, it is observed that two major
weight losses occurred over SB-DABCO. The first and second weight
losses occurred between 250–270 ◦C and 310–330 ◦C, respectively.
Although it was difficult to exactly express the strength on a defi-
nite scale and to count the number of basic sites quantitatively, TPD
could be used to evaluate the relative strength of basic sites. Fig. 5
shows the spectra of CO2-TPD from samples SiPrCl and SB-DABCO,
which indicate that the SB-DABCO is a basic catalyst according
to desorption temperature and intensity of CO2 absorbed on this
catalyst.
To further evaluate the efficacy of our new catalyst, the conden-
sation reaction of C–H activated ketones with aromatic aldehydes
and alkylmalonates for the synthesis of 4H-benzo[b]pyran deriva-
tives was studied. To obtain the optimal reaction conditions,
the condensation of benzaldehyde (3a) (1 mmol) with 5,5-
dimethylcyclohexane-1,3-dione (4a) (1 mmol) and malononitrile
(5) (1 mmol) in the presence of SB-DABCO was selected as a model
reaction to produce compound 6a (Scheme 3).
The reaction was examined in the presence of different molar
ratios of SB-DABCO in ethanol at room temperature. The results
are summarized in Table 1. As Table 1 indicates, higher yield and
shorter reaction time were obtained when the reaction was carried
out in the presence of 6 mol% of the catalyst in ethanol; in these
conditions, the corresponding 4H-benzo[b]pyran (6a) was obtained
in 96% yield within 35 min (Table 1 entry 3). The model reaction was
also examined in the presence of SB-DABCO at room temperature
in several solvents including CHCl3, CH2Cl2, CH3CN, EtOAc and H2O,
(Table 1 entries 7–12). As it can be seen in Table 1, ethanol was the
best solvent for this reaction.
Fig. 2. Diagram of produced CO2 versus temperature for silica bonded n-propyl-4-
aza-1-azoniabicyclo[2.2.2]octane chloride (A) and silica bonded n-propyl chloride
(B).
the same as the results obtained based on the spectroscopic data
shown in Fig. 2.
We also determined the loading level of DABCO (1.014 mmol/g)
based on the chlorine content by titrimetric analysis, with employ-
ing a recent procedure [31], which is shown to be in good agreement
with the results obtained from TGA and conventional elemental
analysis. Nitrogen content of the silica bonded n-propyl-4-aza-
1-azoniabicyclo[2.2.2]octane chloride was 2.85% by conventional
elemental analysis. The thermal stability of SB-DABCO was also
investigated using a self-made TG analysis instrument, and the
results are shown in Fig. 3. Fig. 3 shows the thermogram of the sam-
ple at an air flow of 3 mL min−1 and temperature ramp of 2 ◦C min−1
.
The weight lost at around 90 ◦C can be related to the desorption of
water vapor and other volatile organic compounds which have been
adsorbed on the catalyst. Following the thermogram, the decrease
observed in the slope of the diagram, starting at around 220 ◦C can
be related to the loss of the covalently bound organic group.
The adsorption behavior of nitrogen gas on each silica
bonded n-propyl chloride and silica bonded n-propyl-4-aza-1-
azoniabicyclo[2.2.2]octane chloride have also been studied using
the TG analysis instrumentation system and nitrogen atmo-
sphere (Fig. 4). The results reveal that a significant increase to
∼160 m2 kg−1 was observed in the active surface area of the silica
support when modified with DABCO catalyst.
The total basicity of silica bonded n-propyl chloride (SiPrCl) and
silica bonded n-propyl-4-aza-1-azoniabicyclo[2.2.2]octane chlo-
ride (SB-DABCO) was measured by temperature programmed
desorption (TPD) of CO2 by TGA method. The desorption temper-
The
reaction
of
benzaldehyde
(3a)
with
5,5-
dimethylcyclohexane-1,3-dione (4a) and malononitrile (5) was
also checked in the presence of SiO2 in which a substantial increase
in the reaction time (240 min) and decrease in the yield (70%) were
observed.
Table 1
The reaction of benzaldehyde (1 mmol) with malononitrile (1 mmol), and 5,5-
dimethylcyclohexane-1,3-dione (1 mmol) in the presence of SB-DABCO at room
temperature.
Entry
Solvent (5 ml)
Catalyst (mol %)
Time (min)
Yielda (%)
1
2
3
4
6
7
8
10
11
12
EtOH
EtOH
EtOH
EtOH
EtOH
CHCl3
CH2Cl2
CH3CN
EtOAc
H2O
1.5
3
6
9
-
6
6
6
6
300
150
35
47
85
96
95
Trace
60
68
85
52
30
300
300
300
180
300
90
6
87
Fig. 3. The thermogravimeric analysis diagram of silica bonded n-propyl-4-aza-1-
azoniabicyclo[2.2.2]octane chloride.
a
Isolated yield.

A. Hasaninejad et al. / Applied Catalysis A: General 402 (2011) 11–22
17
Table 2
The synthesis of 4H-benzo[b]pyran derivatives in the presence of SB-DABCO.
Entry
Substrate
R
X
Method
Time (min)
Yielda (%)
M.p. (◦C)
Found
Reported
O
6a
C6H5
CN
A
35
96
227–229
237–239
233–235
173–174
258–260
193–194
220–222
220–221
155–156
188–190
180–182
166–168
226–228 [32]
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
6b
6c
6d
6e
6f
4-ClC6H4
CN
A
A
A
A
A
A
A
B
B
B
B
25
95
91
90
96
96
92
93
90
97
95
95
239–241 [33]
4-EtOC6H4
4-NO2C6H4
2-naphthyl
3-phOC6H4
2-thienyl
C6H5-CO
CN
55
–
CN
20
176–178 [33]
CN
40
–
CN
25
-
6g
6h
6i
CN
50
–
CN
30
–
4-CF3C6H4
2-naphthyl
4-CNC6H4
4-ClC6H4
CO2Et
CO2Et
CO2Me
CO2Me
300
180
140
180
–
6j
–
6k
6l
–
167–168 [34]

18
A. Hasaninejad et al. / Applied Catalysis A: General 402 (2011) 11–22
Table 2 (Continued)
Entry
Substrate
R
X
Method
Time (min)
Yielda (%)
M.p. (◦C)
Found
Reported
O
O
O
O
O
O
O
6m
4-ClC6H4
CN
A
40
95
225–227
236–237
232–233
254–255
209–211
183–184
149–150
224–226 [35]
O
O
O
O
O
O
O
6n
6o
6p
6q
6r
4-NO2C6H4
4-CH3C6H4
2-naphthyl
2-ClC6H4
CN
A
A
A
A
B
B
25
94
92
97
95
98
97
234–236 [35]
CN
40
–
CN
30
–
CN
30
210–212 [35]
4-ClC6H4
CO2Et
CO2Me
120
250
–
–
6s
4-EtOC6H4
O
O
O
N
N
N
6t
4-CNC6H4
4-CF3C6H4
2-thienyl
CN
CN
CN
A
A
A
25
30
40
96
97
96
217–219
182–184
168–169
–
–
–
N
Ph
6u
N
Ph
6v
N
Ph
O
N
N
6w
4-OHC6H4
CN
CN
A
A
60
60
93
93
206–208
158–160
210–212 [36]
N
Ph
O
6x
4-isopropyl-C6H4
–
N
Ph
a
Isolated yield.
To probe the efficiency and the scope of our method, a broad
range of structurally diverse aldehydes (3) were condensed
and alkyl nitriles (5) to furnish the corresponding 4H-
benzo[b]pyrans in high yields and in relatively short
reaction times (Scheme 2). The results are displayed in
Table 2.
with
cyclohexane-1,3-dione
(4a)/5,5-dimethylcyclohexane-
(4c)
1,3-dione
(4b)/3-methyl-1-phenyl-2-pyrazolin-5-one

A. Hasaninejad et al. / Applied Catalysis A: General 402 (2011) 11–22
19
Fig. 4. The nitrogen adsorption isotherm of silica (red), and silica bonded n-propyl-4-aza-1-azoniabicyclo[2.2.2]octane chloride (blue).
In this study, we found that higher temperature
(reflux conditions) was required for the condensa-
were applied successfully in the reaction to provide the corre-
sponding benzo[b]pyrans without by-products (Table 2, entries
tion of alkylcyanoacetates with aromatic aldehyde and
cyclohexane-1,3-dione/5,5-dimethylcyclohexane-1,3-dione/3-
methyl-1-phenyl-2-pyrazolin-5-one in H2O/EtOH (1/1) in the
presence of SB-DABCO (method B, Table 2). This can be attributed
to the lower reactivity of alkylcyanoacetates compared to mal-
ononitrile. Furthermore, as it is shown in Table 2, the presence of
electron-withdrawing substituents on the aromatic ring of aryl
aldehydes accelerated the reaction rate (Table 2, entries 6d, 6h,
6i, 6k, 6n, 6t and 6u), whereas electron-releasing substituents
reduced the reaction rate (Table 2, entries 6c, 6o, 6s, 6w and 6x).
The nature of substituents did not affect the reaction yields. More-
over, aromatic aldehydes bearing sensitive substituent as well
as hetero-aromatic aldehyde (such as thiophene2-carbaldehyde)
(6k, 6t, 6g and 6v).
In
addition,
the
complex
structures
of
8a,
8b
and 8c were synthesized via the condensation of
cyclohexane-1,3-dione/5,5-dimethylcyclohexane-1,3-dione/3-
methyl-1-phenyl-2-pyrazolin-5-one
alkylnitriles (2 equivalents) and terephthalaldehyde (7) (1
equivalents) for the first time (Scheme 4).
On the other hand, it is known that the reaction of car-
bonyl compounds with derivatives of cyaoacetic acid gives
3-cyanopyridine-2(1H)-ones 9 and 2,6-dicyanoanilines 10 as by-
products [37]. Meanwhile, the hydrolysis of the nitrile or ester
groups leads to the formation of by-products 11 or 12 (Scheme 5). A
distinct characterization of the present method, illustrated in this
(2
equivalents)
with
Fig. 5. The CO2-TPD plots of SiPrCl (red) and SB-DABCO (blue).

20
A. Hasaninejad et al. / Applied Catalysis A: General 402 (2011) 11–22
O
X: CO2Me
Method B
O MeO2C
NH2
O
O
O
180 min 90%
H2N
CO2Me O
(8a)
O
X: CN
O
NC
NH2
O
CHO
Method A
O
X
O
+
30 min 93%
CN
H2N
CN
O
(8b)
CHO
O
(5)
(7)
N
N
X: CN
N
Ph
Ph
N
NC
NH2
O
Method A
O
40 min 91%
H2N
CN
N
Ph
N
(8c)
Scheme 4. The reaction of cyclohexane-1,3-dione, 5,5-dimethylcyclohexane-1,3-dione or 3-methyl-1-phenyl-2-pyrazolin-5-one (2 eq) with alkyl nitriles (2 eq) and tereph-
thalaldehyde (1 eq).
R2
CN
X
BH
CO2
-
O
Ar
N
H
9
11
H
R1
O
Ar
O
CN
Ar-CHO
+
X
X
O
O
X
:B
R2
Ar-CHO +
+
O
O
R1
R2
CN
R1
NH2
6
R1
R2
NH2
CN
NC
R1
NC
H
-
CO2
Ar
BH
12
10
R2
Scheme 5. The three-component synthesis of 2-amino-benzo[b]pyran (blue) and theoretically possible by-products (red).
work, is the formation of benzo[b]pyrans 6 without by-product.
the reactions shown in Scheme 6. Based on this mechanism, SB-
DABCO is effective catalyst for the formation of olefin 13, which
readily prepares in situ from Knoevenagel condensation of alde-
hyde 3 with highly active CH-acidic cyanoacetic ester derivative
5. We consider this to be so, because unsaturated nitriles 13 are
Using this method, twenty seven compounds were obtained in good
yield (purity not less than 90%) without additional purification.
The selectivity in the synthesis of 4H-benzo[b]pyrans 6 in the
presence of SB-DABCO can be explained by the strict sequence of

A. Hasaninejad et al. / Applied Catalysis A: General 402 (2011) 11–22
21
Graph 1. The reaction of benzaldehyde (1 mmol) with malononitrile (1 mmol) and
5,5-dimethylcyclohexane-1,3-dione (1 mmol) in ethanol (5 ml) using recovered SB-
DABCO at room temperature.
type reaction). Finally, after the tautomeric proton shift, 2-amino-
4H benzo[b]pyran 6 is formed.
In order to compare the capability and efficiency of our cat-
alyst with respect to the previously reported catalysts for the
preparation of 4H-benzo[b]pyrans, the results for the synthesis of
compound 6a, employing these catalysts, are tabulated in Table 3.
As it is clear from Table 3, SB-DABCO is more efficient than the
others.
In another study, the condensation of benzaldehyde (3a) with
5,5-dimethylcyclohexane-1,3-dione (4a) and malononitrile (5) was
tested in the presence of recovered silica bonded n-propyl-4-aza-
1-azoniabicyclo[2.2.2]octane chloride to establish the reusability
of the catalyst (Graph 1). As it is shown in Graph 1, no loss of
the catalytic activity was observed even after fifteen cycles of the
reaction.
4. Conclusions
We have introduced a highly efficient, heterogeneous, and
reusable novel catalyst for the one-pot, three-component conden-
sation of cyclic ketones/1,3-diketones with aromatic aldehydes and
alkyl nitriles. The promising points for the presented methodol-
ogy are the high efficiencies, generality, short reaction times, mild
reaction conditions, clean reaction profiles, and simplicity which
makes it a desirable and useful method for the synthesis of 4H-
benzo[b]pyrans as biologically interesting compounds.
Scheme 6. The proposed mechanism for the synthesis of 4H-benzo[b]pyrans in the
presence of SB-DABCO.
formed very easily in the absence of compound 4. Then, carbonyl
compound 4, in the presence of SB-DABCO, subsequently converts
to its corresponding enolate form 14, and adds to the unsaturated
nitrile 13 by Michael reaction to produce intermediate 15, and eno-
late oxygen attacks nucleophilically nitrile group (Thorpe-Ziegler
Acknowledgment
We appreciate the Persian Gulf University Research Council for
the financial support of this work. Also, the authors thank from Prof.
H. Eslami for his help.
Table 3
Comparative the condensation of malononitrile with benzaldehyde and 5,5-
dimethy-cyclohexane-1,3-dione using the reported catalysts versus SB-DABCO.
Appendix A. Supplementary data
Entry
Reagents and
conditions
Time (min)
Yield (%)
Ref.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.apcata.2011.04.012.
4
1
Na2SeO4, 0.1 g,
60
97
92
[33]
[35]
EtOH/H2O, reflux
Hexadecyldimethyl
benzyl ammonium
bromide (HDMBAB),
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