β-Cyclodextrin as an efficient catalyst for the one-pot synthesis of tetrahydrobenzo[b]pyran derivatives in water

Article abstract of DOI:10.1007/s11164-015-2027-0

Various 4H-benzo[b]pyran derivatives were synthesized via a one-pot three-component condensation of arylaldehyde, malononitrile and dimedone in water using β-cyclodextrin (β-CD) as an efficient catalyst. This method provides several advantages, including

Full text of DOI:10.1007/s11164-015-2027-0

Res Chem Intermed
DOI 10.1007/s11164-015-2027-0
b-Cyclodextrin as an efficient catalyst for the one-pot
synthesis of tetrahydrobenzo[b]pyran derivatives
in water
Jun Lu1,2,3 Xue-wen Fu1 Ge Zhang2,3
Chun Wang1
•
•
•
Received: 16 January 2015 / Accepted: 19 March 2015
Ó Springer Science+Business Media Dordrecht 2015
Abstract Various 4H-benzo[b]pyran derivatives were synthesized via a one-pot
three-component condensation of arylaldehyde, malononitrile and dimedone in
water using b-cyclodextrin (b-CD) as an efficient catalyst. This method provides
several advantages, including mild reaction conditions, operational simplicity, high
yields and minimal pollution of the environment.
Keywords 4H-benzo[b]pyran Á Aqueous media Á b-Cyclodextrin Á One-pot
reaction
Introduction
Synthesis of 4H-benzo[b]pyran and its derivatives has attracted great interest from
organic and medicinal chemists, because of these products’ useful biological and
pharmacological properties, such as spasmolytic, diuretic, anti-coagulant, anti-
cancer, and anti-anaphylactic activities [1–5]. 4H-pyrans is an important structural
unit of a series of natural products [6, 7]. Additionally, some benzo[b]pyran
derivatives have photochemical activities [8]. Numerous synthetic methods have
been reported for the synthesis of 4H-pyrans, involving use of a variety of catalysts
such as TEBA [9], RE(PFO)3 [10], TBAF [11], TMAH [12], CeCl3 [13], Na2SeO4
&
Chun Wang
wangchun@cib.ac.cn
1
2
3
Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041,
People’s Republic of China
Institute for Advancing Translational Medicine in Bone and Joint Diseases, School of Chinese
Medicine, Hong Kong Baptist University, Hong Kong, People’s Republic of China
Institute of Integrated Bioinformedicine and Translational Science, HKBU Shenzhen Research
Institute and Continuing Education, Shenzhen, People’s Republic of China
123

J. Lu et al.
[14], Phenylboronic acid [15], DABCO [16], ZnO-beta zeolite [17], or the Ru(II)
complex [18]. However, these methods suffer from a variety of drawbacks, such as
the use of hazardous and toxic solvents, high temperature, and difficult workup.
Water is one of the most abundant, cheapest, and environmentally friendly solvents.
However, most organic reactants are not soluble in aqueous media. Thus, an
efficient phase transfer reagent is necessary to ensure the reaction is conducted in
aqueous media. Recently, Azath et al. [19] reported a new method to prepare
2-amino-4H-benzo[b]pyran, using per-6-amino-b-cyclodextrin under a solvent-free
condition. Despite the difficulty in preparing the catalyst, organic solvent(s) were
still needed in the product isolation step.
In this paper, we describe a convenient, inexpensive and environmentally
friendly method for the synthesis of 4H-benzo[b]pyran, using b-CD in water.
Experimental design
All starting materials were purchased from commercial sources and used without
further purification. Melting points were measured by the X-6 (Beijing Fukai Co., Ltd.,
Beijing, China) melting point apparatus and are uncorrected. Infrared (IR) spectra
were recorded on a Perkin Elmer Spectrum One FTIR spectrometer in KBr. 1H and 13
C
nuclear magnetic resonance (NMR) (600 and 150 MHz, respectively) spectra were
determined on Bruker AVANCE-600 spectrometers. Electrospray ionization mass
spectrometry (ESI-MS) spectra were recorded on a BioTOF Q mass spectrometer. All
the spectrometers were provided by Chengdu Institute of Biology, Chinese Academy
of Sciences, P. R. China.
General procedure for synthesis target compounds
Substrates (1a–1p, 1.0 mmol), malononitrile 2 (1.1 mmol), dimedone 3 (1.1 mmol)
and b-CD (0.02 mmol) were added to a round-bottom flask containing 5 mL water. The
mixture was stirred at room temperature for a certain time to complete the reaction
(monitored by TLC, Table 2). After completion, the generated solid was filtered off and
further purified by recrystallization with 95 % ethanol to give a pure product.
2-Amino-4-(4-methoxy-phenyl)-7,7-dimethyl-5-oxo-5,6,7,8-tetrahydro-4H-chromene-
3-carbonitrile (4b) Yellow solid; 1H NMR (600 MHz, CDCl3): d = 1.03 (s, 3 H),
1.10 (s, 3 H), 2.20 (d, J = 16.2 Hz, 1 H), 2.23 (d, J = 16.2 Hz, 1 H), 2.41 (d,
J = 17.7 Hz, 1 H), 2.45 (d, J = 17.7 Hz, 1 H), 3.76 (s, 3 H), 4.36 (s, 1 H), 4.52 (s, 2 H),
6.81 (d, J = 8.6 Hz, 2 H), 7.14 (d, J = 8.7 Hz, 2 H). IR (KBr): mmax = 3381, 3188,
2929, 2192, 1682, 1655, 1606, 1509, 1369 cm-1. ESI–MS: m/z = 347.1 [M?Na]?.
2-Amino-4-(4-hydroxy-phenyl)-7,7-dimethyl-5-oxo-5,6,7,8-tetrahydro-4H-chromene-
1
3-carbonitrile (4d) Yellow solid; H NMR (600 MHz, DMSO-d6): d = 0.93 (s, 3
H), 1.01 (s, 3 H), 2.05 (d, J = 4.1 Hz, 1 H), 2.07 (d, J = 4.1 Hz, 1 H), 2.21 (d,
J = 16.1 Hz, 1 H), 2.44 (d, J = 17.6 Hz, 1 H), 4.04 (s, 1 H), 6.63 (d, J = 8.7 Hz, 2 H),
6.87 (s, 2 H, NH2), 6.91 (d, J = 8.5 Hz, 2 H), 9.21 (s, 1 H). IR (KBr): mmax = 3392,
3322, 2961, 2195, 1682, 1651, 1512, 1369 cm-1. ESI–MS: m/z = 333.1 [M?Na]?.
123

b-Cyclodextrin as an efficient catalyst for the one-pot…
2-Amino-4-(4-fluoro-phenyl)-7,7-dimethyl-5-oxo-5,6,7,8-tetrahydro-4H-chromene-
1
3-carbonitrile (4f) White solid; H NMR (600 MHz, CDCl3): d = 1.03 (s, 3 H),
1.11 (s, 3 H), 2.19 (d, J = 16.4 Hz, 1 H), 2.19 (d, J = 16.4 Hz, 1 H), 2.44 (s, 2 H),
4.40 (s, 1 H), 4.57 (s, 2 H), 6.97 (t, J = 8.6 Hz, 2 H), 7.20 (dd, J = 5.2, 5.3 Hz, 1
H). IR (KBr): mmax = 3368, 3188, 2963, 2189, 1684, 1651, 1604, 1506, 1370 cm-1
ESI–MS: m/z = 335.1 [M?Na]?.
.
2-Amino-4-(4-chloro-phenyl)-7,7-dimethyl-5-oxo-5,6,7,8-tetrahydro-4H-chromene-
3-carbonitrile (4g) White solid; 1H NMR (600 MHz, CDCl3): d = 1.03 (s, 3 H), 1.11
(s, 3H), 2.19(d, J = 16.4 Hz, 1 H), 2.24 (d, J = 16.4 Hz, 1 H), 2.45 (s, 2 H), 4.39 (s, 1 H),
4.56(s, 2 H), 7.17 (d, J = 8.4 Hz, 2 H), 7.26 (d, J = 8.4 Hz, 2 H). IR (KBr): mmax = 3396,
3212, 2961, 2199, 1681, 1660, 1604, 1371 cm-1. ESI–MS: m/z = 351.1 [M?Na]?.
2-Amino-7,7-dimethyl-4-(4-nitro-phenyl)-5-oxo-5,6,7,8-tetrahydro-4H-chromene-3-
1
carbonitrile (4h) Yellow solid; H NMR (600 MHz, CDCl3): d = 1.03 (s, 3 H),
1.13 (s, 3 H), 2.19 (d, J = 16.5 Hz, 1 H), 2.26 (d, J = 16.5 Hz, 1 H), 2.48 (s, 2 H),
4.52 (s, 1 H), 4.65 (s, 2 H), 7.42 (d, J = 8.8 Hz, 2 H), 8.16 (d, J = 8.7 Hz, 1 H). IR
(KBr): mmax = 3396, 3212, 2925, 2192, 1735, 1682, 1651, 1604, 1467 cm-1. ESI–
MS: m/z = 362.1 [M?Na]?.
2-Amino-7,7-dimethyl-4-(3-nitro-phenyl)-5-oxo-5,6,7,8-tetrahydro-4H-chromene-3-
1
carbonitrile (4i) Yellow solid; H NMR (600 MHz, CDCl3): d = 1.04 (s, 3 H),
1.13 (s, 3 H), 2.19 (d, J = 16.3 Hz, 1 H), 2.26 (d, J = 16.3 Hz, 1 H), 2.46 (d,
J = 17.7 Hz, 1 H), 2.51 (d, J = 17.7 Hz, 1 H), 4.53 (s, 1 H), 4.72 (s, 2 H), 7.48 (t,
J = 7.9 Hz, 1 H), 7.67 (d, J = 7.7 Hz, 1 H), 8.04 (t, J = 1.7 Hz, 1 H), 8.08 (d,
J = 7.9 Hz, 1 H). IR (KBr): mmax = 3391, 3181, 2959, 2184, 1682, 1651, 1601,
1425, 1372 cm-1. ESI–MS: m/z = 362.1 [M?Na]?.
2-Amino-7,7-dimethyl-4-(2-nitro-phenyl)-5-oxo-5,6,7,8-tetrahydro-4H-chromene-3-
1
carbonitrile (4j) Yellow solid; H NMR (600 MHz, CDCl3): d = 0.99 (s, 3 H),
1.05 (s, 3 H), 2.12 (d, J = 16.0 Hz, 1 H), 2.19 (d, J = 16.0 Hz, 1 H), 2.45 (s, 2 H),
4.71 (s, 2 H), 5.19 (s, 1 H), 7.32 (m, 2 H), 7.51 (t, J = 7.4, 8.0 Hz, 1 H), 7.79 (d,
J = 8.0 Hz, 1 H). IR (KBr): mmax = 3470, 3372, 2924, 2193, 1687, 1663, 1525,
1469, 1364 cm-1. ESI–MS: m/z = 362.1 [M?Na]?.
2-Amino-4-(3,4-dimethoxy-phenyl)-7,7-dimethyl-5-oxo-5,6,7,8-tetrahydro-4H-chro-
mene-3-carbonitrile (4l) Yellow solid; 1H NMR (600 MHz, CDCl3): d = 1.04 (s,
3 H), 1.10 (s, 3 H), 2.19 (d, J = 16.4 Hz, 1 H), 2.24 (d, J = 16.4 Hz, 1 H), 2.44 (s, 2
H), 3.82 (s, 3 H), 1.86 (s, 3 H), 4.34 (s, 1 H), 4.79 (s, 2 H), 6.75 (dd, J = 1.9, 1.9 Hz,
1 H), 6.79 (d, J = 8.0 Hz, 2 H). IR (KBr): mmax = 3393, 3328, 2932, 2193, 1680,
1657, 1606, 1513, 1365 cm-1. ESI–MS: m/z = 377.1 [M?Na]?.
2-Amino-4-pyridin-7,7-dimethyl-5-oxo-3-yl-5,6,7,8-tetrahydro-4H-chromene-3-car-
bonitrile (4m) Yellow solid; 1H NMR (600 MHz, CDCl3): d = 1.02 (s, 3 H), 1.11
(s, 3 H), 2.19 (d, J = 16.4 Hz, 1 H), 2.24 (d, J = 16.4 Hz, 1 H), 2.44 (d,
J = 17.8 Hz, 1 H), 2.48 (d, J = 17.8 Hz, 1 H), 4.43 (s, 1 H), 4.96 (br, 2 H), 7.24
(dd, J = 4.9, 7.8 Hz, 1 H), 7.62 (td, J = 1.8, 7.8 Hz, 1 H), 8.45 (dd, J = 1.4,
4.7 Hz, 1 H), 8.49 (d, J = 2.2 Hz, 1 H). 13C NMR (150 MHz, CDCl3): d = 27.71,
28.75, 32.22, 33.64, 40.66, 50.55, 61.73, 113.16, 118.38, 123.59, 135.95, 139.00,
123

J. Lu et al.
147.89, 148.79, 158.07, 162.13, 195.79. IR (KBr): mmax = 3431, 3336, 2956, 2186,
1679, 1599, 1530, 1349 cm-1. ESI–MS: m/z = 318.1 [M?Na]?.
2-Amino-4-isopropyl-7,7-dimethyl-5-oxo-5,6,7,8-tetrahydro-4H-chromene-3-car-
bonitrile (4o) White solid; 1H NMR (600 MHz, CDCl3): d = 0.74 (d,
J = 6.7 Hz, 3 H), 1.04 (d, J = 7.1 Hz, 3 H) 1.10 (d, J = 9.6 Hz, 6 H), 1.90 (m,
1 H), 2.26 (d, J = 16.4 Hz, 1 H), 2.30 (d, J = 16.4 Hz, 1 H), 2.38 (s, 2 H), 3.34 (d,
J = 2.3 Hz, 1 H), 4.75 (s, 2 H). IR (KBr): mmax = 3387, 3207, 2924, 2194, 1657,
1380 cm-1. ESI–MS: m/z = 283.1 [M?Na]?.
Results and discussion
b-CD is a water-soluble cyclic oligosaccharide possessing hydrophobic cavities; it
binds substrates selectively and catalyzes chemical reactions by involving the
reversible formation of host–guest complexes with noncovalent bonding, as seen in
enzymes [20, 21]. Therefore, it is widely used as a catalyst for organic reactions in
O
Ar
O
O
CN
NH
-CD 2.0 mol%
H O, r.t.
CN
CN
ArCHO
2
O
2
1
2
3
4
Scheme 1 Synthesis of 4H-benzo[b]pyran derivatives
Table 1 One-pot synthesis of 4H-benzo[b]pyran 4g in the presence of different conditionsa
Entry
Additive (mmol %)
Time (h)
Temp (°C)
Yieldb (%)
1
–
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
3.5
2.5
1.0
r.t.
r.t.
r.t.
r.t.
r.t.
r.t
23c
81
70
53
94
93
82
93
93
92
94
2
TBAC (10)d
HTAB (10)d
TEAI (10)d
b-CD (10)
b-CD (4.0)
b-CD (1.0)
b-CD (2.0)
b-CD (2.0)
b-CD (2.0)
b-CD (2.0)
3
4
5
6
7
r.t.
r.t.
40
60
80
8
9
10
11
a
Condition: the reaction was performed by using 4-chlorobenz-aldehyde (1.0 mmol), malononitrile
(1.1 mmol), dimedone (1.1 mmol), in 5 ml water
b
Yields refer to isolated products
c
Yield of the product isolated after column chromatography
d
TBAC tetrabutyl ammonium chloride, HTAB hexadecyl trimethyl ammonium bromide bromide, TEAI
tetraethyl ammonium iodide
123

b-Cyclodextrin as an efficient catalyst for the one-pot…
Table 2 Synthesis of 4H-benzo[b]pyrans catalyzed by b-CDa
Entry
Ar
Productb
Yieldc (%)
Time (h)
Mp (°C)
Found
Reported
1
C6H5
4a
4b
4c
4d
4e
4f
92
88
91
91
90
94
93
94
93
86
89
83
90
91
72
83
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.5
5.0
9.0
7.5
224–226
199–200
212–214
208–210
230–232
210–212
210–212
177–179
210–212
223–225
253–255
175–177
207–209
225–227
179–181
182–183
226–228 [13]
198–200 [12]
214–216 [12]
204–205 [10]
236–238 [10]
210–211 [13]
207–209 [13]
177–178 [12]
208–211 [12]
224–226 [12]
255–257 [10]
173–174 [13]
2
4-MeO–C6H4
4-Me–C6H4
4-OH–C6H4
3-OH–C6H4
4-F–C6H4
3
4
5
6
7
4-Cl–C6H4
4-NO2–C6H4
3-NO2–C6H4
2-NO2–C6H4
3,4-Cl2–C6H3
3,4-(CH3O)2–C6H3
3-Pyridine
4g
4h
4i
8
9
10
11
12
13
14
15
16
a
4j
4k
4l
d
–
4m
4n
4o
4p
2-Furan
226–228 [13]
e
–
(CH3)2CH
C6H5CH=CH
182–184 [11]
Condition: the reaction was performed by using aldehyde 1 (1.0 mmol), malononitrile 2 (1.1 mmol),
and dimedone 3 (1.1 mmol) in the present of 2.0 mol % of b-CD in 5 mL H2O at the room temperature
b
All products were characterized by 1H NMR, IR spectroscopy and mass spectroscopy
c
Yield refer to isolated products
d
Novel compound
e
Melting point not reported
water [22]. As part of our efforts to develop a green chemistry through the one-pot
synthesis of target molecules in water, we report here the Knoevenagel-Cyclocon-
densation reaction of arylaldehyde 1, malononitrile 2, and dimedone 3, for the
preparation of 4H-benzo[b]pyran derivatives, using b-CD as a catalyst in aqueous
medium (Scheme 1).
In a typical experimental procedure, we examined the effects of the amount of
catalysts, reaction time and temperature on the reaction to optimize the conditions of
the model reaction of 4-chlorobenzaldehyde 1g, malononititrile 2 with dimedone 3
(Scheme 1). Although Azath et al. stated that under b-CD and water condition, no
product was observed [19], our results (Table 1) suggested that b-CD certainly
catalyzed the three-component reaction (Table 1, entries 1 and 5). The three-
component reaction of 4-chlorobenzaldehyde 1g, malononititrile 2 with dimedone 3,
in the absence of any catalyst, in water for 5 h gave a corresponding 4g with only
23 % yield (Table 1, entry 1). In addition, b-CD showed the most catalytic activity
among the screened catalysts (Table 1, entries 2–5). The amount of b-CD was also
critical to the reaction. We found that 2.0 mol % of catalyst was preferred, that
decreasing the amount of catalyst resulted in poor yield, and that increasing the
123

J. Lu et al.
amount of catalyst showed no improvement of yields (Table 1, entries 5–8). Further
study on temperature effects revealed that from 25 to 80 °C, the temperature has little
effect on the yields, but accelerated the reaction from 5 to 1 h (Table 1, entries 8–11).
Having established the reaction conditions, various arylaldehydes were treated
with malononitrile and dimedone to investigate the reaction scope. As summarized
in Table 2, the electron-withdrawing group (such as –F, –Cl, –NO2) or the electron-
donating group (such as –OCH3, –CH3, –OH) on the aromatic ring of aldehyde has
no distinct impact on the reaction (entries 2–12, Table 2). However, the steric
properties of the arylaldehydes have great impact on the efficiency of the reaction.
Arylaldehydes without substituents or with mono-substitutes showed generally
higher efficiency than those with disubstituent aldehydes (entry 1–9 and 11–12,
Table 2). Bulky groups at ortho- positions of the aldehydes showed a relatively
lower yield (entries 10, Table 2). Alkylaldehyde was less reactive compared with
arylaldehydes (entry 15, Table 2). Our results indicate that the catalysis process
involves the formation of a size-selective inclusion complex between arylaldehyde
and b-CD.
Complexation of b-CD and arylaldehydes has been reported by Rao et al. [23].
Hydrophobic interactions between the hydrophobic cavity of b-CD and the aromatic
ring were the driving force in the inclusion process, but hydrogen bonding between
primary or second hydroxyl groups of b-CD and polar substituents of the
arylaldehydes as well as the directions of the substituents may also be important
factors in the formation of the complexes. The catalyst is also found to be reusable.
Up to three times, there is little change in its catalytic efficiency.
N
H
N
C
C
O
H
O
C
H
H
O
O
H
H
O
O
N
C
N
C
H
H
H
CN
OH
O
N
O
H
O
O
O
H
X
X
X
1
5
6
O
H
H
N
C
O
O
O
N
C
O
NH2
N
C
X
X
7
4
Fig. 1 Proposed reaction mechanism of b-Cyclodextrin-catalyzed synthesis of 4H-benzo[b]pyran
derivatives
123

b-Cyclodextrin as an efficient catalyst for the one-pot…
A proposed mechanism for the reaction is outlined in Fig. 1. The reaction was
promoted by the formation of an inclusion complex between b-CD and arylaldehyde
1. The intermediate cyano olefin 5 was readily formed in situ from Knoevenagel
condensation between b-CD solubilized aryladelhyde 1 and active methylene
compound 2 in water. This can be evidenced by the steric effects of the
arylaldehydes on the reaction efficiency (Table 2). b-CD also catalyzed the
formation of the enolic form of dimedone 3 through hydrogen bonding stabilization,
which could easily react with cyano olefin 5 and give intermediate 6, followed by
cyclization and tautomerization of 7 to give the final products 4. It is worth pointing
out that this transformation may not need a base catalysis as suggested by Moustafa
et al. [24], as evidenced by our experimental results and other non-base catalyzed
synthesis of 4H-benzo[b]pyran [9, 13, 15].
Conclusion
We have demonstrated that b-CD is an efficient catalyst for the synthesis of 4H-
benzo[b]pyran derivatives in aqueous media. Compared with previously reported
procedures, our protocol provides advantages, such as operational simplicity,
excellent yields, an environmentally benign catalyst and solvent, and mild reaction
conditions, that make it a useful and attractive method for the preparation of these
compounds.
Acknowledgments The work was supported by funds from the National Natural Science Foundation of
China: 21442012 and the Chinese Academy of Sciences.
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