One-pot synthesis of benzopyrans catalyzed by silica supported dual acidic ionic liquid under solvent-free conditions

Article abstract of DOI:10.1515/hc-2017-0163

A mild and efficient method was developed for the preparation of tetrahydrobenzo[b]pyrans through a one-pot three-component condensation of aldehydes, malononitrile and dimedone in the presence of silica supported dual acidic ionic liquid (DAIL@SiO_2<

Full text of DOI:10.1515/hc-2017-0163

Heterocycl. Commun. 2017; aop
Preliminary Communication
Qiang Zhang*, Huaixin Wei, Jihang Li, Xin Zhao and Jun Luo
One-pot synthesis of benzopyrans catalyzed by
silica supported dual acidic ionic liquid under
solvent-free conditions
https://doi.org/10.1515/hc-2017-0163
compounds can be prepared by multicomponent conden-
sation of dimedone with aldehyde and malononitrile in
the presence of various catalysts including tetra-methyl
Received July 26, 2017; accepted September 14, 2017
Abstract: A mild and efficient method was developed for
the preparation of tetrahydrobenzo[b]pyrans through a
one-pot three-component condensation of aldehydes,
malononitrile and dimedone in the presence of silica sup-
ammonium hydroxide [8], RE(PFO) [9], iodine [10], NaBr
3
[
11], Na SeO [12], solid acids [13, 14], ion-exchange resins
2 4
[
15], magnetic nanocatalysts [16, 17], 1,4-diazabicyclo[2.2.2]
octane based ionic liquids [18] and metal complexes [19].
Many of the reported methods suffer from limitations such
as prolonged reaction times [10, 12], use of volatile organic
solvents [9, 10, 14, 15], use of microwave or ultrasonic irra-
diation [11, 16] and poor catalyst recyclability [8, 10–12].
Moreover, most of them are practical with aromatic alde-
hydes only [13, 15–19] as the reactions with aliphatic alde-
ported dual acidic ionic liquid (DAIL@SiO ) as a powerful
2
catalyst under solvent-free conditions. This procedure is
characterized by mild reaction conditions, simple workup
and environmental friendliness. Moreover, the catalyst
could be recycled for five times with only a slight loss of
catalytic activity.
Keywords: benzopyrans; one-pot; solvent-free; supported hydes furnish low yields [9].
ionic liquid.
Ionic liquids (ILs), as eco-friendly reaction media or
catalysts, have attracted increasing attention due to their
low vapor pressure, high thermal stability, excellent solu-
bility, and ease of recovery and reuse [20, 21]. A concept of
supported ionic liquid catalysis (SILC) has been proposed,
which combines the benefits of ILs and heterogeneous cat-
alysts, providing high designability, high ‘solubility’ of cat-
alytic site and ease of handling, separation and recycling
Introduction
Multicomponent reactions (MCRs) are highly efficient
approaches to access complex structures in a simple syn-
thetic operation from three or more reactants. High atom
economy, great efficiency and procedural convenience in
the construction of heterocycles are the advantages of MCRs
[
22]. Recently, we have prepared some supported ionic
liquid catalysts [23–25], which are effective in the synthe-
sis of amidoalkyl naphthols and benzoxanthenes through
the MCRs. In continuation of our work, herein we report a
mild and efficient procedure for one-pot three-component
[
1–3]. Tetrahydrobenzo[b]pyrans are an important class of
heterocyclic compounds, as they form the essential kernel
structure of emerging drugs with diverse bioactivity, such
as inhibitors of tyrosinase and agents with anti-influenza,
anticancer and anti-anaphylactin activity [4, 5]. Addition-
ally, substituted 4H-pyrans can be employed as pigments,
agrochemicals and photoactive materials [6, 7]. These
O
O
R
O
CN
DAIL@SiO2
CN
R
H
CN
1
00°C, solvent-free
O
O
NH2
1a–d
2
3
4a–d
O
O
O
HSO4
*
Corresponding author: Qiang Zhang, School of Chemistry,
DAIL@SiO2 = SiO2
Si
N
N
SO3H
Biology and Material Engineering, Suzhou University of Science
and Technology, Suzhou 215009, China,
a: R = Ph
f: R = 3-NO2-C6H4
g: R = 4-NO2-C6H4
h: R = 3-Br-C6H4
i: R = 3-Cl-C6H4
j: R = 4-Cl-C6H4
k: R = 2,4-Cl2-C6H3
l: R = 3,4-Cl2-C6H3
m: R = 2-furyl
n: R = C3H7
o: R = C4H9
e-mail: zhangqiang005@gmail.com
b: R = 4-OH-C6H4
c: R = 4-Me-C6H4
d: R = 4-OMe-C6H4
e: R = 2-NO2-C6H4
Huaixin Wei, Jihang Li and Xin Zhao: School of Chemistry, Biology
and Material Engineering, Suzhou University of Science and
Technology, Suzhou 215009, China
Jun Luo: School of Chemical Engineering, Nanjing University
of Science and Technology, Nanjing 210094, China
Scheme 1ꢀThe DAIL@SiO catalyzed synthesis of tetrahydrobenzo[b]
2
pyrans 4.
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ꢀꢀꢀꢀꢁꢀQ. Zhang et al.: One-pot synthesis of benzopyrans
H
H
O
H
O
O
O
R
O
O
R
O
R
H
OH
O
O
H
O
O
S
O
S
–H O
H
N
2
O
O
C
CN
O
N
N
CN
O
DAIL@SiO2
C
O
R
O
R
N
O
R
H
CN
N
CN
NH
DAIL@SiO2
CN
Si
O
DAIL@SiO2
C
O
O
O
OH
O
NH2
DAIL@SiO2
Scheme 2ꢀPlausible mechanism for the synthesis of tetrahydrobenzo[b]pyrans.
synthesis of the tetrahydrobenzo[b]pyrans using silica- transformation under the optimized reaction conditions.
supported dual acidic ionic liquid DAIL@SiO as a recover- It was shown that the aromatic aldehydes with electron-
2
able catalyst under solvent-free conditions (Scheme 1).
withdrawing groups react faster than the aromatic
aldehydes with electron-donating groups, as expected
[
16–18]. Successful synthesis of the 2-furanyl substituted
tetrahydrobenzo[b]pyran derivative 4m and two alkyl-
substituted analogs 4n and 4o in acceptable yields can
also be noted (Scheme 1). As already mentioned, the
reported methods provide alkyl substituted benzopyrans
in low yields [4, 5, 9].
A possible reaction mechanism for the synthesis of
tetrahydrobenzo[b]pyrans is given in Scheme 2. This syn-
thetic scheme is self-explanatory and fully compatible
with other literature reports on the use of acidic catalysts
in the synthesis of these products.
Results and discussion
Under optimal conditions, a model reaction of benzalde-
hyde (2 mmol), malononitrile (2.2 mmol) and dimedone
(
2 mmol) in the presence of DAIL@SiO was preformed
2
under solvent-free conditions at 100°C to give product 4a
in 86% yield. Under similar conditions, products 4b–o
were obtained in the yields ranging from 51% to 91%. In
the absence of the catalyst, only a trace amount of product
could be detected. The optimum amount of DAIL@SiO2
was 60 mg, and no improvement was observed by increas-
ing the amount of the catalyst to 80 mg or 100 mg. Lower
temperatures (40ꢀ~ꢀ90°C) decelerated the reaction rate sig- Conclusions
nificantly and led to lower yields. A higher temperature
(
110°C) did not provide a higher yield due to the increased Silica supported dicationic acidic ionic liquid DAIL@
formation of by-products [26, 27].
SiO catalyzes synthesis of benzopyrans in a one-pot
2
A simple recovery and reuse of catalyst is highly three-component reaction under solvent-free conditions.
preferable in terms of green synthetic process. The recy- The procedure is equally effective with aliphatic and aro-
clability of the DAIL@SiO was investigated using a three- matic aldehydes. The advantages of this method are high
2
component reaction of 3-nitrobenzaldehyde (2 mmol), catalytic activity, short reaction time, simple work-up and
malononitrile (2.2 mmol) and dimedone (2 mmol) under environmental friendliness.
solvent-free conditions at 100°C. When the reaction was
completed, acetone was added to dissolve the product.
The catalyst was simply filtered off and washed with
Experimental
acetone. After being dried, it was subjected to the next
run. The catalyst DAIL@SiO could be recycled five times
2
Melting points were determined on a Perkin-Elmer differential scan-
with only a slight loss of catalytic activity.
1
ning calorimeter and are uncorrected. H NMR spectra were recorded
Aromatic aldehydes with electron-donating or
on a Bruker AVANCE III spectrometer (500 MHz, DMSO-d ). The
6
electron-withdrawing groups undergo smoothly the DAIL@SiO catalyst was synthesized according to our previous report
2
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Q. Zhang et al.: One-pot synthesis of benzopyransꢂꢁꢀꢀꢀꢂ3
[
23]. All commercially available chemicals and solvents were used 2-Amino-4-(4-chlorophenyl)-7,7-dimethyl-5-oxo-5,6,7,8-tetrahy-
without further purification.
dro-4H-chromene-3-carbonitrile (4j)ꢁYield 86% of white solid;
mp 215–217°C, lit mp 215–217°C [8].
2
-Amino-4-(2,4-dichlorophenyl)-7,7-dimethyl-5-oxo-5,6,7,8-
General procedure for the synthesis of benzopyrans 4a–o
tetrahydro-4H-chromene-3-carbonitrile (4k)ꢁYield 88% of white
solid; mp 191–193°C, lit mp 192–194°C [16].
A mixture of aldehyde (2 mmol), malononitrile (2.2 mmol) dimedone
(
2 mmol) and DAIL@SiO (60 mg) was stirred under solvent-free con-
2
2-Amino-4-(3,4-dichlorophenyl)-7,7-dimethyl-5-oxo-5,6,7,8-
tetrahydro-4H-chromene-3-carbonitrile (4l)ꢁYield 90% of white
solid; mp 226–227°C, lit mp 225–227°C [28].
ditions for several hours at 100°C. After completion of the reaction
as indicated by TLC analysis (ethyl acetate/n-hexane, 1:3), acetone
(
15 mL) was added to the mixture and the solid catalyst was sepa-
rated by filtration, washed with acetone and dried under reduced
pressure. Pure benzopyran product was obtained by concentration
of the mixture, followed by crystallization of the residue from 95%
ethanol.
2
-Amino-4-(furan-2-yl)-7,7-dimethyl-5-oxo-5,6,7,8-tetrahy-
dro-4H-chromene-3-carbonitrile (4m)ꢁYield 85% of gray white
1
solid; mp 218–220°C, lit mp 219–221°C [16]; H NMR: δ 7.48–7.45 (m,
1
H), 7.02 (s, 2H), 6.31 (m, 1H), 6.04 (d, Jꢀ=ꢀ4 Hz, 1H), 4.33 (s, 1H), 2.45
(
(
s, 2H), 2.32 (d, Jꢀ=ꢀ16 Hz, 1H), 2.15 (d, Jꢀ=ꢀ16 Hz, 1H), 1.05 (s, 3H), 0.99
2
-Amino-7,7-dimethyl-5-oxo-4-phenyl-5,6,7,8-tetrahydro-4H-
chromene-3-carbonitrile (4a)ꢁYield 86% of white solid; mp 230–
31°C, lit mp 227–229°C [13].
s, 3H).
2
2
-Amino-7,7-dimethyl-5-oxo-4-propyl-5,6,7,8-tetrahydro-4H-
chromene-3-carbonitrile (4n)ꢁYield 56% of white solid; mp 170–
2
-Amino-7,7-dimethyl-4-(4-hydroxyphenyl)-5-oxo-5,6,7,8-tetrahy-
1
1
72°C, lit mp 172–174°C [9]; H NMR: δ 6.89 (s, 2H), 3.16 (t, Jꢀ=ꢀ4.5 Hz,
dro-4H-chromene-3-carbonitrile (4b)ꢁYield 87% of white solid;
1
H), 2.44 (d, Jꢀ=ꢀ17 Hz, 1H), 2.35 (d, Jꢀ=ꢀ17 Hz, 1H), 2.28 (d, Jꢀ=ꢀ16 Hz, 1H),
1
mp 203–205°C, lit mp 204–205°C [8]; H NMR: δ 9.25 (s, 1H), 6.91–6.94
2
.19 (d, Jꢀ=ꢀ16 Hz, 1H), 1.13–1.48 (m, 4H), 1.03 (s, 3H), 1.00 (s, 3H), 0.84
(
m, 4H), 6.66 (d, Jꢀ=ꢀ8 Hz, 2H), 4.07 (s, 1H), 2.49 (s, 2H), 2.24 (d, Jꢀ=ꢀ16 Hz,
(
t, Jꢀ=ꢀ7.5 Hz, 3H).
1
H), 2.09 (d, Jꢀ=ꢀ16 Hz, 1H), 1.03 (s, 3H), 0.95 (s, 3H).
2
-Amino-4-butyl-7,7-dimethyl-5-oxo-5,6,7,8-tetrahydro-4H-
chromene-3-carbonitrile (4o)ꢁYield 51% of white solid; mp 166–
68°C, lit mp 165–167°C [9].
2
-Amino-7,7-dimethyl-4-(4-methylphenyl)-5-oxo-5,6,7,8-tetrahy-
dro-4H-chromene-3-carbonitrile (4c)ꢁYield 84% of white solid;
1
1
mp 218–219°C, lit mp 217–219°C [4]; H NMR: δ 7.09 (d, Jꢀ=ꢀ8 Hz, 2H),
7
.02 (d, Jꢀ=ꢀ8 Hz, 2H), 6.97 (s, 2H), 4.13 (s, 1H), 2.52 (s, 2H), 2.23–2.26 (m,
4
H), 2.09 (d, Jꢀ=ꢀ8 Hz, 1H), 1.04 (s, 3H), 0.95 (s, 3H).
Acknowledgments: This work was financially supported
by the Natural Science Foundation of Jiangsu Province
2
-Amino-4-(4-methoxyphenyl)-7,7-dimethyl-5-oxo-5,6,7,8-tetrahy-
dro-4H-chromene-3-carbonitrile (4d)ꢁYield 82% of white solid; mp
92–194°C, lit mp 195–196°C [5].
(China) (No. BK20150282), the Natural Science Foundation
of the Higher Education Institutions of Jiangsu Province
No. 17KJD430005) and the Priority Academic Program
Development (PAPD) of Jiangsu Higher Education Institu-
1
(
2-Amino-7,7-dimethyl-4-(2-nitrophenyl)-5-oxo-5,6,7,8-tetrahy-
dro-4H-chromene-3-carbonitrile (4e)ꢁYield 90% of pale yellow tions. The authors would like to thank the Excellent Inno-
solid; mp 222–223°C, lit mp 223–224°C [13].
vation Team at the Science and Technology of Education
Department of Jiangsu Province for discussions.
2
-Amino-7,7-dimethyl-4-(3-nitrophenyl)-5-oxo-5,6,7,8-tetrahy-
dro-4H-chromene-3-carbonitrile (4f)ꢁYield 87% of pale yellow
1
solid; mp 213–214°C, lit mp 214–216°C [4]; H NMR: δ 8.08 (d, Jꢀ=ꢀ8 Hz,
1
2
H), 7.98 (s, 1H), 7.61–7.69 (m, 2H), 7.18 (s, 2H), 4.42 (s, 1H), 2.56 (s, 2H),
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