Polypyrrole/Fe3O4/CNT as a recyclable and highly efficient catalyst for one-pot three-component synthesis of pyran derivatives

Article abstract of DOI:10.1002/aoc.4235

Polypyrrole (PPY)/Fe₃O₄/CNT has been synthesized and characterized by FT-IR, TEM and SEM techniques and its catalytic activity has been evaluated in the synthesis of several series of pyran derivatives. Tetrahydrobenzo[b]pyranes, 4H-

Full text of DOI:10.1002/aoc.4235

Received: 9 October 2017
DOI: 10.1002/aoc.4235
Revised: 23 November 2017
Accepted: 25 November 2017
F U L L P A P E R
Polypyrrole/Fe O /CNT as a recyclable and highly efficient
3
4
catalyst for one‐pot three‐component synthesis of pyran
derivatives
Seyedeh Fatemeh Hojati
| Amirhassan Amiri | Nasrin MoeiniEghbali | Sakineh Mohamadi
Department of Chemistry, Hakim
Sabzevari University, Sabzevar, Iran
Polypyrrole (PPY)/Fe O /CNT has been synthesized and characterized by FT‐IR,
3
4
TEM and SEM techniques and its catalytic activity has been evaluated in the
synthesis of several series of pyran derivatives. Tetrahydrobenzo[b]pyranes, 4H‐
pyran‐3‐carboxylates, 4H,5H‐pyrano[3,2‐c]chromenes and dihydropyrano[2,3‐c]
pyrazoles have been successfully prepared from one‐pot three‐component
condensation of aldehyde, malononitrile and active methylene‐containing
compounds (dimedone /ethyl acetoacetate/4‐hydroxycoumarin/3‐methyl‐2‐
pyrazoline‐5‐one) using PPY/Fe O /CNT as a new and reusable heterogeneous
Correspondence
Seyedeh Fatemeh Hojati, Department of
Chemistry, Hakim Sabzevari University,
Sabzevar, Iran.
Email: hojatee@yahoo.com;
sf.hojati@hsu.ac.ir
3
4
catalyst. The present method offer several advantages such as; high yields of
products, short reaction times, easy work‐up procedure and easy separation of
the catalyst from the reaction mixture due to its magnetic character. Furthermore,
chemoselective synthesis of bis‐benzo[b]pyran from terephthalaldehyde can be
achieved by this method.
KEYWORDS
3 4
one‐pot synthesis, polypyrrole/Fe O /CNT nanocomposite, pyran derivatives, three‐component
reaction
1
| INTRODUCTION
component reaction of aldehyde, malononitrile and vari-
[
9–13]
ous β‐diketones
using various conditions like micro-
[
14]
[15]
Recently multi‐component reaction (MCRs) have been
gained considerable attention in combinatorial chemistry
because of their ability for combination of more than two
starting materials in a single flask to prepare a new
wave
and ultrasonic irradiation.
A variety of
[
16]
[17]
[18]
reagents such as Yb(PFO)3,
LiBr,
SB‐DABCO,
[
19,20]
[21]
tetrabutylammonium bromide (TBAB),
Na SeO ,
2
4
[24,25]
[
22,23]
solid acids,
diammonium hydrogen phosphate,
[1,2]
product.
Pyrans are an important class of heterocyclic
silica bonded n‐propyl‐4‐aza‐1‐azoniabicyclo[2.2.2]octane
[
18]
[26]
compounds that plays an important role in pharmaceuti-
cal chemistry. Some pyran derivatives have been used
as spasmolytic, diuretic, anti‐tumor,
anti‐anaphylactin and anti‐coagulant agents. Further-
more, they can be used in several neurodegenerative dis-
eases, such as parkinson, alzheimer, down syndrome,
huntington, schizophrenia and myoclonus diseases as
cognitive enhancer.
reported for the synthesis of these compounds via three‐
chloride
and DBU
were employed for the prepara-
[3]
tion of pyrans. However, most of the reported methods suf-
fer from some disadvantages including long reaction times,
low yields of products and the use of toxic organic solvents
such as DMF or acetic acid that make some complications
[4]
[5]
anti‐cancer,
[6]
[7]
[
27]
in work‐up procedure.
Therefore, there is still a need
for design and development of new catalytic systems for
mild and efficient synthesis of pyran derivatives with
respect to economical and environmental aspects.
[8]
Numerous method have been
Appl Organometal Chem. 2018;e4235.
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Copyright © 2018 John Wiley & Sons, Ltd.
1 of 13
https://doi.org/10.1002/aoc.4235

2
of 13
HOJATI ET AL.
In recent years, design, synthesis and application of
reaction was maintained at 60 °C for 60 min. The
new nanomagnetic catalysts have been made a new field
of challenge in chemistry especially in the synthesis of
biologically active compounds and in drug discovery. Sim-
ple separation of magnetic nanocomposites from the reac-
tion mixture, in combination with nano character of these
compounds makes them an excellent choice for catalytic
applications. Furthermore, the reusable systems are of
great economical and environmental importance espe-
cially in industrial usages due to their reduction of costs
and pollution.
black precipitates obtained (Fe O4 nano‐particles)
3
were collected using a magnet and washed repeatedly
with deionized water until the pH of the washings
became neutral and finally dried under vacuum at
60 °C for 24 h.
2.3 | Preparation of the catalyst
Nanomagnetic polypyrrole (PPY)/Fe O /CNT was pre-
3
4
pared according to the reported procedure in articles with
[
31,32]
some modification.
The PPY/Fe O /CNT nanocom-
3 4
posites were synthesized via oxidative polymerization of
pyrrole monomers in the presence of Fe O NPs and
2
| EXPERIMENTAL
3
4
CNTs (as the charge‐balancing dopant in the polymer)
using potassium persulfate as oxidant. 250 mg of the dried
Fe O NPs and 50 mg of CNT‐COOH were added to
Chemicals were purchased from Merck chemical compa-
nies. IR spectra were recorded on a shimadzu FT‐IR
1
3 4
8
440 s spectrophotometer. H NMR spectra were reco‐
2
0
1
00 ml deionized water under stirring for 5 min and then,
.5 ml of pyrrole monomers were added and stirred for
0 min. The reaction mixture was bubbled by nitrogen
rded on a Bruker AVANCE 300 MHZ spectrometer.
Melting points were determined with Electrothermal
100 apparatus and were uncorrected. The morphology
of PPY/Fe O /CNT and size of nano particles were deter-
9
gas for 10 min under stirring to get rid of oxygen. Subse-
quently, 2.7 g of potassium persulfate was added to the
mixture. After the addition of oxidant, the mixture was
stirred for 16 h at room temperature. The resultant PPY/
Fe O /CNT nano‐composites were collected by a magnet
3
4
mined by scanning electron microscopy (SEM) model Leo
12 AB and Transmission electron microscopy (TEM)
model Leo 1450 VP.
9
3
4
and washed with deionized water, tetrahydrofuran and
methanol several times to remove the unreacted mate-
rials, and dried at 60 °C under vacuum for 24 h and char-
acterized by FT‐IR, transmission electron microscopy
(TEM) and scanning electron microscopy (SEM)
techniques.
2
2
.1 | Synthesis of PPY/Fe O /CNT
3 4
.1.1 | CNTs functionalization
Recently, carbon nano particles have been extensively
used in the preparation of various magnetic nanocom-
posites.
[28–30]
Herein, we wish to report the application
The FT‐IR spectra of Fe O nanoparticle (a), Fe O /
3
4
3 4
of carbon nano tube (CNTs) as a suitable support in
the preparation of PPY/Fe O /CNT and study its cata-
lytic activity. To this aim, initially CNT was functional-
ized. 0.2 g of carbon nano tube (CNTs) and 50 ml of
PPY (b) and PPY/Fe O /CNT have been shown in
3 4
Figure 1.
In the IR spectrum of Fe O , absorptions peaks of Fe–
3
4
3
4
−
1
O were observed at 587 and 3390 cm which demon-
6
0 % HNO aqueous solution were added into 100 ml
strate the successful synthesis of Fe O4 nanoparticles
3
3
flask, and then were subjected to an ultrasonic bath
for 30 min. Thereafter, the mixture was refluxed for
(Figure 1a). The IR spectrum of Fe O /PPy is presented in
3
4
Figure 1b. The IR spectrum shows the typical characteris-
tic pyrrole ring stretching vibration C‐N, out‐of‐plane
vibrations of C–H and ring deformation at about
2
4 h. The resultant CNTs–COOH was filtered through
a 0.22 μm membrane and washed with distilled water
until neutralized and was dried under vacuum for 12 h
at 60 °C.
−
1
−1
−1
−1
1564 cm and 1438 cm ; 1308 cm , 1043 cm and
−
1 [33]
923 cm .
As it can be observed in Figure 1c, the
PPY/Fe O /CNT nano‐composite spectrum is the addi-
3
4
tion of spectra Fe O , CNT and PPy, and has the represen-
3
4
2
.2 | Synthesis of Fe O magnetic
3 4
tative bands of these compounds. These absorption bands
indicate successful synthesis of PPY/Fe O /CNT
nanoparticles
3
4
Magnetic nano‐particles were synthesized by chemical
co‐precipitation method. First, 11.68 g FeCl .6H O and
nanocomposite.
The morphology of PPY/Fe O /CNT and the size dis-
3
2
3 4
4
.3 g FeCl .4H O was dissolved in 400 ml of deionized
tribution of nano‐particles were determined by scanning
electron microscopy (SEM) (Figure 2) and Transmission
electron microscopy (TEM) (Figure 3). These images
clearly show that polypyrrole forms a compact and
2
2
water under nitrogen atmosphere with vigorous stirring
at 60 °C. Then ammonia solution (NH 30%, 20 ml)
was added slowly to the solution under nitrogen. The
3

HOJATI ET AL.
3 of 13
FIGURE 3 TEM micrograph of nano‐magnetic PPY/Fe
3
O
4
/CNT
FIGURE 1 FT‐IR spectra of a) Fe
3
O
4
nanoparticles b) Fe
3
O
4
/PPy
The megnetic property of PPY/Fe O /CNT was stud-
3 4
c) PPY/Fe
3
O
4
/CNT nanocomposite
ied by measurement of saturation magnetization (Ms)
and coercivity (H ) values of this nanocomposite by Yang
c
32]
[
and co‐workers.
The obtained results confirmed the
good magnetic character of PPY/Fe O /CNT. Further-
3
4
more, the thermogeravimetric analysis of PPY/Fe O /
3
4
CNT was shown a satisfactory thermal stability for this
[
32]
magnetic nanocomposite.
It was also shown that the
conductivity of this nanocomposite is more than pure
[
34]
polypyrrole matrix.
2
.4 | General procedure for the synthesis
of pyran derivatives using PPY/Fe O /CNT
3
4
nanomagnetic catalyst
A mixture of aromatic aldehyde (1 mmol), malononitrile
(
(
1 mmol) and an active methylene‐containing compound
dimedone/ cyclohexane‐1,3‐dione/ ethyl acetoacetate/ 4‐
hydroxycoumarin/ 3‐methyl‐2‐pyrazoline‐5‐one) (1 mmol)
was prepared and 0.032 gr of nanomagnetic catalyst
was added to the mixture and heated at 90 °C under
solvent‐free condition. After completion of the reaction
as monitored by TLC (eluent: EtOAc/ n‐hexane, 1:1),
ethanol (10 ml) was added and the catalyst was separated
from the reaction mixture by an external magnet, washed
with ethanol and dried at 60 °C under vacuum for 2 h.
Crushed ice was added to the reaction mixture and the
resulting precipitate was filtered and washed with ethanol
to afford pure product in good to excellent yields
(Table 2).
3 4
FIGURE 2 SEM micrograph of nano‐magnetic PPY/Fe O /CNT
smooth film on Fe O /CNT. The average crystalline size
3
4
of Fe O nano‐particles in PPY/Fe O /CNT was estimated
3
4
3 4
about 30 nm.

4
of 13
HOJATI ET AL.
2
.5 | Physical and Spectral Data of Some
3H, CH
3
), 4.58 (s, 1H), 6.86 (s, 2H, NH
2
), 7.15 (d, 2H, J
Products
= 7.32 Hz), 7.19‐7.22 (m, 1H), 7.28‐7.32 (m, 2H), 12.08
(
s, 1H, NH).
2
.5.1 | 2‐Amino‐3‐cyano‐4‐phenyl‐7,7‐
dimethyl‐5‐oxo‐4H‐5,6,7,8‐
tetrahydrobenzo[b]py‐ran (4a)
′
4
5
,4 ‐(1,4‐Phenylene)bis(2‐amino‐3‐cyano‐7,7‐dimethyl‐
‐oxo‐4H‐5,6,7,8‐tetrahy‐drob‐enzo[b]pyran)
‐1
35
IR (KBr disc, cm ): 3396, 3325, 3211, 2963, 2199, 1664,
mp. 266–268 °C, m.p. 267–269 °C, lit. ; IR (KBr disc,
1
‐1
1
602, 1371, 1214, 1036; H NMR (300 MHz, DMSO‐d ,
cm ): 3448, 3327, 3189, 2960, 2194, 1655, 1602, 1363,
6
‐
1 1
ppm): δH 0.91 (s, 3H, CH ), 1.00 (s, 3H, CH ), 2.06 (d,
J=16.1 Hz, 1H), 2.22 (d, J = 16.1 Hz, 1H), 3.58 (s, 2H,
CH ), 4.13 (s, 1H, CH), 7.09‐7.18 (m, 3H, ArH), 7.23‐7.28
1210, 1148, 1029 cm , H NMR (300 MHz, DMSO‐d
ppm): δ 0.985 (s, 6H, 2CH ), 1.035 (s, 6H, 2CH ), 2.16
(d, J = 16.4 Hz, 2H), 2.23 (d, J = 16.4 Hz, 2H), 2.50 (s,
4H), 4.14 (s, 2H), 6.98 (s, 4H, 2NH ), 7.04 (s, 4H, ArH).
6
,
3
3
H
3
3
2
(m, 2H, ArH).
2
2
.5.2 | Ethyl‐6‐amino‐5‐cyano‐2‐methyl‐4‐
3 | RESULT AND DISCUSSION
phenyl‐4H‐pyran‐3‐carboxylate (6a)
‐
1
1
Here in, we wish to report a simple and convenient
method for the preparation of several classes of pyran
derivatives by condensation of aromatic aldehyde,
malononitrile and β‐diketone using PPY/Fe O /CNT as
IR (KBr disc, cm ): 3412, 3334, 2199, 1693; H NMR
(
300 MHz, DMSO‐d , ppm): δ 1.09 (t, J = 7.12 Hz, 3H),
.38 (s, 3H), 4.06‐4.00 (m, 2H), 4.43 (s, 1H), 4.44 (s, 2H,
NH ), 7.31‐7.19 (m, 5H, ArH).
6
H
2
3
4
2
a new reusable nanomagnetic catalyst.
Initial studies were performed by the reaction of 4‐
chlorobenzaldehyde, malonitrile and dimedone as
model reaction for the synthesis tetrahydrobenzo[b]
pyran derivative under different reaction conditions
2
.5.3 | 2‐Amino‐4‐phenyl‐3‐cyano‐4H,5H‐
pyrano[3,2‐c]chromene‐5‐one (8a)
‐1
IR (KBr disc, cm ): 3375, 3180, 2197, 1709; H NMR
300 MHz, DMSO‐d , ppm): δH 4.46(s, 1H), 7.22‐7.27(m,
(
Scheme 1).
(
6
The effect of solvent, amount of catalyst and tempera-
3
H, ArH) 7.30‐7.34 (m, 2H, ArH),7.42 (s, 2H, NH ), 7.46
2
ture were examined in model reaction (Table 1). The best
result was obtained when the reaction was carried out in
the presence of 32 mg of catalyst in the absence of solvent
at 90 °C, which corresponding benzo[b]pyran was gener-
ated in 95 % yield after 10 minutes (Table 1, entry 3).
The model reaction was also performed in the presence
of CNT, Fe O and PPY as catalyst and without the cata-
(
d, J = 8.3 Hz, 1H, ArH), 7.50 (td, J = 7.6, 0.9 Hz, 1H,
ArH), 7.72 (td, J = 7.8, 1.6 Hz, 1H, ArH), 7.91 (dd, J =
.9, 1.4 Hz, 1H, ArH).
7
2
.5.4 | 6‐Amino‐3‐methyl‐4‐phenyl‐1,4‐
dihydropyrano[2,3‐c]pyrazole‐5‐carbonitrile
10a)
3
4
lyst under optimized reaction conditions. The results
show that CNT has low catalytic activity which led to
the 35 % yields after 10 minutes (Table 1, entry 12).
(
‐1
IR (KBr disc, cm ): 3370, 3171, 2192, 1652, 1599, 1402,
1
1
043; H NMR (300 MHz, DMSO‐d , ppm): δ 1.76 (s,
Fe O4 successfully catalyze the reaction which 85%
6
H
3
SCHEME 1 Synthesis of
tetrahydrobenzo[b]pyran derivatives using
3 4
PPY/Fe O /CNT nanomagnetic catalyst

HOJATI ET AL.
5 of 13
a
TABLE 1 Optimization of reaction conditions for 4b
a
b
Entry
Catalyst (mg)
Conditions
Solvent
Time (min)
Yield (%)
1
PPY/Fe
PPY/Fe
PPY/Fe
PPY/Fe
PPY/Fe
PPY/Fe
PPY/Fe
PPY/Fe
PPY/Fe
PPY/Fe
PPY/Fe
3
3
3
3
3
3
3
3
3
3
3
O
O
O
O
O
O
O
O
O
O
O
4
4
4
4
4
4
4
4
4
4
4
/CNT (15)
/CNT (25)
/CNT (32)
/CNT (50)
/CNT (32)
/CNT (32)
/CNT (32)
/CNT (32)
/CNT (32)
/CNT (32)
/CNT (32)
90 °C
_
10
80
2
3
4
5
6
7
8
9
90 °C
90 °C
90 °C
Rt
_
_
_
_
_
10
10
10
10
10
10
10
90
150
30
10
10
10
120
84
97
90
25
60 °C
90 °C
85 °C
Reflux
Reflux
90 °C
90 °C
90 °C
90 °C
90 °C
37
H
2
O
20
Ethanol
35
Methanol
Chloroform
60
1
1
1
1
1
1
0
1
2
3
4
5
45
H
2
O/ Ethanol(1:1)
75
CNT (32)
Fe (32)
_
35
3
O
4
_
85
PPY (32)
_
_
Trace
Trace
_
a
Benzaldehyde (1 mmol), malononitrile (1 mmol), dimedone (1 mmol),
b
Isolated yields.
product was obtained after 10 minutes, but it is not a good
choice due to its non‐reusability and the loss of its mag-
netic character (Table 1, entry 13). Furthermore, no cata-
lytic activity was observed for the polymer (Table 1, entry
the synthesis of different substituted pyran moieties in dif-
ferent structures.
The chemoselectivity of the current method was also
investigated in the reaction of terephthalaldehyde with 2
equivalents of dimedone and malononitrile under opti-
1
4) and no product was detected in the absence of catalyst
after 120 minutes (Table 1, entry 15).
mized
conditions
which
corresponding
bis‐
The generality of the current method was investigated
in the reaction of aromatic aldehydes, malononitrile and
dimedone or 1,3‐cyclohexandion under optimized reac-
tion condition (Scheme 1). The corresponding
tetrahydrobenzo[b]pyran derivatives were obtained in
good to excellent yields in appropriate times according to
T2 Table 2. It was observed that electron‐withdrawing
substituted aldehydes were reacted faster than electron‐
donating ones which represented in their high yields
and short reaction times (Table 2, entries 1‐17).
tetrahydrobenzo[b]pyran was exclusively produced in
90% yield after 40 minutes (Scheme 3). No mono‐deriva-
tive was detected in the reaction mixture.
Although, the detailed mechanism of this reaction is
unclear, a plausible mechanism may involve the follow-
ing key steps (Scheme 4)
We compared the obtained results with some other
methods for the preparation of 2‐Amino‐3‐cyano‐4‐(4‐
chlorophenyl)‐7,7‐dimethyl‐5‐oxo‐4H‐5,6,7,8‐
tetrahydrobenzo[b]pyran in Table 3. These results clearly
More ever, the efficiency of this method was studied
for the synthesis of a series of pyran ring‐structured com-
pounds by replacing dimedone with some other active
methylene‐containing compounds (Scheme 2). To this
aim, similar reactions were performed between aromatic
aldehydes, malononitrile and ethyl acetoacete/4‐hydroxy
coumarin/3‐methyl‐2‐pyrazoline‐5‐one in the presence
of PPY/Fe O /CNT under optimized reaction conditions
demonstrate that nanomagnetic PPY/Fe O /CNT is more
efficient for this reaction.
3
4
The reusability of the catalyst was also examined in
the reaction of 4‐chlorobenzaldehyde, malononitrile and
dimedone under optimized reaction condition. After com-
pletion of the reaction, EtOH (10 ml) was added and the
nanomagnetic catalyst was separated by an external mag-
net (Figure 4), washed with ethanol and dried at 60 °C
under vacuum for 2 hours. The recovered PPY/Fe O /
3
4
and corresponding 4H‐pyrans (Table 2, entries 18‐22),
dihydropyrano[3,2,c]chromenes (Table 2, entries 23‐24)
and pyrano[2,3‐c]pyrazoles (Table 2, entries 25‐27) were
successfully generated by the current procedure. There-
fore, PPY/Fe O /CNT is a highly efficient catalyst for
3
4
CNT was reused in the similar reaction for 10 times
(Figure 5). The results show that catalyst can be reused
at least 10 times in the preparation of pyran derivatives
without significant loss in its catalytic activity.
3
4

6
of 13
HOJATI ET AL.
3 4
TABLE 2 Syntheses of pyran derivatives in solvent‐free condition catalyzed by nanomagnetic PPY/Fe O /CNT
a
Entry
Ar
β‐ diketone
product
Time (min)
Yield (%)
mp (°C) found
mp (°C) reported
[36]
1
C
6
H
5
3a
15
95
225‐228
226‐228
[
36]
2
4‐(Cl)C
3‐(Cl)C
4
H
H
4
3a
10
95
208‐210
207‐209
[37]
3
4
4
4
3a
3a
20
15
91
94
213‐215
199‐201
215‐216
201‐203
[38]
4 4
4‐(Br)C H
[37]
5
4‐(NO
2
)C
4
H
4
3a
10
95
176‐179
176‐178
[
37]
6
7
3‐(NO
2
)C
4
H
4
3a
3a
15
92
95
212‐213
207‐209
213‐214
208‐210
[38]
4‐(CN)C
4
H
4
5
(Continues)

HOJATI ET AL.
7 of 13
TABLE 2 (Continued)
a
Entry
Ar
β‐ diketone
product
Time (min)
Yield (%)
mp (°C) found
mp (°C) reported
[39]
8
4‐(OH)C
4
H
4
3a
25
84
203‐205
205‐207
[
39]
9
3‐(OH)C
4
H
4
3a
3a
20
30
86
90
228‐231
199‐202
229‐231
199‐201
[40]
1
0
4‐(OMe)C
4
H
4
[
40]
1
1
1
2
3,4‐(OMe)
2
C
4
H
4
3a
3a
40
35
84
83
167‐169
197‐198
168‐170
198‐200
[38]
4‐(iso‐pr)C
4
H
4
[
41]
1
1
3
4
2‐Furyl
3a
3a
25
35
90
88
219‐221
227‐229
220‐222
226‐228
[41]
2‐Thionyl
(Continues)

8
of 13
HOJATI ET AL.
TABLE 2 (Continued)
a
Entry
Ar
β‐ diketone
product
Time (min)
Yield (%)
mp (°C) found
mp (°C) reported
[37]
1
5
4‐(Cl)C
4
H
4
3b
12
95
226‐229
226‐229
[
37]
1
1
6
7
2‐(Cl)C
4
H
4
3b
3b
15
10
90
95
212‐214
233‐234
213‐215
234‐235
[37]
2 4 4
4‐(NO )C H
[
37]
1
1
8
9
3‐(NO
2
)C
4
H
4
3b
3b
15
40
93
82
197‐200
191‐193
198‐200
193‐195
[37]
4 4
4‐(OMe)C H
[
42]
2
2
0
1
C
6
H
5
5
5
75
60
75
78
186‐189
168‐170
189‐191
171‐173
[42]
4 4
4‐(Cl)C H
(Continues)

HOJATI ET AL.
9 of 13
TABLE 2 (Continued)
a
Entry
Ar
β‐ diketone
product
Time (min)
Yield (%)
mp (°C) found
mp (°C) reported
[38]
2
2
3‐(Cl)C
4
H
4
5
68
74
152‐154
155‐156
[42]
2
3
4‐(Br)C
4
H
4
5
70
75
172‐174
174‐175
[42]
2
4
4‐(NO
2
)C
4
H
4
5
60
80
178‐180
180‐182
[
43]
2
2
2
5
6
7
2‐Furyl
5
5
7
70
75
30
75
70
89
202‐204
204‐206
254‐255
203‐204
203‐205
255‐257
[44]
2‐Thionyl
[40]
6 5
C H
[40]
2
8
4‐(Cl)C
4
H
4
7
27
93
259‐261
259‐261
(Continues)

10 of 13
HOJATI ET AL.
TABLE 2 (Continued)
a
Entry
Ar
β‐ diketone
product
Time (min)
Yield (%)
mp (°C) found
mp (°C) reported
[45]
2
9
2‐Furyl
7
25
90
251‐253
252‐253
[
46]
3
0
C
6
H
5
9
9
35
40
92
90
243‐245
248‐249
244‐245
[46]
3
1
4‐(Cl)C
4
H
4
250‐252
[46]
3
2
3‐(Br)C
4
H
4
9
48
85
221‐223
224‐225
a
Isolated Yields.
SCHEME 2 Synthesis of pyran
derivatives using PPY/Fe
nanocomposite
3 4
O /CNT

HOJATI ET AL.
11 of 13
SCHEME 3 Selective synthesis of bis‐
tetrahydrobenzo[b]pyran
SCHEME 4 Proposed mechanism for
the synthesis of pyran derivatives
TABLE 3 The comparison of methods for the synthesis of 2‐amino‐3‐cyano‐4‐(4‐chlorophenyl)‐7,7‐dimethyl‐5‐oxo‐4H‐5,6,7,8‐
tetrahydrobenzo[b]pyran (4b)
Entry
Conditions
PPY/Fe /CNT/ Solvent‐free/ 90 °C (Present work)
TBAB/ H
NaBr/ Solvent‐free/ MW
ZnO‐beta zeolite/ EtOH/ Reflux
Time (min)
Yield (%)
1
3
O
4
10
95
[39]
2
3
4
5
6
7
8
9
2
O/ Reflux
35
10
35
90
360
180
20
60
60
60
94
90
95
86
94
95
95
93
92
91
[47]
[48]
[49]
CeCl
HDMBAB/ H
[bmim][BF ]/ 80 °C
MgO/ H O/EtOH(4:1)/ Reflux
PO / H
PFPA/ H
[TEBSA].HSO
3 2
.7H O/ aq EtOH/Reflux
[50]
2
O
[51]
4
[52]
2
[3]
K
3
4
2
O/EtOH(80:20)/ rt
[53]
1
1
0
1
2
O/EtOH(1:1)/ rt
[54]
4
/ H O/ 90 °C
2

12 of 13
HOJATI ET AL.
FIGURE 4 The use of an external magnetic field for separation of catalyst
must be noted that, it is the first report for the application
of PPY/Fe O /CNT as catalyst in organic
a
3
4
transformations.
ACKNOWLEDGEMENTS
Authors wish to dedicate the present work to Hakim
Sabzevari to research in chemistry and his constant inspi-
rations given to his students.
ORCID
Seyedeh Fatemeh Hojati http://orcid.org/0000-0002-2911-
3 4
FIGURE 5 Reuse of the nanomagnetic polypyrrle/CNT@Fe O
for synthesis of 4b
5245
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