Polystyrene@graphene oxide-Fe3O4 as a novel and magnetically recyclable nanocatalyst for the efficient multi-component synthesis of spiro indene derivatives

Article abstract of DOI:10.1007/s11164-019-04021-w

Polystyrene (PS)-coated magnetic graphene oxide (GO-Fe₃O₄) nanocomposite has been prepared and characterized by FT-IR, TEM and VSM techniques, and its catalytic activity has been evaluated in the multi-component synthesis of two seri

Full text of DOI:10.1007/s11164-019-04021-w

Research on Chemical Intermediates
https://doi.org/10.1007/s11164-019-04021-w
Polystyrene@graphene oxide‑Fe3O4 as a novel
and magnetically recyclable nanocatalyst for the efcient
multi‑component synthesis of spiro indene derivatives
Seyedeh Fatemeh Hojati1 · Amirhassan Amiri1 · Maryam Mahamed1
Received: 28 July 2019 / Accepted: 9 October 2019
© Springer Nature B.V. 2019
Abstract
Polystyrene (PS)-coated magnetic graphene oxide (GO-Fe3O4) nanocomposite has
been prepared and characterized by FT-IR, TEM and VSM techniques, and its cata-
lytic activity has been evaluated in the multi-component synthesis of two series of
indene derivatives. The three-component condensation of ninhydrin/isatin, malon-
onitrile and active methylene-containing compounds and also the four-component
condensation of ninhydrin, o-phenylenediamines, malononitrile and active methyl-
ene-containing compounds were satisfactorily performed in the presence of PS@
GO-Fe3O4 magnetic nanocomposite, and corresponding 2′-aminospiro[indene-
2,4′-pyran]-3′-carbonitriles, 2′-aminospiro[indoline-3, 4′-pyran]-3′-carbonitriles
and 2′-aminospiro[indeno[1,2-b]quinoxaline-11,4′-pyrane]-3′-carbonitriles were
obtained in good-to-excellent yields, respectively. Very shorter reaction times than
the reported methods, easy workup procedure and easy separation and reusability of
the catalyst are noteworthy advantages of the current method.
Keywords Spiro indene derivatives · One-pot synthesis · Polystyrene@GO-Fe3O4
nanocomposite · Multi-component reaction
Introduction
During the years, the synthesis of spiro-type compounds has attracted much interest
as an important target in chemical synthesis because of their extensive biological
activities [1–3]. The best method to get this goal is development of multi-compo-
nent reactions (MCRs). Multi-component reactions are strong tools for the synthe-
sis of multi-functional spiro heterocycles in which three or more reactants combine
together in a one-pot reaction to form new products [4–7]. 4H-pyran derivatives have
*
Seyedeh Fatemeh Hojati
hojatee@yahoo.com; sf.hojati@hsu.ac.ir
1
Department of Chemistry, Hakim Sabzevari University, Sabzevar 96179-76487, Iran
Vol.:(0123456789)
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S. F. Hojati et al.
gained much attention due to their pharmaceutical and biological properties such as
antivirus [8], anticancer [9], anticoagulant [10], antiallergic [11, 12], hypoglycemic
and microbial efects [13]. These compounds have been known as key moieties in
numerous biologically active natural products [14, 15]. Quinoxaline is another bio-
logically active scafold that antibacterial [16], antifungal [17], antidepressant [17]
and antitumor [18] activities have been detected for its derivatives. On the other
hand, more focus has been given to indene and indoline and spiro compounds of
them for their pharmaceutical activities [19–22] such as anti-infammatory [23],
antibacterial [24], analgesic and antioxidant [24] properties. A quick and direct
route to the synthesis of spiro[indene-2,4′-pyran]-3′-carbonitrile, spiro[indoline-3,4′-
pyran]-3′-carbonitrile and 2′-aminospiro[indeno[1,2-b]quinoxaline-11,4′-pyran]-3′-
carbonitriles is multi-component reaction. Several methods have been reported for
the synthesis of these heterocycles, and most of them have some limitations such as
long reaction times [25–27], requiring large amounts of the catalyst [28] and the use
of toxic [28] or nonreusable reagent [26–28]. Therefore, development of a facile and
economical synthetic route to spiro indene and spiro indoline derivatives is still in
demand.
Graphene is a strong and thick honeycomb lattice system and has found extreme
applications in composites [29, 30], transparent conducting flms [31], sensors [32],
supercapacitors [33], nanoelectronics [34], batteries [35], biotechnology [36] and
catalyst supports [37, 38] because of its magical characteristics. The high surface
area, fexibility, porous structure and thermal, chemical, mechanical and structural
stability are valuable properties of graphene. Graphene oxide (GO) is an oxygenated
form of graphene that is usually used as an efcient starting material for the prepa-
ration of nanocomposites [39, 40]. Loading magnetic nanoparticles such as Fe3O4
on the surface of graphene oxide converts it into a magnetic nanocomposite [41].
Recently, diferent polymers have been widely used to coat magnetic nanoparticles
[42]. In this study, the surface of magnetized graphene oxide was coated by a layer
of polystyrene to increase the resistance of Fe3O4 nanoparticles to oxidation and pre-
vent the leaching of nanoparticles from the graphene oxide surface.
In the following of our previous works on the design and development of new
catalytic system for the preparation of biologically active heterocycles [43–49],
herein, we wish to report the preparation of a polystyrene-coated magnetic graphene
oxide (PS@GO-Fe3O4) and its application in the synthesis of spiro indene and spiro
indoline derivatives as a reusable and highly efcient catalyst. This magnetic nano-
composite was characterized by Fourier infrared spectroscopy (FT-IR), scanning
electron microscopy (SEM) and vibrating sample magnetometry (VSM) analyses.
Experimental section
Materials and instruments
Chemicals were purchased from Merck Chemical Company. IR spectra were
1
recorded on a Shimadzu FT-IR 8440 spectrophotometer. H NMR spectra were
recorded on a Bruker Avance 300 MHZ spectrometer in deuterated DMSO. Melting
1 3

Polystyrene@graphene oxide-Fe3O4 as a novel and…
points were determined with electrothermal 9100 apparatus and were uncorrected.
The morphology of PS@GO-Fe3O4 and size of nanoparticles were determined by
transmission electron microscopy (TEM) model Leo 1450 VP. The magnetic char-
acter of catalyst was evaluated by a vibrating sample magnetometer (Meghnatis
Daghigh Kavir Corporation, Kashan Kavir; 114 Iran). Elemental analyses were per-
formed using a Heraeus CHN-O-Rapid analyzer. Mass spectra were recorded on a
VG micromass 7070H and Finnigan Mat 1020B mass spectrometers operating at
70 eV.
Preparation of magnetic graphene oxide
Graphene oxide (GO) was prepared via modifed Hummers’ method from natural
graphite [50]. A concentrated mixture of H2SO4/H3PO4 (9:1, 360:40 mL) was added
to a mixture of graphite plates (3.0 g) and KMnO4 (18.0 g) and then stirred at 50 °C
for 12 h. The reaction mixture was then poured onto a mixture of ice (400 mL) and
H2O2 (30%, 3 mL). The graphene oxide was washed and sequentially centrifuged
with water, HCl (30%) and ethanol. The solid was fltered on a PTFE membrane
(0.45 µm in diameter) and dried under vacuum at room temperature overnight. GO-
Fe3O4 was synthesized by the chemical combination of Fe2+ and Fe3+ in an alka-
line solution in the presence of GO. GO (0.2 g) was suspended in 200 mL solution
containing FeCl3·6H2O (2.34 g, 6.68 mmol) and FeCl2·4H2O (0.86 g, 4.33 mmol)
at 50 °C in N2 atmosphere. The solution was then sonicated for 10 min, and a solu-
tion of aqueous NH4OH (10 mL, 25%) was added dropwise to it under ultrasonic
irradiation. The pH of the fnal mixture should be in the range of 10–11. To aid in
the full growth of nanoparticle crystals, the reaction was uniformly stirred at 50 °C
for 60 min. The precipitate was then separated by external magnetic feld. The impu-
rities in GO-Fe3O4 were removed by washing with double distilled water, and the
precipitate was separated by a permanent magnet. The GO-Fe3O4 nanocomposite
was then washed three times with 10 mL of ethanol and deionized water. Finally, the
nanocomposite was dried under vacuum (Scheme 1).
Preparation of polystyrene@graphene oxide‑Fe3O4 nanocomposite (PS@
GO‑Fe3O4)
For the production of PS@GO-Fe3O4 nanocomposite, 0.3 g of GO-Fe3O4 solution
was dispersed in 20 mL of distilled water under ultrasound for 1 h. Then, the dis-
persed GO-Fe3O4 solution was added to a solution of sodium dodecyl sulfate (SDS)
surfactant (1.5 g) in distilled water (150 mL). The mixture was again sonicated for
30 min to prepare a homogeneous solution. Then, styrene monomer (4.5 g) was
added and rapidly stirred. Afterward, 2,2′-azobis(2-methylpropionitrile) (AIBN,
0.15 g) was added to the solution for 30 min and stirred at 80 °C for 12 h in nitro-
gen atmosphere for polymerization. Finally, the PS@GO-Fe3O4 nanocomposite was
fltered and washed with methanol and deionized water several times and dried at
60 °C under vacuum for 24 h (Scheme 1) [51].
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S. F. Hojati et al.
Scheme 1 Schematic preparation route to PS@GO-Fe3O4 nanocomposite
General method for the three‑component synthesis of 2′‑aminospiro[indene‑2,
4′‑pyran]‑3′‑carbonitrile and 2′‑aminospiro[indoline‑3,4′‑pyran]‑3′‑carbonitrile
derivatives
In a round-bottomed fask, a mixture of ninhydrin/isatin (1 mmol), active methyl-
ene-containing compound (1 mmol) and PS@GO-Fe3O4 (0.01 gr) in H2O (5 mL)
was prepared and stirred at 80 °C for 5 min and then malononitrile (1 mmol) was
added. After completion of the reaction as indicated by TLC (eluent, EtOAc: n-hex-
ane, 1:2), the reaction mixture was left to cool to room temperature. Then, acetone
(10 mL) was added to solve product and the catalyst was separated magnetically,
washed with acetone and distilled water and dried at 60 °C under vacuum to reuse
in the next cycle. The solvent of the reaction mixture was evaporated under vacuum
to aford desired product. Further purifcation was performed by recrystallization in
EtOH (Scheme 2, Table 2, entries 1–5).
General procedure for the four‑component synthesis
of 2′‑aminospiro[indeno[1,2‑b]quinoxaline‑11,4′‑[4′H]pyran]‑3‑carbonitrile
derivatives
A mixture of ninhydrin (1 mmol), o-phenylenediamine (1 mmol) and PS@GO-
Fe3O4 nanocomposite (0.01 gr) in ethanol (5 mL) was prepared and stirred at room
temperature. After 10 min, malononitrile (1 mmol) and active methylene-containing
compound (1 mmol) were added to the reaction mixture. The mixture was stirred for
appropriate times according to Table 2 under refux condition. Then, the reaction
mixture was cooled to room temperature and acetone (10 mL) was added. The nano-
magnetic catalyst was collected by an external magnet, washed several times with
acetone and distilled water and dried at 60 °C under vacuum. The reaction solution
was concentrated under vacuum, and the crude product was purifed by recrystalli-
zation in EtOH (Scheme 3, Table 2, entries 6–14).
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Polystyrene@graphene oxide-Fe3O4 as a novel and…
Scheme 2 Three-component synthesis of 2′-aminospiro[indeno-2,4′-pyran]-3′-carbonitrile in the pres-
ence of PS@GO-Fe3O4 nanocomposite
Physical and spectral data of the products
2′-Amino-5′,6′,7′,8′-tetrahydro-7′,7′-dimethyl-1,3,5′-trioxospiro[indeno-2,4′-
chromene]-3′-carbonitrile (4a), mp; 294–296 °C. FT-IR (KBr, cm−1): 3376, 3308,
3245, 3197, 2190, 1747, 1717, 1686, 1661, 1596. 1H NMR (300 MHz, DMSO-d6,
ppm):1.03 (s, 6H, 2CH3), 2.19 (s, 2H, CH2), 2.67 (s, 2H, CH2), 7.64 (s, 2H, NH2),
7.99–8.05 (4H, ArH).
2′-Amino-5′,6′,7′,8′-tetrahydro-1,3,5′-trioxospiro[indeno-2,4′-chromene]-3′-
carbonitrile (4b), mp; 278–280 °C. FT-IR (KBr, cm−1): 3404, 3319, 3237, 3799,
1
2994, 2896, 2192, 1748, 1644, 1582. H NMR (300 MHz, DMSO-d6, ppm):1.95
(m, 2H, CH2), 2.27–2.30 (m, 2H, CH2), 2.70–2.73 (m, 2H, CH2), 7.63 (s, 2H,
NH2), 2.99–8.05 (4H, ArH).
7′-Amino-1′,2′,3′,4′-tetrahydro-1,2′,3,4′-tetraoxospiro[indene-2,5′-[4′H]
pyrano[2,3-d]pyrimidine]-6′-carbonitrile (4c), mp; 190–192 °C. FT-IR (KBr,
cm−1): 3425, 3301, 3278, 3215, 3138, 2198, 1722, 1705, 1642, 1623, 1520, 1334.
1H NMR (300 MHz, DMSO-d6, ppm): 7.01 (s, 2H), 8.01(d, J = 8.5 Hz, 2H), 8.11
(d, J = 8.5 Hz, 2H), 9.08 (s, 1H), 11.03 (s, 1H).
2′-Amino-1,3,5′-trioxo-5′H-spiro[indene-2,4′-[4′H]pyrano[3,2-c]chromene]-
3′-carbonitrile (4d), mp; 280 °C. FT-IR (KBr, cm−1): 3396, 3321, 3253, 3210,
1
2189, 1745, 1671, 1638, 1610, 1594. H NMR (300 MHz, DMSO-d6, ppm): 7.51
1 3

S. F. Hojati et al.
Scheme 3 Three-component synthesis of 2′-aminospiro[indoline-3,4′-pyran]-3′-carbonitrile in the pres-
ence of PS@GO-Fe3O4 nanocomposite
(d, J = 8.4 Hz, 1H, ArH), 7.54 (t, J = 7.65 Hz, 1H, ArH), 7.78 (t, J = 7.4 Hz, 1H,
ArH), 7.90 (d, J = 7.75 Hz, 1H, ArH), 8.09–8.13 (m, 4H, NH2, ArH).
Ethyl-2ʹ-amino-3ʹ-cyano-6ʹ-methyl-1,3-dioxospiro[indeno-2,4ʹ-[4′H]pyran]-
5ʹcarboxylate (4′), mp; 224–226 °C. FT-IR (KBr, cm−1): 3338, 3183, 2934, 2190,
1675, 1637, 1429, 1278. 1H NMR (300 MHz, DMSO-d6, ppm): 1.42 (m, 3H), 2.26
(s, 3H), 4.15–4.28 (m, 2H), 6.91 (s, 2H, NH2), 7.81–7.76 (m, 1H, ArH), 7.99–7.84
(m, 3H, ArH).
Ethyl-7′-amino-1′,2′,3′,4′-tetrahydro-1,2′,3,4′-tetraoxospiro[indene-2,5′-[4′H]
pyrano[2,3-d]pyrimidine]-6′-carboxylate (4e), mp; 223–225 °C. FT-IR (KBr, cm−1):
3428, 3305, 3266, 3215, 3141, 2197, 1720, 1697, 1639, 1623, 1518, 1329. 1H NMR
(300 MHz, DMSO-d6, ppm): 1.06 (t, J=7.6 Hz, 3H), 3.95 (q, J=7.6 Hz, 2H), 8.03
(d, J=8.7 Hz, 2H), 8.06 (d, J=8.7 Hz, 2H), 9.11 (s, 1H), 10.96 (s, 1H).
2′-Amino-5′,6′,7′,8′-tetrahydro-7′,7′-dimethyl-2,5′-dioxospiro[indoline-3,4′-
chromene]-3′-carbonitrile (5a), mp; 292–294 °C. FT-IR (KBr, cm−1): 3376, 3312,
1
3144, 2928, 2196, 1724, 1656, 1348, 1224, 1056. H NMR (300 MHz, DMSO-
d6, ppm): 1.00 (s, 3H), 1.03 (s, 3H), 2.08–2.19 (m, 2H), 2.56 (s, 2H), 6.78 (d,
J=7.3 Hz, 1H, ArH), 6.89 (t, J=7.3 Hz, 1H, ArH), 6.97 (d, J=7.3 Hz, 1H, ArH),
7.14 (t, J=7.3 Hz, 1H, ArH), 7.23 (s, 2H, NH2), 10,40 (s, 1H, NH).
2′-Amino-5′,6′,7′,8′-tetrahydro-2,5′-dioxospiro[indoline-3,4′-chromene]-3′-
carbonitrile (5b), mp; 297–299 °C. FT-IR (KBr, cm−1): 3352, 3296, 3176, 2952,
1
2204, 1712, 1656, 1352, 1216, 1076. H NMR (300 MHz, DMSO-d6, ppm):
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Polystyrene@graphene oxide-Fe3O4 as a novel and…
1.91–2.00 (m, 2H), 2.10–2.30 (m, 2H), 2.62–2.73 (m, 2H), 6.78 (d, J = 7.4 Hz,
1H, ArH), 6.88 (t, J = 7.4 Hz, 1H, ArH), 7.00 (d, J = 7.4 Hz, 1H, ArH), 7.16 (t,
J = 7.4 Hz, 1H, ArH), 7.23 (s, 2H, NH2), 10.40 (s, 1H, NH).
7′-amino-1′,2′,3′,4′-tetrahydro-2,2′,4′-trioxospiro[indoline-3,5′-[4′H]
pyrano[2,3-d] pyrimidine]-6′-carbonitrile (5c), mp; 296–298 °C. FT-IR (KBr,
1
cm−1): 3559, 3286, 3215, 3199, 1717, 1642, 1324. H NMR (300 MHz, DMSO-
d6, ppm): 6.95 (s, 2H), 7.05 (t, J = 8.3 Hz, 1H), 7.21–7.30 (m, 3H), 9.03 (s, 1H),
9.66 (s, 1H), 11.03 (s, 1H).
2′-amino-2,5′-dioxospiro[indoline-3,4′-[4′H]pyrano[3,2-c]chromene]-3′-
carbonitrile (5d), mp; 286–289 °C. FT-IR (KBr, cm−1): 3397, 3296, 3196, 2206,
1
1710, 1674, 1604, 1359. H NMR (300 MHz, DMSO-d6, ppm): 6.84–6.93 (m,
2H, ArH), 7.16–7.23 (m, 2H, ArH), 7.49–7.58 (m, 2H, ArH), 7.69 (s, 2H, NH2),
7.75– 7.80 (t, J = 7.38 Hz, 1H, ArH), 7.93 (d, J = 7.92 Hz, 1H, ArH), 10.70 (s, 1
H, NH).
6ʹ-amino-3ʹ-methyl-2-oxo-1ʹ-phenylspiro[indoline-3,4′-pyrano[2,3-c]
pyrazole]-5ʹ-carbonitrile (5e), mp; 250–252 °C. FT-IR (KBr, cm−1): 3411, 3330,
3270, 2193, 1716, 1625, 1323. 1H NMR (300 MHz, DMSO-d6, ppm): 1.54
(s, 3H), 6.94 (d, J = 7.7 Hz, 1H, ArH), 7.03 (t, J = 7.4 Hz, 1H, ArH), 7.18 (d,
J = 7.3 Hz, 1H, ArH), 7.28 (t, J = 7.6 Hz, 1H, ArH), 7.35 (t, J = 7.9 Hz, 1H, ArH),
7.52 (t, J = 7.9 Hz, 2H, ArH), 7.57 (s, 2H, NH2), 7.78 (d, J = 7.9 Hz, 2H, ArH),
10.74 (s, 1H, NH).
Ethyl-2ʹ-amino-3ʹ-cyano-6ʹ-methyl-2-oxospiro[indoline-3,4ʹ-[4′H]pyran]-5ʹ-
carboxylate (5′), mp; 268–270 °C. FT-IR (KBr, cm−1): 3480, 3275, 3158, 2976,
1
2188, 1723, 1710, 1676, 1618. H NMR (300 MHz, DMSO-d6, ppm): 0.74 (t,
J=7.0 Hz, 3H) 2.29 (s, 3H), 3.71–3.82 (m, 2H), 6.75 (d, J=7.6 Hz, 1H, ArH), 6.90
(t, J=7.3 Hz, 1H, ArH), 7.00 (d, J=7.1 Hz, 1H, ArH), 7.16 (s, 2H, NH2), 7.18 (t,
J=7.6 Hz, 1H, ArH), 10.41 (s, 1H, NH).
2ʹ-amino-5ʹ,6ʹ,7ʹ,8ʹ-tetrahydro-7ʹ,7ʹ-dimethyl-5-oxospiro[indeno[1,2-b]
quinoxaline-11,4′-[4′H]pyran]-3ʹ-carbonitrile (7a), mp; 280–282 °C. FT-IR (KBr,
1
cm−1): 3460, 3300, 3170, 2960, 2196, 1670, 1600, 1352. H NMR (300 MHz,
DMSO-d6, ppm): 1.00 (s, 3H, CH3), 1.03 (s, 3H, CH3), 1.97–2.08 (m, 2H, CH2),
2.61–2.75 (m, 2H, CH2), 7.33 (s, 2H, NH2), 7.51–7.55 (m, 2H, ArH), 7.59–7.60
(m, 1H, ArH), 7.75–7.78 (m, 1H, ArH), 7.81–7.84 (m, 1H, ArH), 8.05 (dd, J=1.5,
8.2 Hz, 1H, ArH), 8.08 (d, J=7.5 Hz, 1H, ArH), 8.15 (dd, J=1.0, 8.0 Hz, 1H, ArH).
2ʹ-amino-5ʹ,6ʹ,7ʹ,8ʹ-tetrahydro-5ʹ-oxospiro[indeno[1,2-b]quinoxaline-11,4′-[4′H]
pyran]-3ʹ-carbonitrile (7b), mp; 275–277 °C. FT-IR (KBr, cm−1): 3360, 3280, 3165,
1
2920, 2194, 1670, 1600, 1330. H NMR (300 MHz, DMSO-d6, ppm): 1.89–1.94
(m, 2H, CH2), 2.07–2.14 (m, 2H, CH2), 2.73–2.81 (m, 2H, CH2), 7.33 (s, 2H, NH2),
7.52–7.61 (m, 2H, ArH), 7.75–7.84 (m, 2H, ArH), 8.06–8.09 (m, 2H, ArH), 8.16
(dd, J=1.0, 8.0 Hz, 1H, ArH).
6ʹ-amino-3ʹ-methyl-1ʹ-phenylspiro[indeno[1,2-b]quinoxaline-11,4′-[1′H]
pyrano[2,3-c] pyrazole]-5ʹ-carbonitrile (7c), mp; 240–242 °C. FT-IR (KBr, cm−1):
1
3321, 3292, 3145, 2920, 2204, 1653, 1591, 1517, 1392. H NMR (300 MHz,
DMSO-d6, ppm): 1.10 (s, 3H, CH3), 7.37 (t, J=7.5 MHz, 1H, ArH), 7.54 (t,
J=7.7 MHz, 2H, ArH), 7.64–7.71 (m, 5H, ArH), 7.81–7.90 (m, 4H, ArH), 8.12 (d,
J=8.5 MHz, 1H, ArH), 8.20 (t, J=8.5 MHz, 2H).
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S. F. Hojati et al.
2ʹ-amino-5ʹ,6ʹ,7ʹ,8ʹ-tetrahydro-4,7ʹ,7ʹ-trimethyl-5-oxospiro[indeno[1,2-b]
quinoxaline-11,4′-[4′H]pyran]-3ʹ-carbonitrile (7d), mp; 274–276 °C. FT-IR (KBr,
1
cm−1): 3444, 3313, 3047, 2954, 2192, 1666, 1595, 1350. H NMR (300 MHz,
DMSO-d6, ppm): 1.03 (s, 3H, CH3), 1.05 (s, 3H, CH3), 1.97–2.07 (dd, J=16.2,
19.5 Hz, 2H, CH2), 2.59 (s, 3H, CH3), 2.67–2.79 (dd, J=17.7, 26.1 Hz, 2H, CH2),
7.33 (s, 2H, NH2), 7.51–7.61 (m, 3H, ArH), 7.93 (s, 1H, ArH), 7.97 (d, J=2.4 Hz,
2H, ArH), 8.09 (d, J=3.4 Hz, 1H, ArH). 13C NMR (75 MHz, DMSO-d6, ppm): 21.3,
27.1, 29.2, 32.8, 34.6, 51.0, 51.8, 75.3, 108.6, 114.5, 121.9, 125.8, 126.8, 128.3,
128.4, 128.6, 131.9, 134.3, 136.9, 138.1, 141.8, 142.1, 151.5, 158.0, 166.1, 168.5,
194.2. HRMS (EI) Found: M+, 434.1744. C27H22N4O2: requires M+, 434.1743.
Anal. Calcd. for C27H22N4O2: C 74.65, H 5.07, N 12.90; found C 74.57, H 5.11, N
12.88%.
2ʹ-amino-5ʹ,6ʹ,7ʹ,8ʹ-tetrahydro-4-methyl-5ʹ-oxospiro[indeno[1,2-b]quinoxaline-
11,4′-[4′H]pyran]-3ʹ-carbonitrile (7e); mp; 266–268 °C. FT-IR (KBr, cm−1):
1
3352, 3284, 3242, 2920, 2198, 1672, 1598, 1350. H NMR (300 MHz, DMSO-
d6, ppm):1.89–1.94 (m, 2H, CH2), 2.03 (m, 2H, CH2), 2.59 (s, 3H, CH3), 2.79 (m,
2H CH2), 7.37 (s, 2H, NH2), 7.50–7.61 (m, 3H, ArH), 7.93 (s, 1H, ArH), 7.97 (d,
J=2.4 Hz, 2H, ArH), 8.07 (d, J=6.6 Hz, 1H, ArH). 13C NMR (75 MHz, DMSO-d6,
ppm): 21.1, 21.5, 28.3, 37.0, 48.1, 58.3, 113.6, 118.3, 122.7, 126.2, 128.3, 128.6,
129.1, 129.5, 131.2, 139.1, 142.2, 142.3, 145.1, 152.7, 158.4, 160.6, 164.9, 166.1,
194.9. HRMS (EI) Found: M+, 406.1431. C25H18N4O2: requires M+, 406.1430.
Anal. Calcd. for C25H18N4O2: C 73.89, H 4.43, N 13.79; found C 73.94, H 4.51, N
13.72%.
6ʹ-amino-3ʹ,4-dimethyl-1ʹ-phenylspiro[indeno[1,2-b]quinoxaline-11,4′-[1′H]
pyrano[2,3-c] pyrazole]-5ʹ-carbonitrile (7f), mp; 207–210 °C. FT-IR (KBr, cm−1):
1
3311, 3290, 3139, 2914, 2200, 1652, 1591, 1519, 1392. H NMR (300 MHz,
DMSO-d6, ppm):1.09 (s, 3H), 2.47 (s, 3H), 7.36 (s, 2H, NH2), 7.51 (d, J=7.5 MH,
2H), 7.63–7.64 (m, 5H), 7.81–7.90 (m, 4H), 8.16 (s, 1H).
2ʹ-amino-5ʹ,6ʹ,7ʹ,8ʹ-tetrahydro-3,4,7ʹ,7ʹ-tetramethyl-5-oxospiro[indeno[1,2-b]
quinoxaline-11,4′-[4′H]pyran]-3ʹ-carbonitrile (7 g), mp; 222–224 °C. FT-IR (KBr,
1
cm−1): 3436, 3334, 3155, 2950, 2192, 1675, 1600, 1348. H NMR (300 MHz,
DMSO-d6, ppm):1.028 (s, 3H, CH3), 1.047 (s, 3H, CH3), 1.97–2.10 (dd, J=16.2,
20.4 Hz, 2H, CH2), 2.46 (s, 3H, CH3), 2.50 (s, 3H, CH3), 2.62–2.77 (dd, J=16.8,
26.1 Hz, 2H, CH2), 7.34 (s, 2H, NH2), 7.51–7.61 (m, 3H, ArH), 7.82 (s, 1H, ArH),
7.95 (s, 1H, ArH), 8.07 (d, J=7.2 MHz, 1H, ArH). 13C NMR (75 MHz, DMSO-d6,
ppm): 18.8, 18.9, 27.4, 28.3, 32.3, 35.1, 50.8, 51.7, 76.4, 109.0, 114.7, 121.6, 125.6,
126.4, 128.4, 128.6, 128.7, 131.9, 137.7, 139.2, 141.1, 147.3, 148.2, 151.6, 157.0,
165.8, 167.1, 168.2, 194.5. HRMS (EI) Found: M+, 448.1897. C28H24N4O2: requires
M+, 448.1899. Anal. Calcd. for C28H24N4O2: C 75.00, H 5.36, N 12.50; found C
74.93, H 5.42, N 12.47%.
2ʹ-amino-5ʹ,6ʹ,7ʹ,8ʹ-tetrahydro-3,4-dimethyl-5-oxospiro[indeno[1,2-b]
quinoxaline-11,4′-[4′H]pyran]-3ʹ-carbonitrile (7 h), mp; 275–277 °C. FT-IR (KBr,
1
cm−1): 3394, 3352, 3278, 2918, 2192, 1675, 1600, 1338. H NMR (300 MHz,
DMSO-d6, ppm):1.89–1.94 (m, 2H, CH2), 2.03 (m, 2H, CH2), 2.47 (s, 3H, CH3),
2.59 (s, 3H, CH3), 2.80 (m, 2H, CH2), 7.37 (s, 2H, NH2), 7.51–7.61 (m, 3H, ArH),
7.93 (s, 1H, ArH), 7.97 (s, 1H, ArH), 8.07 (d, J=7.2 Hz, 1H, ArH). 13C NMR
1 3

Polystyrene@graphene oxide-Fe3O4 as a novel and…
(75 MHz, DMSO-d6, ppm): 18.6, 18.7, 20.5, 27.7, 37.3, 48.2, 58.3, 111.5, 118.4,
121.7, 125.3, 128.6, 128.8, 129.5, 129.6, 129.7, 141.6, 142.3, 147.9, 154.7, 155.2,
157.8, 158.4, 164.4, 194.6. HRMS (EI) Found: M+, 420.1588. C26H20N4O2: requires
M+, 420.1586. Anal. Calcd. for C26H20N4O2: C 74.29, H 4.76, N 13.33; found C
74.32, H 4.71, N 13.35%.
6ʹ-amino-3,4,3ʹ-trimethyl-1ʹ-phenylspiro[indeno[1,2-b]quinoxaline-11,4′-[1′H]
pyrano[2,3-c]pyrazole]-5ʹ-carbonitrile (7i), mp; 248–250 °C). FT-IR (KBr, cm−1):
1
3336, 3296, 3155, 2916, 2200, 1652, 1595, 1521, 1394. H NMR (300 MHz,
DMSO-d6, ppm): 1.09 (s, 3H, CH3), 2.42 (s, 3H, CH3), 2.47 (s, 3H, CH3), 7.36 (t,
J=7.2 Hz, 1H, ArH), 7.51 (t, J=7.7 Hz, 2H, ArH), 7.63–7.64 (m, 5H, ArH), 7.85
(d, J=9.0 Hz, 3H, ArH), 7.97 (s, 1H, ArH), 8.14 (t, J=3.7 Hz, 1H, ArH).
Results and discussion
Characterizations of nanocomposite
At frst, the polystyrene-coated magnetic graphene oxide (PS@GO-Fe3O4) was
prepared by a two-step procedure as explained in Experimental section. Then, this
magnetic nanocomposite was characterized by Fourier infrared spectroscopy (FT-
IR), scanning electron microscopy (SEM) and vibrating sample magnetometry
(VSM) analyses. The FT-IR spectra of GO, GO-Fe3O4, polystyrene and PS@GO-
Fe3O4 nanocomposite are shown in Fig. 1. In Fig. 1a, a broad absorption band in
Fig. 1 FT-IR spectra of (a) GO, (b) GO-Fe3O4, (c) polystyrene and (d) PS@GO-Fe3O4
1 3

S. F. Hojati et al.
3426 cm−1 is related to the stretching vibration of O–H and shows the presence of
oxygen-containing functional groups in graphene oxide. The stretching vibrations of
C=O, aromatic C=C and epoxy and alkoxy C–O groups are observed in 1730, 1626,
1156 and 1080, respectively. In the FT-IR spectrum of GO-Fe3O4 nanocomposite
(Fig. 1b), an absorption band is present at 580 cm−1 that belongs to the Fe–O vibra-
tion. In the FT-IR spectrum of polystyrene (Fig. 1c), the stretching vibration of CH,
the bending vibration of CH2, the stretching vibration of C=C, the bending vibration
of C–C and the out-of-plane bending vibration of C–H are seen at 2125, 2850, 1610,
1452 and 700 cm−1, respectively [51]. In FT-IR spectrum of PS@GO-Fe3O4 nano-
composite (Fig. 1d), all characteristic peaks of GO-Fe3O4 (1b) and polystyrene (1c)
spectra are observable. This spectrum (1d) indicates that the surface of GO-Fe3O4 is
well covered by polystyrene [51].
The TEM graph of graphene oxide (Fig. 2) shows a fake-like sheet structure. The
TEM image of PS@GO-Fe3O4 nanocomposite exhibits the uniform distribution of
iron oxide nanoparticles on the surface of GO nanosheets. Furthermore, the diferent
morphology appearance of nanocomposite compared to graphene oxide confrms
that Fe3O4 nanoparticles have been satisfactorily formed on the GO-Fe3O4 surface.
As the VSM analyses of GO and PS@GO-Fe3O4 (Fig. 3) nanocomposite show,
the magnetic remanences in both graphs are close to zero. This means that by
removing the external magnetic feld, the magnetic property disappears. Therefore,
both GO-Fe3O4 and PS@GO-Fe3O4 show superparamagnetic behavior. Reducing
the SM value of PS@GO-Fe3O4 nanocomposite relative to GO-Fe3O4 is due to the
fact that the GO-Fe3O4 surface is coated with a layer of polystyrene and confrms the
successful formation of PS@GO-Fe3O4 nanocomposite [51].
After characterization of PS@GO-Fe3O4 nanocomposite, its catalytic activity was
studied in the three-component synthesis of 2-aminospiro[chromene-4,2′-indene]-3-
carbonitrile. Initially, the reaction of ninhydrin 1a, malononitrile 2a and dimedone
3a in water was selected as model reaction (Scheme 2). Diferent catalysts includ-
ing 1,3-dibromo-5,5-dimethylhydantoin (DBH), trichloroicocyanuric acid (TCA),
Bi(NO3)3·5H2O, ZrCl4 and tungstophosphoric acid (TPA) have been used in the
Fig. 2 TEM graph of a graphene oxide and b PS@GO-Fe3O4
1 3

Polystyrene@graphene oxide-Fe3O4 as a novel and…
Fig. 3 VSM curves of GO-Fe3O4 and PS@GO-Fe3O4 nanocomposites
model reaction (Table 1, entries 1–5). As shown in Table 1, all of these reactions
were performed for long times and poor yields of products were obtained. Then,
the catalytic activity of PS@GO-Fe3O4 nanocomposite was examined in the model
reaction which led to an acceptable yield in short time (Table 1, entry 6).
So, the reaction conditions were optimized in the presence of PS@GO-Fe3O4
nanocomposite. To this aim, diferent amounts of catalyst, various solvents and dif-
ferent temperatures were examined in the model reaction (Table 1, entry 6–15). The
best result was obtained in the reaction of ninhydrin 1a (1 mmol), malononitrile
2a (1 mmol) and dimedone 3a (1 mmol) in the presence of nanocatalyst (10 mg)
in water (5 ml) at 80 °C (Table 1, entry 7). Corresponding 2′-amino-5′,6′,7′,8′-
tetrahydro-7′,7′-dimethyl-1,3,5′-trioxospiro[indeno-2,4′-chromene]-3′-carbonitrile
4a was generated in 93% yield after 2 h.
The model reaction was also performed in the presence of PS, GO and Fe3O4
nanoparticles that low catalytic activities were observed for them (Table 1, entry
16–18). Furthermore, the model reaction was down in the absence of catalyst to
show the efciency of the nanomagnetic catalyst. Analysis of the reaction mixture
showed that no product was found even after 8 h (Table 1, entry 19).
To scope the generality of this method, the three-component condensations of
ninhydrin 1a, malononitrile 2a/ethyl cyanoacetate 2b and compounds contain-
ing active methylene group 3 (dimedone 3a, 1,3-cyclohexanedione 3b, barbitu-
ric acid 3c, 4-hydroxycoumarin 3d and ethyl acetoacetate 3′) were performed in
the presence of PS@GO-Fe3O4 nanocomposite under optimized reaction con-
ditions (Scheme 2, Table 2, entries 1–6). As shown in Table 2, corresponding
2-aminospiro[indeno-2,4′-pyran]-3′-carbonitriles 4 & 4′ were generated in high
yields. In the next step, the catalytic activity of PS@GO-Fe3O4 was studied in the
1 3

S. F. Hojati et al.
Table 1 Application of various catalysts and optimization of the conditions in the reaction of ninhydrin
1, malononitrile 2a and dimedone 3a
Entrya
Catalyst (mg)
Solvent
Temp (°C)
Time (h)
Yieldb (%)
1
2
3
4
5
6
7
8
DBDMH (10)
TCA (10)
Bi(NO3)3·5H2O (10)
ZrCl4 (10)
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
100
100
100
100
100
100
80
50
80
80
80
80
80
80
80
80
80
80
80
5
3
5
4
4
2
2
2
2
2
3
3
3
3
3
3
3
3
8
30
Trace
40
30
20
90
93
65
70
90
70
40
30
65
Trace
50
30
15
TPA (10)
PS@GO-Fe3O4 (10)
PS@GO-Fe3O4 (10)
PS@GO-Fe3O4 (10)
PS@GO-Fe3O4 (5)
PS@GO-Fe3O4 (15)
PS@GO-Fe3O4 (10)
PS@GO-Fe3O4 (10)
PS@GO-Fe3O4 (10)
PS@GO-Fe3O4 (10)
PS@GO-Fe3O4 (10)
Fe3O4 (10)
9
H2O
H2O
10
11
12
13
14
15
16
17
18
19
EtOH
EtOH:H2O (1:1)
CH3CN
MeOH
Acetone
H2O
H2O
H2O
H2O
GO (10)
PS (10)
–
10
a1 mmol of all starting materials was used
bIsolated yields
reaction of isatin 1b with malononitrile 2a and active methylene-containing com-
pounds 3 such as dimedone, 1,3-cyclohexanedione, barbituric acid, 4-hydroxy
coumarin, 1-phenyl-3-methypyrazoline-5-one and ethyl acetoacetate 3′ under
optimized reaction conditions (Scheme 3). Fortunately, desired products 5 & 5′
were generated in high-to-excellent yields (Table 2, entries 7–12).
Then, we examined the catalytic activity of PS@GO-Fe3O4 in the one-pot
four-component synthesis of 2′-aminospiro[indeno[1,2-b]quinoxaline-11,4′-
pyran]-3′-carbonitrile. To this aim, equimolar amounts of ninhydrin 1a, o-phe-
nylenediamine 6a, malononitrile 2a and dimedone 3a reacted in the presence
of PS@GO-Fe3O4 in water and the desired product was obtained in 10% yield
after 2 h under optimized condition (Scheme 4). To improve the result, difer-
ent solvents and temperatures were applied in this reaction. Finally, ethanol was
chosen as the best solvent under refux condition and corresponding 2ʹ-amino-
5ʹ,6ʹ,7ʹ,8ʹ-tetrahydro-7ʹ,7ʹ-dimethyl-5-oxospiro[indeno[1,2-b]quinoxaline-11,4′-
[4′H]pyran]-3ʹ-carbonitrile 7a was obtained in 87% yield after 2.5 h (Table 2,
entry 13). Similarly, the reactions of ninhydrin 1a, various o-phenylediamines 6,
malononitrile 2a and diferent active methylene-containing compounds 3 were
performed in ethanol under refux condition to aford expected products as the
1 3

Polystyrene@graphene oxide-Fe3O4 as a novel and…
Table 2 Syntheses of indene derivatives catalyzed by nanomagnetic PS@GO-Fe3O4
Entry
1
2
3
6
Product
Time (h)
Yield (%)a
Mp (°C) [Ref.]
1
2
3
4
5
6
7
8
1a
1a
1a
1a
1a
1a
1b
1b
1b
1b
1b
1b
1a
1a
1a
1a
1a
1a
1a
1a
1a
2a
2a
2a
2a
2a
2b
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
3a
3b
3c
3d
3′
3c
3a
3b
3c
3d
3e
3′
3a
3b
3e
3a
3b
3e
3a
3b
3e
–
–
–
–
–
–
–
–
–
–
–
–
6a
6a
6a
6b
6b
6b
6c
6c
6c
4a
4b
4c
4d
4′
4e
5a
5b
5c
5d
5e
5′
7a
7b
7c
7d
7e
7f
7g
7h
7i
2
2
1
3
5.5
2
0.5
0.4
0.8
0.8
1.5
3
2.5
4
4
93
85
87
90
73
95
96
90
95
95
80
80
87
73
65
95
75
97
90
68
82
290–292 [51]
274–280 [51]
190–192 [52]
280 [51]
224–226 [53]
223–225 [52]
292–294 [52]
297–299 [52]
296–298 [52]
286–289 [52]
250–252 [52]
268–270 [53]
280–282 [25]
275–277 [25]
240–242 [25]
274–276
266–268
207–210 [54]
222–224
275–277
248–250 [25]
9
10
11
12
13
14
15
16
17
18
19
20
21
3
1.5
1.5
4
4
2.5
aIsolated yields
times and yields reported in Table 2 (entries 13–21). So, the present magnetic
nanocatalyst can be efciently used for the three- and four-component synthesis
of spiro indene and spiro indoline derivatives.
Although the actual mechanism for the synthesis of 2′-aminospiro[indeno-2,4′-
pyran]-3′-carbonitrile catalyzed by PS@GO-Fe3O4 is unclear, a plausible mecha-
nism has been proposed in Scheme 5.
In the next step, the reusability of PS@GO-Fe3O4 nanocatalyst was investi-
gated in the reaction of ninhydrin, dimedone and malononitrile in optimized reac-
tion conditions. After completion of the reaction, the catalyst was separated by an
external magnet, washed with acetone and dried under vacuum at 60 °C for 2 h.
The recovered catalyst was then reused in the same reaction. The recovery and
reuse of PS@GO-Fe3O4 were performed eight times (Table 3), and its catalytic
activity did not reduce signifcantly after eight runs.
1 3

S. F. Hojati et al.
Scheme 4 Four-component synthesis of 2′-aminospiro[indeno[1,2-b]quinoxaline-11,4′-pyran]-3′-
carbonitrile in the presence of PS@GO-Fe3O4 nanocomposite
Finally, we compared the current study for the synthesis of 2ʹ-amino-5ʹ,6ʹ,7ʹ,8ʹ-
tetrahydro-7ʹ,7ʹ-dimethyl-5-oxospiro[indeno[1,2-b]quinoxaline-11,4′-[4′H]
pyran]-3ʹ-carbonitrile 7a with other methods reported in the literatures (Table 4).
The results clearly prove the preference of the present procedure.
Conclusion
In conclusion, PS@GO-Fe3O4 nanocomposite was prepared and characterized by
FT-IR, TEM and VSM analyses. The catalytic activity of this nanocomposite was
evaluated in the synthesis of two series of spiro indene and spiro indoline deriva-
tives. It was found that this novel heterogeneous catalyst is an excellent choice for
the synthesis of these biologically active heterocycles due to its efciency, nontoxic-
ity, thermal stability, mechanical stretch, low cost, simple manufacturing procedure,
reusability, high surface area, nanosize and magnetic behavior. Furthermore, short
reaction times, mild reaction conditions, easy workup procedure, high yields of
products and magnetic separation of the catalyst are worthy benefts of this method.
1 3

Polystyrene@graphene oxide-Fe3O4 as a novel and…
Scheme 5 Proposed mechanism for the synthesis of 2′-aminospiro[indeno-2,4′-pyran]-3′-carbonitriles in
the presence of PS@GO-Fe3O4 nanocomposite
Table 3 Investigation of
No. of runs
Yield (%)a
aIsolated yields after 2 h
1
2
3
4
5
6
7
8
reusability of nanomagnetic
PS@GO-Fe3O4 in the model
reaction
93
93
91
90
90
88
88
85
Table 4 Comparison of methods for the synthesis of 2ʹ-amino-5ʹ,6ʹ,7ʹ,8ʹ-tetrahydro-7ʹ,7ʹ-dimethyl-5-
oxospiro[indeno[1,2-b]quinoxaline-11,4′-[4′H]pyran]-3ʹ-carbonitrile (7a)
Entry
Reaction conditions
Time (h)
Yield (%)
1
2
3
4
5
PS@GO-Fe3O4 (10 mg)a, EtOH, refux
InCl3 (15 mol%), CH3CN, refux [25]
AcONH4 (20 mol%), EtOH, refux [26]
Na2CO3 (10 mol%), EtOH, refux [27]
Et3N (2 equiv.), EtOH, refux [28]
2.5
11
12
12
2
85
91
91
93
81
a1 mmol of all starting materials was used under optimized reaction conditions
1 3

S. F. Hojati et al.
Acknowledgements The authors thank Hakim Sabzevari University for the fnancial support of this
work.
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