Na2EDTA: an efficient, green and reusable catalyst for the synthesis of biologically important spirooxindoles, spiroacenaphthylenes and spiro-2-amino-4H-pyrans under solvent-free conditions

Article abstract of DOI:10.1007/s13738-017-1148-3

For the first time, the organic salt Na₂EDTA was used as a catalyst for an effective and facile preparation of spiro-4H-pyrans via single-pot three-component condensation of isatin/acenaphthoquinone/ninhydrin, malononitrile, and CH-acids throug

Full text of DOI:10.1007/s13738-017-1148-3

J IRAN CHEM SOC
DOI 10.1007/s13738-017-1148-3
ORIGINAL PAPER
Na2EDTA: an effcient, green and reusable catalyst
for the synthesis of biologically important spirooxindoles,
spiroacenaphthylenes and spiro‑2‑amino‑4H‑pyrans
under solvent‑free conditions
Tayebeh Jazinizadeh1 · Malek Taher Maghsoodlou1 · Reza Heydari1 ·
Afshin Yazdani‑Elah‑Abadi2
Received: 10 February 2017 / Accepted: 25 May 2017
© Iranian Chemical Society 2017
Abstract For the frst time, the organic salt Na2EDTA was
used as a catalyst for an effective and facile preparation of
spiro-4H-pyrans via single-pot three-component condensa-
tion of isatin/acenaphthoquinone/ninhydrin, malononitrile,
and CH-acids through Knoevenagel–Michael–annulation
sequence. This new protocol employing Na2EDTA, which
is a green, recyclable, and inexpensive catalyst, offers
advantages such as solvent-free and highly effcient reac-
tion conditions, short reaction times (10–15 min), easy
work-up and high yields which make it more economic
than other environmentally synthetic methods.
the combination of multi-component reactions (MCRs)
and solvent-free conditions leads to a signifcant reduction
in reaction times, enhancements in conversions, improved
selectivity, with several advantages of the eco-friendly
approach such as energy savings, waste reduction, easy
work‐ups, and the avoidance of hazardous organic solvents
[6, 7].
So, the design of novel MCRs using solvent-free con-
ditions for the synthesis of simple and complex bioactive
heterocycles has remained as a signifcant topic in the drug
discovery process, and analysis of drugs [8, 9]. Among
these bioactive heterocycles, pyran ring systems are an
important category of oxygen-containing heterocycles.
Also, they have broad existence in a variety of important
natural compounds, including carbohydrates, alkaloids,
polyether antibiotics, pheromones, and iridoids [10].
Pyran-based compounds are widely applied as cosmetics,
pigments [11], and potential biodegradable agrochemi-
cals [12]. These compounds display a variety of biological
functions including anti-leishmanial [13], anti-HIV [14],
antioxidant [15], anti-tumor [16], and central nervous sys-
tem (CNS) activities and effects [17]; they are also used for
the treatment of Alzheimer’s disease [18] and schizophre-
nia [19].
Keywords Multi-component reactions (MCRs) ·
Solvent-free reaction · Green chemistry · Na2EDTA ·
Spiro-4H-pyrans
Introduction
In recent years, interest in green chemistry [1–3] has devel-
oped, and reducing the use of organic solvents and toxic
reagents for facile, effcient, and nonpolluting synthetic
procedures has become a major challenge for organic
chemists. In this area, use of natural materials as a promis-
ing catalyst in organic reactions has received a considerable
attention due to their green credentials [4, 5]. Furthermore,
Moreover, spiroheterocycle compounds containing one
sp3 carbon atom common to two rings are found in a num-
ber of natural or synthetic molecules [20, 21] and have
plenty inimitable virtues [22, 23]. For example, this type
of framework has been found as a core structure of many
bioactive natural alkaloids such as spirotryprostatins, gel-
semine, mitraphylline, horsfline, chitosenine (Fig. 1)
[24]. Molecules with spirocyclic structures are exclusively
attractive because the conformational restriction associated
with the structural rigidity affects signifcantly their biolog-
ical and pharmaceutical activity [25, 26].
* Malek Taher Maghsoodlou
mt_maghsoodlou@yahoo.com;
mt_maghsoodlou@chem.usb.ac.ir
1
Department of Chemistry, Faculty of Science, University
of Sistan and Baluchestan, P. O. Box 98135-674, Zahedan,
Iran
2
Department of Biology, Science and Art University, Yazd,
Iran
1 3

J IRAN CHEM SOC
Fig. 1 Some biologically active
alkaloids
Furthermore, EDTA (ethylenediaminetetraacetic acid)
and its salts are substituted diamines and are used in foods,
cosmetic formulations, pharmaceutical products, and man-
ufacturing. Moreover, they are used to treat heavy metal
poisoning and to reduce blood cholesterol [27]. Among
these salts, we used the ethylenediaminetetraacetic acid dis-
odium salt dehydrate (organic salt Na2EDTA, Fig. 2) as a
solid acid–base bifunctional catalyst for organic synthesis.
Considering the signifcant potential of spirocyclic
compounds, especially when fused to pyran derivatives as
a source of valuable drug candidates and with our contin-
ued interest in multi-component reactions and our ongoing
program for the synthesis of heterocyclic systems based
on green chemistry protocols [28–32], herein, we report
a green and effcient procedure for the synthesis of spiro-
2-amino-4H-pyrans, spiroacenaphthylenes, and spiroox-
indoles 4/5/6 through a single-pot, three-component con-
densation reaction between isatin/acenaphthoquinone/
ninhydrin 1, malononitrile 2, and CH-acids 3 in the pres-
ence of the catalytic amount of Na2EDTA as an effcient,
eco-friendly, and reusable catalyst under solvent-free con-
ditions at 70 °C (Scheme 1).
Fig. 2 Structure of Na2EDTA
at 300, 400, 75, and 100 MHz, respectively. Thin-layer
chromatography (TLC) was performed on silica-gel Poly-
gram SILG/UV 254 plates. All chemicals were received
from chemical producer Merck (Darmstadt, Germany)
and Fluka (Buchs, Switzerland) and used without further
purifcation.
General procedure for the synthesis of spirooxindoles,
spiroacenaphthylenes, and spiro‑2‑amino‑4H‑pyrans
(4–6)
A mixture of isatin/acenaphthoquinone/ninhydrin)1 mmol)
1a-c, malononitrile 2 (1 mmol), CH-acid 3a-g (1 mmol),
and 15 mol % of Na2EDTA was heated under solvent-
free conditions at 70 °C for the mentioned time shown in
tables. The progress of the reaction was monitored by TLC
using EtOAc/n-hexane (1:3) as an eluent. Upon comple-
tion, the reaction mixture was allowed to cool to room
temperature. Then, 5 mL of water was then added to the
reaction mixture, the resulting solid was collected by fltra-
tion and washed twice with water (2 × 5 mL), and then the
pure solid products 4/5/6 were recrystallized from ethanol.
Experimental
General
Melting points and IR spectra of all compounds were deter-
mined by using an Electro thermal 9100 apparatus and
1
JASCO FT/IR-460 plus spectrometer. The H NMR and
13C NMR spectra were recorded on a Bruker DRX-300 and
400 Avanve instrument with deuterated dimethyl sulfoxide
(DMSO-d6) as solvent and using TMS as internal reference
1 3

J IRAN CHEM SOC
Scheme 1 One-pot, three-com-
ponent synthesis of spiro-4H-
pyran derivatives, catalyzed by
Na2EDTA
Selected spectroscopic data of selected and known products
are given below:
nitrile (5a) Mp 271–273 °C; IR (KBr): νmax = 3351,
3274, 3187, 2942, 2194, 1735, 1657, 1461, 1342, 1213,
1
1154, 1022, 901 cm−1; H NMR (400 MHz, DMSO-d6): δ
2‑Amino‑7,7‑dimethyl‑2′,5‑dioxo‑5,6,7,8‑tetrahydrosp
1.03 (s, 3H, CH3), 1.05 (s, 3H, CH3), 2.04–2.14 (m, 2H,
CH2), 2.64 (s, 2H, H2), 7.32 (s, 2H, NH2), 7.40 (d, 1H,
J = 6.8 Hz, ArH), 7.66 (t, 1H, J = 6.8 Hz, ArH), 7.83 (t,
1H, J = 8.0 Hz, ArH), 7.92–7.95 (m, 2H, ArH), 8.27 (d,
1H, J = 7.6 Hz, ArH).
iro[chromene‑4,3′‑indoline]‑3‑carbonitrile
(4a) Mp
292–294 °C; IR (KBr): νmax = 3375, 3310, 3143, 2960,
2191, 1725, 1656, 1603, 1465, 1352, 1222, 1178, 1052,
1
907 cm−1; H NMR (400 MHz, DMSO-d6): δ 1.01 (s, 3H,
CH3), 1.04 (s, 3H, CH3), 2.08–2.20 (m, 2H, CH2), 2.53
(s, 2H, CH2), 6.80 (d, 1H, J = 7.6 Hz, ArH), 6.90 (t, 1H,
J = 7.6 Hz, ArH), 6.98 (d, 1H, J = 7.2 Hz, ArH), 7.14 (t,
1H, J = 7.6 Hz, ArH), 7.22 (s, 2H, NH2), 10.40 (s, 1H,
NH).
2′‑Amino‑2,5′‑dioxo‑2H,5′H‑spiro[acenaphthylene‑1,
4′‑pyrano[3,2‑c]chromene]‑3′‑carbonitrile
(5b) Mp
295–297 °C; IR (KBr): νmax = 3385, 3280, 3157, 2936,
2192, 1717, 1685, 1652, 1474, 1331, 1226, 1172, 1020,
1
914 cm−1; H NMR (300 MHz, DMSO-d6): δ 7.50 (d, 1H,
2‑Amino‑5′‑chloro‑7,7‑dimethyl‑2′,5‑dioxo‑5,6,7,8‑tetrahy
drospiro[chromene‑4,3′‑indoline]‑3‑carbonitrile (4f) Mp
294–295 °C; IR (KBr): νmax = 3360, 3150, 2955, 2192,
1722, 1677, 1648, 1590, 1473, 1347, 1220, 1033, 806,
J = 8.1 Hz, ArH), 7.57 (t, 1H, J = 7.5 Hz, ArH), 7.64–7.81
(m, 5H, ArH, NH2), 7.89 (t, 1H, J = 7.8 Hz, ArH), 7.99–
8.07 (m, 3H, ArH), 8.36 (d, 1H, J = 7.8 Hz, ArH); 13C
NMR (300 MHz, DMSO-d6): δ 52.01, 58.2, 102.6, 112.9,
117.2, 117.6, 121.6, 122.6, 123.2, 125.6, 129.18, 129.5,
130.3, 131.7, 132.7, 134.1, 141,6, 142.1, 152.5, 155.8,
158.8, 158.9, 159.4, 203.6 ppm.
1
552 cm−1; H NMR (300 MHz, DMSO-d6): δ 1.03 (s, 6H,
2CH3), 2.16 (s, 2H, CH2), 2.50–2.58 (m, 2H, CH2), 6.81
(d, 1H, J = 8.1 Hz, ArH), 7.11 (s, 1H, ArH), 7.21 (dd, 1H,
J = 8.1 Hz, J = 2.1 Hz, ArH), 7.36 (s, 2H, NH2), 10.58 (s,
1H, NH); 13C NMR (300 MHz, DMSO-d6): δ 27.6, 27.9,
32.4, 47.5, 50.3, 57.1, 110.6, 111.1, 117.7, 123.7, 126.1,
128.5, 136.9, 141.3, 141.4, 159.3, 165.1, 178.3, 195.6 ppm.
2‑Amino‑7,7‑dimethyl‑1′,3′,5‑trioxo‑1′,3′,5,6,7,8‑hexahy
drospiro[chromene‑4,2′‑indene]‑3‑carbonitrile (6a) Mp
288–290 °C; IR (KBr): νmax = 3370, 3240, 2955, 2190,
1743, 1712, 1683, 1656, 1592, 1347, 1258, 1161, 1050,
1
2′‑Amino‑7′,7′‑dimethyl‑2,5′‑dioxo‑5′,6′,7′,8′‑tetrahyd
ro‑2H‑spiro[acenaphthylene‑1,4′‑chromene]‑3′‑carbo
791 cm−1; H NMR (300 MHz, DMSO-d6): δ 1.04 (s,
6H, 2CH3), 2.21 (s, 2H, CH2), 2.63 (s, 2H, CH2), 7.71 (s,
1 3

J IRAN CHEM SOC
Table 1 Optimization of the amount of catalyst (Na2EDTA) and temperature in a one-pot synthesis of the model reaction
Entry
Catalyst (mol %)
Reaction conditions
Time (min)
Isolated yield (%)
1
–
Solvent-free, r.t
100
75
45
40
15
10
10
10
7
Trace
50
2
10
15
15
15
15
15
20
15
15
15
–
Solvent-free, r.t
3
Solvent-free, r.t
72
4
Solvent-free, 50 °C
Solvent-free, 60 °C
Solvent-free, 70 °C
Solvent-free, 80 °C
Solvent-free, 70 °C
Solvent-free, 70 °C
H2O, 70 °C
80
5
90
6
94
7
95
8
92
9
90
10
11
12
10
10
10
90
EtOH, 70 °C
87
Solvent-free, 70 °C
43
2H, NH2), 8.00–8.07 (m, 4H, ArH); 13C NMR (300 MHz,
DMSO-d6): δ 27.6, 32.9, 49.3, 52.2, 53.5, 110.4, 117.3,
123.6, 137.1, 141, 160.3, 160.3, 160.35, 166.9, 196.5,
200.2 ppm.
tetrahydrospiro[chromene-4,3′-indoline]-3-carbonitrile
4a in 10 min with 94% of yield (Table 1, entry 6).
To explore the scope of the reaction further, the present
study is extended to various cyclic ketones and different acti-
vated CH-acids using these optimized conditions. All the
reactions were complete in 10–15 min and resulted in the
formation of the target structures in high yields without the
formation of any side products. This one-pot reaction was
effciently promoted using isatin with reduced reaction times
and increased yields rather than other cyclic ketones and
dimedone reacted rapidly and gave higher yields in compari-
son with other activated CH-acids (Table 2, entries 1–17).
Recovery of the catalysts is a signifcant feature in green
organic synthesis. Thus, for recyclability of the catalyst, we
also investigated the recycling of Na2EDTA under solvent-
free conditions at 70 °C using a selected model reaction
of isatin, malononitrile, and dimedone in the presence of
Na2EDTA as a homogeneous catalyst. After the comple-
tion of the reaction, 5 mL of water was added to the mix-
ture. The Na2EDTA was dissolved in water and fltered for
the separation of the crude product. The separated product
was washed twice with water (2 × 5 mL). The resulting
product was subsequently recrystallized from ethanol to
give the pure solid. In order to recover the catalyst, since
Na2EDTA is soluble in water, the fltrate was extracted with
diethyl ether. The aqueous layer was separated, its solvent
was evaporated under reduced pressure, and Na2EDTA was
recovered and reused (Fig. 3).
Results and discussion
Considering the importance of spiro-4H-pyrans, we were
willing to fnd a practical and general method for their
synthesis in high yields and purities and also, because the
development of effcient and environmentally friendly syn-
thetic procedures is always desirable, we decided to peruse
whether those compounds could be prepared by condensa-
tion of isatin/acenaphthoquinone/ninhydrin, malononitrile,
and CH-acids through Knoevenagel–Michael–annulation
sequence in the absence of any hazardous or toxic cata-
lysts and organic solvents. For this purpose, the conden-
sation reaction between isatin 1a (1 mmol), malononitrile
2 (1 mmol), and dimedone 3a (1 mmol) was selected as
a model reaction in the presence of different amounts of
Na2EDTA as a catalyst (10, 15 and 20 mol %) at various
temperatures (25, 50, 60, 70 and 80 °C). As can be seen
in Table 1, the best result was obtained when the reaction
was carried out in the presence of 15 mol% of Na2EDTA
at 70 °C in solvent-free conditions, which afforded the
corresponding 2-amino-7,7-dimethyl-2′,5-dioxo-5,6,7,8-
1 3

J IRAN CHEM SOC
Table 2 Solvent-free synthesis of spiro-4H-pyran derivatives in the presence of Na2EDTA (15 mol%) as a catalyst at 70 °C
M.P. (oC)
Time
(min)
Yield
(%)a
Entry
Cyclic ketone
C−H activated
Product
Observed
Reported
1
10
10
15
94
92
89
292–294
289–290 [33]
2
3
295–296
292–294 [33]
278–280
275–276 [33]
4
15
85
230–231
225–228 [34]
5
6
15
10
90
95
252–254
294–295
255–256 [35]
289–291 [36]
7
8
10
12
15
10
92
87
89
94
>300
>300 [36]
226–228 [37]
256–258 [37]
270 [38]
230–232
254–256
271–273
9
10
1 3

J IRAN CHEM SOC
Table 2 continued
M.P. (oC)
Time
(min)
Yield
(%)a
Entry
Cyclic ketone
C−H activated
Product
Observed
Reported
11
12
13
14
12
15
15
12
85
84
90
92
295–297
288–292 [39]
>300 [40]
>300
200–202
288–290
197–198 [41]
290–292 [38]
15
15
84
276–278
280–285 [38]
16
17
15
88
277–278
275–277 [38]
15
85
256–258
255–260 [38]
a
Isolated yields
As shown in Fig. 3, the catalytic system worked well up
to fve catalytic runs and slightly reduced the product yield,
which may be due to little weight loss of catalyst during
each recovery process.
The probable mechanism for the formation of the prod-
ucts using Na2EDTA, which act as an acid–base bifunc-
tional catalyst in all steps, is outlined in Scheme 2. On
the basis of this suggested mechanism, the synthesis of
spiro-4H-pyrans 4‑6 could be achieved through two ways.
In two paths, Na2EDTA is an effcient catalyst to form the
olefn I, which readily prepares in situ from Knoevenagel
condensation of carbonyl group of cyclic ketone 1a–c with
malononitrile 2 (path A) or C–H activated 3a‑g (path B). In
continue, Michael addition of C–H activated 3a–g (path A)
or malononitrile 2 (path B) with olefn I in the presence of
Na2EDTA fnally give intermediate II. At the end, interme-
diate II through an intramolecular cyclization by nucleo-
philic attack of the hydroxyl group on the cyano group pro-
ducing the desired products 4–6.
On this mechanism, we suggest that the Na2EDTA
plays a dual role: frst, to electrophilically activate the
cyclic ketone carbonyl via H-bond formation between one
1 3

J IRAN CHEM SOC
H-atom of Na2EDTA and the O-atom of the C=O group,
and second, to enhance the nucleophilicity of the C–H acti-
vated or malononitrile through deprotonation of the Cα-H
by Na2EDTA.
In order to assess the effciency and generality of this
methodology, the obtained result from the reaction of
isatin and malononitrile with dimedone by this method
has been compared with those of the previously reported
methods (Table 3). It was found that the present method
is convincingly superior to the reported methods with
respect to reaction time and exhibits broad applicability
in terms of yields.
Conclusions
94
92
90
88
86
84
82
80
In this work, we have demonstrated a simple single-pot,
three-component synthesis of spiro-4H-pyran deriva-
tives in excellent yields and purities with very short
reaction times, from readily available starting materials
by using catalytic amount of Na2EDTA as an environ-
mentally benign solid acid–base bifunctional catalyst,
under solvent-free conditions. This green and effcient
procedure has a number of advantages such as opera-
tional simplicity, easy work-up, use of inexpensive,
non-toxic, reusable, easy to handle catalyst without any
byproduct, avoidance of hazardous organic solvents, and
it may fnd a wide range of applications in diversity-
oriented synthesis, and drug discovery, which make the
methodology more attractive than the other conventional
Run 1
94
Run 2
92
Run 3
91
Run 4
88
Run 5
85
Product (%)
Fig. 3 Results of recycling over fve consecutive recycling experi-
ments
Scheme 2 Proposed mechanism for the formation of spiro-4H-pyran derivatives in the presence of Na2EDTA
1 3

J IRAN CHEM SOC
References
Table 3 Comparison of the effciency of Na
2EDTA with other reported catalysts in the literature for the synthesis of 4a
Entry
Catalyst/condition
Time (min)
Yield (%)a
1
TEBA (20 mol %)/H2O, 60 °C
120
20
94
75
90
95
94
92
90
75
92
90
93
91
90
94
86
81
94
Previous work [33]
Previous work [34]
Previous work [35]
Previous work [36]
Previous work [37]
Previous work [38]
Previous work [39]
Previous work [42]
Previous work [43]
Previous work [44]
Previous work [45]
Previous work [46]
Previous work [47]
Previous work [48]
Previous work [49]
Previous work [50]
Present work
2
[γ-Fe2O3@HAp-Si(CH2)3SO3H] (2 mol %)/H2O, 30 °C
EDDA (10 mol %)/H2O, 60 °C
3
60
4
Sodium stearate (10 mol %)/H2O, 60 °C
l-Proline (10 mol %)/H2O, 80 °C
180
20
5
6
Ni nps/ethylene glycol, rt
5
7
DBU (10 mol %)/H2O, refux
10
8
InCl3 (20 mol %)/CH3CN, refux
90
9
NH4Cl (20 mol %)/H2O, 80 °C
10
10
11
12
13
14
15
16
17
β-Cyclodextrin/H2O, 60 °C
300
120
30
Nano MgO (15 mol %)/H2O, 80 °C
Mg(ClO4)2 (10 mol %)/EtOH, H2O, 50 °C
DMAP (10 mol %)/solvent-free, MWI, 100 °C
AHST-MNP (0.07 g)/H2O, ultrasonic irradiation, 60 °C
Cu(OAc)2.H2O (15 mol %)/solvent-free, 80 °C
Citric acid (20 mol %)/EtOH, H2O, 80 °C
Na2EDTA (15 mol %)/solvent-free, 70 °C
5
105
240
10
10
a
Isolated yields
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