Synthesis of mono- and bis-spiro-2-amino-4H-pyrans catalyzed by S-alkyl O-hydrogen sulfothioate functionalized silica-coated magnetic nanoparticles under ultrasound irradiation

Article abstract of DOI:10.1007/s11164-014-1834-z

New S-alkyl O-hydrogen sulfothioate functionalized silica-coated magnetic nanoparticles were prepared in a simple method and evaluated as an efficient catalyst in synthesis of mono- and bis-spiro-2-amino-4H-pyrans through three or pseudo-five component re

Full text of DOI:10.1007/s11164-014-1834-z

Res Chem Intermed
DOI 10.1007/s11164-014-1834-z
Synthesis of mono- and bis-spiro-2-amino-4H-pyrans
catalyzed by S-alkyl O-hydrogen sulfothioate
functionalized silica-coated magnetic nanoparticles
under ultrasound irradiation
•
Ali Reza Karimi Reyhaneh Davood Abadi
Zeinab Dalirnasab
•
Received: 5 July 2014 / Accepted: 24 September 2014
Ó Springer Science+Business Media Dordrecht 2014
Abstract New S-alkyl O-hydrogen sulfothioate functionalized silica-coated
magnetic nanoparticles were prepared in a simple method and evaluated as an
efficient catalyst in synthesis of mono- and bis-spiro-2-amino-4H-pyrans through
three or pseudo-five component reaction of isatins or bis-isatins and malononitrile
with dimedone or 4-hydroxycoumarin. The yields were excellent, and the catalyst
could be recovered simply from the reaction mixture using an external magnet and
reused at least five times without noticeable loss of catalytic activity.
Keywords Magnetic nanoparticles ꢀ Mono- and bis-spiro-2-amino-4H-pyrans ꢀ
Ultrasound irradiation ꢀ 1,3-Dicarbonyl compounds
Introduction
Among the heterocyclic compounds, 2-amino-4H-pyrans have received consider-
able attention due to a wide range of biological properties such as antiallergic [1],
antitumor [2] and antibacterial activities [3]. They have been used in pigments and
cosmetics and as potentially biodegradable agrochemicals [1, 4]. Spiropyrans are
used in photochromic compounds, and they have been widely studied because of
their potential utility in various high-tech applications [5]. Spirooxindole derivatives
display various bioactive effects such as antitumor and antimicrobial, and as
inhibitors of the human NKI receptor [6]. The existence of spiroindoline derivatives
in the structure of organic compounds could potentially have novel therapeutic
activities and thus there is an increased interest in obtaining spiro-2-amino-4H-
pyrans containing oxindole moiety [7–21].
A. R. Karimi (&) ꢀ R. Davood Abadi ꢀ Z. Dalirnasab
Department of Chemistry, Faculty of Science, Arak University, 38156-8-8349 Ara¯k, Iran
e-mail: ar_karimi55@yahoo.com; a-karimi@araku.ac.ir
123

A. R. Karimi et al.
Recently, spiro-2-amino-4H-pyrans were synthesized by multi-component con-
densation reaction of cyclic ketone such as isatin with malononitrile and b-
dicarbonyl compounds such as 4-hydroxycoumarin, dimedone or barbituric acid.
This condensation has been catalyzed by a variety of reagents, such as ammonium
salt [7], triethylbenzylammonium chloride (TEBA) [8], [BMIm]BF4 [9], nano-MgO
[10], InCl3/SiO2 [11], (SB-DBU)Cl [12], alum [13], sodium stearate [14], SBA-Pr-
NH2 [15], L-proline [16], magnesium perchlorate [17], ethylenediamine diacetate
[18, 19], mesoporous silica nanoparticles [20], and sulfuric acid-modified
poly(ethylene glycol) [21]. Also, this condensation has been performed in an
electrocatalytic procedure [22]. Although each of the methods has their own merits,
some methods suffer from long reaction times, low yields, harsh reaction conditions,
and tedious workup. The recovery of the catalysts is an important problem.
Therefore, the development of alternative methods for the synthesis of these
valuable compounds could be very worthwhile.
The use of acid-functionalized silica-coated magnetic nanoparticles has received
considerable attention in organic synthesis due to their environmental compatibility;
ease of handling, non-toxic nature, their reusability, and facile separation from the
products [23–29]. Various acid-functionalized silica-coated magnetic nanoparticles
have been prepared and used as efficient catalysts for different organic transfor-
mations, such as deprotection of benzaldehyde dimethylacetals [23], synthesis of a-
amino nitriles [24], synthesis of mono-, di- and tri-[bis(6-aminopyrimidonyl)
methanes] [25], quinolones [26], synthesis of benzo[a]xanthenone derivatives [27],
aminoimidazopyridine skeletons [28], and 3,4-dihydropyrimidinones/thiones [29].
Although three-component reaction of dimedone with isatin has been investi-
gated, there is no report on the reaction of dimedone with bis-isatins for the
synthesis of bis-spiro-2-amino-4H-pyrans. As a continuation of our research into the
preparation and catalytic investigation of new acid-functionalized silica-coated
magnetic nanoparticles [25], and due to the biological activity of spiro-2-amino-4H-
pyrans, we prepared new S-alkyl O-hydrogen sulfothioate functionalized silica-
coated magnetic nanoparticles (AHST-MNPs) by direct reaction of chlorosulfonic
acid with mercaptopropyl silica-coated magnetic nanoparticles (MPS-MNPs), and it
was successfully used as a catalyst in the synthesis of mono- and bis-spiro-2-amino-
4H-pyrans under ultrasonic irradiation at 60 °C (Scheme 1).
Experimental
General
Isatin 1, malononitrile 2, dimedon 3, 4-hydroxycoumarin 4, FeCl3, 3-(trimethoxy-
sily)-1-propanthiol (TMSPT), and solvents were used without further purification.
Fe3O4 nanoparticles (MNP) and citric acid-modified nanoparticles (CMNPs) were
prepared according to the literature procedure [30]. Sonication was performed in a
Struers Metason 200 HT ultrasonic cleaner with a frequency of 50–60 Hz and an
output power of 140 W. The products were characterized by elemental analysis and
1
by IR, H NMR, and 13C NMR spectroscopy. Fourier-transform IR spectra were
123

Functionalized silica-coated magnetic nanoparticles
MeO
Si
SH
MeO
ClSO3H
CA
SO3H
OMe
Fe3O4
MNP
Fe3O4
Fe3O4
S
SH
CMNP
AHST-MNP
MP-MNP
H2N
NC
O
H2N
NC
O
O
O
R1
CN
O
R1
O
+
O
N
O
R1
N
R2
CN
2
O
N
1a-c
1a: R1= H, R2= H
1b: R1=Br, R2=H
1c: R1=H, R2= CH2Ph
1d: R1=Br, R2= CH2Ph
OH
CH2PhCH2
N
N
R1
CN
1e: R1=H, R2
=
O
O
H2N
NC
O
N
H2N
NC
O
O
N
4
O
3
O
R1
O
O
O
O
AHST-MNP
60 o
O
O
CN
CH2PhCH2
N
O
1f: R1=Br, R2=
AHST-MNP
60 o
+
NH2
O
+
O
R1
O
R1
O
O
C
C
O
Br
N
O
5e-f
NH2
O
R2
R2
5a-d
6e-f
6a-d
Scheme 1 Preparation of S-alkyl O-hydrogen sulfothioate functionalized silica-coated magnetic
nanoparticles (AHST-MNP) and synthesis of mono- and bis-spiro-2-amino-4H-pyrans catalyzed by
AHST-MNP
1
recorded by using a Unicom Galaxy Series FTIR 5000 Spectrophotometer. H and
13C NMR spectra were recorded on a Bruker Avance 400 MHz spectrometer at 400
and 100 MHz, respectively. Elemental analyses were performed by using Vario EL
III elemental analyzer. Check spectroscopy, X-ray diffraction (XRD) by X00 3064
Pert Pw done. The size and shape of nanoparticles by scanning electron microscope
(SEM; Hitachi S-4160) were identified as devices. TGA data samples by TG Perkin-
Elmer 6300 model PYRIS TM Diamond were recorded.
General procedure for the preparation of mercaptopropyl silica-coated magnetic
nanoparticles (MPS-MNPs)
An amount of 1.5 g of CMNPs was dispersed in 250 mL ethanol:water (1:1)
mixture and sonication was carried out for 30 min to maintain proper dispersion.
Under continuous mechanical stirring, 2.5 mL of TMSPT was added. After
mechanical agitation at 40 °C for 4 h, the black precipitate was isolated by magnetic
decantation and washed with de-ionized water and ethanol, and then dried at room
temperature.
General procedure for the preparation of S-alkyl O-hydrogen sulfothioate
functionalized silica-coated magnetic nanoparticles (AHST-MNPs)
The prepared MPS-MNPs were added to a two-necked flask fitted with a constant-
pressure dropping funnel and a tube to remove the HCl gas formed, by conducting it
to an adsorbent solution. Chlorosulfonic acid (1.5 mL) was added dropwise over a
period of 30 min at room temperature and followed by slow mechanical stirring.
HCl gas immediately evolved from the reaction vessel. After that, the mixture was
shaken well for 30 min. The AHST-MNPs were washed with acetone and distilled
water to remove excess chlorosulfonic acid and finally dried in an oven at 60 °C for
6 h.
123

A. R. Karimi et al.
General procedure for the preparation of mono- and bis-spiro-2-amino-4H-pyrans
5a–f and 6a–f
A mixture of isatin 1 or 2 (1 mmol), malononitrile (1 mmol for 1 and 2 mmol for
2a, b), dimedone or 4-hydroxycoumarin (1 mmol for 1a, b and 2 mmol for 2a, b)
and AHST-MNPs (0.07 g) in H2O or EtOH/H2O (4:1) (10 mL) was exposed to US
irradiation at 60 °C for the appropriate time (see Table 2, below). Upon completion
of the reaction as monitored by TLC, the AHST-MNPs were removed under applied
external magnetic field. Next, the solution was reduced in volume and left for slow
evaporation. The solid was collected by filtration and washed with H2O (15 mL)
and cold EtOH (15 mL) to give the desired products. The crude products were
recrystallized from EtOH.
Spiro-2-amino-4H-pyrans (5a)
IR (KBr) (vmax, cm-1): 3,302, 3,136, 2,960, 2,928, 2,193, 1,722, 1,649, 1,604,
1
1,471, 1,348, 1,055, 746. H-NMR (DMSO-d6, 400 MHz) dH: 10.40 (1H, s, NH),
7.23 (2H, s, NH2), 7.12–7.16 (1H, t, J = 7.2 Hz, Harom), 6.97–6.99 (1H, d,
J = 7.2 Hz, Harom), 6.87–6.91(1H, t, J = 7.2 Hz, Harom), 6.78–6.80 (1H, d,
J = 7.6 Hz, Harom), 2.50–2.57 (2H, ABq, CH2), 2.12–2.16 (2H, ABq, CH2), 1.04
(3H, s, CH3), 1.00 (3H, s, CH3).
Spiro-2-amino-4H-pyrans (5b)
IR (KBr) (vmax, cm-1): 3,311, 3,149, 2,958, 2,928, 2,195, 1,724, 1,651, 1,604,
1
1,475, 1,348, 1,057, 810, 667. H-NMR (DMSO-d6, 400 MHz) dH: 10.56 (1H, s,
NH), 7.33 (2H, s, NH2), 7.30 (1H, s, Harom), 7.21(1H, s, Harom), 6.75–6.77 (1H, d,
J = 8 Hz, Harom), 2.50–2.58 (2H, ABq, CH2), 2.12–2.16 (2H, ABq, CH2), 1.03 (6H,
s, CH3). Anal. calc. for C19H16BrN3O3: C, 55.09; H, 3.89; Br, 19.29; N, 10.14 %.
Found: C, 55.20; H, 3.80; Br, 19.33; N, 10.22 %.
Spiro-2-amino-4H-pyrans (5c)
IR (KBr) (vmax, cm-1): 3,381, 3,319, 3,205, 2,964, 2,197, 1,712, 1,662, 1,601,
1
1,467, 1,352, 1,051, 893. H-NMR (DMSO-d6, 400 MHz) dH: 7.48–7.50 (2H, d,
J = 7.2 Hz, Harom), 7.26–7.33 (4H, m, NH2, Harom), 7.08–7.13 (3H, m, Harom),
6.94–6.98 (1H, t, J = 7.6 Hz, Harom), 6.68–6.70 (1H, d, J = 7.6 Hz, Harom),
4.86–4.96 (2H, ABq, CH2), 2.50–2.62 (2H, ABq, CH2), 2.15–2.24 (2H, ABq, CH2),
1.06 (3H, s, CH3), 1.02 (3H, s, CH3).
Spiro-2-amino-4H-pyrans (5d)
IR (KBr) (vmax, cm-1): 3,317, 3,252, 3,176, 2,958, 2,197, 1,710, 1,674, 1,608,
1
1,467, 1,352, 1,053,748, 669. H-NMR (DMSO-d6, 400 MHz) dH: 7.47 (1H, s,
H
arom), 7.43–7.46 (1H, d, J = 9.6 Hz, Harom), 7.25–7.35 (7H, m, NH2, Harom),
123

Functionalized silica-coated magnetic nanoparticles
6.66–6.68 (1H, d, J = 8.8 Hz, Harom), 4.86–4.95 (2H, ABq, CH2), 2.50–2.66 (2H,
ABq, CH2), 2.20–2.24 (2H, t, J = 16.8 CH2), 1.04 (6H, s, CH3).
Bis-spiro-2-amino-4H-pyrans (5e)
IR (KBr) (vmax, cm-1): 3,393, 3,292, 3,167, 2,958, 2,197, 1,710, 1,674, 1,608,
1
1,467, 1,352, 1,053, 748. H-NMR (DMSO-d6, 400 MHz) dH: 7.34 (4H, s, NH2),
7.24 (2H, s, Harom), 6.98–7.05 (6H, m, Harom), 6.85–6.89 (2H, t, J = 15.2 Hz,
H
arom), 6.58–6.60 (2H, d, J = 7.6, Harom) 4.79 (4H, s, CH2), 2.41–2.52 (4H, m,
CH2), 2.05–2.11 (4H, ABq, CH2), 0.96 (6H, s, CH3), 0.93 (6H, s, CH3). 13C-NMR
(DMSO-d6, 100 MHz) dC: 26.98, 27.59, 31.96, 43.06, 49.84, 58.40, 70.58, 108.91,
109.94, 110.59, 117.34, 122.53, 122.89, 127.09, 128.26, 133.54, 134.99, 142.54,
158.87, 164.49, 176.68, 195.04.
Bis-spiro-2-amino-4H-pyrans (5f)
IR (KBr) (vmax,cm-1): 3,433, 3,393, 2,975, 2,474, 2,193, 1,709, 1,674, 1,639, 1,481,
1,352, 1,101, 808, 617. 1H-NMR (DMSO-d6, 400 MHz) dH: 7.34 (4H, s, NH2), 7.32
(2H, s, Harom), 7.22–7.25 (6H, m, Harom), 6.56–6.58 (2H, d, J = 9.2 Hz, Harom),
4.98 (4H, s, CH2), 2.44–2.53 (4H, m, CH2), 2.03–2.10 (4H, t, J = 28.4 Hz, CH2),
0.93 (12H, s, CH3). 13C-NMR (DMSO-d6, 100 MHz) dC: 27.15, 27.51, 32.05, 43.46,
49.79, 67.99, 81.51, 103.64, 109.67, 110.89, 114.40, 117.25, 117.82, 127.10,
131.01, 134.70, 135.90, 140.33, 140.96, 158.99, 176.34, 195.32.
Results and discussion
The activity of the AHST-MNP catalyst was evaluated for the synthesis of mono-
and bis-spiro-2-amino-4H-pyrans. AHST-MNP behaves as an organic/inorganic
hybrid (interphase) in which a Brønsted acid site has been created. The catalyst is
isolated easily with a magnet and finally the high surface area of the AHST-MNP
means that they can accommodate large amounts of the catalytic species, thus
making the catalyst highly active. In order to optimize the conditions, the reactions
were carried out under different conditions. The condensation of isatin 1a,
malononitrile 2 and dimedone 3 was chosen as a model.
The effect of the amount of catalyst on the yield was investigated (Table 1,
entries 1–4). It was found that 0.07 g of catalyst for 1 mmol of isatin was the
appropriate amount for the reaction (Table 1, entry 3). The solvents also played an
important role in this reaction catalyzed by AHST-MNPs. The use of EtOH:H2O,
DMF, THF and DMSO as solvents furnished poor yields (Table 1, entries 6–9). The
reaction hardly proceeded in THF. However, the reaction in water afforded the
product in high yield with nearly complete conversion. Therefore, water was
selected as the reaction solvent in the following investigation (Table 1, entry 3).
Hence, the best reaction conditions were obtained by using 0.07 g of AHST-MNP in
water at 60 °C.
123

A. R. Karimi et al.
Table 1 Optimization of reaction for the synthesis of 5a under ultrasonic irradiation at 60 °C
Entrya
AHST-MNPs
Solvent
Yield
1
2
3
4
5
6
7
8
9
a
0.03
0.05
0.07
0.10
–
H2O
64
85
94
94
28
67
58
20
40
H2O
H2O
H2O
H2O
0.07
0.07
0.07
0.07
EtOH:H2O
DMF
THF
DMSO
Isatin (1 mmol), malononotrile (1 mmol), dimedone (1 mmol). Time: 105 min, temp.: 60 °C
Mono-spiro-2-amino-4H-pyrans 5a–d and 6a–d were obtained by the three-
component condensation of 1 mmol of isatin 1a–c and 1 mmol malononitrile 2 and
1 mmol dimedone 3 or 4-hydroxycoumarin 4 in the presence of 0.07 gr AHST-MNP
as heterogeneous catalyst. The reaction was carried out in water (10 mL) at 60 °C
under ultrasonic conditions to give products 5a, b and 6a–d in high yields. Bis-
spiro-2-amino-4H-pyrans 5e, f and 6e, f were achieved by pseudo five-component
reaction of 1d, e (1 mmol) with malononitrile 2 (2.1 mmol) and dimedone or
4-hydroxycoumarin (2.1 mmol) in the presence of 0.07 g AHST-MNP in water
(10 mL) under ultrasonic irradiation at 60 °C. We found that the catalyst AHST-
MNP showed high catalytic activity and could be recovered and recycled several
times without significant loss of activity (Table 2).
AHST-MNPs were obtained in a simple one-step procedure with direct reaction
of chlorosulfonic acid with mercaptopropyl silica-coated magnetic nanoparticles.
For the synthesis of mercaptopropyl silica-coated magnetic nanoparticles, prior to
functionalizing the magnetic particles with chlorosulfonic acid, modification of the
nanoparticles’ surface with negatively charged citrate groups was carried out and
then the surface of these particles (CMNPs) was coated with mercaptopropyl
trimethoxy silane to afford mercaptopropyl silica-coated magnetic nanoparticles.
The prepared catalyst (AHST-MNP) was characterized with IR, XRD, TGA and
SEM. In FT-IR spectra, a visible spectrum is absorbed Fe–O bond stretching has
appeared at 559 cm-1. The peaks at 1,003 and 1,170 cm-1 correspond to the Si–O
stretch and the broad band at 3,000–3,500 cm-1 and peak at 2,931 are due to –SO3H
and –CH stretching vibrations, respectively.
Although we have not yet established the mechanism, a possible explanation is
given in Scheme 2.
The sizes of nanoparticles were determined by scanning electron microscopy
(SEM) (Fig. 1). SEM images of AHST-MNP are shown in Fig. 1. The SEM
photograph illustrated that the AHST-MNP is spherical in shape and the average
size of AHST-MNP is about 28 nm.
The thermal properties of AHST-MNP were analyzed by thermal gravimetric
analysis (TGA) in the temperature range 40–850 °C under a nitrogen atmosphere.
123

Functionalized silica-coated magnetic nanoparticles
SSO3
SSO3
H
H
SSO3
HN
O
N
C
SSO3
C
H
O
NC
NC
H
H
H
H
H
H
CN
O
H
NC
O
O
NC
O
O
CN
N
O
O
Product
O
O
O
O
NH
N
N
H
N
H
N
H
CN
H
Scheme 2 Plausible mechanism of the AHST-MNP catalyzed synthesis of 2-amino-4H-pyrans
Table 2 AHST-MNP catalyzed synthesis of mono- and bis-spiro-2-amino-4H-pyrans at 60 °C under
ultrasonic irradiation
Entry
Isatin
Product
Time (h)/yield (%)
Mp (°C)
Mp (°C)Lit.
1a
2a
3a
1a
1b
1c
1d
1e
1f
Spiro-2-amino-4H-pyran (5a)
Spiro-2-amino-4H-pyran (5b)
Spiro-2-amino-4H-pyran (5c)
Spiro-2-amino-4H-pyran (5d)
Bis-spiro-2-amino-4H-pyran (5e)
Bis-spiro-2-amino-4H-pyran (5f)
Spiro-2-amino-4H-pyran (6a)
Spiro-2-amino-4H-pyran (6b)
Spiro-2-amino-4H-pyran (6c)
Spiro-2-amino-4H-pyran (6d)
Bis-spiro-2-amino-4H-pyran (6e)
Bis-spiro-2-amino-4H-pyran (6f)
1:45/94
1:45/92
2:15/91
2:15/89
4/77
305
292 [9]
313
275
268 [9]
4a
300
5b
6b
7a
8a
9a
10a
11b
12b
a
[300
[300
299–301
[300
275–277
[300
[300
268–271
4/79
1a
1b
1c
1d
1e
1f
2.5/90
2.5/89
2.5/91
2.5/88
4/76
292–294 [7]
[300 [7]
277–279 [7]
318 [13]
268 [13]
4/77
Solvent: H2O
b
Solvent: EtOH/H2O (4:1)
Fig. 1 SEM image of AHST-MNP
The primary weight loss up to 160 °C was related to the removal of physically
adsorbed solvent. The rate of weight loss between 160 and 630 °C is relatively slow
representing the high thermal stability of the AHST-MNP, which is generally
123

A. R. Karimi et al.
thermally stable until 630 °C, and the maximum rate of lost weight for these
nanoparticles was started from 540 °C. There is a well-defined mass weight loss of
44 % between 160 and 700 °C related to the breakdown of the sulfuric acid and
alkyl thiol moieties. In XRD patterns of the AHST-MNP, the intensity of the 43.61
reflection of the AHST-MNP was decreased after the introduction of the sulfonic
acid (SA) group.
Conclusions
In conclusion, we have described an efficient and environmentally benign method
for the preparation of mono- and bis-spiro-2-amino-4H-pyrans. This multi-
component condensation reaction is efficiently catalyzed by AHST-MNPs in water
at 60 °C under ultrasound irradiation. Operational simplicity, mild reaction
conditions, enhanced rates, and high isolated yields of the pure products are
significant advantages of the protocol presented here. AHST-MNP are the most
promising catalyst because of their ease of handling and ease of recovery with
external magnetic field.
Acknowledgment We gratefully acknowledge the financial support from the Research Council of Arak
University.
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