Ionic tagged amine supported on magnetic nanoparticles: Synthesis and application for versatile catalytic Knoevenagel condensation in water

Article abstract of DOI:10.1039/c4ra05540c

Propylamine modified with imidazolium ionic moiety grafted onto magnetic nanoparticles (MNPs) was prepared and evaluated as a catalyst for Knoevenagel condensation in water at room temperature. The catalyst was efficient in the reaction to give the condensation products in good yields. It is worth noting that the ionic-tagged catalyst performed significantly better than its ionic tag-free counterpart. Finally, the catalyst could be reused for 8 times with a slight loss in its catalytic activity. the Partner Organisations 2014.

Full text of DOI:10.1039/c4ra05540c

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Ionic tagged amine supported on magnetic
nanoparticles: synthesis and application for
versatile catalytic Knoevenagel condensation in
water
Cite this: RSC Adv., 2014, 4, 33175
*
*
Anguo Ying, Fangli Qiu, Chenglin Wu, Huanan Hu and Jianguo Yang
Propylamine modified with imidazolium ionic moiety grafted onto magnetic nanoparticles (MNPs) was
prepared and evaluated as a catalyst for Knoevenagel condensation in water at room temperature. The
catalyst was efficient in the reaction to give the condensation products in good yields. It is worth noting
that the ionic-tagged catalyst performed significantly better than its ionic tag-free counterpart. Finally,
the catalyst could be reused for 8 times with a slight loss in its catalytic activity.
Received 4th April 2014
Accepted 26th June 2014
DOI: 10.1039/c4ra05540c
www.rsc.org/advances
Magnetic nanoparticles (MNPs) are extensively studied as
efficient supports for immobilizing homogeneous catalysts for
1. Introduction
various organic transformations because of their interesting
properties such as high surface area and paramagnetic prop-
erties, facilitating their separation from reaction media aer
magnetization with an external permanent magnetic eld.12
MNPs-supported guanidine was developed and used to catalyze
the cyanosilylation of carbonyl compounds to achieve good to
high yields of the desired products.13 In addition, the nano-
catalyst can be reused up to 20 times. Gawande and coworkers
reported a sulfonic acid catalyst graed on magnetite and
subsequently served as a highly efficient magnetic catalyst for
the Ritter and multicomponent reactions.14 Meanwhile, a new
concept of ion-tag strategy that can be achieved by installing an
ionic substituent on the catalyst has been presented.15 Catalysts
optimized and designed according to the ion-tag strategy have
three advantages, including water compatibility, readily recy-
clable and higher catalytic activities compared to the parent tag-
free catalysts, which, to some extent, is a working hypothesis.
Thus, a series of novel ionic tagged catalysts have emerged and
have been exploited in versatile organic transformations such as
aza-Michael addition,16 selective hydroformylation,17 olen
reduction,18 Suzuki–Miyaura reaction,19 asymmetric Henry
reaction,20 enantioselective a-aminoxylations of ketones and
aldehydes,21 asymmetric allylic etherication,22 and asymmetric
addition.23 Based on the unique properties of magnetic nano-
particle support and ion tag of ionic liquid, a new model for the
design of efficient and recoverable catalysts has been developed
via the combination of magnetite and ionic liquid (Scheme 1).
Consequently, with the principle for the construction of cata-
lysts in hand and in continuation of our research endeavors on
the development of environmentally benign and sustainable
chemical processes,24 herein, we report a novel MNPs supported
amine with ionic tag and its application as a highly efficient and
The Knoevenagel condensation of aldehydes with acidic active
methylene compounds represents one of the most fundamental
carbon–carbon formation reactions in the eld of organic
transformations.1–6 The corresponding condensation products
are electrophilic trisubstituted alkenes, which have been widely
used not only as starting materials for Michael addition7 and
domino or one-pot reactions,8 but also as important interme-
diates for the preparation of functional polymers, ne chem-
icals and pharmaceutical drugs.9 Traditionally, this type of
condensation reactions are performed in homogeneous solu-
tion in the presence of organic bases as well as their salts as
catalysts, including dimethylamino pyridine, piperidine,
guanidine and ethylenediamine.10 These methods are obviously
limited by the difficulties of catalyst separation and recycla-
bility. Therefore, several methodologies for the Knoevenagel
condensation catalyzed by heterogeneous catalysts were devel-
oped, in which the catalysts are readily recoverable and are
recycled. For example, MgO/ZnO,11a amine-functionalized
polyacrylonitrile ber,11b,c La2O3/MgO,11d Ni–SiO2,11e Si-MCM-41
supported basic materials11f and IRMOF-3 (ref. 11g) have been
tested to catalyze the condensation reactions. Each of the
abovementioned methods has its own merits with at least one
of the limitations of low yields, narrow substrate scope, harsh
reaction conditions and the involvement of large amounts of
harmful and toxic organic solvents. Hence, improved methods
for the Knoevenagel condensation using inexpensive, readily
available catalysts and less scavenger reagents coupled with
easier work-up procedures are highly desirable.
School of Pharmaceutical and Chemical Engineering, Taizhou University, Taizhou
318000, China. E-mail: agying@tzc.edu.cn; yinganguo@163.com; yjg@tzc.edu.cn;
Fax: +86 576 88660359; Tel: +86 576 88660359
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Scheme 1 A model for the design of novel catalysts.
magnetically recoverable catalyst for the versatile Knoevenagel
condensations.
2. Results and discussion
2.1 Preparation and characterization of catalysts
The magnetic nanoparticle supported catalyst 4 (MNPs-IT-PA)
was prepared in multiple steps from several commercially
available chemicals (Scheme 2). SiO2@Fe3O4 1 (MNPs) was
synthesized by a chemical co-precipitating method reported in
the literature,25 followed by silica coating.26 The outer silica
shell can not only prevents the aggregation of nanoparticles but
also provides suitable surface Si–OH groups for further func-
tionalization.27 N-(3-propyltriethoxysilane) imidazole 2 was
prepared via the condensation of imidazole and 3-chloro-
propyltriethoxysilane, and was then graed on the MNPs to give
the supported imidazole 3. Subsequently, 3 was reuxed with
3-bromine propylamine in dry toluene under nitrogen
atmosphere to afford the nal catalyst MNPs-IT-PA 4. For
comparison, ion-free counterpart 6 (MNPs-PA), in which 3-
aminopropyltriethoxysilane 5 was directly immobilized onto the
magnetic nanoparticles, was prepared, as outlined in Scheme 2.
The transmission electron microscopy (TEM) images in
Fig. 1 show that MNPs (a), MNPs-PA (b) and MNPs-IT-PA (c) are
uniformly sized magnetic nanoparticles with an almost spher-
ical morphology. The diameter of the all the three kinds of
particles is approximately 16 nm, which is signicantly larger
than naked Fe3O4 particles. The similar size and morphology of
blank support (a) and amine anchored (b and c) implies that the
immobilization process did change the magnetic ferrite core,
Fig. 1 TEM images of MNPs (a), MNPs-PA (b) and MNPs-IT-PA (c).
and the modication reaction for catalyst loading only occurred
on the silica shell surface.
The X-ray diffraction (XRD) spectra of anchored catalysts
MNPs-IT-PA, MNPs-PA and MNPs have the same typical peaks
with respect to their positions and relative intensities (Fig. 2). A
broad peak from 2q ¼ 18ꢀ to 28ꢀ is attributed to the amorphous
silica shell formed surrounding the Fe3O4 core.28 The peaks at
30.07ꢀ, 35.41ꢀ, 43.04ꢀ, 53.39ꢀ, 56.91ꢀ, and 62.49ꢀ correspond to
the (220), (311), (400), (422), (511), and (440) reections of the
crystalline cubic spinel structure of standard naked Fe3O4
sample (JCPDS 19-0629), respectively. As shown in Fig. 2, the
phase composition of MNPs remained intact aer surface
modication on nanoparticles.
Scheme 2 Preparation of magnetic nanoparticle supported catalyst MNPs-IT-PA 4 and MNPs-PA 6.
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new bands at 1211 cmꢁ1 and 1153 cmꢁ1 corresponding to the
N–H stretching vibration of primary amine indicate that the
MNPs are functionalized with propylamine modied by imi-
dazolium-based ionic liquid.
The magnetic properties of neat SiO2@Fe3O4 (a), ionic-free
supported amine (b) and ionic tagged amine anchored on MNPs
(c) were investigated at room temperature (Fig. 4). The satura-
tion magnetizations were 32.2, 36.4, and 56.4 emu gꢁ1
,
respectively. It should be noted that the high magnetization and
superparamagnetism of the ionic-tagged amine loaded sample
exhibits good magnetic character and re-dispersion properties,
which enables the catalyst to be well-dispersed in the reaction
solution and to be easily recovered by an external magnetic
force (Fig. 5).
The thermal stabilities of the two immobilized catalysts were
determined by thermogravimetric (TG) analysis. The results are
shown in Fig. 6. The two TG curves were divided into several
regions corresponding to different mass loss ranges. The rst
weight loss for both the samples, which occurred below 200 ꢀC
Fig. 2 XRD spectra of MNPs (a), MNPs-PA (b) and MNPs-IT-PA (c).
Successful functionalization of MNPs can be veried from
the FT-IR spectra shown in Fig. 3.
In Fig. 3, the band at 579 cmꢁ1 was assigned to the charac-
teristic Fe–O vibrations and conrmed the existence of Fe3O4
component in all the three samples. A broad peak at around
3400 cmꢁ1 is attributed to the Si–OH group. Moreover, the
presence of Si–O bond in three samples is evident from two
characteristic vibrations at 953 cmꢁ1 and 1086 cmꢁ1. The
samples b and c exhibit adsorptions at 2965 cmꢁ1, 2874 cmꢁ1
,
and 1465 cmꢁ1, as attributed to the C–H stretching vibration of
linker 3-chloropropyltriethoxysilane anchored on the surface of
SiO2@Fe3O4.29 The imidazole tag was responsible for the cova-
lent anchoring of propylamine by forming an imidazolium-
based ionic liquid moiety, which was evident from character-
istic bands at 1507 cmꢁ1 of C]N vibration and at 3143 cmꢁ1 of
C–H stretching on the imidazole ring,30 as shown in Fig. 3c. Two
Fig. 4 Room temperature magnetization curves for MNPs (a), MNPs-
PA (b) and MNPs-IT-PA (c).
Fig. 5 Photographs of the dispersion of catalyst MNPs-IT-PA (a) and
Fig. 3 FT-IR spectra of MNPs (a), MNPs-PA (b) and MNPs-IT-PA (c).
the separation of the catalyst using an external magnet.
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Fig. 6 TG-DTG analysis for SiO2@Fe3O4-PA(a) and MNPs-IT-PA (b).
was probably because of the loss of adsorbed solvent or trapped
water on the surface and structural water within amorphous
silica outside the Fe3O4 core. A mass loss of approximately 4.5%
of SiO2@Fe3O4-PA occurring between 198 ꢀC and 510 ꢀC was
attributed to the loss of propylamine. Further mass loss of the
catalyst MNPs-PA at higher temperature was a result of the
decomposition of silica shell (Fig. 6a).31 For catalyst MNPs-IT-
PA, the second weight loss in the range of 199 ꢀC to 350 ꢀC was
accounted by the cleavage of imidazolium ionic liquid-modied
amine, which was very obvious in the DTG curve (Fig. 6b). The
occurrence of further decomposition beyond 351 ꢀC could be
designated as the complete loss of imidazolium-functionalized
trialkoxysilane moiety.32 The loading amount of propylamine
and amine combined with ionic moiety were determined to be
0.21 mmol gꢁ1 and 0.34 mmol gꢁ1, respectively, by elemental
analysis, well in accordance with the TG analysis.
2.2 Catalytic performances in versatile Knoevenagel
condensation
The catalytic activities of MNPs-PA and MNPs-IT-PA were
investigated using the Knoevenagel condensation between 2-
(cyanomethyl)benzimidazole (5 mmol) and 2-thenaldehyde (5
mmol). According to the results provided in Table 1, the catalyst
MNPs-IT-PA performed well to give the desired product within
2 h in 79% yield, while ionic tag-free catalyst MNPs-PA gave the
same desired product in 62% yield (Table 1, entries 2 and 3).
The results conrmed that MNPs-IT-PA catalyzes the model
reaction signicantly better than its counterpart ionic tag-free
MNPs-PA, which may be attributed to the improved mass
transfer originating from the hydrophobic ionic moiety.33 Only
28% yield of the product was obtained when the reaction was
carried out in the presence of a blank support (SiO2@Fe3O4)
even if the reaction time was prolonged to 5 h (Table 1, entry 1).
Table 1 Evaluation of the effects of the catalyst and solvent on the Knoevenagel condensation reaction of 2-(cyanomethyl)benzimidazole and
2-thenaldehyde at room temperature
Entry
Catalyst (mol%)
Solvent (10 mL)
Time (h)
Yield (%)a
1
2
3
4
5
6
7
8
MNPs (SiO2@Fe3O4) (73.5 mg)
MNPs-PA (5.0)
H2O
H2O
H2O
H2O
H2O
H2O
H2O
Methanol
Methanol
Toluene
Toluene
CH2Cl2
CH2Cl2
5
2
2
2
3
2
3
3
2
3
3
3
3
28
62
79
79
80
63
37
58
68
52
65
57
61
MNPs-IT-PA (5.0)
MNPs-IT-PA (10.0)
MNPs-IT-PA (20.0)
MNPs-IT-PA (2.0)
MNPs-IT-PA (0.5)
MNPs-IT-PA (5.0)
MNPs-PA (5.0)
MNPs-IT-PA (5.0)
MNPs-PA (5.0)
MNPs-IT-PA (5.0)
MNPs-PA (5.0)
9
10
11
12
13
a
Isolated yield.
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Table 2 MNPs-IT-PA catalyzed the Knoevenagel condensation of various aromatic aldehydes with 2-(cyanomethyl)benzimidazole, 2-(cya-
nomethyl)benzothiazole and phenylacetonitrile and indole-2-acetonitrilea
Entry
1
Substrate
Aldehyde
Time (h)
2
Yield (%)b
83
2
3
4
5
1.5
1
85
88
84
83
2
4
6
2
80
7
8
9
3
76
84
85
1.5
2
10
11
2
3
85
90
12
3
78
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Table 2 (Contd.)
Entry
13
Substrate
Aldehyde
Time (h)
3
Yield (%)b
85
14
15
5
5
82
86
16
5
81
a
b
Reaction conditions: methyl active compounds (5 mmol), aldehydes (5 mmol), water (10 mL), MNPs-IT-PA (5 mol%), rt. Isolated yield.
The reaction conditions were further optimized at different relatively longer reaction times were required for indole-2-
catalyst loadings, revealing that 5 mol% of the catalyst acetonitrile (Table 2, entries 15 and 16). It is worth noting that
MNPs-IT-PA afforded the best catalytic efficiency in the terms of all the obtained products were exclusively E-isomers.
reaction rate and yield (Table 1, entries 4–7). For comparison,
Encouraged by the exciting results of cyano-substituted
several organic solvents were also exploited as media for the methylene active compounds in the present catalytic system, we
reaction. The reactions catalyzed by MNPs-IT-PA in methanol, also attempted to conduct the condensation of non-cyano
toluene and dichloromethane resulted in the product with lower substituted ketone (I) and benzaldehyde to form the product 4-
yields (Table 1, entries 8, 10 and 12). It is worth noting that the methyl-3-oxo-N-phenyl-2-(phenylmethylene)pentanamide (II),
ionic tag-free catalyst performed better in organic solvents than which is a key intermediate for the preparation of Atorvastatin
the ionic-tagged catalyst MNPs-IT-PA (Table 1, entries 8–13). calcium(III), which can inhibit 3-hydroxy-3-methylglutaryl-
Considering reaction efficiency as well as the principle of green coenzyme (HMG-CoA) reductase (Scheme 3).34 To our pleasure,
chemistry, the reaction catalyzed by MNPs-IT-PA in water at room the reaction proceeded smoothly in the presence of catalyst
temperature was used for further examinations.
MNPs-IT-PA in water, and 84% yield of the product (II) was
With optimal reaction conditions in hand, we proceeded to achieved within 4 h (reaction condition A in Scheme 3). Only
investigate the scope of methyl active compounds and various 59% product yield was obtained when the reaction was
substituted arylaldehydes, and the results are shown in Table 2. promoted by ionic tag-free catalyst SiO2@Fe3O4-PA (condition
A wide range of aromatic aldehydes reacted with 2-(cyano- B). The traditional method for the preparation of III requires a
methyl)benzimidazole to give products in high yields (Table 2, large amount of organic solvent and acid (Condition C).
entries 1–7). The reaction rate of aldehydes with electron-with- Compared with B and C, the reaction conditions A using ionic-
drawing groups at the aromatic ring is slightly faster than that tagged MNPs-IT-PA as catalyst may provide an environmentally
with electron-donating groups (Table 2, entries 1–2 vs. 3–6). On friendly alternative route for the synthesis of Atorvastatin
the other hand, the reaction of mono-, di-, tri-substituted or 9- calcium on an industrial scale.
anthraldehyde proceeded more slowly than that of benzalde-
The obvious catalytic role of MNPs-IT-PA in Knoevenagel
hyde because of the steric hindrance of substitutents at the ring condensation could be attributed to two factors. As depicted in
(Table 2, entries 1 vs. 3–5 and 7). Gratifyingly, 2-(cyanomethyl) Fig. 7, nitrogen with a lone pair electron at the primary amine of
benzothiazole, phenylacetonitrile and indole-2-acetonitrile MNPs-IT-PA (Function domain) could act as an acceptor to form
were also found to be efficient methylene active ingredients to a hydrogen bond with a methylene active ingredient. The
give the desired condensation products in good yields albeit resulting carbon anion would attack the aldehyde, followed by
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Fig. 8 Recyclability study of the catalyst MNPs-IT-PA in an aqueous
reaction of 2-(cyanomethyl)benzimidazole (5 mmol) and 2-the-
naldehyde (5 mmol) in water (10 mL) within 2 h.
the reaction, the magnetic catalyst was readily recovered by an
external magnet (Fig. 5b), and was reused in the next run before
it was successively washed with ethanol and ethyl acetate. As
shown in Fig. 8, the catalyst MNPs-IT-PA could be reused for 8
times and no signicant decrease in the product yield was
observed. In addition, the amine loading of the catalyst sub-
jected to 8 runs was 0.31 mmol gꢁ1, demonstrating the covalent
connection between the ionic-modied amine and MNPs.
3. Conclusions
Scheme
3 Aqueous Knoevenagel condensation of non-cyano
substituted ketone with benzaldehyde under various reaction
conditions.
In conclusion, the rst magnetic nanoparticles supported pro-
pylamine with an ionic liquid modication was designed and
prepared. The ionic-tagged supported catalyst MNPs-IT-PA was
used as highly efficient promoter for the Knoevenagel condensa-
tion to afford products in good yields. Moreover, MNPs-IT-PA
could also be used as a catalyst to prepare 4-methyl-3-oxo-N-
phenyl-2-(phenylmethylene)pentanamide, which is a key inter-
mediate for the synthesis of Atorvastatin calcium. The compar-
ison between MNPs-IT-PA and MNPs-PA shows that the ionic
moiety efficiently facilitates the reaction. The catalyst MNPs-IT-PA
can be reused 8 times with a slight loss of catalytic activity.
4. Experimental
4.1 Materials and instruments
Fig. 7 Proposed explanation of MNPs-IT-PA as a catalyst for the
Knoevenagel condensation.
All the chemical reagents were used without further purica-
tion. The reaction monitoring was accomplished by thin layer
chromatography (TLC) on gel F254 plates. Powder X-ray
diffraction data were obtained using Cu Ka radiation. Fourier
transform infrared spectroscopy (FT-IR) was performed on a
spectrometer using KBr pellets. Transmission electron micros-
copy (TEM) was performed with an instrument operating at 40–
the removal of a molecule of H2O to provide the nal conden-
sation product. Second, the hydrophilic domain of ionic moiety
in the catalyst could play the role of a phase transfer catalyst
(PTC), which would increase the solubility of the reagent in
water. It is clear that the poor water solubility of a methylene
active compound decreases the catalytic activity of the primary
amine, which was veried by ionic-free SiO2@Fe3O4-PA
promoted processes (Table 1, entry 2 vs. entry 3 and Scheme 3,
condition A vs. condition B). Moreover, the “ionic environment”
present electrosteric activation to stablize the transition state of
the reaction.15 Both the hydrophic property and the presence of
a good acceptor on the nitrogen of MNPs-IT-PA efficiently
facilitate the reaction.
100 kV. Magnetic measurements were carried out in a vibrating
1
sample magnetometer (VSM) at room temperature. H and 13
C
NMR were recorded on a spectrometer at 400 MHz and 100 MHz
in CDCl3, respectively. Chemical shis were reported in parts
per million (d), relative to the internal standard of tetramethyl-
silane (TMS).
4.2 Preparation of silica coated magnetic nanoparticle-
SiO2@ Fe3O4 1 (MNPs)
One of the main advantages of the supported catalyst is its
recyclability. Thus, we turned our attention to the reusability of Magnetic (Fe3O4) nanoparticles were prepared by co-precipita-
the ionic-tagged catalyst MNPs-IT-PA. Upon the completion of tion.25 FeCl3$6H2O (8.1 g, 0.03 mmol) and FeCl2$4H2O (4.97 g,
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0.025 mmol) were added to deionized water (100 mL) and
sonicated until the salts dissolved completely. Then, the
transparent solution was heated at 85 ꢀC with vigorous
mechanically stirring under N2 atmosphere for 1 h. pH was
then adjusted to 9 using concentrated aqueous ammonia (25
wt%). The black precipitate was washed several times with
deionized water until the pH of the eluent decreased to 7. The
coating of a layer of silica on the surface of the naked Fe3O4
was achieved by the sol–gel method.26 The naked Fe3O4 (1.0 g)
was diluted with ethanol (200 mL) by ultrasonic irradiation.
6 mL concentrated NH3$H2O and 2 mL of tetraethoxysilane
(TEOS) were added to the well-dispersed magnetic nano-
particles solution and stirred for 24 h at room temperature.
The resulting MNPs 1 was collected by an external magnet and
washed with water until the solution was neutral. Then, it was
washed with ethanol and diethyl ether successively and dried
under vacuum.
4.4 General procedure for the MNPs-IT-PA catalyzed
ambient Knoevenagel condensation in water
Benzaldehyde (5 mmol), methylene active compound (5 mmol),
and MNPs-IT-PA (735 mg) were mixed in water (10 mL). The
mixture was allowed to react at room temperature for a suitable
length of time, which was decided by TLC. Separated from the
reaction solution by a magnet, the catalyst was washed with
ethanol and ethyl acetate, followed by drying under vacuum and
reusing for subsequent runs. The decanted solution was directly
ltered and the remaining residue was puried with recrystal-
lization using ethanol or column chromatography using petro-
leum ether/ethyl acetate as the eluent. The products were
1
characterized by H NMR and 13C NMR.
NMR data for representative products
2-(1H-Benzoimidazol-2-yl)-3-(thiophen-2-yl)acrylonitrile (Table
1
1, model reaction). H NMR (400 MHz, CDCl3): d 7.15–7.22 (m,
1H), 7.30–7.37 (m, 2H), 7.50–7.52 (m, 1H), 7.66–7.70 (m, 2H),
7.76–7.77 (m, 1H), 7.87–7.89 (m, 1H), 8.63 (s, 1H) ppm; 13C NMR
(100 MHz, CDCl3): d 98.1, 115.6, 115.7, 116.7, 123.6, 129.1,
134.5, 136.8, 137.0, 139.3, 147.6 ppm.
4.3 Synthesis of the catalysts MNPs-IT-PA and MNPs-PA
Synthesis of MNPs-IT-PA 4. To a solution of imidazole (6.8 g,
100 mmol) in dry toluene (100 mL), 3-chloropropyltriethoxy-
silane (24 mL, 100 mmol) was added in one portion. The
reaction solution was reuxed for 24 h under nitrogen
protection, And the mixture was evaporated under reduced
pressure to remove the organic solvent. The residue was then
puried with neutral alumina column chromatography
(eluent: ethyl acetate) to give the intermediate 2. 1.0 g of
SiO2@ Fe3O4 1 (MNPs) was dispersed in 20 mL dry toluene by
sonication for 1 h, and then the intermediate 2 (0.5 g) was
added to the solution. Aer mechanical stirring under
nitrogen atmosphere at reux conditions for 48 h, the solid
was magnetically separated and washed with ethanol, fol-
lowed by drying under vacuum to afford Im-MNPs 3. The
resultant 3 (1.0 g) was dispersed in 50 mL dry ethanol by
sonication for 1 h. 3-Bromopropylamine (0.27 g, 2.0 mmol) in
20 mL dry ethanol was added dropwise to the mixture and was
further reuxed for 48 h under nitrogen protection. The solid
catalyst MNPs-IT-PA 4 was collected by an external magnetic
force, rinsed with ethanol, and then dried under vacuum for 6
h. Finally, 0.96 g grey nanoparticles (MNPs-IT-PA, 4) were
obtained with a loading of 0.34 mmol gꢁ1, as determined by
elemental analysis.
2-(1H-Benzoimidazol-2-yl)-3-phenylacrylonitrile (Table 2, entry
1
1). H NMR (400 MHz, CDCl3): d 7.31–7.34 (m, 2H), 7.50–7.52
(m, 3H), 7.65 (s, 2H), 7.98–7.80 (m, 2H), 8.51 (s, 1H) ppm; 13C
NMR (100 MHz, CDCl3): d 111.2, 116.8, 119.7, 123.6, 124.2,
129.3, 130.0, 132.1, 132.7, 146.3, 146.8 ppm.
2-(1H-Benzoimidazol-2-yl)-3-(3-methoxyphenyl)acrylonitrile
(Table 2, entry 4). 1H NMR (400 MHz, CDCl3): d 3.89 (s, 3H),
7.07–7.09 (m, 1H), 7.33–7.44 (m, 3H), 7.55–7.59 (m, 2H), 7.66 (s,
2H), 8.53 (s, 1H) ppm; 13C NMR (100 MHz, CDCl3): d 55.5, 105.8,
114.1, 116.5, 119.0, 121.7, 123.4, 123.7, 126.0, 127.0, 130.2,
133.6, 135.0, 146.9, 153.6, 160.0, 162.7 ppm.
2-(1H-Indol-2-yl)-3-phenylacrylonitrile (Table 2, entry 15). 1H
NMR (400 MHz, CDCl3): d 7.28–7.33 (m, 2H), 7.41–7.49 (m, 4H),
7.60–7.63 (m, 2H), 7.88 (d, 2H, J ¼ 5.6 Hz), 8.00 (d, 1H, J ¼
6.0 Hz) ppm, 8.58 (s, 1H); 13C NMR (100 MHz, CDCl3): d 106.5,
112.4, 113.1, 118.9, 120.0, 121.5, 123.6, 124.4, 125.8, 128.9,
129.1, 129.8, 134.9, 137.3, 138.2 ppm.
2-(1H-Indol-2-yl)-3-p-tolylacrylonitrile (Table 2, entry 16). 1H
NMR (400 MHz, CDCl3): d 2.42 (s, 3H), 7.26–7.33 (m, 4H), 7.45(d,
1H, J ¼ 6.4 Hz), 7.57–7.60 (m, 2H), 7.79 (d, 2H, J ¼ 6.4 Hz), 8.00
(d, 1H, J ¼ 6.0 Hz), 8.46 (s, 1H) ppm; 13C NMR (100 MHz, CDCl3):
d 21.8, 105.3, 112.3, 113.3, 119.1, 120.0, 121.4, 123.5, 124.4,
125.4, 128.9, 129.8, 132.1, 137.2, 138.5, 140.2 ppm.
Synthesis of MNPs-PA 6. 0.5 g of silica coated magnetic
nanoparticles 1 (MNPs) was dispersed in dry toluene (30 mL) by
ultrasonication for 5 min. (3-Aminopropyl)triethoxy silane
(1.8 g) were added and the reaction mixture was reuxed for
12 h under nitrogen atmosphere. The supported catalyst
MNPs-PA 6 was obtained by magnetic separation and washed
with ethanol, and then dried in a vacuum oven at 60 ꢀC for 6 h.
The loading of the catalyst was determined to be 0.21 mmol gꢁ1
by elemental analysis.
4-Methyl-3-oxo-N-phenyl-2-(phenylmethylene)pentanamide
(Scheme 3, II). 1H NMR (400 MHz, CDCl3): d 1.21 (d, 6H, J ¼ 6.4
Hz), 3.36 (m, 1H), 7.14–7.18 (m, 1H), 7.32–7.38 (m, 5H), 7.47 (d,
2H, J ¼ 7.6 Hz), 7.56–7.59 (m, 3H), 7.64 (s, 1H) ppm; 13C NMR
(100 MHz, CDCl3): d 19.1, 36.7, 120.3, 125.0, 129.0, 129.1, 130.0,
130.1, 133.0, 136.2, 137.4, 140.7, 165.5 ppm.
Acknowledgements
1
NMR data for intermediate 2. H NMR (400 MHz, CDCl3): d
0.46–0.50 (m, 2H), 1.13–1.15 (m, 9H), 1.81 (t, J ¼ 8 Hz, 2H), 3.74 We are grateful for the nancial supports for this research by
(t, J ¼ 7.2 Hz, 6H), 3.86 (t, J ¼ 7.2 Hz, 2H), 6.84 (d, J ¼ 1.2 Hz, the National Natural Science Foundation of China (Grant
1H), 6.96 (s, 1H), 7.40 (s, 1H) ppm; 13C NMR (100 MHz, CDCl3): d 21106090 and 21272169), Foundation of Low Carbon Fatty
7.3, 18.2, 24.8, 49.0, 58.4, 118.7, 129.2, 137.1 ppm.
Amine Engineering Research Center of Zhejiang Province
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(2012E10033), and Zhejiang Provincial Natural Science Foun- 17 X. Jin, D. Yang, X. Xu and Z. Yang, Chem. Commun., 2012, 48,
dation of China (no LY12B02004 and LQ13B070002).
9017.
18 M. R. dos Santos, A. F. Gomes, F. C. Gozzo, P. A. Z. Suarez
and B. A. D. Neto, ChemSusChem, 2012, 5, 2383.
19 M. Lombardo, M. Chiarucci and C. Trombini, Green Chem.,
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