A silica gel supported dual acidic ionic liquid: An efficient and recyclable heterogeneous catalyst for the one-pot synthesis of amidoalkyl naphthols

Article abstract of DOI:10.1039/c0gc00472c

A supported dual acidic ionic liquid catalyst was prepared via anchoring 3-sulfobutyl-1-(3-propyltriethoxysilane) imidazolium hydrogen sulfate onto silica gel by covalent bonds. The novel immobilized acidic ionic liquid effectively catalyzed the one-pot synthesis of amidoalkyl naphthols by the multicomponent condensation of aldehydes with 2-naphthol and amides under solvent-free conditions. Moreover, the catalyst could be recycled six-times without a significant loss of catalytic activity.

Full text of DOI:10.1039/c0gc00472c

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PAPER
www.rsc.org/greenchem | Green Chemistry
A silica gel supported dual acidic ionic liquid: an efficient and recyclable
heterogeneous catalyst for the one-pot synthesis of amidoalkyl naphthols
Qiang Zhang, Jun Luo* and Yunyang Wei
Received 22nd August 2010, Accepted 21st October 2010
DOI: 10.1039/c0gc00472c
A supported dual acidic ionic liquid catalyst was prepared via anchoring
3-sulfobutyl-1-(3-propyltriethoxysilane) imidazolium hydrogen sulfate onto silica gel by covalent
bonds. The novel immobilized acidic ionic liquid effectively catalyzed the one-pot synthesis of
amidoalkyl naphthols by the multicomponent condensation of aldehydes with 2-naphthol and
amides under solvent-free conditions. Moreover, the catalyst could be recycled six-times without a
significant loss of catalytic activity.
existence of both SO3H functional groups and hydrogen sulfate
1. Introduction
counteranions can obviously enhance their acidities.18 These
Multicomponent reactions (MCRs) are very elegant and effi-
strongly acidic ILs have been exploited as efficient catalysts for
cient methods to access complex structures in a single syn-
many organic reactions, and generally can afford higher yields
thetic operation from simple building blocks, and can show
and selectivities against traditional acid catalysts.19 Despite
simple procedures, high atom-economy and high selectivity due
their widespread use in acid-catalyzed reactions, a series of
to the formation of carbon–carbon and carbon–heteroatom
drawbacks, such as product isolation, catalyst recovery and the
bonds in one-pot.1 Compounds bearing 1,3-amino-oxygenated
use of large amounts of ILs in biphasic systems, which is costly
functional groups are usually found in various biologically
and may cause toxicological concerns, still exist.20 Immobilized
important natural products and potent drugs, including nucle-
ILs combine the benefits of ILs and heterogeneous catalysts,
oside antibiotics and HIV protease inhibitors.2 Among them,
such as high designability, high “solubility” of the catalytic
1-amidoalkyl-2-naphthol derivatives are of particular value
site, ease of handling, separation and recycling. Thus, some
because of their promising biological and pharmacological
immobilization processes for acidic ILs on solid supports have
activities.3 Amidoalkyl naphthols can be prepared by the multi-
been designed.21 These immobilized acidic ILs have been widely
component condensation of aldehydes, 2-naphthols and amides
applied as novel solid catalysts, e.g., in esterification, nitration,22
using different catalysts, such as montmorillonite K10,4 p-TSA,5
Baeyer–Villiger reactions,23 acetal formation24 and the hydrolysis
iodine,6 Fe(HSO4)3,7 K5CoW12O40·3H2O,8 HClO4–SiO2,9 cation-
of cellulose.25
exchange resins,10 silica sulfuric acid,11 thiamine hydrochloride,12
In our continuous work on the development of efficient and
zwitterionic salts,13 acidic ionic liquids14 and [FemSILP]L-
environmental benign procedures using dual acidic ILs,26 herein,
prolinate.15 However, these procedures each have some draw-
we report a simple and efficient procedure for the one-pot, three-
backs, such as high reaction temperature, prolonged reaction
component synthesis of amidoalkyl naphthols using a silica gel
time, the use of toxic solvents or low yields. The recovery and
supported dual acidic IL as an effective and reusable catalyst
reusability of the catalyst is also a problem. Therefore, it is still
under solvent-free conditions (Scheme 1). To the best of our
desirable to seek a green and eco-friendly protocol that uses
knowledge, no attempt to use immobilized acidic ILs as catalysts
a highly efficient and reusable catalyst for the preparation of
for this three-component reaction has been made so far.
amidoalkyl naphthols.
Ionic liquids (ILs), as eco-friendly reaction media or catalysts,
have attracted increasing attention due to their particular
properties, such as undetectable vapor pressure, high thermal
2. Results and discussion
stability, excellent solubility, and ease of recovery and reuse.16
Among them, Brønsted acidic ILs used in some acid-catalyzed
processes have aroused considerable interest because they have
the combined advantages of solid acids and mineral acids.17
Moreover, SO3H-functionalized ILs with a hydrogen sulfate
counteranion have been intensively studied as a class of dual
acidic functionalized ILs during the last five years, because the
2.1 Preparation and characterization of the catalyst
Supported ionic liquid catalysts (SILC) are prepared either by
simple physical adsorption or covalent attachment of ILs onto
the surface of a solid support. We chose the latter method to
immobilize the IL since this provides better stability in the
catalytic reaction and less leaching during the work-up. The
supported dual acidic IL catalyst was prepared via anchoring
3-sulfobutyl-1-(3-propyltriethoxysilane) imidazolium hydrogen
sulfate onto common silica gel by covalent bonds. During
the preparation of the silica gel supported dual acidic IL
catalyst, (3-chloropropyl)triethoxysilane was first treated with
imidazole to give N-(3-propyltriethoxysilane) imidazole (1)
School of Chemical Engineering, Nanjing University of Science &
Technology, Nanjing, 210094, P. R. China.
E-mail: luojun@mail.njust.edu.cn; Fax: +86 25-84315030; Tel: +86
25-84315030
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Scheme 1 Synthesis of amidoalkyl naphthols.
(Scheme 2), which was reacted with 1,4-butane sultone and
further treated with sulfuric acid to form precursor IL 2.
In the last immobilization step, the common silica gel with
an ethanol solution of complex 2 was refluxed for 24 h to
undergo a condensation reaction, which afforded immobilized
IL 3.
Fig. 1 FT-IR spectra comparison of silica gel and immobilized IL 3.
Fig. 2 compares the 13C NMR spectrum of pure IL 2 (liquid
state NMR, Fig. 2a) with immobilized IL 3 (solid state NMR,
Fig. 2b). Some important carbon signals attributed to the
imidazole ring and alkyl chain are all observed in the two spectra.
Moreover, the absence of the strong characteristic peaks of the
triethoxysilyl group [–Si(OEt)3] at 18.6 and 58.3 ppm in immo-
bilized IL 3 excludes the possibility of IL 2 adsorbing a homolo-
gous material. Hence, the above results convinced us that the IL
was successfully grafted onto the silica gel by covalent bonds.
The shape and surface morphology of the samples were
investigated by SEM. As shown in Fig. 3, the particle size of
the silica gel supported IL 3 is similar to that of silica gel,
which demonstrates that the particles of silica gel had a good
mechanical stability during the immobilization step. However,
the surface morphology of these two samples is different. Fig.
3a shows that the surface of the SiO2 was very slick, and a small
aggregate was obvious on the surface of silica gel supported IL
3 (Fig. 3b).
Scheme 2 Synthesis of the silica gel supported IL catalyst.
Supported IL 3 was characterized by FT-IR spectroscopy,
13C NMR cross-polarization magic-angle spinning (CP/MAS),
scanning electron microscope (SEM), thermogravimetric-
derivative thermogravimetric analysis (TG-DTG) and elemental
analysis. As can be seen from Fig. 1, the FT-IR spectra of
immobilized IL 3 exhibits two characteristic peaks at 1563 and
1635 cm-1, which are due to C N and C C vibrations of the
imidazole ring.27 Additional bands at 3154, 2971 and 1452 cm-1
are due to C–H stretching and deformation vibrations of the
imidazole moiety and alkyl chain. Moreover, two important
peaks at 1165 and 1046 cm-1, assigned to the S O stretching
vibration, are observed.28 All of these characteristic peaks of
the functionalized IL cannot be observed in the IR spectrum of
silica gel. The Si–O–Si stretching modes of the silica gel can be
observed as a strong peak at 1101 cm-1 and a broad feature is
seen at 3421 cm-1 belonging to the Si–OH groups and adsorbed
water in silica.
The stability of supported IL 3 was determined by thermo-
gravimetric analysis (Fig. 4). The TG curve indicates an initial
weight loss of 5.1% up to 110 ◦C due to the adsorbed water in
silica. Complete loss of the IL covalently grafted onto the silica is
seen in the temperature range 230 to 480 ◦C, and the amount of
organic moiety was about 23.8% against the total solid catalyst.
Meanwhile, the DTG curve shows that decomposition of the
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Fig. 2 13C NMR spectra of IL 2 in the liquid state (a) and immobilized IL 3 in the solid state (b).
organic structure mainly occurred in one step from 280 to 420◦C,
2.2 Synthesis of 1-amidoalkyl-2-naphthols catalyzed by the
immobilized IL 3
which is related to the main weight loss of 18.5%. The peak in
the DTG curve shows that the fastest loss of the IL occurred
◦
at 360 C. Therefore, the supported IL catalyst is stable below
To investigate the feasibility of the synthetic methodology for
amidoalkyl naphthols, the reaction was initially carried out
by simply mixing 3-nitrobenzaldehyde (2 mmol), 2-naphthol
(2 mmol) and acetamide (2.4 mmol) in the presence of 40 mg of
immobilized IL 3 under solvent-free conditions. The mixture was
stirred at 85 ◦C for 10 min, and the corresponding product was
obtained in 81% yield. Encouraged by this result, we gradually
about 230 ◦C.
The loading amount of the acidic IL on silica gel was
determined by elemental analysis. The nitrogen analysis of
supported IL 3 (N, 1.39 mmol g-1) indicates that 0.696 mmol
g-1 of acidic IL 2 was grafted onto the surface of the silica gel
(theoretical loading 0.725 mmol g-1).
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Table 1 Effect of different amounts of immobilized IL on the reaction
of 3-nitrobenzaldehyde, 2-naphthol and acetamide
Entry
Immobilized IL/mg
Time/min
Yield (%)a
1
2
3
4
5
6
7
0
20
40
80
120
160
200
30
15
10
5
5
5
< 5b
45
81
92
93
91
90
5
a Isolated yield. b Determined by HPLC.
Fig. 4 TG-DTG analysis for the supported IL catalyst.
we used 80 mg of immobilized IL 3 for the one-pot synthesis
of amidoalkyl naphthols from various aldehydes, amides or
urea and 2-naphthol under solvent-free conditions at 85 ◦C.
The results are summarized in Table 2.
As seen from Table 2, the procedure was highly effective for the
preparation of amidoalkyl naphthols. A variety of aromatic alde-
hydes with electron-donating and electron-withdrawing groups
were converted to amidoalkyl naphthols in excellent yields (80–
94%) with a high TOF in the range 1.91–6.73 min-1 and in
short reaction time (5–15 min). Acetamide, benzamide and
urea all underwent smooth transformations under the reaction
conditions. In particular, n-butyraldehyde, as a typical aliphatic
aldehyde, was tested under the reaction conditions and the
corresponding desired products were isolated in good yields
(Table 2, entries 10 and 18). In all cases, amidoalkyl naphthols
were the sole products and no by-product was observed.
A mechanistic rationale portraying the probable sequence
of events is given in Scheme 3. We suppose that the reaction
proceeds via ortho-quinone methides (o-QMs),29 which form by
the nucleophilic addition of 2-naphthol to the aldehyde, assisted
by immobilized IL 3. The o-QMs then react with amides or
urea via a Michael addition to afford the expected amidoalkyl
naphthols. The immobilized IL 3 could provide dual acidic sites
for activating aldehydes efficiently, so facilitating the reaction.
In comparison with other catalysts employed for the synthesis
of N-[(3-nitro-phenyl)-(2-hydroxy-naphthalen-1-yl)-methyl] ac-
etamide from 3-nitrobenzaldehyde, 2-naphthol and acetamide,
immobilized IL 3 showed a much higher catalytic activity in
terms of very short reaction time and mild conditions (Table 3).
Fig. 3 Scanning electron micrographs (SEM) images of silica gel (a),
immobilized IL 3 (b) and six-times reused catalyst (c).
increased the amount of immobilized IL 3 from 0 to 200 mg
(Table 1).
As shown in Table 1, only trace product was detected in
the absence of immobilized IL 3 (Table 1, entry 1). The yield
improved as the amount of immobilized IL increased from
0 to 80 mg and became almost steady when the amount of
immobilized IL 3 was further increased beyond this. Therefore,
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Table 2 Immobilized IL 3 catalyzed one-pot synthesis of amidoalkyl naphthols
Entry
1
Aldehyde R1
Ph
Amide R2
CH3
Time/min
5
Product
Yield (%)a
90
TOF/min-1
6.43
mp/◦C
242–244
2
3
4
4-Cl–C6H4
2,4-Cl2–C6H3
4-Br–C6H4
CH3
CH3
CH3
10
8
89
86
88
3.18
3.84
3.15
226–228
202–204
228–230
10
5
6
3-NO2–C6H4
4-NO2–C6H4
CH3
CH3
5
5
92
93
6.59
6.65
241–242
243–245
7
8
3-MeO–C6H4
4-Me–C6H4
CH3
CH3
10
10
86
87
3.07
3.11
203–205
221–223
9
4-MeO–C6H4
CH3
15
80
1.91
181–183
10
11
n-C3H7
CH3
Ph
10
5
85
92
3.04
6.59
222–223
232–234
Ph
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Table 2 (Contd.)
Entry
12
Aldehyde R1
Amide R2
Ph
Time/min
10
Product
Yield (%)a
89
TOF/min-1
3.19
mp/◦C
4-Br–C6H4
181–183
13
4-Cl–C6H4
Ph
10
91
3.26
179–181
14
15
3-NO2–C6H4
2-NO2–C6H4
Ph
Ph
5
7
94
90
6.73
4.60
240–242
263–265
16
17
4-Me–C6H4
Ph
Ph
10
15
88
83
3.15
1.98
213–215
196–198
4-MeO–C6H4
18
19
n-C3H7
Ph
10
5
83
81
2.97
5.80
220–222
175–177
Ph
NH2
20
21
3-NO2–C6H4
3-MeO–C6H4
NH2
NH2
5
84
80
6.01
2.86
191–193
167–169
10
a Isolated yield.
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Table 3 Comparison of different catalysts for the one-pot three-component reaction of 3-nitrobenzaldehyde, 2-naphthol and acetamide
Entry
Catalyst
Conditions/◦C
Time/min
Yield (%)
Reference
1
2
3
4
5
6
7
8
Zwitterionic salt
[TEBSA][HSO4]
Fe(HSO4)3
Montmorillonite K10
p-TSA
Iodine
80
120
85
125
125
125
125
110
100
85
90
10
25
30
240
300
180
30
300
5
88
89
97
96
90
81
78
95
87
92
13
14
7
4
5
6
8
9
K5CoW12O40·3H2O
HClO4–SiO2
9
10
[FemSILP]L-prolinate
Immobilized IL 3
15
This work
Scheme 3 A plausible mechanism for the synthesis of amidoalkyl
naphthols using immobilized IL 3.
Fig. 5 Recycling experiment of immobilized IL 3.
2.3 Reusability of immobilized IL 3
The recovery and reuse of catalysts is highly preferable for
a greener process. Thus, the reusability of the catalyst was
investigated by using 3-nitrobenzaldehyde, 2-naphthol and ben-
zamide as model substrates. The catalyst was easily recovered
by filtration after the reaction and washed with acetone. After
being dried, it was subjected to another reaction with identical
substrates. The procedure was repeated and the results indicated
that the catalyst could be cycled six times with only a slight loss
of catalytic activity (Fig. 5).
The recovered catalyst after six runs had no obvious change in
structure, referring to the FT-IR spectrum in comparison with
fresh catalyst (Fig. 6). An SEM observation of the recovered
catalyst after six runs was also made, and there was no obvious
change in the morphology and size in comparison with fresh
catalyst (Fig. 3c). Furthermore, the loading amount of the six
times used catalyst was determined by elemental analysis, and it
was found that 0.637 mmol g-1 of acidic IL 2 was grafted onto
the surface of the silica gel against 0.696 mmol g-1 for the fresh
catalyst. These results indicate that the catalyst was very stable
and could endure this reaction’s conditions.
Fig. 6 FT-IR spectrum comparison of the fresh catalyst and the six
times used catalyst.
(2 mmol), 2-naphthol (2 mmol) and acetamide (2.4 mmol)
catalyzed by immobilized IL 3 (80 mg) was investigated. When
the neat mixture was stirred at 85 ◦C for 4 min, hot acetone
(20 mL) was added and the solid catalyst quickly removed by hot
filtration. The solution was averagely divided into two sections
(S1 and S2). The corresponding product of S1 was obtained in
2.4 Hot filtration test for immobilized IL 3
To figure out whether the catalytic process involved in the
participation of homogenous species in equilibrium with the
heterogeneous catalyst, the reaction of 4-methylbenzaldehyde
◦
39% yield. Meanwhile, the neat S2 was stirred at 85 C for an
additional 30 min to afford the product in 43% yield, which was
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similar to S1 and much less than normal (87%; Table 2, entry
8). Therefore, the above results convinced us that the catalytic
process did not involve the participation of any homogeneous
species in equilibrium with the heterogeneous catalyst.
4.2.2 Synthesis of 3-sulfobutyl-1-(3-propyltriethoxysilane)
imidazolium hydrogen sulfate (2). IL 2 was synthesized accord-
ing to our previous method.26 1,4-Butane sultone (1,4-PS, 1.42 g,
10.5 mmol) was added dropwise into a solution of 1 (2.72 g,
10 mmol) in toluene (30 mL) over 30 min, and the mixture
was then stirred for 8 h and evaporated under reduced pressure.
Then, conc. H2SO4 (0.54 mL, 10 mmol) was added dropwise
into the solution of the above residual in ethanol (30 mL) over
3. Conclusion
In summary, we have developed a facile, efficient and eco-
friendly procedure for the one-pot synthesis of amidoalkyl naph-
thols via a three-component condensation reaction of aldehydes
with 2-naphthol and amides using a silica gel supported dual
acidic IL as a powerful and recyclable catalyst under solvent-
free conditions. The notable advantages of this method are high
catalytic activity, short reaction time, excellent yields, simple
work-up, reusable catalyst and mild reaction conditions. Thus,
this procedure is a better and more practical alternative to
existing methods.
◦
30 min. The final mixture was stirred at 50 C for another 8 h
and evaporated under reduced pressure to give intermediate 2
as a viscous yellow liquid in 97% yield.
1H NMR (500 MHz, DMSO-d6): d 9.19 (s, 1H), 7.80 (s, 2H),
4.18 (t, J = 7.5 Hz, 2H), 4.13 (t, J = 7.5 Hz, 2H), 3.75 (q, J =
7.0 Hz, 6H), 2.44 (t, J = 7.5 Hz, 2H), 1.89–1.83 (m, 4H), 1.54
(m, 2H), 1.15 (t, J = 7.0 Hz, 9H), 0.51 (t, J = 8.0 Hz, 2H); 13C
NMR (125 MHz, DMSO-d6): d 7.3, 18.6, 22.1, 24.5, 29.0, 49.0,
50.9, 51.6, 58.3, 122.8, 123.0, 136.6; FT-IR (KBr, cm-1): 3432.5,
3148.7, 2954.2, 2878.2, 1637.9, 1563.3, 1456.5, 1216.7, 1191.8,
1047.0, 889.1, 757.4, 599.4; ESI-MS: m/z 409 (M+–HSO4); Anal.
calc. for C16H34N2O10S2Si: C, 37.93; H, 6.76; N, 5.53. Found: C,
37.14; H, 6.94; N, 5.50.
4. Experimental
4.1 Materials and equipment
4.2.3 Grafting of 3-sulfobutyl-1-(3-propyltriethoxysilane) im-
idazolium hydrogen sulfate on silica gel (3). The IL 2 (1.0 g) was
dissolved in absolute ethanol (30 mL) and treated with silica gel
(2.0 g). After heating the slurry under reflux conditions for 24 h,
the solid was isolated by filtration and washed with ether (3 ¥
30 mL). The resulting material was dried under vacuum to give
supported dual acidic IL 3 as a slightly yellow powder in 96%
yield (theoretical loading: 0.725 mmol g-1).
FT-IR (KBr, cm-1): 3421.4, 3154.5, 2971.8, 2854.2, 1635.5,
1563.3, 1452.1, 1165.5, 1046.3, 1101.2, 792.7, 578.6; 13C NMR
(CP/MAS, 400 MHz); d 9.3, 21.7, 24.1, 28.7, 50.9, 122.8, 135.5;
Anal. found: C, 8.85; H, 1.91; N, 1.95; S, 4.50.
Melting points were determined on a Perkin-Elmer differential
scanning calorimeter and uncorrected. The IR spectra were
run on a Nicolete spectrometer (KBr). H NMR spectra were
1
recorded on a Bruker DRX500 (500 MHz) and 13C NMR spectra
on Bruker DRX500 (125 MHz) spectrometer. Solid-state Bloch
decay and cross-polarization magic-angle spinning (CP/MAS)
13C NMR spectra were recorded on a Bruker Avance III
(400 MHz) spectrometer. Elemental analysis was performed on
an Elementar Vario MICRO spectrometer. Thermogravimetric
analysis was carried out in nitrogen using a Shimadzu TGA-50
spectrometer. Mass spectra were obtained with an automated
Fininigan TSQ Advantage mass spectrometer. The shape and
surface morphology of the samples were examined on a scanning
electron microscope (SEM) (Hitachi S-3400N, Japan). Silica gel
(60–100 mesh) was dried at 300 ◦C for 6 h before use. All solvents
used were strictly dried according to standard operations and
stored over 4A molecular sieves. All other chemicals (AR
grade) were commercially available and used without further
purification.
4.3 General method for the synthesis of amidoalkyl naphthols
A mixture of aldehyde (2 mmol), 2-naphthol (2 mmol), amide
(2.4 mmol) and immobilized IL 3 (80 mg) was stirred at
85 ◦C in an oil bath for 5–15 min, using TLC to indicate
a complete reaction. Then, acetone (15 mL) was added and
the reaction mixture filtered. The solid catalyst was washed
with acetone (2 ¥ 15 mL) and dried under vacuum. Pure
amidoalkyl naphthols were afforded by evaporation of the
solvent followed by recrystallization from ethanol. All were
characterized by spectral data and comparison of their physical
data with the literature. Spectral data for N-[(3-nitro-phenyl)-
(2-hydroxy-naphthalen-1-yl)-methyl] benzamide (Table 2, entry
14).
1H NMR (500 MHz, DMSO-d6): d 10.43 (s, 1H), 9.14 (d, J =
8.0 Hz, 1H), 8.12–8.08 (m, 3H), 7.90–7.84 (m, 4H), 7.72 (d, J =
7.5 Hz, 1H), 7.61–7.49 (m, 5H), 7.40 (d, J = 8.0 Hz, 1H), 7.33
(t, J = 7.5 Hz, 1H), 7.26 (d, J = 8.5 Hz, 1H); 13C NMR (125
MHz, DMSO-d6): d 166.7, 153.9, 148.3, 145.0, 134.5, 133.8,
132.7, 132.0, 130.5, 130.2, 129.2, 128.9, 128.8, 127.8, 127.5,
123.3, 122.9, 122.1, 121.4, 119.1, 117.4, 49.4; FT-IR (KBr, cm-1):
3375, 3260, 3055, 2972, 1632, 1530, 1506, 1477, 1439, 1346, 1252,
1146, 733; Anal. calc. for C24H18N2O4: C, 72.35; H, 4.55; N, 7.03.
Found: C, 72.28; H, 4.61; N, 6.97.
4.2 Preparation of the silica gel supported dual acidic IL
catalyst
4.2.1 Synthesis of N-(3-propyltriethoxysilane) imidazole (1).
Compound 1 was prepared according to known process.30 To a
solution of imidazole (3.4 g, 53 mmol) in dry toluene (50 mL), 3-
chloropropyltriethoxysilane (9.2 mL, 50 mmol) was added and
the mixture was refluxed overnight under a nitrogen atmosphere.
The solvent was removed by rotatory evaporation under re-
duced pressure, and the product N-(3-propyltrimethoxysilane)
imidazole was obtained as a transparent liquid by neutral Al2O3
column chromatography.
1H NMR (500 MHz, CDCl3): d 7.53 (s, 1H), 7.07 (s, 1H), 6.93
(s, 1H), 3.96 (t, J = 7.5 Hz, 2H), 3.82 (q, J = 7.0 Hz, 6H), 1.90
(m, 2H), 1.23 (t, J = 7.0 Hz, 9H), 0.57 (t, J = 8.0 Hz, 2H); 13C
NMR (125 MHz, CDCl3): d 7.2, 18.1, 24.8, 48.9, 58.2, 118.6,
129.0, 137.0.
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Acknowledgements
We are grateful for the financial support from the Natu-
ral Science Foundation of Jiangsu Province of China (No.
BK2010485), the Doctoral Fund of Ministry of Education of
China for New Teacher (No. 200802881029), and the Science
and Technology Development Fund of Nanjing University of
Science and Technology (No. XKF09066).
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