Conjugate addition of indole to α,β-unsaturated ketones catalyzed bylewis acid immobilized on a biorenewable support

Article abstract of DOI:10.1002/jccs.201000184

Sulfonated carbonaceous solid acid was prepared straightforwardly from household granulated sucrose through a one-pot carbonization-sulfonation process. The performance of this solid Bronsted acid was tested by the 1,1-diacylation of aldehydes. Lewis acid, such as indium chloride, was supported on sucrose- derived carbonaceous solid acid through anion metathesis and successfully applied to the conjugate addition of indole to α,β- unsaturated ketones.

Full text of DOI:10.1002/jccs.201000184

Journal of the Chinese Chemical Society, 2010, 57, 1243-1247
1243
Communication
Conjugate Addition of Indole to a,b-Unsaturated Ketones Catalyzed by
Lewis Acid Immobilized on a Biorenewable Support
Bei-Yao Li (
), Miao Zhang (
),
Xin-Min Yan (
Shanghai Key Laboratory of Chemical Biology, Institute of Pesticides and Pharmaceuticals,
) and Yan-Qing Peng* (
)
East China University of Science and Technology, Shanghai 200237, P. R. China
Sulfonated carbonaceous solid acid was prepared straightforwardly from household granulated su-
crose through a one-pot carbonization–sulfonation process. The performance of this solid Brønsted acid
was tested by the 1,1-diacylation of aldehydes. Lewis acid, such as indium chloride, was supported on su-
crose-derived carbonaceous solid acid through anion metathesis and successfully applied to the conjugate
addition of indole to a,b-unsaturated ketones.
Keywords: Heterogeneous catalysis; Sucrose; Sulfonation; Lewis acid.
INTRODUCTION
Increasing petroleum prices and concerns about cli-
Hence we decided to prepare the sugar catalyst through a
one-pot carbonization–sulfonation procedure.
mate change are major drivers in the search for alternative
biorenewable resources. Carbohydrates, such as glucose
and sucrose, are of important natural feedstock for chemi-
cal laboratories and manufactures because they are green,
renewable, inexpensive, and available in large amounts
On the other hand, although homogeneous catalysts
are superior in terms of activity and selectivity, the wider
use of homogeneous catalysis is hampered by the difficul-
7
ties in catalyst recovery and recycling. Replacement of
Lewis acid catalysts (sometimes toxic, expensive, and cor-
rosive) with reusable solid heterogeneous catalysts has
many advantages such as reduced equipment corrosion,
ease of product separation, recycling of the catalyst and en-
vironmentally acceptability. Four heterogenization strate-
gies have been developed including covalent binding, ad-
sorption, ion pair formation, entrapment (ship in a bottle
1
from different sources. The preparation of catalytic mate-
2
rials from sugars is a relatively new area. In 2005, Hara re-
ported the preparation of an acidic “sugar catalyst” suitable
for biodiesel production. In the first step, pyrolysis of D-
glucose or sucrose gave an incompletely carbonized mate-
rial. Sulphonation of this material with sulphuric acid
readily generated a stable solid with a high density of
8
concept). In the cases using supported Lewis acidic cata-
sulfonic acid groups (–SO
3
H). In the next year, they re-
lysts, immobilization on sulfonated polymeric supports
through ion pair formation is a very convenient method
with several successful examples. For example, scandium-
vealed the further application of carbonaceous solid acid in
3
-4
the reactions such as hydration and esterification. Re-
search group of Zong and Smith has also investigated these
type of catalysts derived from D-glucose, and gave their
9
based Lewis acids could be immobilized on Nafion NR-50
1
0
or sulfonated polystyrene resin for catalytic use. Very re-
cently, Halligudi and co-workers reported the immobiliza-
tion of cobalt complex of 1,2-bis(pyridine-2-carboxami-
do)benzene, an efficient catalyst for epoxide ring opening
by amines, on sulfonic acid-functionalized SBA-15 molec-
5
catalytic properties and structure data in detail. Recently,
the activation/deactivation behaviors of sulphonated sugar
catalysts were investigated through the esterification of
6
free fatty acids. Up to now, however, most of the synthetic
11
approaches to sugar catalysts have two steps, namely, py-
rolysis (carbonization) and sulfonation. It is well known
that concentrated sulphuric acid is a strong dehydration
agent by which the carbohydrates could be carbonized.
ular sieve by the formation of ion pair.
As a part of our green technology program on the uti-
lization of biorenewable resources, we report herein our re-
sults in the one-step preparation of carbon-based sulfonic
*
Corresponding author. Fax: +86-21-64252603; E-mail: yqpeng@ecust.edu.cn

1
244 J. Chin. Chem. Soc., Vol. 57, No. 6, 2010
Li et al.
acid with sucrose as a carbonaceous support and its appli-
cation in Lewis acid immobilization. To the best of our
knowledge, it is the first example of the immobilization of
Lewis acid on sugar carbon support.
tained using nitrogen adsorption at -196 °C. To our delight,
2
the N -adsorption data provide the BET area of 2 as 11.56
2
-1
2
-1, 3-4
m .g , larger than those reported in literatures [2 m .g
2
-1
5
2
-1 6
4.13 ± 0.03 m .g , 1-1.4 m .g ]. Powder X-ray diffrac-
tion (XRD) patterns of carbon-based solid acid exhibited a
broad diffraction peak centered around 2q = 25°, which can
typically be attributed to amorphous carbon (Fig. 2).
The sulfonic acid site density of the catalysts calcu-
lated from quantitative elemental sulfur analysis was 0.81
RESULTS AND DISCUSSION
A schematic illustration of the synthetic pathway for
the sucrose-derived solid acid 1 and supported indium cata-
lyst 2 is shown in Scheme I. Initially, sulfonated sugar car-
bon 1 was obtained readily through a one-pot carboniza-
tion–sulfonation process by heating sucrose at 140 °C in
concentrated sulfuric acid (98%). It is noteworthy that con-
-
1
mmol.g , assuming that all immobilized S atoms in the cat-
alysts were in –SO H form. This means the SO H density
3
3
-
1
of our solid acid (0.81 mmol.g ) is comparable to that of
commercially available perfluorosulfonated resin Nafion
centrated H
can oxidizes the carbon to give gaseous byproducts such as
CO and SO . The total yield of the product 1 based on car-
2 4
SO is also a powerful oxidizing agent which
-
1
NR-50 (0.93 mmol.g ), but lower than many of published
-
1 3
-1 4
-1 5
2
2
data [1.34 mmol.g , 1.2 mmol.g , 1.5 mmol.g , 0.64
-
1 6
bons in sugar is 61%. The resulting black powder is insolu-
ble in a range of solvents such as water, ethanol, aceto-
nitrile and so on even under refluxing. As-synthesized 1
could be transformed into 2 through anion metathesis.
2 4
mmol.g ]. The influence of fuming H SO on the sulfona-
tion of sugar carbon was next investigated. Considering the
sulfuric acid was “diluted” during dehydration, certain
amount of 30% oleum was added after the reaction had
been performed for 1 h. However, no remarkable enhance-
3
Scheme I Preparation of InCl -supported sucrose-de-
rived solid acid
Fig. 1. FTIR spectra of the samples during carboniza-
tion–sulfonation processes.
The carbonaceous solid acid 1 was characterized by
FTIR, surface area analysis (BET), powder XRD, elemen-
tal analysis, and acid–base titration. The FTIR spectra of
carbonaceous materials sampled at different stage of sulfo-
nation are shown in Fig. 1 (reaction time; a: 1 h, b: 4 h, c: 15
h). It indicates the appearance of absorption bands at 1021-
-
1
-1
1
026 cm (S=O stretching), 1154-1160 cm (O=S=O sym-
metric stretching), confirming the attachment of the –SO
3
H
-
1
group on the carbon. The peak centered around 1,704 cm
can be attributed to C=O stretching of carboxyl groups.
Fig. 2. XRD pattern of sugar catalyst 1.
BET (Brunauer–Emmett–Teller) surface area was ob-

Lewis Acidic Catalyst Supported on Carbonaceous Solid
J. Chin. Chem. Soc., Vol. 57, No. 6, 2010 1245
-
1
ment in SO
3
H density was observed (0.82 mmol.g ) while
Table 1. 1,1-Diacylation of aromatic aldehydes
the yield of solid acid was decreased from 61% to 55%. Al-
though it has been reported that the solid acid prepared us-
OAc
OAc
Ac O
2
ArCHO
Ar
C
SO H
3
ing fuming H
activity than those sulfonated in concentrated H
results indicated that fuming H SO has no invigorative
2 4
SO showed higher acid density and catalytic
1
4
2
4
SO , our
Entry
Ar
Time (h)
Yield (%)
2
4
1
2
3
4
5
6
7
8
9
C
6
H
5
1
1
87 (run 1)
93 (run 2)
85 (run 3)
96 (run 4)
84 (run 5)
93
effects in the presented one-pot approach to sulfonated
sugar carbon.
1
The total acid density of the sample was determined
1
-
1
as 2.04 mmol.g by standard acid–base back-titration us-
ing NaOH aqueous solution. It could be seen that the total
acid density is significantly higher than the estimations
based on sulfur elemental analysis, due to other acidic
functionalities such as carboxylic acid groups formed dur-
1
4-Cl-C
4-CH -C
3-NO -C
3-Br-C
6
H
4
0.5
0.5
1
3
6
H
4
74
2
6
H
4
87
6
H
4
1
85
3
-4
ing the carbonization and sulfonation processes. In view
of only the sulfonic groups have sufficient acidity in Lewis
rized in Table 2 clearly indicate the scope and generality of
the reaction with respect to various chalcones and indole.
One aspect of relevance in heterogeneous catalysis is
the recycle of the catalyst and its reactivation upon exten-
sive reuse. To evaluate the reusability and operational sta-
bility of the supported Lewis acid catalyst 2, the model re-
action was performed five times. After completion of the
reaction, the catalyst was quantitatively recovered by filtra-
3
acid immobilization, the SO H density from elemental sul-
fur analysis was chosen for calculation in subsequent ex-
periments.
The catalytic performance of sucrose-derived solid
acid 1 was initially tested by the 1,1-diacylation of alde-
hydes, which are among the most popular protection reac-
1
2
tions in organic synthesis. The results for a variety of al-
dehydes are depicted in Table 1. The catalyst is active, sta-
ble to air and moisture, non-corrosive and inexpensive. All
of the studied substrates were smoothly converted to the
corresponding 1,1-diacetates with satisfactory to excellent
yields in short times. It is noteworthy that the catalyst can
be repeatedly recycled and reused without significant loss
of its activity. The yields for each of the five cycles were
good, although with some variations (Table 1, entry 1-5).
With successfully prepared carbonaceous solid acid
in hand, we next turned our attention to the immobilization
of Lewis acid on acidic carbon support. The solid acid 1
was suspended in acetonitrile contain indium chloride and
the mixture stirred under refluxing for 12 h. After anion
metathesis, the Lewis acidic catalyst 2 was collected by fil-
tration, thoroughly washed with acetonitrile, and dried un-
der vacuum. The loading of indium on the catalyst was
tion, extensive washing with CH CN, dried in the open air
3
and used again for consecutive run after adding fresh sub-
strates under similar reaction conditions, and the activity of
the recovered catalyst was comparable to the fresh one (Ta-
ble 2, entries 1–5). Although the catalytic activity gradu-
Table 2. Conjugate addition of indoles to a,b-unsaturated
ketones catalyzed by indium chloride on sulfonated
sugar carbon
1
O
Ar
2
Ar
1
Ar
2
Ar
O
N
H
N
H
C
SO InCl2
3
2
1
2
Entry
Ar
Ar
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
4-Cl-C
6
H
4
C
6
H
5
24
24
24
24
24
26
24
30
23
25
89 (run 1)
80 (run 2)
81 (run 3)
87 (run 4)
80 (run 5)
82
-
1
found to be 0.68 mmol.g determined by analyzing the fil-
trate solution with atomic absorption spectroscopy (AAS),
which approximately agreed with the results of sulfur ele-
-
1
ment analysis (0.81 mmol.g ).
C
6
H
5
C
C
C
C
6
6
6
6
H
5
H
5
H
5
H
5
4-CH
3,4-(CH OCH
4-CH O-C
3
-C
6
H
4
88
The Lewis acidic catalyst 2 was next employed in
conjugate addition of indoles to a,b-unsaturated ketones,
2
2
)-C
6
H
3
80
3
6
H
4
74
1
3
14
which could be catalyzed by InCl
3
3
and InBr . Various
1
0
C
6
H
5
4-NO
2
-C
6
H
4
76
substrates afforded satisfactory yields. The results summa-

1
246 J. Chin. Chem. Soc., Vol. 57, No. 6, 2010
Li et al.
ally diminished and the yields were decreased to certain ex-
tent in runs carried out using recycled catalyst over five
runs, the yield was still 80% even after the fourth reuse. It
should be noted that the yield in forth run using recovered
catalyst afforded similar yields to that obtained in the first
run.
tion (l = 1.54056 Å) was used to collect X-ray diffraction
(XRD) patterns in the 2q range from 0° to 50°.
Preparation of carbonaceous solid acid 1
To 80 mL of concentrated sulfuric acid (98%) was
added 13.90 g (40 mmol) of powdered sucrose at room tem-
perature. The mixture turns yellow as the dehydration be-
gins. It was then heated at 140 °C for 4 h. After cooling
down to room temperature, carbonaceous product was col-
lected by centrifugation, washed repeatedly with deionized
water until no sulfate ions were detected in the filtrate, and
dried in an oven (110 °C). The yield was 61% based on the
total carbon in sucrose. The sulfonic acid site density was
In order to compare the supported indium catalyst 2
with its homogeneous conterpart, the model reaction be-
tween indole and 4-chlorochalcone was also carried out us-
3
ing InCl as the catalyst under similar conditions (catalyst/
substrate ratio: 0.2; temperature: 60 °C; solvent: acetoni-
trile). The reaction finished in 5 hours with 84% yield of
purified product. In spite of its higher catalytic activity than
-
1
determined as 0.81 mmol.g by quantitative elemental
sulfur analysis.
3
the supported indium catalyst, InCl is an expensive cata-
lyst that cannot be readily recycled. This problem will not
be obviated from the viewpoints of environment protection
and economy especially in large scale production.
In summery, sucrose-derived solid acid was perpared
by one-pot carbonization–sulfonation process. It was char-
acterized and successfully applied as a support for indium
immobilization by treating with indium chloride. The re-
sulted heterogeneous Lewis acidic catalyst was found to be
efficient, environmentally friendly and recyclable hetero-
geneous catalyst for the conjugate addition of indoles to
chalcones.
General procedure of 1,1-diacylation of aldehydes
A mixture of aldehyde (10 mmol), freshly distilled
acetic anhydride (3.06 g, 30 mmol) and solid acid catalyst 1
3
(1.23 g, 1 mmol SO H) was stirred at 60 °C for a certain pe-
riod of time as required to complete the reaction (monitored
by TLC). On completion, the reaction mixture was washed
with saturated aqueous NaHCO
with CH Cl (5 mL × 3). The combined extract was dried
over anhydrous Na SO , and evaporated to give the crude
3
(15 mL × 3), extracted
2
2
2
4
product. The crude product thus obtained was purified by
recrystallization from petroleum ether.
Preparation of supported indium catalyst 2
EXPERIMENTAL SECTION
The solid acid 1 (1.23 g, 1 mmol SO
3
H) was treated
The household granulated sucrose was purchased
from supermarket. Other reagents were obtained from com-
mercial suppliers and used without further purification. All
products are known compounds; their physical and spec-
troscopic data were compared with those reported in litera-
tures and found to be identical. Melting points were mea-
sured on a BÜCHI B-540 apparatus. IR spectra were re-
corded on a Nicolet Nexus 470 spectrophotometer in KBr
with InCl .4H O (0.55 g, 1.8 mmol) in acetonitrile (4 mL)
3
2
at reflux temperature for 12 h. After cooling to room tem-
perature, the mixture was filtered and thoroughly washed
3
with CH CN (4 mL × 2) and dried under vacuum to yield
the Lewis acidic catalyst 2.
General procedure of conjugate addition of indole to
chalcones
To a stirred suspension of catalyst 2 (0.30 g, 0.2 mmol
In, 20%mol) in 3 mL of anhydrous acetonitrile was added
indole (0.14 g, 1.2 mmol) and chalcone (1 mmol), and the
mixture was heated at 60 °C until the disappearance of the
starting chalcone (monitored by thin-layer chromatogra-
phy, TLC). The catalyst was recovered by filtration and
wished with acetonitrile (3 mL × 3). Solvent in combined
filtrate was removed using rotary evaporator, and the resi-
due obtained was washed with warm petroleum ether (5 mL
× 2) and recrystallized from absolute ethanol to afford pure
product as crystalline solid.
1
pellets. H NMR spectra were recorded on Bruker AV 400
6
spectrometer in DMSO-d with TMS as internal standard.
The sulfur contents of the sulfonated carbon-based cata-
lysts were determined by elemental analysis using ZCL-S
analyzer. Nitrogen physisorption measurements were con-
ducted on a Micromeritics ASAP 2020 instrument at 77.3
K. Prior to nitrogen adsorption, the sample was degassed
-
2
for 6 h at 180 °C under vacuum (<10 Pa) and subsequently
analyzed. The linear part of the BET equation was used for
the determination of the specific surface area. The X-ray
diffraction spectrum was recorded on a Rigaku D/max
Selected spectra data
2
550VB X-ray diffractometer equipped with CuKa1 radia-
3-(3-Indolyl)-1-phenyl-3-(4-methylphenyl)-propan-

Lewis Acidic Catalyst Supported on Carbonaceous Solid
J. Chin. Chem. Soc., Vol. 57, No. 6, 2010 1247
1
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3
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. Okamura, M.; Takagaki, A.; Toda, M.; Kondo, J. N.; Domen,
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0.0, 6.8 Hz, 1H, CH ), 3.80 (dd, J = 10.0 Hz, 6.8 Hz, 1H,
CH ), 5.03 (t, J = 7.2 Hz, 1H, CH), 6.98-7.07 (m, 4H, ArH),
.14 (t, J = 8.0 Hz, 1H, ArH), 7.22-7.25 (m, 2H, ArH), 7.31
d, J = 8.0 Hz, 1H, ArH), 7.40-7.45 (m, 3H, ArH), 7.53 (t, J
7.4 Hz, 1H, ArH), 7.93 (d, J = 7.2 Hz, 2H, ArH), 8.00 (bs,
H 3
2.27 (s, 3H, CH ), 3.70 (dd, J =
1
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Received September 9, 2010.
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