Selective C3-alkenylation of oxindole with aldehydes using heterogeneous CeO2 catalyst

Article abstract of DOI:10.1016/S1872-2067(19)63515-1

We report herein that a commercially available CeO₂ is an active and reusable catalyst for the C3-selective alkenylation of oxindole with aldehydes under solvent-free conditions. This catalytic method is generally applicable to different aromatic and aliphatic aldehydes, giving 3-alkyledene-oxindoles in high yields (87%–99%) and high stereoselectivities (79%–93% to E-isomers). This is the first example of the catalytic synthesis of 3-alkenyl-oxindoles from oxindole and various aliphatic aldehydes. The Lewis acid-base interaction between Lewis acid sites on CeO₂ and benzaldehyde was studied by in situ IR. The structure-activity relationship study using CeO₂ catalysts with different sizes suggests that defect-free CeO₂ surface is the active site for this reaction.

Full text of DOI:10.1016/S1872-2067(19)63515-1

Chinese Journal of Catalysis 41 (2020) 970–976
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article
Selective C3-alkenylation of oxindole with aldehydes using
heterogeneous CeO2 catalyst
Md. Nurnobi Rashed a, Abeda Sultana Touchy a, Chandan Chaudhari b, Jaewan Jeon a,
S. M. A. Hakim Siddiki a,*, Takashi Toyao a,c, Ken-ichi Shimizu a,c,#
a Institute for Catalysis, Hokkaido University, N-21, W-10, Sapporo 001-0021, Japan
b Department of Chemical Systems Engineering, Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
c Elements Strategy Initiative for Catalysts and Batteries, Kyoto University, Katsura, Kyoto 615-8520, Japan
A R T I C L E I N F O
A B S T R A C T
Article history:
We report herein that a commercially available CeO2 is an active and reusable catalyst for the
C3-selective alkenylation of oxindole with aldehydes under solvent-free conditions. This catalytic
method is generally applicable to different aromatic and aliphatic aldehydes, giving
3-alkyledene-oxindoles in high yields (87%–99%) and high stereoselectivities (79%–93% to
E-isomers). This is the first example of the catalytic synthesis of 3-alkenyl-oxindoles from oxindole
and various aliphatic aldehydes. The Lewis acid-base interaction between Lewis acid sites on CeO2
and benzaldehyde was studied by in situ IR. The structure-activity relationship study using CeO2
catalysts with different sizes suggests that defect-free CeO2 surface is the active site for this reaction.
© 2020, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Received 30 July 2019
Accepted 18 September 2019
Published 5 June 2020
Keywords:
Oxindole
Aldehyde
Aldol condensation
C3-alkenylation
CeO2 catalyst
Published by Elsevier B.V. All rights reserved.
1. Introduction
biologically appealing spirooxindoles [6–13]. Conventionally,
secondary
amine
(piperidine/pyrrolidine)-assisted
Indoles, oxindoles, isatins, and their derivatives are relevant
nitrogen-containing heterocycles widely distributed in natural
products and pharmaceutical compounds [1]. Oxindole is used
as a neurodepressant tryptophan metabolite and physiologi-
cally present in mammalian brain/blood, and can influence
brain functions [2]. 3-Alkyledene-oxindole derivatives are me-
dicinally important and exist in anticancer kinase inhibitors
and anti-inflammatory drugs including Sunitinid and Tedinap,
respectively [3–5]. They are also well-known synthetic inter-
mediates of natural products named TMC-95, Gelsemine and
Knoevenagel condensation reaction is applied to synthesize
3-alkyl/arylidene-oxindoles from oxindole and carbonyl com-
pounds [14–17]. Lee et al. [18] reported (Z)-selective synthesis
of 3-arylidene-oxindoles employing stoichiometric amounts of
Ti(OiPr)4/pyridine with unsymmetrical ketones. Villemin et al.
[19] reported 3-alkenylation of oxindole with aromatic alde-
hydes promoted by an excess amount (10 equiv.) of solid base
(KF/Al2O3) under microwave radiation. Brønsted acidic ionic
liquids [20] were reported to promote 3-alkenylation reactions
of oxindole with aromatic aldehydes, but this method used an
* Corresponding author. Fax: +81-11-706-9163; E-mail: hakim@cat.hokudai.ac.jp
# Corresponding author. E-mail: kshimizu@cat.hokudai.ac.jp
This study was supported financially by a series of JSPS KAKENHI grants: 17H01341, 18K14051, 18K14057, and 19K05556 from the Japan Society for
the Promotion of Science (JSPS) and by the Japanese Ministry of Education, Culture, Sports, Science, and Technology (MEXT) within the projects "In-
tegrated Research Consortium on Chemical Sciences (IRCCS)" and "Elements Strategy Initiative to Form Core Research Center", as well as by the
JST-CREST project JPMJCR17J3.
DOI: S1872-2067(19)63515-1 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 41, No. 6, June 2020

Md. Nurnobi Rashed et al. / Chinese Journal of Catalysis 41 (2020) 970–976
971
excess amount (>6.6 equiv.) of the Brønsted acids with respect
to the substrates. Apart from these non-catalytic methods,
Vankelecom and co-workers [21] showed the catalytic synthe-
sis of 3-benzylidene-oxindole by the reaction of oxindole with
benzaldehyde using a Zr-incorporated UiO-66 MOF catalyst.
Recently, Zhu and co-workers [22] reported that a homogene-
ous Re-complex catalyzed dehydrogenative 3-alkenylation of
N-substituted oxindoles with benzylic alcohols. However, these
two catalytic methods are applicable to activated (aromatic and
allylic) aldehydes and suffer from the difficulties in catalyst
reuse. Gholamzadeha et al. [23] demonstrated a reusable cata-
lytic method using SO3H-loaded silica catalyst, but the method
is applicable only for activated aromatic aldehydes. Hence, it is
desirable to develop a reusable general heterogeneous catalyst
for the 3-alkenylation of oxindoles with aldehydes including
aliphatic (non-aromatic) aldehydes.
g–1) was prepared by calcination of the niobic acid at 500 °C for
3 h. ZrO2 (73 m2 g–1) and SnO2 (25 m2 g–1) were prepared by
calcination (500 °C, 3 h) of ZrO2∙nH2O and H2SnO3 (Kojundo
Chemical Laboratory Co., Ltd.). Hydroxides of Ca, Zn, and Mg
were commercially available. Hydroxides of La were prepared
by hydrolysis of La(NO3)3·6H2O with aqueous NH4OH solution,
followed by filtration, washing with distilled water, drying at
100 °C for 12 h, and calcination at 500 °C for 3 h. Oxides of Ca
(22 m2 g–1), Zn (12 m2 g–1) and La were prepared by calcination
of these hydroxides at 500 °C for 3 h. Hβ-20 (HSZ-940HOA, 530
m2 g–1) was purchased from Tosoh Co. A sulfonic resin (Am-
berlyst-15, 45 m2 g–1) and montmorillonite K10 clay (mont.
K10, 220 m2 g–1) were purchased from Sigma-Aldrich. Scandi-
um(III) trifluoromethanesulfonate Sc(OTf)3, Ce(NO3)4, and
Ce3(PO4)4 were purchased from Tokyo Chemical Industry.
Organic synthesis employing heterogeneous CeO2 catalysis
fascinates much attention in recent years [24–26]. Our group
has studied a series of catalytic transformation of carboxylic
acid derivatives using heterogeneous CeO2 catalysts [27–36].
This access has advantages combined with the facility of cata-
lyst preparation and exploitation of a recyclable heterogeneous
catalyst. It is anticipated that this catalytic system would find
applications to other challenging reactions that produce val-
ue-added chemicals in one-pot manner. Herein, we report a
simple heterogenous catalytic method using CeO2 for the
C3-alkenylation of oxindole with aldehydes including unacti-
vated aliphatic aldehydes into the corresponding
3-alkenyl-oxindoles.
2.3. Catalytic tests
The solid catalysts, stored under ambient conditions, were
used without any pretreatment. In a typical procedure, oxin-
dole (1 mmol) and each of the aldehydes (1.25 mmol) were
subjected to condensation reaction in the presence of 20 mg of
catalysts. The reaction mixture was added to a reaction tube
(Pyrex pressure tube, 13 mL), with a magnetic stirrer bar and
placed in a heated reactor at 100 °C under N2 with stirring at
400 rpm. After completion of the reaction, the reaction mixture
was diluted with 2-propanol (3 mL), and n-dodecane (0.2
mmol) was added as an internal standard and the mixture was
analyzed by GC-FID to determine the conversion and yield of
the products. The GC-FID sensitivity of the product was deter-
mined using the isolated 3-alkeny-oxindole. After the reaction,
the catalyst was separated through filtration, and the solvent
was evaporated from the reaction mixture. The E/Z ratio of the
isomers and total yield were determined by 1H NMR analyses of
crude reaction mixture using mesitylene as an internal. The E
and Z isomers were assigned and confirmed in comparison
2. Experimental
2.1. General
Commercial compounds (Tokyo Chemical Industry, Sig-
ma-Aldrich or Wako Pure Chemical Industries) were used
without further purification. Substrates and products were
analyzed by GC (Shimadzu GC-2014) and GCMS (Shimadzu
GCMS-QP2010) with an Ultra ALLOY+-1 capillary column
(Frontier Laboratories Ltd.) using N2 and He as the carrier.
Column chromatography was performed with silica gel 60
(spherical, 40-100 μm, Kanto Chemical Co. Ltd.). 1H and 13C
NMR spectra were recorded at ambient temperature on a
JEOL-ECX 600 (1H: 600.17 MHz; 13C: 150.92 MHz) spectrometer
with tetramethylsilane as an internal standard.
1
with their reported H NMR data [18]. The major product was
isolated by column chromatography using silica gel 60 (spher-
ical, 40-100 μm, Kanto Chemical Co. Ltd.) with hexane/ethyl
acetate (95/5 to 80/20) as the eluting solvent. The isolated
product was analyzed by 1H NMR, 13C NMR, and GC-MS
equipped with the same column as GC-FID.
2.4. Characterization
In situ IR spectra were recorded using a JASCO FT/IR-4200
spectrometer equipped with a mercury cadmium telluride de-
tector. For the benzaldehyde adsorption IR study, a closed IR
cell surrounded by a Dewar vessel was connected to an evacua-
tion system. During the IR measurement, the IR cell was cooled
with a freezing mixture of dry-ice/acetone in the Dewar vessel,
and the thermocouple near the sample showed T = (–50 ± 5) °C.
The sample was pressed into a self-supporting wafer (40 mg)
and mounted into the IR cell with CaF2 windows. Spectra were
measured by accumulating 15 scans at a resolution of 4 cm–1.
After in situ pre-evacuation of the sample at 500 °C for 0.5 h, a
reference spectrum of the sample disc was measured at T =
2.2. Catalyst preparation
CeO2 (JRC-CEO-1, 185.3 m2 g–1, supplied by Santoku Co.),
MgO (JRC-MGO-3, 19 m2 g–1), and TiO2 (JRC-TIO-4, 47 m2 g–1)
were obtained from Catalysis Society of Japan. SiO2 (Q-10, 300
m2 g–1) was supplied by Fuji Silysia Chemical Ltd. Different
CeO2 catalysts were prepared with CeO2 (JRC-CEO-1) by cal-
cining at four different temperatures (500, 600, 800, and 1000
°C) for 3 h. γ-Al2O3 (124 m2 g–1) was prepared by calcination of
γ-AlOOH (Catapal B Alumina purchased from Sasol) at 900 °C
for 3 h. Niobic acid was supplied by CBMM, and Nb2O5 (54 m2

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Md. Nurnobi Rashed et al. / Chinese Journal of Catalysis 41 (2020) 970–976
(–50 ± 5) °C. The sample was then exposed to benzaldehyde (1
μL) under 650 Pa at T = –50 °C for 600 s, followed by evacua-
tion for 600 s. A differential IR spectrum, with respect to the
reference spectrum, was then recorded at T = (–50 ± 5) °C. XRD
measurements were conducted using a Rigaku Miniflex with a
Cu-Kα radiation source. N2 adsorption measurements were
carried out by using AUTOSORB 6AG (Yuasa Ionics Co.). X-ray
photoelectron spectroscopy (XPS) measurements were carried
out using a JEOL JPS-9010MC with an Mg Kα anode operated at
10 mA and 10 kV. Binding energies were calibrated with re-
spect to C 1s at 284.2 eV.
zeolite Hβ-20 (entry 13), montmorillonite K10 clay (entry 14),
and a sulfonic resin Amberlyst-15 (entry 15), gave 3a in
15%–40% yields. Homogeneous Lewis acid Sc(OTf)3 (entry 16)
afforded 3a in 52% yield. We also screened Ce salts (entries 17
and 18), Ce(NO3)4 and Ce3(PO4)4, which gave 3a in 57% and
49% yield, respectively. Screening test in Table 1 exhibits that
CeO2 is the most effective catalyst for the 3-alkenylation of 1a
with 2a.
Admitting CeO2 as the best catalyst, we optimized the reac-
tion conditions for the model 3-arenylation reaction as shown
in Table 2. For the reaction at 80 °C, the yield of 3a depends on
the molar amount of 2a; the reaction with 1.25 equiv. of 2a
gave higher yield (78%) than that with 1 equiv. of 2a (68%).
The reactions of 1a with 1.25 equiv. of 2a at different temper-
atures (80–100 °C) under solvent-free conditions were tested
(entries 2–4). The reaction at 100 °C gave the highest yield of
3a (99%). The reactions of 1a with 1.25 equiv. of 2a at 100 °C
in different solvents (entries 5–7) gave slightly lower yields
(93%–96%) than the solvent-free conditions. Under the opti-
mized conditions (100 °C, 20 mg CeO2, 1 mmol 1a, and 1.25
mmol 2a), the time course of the reaction (Fig. 1) shows that a
reaction time of 10 h was sufficient to obtain the maximum
yield of 3a (99%).
3. Results and discussion
3.1. Optimization of the catalyst and reaction conditions
To find the optimal catalyst, we employed a series of poten-
tial catalysts for the 3-alkenylation of oxindole (1a) with ben-
zaldehyde (2a) into the corresponding 3-benzylidene-oxindole
product (3a). A series of acidic or basic heterogeneous and
homogeneous catalysts (20 mg) were tested for the
3-alkenylation of 1a (1 mmol) and 2a (1.2 mmol) under N2 at
100 °C for 10 h. The conversions of 1a and the yield of 3a based
on 1a using different catalysts are summarized in Table 1.
Without catalyst (entry 1), only 4% yield of 3a was observed.
Among the metal oxides (entries 2–11), CeO2 (entry 2) showed
the highest yield of 3a (97%). Lewis acidic oxides including
Nb2O5, TiO2, and ZrO2 gave 3a in good yields (54%–73%), and
SiO2, SnO2, and amphoteric oxides Al2O3 and ZnO showed low
yields of 3a (19%–32%). Basic oxides such as CaO, MgO, and
La2O3 (entries 10–12) provided 3a in low yields (16%–27%).
Commercially available solid acids, including proton-exchanged
3.2. Catalytic performance
We studied the reusability of CeO2 for the alkenylation of 1a
with 2a under the optimized conditions (Fig. 2). After comple-
tion of the reaction of each cycle, 2-propanol (3 mL) was added
to the reaction mixture and CeO2 was separated by centrifuga-
tion, followed by consecutive washing with 2-propanol (3 mL)
and acetone (3 mL), and drying at 110 °C for 6 h. The recovered
catalyst was then used for the next reaction cycle. The result
shows that the catalyst was reusable for five cycles with slight
gradual decrease in the 3a yield (99%–92%). Initial product
formation rates were examined (at conversion less than 30%)
for each cycle in addition to the final yields (Fig. 2). A significant
loss of the initial rate was not observed, but a slight decrease in
the yield was observed. The yield was recovered after calcina-
tion of the CeO2 catalyst at 400 °C for 3 h. This indicates that the
decrease in the final yield is not due to changes in the catalyst
Table 1
C3-alkenylation of oxindole with benzaldehyde by various catalysts.
Entry
1
Catalyst
Blank
1a conv. (%)
3a yield a (%)
8
4
2
3
4
5
CeO2
Nb2O5
TiO2
ZrO2
SiO2
100
76
58
67
25
35
26
22
20
29
31
23
18
99
73
54
64
21
32
22
19
16
25
27
20
15
Table 2
Optimization of the conditions for C3-alkenylation of oxindole with
benzaldehyde.
6
7
8
9
10
11
12
SnO2
Al2O3
ZnO
CaO
MgO
La2O3
Hβ-20
mont. K10
Entry CeO2 (mg) 2a (mmol)
Solvent T (oC) t (h) 3a yielda (%)
1
2
3
4
1
20
20
20
20
20
20
20
No
No
No
No
80 15
80 15
90 15
100 10
68
78
92
99
93
96
94
1.25
1.25
1.25
1.25
1.25
1.25
13
14
15
16
Amberlyst-15
Sc(OTf)3
43
55
40
52
5
6
7
n-Decane 100 10
Toluene 100 10
1,4-Dioxane 100 10
17
18
Ce(NO3)3
Ce3(PO4)4
61
53
57
49
a GC yield.
a GC yield.

Md. Nurnobi Rashed et al. / Chinese Journal of Catalysis 41 (2020) 970–976
973
group at the ortho position exceptionally formed Z isomer
(84%, E/Z = 8:92, 3f) as a major product. Benzaldehyde homo-
logue, i.e., 1-naphthaldehyde, is also well tolerated in this
E-selective 3-arenylation reaction and affords high yield of
3-nepthalen-1-ylmethylene-oxindole (87%, E/Z = 93:7, 3i).
Heteroaromatic aldehydes (e.g., isonicotinyl and furanyl
groups) were successfully transformed into the corresponding
3-arylidene-oxindoles in high yield (90%, E/Z = 84:16, 3j; and
93%, E/Z = 85:15, 3k). An allylic aldehyde also underwent
alkenylation to give 3-phenylallylidene-oxindole 3l in high
yield and high E selectivity. Aliphatic aldehydes including linear
and branched substituents at α-carbon atoms were successfully
converted to the corresponding 3-alkelidene-oxindoles
(3m–3p) in high yields and high
E selectivity. To our
Fig. 1. Time course of the reaction of oxindole (1 mmol) with benzal-
dehyde (1.25 mmol) by CeO2 (20 mg) at 100 °C.
knowledge, this is the first example of the catalytic
C3-alkenylation of oxindole with aliphatic aldehydes.
We also demonstrated the gram scale reaction for this
CeO2-promoted 3-alkenyl-oxindole synthesis using different
aldehydes (12.5 mmol) with 10 mmol of 1a and 20 mg of CeO2
catalysts. The yields of the corresponding 3-alkenyl-oxindole
products are shown in Scheme 2. The reaction of 1a with ben-
zaldehyde 2a, p-methyl-benzaldehyde 2b, p-chloro-benzal-
dehyde 2g, isonicotinaldehyde 2j, and 1-octanal 2o gave the
corresponding 3-alkenyl-oxindoles in 82%–93% yield.
3.3. Active sites and possible mechanism
We prepared CeO2 catalysts calcined at four different tem-
peratures (500, 600, 800, and 1000 °C), and the structure and
catalytic activity of these comparative catalysts were compared
with the standard CeO2 catalyst (as received JRC-CEO-1), which
was originally calcined at 300 °C. X-ray diffraction patterns of
Fig. 2. Catalyst reuse for the synthesis of 3a from 1a and 2a, promoted
by CeO2 catalysts under standard condition as shown in Table 1 (entry
2): (black bars) 3a yields after 10 h and (green bars) initial rates of 3a
formation after 1 h.
R
CeO2 (20 mg)
100 oC, 10 h
H2
O
+
+
R
O
O
O
N
H
N
H
1a
2a-2p
3a-3p
1 mmol
1.25 mmol
H3
H3
C
CH3
structure but due to carbonaceous compounds on the surface.
The result in Fig. 2 shows that CeO2 is a robust heterogeneous
catalyst. XRD pattern of the catalyst after the fifth cycle is near-
ly consistent with that of fresh catalyst (Fig. S1), which suggests
no change in the catalyst structure after the reaction.
CH3
C
H3C
H3
C
N
H3CO
HO
O
O
O
O
O
O
N
H
N
N
N
H
N
H
N
H
H
H
3a, 85%
3b, 83%
3c, 90%
3d, 85%
3e, 78%
3f, 84%
(96%, E/Z = 89:11)
(99%, E/Z = 88:12)
(98%, E/Z = 93:7)
(96%, E/Z = 92:8)
(92%, E/Z = 87:13) (88%, E/Z = 8:92)
Under the optimized reaction conditions, we investigated
the substrate scope for the C3-alkenylation of oxindole with
various aromatic and aliphatic aldehydes by CeO2. The yields of
alkylidene-oxindoles are shown in Scheme 1. Note that the
yields of the major products (E isomers) were estimated from
the weight of the isolated E isomers, while the total yields of E
and Z isomers and the E/Z ratios in parenthesis were deter-
mined by 1H NMR. The benzaldehydes, including elec-
tron-donating (methyl, t-butyl, N,N-dimethyl, and methoxy at
the para positions, 2b–2e; hydroxy at ortho position, 2f) and
electron-withdrawing groups (chloride and nitro at the para
positions, 2g and 2h) were successfully transformed into the
corresponding 3-benzylidene-oxindoles (3a–3h) in high total
yield (88%–99%). Regardless of the electronic nature, sub-
strates with substituents at the para position selectively afford
E isomers. Sterically congested substrate 2f with hydroxy
Cl
O2N
N
O
O
N
O
O
N
O
N
O
O
N
N
N
H
H
H
H
H
H
3g, 70%
3h, 73%
3i, 78%
3j, 72%
3k, 77%
3l, 81%
(94%, E/Z = 80:20)
(90%, E/Z = 84:16)
(92%, E/Z = 79:21)
(87%, E/Z = 93:7)
(93%, E/Z = 85:15) (95%, E/Z = 88:12)
C4H9
C2H5
C7H15
C2H5
O
O
O
N
O
N
N
H
N
H
H
H
3p
3m, 83%
3n, 74%
3o, 72%
(98%, E/Z = 87:13) (89%, E/Z = 85:15) (88%, E/Z = 84:16) (87%, E/Z = 83:17)
Isolated yield of major isomers are shown, total yield and ratio of E/Z isomers are in parenthesis based on 1H NMR spectra
Scheme 1. CeO2-catalyzed C3-alkenylation of oxindole with aromatic
and aliphatic aldehydes (2a–2p) to synthesize the corresponding
3-alkyledene-oxindoles (3a–3p).

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Md. Nurnobi Rashed et al. / Chinese Journal of Catalysis 41 (2020) 970–976
300 oC Cal.
500 oC Cal.
80
60
40
20
600 oC Cal.
800 oC Cal.
1000 oC Cal.
0
0.2
0.4
0.6
0.8
1
Relative pressure (P/P0)
Fig. 4. N2 adsorption isotherms for different CeO2 catalysts calcined at
Scheme 2. CeO2-catalyzed gram scale alkenylation of oxindole to pro-
different temperatures.
duce corresponding 3-alkylidene-oxindoles.
catalysts are basically in Ce4+ state and Ce3+ species are present
at the surface as a minor Ce species.
the CeO2 catalysts (Fig. 3) show that the samples show the
same crystal phase (fluorite structure). Average size of CeO2
crystals, calculated from the half-width of the peak at 28.5°
using the Scherrer equation, was plotted versus calcination
temperature in Fig. 5(B). The crystal size increases with the
calcination temperature. The BET surface area (Table S1) esti-
mated using the N2 adsorption isotherms (Fig. 4) is plotted in
Fig. 5(B) as a function of calcination temperature. The surface
area of the CeO2 catalysts decreased with the calcination tem-
perature. We carried out catalytic tests for the standard reac-
tion of 1a and 2a using these CeO2 catalysts to obtain the rates
of 3a formation per catalyst weight (Table S1). As shown in Fig.
5(A), the rate per catalyst weight decreases with increase in the
calcination temperature. The rates per catalyst weight were
divided by the BET surface areas to give the rate per surface
area. As shown in Fig. 5(A), the rate per surface area of the CeO2
catalysts increases with the calcination temperature. Clearly,
the intrinsic catalytic activity of CeO2 increases with decrease in
surface area of CeO2. This suggests that defect-free CeO2 sur-
face, possibly the most stable (111) surface, is the active site for
this alkenylation reaction.
The high activity of CeO2 in the present reaction may be due
to acid-base bifunctional properties [27,35,36] of CeO2 as
shown in Scheme 3. First, we studied Lewis acid-base interac-
tion between surface Ce cation and carbonyl oxygen of benzal-
dehyde using in situ IR experiment of benzaldehyde adsorbed
on CeO2 (calcined at 300, 600, and 800 °C) at –50 °C (Fig. 7).
The benzaldehyde adsorbed on CeO2 catalysts gave the C=O
stretching band at lower wavenumber (1682–1685 cm–1) than
200
(B)
50
40
150
30
100
20
50
10
0
8
0
(A)
1.5
6
4
2
0
1
To check the presence of surface Ce3+, we studied X-ray
photoelectron spectroscopy (XPS) analysis for CeO2 catalysts
(Fig. 6). A strong peak due to Ce4+ species (918 eV) [37,38] is
observed in the Ce 3d XPS spectra for all the catalysts. A weak
shoulder peak at 884 eV due to Ce3+ species [37,38] is observed
for the catalyst calcined at 300–800 °C, but another character-
istic peak for Ce3+ species at 904 eV is not clearly observed for
these catalysts. These results suggest that Ce species in all the
0.5
0
400
600
800
1000
o
Calcination Temperature ( C)
Fig. 5. Effect of calcination temperature of CeO2 on (▲) the rate of 3a
formation per catalyst weight, () rate of 3a formation per surface
areas of CeO2, () crystal size of CeO2, and (■) BET surface area of CeO2.
Reactions were performed under conditions where 1a conversions
were below 30%.
1000oC Cal. (48.4 nm)
Ce4+
Ce3+ Ce 3d
Ce3+
800 oC Cal. (43.0 nm)
600 oC Cal. (13.4 nm)
1000 o
C
800 o
600 o
C
500 oC Cal. (8.2 nm)
300 oC Cal. (6.2 nm)
C
500 oC
300 o
20
30
40
50
60
70
80
90
C
2 (deg. Cu-K)
(as received)
920 910 900 890 880
Binding energy (eV)
Fig. 3. XRD patterns of different CeO2 catalysts calcined at different
Fig. 6. XPS results of CeO2 catalysts calcined at different temperatures.
temperature, with particle sizes in parentheses.

Md. Nurnobi Rashed et al. / Chinese Journal of Catalysis 41 (2020) 970–976
975
Acknowledgments
The authors are indebted to the technical division of the In-
stitute for Catalysis (Hokkaido University) for manufacturing
experimental equipment.
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Scheme 3. Plausible reaction mechanism for the CeO2-catalyzed
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Md. Nurnobi Rashed et al. / Chinese Journal of Catalysis 41 (2020) 970–976
Graphical Abstract
Chin. J. Catal., 2020, 41: 970–976 doi: S1872-2067(19)63515-1
Investigation of surface processes in electrocatalysis by scanning
tunneling microscopy
Md. Nurnobi Rashed, Abeda Sultana Touchy, Chandan Chaudhari,
Jaewan Jeon, S. M. A. Hakim Siddiki *, Takashi Toyao, Ken-ichi Shimizu *
Hokkaido University, Japan; Nagoya University, Japan;
Kyoto University, Japan
CeO2 promotes the C3 selective alkenylation of oxindole with aldehydes
in high yields and high E-selectivity. The structure-activity relationship
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多相CeO2催化剂上氧化吲哚与醛的选择性C3烯基化反应
Md. Nurnobi Rashed a, Abeda Sultana Touchy a, Chandan Chaudhari b, Jaewan Jeon a,
S. M. A. Hakim Siddiki a,*, Takashi Toyao a,c, Ken-ichi Shimizu a,c,#
a北海道大学催化科学研究所, N-21, W-10, 札幌001-0021, 日本
b名古屋大学工程研究生院, 化学系统工程系, 名古屋464-8603, 日本
c京都大学催化剂与电池元素战略基地, 桂校区, 京都615-8520, 日本
摘要: 本文报道了将市售CeO2作为一种高活性和可重复使用的催化剂用于无溶剂条件下氧化吲哚与醛的C3选择性烷基化
反应. 这种催化方法一般适用于不同的芳香族和脂肪族醛, 得到3-烷基二烯-辛醇, 产率高(87%–99%), 立体选择性高
(79%–93%为E-异构体). 这是从氧化吲哚与各种脂肪族醛催化合成3-烯基氧化吲哚的首例. 采用原位红外光谱研究了
CeO2上Lewis酸位点与苯甲醛之间的Lewis酸-碱相互作用. 不同粒径CeO2催化剂的构效关系研究表明, 无缺陷CeO2表面是
该反应的活性中心.
关键词: 氧化吲哚; 醛; 羟醛缩合; C3-烯基化; 二氧化铈催化剂
收稿日期: 2019-07-30. 接受日期: 2019-09-18. 出版日期: 2020-06-05.
*通讯联系人. 传真: +81-11-706-9163; 电子信箱: hakim@cat.hokudai.ac.jp
#通讯联系人. 电子信箱: kshimizu@cat.hokudai.ac.jp
本文的电子版全文由Elsevier出版社在ScienceDirect上出版(http://www.sciencedirect.com/science/journal/18722067).