Efficient, recyclable and phosphine-free carbonylative Suzuki coupling reaction using immobilized palladium ion-containing ionic liquid: Synthesis of aryl ketones and heteroaryl ketones

Article abstract of DOI:10.1039/c3ra40730f

The carbonylative Suzuki coupling reaction of aryl and heteroaryl iodides was studied by using immobilized palladium ion-containing ionic liquid (ImmPd-IL). The protocol was optimized with respect to various reaction parameters, applied to a wide variety of substituted aryl/heteroaryl iodides and various aryl/heteroaryl boronic acids with different steric and electronic properties, and afforded the corresponding products in good to excellent yield. This is an efficient, heterogeneous catalyst which avoids the use of phosphine ligands, and its reusability was tested in up to four consecutive cycles. The recycled catalyst was characterized by using XPS analysis.

Full text of DOI:10.1039/c3ra40730f

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PAPER
Efficient, recyclable and phosphine-free carbonylative
Suzuki coupling reaction using immobilized palladium
ion-containing ionic liquid: synthesis of aryl ketones
and heteroaryl ketones3
Cite this: RSC Advances, 2013, 3,
7
791
a
b
a
Mayur V. Khedkar, Takehiko Sasaki and Bhalchandra M. Bhanage*
The carbonylative Suzuki coupling reaction of aryl and heteroaryl iodides was studied by using
immobilized palladium ion-containing ionic liquid (ImmPd-IL). The protocol was optimized with respect
to various reaction parameters, applied to a wide variety of substituted aryl/heteroaryl iodides and various
aryl/heteroaryl boronic acids with different steric and electronic properties, and afforded the
corresponding products in good to excellent yield. This is an efficient, heterogeneous catalyst which
avoids the use of phosphine ligands, and its reusability was tested in up to four consecutive cycles. The
recycled catalyst was characterized by using XPS analysis.
Received 11th February 2013,
Accepted 11th March 2013
DOI: 10.1039/c3ra40730f
www.rsc.org/advances
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copper, zinc, magnesium, silicon, aluminium and tin
Introduction
have been reported for carbonylative coupling reactions.
However, these carbonylative cross-coupling reactions have
several drawbacks due to the formation of biaryl side products
ensuing from direct coupling of the aryl groups without
carbon monoxide insertion. In 1993, Suzuki and co-workers
firstly reported an aryl boron reagent for the carbonylative
Biaryl and hetero aryl carbonyls are important moieties
present in numerous natural products, biologically active
compounds, agrochemicals and pharmaceutical compounds.
1
Owing to their increasing biological and industrial importance
researchers have emphasized the development of many
economical and efficient synthetic strategies for these biaryl
carbonyl compounds.
The most common synthetic route to biaryl ketones
involves Friedel–Crafts acylation of aromatic cycles with acyl
halides using an over stoichiometric amount of aluminium
trichloride. However, this methodology is incompatible with
many functional groups.
synthesis of biaryl ketones is the acylation of aryl metal species
with carboxylic acid derivatives. The most promising method
for the synthesis of unsymmetrical biaryl ketones is the
transition metal-catalyzed three-component cross-coupling
reaction of aryl metal reagents, carbon monoxide (CO) and
12
coupling reaction using a palladium catalyst. This reaction
provides a versatile tool for the direct synthesis of biaryl
ketones using boronic acids as a reagent, which are generally
non-toxic, and stable in air and moisture. After the first report
by Suzuki, significant advances have been made for this
transformation to date, by using a variety of palladium-based
2
,3
An alternative method for the
13,14
homogeneous catalytic systems.
However, despite their potential utility, all of the above
catalysts employed so far for the carbonylative Suzuki coupling
reactions were homogeneous and palladium–phosphine based
complexes, without any consideration of a recyclability aspect.
Furthermore, the use of expensive, toxic and air/moisture
sensitive phosphine ligands along with difficulties associated
with catalyst–product separation thereby, limited their appli-
cations. To resolve this issue, some ligand free protocols for
the carbonylative Suzuki coupling reaction have been devel-
oped, but problems with the recycling of the precious metal
4
5
aryl electrophiles. This process is one of the most efficient
and direct routes to several aryl ketones, as it introduces a
carbonyl group in a single step, which is now considered to be
a useful tool for the synthesis of a wide variety of carbonyl
compounds. Since then, a range of aryl metal reagents, such as
1
5
catalysts occurred.
a
Department of Chemistry, Institute of Chemical Technology, N. Parekh Marg,
Hence, due to the high costs of the transition metal
catalysts and their toxicity in pharmaceutical applications, an
increased interest in immobilizing catalysts has arisen.
Immobilized catalysis avoids the possible metal/ligand con-
tamination of the desired product, and also minimizes waste
derived from the reaction workup, appending to the develop-
Matunga, Mumbai-400 019, India. E-mail: bhalchandra_bhanage@yahoo.com;
bm.bhanage@ictmumbai.edu.in; Fax: +91-22-3361-1020
b
Department of Complexity Science and Engineering, Graduate School of Frontier
Sciences, The University of Tokyo, 5-1-5, Kashiwanoha, Kashiwa, Chiba 277-8561,
Japan
3
Electronic supplementary information (ESI) available. See DOI: 10.1039/
c3ra40730f
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6,17
ment of green chemical processes.
Considering this,
various immobilization strategies for metal complexes have
been developed, wherein the metal/ion is coordinated by a
1
8
ligand grafted on to an inorganic or organic solid support.
Recently, ionic liquids containing metal ions have been used
as catalytic precursors; furthermore, they can be immobilized
on solid supports to facilitate the reuse of this immobilized
catalyst. These immobilized palladium catalysts have been
1
9–21
successfully used for various organic transformations.
In spite of significant advances in this area, there are very
few reports that employ immobilized palladium complexes as
catalysts for the carbonylation reaction. Moreover, a literature
survey reveals that there is a limited number of reports on
carbonylative Suzuki coupling reactions using heteroaryl
halides and heteroaryl boronic acid derivatives.
Scheme 2 The preparation of the immobilized palladium ion-containing ionic
liquid.
under nitrogen. After reflux, the toluene was removed by
filtration using a glass filter, and the excess ionic liquid was
removed by washing with dichloromethane several times. The
resultant solid is denoted as Imm-IL. In the next step, Imm-IL
In this regard, an immobilized palladium ion-containing
ionic liquid [ImmPd-IL] was prepared, characterized and
2
2
applied in the coupling reactions. Recently, we have explored
the ImmPd-IL catalyst for alkoxy and amino carbonylation
2
was added to an acetonitrile solution of PdCl and refluxed for
2
3
24 h. Acetonitrile and excess metal chloride were removed by
washing with acetone using a glass filter several times. The
metal loading of ImmPd-IL was 3.4 wt% as determined by XRF
measurements.
reactions. Inspired by all the prominent preliminary results
of ImmPd-IL and continuing interest in developing efficient,
phosphine free, recyclable protocols for the carbonylation
2
4
reactions, herein, we have explored the ImmPd-IL catalyst for
carbonylative Suzuki coupling reactions (Scheme 1).
For testing this prepared ImmPd-IL catalyst, the carbony-
lative cross coupling reaction of iodobenzene with phenyl
boronic acid was chosen as a model system. The influence of
various reaction parameters such as solvent, base, tempera-
ture, time and CO pressure were examined on the model
reaction, and results obtained are summarized in Table 1.
It was observed that the nature of the solvent affects the
reaction outcome: when the reaction was conducted in polar
solvents such as N,N-dimethylformamide (55%), water (10%),
a lower yield of the desired product was obtained (Table 1,
entries 1–2), whereas non polar solvents such as THF (62%),
anisole (60%) and toluene (90%) provided good results
Results and discussion
In this study, the ImmPd-IL used was synthesized according to
2
2
the procedures based on our previous publications, The
synthesis of the immobilized palladium ion-containing ionic
liquid catalyst is as follows (Scheme 2).
1
-methyl-3-(3-trimethoxysilylpropyl) imidazolium chloride
was synthesized by mixing N-methylimidazole (0.690 mol) and
-trimethoxysilylpropyl chloride (0.690 mol) in a dry 300 mL
3
flask under a nitrogen atmosphere and refluxing for 48 h. After
cooling to room temperature, the resultant liquid was washed
with dehydrated ethyl acetate five times and dried at room
temperature under reduced pressure for 48 h. The obtained
compound was stored at 253 K under dry nitrogen.
Silica (Aerosil 300, surface area 300 m g , calcined at 573
K for 1.5 h in air) and 1-methyl-3-(3-trimethoxysilylpropyl)
imidazolium chloride (weight ratio 1 : 1) was dispersed in
dehydrated toluene and the mixture was refluxed for 48 h
Table 1 The effect of reaction parameters on the carbonylative Suzuki coupling
a
reaction of iodobenzene with phenyl boronic acid
b
Entry
Solvent
Base
Time (h)
Temp. (uC)
Yield (%)
2
21
The effect of the solvent
1
2
3
4
5
DMF
Water
THF
Anisole
Toluene
K
K
2
CO
CO
3
8
8
8
8
8
100
100
100
100
100
55
10
62
60
90
2
3
K2CO3
K
K
2
CO
CO
3
2
3
The effect of the base
6
7
8
Toluene
Toluene
Toluene
Cs
Na
Et
2
CO
CO
N
3
8
8
8
100
100
100
72
69
40
2
3
3
The effect of the temperature
9
1
Toluene
Toluene
K
K
2
CO
CO
3
8
8
90
80
80
75
0
2
3
The effect of the time and the CO pressure
1
1
1
2
Toluene
Toluene
K
K
2
CO
CO
3
6
8
100
100
81
76
c
2
3
a
Reaction conditions: iodobenzene (1 mmol), phenyl boronic acid
Scheme 1 The carbonylative Suzuki coupling reaction of aryl and heteroaryl
(1.2 mmol), ImmPd-IL (2 mol%), Base (3 mmol), solvent (10 mL), CO
pressure = 1 MPa. GC yield. CO pressure = 0.5 MPa.
b c
iodides with aryl/heteroaryl boronic acids using the ImmPd-IL catalyst.
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Table 1, entries 3–5). As toluene furnishes the maximum yield
of the desired product, it was used for further studies (Table 1,
entry 5). Next, we turned our attention to the study of the effect
of bases on the reaction outcome; hence, we attempted a
reaction using various organic and inorganic bases (Table 1,
Paper
(
Table 2 The carbonylative Suzuki coupling reaction of aryl iodides with various
a
aryl boronic acids
b
Entry Aryl iodide Aryl boronic acid Product
1
Yield (%)
88
2 3
entries 5–8). Among the inorganic bases screened, K CO was
found to give the desired product in excellent yield (Table 1,
entry 5). The organic base triethylamine was found to be
ineffective for the carbonylative Suzuki coupling reaction
2
3
90
84
(Table 1, entry 8). Decreasing reaction temperatures to up to
80 uC decreased the yield of the desired product (Table 1,
entries 9–10); hence, 100 uC was chosen as the optimum
reaction temperature for further reactions. When the reaction
time was decreased, a lower yield of the desired product was
observed (Table 1, entry 11). Then, the influence of the CO
pressure was also studied (Table 1, entry 12), and the optimum
pressure was used for further studies.
4
76
Therefore, the optimized reaction conditions for the
carbonylative Suzuki coupling reaction were: ImmPd-IL (2
2 3
mol%) as a catalyst, K CO (3 mmol) as a base in toluene as a
5
6
69
81
solvent (10 mL) under 1 MPa CO pressure at 100 uC for 8 h.
With these optimized reaction conditions in hand, we
investigated the scope of the developed protocol for the
coupling of a variety of phenyl boronic acids with a range of
aryl and heteroaryl iodides. Various electron-donating and
electron-withdrawing groups such as –CH
3 3 3
, –OCH , –COCH ,
–
NO and –Br on aryl iodides and phenyl boronic acids were
2
well tolerated to give the corresponding biaryl ketones in good
to excellent yields. Iodobenzene reacts with phenyl boronic
acid to give 88% yield of benzophenone (Table 2, entry 1).
7
8
80
79
4-iodotoluene furnishes an excellent yield of 4-methyl benzo-
phenone (Table 2, entry 2), whereas the reactions of sterically
hindered 2-iodoaniline with phenyl boronic acid provided 84%
yield of the desired biaryl ketones (Table 2, entry 3).
4
-acetyliodobenzene provides a moderate yield of the desired
product (Table 2, entry 4). It was observed that the presence of
strong electron-withdrawing groups, such as –NO on aryl
a
Reaction conditions: aryl iodide (1 mmol), aryl boronic acid (1.2
mmol), CO pressure = 1 MPa, ImmPd-IL (2 mol%), K
toluene (10 mL), 100 uC, 8 h. Isolated yield.
2
CO
3
(3 mmol),
2
b
iodide, decreases the yield of the corresponding carbonylated
products (Table 2, entry 5). We probed the carbonylative
Suzuki coupling reaction of bromobenzene and chloroben-
zene, but it only gave traces of the desired products even after
a prolonged reaction times.
It is noteworthy that the reaction of various substituted
phenyl boronic acids such as (4-methylphenyl)boronic acid, (4-
methoxyphenyl)boronic acid and (4-bromophenyl)boronic acid
with iodobenzene furnishes good to excellent yields of the
desired biaryl ketones (Table 2, entries 6–8).
yields of the expected carbonylated products (Table 3, entries
2–3). 2-iodothiophene reacts with the phenyl boronic acids (4-
methylphenyl)boronic acid and (4-methoxyphenyl)boronic
acid, which provides 80%, 79% and 77% yield of the
corresponding ketones, respectively (Table 3, entries 4–6).
Gratifyingly, heterocyclic boronic acids were also well
tolerated in the carbonylative coupling reaction with aryl
iodides. Thiophen-3-ylboronic acid reacts with iodobenzene
and 4-iodotoluene, which provided 85% and 80% yields of the
expected heteroaryl ketones, respectively (Table 3, entries 7–8).
In an effort to make the synthesis more applicable, the
reusability of the catalyst was also examined for the standard
reaction of iodobenzene with phenyl boronic acid. After
completion of the reaction, the mixture was filtered, the
catalyst was washed with distilled water and methanol, and
With the aim of developing a more general protocol for the
preparation of heterocyclic biaryl ketones, we examined the
carbonylative cross coupling reaction of heterocyclic aryl
iodides with different aryl boronic acids (Table 3, entries 1–
8). Initially, we examined the carbonylative cross-coupling
reaction of 3-iodopyridine with phenyl boronic acid, which
provides 89% yield of the respective heteroaryl ketone (Table 3,
entry 1). Encouraged by this result, we screened substituted
aryl boronic acid derivatives, which provided moderate to good
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a
Table 3 The carbonylative Suzuki coupling reaction of heteroaryl iodides with various aryl boronic acids
b
Entry
1
Aryl/hetero iodide
Aryl/hetero aryl boronic acid
Product
Yield (%)
89
2
81
3
4
80
80
5
79
6
7
77
85
8
80
a
Reaction conditions: aryl/hetero aryl iodide (1 mmol), aryl/hetero aryl boronic acid (1.2 mmol), CO pressure = 1 MPa, ImmPd-IL (2.5 mol%),
b
2 3
K CO (3 mmol), toluene (10 mL), 100 uC, 10 h. Isolated yield.
dried under reduced pressure. The ImmPd-IL was found to be
effectively reused in up to four consecutive cycles while
maintaining high activity and selectivity (Fig. 1).
The slight decrease in yield up to the forth recycle might be
due to handling loss of the catalyst. To confirm whether there
is any leaching of the Pd catalyst from the immobilized solid
support, we carried out the ICP-AES analysis of the 1st and the
4th recycle run, where the Pd content was found to be below
the limit of detection (0.01 ppm). Thus, we conclude that the
ImmPd-IL catalyst was successfully recycled and the reusa-
bility procedure was tested for up to four consecutive cycles.
XPS spectra were measured for the fresh ImmPd-IL for the
1st recycle and the 4th recycle catalysts. The wide scan and the
Pd 3d region are shown in Fig. 2. The wide scans show no large
difference, indicating that the fresh and retrieved catalysts do
not differ much. As for the Pd 3d region, two peaks at 337 eV
and 342.4 eV for the fresh ImmPd-IL correspond to 3d and
5
/2
2
+
3d3/2 for the Pd species, respectively. For the 1st and 4th
recycle catalysts, both peaks tend to shift to lower values,
suggesting that the catalysts are slightly reduced after the 1st
Fig. 1 ImmPd-IL catalyst reusability.
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Experimental section
All chemicals and reagents were procured from commercial
suppliers and used without further purification. The products
1
were characterized using H NMR (Varian Mercury 300 NMR
Spectrometer) and GC-MS (Shimadzu GC-MS QP 2010). The
progress of the reaction was monitored using GC analysis
(Perkin-Elmer, Clarus 400). The product was purified by
column chromatography on silica gel (100–200 mesh). All the
products are well known in the literature.
A typical experimental procedure for the carbonylative Suzuki
reaction of aryl iodides
To a 100 ml autoclave, aryl iodide (1.0 mmol), aryl boronic acid
(
1.2 mmol), ImmPd-IL (2 mol%), toluene (10 mL) and K CO (3
2 3
mmol) were added. The mixture was first stirred for 10 min
and then flushed with CO three times, then 1 MPa of CO was
applied, and the reaction mixture was heated at 100 uC for 8 h.
After completion of the reaction, the reaction mixture was
cooled to room temperature and the remaining CO gas was
carefully vented and the reactor was opened. The reactor vessel
was thoroughly washed with ethyl acetate (2 6 10 mL) to
remove any traces of product and catalyst if present. The
catalyst was filtered and the residue obtained was purified by
column chromatography (silica gel, 100–200 mesh; petrol
ether (b. p. 60 uC–70 uC)/ethyl acetate) to afford the desired
carbonylated product. The products were confirmed by GC,
1
GC-MS, and H NMR spectroscopic techniques. The purity of
the compounds was determined by GC-MS analysis.
A typical experimental procedure for the carbonylative Suzuki
reaction of heteroaryl iodides
Fig. 2 XPS spectra for the fresh and recycled catalysts (a) wide scan, (b) Pd 3d
To a 100 ml autoclave, heteroaryl iodide (1.0 mmol), aryl
boronic acid (1.2 mmol), ImmPd-IL (2.5 mol%), toluene (10
region.
mL) and K
stirred for 10 min and then flushed with CO three times, then
MPa of CO was adjusted, and the reaction mixture was
heated at 100 uC for 10 h. After the completion of the reaction,
the reaction mixture was cooled to room temperature, the
remaining CO gas was carefully vented and the reactor was
opened. The reactor vessel was thoroughly washed with ethyl
acetate (2 6 10 mL) to remove any traces of the product and
the catalyst if present. The catalyst was filtered and the residue
obtained was purified by column chromatography (silica gel,
2 3
CO (3 mmol) were added. The mixture was first
1
recycle and significantly reduced after the 4th recycle. The
decrease of Cl 2p was also observed after the recycles.
Conclusions
In conclusion, the present study reports an efficient and
reusable protocol for the carbonylative Suzuki coupling
reaction of aryl and heteroaryl iodides with different phenyl
boronic acids by using a well-defined heterogeneous ImmPd-
IL complex as a versatile catalyst. The reaction system was
optimized with respect to various reaction parameters and
applied to the carbonylative Suzuki coupling reaction of a
range of aryl/heteroaryl boronic acids with a variety of aryl and
heteroaryl iodides, furnishing good to excellent yields of the
corresponding products. Furthermore, the catalytic system was
also recycled up to four consecutive times without any
significant loss in catalytic activity.
100–200 mesh; petrol ether (b. p. 60 uC–70 uC)/ethyl acetate) to
afford the desired carbonylated product. The products were
1
confirmed by GC, GC-MS, and
H NMR spectroscopic
techniques. The purity of the compounds was determined by
GC-MS analysis.
A typical procedure for recycling the ImmPd-IL catalyst
The catalyst obtained after filtration was washed with distilled
water (5 mL 6 3) and then with methanol (5 mL 6 3) to
remove any organic material present. The resulting catalyst
was dried under reduced pressure and used for the next cycle.
Characterization of the products
1
4
-methylbenzophenone (Table 2, entry 2). (172 mg, 88%), H
NMR (300 MHz, CDCl
3
, 25 uC): d = 7.77–7.75 (d, 2H, J = 7.0 Hz),
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2
.71–7.69 (d, 2H, J = 8.2 Hz), 7.54–7.42 (m, 3H), 7.26–7.24 (d,
under the Japan–India cooperative Science program by JSPS
and DST.
H, J = 7.9 Hz), 2.4 (s, 3H); GC-MS (EI, 70 eV): m/z (%) = 196
+
[M ] (72), 119 (100), 105 (35), 91 (39), 77 (28).
1
4
-Acetylbenzophenone (Table 2, entry 4). (170 mg, 76%), H
NMR (300 MHz, CDCl
3
): d = 8.07–8.04 (d, J = 8.8 Hz, 2 H), 7.88–
Notes and references
7.87 (d, J = 8.4 Hz, 2 H), 7.82–7.79 (d, J = 8.4 Hz, 2 H), 7.65–7.59
1
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(
t, J = 8.8 Hz, 2 H), 7.52–7.47 (t, J = 7.5 Hz, 1 H), 2.66 (s, 3 H);
+
GCMS (EI, 70 eV): m/z (%) = 224 [M ] (50), 209 (100), 181 (20),
1
47 (30), 105 (75), 77 (79), 43 (30).
1
4-Nitrobenzophenone (Table 2, entry 5). (204 mg, 90%), H
2
3
4
NMR (300 MHz, CDCl
7
7
3
, 25 uC): d = 8.35–8.34 (d, 2H, J = 8.8 Hz),
.95–7.93 (d, 2H, J = 8.4 Hz), 7.81–7.79 (d, 2H, J = 6.8 Hz), 7.65–
+
.49 (m, 3H); GC-MS (EI, 70 eV): m/z (%) = 227 [M ] (45), 105
(100), 77 (55).
1
4
-Bromobenzophenone (Table 2, entry 8). (206 mg, 79%), H
NMR (300 MHz, CDCl
7
7
3
, 25 uC): d = 7.78–7.76 (d, 2H, J = 7.3 Hz),
.69–7.67 (d, 2H, J = 8.2 Hz), 7.63–7.61(d, 2H, J = 8.2 Hz), 7.60–
105, 6129; (b) Y. Hatanaka, S. Fukushima and T. Hiyama,
+
.47 (m, 3H); GC-MS (EI, 70 eV): m/z (%) = 260 [M ] (45), 181
Tetrahedron, 1992, 48, 2113; (c) L. J. Goossen and K. Ghosh,
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(40), 105 (100), 77 (55).
1
3
-Benzoylpyridine (Table 3, entry 1). (162 mg, 89%), H NMR
(
8
3
300 MHz, CDCl , 25 uC): d = 9.03–9.01 (d, J = 1.2 Hz, 1H), 8.86–
.85 (dd, J = 4.8 and 1.8 Hz, 1H), 8.18–8.16 (dd, J = 7.9 and 1.8
Hz, 1H), 7.78 (d, J = 7.9 Hz, 2H), 7.79–7.39 (m, 4H); GC-MS (EI,
7
+
0 eV): m/z (%) = 183 [M ] (100), 105 (90) 77 (85), 51 (40).
Pyridin-3-yl-p-tolyl-methanone (Table 3, entry 2). (160 mg,
1
8
8
1%), H NMR (300 MHz, CDCl
3
, 25 uC): d = 8.90 (s, 1H), 8.74–
.72 (d, J = 4.4 Hz, 1H), 8.09–8.06 (d, J = 1.4 Hz, 1H), 7.72–7.70
5
6
(d, J = 7.8 Hz, 2H), 7.43–7.46 (dd, J = 4.87 & 4.87 Hz, 1H), 7.29–
7
=
.25 (d, J = 7.8 Hz, 2H), 2.45 (s, 3H); GC-MS (EI, 70 eV): m/z (%)
+
197 [M ] (51), 182 (50), 119 (100), 91 (39), 77 (40).
2
1
-Benzoylthiophene (Table 3, entry 4). (151 mg, 80%),
NMR (300 MHz, CDCl
.73–7.71 (m, 5H), 7.15–7.17 (m, 1H); GC-MS (EI, 70 eV): m/z
H
3
, 25 uC): d = 7.88–7.85 (d, J = 7.6 Hz, 2H),
7
8
Q. Wang and C. Chen, Tetrahedron Lett., 2008, 49, 2916.
Y. Yamamoto, T. Kohara and A. Yamamoto, Chem. Lett.,
7
(
+
%) = 188 [M ] (70), 111 (100), 77 (31).
1976, 5, 1217.
Thiophen-2-yl-p-tolyl-methanone (Table 3, entry 5). (159 mg,
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1
7
9%) H NMR (300 MHz, CDCl , 25 uC): d = 7.75–7.70 (d, J = 8.5
3
Hz, 2H), 7.65–7.73 (m, 1H), 7.60–7.58 (m, 1H), 7.29–7.28 (d, J =
.6 Hz, 2H), 7.14–7.11 (m, 1H), 2.45 (s, 3H); GC-MS (EI, 70 eV):
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7
+
m/z (%) = 202 [M ] (100), 187 (55), 119 (80), 111 (71), 77 (35).
4-methoxyphenyl)(thiophen-2-yl)methanone (Table 3, entry
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(
1
S. Ho, J. Org. Chem., 1996, 61, 9082; (c) E. Morera and
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6
7
6
3
). (168 mg, 77%), H NMR (300 MHz, CDCl , 25 uC): d = 7.91–
.89 (d, J = 8.5 Hz, 2H), 7.69–7.67 (m, 2H), 7.17–7.15 (m, 1H),
.95–6.98 (d, J = 8.5 Hz, 2H), 3.89 (s, 3H); GC-MS (EI, 70 eV): m/
+
z (%) = 218 [M ] (75), 187 (35), 135 (100), 77 (39).
1
1
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Acknowledgements
The author M. V. K. is greatly thankful to the University Grant
Commission (UGC) India, for providing a Senior Research
Fellowship (SRF). XPS measurements were conducted at the
Research Hub for Advanced Nano Characterization, the
University of Tokyo, supported by the Ministry of Education,
Culture, Sports, Science and Technology (MEXT), Japan. T. S.
acknowledges special coordination funds for promoting
Science and Technology ‘‘Development of sustainable catalytic
reaction system using carbon dioxide and water’’ from MEXT,
Japan. This work is also supported by the exploratory exchange
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