Pd/C: An efficient and reusable catalyst for the synthesis of flavones via carbonylation of aryl halides

Article abstract of DOI:10.1002/aoc.4163

This work describes an efficient and mild approach for the synthesis of flavones via catalytic carbonylation of aryl halides with 2-hydroxyacetophenone using the commercial Pd/C as an efficient, heterogeneous and recyclable catalyst. Under balloon pressure of CO, 0.6?mol% Pd/C is sufficient for moderate yields of flavones for the carbonylation of aryl iodides under phosphine-free conditions and aryl bromides in the presence of phosphine ligand. The catalyst is easily separable and shows significant recyclability. Moreover, the reaction mechanism was discussed, and a possible mechanism that contains two different cyclisation pathways was proposed.

Full text of DOI:10.1002/aoc.4163

Received: 25 July 2017
DOI: 10.1002/aoc.4163
Revised: 5 October 2017
Accepted: 6 October 2017
F U L L P A P E R
Pd/C: An efficient and reusable catalyst for the synthesis of
flavones via carbonylation of aryl halides
Yizhu Lei1
| Zhi Li1 | Yali Wan1 | Xiao‐Yu Zhou1 | Guangxing Li2 | Kaiyi Shi1
1 School of Chemistry and Materials
Engineering, Liupanshui Normal
University, Liupanshui, Guizhou 553004,
PR China
2 School of Chemistry and Chemical
Engineering, Huazhong University of
Science and Technology, Luoyu Road
1037, Wuhan, Hubei 430074, PR China
This work describes an efficient and mild approach for the synthesis of flavones
via catalytic carbonylation of aryl halides with 2‐hydroxyacetophenone using
the commercial Pd/C as an efficient, heterogeneous and recyclable catalyst.
Under balloon pressure of CO, 0.6 mol% Pd/C is sufficient for moderate yields
of flavones for the carbonylation of aryl iodides under phosphine‐free
conditions and aryl bromides in the presence of phosphine ligand. The catalyst
is easily separable and shows significant recyclability. Moreover, the reaction
mechanism was discussed, and a possible mechanism that contains two
different cyclisation pathways was proposed.
Correspondence
Dr. Yizhu Lei, School of Chemistry and
Materials Engineering, Liupanshui
Normal University, Liupanshui, Guizhou,
553004 (PR China).
KEYWORDS
Email: yzleiabc@126.com
aryl halide, carbonylation, flavone, heterogeneous catalysis, palladium on charcoal
Professor Guangxing Li, School of
Chemistry and Chemical Engineering,
Huazhong University of Science and
Technology, Wuhan, 430074 (P.R. China).
Email: ligxabc@163.com
Funding information
the National Natural Science Foundation
of China, Grant/Award Number: No.
21763017; the Youth Talent Growth
Project of Educational Department of
Guizhou Province, Grant/Award Number:
qian jiao he KY [2016]264; the School‐
Level Key Discipline of Chemistry, Grant/
Award Number: LPSSYZDXK201602;
Guizhou Key Built Discipline Project,
Grant/Award Number: ZDXK[2016]24;
the Science and Technology Fund Project
of Guizhou Province, Grant/Award Num-
ber: qian ke he ji chu [2016]1133; the Sci-
ence and Technology Creative Team
Project of Liupanshui Normal University,
Grant/Award Number:
LPSSYKJTD201501
1 | INTRODUCTION
and material chemists in nowadays.[1–3] Generally,
heterogeneous catalysts present several advantages over
The use of heterogeneous catalysts for advanced organic
transformation to minimize waste production and
optimize catalyst efficiency is of great interest for organic
the homogeneous systems, such as easy catalyst separa-
tion, good recyclability and less wastes production.[4,5]
These are of particular importance when the catalyst is
Appl Organometal Chem. 2017;e4163.
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Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4163

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LEI ET AL.
based on expensive noble metals and the product is for
pharmaceutical uses.[6]
Chemical Reagent Co. Ltd. (China). All solvents were analyt-
ical grade and distilled prior to use. CO with a purity of
99.99% was purchased from the local manufacturer.
Pd(PPh3)2Cl2 was synthesized according to the literature.[39]
Pd@UPOP[35] and Pd@KAPs(Ph‐PPh3)[36] were prepared as
we previously reported. The intermediates, 2‐acetylphenyl
benzoate (c) and 1‐(2‐hydroxyphenyl)‐3‐ phenylpropane‐
1,3‐dione (d), were synthesized according to procedures
described in the Supporting Information.
Flavones, also known as 2‐phenylchromones, are a
major group of secondary metabolites that widely distrib-
uted in the plant kingdom.[7,8] Due to their wide range of
biological activities and usefulness in the treatment of
various diseases, a number of synthetic approaches to this
important class of molecules have been extensively
investigated.[9,10] However, most of the developed
methods suffer from harsh reaction conditions. To take
the classical Baker‐Venkatraman method as an example,
the need for acyl chloride substrates, tedious reaction
procedures and relatively harsh reaction conditions have
limited its practical applications.[11,12]
2.2 | Typical procedure for carbonylation
of aryl halide
The carbonylation reactions were performed in a 10 ml
reaction flask and fitted with carbon monoxide balloon.
In a typical procedure, Pd/C (0.6 mol%), aryl halide
(1 mmol), 2‐hydroxyacetophenone (1 mmol), DBU
(2 mmol) were added to DMSO solvent (2 ml). For the car-
bonylation of aryl bromide, DPPB (0.6 mol%) was also
needed for the catalytic system. Then, air in the system
was exchanged with CO. After that, the reaction flask
was fitted with carbon monoxide balloon, and stirred
(400 rmp) at 130 °C for 9 h. After reaction completion,
the flask was cooled to room temperature and the catalyst
was separated by simple centrifugation. For the recycling
experiments, the solid catalyst was separated by centrifu-
gation, washed three times with DMSO, and then engaged
in a new catalytic cycle. The reaction conditions for the
recycling experiments are: Pd/C (0.6 mol%), aryl halide
(1 mmol), 2‐hydroxyacetophenone (1 mmol), DBU
(2 mmol), DMSO (2 ml), 130 °C, 9 h. For the catalyst
recycling experiments in the carbonylation of aryl bro-
mide, DPPB (0.6 mol%) was needed for each run.
For both the model reaction and the recycling experi-
ments, the obtained filtrate was quantitatively analyzed
by a FL2000 HPLC system coupled with a UV detector.
Samples were separated by a Hypersil C18 column
(4.6 mm x 250 mm, 5 um) at 30 °C. The detection wave-
length for 1‐(2‐hydroxyphenyl)‐3‐phenylpropane‐1,3‐
dione, 2‐hydroxyacetophenone, flavone, 2‐acetylphenyl
benzoate were 363 nm, 324 nm, 294 nm, 234 nm, respec-
tively. The samples were eluted at 1.0 mL/min with
methanol and 0.1 wt.% phosphoric acid aqueous solution
(V:V = 7:3). The concentrations of flavone and intermedi-
ates were calculated based on external standard curves,
which were constructed with authentic standards. For
the study of substrate scope, the filtrate was washed with
NH4Cl dilute solution (10 ml), and the solution was
extracted 4 times with ethyl acetate (5 ml). The organic
layer thus collected was dried over anhydrous Na2SO4,
filtered, and then concentrated. The obtained residue
was purified by preparative thin‐layer chromatography
(PTLC) using cyclohexane/AcOEt (10:1, v/v) as the
Palladium‐catalyzed carbonylation reaction represents
a powerful method for the synthesis of heterocycles,[13–23]
and has achieved great success during the past decades.
The application of a carbonylation reaction in flavones
synthesis has also been developed by different
groups[10,13,24–27] Recent progress in palladium catalyzed
aryl bromides with 2‐hydroxyacetophenones to form the
scaffold of flavones has shown this methodology to be
particularly attractive for the synthesis of flavones.[25]
However, this reported reaction system suffered from
high palladium usage (2.0 mol%), relatively high CO
pressure (5 bar) and homogeneous system. In consider-
ation of good application prospect, it is very valuable to
develop heterogeneous catalyst, optimize catalyst
efficiency as well as investigate the reaction mechanism.
Pd/C has been widely used as an efficient, heteroge-
neous, recyclable and environmentally benign catalyst in
various carbonylation reactions.[24,28–34] In continuation
of our long‐standing interest in heterogeneous carbonyla-
tion reactions,[35–38] herein we report a facile protocol for
the synthesis of flavones via catalytic carbonylation of aryl
halides with 2‐hydroxyacetophenone using the commer-
cial Pd/C as
a recyclable catalyst. The principal
advantages of this synthetic approach are the low catalyst
dosage, balloon CO pressure and good catalyst
recyclability.
2 | EXPERIMENTAL
2.1 | Materials
2‐Hydroxyacetophenone (99%) were purchased from Meryer
(Shanghai) Chemical Technology Co. Ltd., China. Palladium
chloride, aryl iodides, aryl bromides, 1,8‐diazabicyclo[5.4.0]
undec‐7‐ene (DBU), 1,4‐bis(diphenylphosphino)butane
(DPPB), ( )‐2,2'‐bis(diphenylphosphino)‐1,1'‐binaphthalene
(BINAP), PtBu3, and PPh3 were purchased from Energy
Chemical and used as received without further purification.
10 wt.% Pd/C catalyst was purchased from Sinopharm

LEI ET AL.
3 of 7
eluting solvent. The products were analyzed by NMR and
yields were based on aryl halides.
usage was then tested. As expected, a similar yield (55%)
was preserved with 2 mol% Pd/C usage (Table 1, entry
6). Then, we tried to lower the catalyst usage. When the
Pd usage was decreased to 0.6 mol%, a 55% yield of
flavone was still maintained (Table 1, entry 7). Further
to lower the Pd usage, a decrease in the yield of target
product was observed (Table 1, entries 8 and 9).
3 | RESULTS AND DISCUSSION
3.1 | Catalyst screening
For the purpose to develop an efficient, heterogeneous
and recyclable catalyst for the carbonylative synthesis of
flavones, the effect of catalyst was investigated using the
carbonylation of iodobenzene as a model reaction. As
shown in Table 1, the homogeneous Pd(PPh3)2Cl2 gave a
56% yield of flavone in the presence of DBU as a base
(Entry 1). A triphenylphosphine functionalized porous
organic polymer supported palladium catalyst,
Pd@KAPs(Ph‐PPh3), was then assessed, and a similar
yield of flavone was gained (Table 1, entry 2). Considering
the advantage of phosphine free catalyst, Pd@UPOP, a
heterogeneous and phosphine free palladium catalyst,
was also tested. Notably, Pd@UPOP afforded the flavone
in a 55% yield (Table 1, entry 3), which was comparable
to the results of homogeneous Pd(PPh3)2Cl2 and heteroge-
neous Pd@KAPs(Ph‐PPh3). With these results in hand,
ligand free PdCl2 and Pd/C were also tested. Interestingly,
they both gave the target product in about 55% yields
(Table 1, entries 4 and 5). All of the tested catalysts exhibit
similar catalytic activities, which seems to suggest that the
carbonylation reaction might not be the rate‐limiting step
for this reaction. Hence, the amount of the palladium
3.2 | Reaction optimization
Previous studies have shown that bases and solvents have
marked influences on the activity of the carbonylation
reactions of aryl halides.[40] To optimize the reaction con-
ditions, several inorganic and other organic bases were
tested (Table 2, entries 1‐8). The results showed that bases
have significant influence on the yield of flavone, and the
other bases resulted in generally lower yields (0‐18%)
TABLE 2 Effect of base and solventa
Base
Yield
Yield
Entry
Solvent
(mole equiv.)
(%) ab
(%) bb
1
DMSO
K2CO3 (2)
KHCO3 (2)
KOH (2)
K3PO4 (2)
DBACO (2)
DMAP (2)
Pyridine (2)
Bu3N (2)
‐
18
8
32
18
9
15
‐
2
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
NMP
3
10
14
2
TABLE 1 Effect of the catalysta
4
5
6
‐
‐
7
‐
‐
8
2
‐
9
‐
‐
Catalyst
(Pd [wt%])
Pd usage
(mol%)b
Yield
(%)b
10
11
12
13
14
15
16
17
18
19
DBU(1.2)
DBU(1.5)
DBU(2.5)
DBU(4)
30
43
47
25
13
41
3
1
1
1
3
1
2
‐
Entry
1
Pd(PPh3)2Cl2
Pd@KAPs(Ph‐PPh3) (0.8)
Pd@UPOP (2.0)
PdCl2
1
56
55
55
54
55
55
55
47
15
2
3
4
5
6
7
8
9
1
1
1
DBU (2)
DBU (2)
DBU (2)
DBU (2)
DBU (2)
DBU (2)
Pd/C(10)
1
DMAc
Toluene
Anisole
Dioxane
Water
Pd/C(10)
2
Pd/C(10)
0.6
0.4
0.2
46
‐
1
‐
Pd/C(10)
Pd/C(10)
‐
‐
aReaction conditions: Iodobenzene (1 mmol), 2‐hydroxyacetophenone
(1 mmol), DBU (2 mmol), DMSO (2 ml), 120 °C, 8 h, CO (balloon), stirring
speed (400 rpm).
aReaction conditions: Pd/C (0.6 mol%), iodobenzene (1 mmol), 2‐
hydroxyacetophenone (1 mmol), 120 °C, 8 h, base, solvent (2 ml), stirring
speed (400 rpm), CO (balloon).
bHPLC yields.
bHPLC yields.

4 of 7
LEI ET AL.
TABLE 4 Carbonylation of aryl bromidea
when compared with DBU. Considering the importance
of DBU, the effect of DBU amount was also investigated
(Table 2, entries 9‐13). The results show that the reaction
hardly occurred in the absence of DBU, and 2 molar
equivalent of DBU afforded the highest yield (Table 1,
entry 5). However, further increase the amount of DBU
afforded a lower yield of flavone (Table 1, entry 13). With
DBU as the base, the influence of the solvent was also
checked (Table 1, entries 14‐19). Among all the solvents
screened, DMSO displayed the best performance, with
which a 55% yield could be obtained (Table 1, entry 5).
Another point worth noting is that during the investiga-
tion of bases and solvents effect, 1,3‐dione b was produced
as a main byproduct. And the yield could be up to 32%
when K2CO3 was used as the base (Table 2, entry 1).
In the following experiments, we studied the effect of
temperature and reaction time (Table 3). When the
reaction temperature varied from 80 to 130 °C, the yield
of flavone was significantly increased, and a 76% yield of
flavone was gained at 130 °C (Table 3, entries 1‐6).
Further increase the reaction temperature to 140 °C, a
slight decrease of yield was observed (Table 3, entry 7).
Then, we tried to prolong the reaction to increase the
yield of target flavone, and an 82% yield of flavone was
obtained after 9 h at the optimal reaction temperature
(Table 3, entry 8).
Entry
Ligand (mol%)
Yield% ab
1
‐
‐
2
3
4
5
PtBu3 (1.2)
PPh3 (1.2)
DPPB (0.6)
BINAP (0.6)
7
18
75
33
aReaction conditions: Pd/C (0.6 mol%), bromobenzene (1 mmol), 2‐
hydroxyacetophenone (1 mmol), 130 °C, 9 h, DBU (2 mmol), DMSO (2 ml),
stirring speed (400 rpm), CO (balloon).
bHPLC yields.
BINAP, gave higher yields, and a 75% yield was observed
when DPPB was used as the ligand (Table 4, entry 4). The
results confirmed that the presence of phosphine ligand is
crucial for the success of the carbonylation of aryl
bromide. The adsorbed phosphine ligand could either
alter the electronic properties to facilitate the oxidative
addition step or promote the reductive elimination step
by steric bulk around Pd nanoparticles, as suggested by
Tagata and Nishida.[41]
3.3 | Catalyst recycling
Apart from the catalytic activity, recovery, reuse of the
catalyst and the amount of palladium leaching are also
crucial for an excellent heterogeneous catalyst. Under
the optimized conditions, recycling capacity was evalu-
ated for the carbonylation of iodobenzene and
bromobenzene in the presence of 0.6 mol% palladium,
respectively (Figure 1). After every cycle, the catalyst
was separated by simple centrifugation. The results
showed that the Pd/C catalyst was efficiently recycled
seven times without any significant loss in catalytic
With the above optimal conditions in hand,
bromobenzene was also tested (Table 4). However, no
target product was detected (Table 4, entry 1). Previous
studies showed that a phosphine ligand was generally
found to be necessary for the carbonylation of aryl
bromide.[25] Hence, the effect of phosphine ligand was
investigated for the carbonylation of bromobenzene.
Monodentate ligands, PtBu3 and PPh3, gave lower yields
(7% and 18%, respectively). Bidentate ligands, DPPB and
TABLE 3 Effect of temperature and reaction timea
Entry
T (°C)
Time (h)
Yield (%) ab
1
80
8
‐
2
3
4
5
6
7
8
9
90
8
17
28
43
56
76
72
82
82
100
110
120
130
140
130
130
8
8
8
8
8
9
10
aReaction conditions: Pd/C (0.6 mol%), iodobenzene (1 mmol), 2‐
hydroxyacetophenone (1 mmol), DBU (2 mmol), DMSO (2 ml), stirring speed
(400 rpm), CO (balloon).
FIGURE
carbonylation reactions
1
Recycling of the Pd/C catalyst in successive
bHPLC yields.

LEI ET AL.
5 of 7
activity for the carbonylation of iodobenzene. For the
carbonylation of bromobenzene, Pd/C catalyst also exhib-
ited good reusability and could be reused four cycles with
only a slight decrease of catalytic activity. ICP‐AES analy-
sis was carried out using the filtrate after each run, the
palladium leaching was found to be less than 1.2 ppm
for the carbonylation of iodobenzene in each run, while
7.4, 6.2, 5.4, 5.9, 4.7 ppm of palladium leaching were
detected in five consecutive runs for the carbonlyation of
bromobenzene. The results suggested that the presence
of phosphines enhance the palladium leaching.
para‐substituted iodobenzenes were converted efficiently
to the desired flavones in moderate yields in 9 h. The
influence of the steric hindrance of the substituent groups
on aromatic iodoarenes was also tested. Para‐ and meta‐
iodotoluenes were transformed into the corresponding
flavones in similar yields (Table 5, entries 2 and 3). While
the bulky iodoarene substituents, ortho‐iodotoluene and
2,6‐dimethyl‐1‐iodobenzene gave no target flavones under
the same reaction conditions. These results suggested that
the steric hindrance of the substituent groups on
iodoarenes has a marked influence on the catalytic
activities. Then, the carbonylation of aryl bromides was
also investigated. p‐Me, p‐Et, p‐OMe, p‐CF3, p‐Cl, and
p‐F substituted bromobenzenes afforded the target
flavones in moderate yields under the standard conditions
(80‐70% yields; Table 5, entries 10‐15). To further verify
the recycle ability of Pd/C in the above cases, recycling
capacity was evaluated for the carbonylation of 4‐
chloroiodobenzene and p‐bromotoluene, respectively.
The results showed that 76% and 68% yields of corre-
sponding flavones were still preserved after five catalytic
runs (Table 5, entries 5 and 10).
3.4 | Scope evaluation
Adopting the optimized conditions, the generality of the
catalytic system was determined by evaluating different
aryl halides. Firstly, the carbonylation of various aryl
iodides was examined. As shown in Table 5, this
carbonyltion reaction was almost equally effective with
both electron‐rich and electron‐deficient aromatic
iodoarene derivatives (Table 5, entries 1‐8). The various
TABLE 5 Pd/C‐catalyzed carbonylative synthesis of flavonesa
3.5 | Mechanistic considerations
Based on the above results and taking into account that
1,3‐dione b was produced as a byproduct. We proposed
two possible reaction pathways for the formation of fla-
vone in this work. The proposed mechanism is depicted
in Scheme 1.
Entry
R
X
Yield (%)b
1
H
I
81
In the first step, phenoxycarbonylation of benzene
halide with 2‐hydroxyacetophenone results in the 2‐
acetylphenyl benzoate intermediate c. In the presence of
DBU, the enolate of the acetyl group is formed and attacks
the carbonyl of the ester to give the hemiacetal intermedi-
ate d. Then, the hemiacetal intermediate d either dehy-
drates to produce target flavone (Path I) or undergoes
ring‐opening to give the 1,3‐diketone b intermediate, the
Baker‐Venkataraman rearrangement product. Besides
that, cyclisation of the 1,3‐diketone b intermediate under
basic conditions could also occur, thus afforded the target
flavone in another pathway (Path II).
However, it is known that cyclisation of 1,3‐diketone
usually occurs in strongly acidic medium, cyclisation
under basic conditions is uncommon, although the forma-
tion of flavones has been observed during the one pot
Baker‐Venkataraman reaction in the K2CO3/acetone
system.[42,43] To elucidate the second reaction pathway
(Path II), a control experiment was, therefore, performed
by heating 1,3‐dione b in the presence of DBU (Table 6).
The results revealed that flavone could be formed in the
DBU/DMSO system, and a high reaction temperature
was needed for moderate yield of flavone. Considering
2
p‐me
m‐me
p‐OMe
p‐cl
I
85
3
I
80
4
I
74
77(76)c
5
I
6
p‐F
I
75
7
3,5‐Cl2
p‐Ph
H
I
82
8
I
67
9
Br
Br
Br
Br
Br
Br
Br
77
79(68)d
10
11
12
13
14
15
p‐me
p‐et
75
p‐OMe
p‐CF3
p‐cl
70
80
74
p‐F
73
aReaction conditions: Pd/C (0.6 mol%), and/or DPPB (0.6 mol%), aryl halides
(1 mmol), 2‐hydroxyacetophenone (1 mmol), DBU (2 mmol), DMSO (2 ml),
stirring speed (400 rpm), CO (balloon), 130 °C, 9 h.
bIsolated yields.
cThe yield of 2‐(4‐chlorophenyl)‐4H‐chromen‐4‐one in the fifth catalytic run.
dThe yield of 2‐(p‐tolyl)‐4H‐chromen‐4‐one in the fifth catalytic run.

6 of 7
LEI ET AL.
O
OH
O
a
CH3
OH
OCOPh
CH3
O
O
Pd
O
I
+
CO, base
OH
O
Ph
d
c
O
O
b
SCHEME 1 Possible reaction pathways
TABLE 6 Cyclisation of 1,3‐diketone b in the DBU/DMSO
TABLE 7 Cyclisation of ester c in the DBU/DMSO systema
systema
Entry
T(°C)
Yield (%) ab
Yield (%) bb
1
130
85
1
Entry
t (h)
T(°C)
Yield (%) ab
2
3
110
90
57
39
21
34
1
8
130
61
2
3
4
8
100
80
34
7
aReaction conditions: 2‐acetylphenyl carboxylate c (1 mol), DMSO (2 ml),
DBU (1 mmol), stirring speed (400 rpm), 8 h.
bHPLC yields.
8
10
130
62
aReaction conditions: 1,3‐diketone b (1 mol), DMSO (2 mL), DBU (1 mmol),
stirring speed (400 rpm).
bHPLC yields.
Based on the above results and discussion, we can
conclude that the reaction should proceed via a hemiace-
tal intermediate which can undergo two possible path-
ways to form the target flavone.
the presence of 1,3‐dione b in the product of the above
carbonylation reaction, we could conclude that the forma-
tion of flavone via Path B is possible. However, heating
1,3‐dione b at 130 °C for 8 h afforded a 61% yield of
flavone (Table 6, entry 1), which was around 15% less
than the yield for the carbonylation of iodobenzene under
similar condition (Table 3, entry 6). Further prolonged the
reaction time to 10 h, no obvious increase of yield was
observed (Table 6, entry 4). These results gave us a hint
that the formation of flavone via Path I might also be
existed, and this pathway should give a much higher
selectivity.
To verify the first pathway (Path I), a control experi-
ment was, therefore, performed by heating 2‐acetylphenyl
carboxylate in the presence of DBU. The results showed
that an 85% yield of flavone was obtained (Table 7, entry
1). The yield was much higher than that of heating 1,3‐
dione b under the same reaction conditions (Table 6,
entry 1). Thus, the first path way (Path I) is possible.
Effect of temperature on this reaction was tested. The
results suggested that lowering the reaction temperature
favored the producing of 1,3‐diketone product (Table 7,
entries 2 and 3), and a 34% yield of 1,3‐dione b was
obtained when the reaction proceeded at 90 °C. These
results further confirmed that cyclisation of 1,3‐dione b
needs a high reaction temperature.
4 | CONCLUSIONS
In summary, this work demonstrates a simple, mild and
reusable catalytic system for the carbonylative synthesis
of flavones. With 2‐hydroxyacetophenone and aryl halides
as the substrates, the target flavones were obtained in
moderate yields. Additionally, the commercial Pd/C cata-
lyst could be well‐recycled without significant loss of its
catalytic activity. Thus, this heterogeneous catalyst has
significant advantages over the corresponding homoge-
neous catalysts due to its salient features such as simplic-
ity in handling of the catalyst, low Pd dosage, balloon CO
pressure, negligible palladium leaching and good catalyst
recyclability. Moreover, the reaction mechanism was also
discussed in detail, and a reaction mechanism which con-
tains two possible pathways for the formation of target fla-
vone was proposed.
ACKNOWLEDGEMENTS
This work is partially supported by the Youth Talent
Growth Project of Educational Department of Guizhou

LEI ET AL.
7 of 7
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Foundation of China (No. 21763017), the Science and
Technology Creative Team Project of Liupanshui Normal
University (LPSSYKJTD201501), Guizhou Key Built Dis-
cipline Project (ZDXK[2016]24), and the School‐Level
Key Discipline of Chemistry (LPSSYZDXK201602).
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ORCID
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How to cite this article: Lei Y, Li Z, Wan Y,
Zhou X‐Y, Li G, Shi K. Pd/C: An efficient and
reusable catalyst for the synthesis of flavones via
carbonylation of aryl halides. Appl Organometal
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