Synthesis of aromatic cycloketones via intramolecular Friedel-Crafts acylation catalyzed by heteropoly acids

Article abstract of DOI:10.1071/CH06277

Under liquid-phase conditions, the intramolecular Friedel?Crafts acylation of aryl benzoic acids catalyzed by heteropoly acids were investigated for the first time. Several aryl benzoic acids were refluxed and dehydrated in chlorobenzene in the presence of 0.2 equivalents of a heteropoly acid, and anthraquinone, anthrone, and xanthone were obtained in good yield. At the same time, an intermolecular Friedel?Crafts acylation and decarboxylation reaction were observed in this experiment. CSIRO 2007.

Full text of DOI:10.1071/CH06277

Communication
CSIRO PUBLISHING
Aust. J. Chem. 2007, 60, 80–82
www.publish.csiro.au/journals/ajc
Synthesis of Aromatic Cycloketones via Intramolecular
Friedel–Crafts Acylation Catalyzed by Heteropoly Acids
A
A
A,B
Kun Lan, Shao Fen, and Zixing Shan
A
Department of Chemistry, Wuhan University, Wuhan 430072, China.
Corresponding author. Email: zxshan@sohu.edu.cn
B
Under liquid-phase conditions, the intramolecular Friedel–Crafts acylation of aryl benzoic acids catalyzed by heteropoly
acids were investigated for the first time. Several aryl benzoic acids were refluxed and dehydrated in chlorobenzene in
the presence of 0.2 equivalents of a heteropoly acid, and anthraquinone, anthrone, and xanthone were obtained in good
yield. At the same time, an intermolecular Friedel–Crafts acylation and decarboxylation reaction were observed in this
experiment.
Manuscript received: 2 August 2006.
Final version: 24 October 2006.
The intramolecular Friedel–Crafts acylation of aryl acids is
an important route for the preparation of aromatic cyclo-
ketones. Conventionally, the Friedel–Crafts acylation can also
be achieved by treating the free acid with a variety of condens-
ing agents including liquid HF, H2SO4, polyphosphoric acid,
AlCl3, andAlCl3/NaCl.[ However using these methods, a mass
of acidic waste water is inevitably produced which leads to
corrosion problems after the reaction.
(entry 10) is the best catalyst for the reaction while H3PMo12O40
(entries 5 and 6) shows no catalytic activity.
It is also observed that the reaction medium considerably
influences the conversion and selectivity of the acylation prod-
uct. When using chlorobenzene, the reaction is achieved with the
highest conversion rate (75–90%, entries 4, 10, 12) in compari-
son to toluene (23–32%, entries 2, 8, 14), p-xylene (50–62%,
entries 3, 9, 15), and benzene (0%, entry 1). However, the
selectivity is lower in chlorobenzene (68–75%) than in toluene
(85–90%) and xylene (72–77%). It is shown that a higher reflux
temperature may be beneficial to the conversion of aryl acids,
though may promote other competitive reactions at the same
time. As far as the amount of the catalyst used is concerned,
0.2 equivalents of the catalyst offers the desired product in
the highest yield; more catalyst does not improve the yield
further.
1]
In view of the increasing environmental problem, the appli-
cation of heterogeneous catalysis has become attractive.[ In the
last decades, considerable efforts have been made to develop het-
erogeneous catalysis in Friedel–Crafts acylation using solid-acid
2]
catalysts such as zeolites,[ bentonite, clays, Nafion-H,
3]
[4]
[5]
[6]
heteropoly acids (HPA), etc. In particular, HPAs have unique
physical chemical properties.[ Their acidity is significantly
higher than that of traditional mineral acids. Furthermore,
HPAs are capable of protonating and activating the substrate;
in some cases, HPAs are more effective than usual inorganic
acids and traditional acid catalysts. Therefore, they are widely
used as homogeneous and heterogeneous acid catalyst for syn-
7]
Some interesting phenomena are noted in this reaction. Under
the same conditions, when 2-(phenylamino)benzoic acid 1d is
heated to reflux, the decarboxylation reaction occurs instead of
the Friedel–Crafts reaction and diphenylamine is obtained in
low conversion and high selectivity (entry 16). It reveals the
unusual character of the amine-containing compound. When 2-
benzoylbenzoic acid was heated to reflux in toluene or xylene,
an intermolecular Friedel–Crafts reaction occurs instead of
an intramolecular acylation, and compounds 3a1 or 3a2 are
obtained at a low conversion rate and high selectivity.The results
follow the classic Brown selectivity relationship theory in the
[
8]
thesis reactions. However, few intramolecular Friedel–Crafts
acylation reaction of aromatic compounds catalyzed by HPAs
have been reported. Recently, Tesser and co-workers synthe-
sized anthraquinone under molten conditions using a HPA as
[
9]
a heterogeneous catalyst, however, the yield is low.
ꢀ
In previous research, 1,1 -spirobiindanes were synthesized
in high yield by an intramolecular cyclodehydration cat-
[
10]
[11]
alyzed by a HPA.
This method was further investigated in
Friedel–Crafts acylation reaction. As such, a phenyl ring with
other intramolecular cyclodehydrations of aromatic compounds.
Herein, we report the synthesis of anthraquinone, anthrone, and
xanthone by an intramolecular Friedel–Crafts acylation of aryl
acids catalyzed by HPAs as heterogeneous catalysts.
The Friedel–Crafts acylation of aryl benzoic acid has been
catalyzed by HPAs under different conditions and the results of
the acylation are shown in Table 1. It can be seen that the three
kinds of HPAs (H3PW12O40, H3PMo12O, and H4SiW12O40)
used in the experiments show different catalytic activity towards
the Friedel–Crafts acylation (entries 5–10), and H4SiW12O40
an electron-withdrawing substituent is less reactive than a phenyl
ring with an electron-donating substituent in the Friedel–Crafts
acylation.
In conclusion, the intramolecular Friedel–Crafts acylation
of aryl acids has been achieved in the presence of a HPA.
Anthraquinone, anthrone, and xanthone are obtained in good
yield when the corresponding aryl acids and H4SiW12O40 are
refluxed and dehydrated in chlorobenzene. In addition, inter-
molecular Friedel–Crafts acylation and decarboxylation reac-
tions are observed under these experimental conditions. The
©
CSIRO 2007
10.1071/CH06277
0004-9425/07/010080

Synthesis of Aromatic Cycloketones
81
Table 1. Friedel–Crafts acylation of aryl acids catalyzed by HPAs
X
2
X
HPAs
O
O
Arene/reflux
HOOC
X
1
R 3
X ꢀ CO, CH , O
R ꢀ 4-methyl, 2,5-dimethyl
2
Substrate
10 mmol)
Entry
Catalyst
(quantity [mmol])
Solvent
Product
Conversion
[%]
Selectivity
[%]
(
2
-Benzoylbenzoic acid
1
2
3
4
5
6
7
8
9
H4SiW12O40 (2.0)
H4SiW12O40 (2.0)
H4SiW12O40 (2.0)
H4SiW12O40 (2.0)
H3PMo12O40 (2.0)
H3PMo12O40 (2.0)
H3PW12O40 (2.0)
H4SiW12O40 (2.0)
H4SiW12O40 (2.0)
H4SiW12O40 (2.0)
H4SiW12O40 (1.0)
H4SiW12O40 (2.0)
H4SiW12O40 (3.0)
H4SiW12O40 (2.0)
H4SiW12O40 (2.0)
H4SiW12O40 (2.0)
Benzene
Toluene
p-Xylene
Chlorobenzene
Toluene
Chlorobenzene
Chlorobenzene
Toluene
None
3a1
3a2
2a
None
None
2b
2b
2b
2b
2c
2c
2c
2c
2c
0
28
62
90
0
0
90
77
75
0
2
-Phenylmethyl-benzoic acid
0
0
53
32
63
86
25
75
76
23
50
26
76
86
72
68
87
73
70
85
75
92
p-Xylene
10
Chlorobenzene
Chlorobenzene
Chlorobenzene
Chlorobenzene
Toluene
2
-Phenoxybenzoic acid
11
1
1
1
1
2
3
4
5
p-Xylene
Toluene
2
-Phenylamino-benzoic acid
16
Diphenylamine
results will help us to further understand the characteristics of
HPAs and the Friedel–Crafts acylation.
(2-Benzoylphenyl)(4-methylphenyl)methanone 3a1: colour-
less oil. δH 2.32 (s, 3H), 7.12 (d, J 4, 2H), 7.24 (d, J 4, 2H),
7.27–7.38 (m, 5H) 7.50–7.57 (m, 2H), 7.67 (t, J 7.2, 1H), 7.92 (d,
J 4, 1H). δC 21.0, 124.5, 125.9, 126.3, 127.4, 128.8, 129.5, 129.7,
Experimental
−1
134.5, 138.3, 138.9, 141.4, 152.6, 170.4. νmax/cm 1774, 1608,
1
463, 1102, 945, 749. (Found C 83.53, H 5.56%. C21H16O2
IR spectra were recorded on a Testscan Shimadzu FTIR 8000
1
13
requires C 83.98, H 5.37%.)
2-Benzoylphenyl)(2,5-dimethylphenyl)methanone 3a2: col-
orless solid, mp 396–398 K. δH 2.06 (s, 3H), 2.22 (s, 3H), 6.94
s, 1H), 7.09 (t, J 7.5, 2H), 7.21–7.35 (m, 5H), 7.45 (d, J 4,
in KBr plates. H NMR (300 MHz) and C NMR (75 MHz)
spectra were performed on a Varian Mercury VS 300 in CDCl3.
Elemental analyses were carried out on aVarioEL III instrument.
Melting points were determined on a VEB Wagetechnik Rapio
PHMK05 instrument and are uncorrected.
All experiments were operated according to the following
general procedure: aryl acids (10 mmol), HPAs (1–3 mmol), and
the arene solvent (30 mL) were charged into a 50 mL flask with a
water segregator and reflux condensor. The mixture was heated
to reflux and dehydrated until no further water was separated
(
(
1
2
1
1
H), 7.52 (t, J 7.2, 1H), 7.66 (t, J 7.2, 1H), 7.93 (d, J 4, 1H). δC
1.3, 29.7, 125.1, 125.5, 126.3, 128.1, 129.0, 129.4, 129.9, 133.1,
34.0, 134.7, 136.2, 137.2, 142.3, 152.8, 170.4. νmax/cm 1770,
598, 1465, 1286, 1106, 969, 751. (Found C 83.67, H 5.82%.
−
1
C22H18O2 requires C 84.05, H 5.77%.)
(
∼6–12 h). The reaction was then cooled, filtered, and washed
Acknowledgment
withCHCl3 andethylacetate.Theorganicphaseswerecombined
and then eluted through a pad of celite. The product was purified
by recrystallization or column chromatography on SiO2.
Anthraquinone 2a: light-yellow solid, mp 554–557 K. δH 7.81
The authors are grateful the National Natural Science Foundation of China
(
20372053 and 29972033) for financial support.
−
1
(
t, J 14, 4H), 8.31 (d, J 8, 6H). νmax/cm 1678, 1287, 694.
Anthrone 2b: colourless solid, mp 428–430 K. δH 4.37 (s,
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