Efficient oxidative aromatization of 9,10-dihydroanthracenes with molecular oxygen catalyzed by ruthenium porphyrin complex

Article abstract of DOI:10.1055/s-2003-37531

In the presence of a catalytic amount of a ruthenium porphyrin complex, various 9,10-dihydroanthracene derivatives were aromatized with molecular oxygen to the corresponding anthracenes. It was found that the addition of sulfuric acid accelerated the aromatization at room temperature under atmospheric pressure of oxygen to afford various anthracenes in high yields.

Full text of DOI:10.1055/s-2003-37531

5
76
LETTER
Efficient Oxidative Aromatization of 9,10-Dihydroanthracenes with
Molecular Oxygen Catalyzed by Ruthenium Porphyrin Complex
O
H
xidative Aromati
i
zation
r
of 9,10-d
o
ihydroanthra
t
cenes aka Tanaka, Taketo Ikeno, Tohru Yamada*
Department of Chemistry, Faculty of Science and Technology, Keio University, Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan
Fax +81(45)5661716; E-mail: yamada@chem.keio.ac.jp
Received 24 December 2002
Table 1 Additives and Solvents for Aromatization Catalyzed by
Abstract: In the presence of a catalytic amount of a ruthenium por-
phyrin complex, various 9,10-dihydroanthracene derivatives were
aromatized with molecular oxygen to the corresponding an-
thracenes. It was found that the addition of sulfuric acid accelerated
the aromatization at room temperature under atmospheric pressure
of oxygen to afford various anthracenes in high yields.
Ruthenium-porphyrina
Ru (tmp)(O)2 (cat.)
O2 (1 atm)
Additive
Solvent
1a
1b
Key words: catalysis, complexes, oxidations, oxygen, ruthenium
Entrya,g
Additive
–
Yield (%)b
1
21
The polyacene family has been attracting much attention
as organic conductive materials. As examples, it was re-
cently reported that the pentacene derivatives were ap-
2c
49d
–
3
4
5
6
7
8f
9
Hcle
9
1
plied to organic transistors and semiconductors. Among
AcOH
TsOH
H SO
14
the various preparative methods for the synthesis of these
polyacene derivatives, the aromatization reaction of the
corresponding hydroaromatic compounds is one of the
most reliable procedures, including the Pd/C catalyzed de-
32
2 (without catalyst)
2
4
4
4
2
hydrogenative aromatization of dihydropentacene, the
H SO
98
2
3
oxidative aromatization by chloranil or DDQ, the aroma-
4
H
2
SO
96 (1 atm of air)
tization using n-BuLi/TMEDA/MeI, etc. As these syn-
thetic procedures required a stoichiometric amount of the
oxidation reagents or relatively drastic reaction condi-
tions, an alternative efficient procedure such as catalytic
and aerobic oxidation systems have been expected. In this
paper, we describe the successful application of the effec-
tive oxidative aromatization with molecular oxygen to
various 9,10-dihydroanthracene derivatives to afford the
corresponding anthracenes in high yields.
THF
trace
66
1
0
1
2
hexane
PhCl
1
85
1
CHCl3
94
a
The reaction was carried out using 0.14 mmol of substrate, 5 mol%
of Ru(tmp)(O) , 1 equiv of additive, and 14 mL of benzene under 1
atm of oxygen at 50 °C for 5 h.
Isolated yield.
2
During the course of our research on nitrous oxide oxida-
tion catalyzed by ruthenium porphyrin complexes,5 it
was found that 9,10-dihydroanthracene was converted to
the corresponding aromatized anthracene and that the ad-
dition of a catalytic amount of sulfuric acid accelerated
the reaction and improve the selectivity for aromatiza-
b
,6
c
1
0 mol% of Ru(tmp)(O) , and refluxed for 7 h.
2
d
e
f
Anthraquinone was also obtained in 49% yield.
HCl/Et O solution was used.
The reaction was performed for 11 h.
The reaction was carried out using 0.14 mmol of substrate, 5 mol%
of Ru(tmp)(O) , 1 equiv of sulfuric acid, and 14 mL of solvent under
2
g
7
2
tion. The effect of the additives during the oxidative aro-
1
atm of oxygen at 50 °C for 5 h.
matization with molecular oxygen was then examined
(
Table 1). The 9,10-dihydroanthracene (1a) was subject-
in 49% yield (entry 2). When hydrochloric acid (entry 3)
and acetic acid (entry 4) were added to the reaction sys-
tem, no improvement in the yield was observed. The ad-
dition of p-toluenesulfonic acid somewhat accelerated the
reaction and the product yield was slightly improved (en-
try 5). Finally, it was found that sulfuric acid is an effec-
tive additive for the oxidative aromatization of 9,10-
dihydroanthracene. It was confirmed that the aromatiza-
tion reaction did not proceed with sulfuric acid itself in the
absence of the ruthenium complex (entry 6). By adding 1
equivalent of H SO vs. the substrate, the aromatized
ed to the aerobic oxidation without any additives cata-
lyzed by the dioxoruthenium complex to afford the
corresponding aromatized product in 21% yield (entry 1).
Although an increase in the loading amount of the catalyst
and higher reaction temperature improved the product
yield to 49%, anthraquinone was obtained as a by-product
Synlett 2003, No. 4, Print: 12 03 2003.
Art Id.1437-2096,E;2003,0,04,0576,0578,ftx,en;U14602ST.pdf.
©
Georg Thieme Verlag Stuttgart · New York
2
4
ISSN 0936-5214

LETTER
Oxidative Aromatization of 9,10-Dihydroanthracenes
577
product was selectively obtained in 98% yield (entry 7). It Table 3 Ruthenium Catalyzed Aromatization of Various 9,10-
a
should be pointed out here that the present reaction pro- Dihydroanthracene Derivatives
ceeded at 50 °C whereas a high temperature (120 °C) was
En- Substrate
try
Temp. (°C)/ Product
Time (h)
Yield
(%)
required in a similar reaction with nitrous oxide as the ox-
b
7
idant. Even under atmospheric pressure in air, the present
1
2
r.t./31
r.t./61
97c
reaction proceeded at 50 °C to afford the aromatized prod-
uct in 96% yield (entry 8). The effect of solvents was then
examined. When the reaction was performed in tetrahy-
drofuran, the reaction hardly proceeded (entry 9). Al-
though in hexane (entry 10), chlorobenzene (entry 11),
and chloroform (entry 12), anthracene was obtained in
moderate-to-high yields, it was found that benzene was
the most suitable solvent for the aerobic oxidative aroma-
tization of the 9,10-dihydroanthracene (1a).
90c
Et
Et
quant.c
3
r.t./5
4
Et
Et
Et
50–60/46
Et
Et
Et
53d
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
The reaction temperature and the loading amount of cata-
lyst were then investigated in order to determine milder
reaction conditions (Table 2). Although the reaction time
was slightly longer, the loading amount of the dioxoruthe-
nium complex catalyst could be reduced to 0.5 mol% and
maintain the product yield (entries 1 and 2). When the re-
action carried out at room temperature using 5 mol% of
the catalyst, anthracene was obtained in high yield in 79
hours (entry 3). When using only 0.5 mol% of the catalyst
at the same temperature, the reaction hardly proceeded
5
6
50/29
50/28
82e
85f
Et
Et
7
8
a
Ph
50/12
50/27
Ph
quant.c
70g
(
entry 4). By using ca. 10 equivalents of sulfuric acid vs.
the substrate, however, 9,10-dihydroanthracene was
quantitatively converted to the corresponding anthracene
even at room temperature under a 1 atmospheric pressure
of oxygen (entry 5).
The reaction was carried out using 0.06–0.24 mmol of substrate, 0.5
mol% of Ru(tmp)(O) , 10 equiv of H SO , and 14 mL of benzene un-
2
2
4
der 1 atm of oxygen.
b
Isolated yield.
The present oxidative aromatization reaction was success-
fully applied to various 9,10-dihydroanthracene deriva-
c
1
00% conversion.
d
e
f
8
8
8
4% conversion.
9% conversion.
7% conversion.
8
tives (Table 3). The alkyl substituted substrates, such as
2
-methyl-, 2-ethyl-, and 2,3-dimethyl-9,10-dihydroan-
g
thracenes, were smoothly converted to their correspond-
ing aromatized products at room temperature. The
oxidized products at the benzylic position were not ob-
97% conversion.
served for these substrates (entries 1–3). When cause of the bulkiness to afford the corresponding an-
,2,3,4,5,6,7,8-octaethyl-9,10-dihydroantharacene was thracene in moderate yield at 50 °C (entry 4). Although
1
reacted, the aromatization proceeded slowly probably be- the aromatization reactions of the 9-substituted substrates,
such as 9-methyl-, 9-ethyl-, and 9-phenyl-9,10-dihy-
droanthracenes, were retarded at room temperature, at 50
Table 2 Loading Amount of Catalyst and Sulfuric Acida
°
C they were easily aromatized to afford the correspond-
Temp. (°C)/ Yield (%)b
Time (h)
ing products (entries 5–7). Under the same conditions,
1,2-dimethyl-3,4-dihydronaphthalene could be aroma-
tized in 70% yield (entry 8).
Entry
Amount of
Catalyst
H SO (equiv) (mol%)
2
4
1
2
3
4
1
1.5
0.5
5.0
0.5
0.5
50/12
50/26
r.t./79
r.t./82
r.t./83
93
It is noted that an efficient procedure for the catalytic and
oxidative aromatization with molecular oxygen of various
1
1
92
9
,10-dihydroanthracenes was realized by using a catalytic
86
amount of the ruthenium porphyrin complex and by the
addition of sulfuric acid. Although several additives, such
1
16
9
10
11
as N-methylimidazole, HCl/HBr, or carboxylic acid
5
10
quant.
were reported for the combined use of an oxo-metal catal-
yst, the detailed investigation on the additive effects in the
a
The reaction was carried out using 0.14 mmol of substrate in 14 mL
of benzene under 1 atm of oxygen.
12
present reaction is now underway.
b
Isolated yield.
Synlett 2003, No. 4, 576–578 ISSN 0936-5214 © Thieme Stuttgart · New York

5
78
H. Tanaka et al.
LETTER
References
(8) Typical procedure: To a suspension of sulfuric acid (136
mg, 1.4 mmol) in benzene (1 mL) was added a benzene (6
(
1) (a) Afzali, A.; Dimitrakopoulos, C. D.; Breen, T. L. J. Am.
Chem. Soc. 2002, 124, 8812. (b) Dimitrakopoulos, C. D.;
Purushothaman, S.; Kymissis, J.; Callegari, A.; Shaw, J. M.
Science 1999, 283, 822. (c) Nelson, S. F.; Lin, Y.-Y.;
Gundlach, D. J.; Jackson, T. N. Appl. Phys. Chem. 1998, 72,
mL) solution of Ru(tmp)(O) (0.6 mg, 0.007 mmol) under an
2
oxygen atmosphere. A benzene (7 mL) solution of 9,10-
dihydroanthracene (25 mg, 0.14 mmol) was then added and
the mixture was stirred for 83 hours at room temperature.
The reaction mixture was directly evaporated and purified
by silica gel column chromatography (hexane) to give the
aromatized anthracene in quantitative yield.
1854.
(
(
2) Luo, J.; Hart, H. J. Org. Chem. 1987, 52, 4833.
3) (a) Takahashi, T.; Kitamura, M.; Shen, B.; Nakajima, K. J.
Am. Chem. Soc. 2000, 122, 12876. (b) Harwig, P. T.;
Müllen, K. Adv. Mater. 1999, 11, 480.
(9) Imagawa, K.; Nagata, T.; Yamada, T.; Mukaiyama, T.
Chem. Lett. 1994, 527.
(
(
(
10) Ohtake, H.; Higuchi, T.; Hirobe, M. J. Am. Chem. Soc. 1992,
14, 10660.
(
4) (a) Kitamura, M.; Shen, B.; Liu, Y.; Zheng, H.; Takahashi,
T. Chem. Lett. 2001, 646. (b) Harvey, R. G.; Cho, H. J. Am.
Chem. Soc. 1974, 96, 2434. (c) Fu, P. P.; Harvey, R. G.
Chem. Rev. 1978, 78, 317.
1
11) Banfi, S.; Maiocchi, A.; Moggi, A.; Montanari, F.; Quici, S.
J. Chem. Soc., Chem. Commun. 1990, 1794.
12) By FAB-Mass measurement of the
(5) (a) Groves, J. T.; Roman, J. S. J. Am. Chem. Soc. 1995, 117,
dioxoruthenium(VI)porphyrin complex and the mixture of
the complex and sulfuric acid, the peak at MW 783, assigned
as tetramesitylporphyrin ligand, was not observed. Several
ruthenium salts, such as 5 mol% of ruthenium(III) chloride,
ruthenium(II) tris(triphenylphosphine)dichloride, or
tetrapropylammonium perruthenate were employed for the
reaction at 50 °C for 5 hours in benzene in the presence of
sulfuric acid (the same conditions as entry 7 in Table 1), and
the aromatized product was obtained in 1%, 14%, and 1%
yields, respectively. Therefore, it is reasonable to consider
that the ruthenium salt released from porphyrin complex
could scarcely contribute to the present aromatization
reaction.
5594. (b) Groves, J. T.; Quinn, R. J. J. Am. Chem. Soc. 1985,
107, 5790.
(6) (a) Yamada, T.; Hashimoto, K.; Kitaichi, Y.; Suzuki, K.;
Ikeno, T. Chem. Lett. 2001, 268. (b) Hashimoto, K.;
Kitaichi, Y.; Tanaka, H.; Ikeno, T.; Yamada, T. Chem. Lett.
2001, 922.
(
7) Hashimoto, K.; Tanaka, H.; Ikeno, T.; Yamada, T. Chem.
Lett. 2002, 582.
Synlett 2003, No. 4, 576–578 ISSN 0936-5214 © Thieme Stuttgart · New York