Electrophilic aromatic addition reaction (AdEAr) to anthracene

Article abstract of DOI:10.1016/j.tet.2008.04.032

After finding in a previous study that naphthalene and quinoline can react via electrophilic aromatic addition reaction (Ad_EAr), we applied this to anthracene. When anthracene was reacted with bromine in methanol in the presence of NaHCO₃ and pyridine, 9,10-dihydro-9,10-dimethoxyanthracene (2) was obtained in 82% yield in the absence of substitution products or oxidative demethylation products like anthraquinone. The same reaction in ethanol produced 9,10-diethoxy-9,10-dihydroanthracene (9) in much lower yield (45%). In addition, we investigated the reactivity of addition product 2. Treatment of 2 with DDQ in benzene at 65 °C for 12 h produced 9,10-dimethoxyanthracene (3) in 62% yield, and 2 was rapidly transformed to 9-methoxyanthracene (4) in methanolic NaOH in 10 min. Moreover, the acid-catalyzed aromatization of 2 in 1-propanol at 75 °C for 10 min gave 9-n-propoxyanthracene (8) in 65% yield.

Full text of DOI:10.1016/j.tet.2008.04.032

Tetrahedron 64 (2008) 5666–5671
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Electrophilic aromatic addition reaction (AdEAr) to anthracene
*
Keun Sam Jang, Hee Young Shin, Dae Yoon Chi
Department of Chemistry, Inha University, 253 Yonghyungdong Namgu, Inchon 402-751, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
After finding in a previous study that naphthalene and quinoline can react via electrophilic aromatic
addition reaction (AdEAr), we applied this to anthracene. When anthracene was reacted with bromine in
methanol in the presence of NaHCO3 and pyridine, 9,10-dihydro-9,10-dimethoxyanthracene (2) was
obtained in 82% yield in the absence of substitution products or oxidative demethylation products like
anthraquinone. The same reaction in ethanol produced 9,10-diethoxy-9,10-dihydroanthracene (9) in
much lower yield (45%). In addition, we investigated the reactivity of addition product 2. Treatment of 2
with DDQ in benzene at 65 ꢀC for 12 h produced 9,10-dimethoxyanthracene (3) in 62% yield, and 2 was
rapidly transformed to 9-methoxyanthracene (4) in methanolic NaOH in 10 min. Moreover, the acid-
catalyzed aromatization of 2 in 1-propanol at 75 ꢀC for 10 min gave 9-n-propoxyanthracene (8) in 65%
yield.
Received 5 April 2008
Accepted 9 April 2008
Available online 11 April 2008
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
applied to optical, electronic, and magnetic switches, and in-
corporated into polymers, films, and crystals.10 In biological sys-
During electrophilic aromatic substitution,
s
-complex formation
tems, anthracene based compounds are also useful for probing DNA
cleavage.11 Recently, several epoxy-anthracenes and their de-
rivatives have been synthesized by bromination and sequential
base treatment.12
Generally speaking, the central B-ring of anthracene is consid-
erably more reactive than the other two rings. Moreover, s-com-
plex at the C9-position of anthracene could be stabilized by the two
benzene rings, which might prevent rearomatization.1a However,
no straightforward efficient method of preparing symmetrical
9,10-dialkoxy-9,10-dihydroanthracene with a trans stereochemis-
try has been reported in the literature. Here, we describe the AdEAr
chemistry of anthracene, and of the related compounds, alkox-
yanthracene, alkylanthracene, and phenanthrene. In addition, the
reactivities of the AdEAr adducts were investigated to determine
whether they are likely to have applicable utility.
is generally the rate determining step as compared with aromati-
zation step by deprotonation.1
s
-Complexes may proceed via two
compatible pathways, i.e., rearomatization1 or nucleophilic addi-
tion.2 Recently, the transition-metal catalyzed ring openings of
oxabenzonorbornadienes3 and azabenzonorbornadienes4 by vari-
ous nucleophiles have provided dihydronaphthalene derivatives,
consequently constructing multiple stereocenters. During electro-
philic aromatic substitution, if addition of various nucleophile to
s
-complex are controlled, it might be possible to generate addition
products with two stereocenters. In particular, dihydropolycyclic
aromatic hydrocarbon skeletons have been found in a wide range of
natural compounds and exhibit a plethora of biological activities.5
Moreover, when the rearomatization of a
s-complex by deproto-
nation is blocked, ipso attack at a pre-substituted position provides
the possibility of nucleophile addition in benzenoid systems.6
Recently, we described the isolation of addition products in fused
systems.7 The identification of one unusual adduct by X-ray crys-
tallography suggested that electrophilic aromatic addition (AdEAr)
reaction may provide a useful method of introducing functionali-
zation into fused aromatic systems.
2. Results and discussion
2.1. AdEAr reaction of anthracene in methanol
AdEAr reaction of anthracene (1) under previously reported
optimized basic methanolic conditions,7 produced 9,10-dihydro-
9,10-dimethoxyanthracene (2), with a trans stereochemistry in high
yield (82%, Table 1, entry 2). Reaction of anthracene with 3 equiv of
bromine in methanolic NaHCO3 (2.0 equiv) solution in the presence
of pyridine at rt provided a new spot by TLC. Initially, we thought
that it was 9,10-anthraquinone, because 9,10-dimethoxyanthracene
can be oxidized to anthraquinone by either direct oxidation or
Anthracene and its derivatives have been extensively in-
vestigated in many fields, e.g., material chemistry,8 high fluores-
cence, thermochromic or photochromic fields,9 and they have been
* Corresponding author. Tel.: þ82 505 860 7686; fax: þ82 32 867 5604.
E-mail address: dychi@inha.ac.kr (D.Y. Chi).
0040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.04.032

K.S. Jang et al. / Tetrahedron 64 (2008) 5666–5671
5667
Table 1
Effect of amine base on the rate of AdEAr reaction of anthracenea
Entry
Amine base
Yield of productb (%)
1
2
3
4
5
6
1
2
3
4
5
6
7c
Urea
d
d
24
8
5
10
5
64
82
d
d
54
d
d
2
1
4
8
2
7
9
3
Trace
Trace
Trace
Trace
Trace
Trace
Trace
d
d
5
4
d
Pyridine
Imidazole
DMAP
DABCO
DBU
1
10
6
10
11
7
7
43
None
a
All reactions were carried out on the 2.0 mmol of anthracene (1) reaction scale using 3.0 equiv of bromine and 2.0 equiv of NaHCO3 with 6.0 mL of MeOH at rt for 15 min.
Isolated yield.
10-Methoxy-10H-anthracene-9-one (7) was also obtained in 20% isolated yield.
b
c
demethylation–oxidation by NBS under acid conditions.13 However,
steric hindrance around their nucleophilic nitrogens, such as DMAP
and DBU (entries 4 and 6), produced no conversion of 2 under the
same conditions. However, bromination with DBU in acetic acid
improved the yield of 5.16 9,10-Dibromoanthracene was always
produced only in trace amounts regardless the reaction conditions.
When the moderately hindered weak base DABCO was used,
compound 2 was obtained in 54% yield. Interestingly, when we
used highly basic amines, such as imidazole, DMAP, or DBU (entries
3, 4, and 6), we obtained the oxidatively demethylated compound,
anthraquinone (6) instead of 2. In terms of the AdEAr reaction of
anthracene without pyridine, anthraquinone (6) was obtained
in 43% yield with 10-methoxy-10H-anthracen-9-one (7, 20%) as
a by-product (entry 7).
we obtained AdEAr adduct 9,10-dihydro-9,10-dimethoxyan-
thracene (2) instead of anthraquinone. It was reported that an iso-
lated addition adduct of anthracene in the nitration of anthracene
could be proceeded either by elimination (giving an anthracene
ring) or by remaining adduct intermediate (stabilization by two
benzenoid rings).1a This is a result of the relatively close balance in
resonance stabilization of two different routes. During the nitration
of anthracene, the fact that addition takes place in the presence
of HCl to produce 9-chloro-9,10-dihydro-10-nitroanthracene could
provide an example of an aromatic addition reaction.14 This result
means that it could be possible to control the formation of either the
adduct or the substitution product by changing the reaction
condition.
In this study, we were also able to selectively rearomatize AdEAr
adduct using various methods, i.e., oxidation using DDQ, basic-
catalyzed elimination in MeOH, acid-catalyzed transetherification
using 1-propanol, and introduction of an additional mechanism on
the electrophilic substitution reaction. The 1H NMR spectrum of the
isolated new product clearly showed symmetrical peaks at
3.40 ppm (s, 6H), 5.40 ppm (s, 2H) and 7.24–7.40 ppm (m, 4H),
7.55–7.62 ppm (m, 4H). We fully identified this TLC separated ad-
duct as 9,10-dihydro-9,10-dimethoxyanthracene (2), which was
formed as a result of AdEAr. To the best of our knowledge, this is the
first reported isolation of a dimethoxy addition, which does not
contain bromine, and which has a trans stereochemistry. Rindone
and Scolastico reported that the oxidation of anthracene using lead
tetraacetate Pb(OAc)4 gave a mixture of cis- and trans-9,10-dihydro-
9,10-dimethoxyanthracene.15 Based on their 1H NMR analysis, the
We also examined the effects of bromine sources and inorganic
bases on the AdEAr reaction of anthracene, as shown in Table 2. To
determine the effects of inorganic bases on the AdEAr reaction of
Table 2
AdEAr reactions of anthracene using different conditionsa
Entry
Condition
Inorganic base
Yield of productb (%)
Others
1
2
6
1
2
3
4
5
6
7
8
9
10
Br2/Py
Br2/Py
Br2/Py
Br2/Py
Br2/Py
Br2/Py
Br2e/Py
Br2f/Py
Py$HBr3
NBS/Py
t-BuOK
Cs2CO3
K2CO3
23
22
d
27
23
d
d
19
5
d
49
25
d
d
59
52
27
d
d
9
3 (5), 4 (38)
d
protons of the cis and trans compounds produced peaks at
d 3.29
d
d
14
d
d
d
d
27
d
(s), 5.25 (s) and 3.39 (s), 5.38 (s) ppm, respectively. As the peaks of 2
prepared by AdEAr reaction are at 3.42 (s) and 5.40 (s), respectively,
compound 2 has a trans stereochemistry. Small amounts of
substitution compounds, such as 9,10-dimethoxyanthracene (3)
and 9-methoxyanthracene (4) were also isolated. In addition, the
brominated compound, 9,10-dibromoanthracene (5), was present
in trace amounts.
d
NaOH
3 (20), 4 (16)
3 (4)
d
NaOMec
d
NaHCO3
NaHCO3
NaHCO3
NaHCO3
NaHCO3
d
4 (6)
3 (11), 4 (6)
d
4 (48)g
To optimize the AdEAr reaction of anthracene, we checked the
effects of various amine bases, as shown in Table 1. When bromine
was added dropwise in the presence of pyridine (entry 2), the
yellow color of reaction mixture became red, but when bromine
was added in DMAP, the yellow color remained (entry 4). Based on
the results shown in Table 1, pyridine was the optimal base for the
AdEAr reaction of anthracene to produce adduct 2 in high yield
(entry 2). On the other hand, amines with high basicity and low
a
All reactions were carried out on the 2.0 mmol of anthracene (1) reaction scale
using 3.0 equiv of bromine and 2.0 equiv of NaHCO3 with 6.0 mL of MeOH at rt for
15 min.
b
Isolated yield.
Used in 0.5 M methanol solution.
NaHCO3 was present at 3.0 equiv.
Bromine was used at 2.0 equiv and acetone was used as a solvent for work up.
c
d
e
f
Bromine was used at 1.0 equiv and acetone was used as a solvent for work up.
g
Yields were determined based on 1H NMR findings.

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K.S. Jang et al. / Tetrahedron 64 (2008) 5666–5671
anthracene, we used a range of weak (e.g., alkali metal carbonates)
to strong bases. AdEAr reaction of 1 under various conditions in the
presence of NaHCO3 gave 2 in 59%, 52%, and 82% yields (entries 6
and 7 in Table 2 and entry 2 in Table 1), respectively. On the other
hand, AdEAr reaction of 1 in the presence of strong bases, such as
potassium tert-butoxide, sodium hydroxide, or sodium methoxide
resulted in little or no adduct 2 formation (entries 1, 4, and 5).
Reactions in the presence of alkali metal carbonates, including
cesium and potassium carbonates, using the same procedure pro-
duced 2 (entries 2 and 3). Thus, it appears likely that the adduct 2
can be preferentially obtained by controlling the amount of weak
base used.
elimination reaction in strong basic methanolic solution at rt for
10 min. In addition, an interesting transetherification occurred
when product 2 was reacted with 1-propanol under acid-catalyzed
(H2SO4) conditions at 75 ꢀC for 10 min. Moreover, the trans-
etherification product, 9-n-propoxyanthracene (8, 65%), was
obtained with 9-methoxyanthracene (4, 15%) and anthracene (1,
trace amount) as minor products.
When EtOH was used instead of MeOH using the same reaction
conditions, a new adduct 9,10-diethoxy-9,10-dihydro-anthracene
(9) was obtained as a white solid with trans stereochemistry. This
product did not contain bromine as was expected, but its yield was
lower than that in methanol (Scheme 2).
AdEAr reaction was also carried out using other brominating
agents, namely, pyridinium hydrobromide perbromide (Py$HBr3)17
and NBS (entries 10 and 11). We considered that Py$HBr3 might be a
more convenient brominating agent, but it was ineffective (entry 9).
When NBS was used, 9-methoxyanthracene (4) was only obtained
in 48% yield. It has been reported that bromination of anthracene
with NBS in CCl4 afforded 9-bromoanthracene in good yield.18 Thus,
AdEAr reaction in the presence of NBS under basic methanolic
conditions proceeds in a different manner from bromination with
NBS in CCl4. These results indicate that the base and the bromina-
tion reagent are important for obtaining the addition product in
high yield. When 3 equiv of NaHCO3 were used, the yield of addition
product 2 decreased to 59% (entry 6). Also when we reduced the
amount of bromine to 2.0 and 1.0 equiv, we obtained 2 in lower
yields of 52 and 27%, respectively (entries 7 and 8).
Scheme 2. AdEAr reaction to anthracene (1) in EtOH.
2.3. AdEAr reaction of other anthracene derivatives
As shown in Table 3, AdEAr reactions of 9-methoxy-, 9,10-
dimethoxy-2-ethyl-, 9-cyano-, 2-methyl-, and 9-methylanthracene
derivatives were carried out at the same reaction conditions.
9-Methoxyanthracene (4) readily underwent AdEAr reaction to
provide the new addition product 9,10-dihydro-9,9,10-trimethox-
yanthracene (10) in high yield (92%, entry 1). Moreover, the dime-
thoxy derivative, 9,10-dimethoxy-2-ethylanthracene (11), produced
the new addition product 2-ethyl-9,9,10,10-tetramethoxyan-
thracene (12) in 70% of yield, which was formed via the same
mechanism as anthracene (1) and 9-methoxyanthracene (4). AdEAr
reactions of 9-methylanthracene (14) and 2-methylanthracene (16)
also produced newadducts in highyields (entries 4 and 5). However,
in the case of 9-cyanoanthracene (13), which has a strong electron
withdrawing group, AdEAr reaction did not occur (entry 3). When
AdEAr reaction was applied to phenanthrene (another tricyclic ar-
omatic compound, entry 6), we obtained a different addition prod-
uct, 9-bromo-10-methoxy-9,10-dihydrophenanthrene (19). We
attribute the formation of different addition product to the different
reactivities of phenanthrene and anthracene.
The selection of the base is a critical factor in this reaction. To
find out the key role of pyridine, we have performed the experi-
ments as described in Tables 1 and 2. At this moment, we cannot
explain the role of pyridine.
2.2. Reactions of AdEAr product 2
During AdEAr reaction of anthracene in methanol, substituted
products, such as 3 and 4 were isolated (Scheme 1). The formation
of these by-products was thought to provide useful information on
the mechanism of AdEAr reaction and on the applicabilities of
AdEAr product 2.
2.4. Proposed mechanism
A suggested mechanism of the AdEAr reaction of anthracene (1)
is shown in Scheme 3. First, bromination at the 9-position of an-
thracene occurs, and the brominated cation formed is stabilized by
methoxide addition. The finding that 9,10-dibromoanthracene (5)
was obtained in trace amounts suggests that methoxide reacts
more rapidly than bromide at the 10-position of the brominated
cation. Thus, attack by methoxide may be an important step in the
formation of 9,10-dihydro-9,10-dimethoxyanthracene (2).
Methoxide then attacks the bromo group at the benzylic position
of the 9-bromo-9,10-dihydro-10-methoxyanthracene intermediate
either in an SN1 or SN2 manner to produce 9,10-dihydro-9,10-
dimethoxyanthracene (2). 9-Methoxyanthracene (4) was obtained
as a by-product via the dehydrobromination of 9-bromo-9,10-
dihydro-10-methoxyanthracene intermediate. We believe that
9,10-dimethoxyanthracene (3) might be formed by oxidation in air.
Further bromination and methoxide addition to 9-methoxyan-
thracene (4) might have produced the new adduct 9,10-dihydro-
9,9,10-trimethoxyanthracene (10) via a repetition of the same
process.
Scheme 1. Aromatization of the AdEAr adduct under various condition.
Product 2 was oxidized by DDQ to produce the rearomatized
9,10-dimethoxyanthracene (3) in 62% yield. Product
2 was
also selectively rearomatized to 9-methoxyanthracene (4) by an

K.S. Jang et al. / Tetrahedron 64 (2008) 5666–5671
5669
Table 3
3. Conclusion
AdEAr reaction of various aromatic compounds under methanolic NaHCO3
conditionsa
The present study demonstrates that AdEAr reaction could pro-
vide a useful means for preparing various anthracene derivatives.
Treatment of anthracene with bromine in alcoholic (MeOH, EtOH)–
NaHCO3 afforded the corresponding addition product 9,10-di-
alkoxy-9,10-dihydroanthracene in excellent yield at high purity
with a trans stereochemistry. The selective rearomatizations of
the addition product 2 to 9,10-dimethoxyanthracene (3) and 9-
methoxyanthracene (4) were achieved by DDQ oxidation in the
former and by methanol elimination under basic conditions in the
latter. Transetherification of 2 with 1-propanol underacid-catalyzed
(H2SO4) conditions formed 9-n-propoxyanthracene (8) in moderate
yield (65%). Further studies on the use of transetherification to make
9-anthryl ethers under acid conditions are in progress.
Entry
Aromatics
Product
Yieldb (%)
1
92
2
70
4. Experimental
3
4
d
No Rx
4.1. Typical procedure used for electrophilic aromatic
addition (AdEAr) reaction
Sodium bicarbonate (336 mg, 4.0 mmol) was added to solution
of anthracene (356 mg, 2.0 mmol) in MeOH (6.0 mL) with stirring
79
for 3 min at rt. Pyridine (165
later a solution of Br2 (307
m
L, 2.0 mmol) was added, and 2 min
mL, 6.0 mmol) in MeOH (1.5 mL) was
added dropwise. The reaction mixture was then stirred at rt for
10 min. Water (3.0 mL) was then added, the reaction was stirred for
another 15 min, and then H2O (30 mL) and Na2SO3 (0.32 g) were
added. The mixture was extracted with CH2Cl2 (20 mLꢁ2) and the
combined organic layers were washed with brine, dried (Na2SO4),
and concentrated in vacuo. The purification of the residue by flash
column chromatography (2% EtOAc/hexane) yielded trans-9,10-
dihydro-9,10-dimethoxyanthracene (2, 265 mg, 82%) as a colorless
5
77
22
liquid: 1H NMR (400 MHz, CDCl3)
d
3.42 (s, 6H), 5.40 (s, 2H), 7.24–
56.6,
7.40 (m, 4H), 7.55–7.62 (m, 4H); 13C NMR (100 MHz, CDCl3)
d
6
77.9, 126.8, 127.5, 137.2; MS (EI) 240 (Mþ), 225, 208 (100), 193, 178,
165, 152, 151, 139, 104. HRMS (EI) calcd for C16H16O2 (Mþ) 240.1150,
found 240.1147.
a
All reactions were carried out using 2.0 mmol of each material under the same
conditions.
4.2. 9,10-Dimethoxyanthracene (3)
b
Isolated yield.
Yellow solid; mp 196.5–196.6 ꢀC; 1H NMR (200 MHz, CDCl3)
d
4.13 (s, 6H), 7.48–7.53 (m, 4H), 8.28–8.33 (m, 4H); 13C NMR
Scheme 3. Suggested mechanism of AEAr reaction of anthracene.

5670
K.S. Jang et al. / Tetrahedron 64 (2008) 5666–5671
(100 MHz, CDCl3)
d
63.2,122.5,124.8,125.3,148.4; MS (EI) 238 (Mþ),
4.8. 9,10-Dihydro-9,9,10-trimethoxyanthracene (10)
223 (100), 208, 180, 152, 125, 111. HRMS (EI) calcd for C16H14O2 (Mþ)
238.0994, found 238.1000. Registry No. 2395-97-3. Procedure for the
DDQ oxidation of trans-9,10-dihydro-9,10-dimethoxyanthracene:
DDQ (340 mg, 1.5 mmol) was added to a solution of trans-9,10-
dihydro-9,10-dimethoxyanthracene (120 mg, 0.5 mmol) in benzene
(5 mL), and the mixture was heated at 65 ꢀC for 12 h. The mixture
obtained was concentrated and filtered to remove insoluble mate-
rial, the filtrate was extracted with EtOAc (10 mLꢁ3). Combined
organic layers were washed with brine, dried (Na2SO4), and con-
centrated in vacuo. Purification of the residue by flash column
chromatography (10% EtOAc/hexane) yielded 9,10-dimethoxyan-
thracene (3, 74 mg, 62%) as a yellow solid.
Pale yellow solid; mp 45.1–45.2 ꢀC; 1H NMR (400 MHz, CDCl3)
d
2.92 (s, 3H), 3.11 (s, 3H), 3.17 (s, 3H), 5.50 (s,1H), 7.45–7.47 (m, 4H),
7.67–7.69 (m, 2H), 7.77–7.79 (m, 2H); 13C NMR (100 MHz, CDCl3)
d
51.5, 52.2, 53.5, 74.0, 98.7 126.8, 127.4, 128.0, 128.8, 134.7, 137.4;
MS (EI) 269 (Mþ), 255, 239, 238, 208, 193 (100), 180, 165, 152, 139,
104. HRMS (EI) calcd for C17H18O3 (Mþ) 270.1256, found 270.1253.
4.9. 2-Ethyl-9,9,10,10-tetramethoxyanthracene (12)
White solid; mp 48.3–48.5 ꢀC; 1H NMR (400 MHz, CDCl3)
d 1.32
(t, J¼7.6 Hz, 3H), 2.77 (q, J¼7.6 Hz, 2H), 2.96 (s, 12H), 7.37 (dd, J¼8.4,
1.2 Hz, 1H), 7.51–7.54 (m, 2H), 7.63 (s, 1H), 7.71 (d, J¼8.0 Hz, 1H),
4.3. 9-Methoxyanthracene (4)
7.79–7.83 (m, 2H); 13C NMR (100 MHz, CDCl3)
d 47.7, 56.9, 81.4,
124.3, 124.5, 127.9, 128.4, 129.8, 129.9, 131.0, 131.2, 132.3, 132.4,
133.4; MS (EI) 328 (Mþ), 297 (100), 266, 251, 223, 193, 165, 152, 133.
HRMS (EI) calcd for C20H24O4 (Mþ) 328.1675, found 328.1667.
Pale yellow solid; mp 93.2–93.3 ꢀC; 1H NMR (400 MHz, CDCl3)
d
4.16 (s, 3H), 7.46–7.51 (m, 4H), 7.99 (dd, J¼7.2, 2.0 Hz, 2H), 8.23 (s,
1H), 8.30 (d, J¼6.8 Hz, 1H), 8.31 (d, J¼1.6 Hz, 1H); 13C NMR
(100 MHz, CDCl3)
d 63.2, 122.2, 122.3, 124.4, 125.2, 125.5, 128.4,
132.4, 152.2; MS (EI) 208 (Mþ), 193 (100), 176, 165, 163, 139, 115,104.
HRMS (EI) calcd for C15H16O (Mþ) 208.0888, found 208.0890. Reg-
istry No. 2395-96-2. Procedure for the treatment of trans-9,10-dihy-
dro-9,10-dimethoxyanthracene with methanolic NaOH: A solution of
trans-9,10-dihydro-9,10-dimethoxyanthracene (120 mg, 0.5 mmol)
in NaOH methanol solution (5 mL) was stirred at rt for 10 min. The
mixture was then concentrated and the residue extracted with
EtOAc (10 mLꢁ3). Combined organic layers were washed with
brine, dried (Na2SO4), and concentrated in vacuo. Purification of the
residue by flash column chromatography (10% EtOAc/hexane)
yielded 9-methoxyanthracene (4, 75 mg, 72%) as a yellow solid.
4.10. 9,10-Dihydro-9,10-dimethoxy-9-methylanthracene (15)
Yellow solid; mp 55.3–55.6 ꢀC; 1H NMR (400 MHz, CDCl3)
d 1.78
(s, 3H), 2.83 (s, 3H), 3.23 (s, 3H), 5.23 (s, 1H), 7.37–7.39 (t, J¼7.2 Hz,
2H), 7.74 (d, J¼6.4 Hz, 1H), 7.75 (d, J¼0.8 Hz, 1H); 13C NMR
(100 MHz, CDCl3)
d 35.6, 51.8, 54.9, 77.1, 78.0, 126.1, 127.1, 128.7,
129.4, 134.2, 141.7; MS (EI) 254 (Mþ), 239, 222 (100), 207, 193, 178,
165, 152. HRMS (EI) calcd for C17H18O2 (Mþ) 254.1307, found
254.1317.
4.11. 9,10-Dihydro-9,10-dimethoxy-2-methylanthracene (17)
4.4. 9,10-Dibromoanthracene (5)
Colorless oil; 1H NMR (400 MHz, CDCl3)
d 2.38 (s, 3H), 3.35 (s,
3H), 3.41 (s, 3H), 5.35 (s, 1H), 5.38 (s, 1H), 7.15 (d, J¼7.6 Hz, 1H),
Yellow solid; mp 211.8–213.6 ꢀC; 1H NMR (400 MHz, CDCl3)
7.32–7.34 (m, 2H), 7.41 (s, 1H), 7.45 (d, J¼8.0 Hz, 1H), 7.55–7.59 (m,
d
d
7.62–7.65 (m, 4H), 8.58–8.61 (m, 4H); 13C NMR (100 MHz, CDCl3)
2H); 13C NMR (100 MHz, CDCl3)
d 21.2, 56.1, 56.5, 77.7, 126.7, 127.0,
123.5, 127.5, 128.3, 131.1; MS (EI) 338 (Mþ), 336 (Mþ), 334 (Mþ),
295, 279, 240, 208 (100), 178, 165, 152, 139. HRMS (EI) calcd for
14H8Br2 (Mþ) 333.8993, found 333.8989. Registry No. 523-27-3.
127.3, 127.46, 127.50, 128.2, 134.0, 137.23, 137.30, 137.35, 137.5; MS
(EI) 254, 239, 222 (100), 207, 192, 178, 165, 152. HRMS (EI) calcd for
C
C
17H18O2 (Mþ) 254.1307, found 254.1312.
4.5. Anthraquinone (6)
4.12. 9-Bromo-9,10-dihydro-10-methoxyphenanthrene (19)
1H NMR (400 MHz, CDCl3)
d 7.79–7.81 (m, 4H), 8.30–8.33 (m,
d 127.2, 133.5, 134.1, 183.2; MS (EI)
Greenish solid; mp 88.6–88.8 ꢀC; 1H NMR (400 MHz, CDCl3)
4H); 13C NMR (100 MHz, CDCl3)
208 (Mþ, 100), 180, 152, 126. HRMS (EI) calcd for C14H8O2 (Mþ)
208.0524, found 208.0524. Registry No. 84-65-1.
d
3.30 (s, 3H), 4.55 (d, J¼2.4 Hz,1H), 5.45 (d, J¼2.8 Hz,1H), 7.32–7.52
(m, 6H), 7.87–7.91 (m, 2H); 13C NMR (100 MHz, CDCl3)
d
47.7, 56.9,
81.4, 124.3, 124.5, 127.9, 128.4, 129.8, 129.9, 131.0, 131.2, 132.3, 132.4,
133.4; MS (EI) 290 (Mþ), 288 (Mþ), 286 (Mþ), 272, 243, 223, 208,
194, 178 (100), 165, 151, 139, 104. HRMS (EI) calcd for C15H13BrO
(Mþ) 288.0150, found 288.0141.
4.6. 10-Methoxy-10H-anthracen-9-one (7)
Yellow solid; mp 99.6–99.8 ꢀC; 1H NMR (400 MHz, CDCl3)
d 2.93
(s, 3H), 5.81 (s, 1H), 7.52–7.56 (m, 2H), 7.68–7.72 (m, 2H), 7.79–7.81
(m, 2H), 8.33 (dd, J¼8.4, 1.2 Hz, 2H); 13C NMR (100 MHz, CDCl3)
4.13. 9-n-Propoxyanthracene (8)
d
51.5, 72.3, 127.6, 128.7, 128.9, 132.7, 133.7, 140.4, 183.6; MS (EI) 224
(Mþ), 209, 193 (100), 180, 165, 152, 139, 115, 105. HRMS (EI) calcd
for C15H12O2 (Mþ) 224.0837, found 224.0842. Registry No. 14629-
83-5.
A catalytic amount of sulfuric acid (2.0 mL) was added to a solu-
tion of trans-9,10-dihydro-9,10-dimethoxyanthracene (2, 120 mg,
0.5 mmol) in 1-propanol (2.0 mL). The mixture was then heated at
75 ꢀC for 10 min. After cooling to rt, the mixture was extracted with
ethyl acetate (10 mLꢁ3) and water (10 mL). Combined organic
layers were then washed with brine, dried (Na2SO4), and concen-
trated in vacuo. Purification of the residue by flash column
chromatography gave 8 (30% CH2Cl2/hexane) as a white solid: mp
4.7. trans-9,10-Diethoxy-9,10-dihydroanthracene (9)
White solid; mp 46.6–46.9 ꢀC; 1H NMR (200 MHz, CDCl3)
(t, J¼7.0 Hz, 3H), 3.70 (q, J¼7.0 Hz, 4H), 5.49 (s, 2H), 7.31–7.39 (m,
d 1.32
4H), 7.57–7.65 (m, 4H); 13C NMR (50 MHz, CDCl3)
d
15.4, 65.0, 77.0,
75.5–77.6 ꢀC; 1H NMR (400 MHz, CDCl3)
d
1.24 (t, J¼7.4 Hz, 3H),
126.6, 127.4, 138.1; MS (EI) 268 (Mþ), 240, 212 (100), 193, 178, 165,
152, 151, 139, 104. HRMS (EI) calcd for C18H20O2 (Mþ) 248.1463,
found 248.1458.
2.07–2.12 (m, 2H), 4.18 (t, J¼6.8 Hz, 2H), 7.45–7.50 (m, 4H), 7.98–
8.01 (m, 2H), 8.22 (s, 1H), 8.30–8.33 (m, 2H); 13C NMR (100 MHz,
CDCl3) d 10.7, 23.9, 77.6, 121.9, 122.4, 124.7, 125.0, 125.4, 128.4, 132.4,

K.S. Jang et al. / Tetrahedron 64 (2008) 5666–5671
5671
151.4; MS (EI) 236 (Mþ), 194 (100), 165, 139. HRMS (EI) calcd for
17H16O (Mþ) 236.1201, found 236.1204. Registry No. 92830-42-7.
4. Cho, Y. H.; Zunic, V.; Senboku, H.; Olsen, M.; Lautens, M. J. Am. Chem. Soc. 2006,
128, 6837–6846.
C
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Acknowledgements
This work was supported by an Inha University Research Grant
(Inha-2007). High resolution mass spectra were carried out at the
Korea Basic Science Institute (Daegu, Korea).
7. Choi, H. Y.; Srisook, E.; Jang, K. S.; Chi, D. Y. J. Org. Chem. 2005, 70, 1222–
1226.
Supplementary data
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Supplementary data associated with this article can be found in
the online version, at doi:10.1016/j.tet.2008.04.032.
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