Synthesis of 8-bromo-5,12-tetracenequinone and 2-bromotetracene derivatives

Article abstract of DOI:10.1007/s11164-012-0638-2

A series of bromotetracenequinones 1 and bromotetracenes 2 were prepared from 4-bromophthalic anhydride. The parent tetracenequinone 1a and tetracene 2a were sparingly soluble in organic solvents. In contrast, dipropyl-substituted tetracenequinone 1b and

Full text of DOI:10.1007/s11164-012-0638-2

Res Chem Intermed (2013) 39:139–146
DOI 10.1007/s11164-012-0638-2
Synthesis of 8-bromo-5,12-tetracenequinone
and 2-bromotetracene derivatives
Chitoshi Kitamura
•
Naohiro Taka Takeshi Kawase
•
Received: 26 September 2011 / Accepted: 30 November 2011 / Published online: 12 June 2012
Ó Springer Science+Business Media B.V. 2012
Abstract A series of bromotetracenequinones 1 and bromotetracenes 2 were
prepared from 4-bromophthalic anhydride. The parent tetracenequinone 1a and
tetracene 2a were sparingly soluble in organic solvents. In contrast, dipropyl-
substituted tetracenequinone 1b and tetracene 2b were a little more soluble. Prepa-
ration of dihexyl-substituted tetracene 2c proved to be difficult. Sonogashira coupling
of 1b with trimethylsilylacetylene afforded the corresponding product.
Keywords Tetracene Á Tetracenequinone Á Bromo derivative Á Alkyl side-chain Á
Solubility
Introduction
Oligoacenes have been intensively studied owing to their importance as organic
semiconducting materials [1, 2]. Tetracene and pentacene are among the most
promising molecular conductors for organic field-effect transistors, organic light-
emitting diodes, and photovoltaic cells. However, they have limited solubility in
organic solvents. Therefore, to improve the solubility of these molecules, many
research groups have investigated acene functionalization and have reported the
synthesis of various substituted oligoacenes [3–5]. Because oligomerization of
anthracene has afforded some organic semiconductors with high field-effect
mobilities [6], oligomerization of tetracene is also expected to improve its
semiconducting properties. Very few studies of tetracene oligomers have been
reported, with the exception of publications from the Merio et al. [7], M u¨ ller et al.
[
8], and Kimoto et al. [9] groups. This lack of extensive research can be attributed to
C. Kitamura (&) Á N. Taka Á T. Kawase
Department of Materials Science and Chemistry, Graduate School of Engineering,
University of Hyogo, 2167 Shosha, Himeji, Hyogo 671-2280, Japan
e-mail: kitamura@eng.u-hyogo.ac.jp
123

140
C. Kitamura et al.
the limited availability of bromo-substituted tetracene as the building block required
for various metal-catalyzed cross-coupling reactions [10]. Although 5-bromotetra-
cene can be readily prepared via the bromination of tetracene with CuBr [11] or
N-bromosuccinimide (NBS) [8], the preparation of 2-bromotetracene 2a and its
precursor 8-bromo-5,12-tetracenequinone 1a has not been reported (Scheme 1). We
became aware that commercially available 4-bromophthalic anhydride is a desirable
starting material for preparing bromotetracenes 2 via bromotetracenequinones 1
(
Scheme 1). Therefore, we decided to prepare 1 and 2.
Results and discussion
As shown in Scheme 2, the parent 1a and 2a were synthesized. Reduction of
4
1
1
-bromophthalic anhydride with diisobutylaluminum hydride (DIBAL-H) produced
,2-bis(hydroxymethyl)benzene 3 in 79 % yield. Treatment of 3 with PBr afforded
,2-bis(bromomethyl)benzene 4 in 97 % yield. To obtain 1, we adopted McOmie’s
3
protocol [12]. Reaction of 4 with 1,4-naphthoquinone in the presence of NaI at
10 °C in N,N-dimethylformamide (DMF), which generated the corresponding
o-quinodimethane in situ, followed by subsequent Diels–Alder reaction with
,4-naphthoquinone and oxidation afforded 1a as a yellow solid in 44 % yield.
1
1
Compound 1a had poor solubility in common organic solvents. To transform 1a into
the corresponding tetracene 2a, we utilized an improved Meerwein–Ponndorf
reaction as described by Coffey and Boyd [13]. Heating 1a with aluminum
tri(cyclohexyl oxide), which was formed in situ by the reaction of aluminum tri(s-
butoxide) and cyclohexanol, at 155 °C for 2 days, followed by vacuum sublimation
using a gradient furnace gave 2a as an orange solid in 32 % yield. We found that 2a
1
13
had lower solubility in organic solvents than 1a. Thus, the H and C nuclear
magnetic resonance (NMR) spectra of 2a could not be recorded. On the other hand,
1
3
as for 1a, the C NMR spectrum could not be recorded. The structure of 2a
was supported by elemental analysis, infrared (IR) and mass spectrometry, while 1a
1
was characterized by elemental analysis, IR, H NMR, and mass spectrometry.
Therefore, 2a may be an inadequate substrate for cross-coupling reactions.
To improve the solubility of 1a and 2a in organic solvents, we attempted to
introduce alkyl side-chains onto the tetracene frameworks of 1a. We anticipated that
the use of alkyl-substituted 1,4-naphthoquinone would afford alkyl-substituted
bromotetracenequinones 1 and bromotetracenes 2 (Scheme 2). Recently, we
achieved the synthesis of 2,3-dialkyl-5,12-tetracenequinone via a Diels–Alder
reaction between 1,4-anthraquinone and 3,4-dialkylthiophene-1,1-dioxides 5 [14].
O
R
OH
O
O
O
Br
R
Br
R
R
Br
R
R
a: R = H
b: R = Pr
c: R = Hex
O
NaI
O
Al(O-s-Bu)
3
O
2
1
Scheme 1 Transformation of 4-bromophthalic anhydride into 2 via 1
1
23

Synthesis of 8-bromo-5,12-tetracenequinone and 2-bromotetracene derivatives
141
O
Br
Br
Br
DIBALH
OH
OH
PBr3
Br
Br
O
toluene, rt
CHCl
3
, rt
O
3
4
O
O
OH
O
O
Br
Br
NaI
Al(O-s-Bu)3
DMF, 110 °C
155 °C
1
a
2a
Scheme 2 Synthesis of 1a and 2a
Therefore, instead of 1,4-anthraquinone, we used 1,4-benzoquinone to obtain
,7-dialkyl-1,4-naphthoquinones 6 (Scheme 3). The Diels–Alder reactions of 5b
6
and 5c with 1,4-benzoquinone, followed by the loss of sulfur dioxide and oxidation,
afforded naphthoquinones 6b and 6c in 42 % and 37 % yields, respectively. As a
by-product of the reaction, anthraquinones 7b and 7c, which were double Diels–
Alder adducts, could also be isolated in 8 % and 10 % yields, respectively.
Next, we tried to prepare the dipropyl-substituted bromotetracenequinone 1 and
bromotetracene 2 (Scheme 4). The iodine-induced reaction of 4 with 6b afforded
8
-bromo-2,3-dipropyl-5,12-tetracenequinone 1b in 39 % yield. A Meerwein–Ponn-
dorf reaction of 1b gave 8-bromo-2,3-dipropyltetracene 2b in 17 % yield. The
dipropyl-substituted molecules 1b and 2b did not have high solubilities but were
more soluble than the parent 1a and 2a. The tetracenequinone 1b was relatively
1
3
more soluble than the tetracene 2b. The C NMR spectrum of 2b could not be
recorded due to the low solubility. Thus, 1b was fully characterized by elemental
1
analysis, IR, H and C NMR, and mass spectroscopy, while 2b was characterized
13
1
by elemental analysis, IR, H NMR, and mass spectroscopy.
To improve the solubility, we attempted to prepare the dihexyl-substituted
bromotetracenequinone 1 and bromotetracene 2 (Scheme 5). The reaction of 4
and naphthoquinone 6b in the presence of NaI gave 8-bromo-2,3-dihexyl-5,
1
2-tetracenequinone 1c in 8 % yield. The compound 1c had good solubility and was
1
13
completely characterized by elemental analysis, IR, H and C NMR, and mass
spectroscopy. We were not able to perform the subsequent Meerwein–Ponndorf
reaction of 1c because the obtained amount of 1c was small. Although introducing a
longer alkyl chain length in bromotetracene is desirable for improving its solubility
in organic solvents, it was found that the introduction of a longer alkyl chain
O
O
O
O
O
O
R
R
R
R
R
R
R
R
a: R = H
b: R = Pr
c: R = Hex
+
O S
2
+
AcOH, reflux
5
6
7
Scheme 3 Synthesis of 6
123

142
C. Kitamura et al.
O
O
O
O
Br
Pr
Pr
Br
Pr
Pr
Br
Br
NaI
+
DMF, 110 °C
4
6b
1b
OH
Br
Pr
Pr
Al(O-s-Bu)3
55 °C
1
2
b
Scheme 4 Synthesis of 1b and 2b
inhibited the synthesis of bromotetracenequinones and bromotetracenes using our
synthetic method.
As we were able to prepare 1b in reasonable quantities compared with the other
isolated compounds such as 2b and 1c, we evaluated the Sonogashira coupling of 1b
with trimethylsilylacetylene. Reaction of 1b with trimethylsilylacetylene in the
presence of PdCl (PPh ) , and CuI in i-Pr NH/tetrahydrofuran (THF) gave (trimeth-
2
3 2
2
ylsilylethynyl)tetracenequinone 8b in 84 % yield (Scheme 6). Hence, oligomeriza-
tion of 1b and subsequent transformation into the corresponding soluble tetracene
derivatives may prove to be an effective route to obtain tetracene-based oligomers.
Experimental
All reagents were commercially available and used without further purification.
3
,4-Dialkylthiophene-1,1-dioxides were prepared according to the literature method
14]. All reactions were performed under a nitrogen atmosphere. Column chroma-
[
tography was performed using a Wako C-300 silica-gel column (45–75 lm). Melting
points were measured on a Yanaco melting-point apparatus. IR spectra of KBr
pressed pellet samples were measured with a Shimadzu FTIR-8400 spectrometer.
1
13
H and C NMR spectra were measured using a Bruker-Biospin DRX500 FT
spectrometer. Electron impact (EI) mass spectra were measured on a Shimadzu
GCMS-QP5050A mass spectrometer. Elemental analyses were performed using a
Yanaco MT-5 CHN corder.
O
O
O
Br
Hex
Hex
Br
Hex
Hex
Br
Br
NaI
+
DMF, 110 °C
O
4
6c
1c
OH
Br
Hex
Hex
Al(O-s-Bu)3
2
c
Scheme 5 Synthesis of 1c
1
23

Synthesis of 8-bromo-5,12-tetracenequinone and 2-bromotetracene derivatives
143
O
O
TMS
O
O
PdCl (PPh )
CuI
Br
Pr
Pr
2
3 2
Pr
Pr
TMS
+
i-Pr NH/THF, 50 °C
2
1
b
8b
Scheme 6 Sonogashira coupling of 1b
Synthesis of 4-bromo-1,2-bis(hydroxymethyl)benzene 3
To an ice-cooled solution of 4-bromophthalic anhydride (459 mg, 2.02 mmol) in
toluene (8 mL), 1 M DIBAL-H in toluene (10 mL, 10 mmol) was added dropwise.
Then, the mixture was stirred at room temperature for 20 h. After cooling with ice,
the reaction mixture was quenched with MeOH (2 mL) and conc. HCl (60 mL).
After separation of the organic layer, the aqueous layer was extracted with AcOEt.
The combined organic layers were washed with brine and dried over Na SO . After
2
4
evaporation of the solvents, column chromatography (CH Cl /AcOEt = 1:1) on
2
2
1
silica gel afforded 3 (348 mg, 79 %) as a white solid: mp 65.5–66.5 °C; H NMR
(
500 MHz, CDCl ) d 3.33 (brs, 2H), 4.63 (s, 2H), 4.63 (s, 2H), 7.19 (d, J = 8.0 Hz,
3
13
1
H), 7.43 (d, J = 8.0 Hz, 1H), 7.48 (s, 1H); C NMR (126 MHz, CDCl ) d 63.4,
3
6
3.4, 122.2, 131.2, 131.3, 132.4, 138.0, 141.4.
Synthesis of 4-bromo-1,2-bis(bromomethyl)benzene 4
To an ice-cooled solution of 3 (872 mg, 4.02 mmol) in CHCl (40 mL), a solution of
3
PBr (0.95 mL, 10.1 mmol) in CHCl (5 mL) was added dropwise. The mixture was
3
3
stirred at room temperature for 4 h and then poured into ice water. The organic layer
was separated, washed with aqueous Na CO and brine, and then dried over Na SO .
After removal of the solvent and drying under vacuum, 4 was obtained as a pale yellow
2
3
2
4
solid (1.33 g, 97 %) and used in the next reaction without further purification:
1
mp 54–55 °C; H NMR (500 MHz, CDCl ) d 4.58 (s, 2H), 4.59 (s, 2H), 7.24
3
1
3
(
d, J = 8.2 Hz, 1H), 7.43 (dd, J = 2.1, 8.2 Hz, 1H), 7.52 (d, J = 2.1 Hz, 1H);
C
NMR (126 MHz, CDCl ) d 28.7, 29.0, 123.0, 132.4, 132.5, 133.9, 135.5, 138.5.
3
Synthesis of 8-bromo-5,12-tetracenequinone 1a
A mixture of 4 (1.36 g, 3.96 mmol), 1,4-naphthoquinone (769 mg, 4.86 mmol), and
NaI (2.97 g, 19.8 mmol) in DMF (18 mL) was stirred at 110 °C for 22 h. The reaction
mixture was cooled to room temperature and then poured into aqueous Na SO . The
2
3
resulting solid was filtered and washed with water and acetone. After drying under
vacuum, 1a was obtained as a yellow solid (591 mg, 44 %) and used in the next reaction
-1
without further purification: mp[300 °C; IR (cm ) 3,065, 1,672, 1,611, 1,593, 1,580,
1
1
7
8
8
,449, 1,398, 1,325, 1,288, 1,063, 964, 939, 818, 708; H NMR (500 MHz, CDCl ) d
3
.78 (d, J = 8.7 Hz, 1H), 7.84–7.86 (m, 2H), 7.98 (d, J = 8.7 Hz, 1H), 8.28 (s, 1H),
?
.40–8.42 (m, 2H), 8.78(s, 1H), 8.84(s, 1H);MSm/z 100 (100), 336 (M , 88), 338 (M ,
6); Anal. Calcd. for C H BrO : C, 64.12, H, 2.69; found: C, 64.22, H, 2.98.
1
?
8
9
2
123

144
C. Kitamura et al.
Synthesis of 2-bromotetracene 2a
A mixture of 1a (999 mg, 2.96 mmol) and Al(O-s-Bu) (7.83 g, 31.8 mmol) in
3
cyclohexanol (20 mL) was stirred for 48 h at 155 °C. After cooling to room
temperature, the reaction mixture was quenched with a solution of MeOH (18 mL),
water (10 mL), and conc. HCl (5 mL). The resulting solid was filtered, washed with
MeOH, and dried under vacuum. Vacuum sublimation using a gradient furnace
-
1
provided 2a as an orange solid (131 mg, 32 %): Decomp. 270 °C; IR (cm ) 3,048,
?
,612, 1,601, 1,559, 1,458, 1,292, 1,047, 957, 934, 903, 793, 739; MS m/z 306 (M ,
1
?
00), 308 (M , 80); Anal. Calcd. for C H Br: C, 70.38, H, 3.61; found: C, 70.74,
1
H, 3.93.
1
8 11
Synthesis of 6,7-dipropyl-1,4-naphthoquinone 6b
A mixture of 3,4-dipropylthiophene-1,1-dioxide 5b (499 mg, 2.49 mmol) and
1
1
,4-benzoquinone (1.35 g, 12.5 mmol) in AcOH (20 mL) was stirred at reflux for
6 h. After cooling to room temperature, the reaction mixture was poured into
water, extracted with CH Cl , washed with brine, and dried over Na SO . After
2
2
2
4
removal of the solvent, the residue was subjected to column chromatography
(
(
CH Cl /hexane = 1:1 ? CH Cl ) on silica gel, affording 6b as a yellow solid
2
2
2
2
253 mg, 42 %) and anthraquinone by-product 7b as a pale yellow solid (72 mg,
1
8
J = 7.4 Hz, 6H), 1.63–1.71 (m, 4H), 2.72 (t, J = 7.9 Hz, 4H), 6.91 (s, 2H), 7.85 (s,
2
1
%). Data for 6b: mp 53–54 °C; H NMR (500 MHz, CDCl ) d 1.02 (t,
3
1
3
H); C NMR (126 MHz, CDCl ) d 14.1, 23.8, 34.9, 127.1, 129.7, 138.6, 147.6,
3
85.4. Data for 7b: mp 129–131 °C; d 1.03 (t, J = 7.4 Hz, 12H), 1.66–1.74
1
3
(
m, 8H), 2.74 (t, J = 7.9 Hz, 8H), 8.05 (s, 4H); C NMR (126 MHz, CDCl ) d
3
1
4.2, 23.9, 34.9, 127.7, 131.5, 147.5, 183.6.
Synthesis of 6,7-dihexyl-1,4-naphthoquinone 6c
This compound was synthesized following the same procedure as for 6b except
that reagents 3,4-dihexylthiophene-1,1-dioxide 5c (576 mg, 2.03 mmol) and 1,4-
benzoquinone (1.09 g, 10.1 mmol) were used. Compound 6c was obtained as a
yellow oil (246 mg, 37 %), and the anthraquinone by-product 7c was also obtained
1
as a yellow solid (112 mg, 10 %). Data for 6c: H NMR (500 MHz, CDCl ) d
3
0
4
3
.89–0.91 (m, 6H), 1.31–1.42 (m, 12H), 1.59–1.65 (m, 4H), 2.72 (t, J = 8.0 Hz,
1
3
H), 6.91 (s, 2H), 7.84 (s, 2H); C NMR (126 MHz, CDCl ) d 14.1, 22.6, 29.3,
3
1
0.7, 31.6, 32.9, 127.1, 129.7, 138.6, 147.9, 185.4. Data for 7c: mp 90–91.5 °C; H
NMR (500 MHz, CDCl ) d 0.90 (t, J = 6.9 Hz, 12H), 1.33–1.42 (m, 24H),
3
1
.62–1.68 (m, 8H), 2.75 (t, J = 8.0 Hz, 8H), 8.04 (s, 4H); C NMR (126 MHz,
3
1
CDCl ) d 14.1, 22.6, 29.4, 30.8, 31.7, 33.0, 127.7, 131.5, 147.7, 183.6.
3
Synthesis of 8-bromo-2,3-dipropyl-5,12-tetracenequinone 1b
This compound was synthesized following the same procedure as for 1a except
that reagents 4 (363 mg, 1.06 mmol), 6b (250 mg, 1.03 mmol), NaI (773 mg,
1
23

Synthesis of 8-bromo-5,12-tetracenequinone and 2-bromotetracene derivatives
145
5.16 mmol), and DMF (5 mL) were used and the product was recrystallized from
THF–hexane. Compound 1b was obtained as a yellow solid (171 mg, 39 %): mp
-
1
2
1
1
1
56–258 °C; IR (cm ) 3,067, 2,957, 2,928, 2,870, 1,672, 1,597, 1,452, 1,398,
1
,314, 1,296, 1,184, 1,063, 997, 930, 806, 739; H NMR (500 MHz, CDCl ) d
.04–1.07 (m, 6H), 1.71–1.75 (m, 4H), 2.76–2.79 (m, 4H), 7.76 (d, J = 8.8 Hz,
H), 7.97 (d, J = 8.8 Hz, 1H), 8.16 (s, 2H), 8.27 (s, 1H), 8.74 (s, 1H), 8.81 (s, 1H);
3
1
3
C NMR (126 MHz, CDCl ) d 14.2, 23.9, 35.0, 123.8, 128.1, 129.1, 130.3, 130.9,
3
?
31.4, 132.0, 132.1, 132.7, 133.4, 136.0, 148.2, 148.2, 182.8; MS m/z 420 (M , 99),
1
4
5
?
22 (M , 100); Anal. Calcd. for C H BrO : C, 68.42, H, 5.02; found: C, 68.57, H,
.27.
2
4
21
2
Synthesis of 2-bromo-8,9-dipropyltetracene 2b
This compound was synthesized following the same procedure as for 2a except that
reagents 1b (190 mg, 0.45 mmol), Al(O-s-Bu) (1.12 g, 4.54 mmol), and cyclo-
3
hexanol (10 mL) were used and the product was recrystallized from THF–hexane.
Compound 2b was obtained as an orange solid (29 mg, 17 %). The bromotetracene
2
b in solution was slightly unstable when exposed to light and air, and therefore it
-
1
required handling in the dark: Decomp. 270 °C; IR (cm ) 3,005, 2,955, 2,930,
2
1
,870, 1,636, 1,605, 1,464, 1,458, 1,381, 1,296, 1,121, 1,044, 910, 895, 790; H
NMR (500 MHz, CDCl ) d 1.07–1.10 (m, 6H), 1.56–1.80 (m, 4H), 2.77–2.80 (m,
3
4
H), 7.39 (d, J = 9.1 Hz, 1H), 7.75 (s, 2H), 7.85 (d, J = 9.1 Hz, 1H), 8.15 (s, 1H),
?
.51 (s, 1H), 8.53 (s, 1H), 8.54 (s, 1H), 8.58 (s, 1H); MS m/z 390 (M , 100), 392
8
?
M , 99); Anal. Calcd. for C H Br: C, 73.66, H, 5.92; found: C, 73.84, H, 6.09.
(
2
4 23
Synthesis of 8-bromo-2,3-dihexyl-5,12-tetracenequinone 1c
This compound was synthesized following the same procedure as for 1a except
that reagents 4 (175 mg, 0.51 mmol), 6c (166 mg, 0.51 mmol), NaI (386 mg,
2
.57 mmol), and DMF (3 mL) were used and the product was recrystallized from
THF–hexane. Compound 1c was obtained as a yellow solid (20 mg, 8 %): mp
-
1
2
1
6
37–238 °C; IR (cm ) 3,067, 2,955, 2,924, 2,855, 1,672, 1,597, 1,455, 1,402,
1
,312, 1,298, 1,184, 1,065, 943, 739; H NMR (500 MHz, CDCl ) d 0.90–0.93 (m,
3
H), 1.34–1.44 (m, 12H), 1.65–1.71 (m, 4H), 2.76–2.80 (m, 4H), 7.75 (d,
J = 8.7 Hz, 1H), 7.96 (d, J = 8.8 Hz, 1H), 8.15 (s, 2H), 8.26 (s, 1H), 8.73 (s, 1H),
1
3
8
1
1
.80 (s, 1H); C NMR (126 MHz, CDCl ) d 14.1, 22.6, 29.4, 30.8, 31.7, 33.0,
3
23.8, 128.1, 129.2, 130.4, 130.9, 131.5, 132.0, 132.1, 132.7, 133.4, 136.0, 148.5,
?
48.5, 182.9; MS m/z 421 (100), 504 (M , 34), 506 (M , 42); Anal. Calcd. for
?
C H BrO : C, 71.04, H, 6.69; found: C, 71.28, H, 6.58.
2
3
0
33
Synthesis of 2,3-dipropyl-8-trimethylsilylethynyl-5,12-tetracenequinone 8b
To a degassed THF solution (15 mL) of 1b (106 mg, 0.25 mmol), trimethylsilyl-
acetylene (0.2 mL, 1.42 mmol), CuI (8 mg, 0.058 mmol), and i-Pr NH (2 mL),
2
PdCl (PPh ) (9 mg, 0.026 mmol) was added. The reaction mixture was stirred
2
3 2
at 50 °C for 16 h. After cooling to room temperature and then evaporating
123

146
C. Kitamura et al.
the solvents, the residue was subjected to column chromatography (CH Cl /
2
2
hexane = 1:1 ? CH Cl ) on silica gel to afford 8b (92 mg, 84 %) as a yellow
2
2
-
1
solid: mp 211–213 °C; IR (cm ) 3,056, 2,954, 2,928, 2,870, 2,151, 1,674, 1,601,
1
,587, 1,460, 1,404, 1,317, 1,302, 1,248, 1,194, 995, 868, 839, 758, 739; H NMR
1
(
500 MHz, CDCl ) d 0.31 (s, 9H), 1.04–1.07 (m, 6H), 1.69–1.77 (m, 4H), 2.76–2.79
3
(
m, 4H), 7.68 (d, J = 8.5 Hz, 1H), 8.02 (d, J = 8.5 Hz, 1H), 8.16 (s, 2H), 8.21 (s,
1
3
1
9
1
H), 8.77 (s, 1H), 8.79 (s, 1H); C NMR (126 MHz, CDCl ) d 0.0, 14.3, 23.9, 35.0,
3
7.8, 104.3, 124.1, 128.0, 129.0, 130.0, 130.5, 130.6, 131.9, 132.1, 132.2, 133.6,
?
34.4, 134.6, 148.1, 148.1, 182.8, 182.9; MS m/z 423 (100), 438 (M , 60); Anal.
Calcd. for C H O Si: C, 79.24, H, 7.02; found: C, 79.41, H, 6.89.
4 30 2
2
Conclusions
We have developed a synthetic route to 8-bromo-5,12-tetracenequinone and
-bromotetracene derivatives (1 and 2) from 4-bromophthalic anhydride. To
2
improve the solubility of 1a and 2a in organic solvents, dialkyl-substituted
bromotetracenequinones 1b–c and bromotetracene 2b were prepared. Bromotetra-
cenequinones 2 were found to be slightly more soluble than bromotetracenes 1.
Sonogashira coupling of 8-bromo-2,3-dipropyl-5,12-tetracenequinone 1b with
trimethylsilylacetylene afforded the corresponding product 8b in high yield.
Acknowledgments This work was supported by Grants-in-Aid for Scientific Research (nos. 23550161
and 23108720) from JSPS and MEXT.
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