Facile synthesis of 2,3-disubstituted quinoxalines by Suzuki-Miyaura coupling

Article abstract of DOI:10.1055/s-2004-831194

A versatile synthetic route to symmetrical and unsymmetrical 2,3-disubstituted quinoxalines was developed by palladium-catalyzed Suzuki-Miyaura coupling of 2,3-dichloroquinoxaline with various boronic acids. Their photophysical and electrochemical properties were investigated.

Full text of DOI:10.1055/s-2004-831194

PAPER
2535
Facile Synthesis of 2,3-Disubstituted Quinoxalines by Suzuki–Miyaura
Coupling
F
acile Synthesis
i
of 2, 3
s
-Disubstit
h
uted Quinox
e
n
zuki-Miyau
g
ra
C
oupling Mao, Hidehiro Sakurai,* Toshikazu Hirao*
Handai FRC (Frontier Research Center) and Department of Applied Chemistry, Graduate School of Engineering, Osaka University, Yama-
da-oka, Suita, Osaka 565-0871, Japan
Fax +81(6)68797415; E-mail: hirao@chem.eng.osaka-u.ac.jp; E-mail: hsakurai@chem.eng.osaka-u.ac.jp
Received 2 June 2004; revised 21 June 2004
Refluxing for 48 hours in the mixture solvent of toluene
Abstract: A versatile synthetic route to symmetrical and unsym-
and EtOH, the desired 2,3-diphenylquinoxaline was iso-
lated in 92% yield. On the basis of initial success, a wide
metrical 2,3-disubstituted quinoxalines was developed by palladi-
um-catalyzed Suzuki-Miyaura coupling of 2,3-dichloroquinoxaline
array of electrically and structurally diverse boronic acids
was examined to react with 2,3-dichloroquinoxaline un-
der the same conditions. Some representative examples
are listed in Table 1.
with various boronic acids. Their photophysical and electrochemi-
cal properties were investigated.
Key words: Suzuki–Miyaura coupling, 2,3-disubstituted quinoxa-
line, unsymmetrical quinoxaline
As shown in Table 1, different kinds of 2,3-disubstituted
quinoxalines are prepared with ease in good or excellent
yields by Pd(PPh3)4-catalyzed Suzuki–Miyaura reaction.
In agreement with the results described in the literatures,
all the electron-poor and electron-rich boronic acids were
found to be good coupling reagents. It is particularly note-
worthy that ortho-substituted aryl boronic acids were also
employed for the synthesis of sterically hindered 2,3-di-
substituted quinoxalines (Table 1, entries 4–7).
Quinoxaline derivatives are very important nitrogen-con-
taining heterocycles and have been widely used in dyes,1
pharmaceuticals,2 and electrical/photochemical materi-
als.3,4 As part of our ongoing research, a versatile method
for the preparation of a large number of 2,3-disubstituted
quinoxalines should be developed. Traditionally, 2,3-di-
substituted quinoxalines are prepared by condensation of
aryl-1,2-diamines with a-dicarbonyl compounds or their
equivalents.5 However, very limited a-dicarbonyl com-
pounds are commercially available. In particular, unsym-
metrical a-dicarbonyl compounds are not readily
available or need to be prepared by multi-step proce-
dures.6 Although some recent publications demonstrated
different approaches to 2,3-disubstituted quinoxalines,7
these approaches remain inconvenient due to some disad-
vantages such as unavailability of starting materials.
Table 1 Synthesis of Symmetrical 2,3-Disubstituted Quinoxalines
by Pd(PPh3)4-Catalyzed Coupling of 2,3-Dichloroquinoxaline with
Boronic Acids
Cl
Cl
Ar
Ar
220 mol% ArB(OH)2
6 mol% Pd(PPh3)4
N
N
N
N
2M K2CO3
toluene – ethanol
reflux, 48 h
1a–g
In the past decades, Suzuki–Miyaura coupling reaction
has emerged as an extremely powerful tool in organic syn-
thesis.8 Especially in recent years, the development of var-
ious catalyst systems has led to extension of reaction
substrates from aryl iodides, bromides, and triflates to in-
expensive aryl chlorides.9 In addition, organoboron re-
agents as coupling partner possess many attractive
features. They are nontoxic, thermally stable, and widely
available from various commercial sources. With these
considerations in mind, a new strategy for the synthesis of
2,3-disubstituted quinoxalines directly from readily avail-
able 2,3-dichloroquinoxaline and various boronic acids
using the palladium-catalyzed coupling reaction is de-
scribed herein.10
Entry
Ar
Yield (%)
1a (92)
1b (91)
1c (91)
1d (79)
1e (91)
1f (77)
1g (85)
1
2
3
4
5
6
7
Ph
4-MeC6H4
4-MeOC6H4
2-MeC6H4
2-MeOC6H4
2-CF3C6H4
4-Naphthyl
After successful preparation of symmetrical 2,3-disubsti-
tuted quinoxalines, we turned our attention to more inter-
esting unsymmetrical quinoxaline derivatives. In order to
achieve this goal, two-step Suzuki–Miyaura reactions
were designed. The key step was the selective mono-cou-
pling. In general, selective termination at the mono-sub-
stitution is difficult in the metal-catalyzed cross-coupling
The reaction of 2,3-dichloroquinoxaline with 2.2 molar
amounts of phenylboronic acid was first attempted using
6 mol% Pd(PPh3)4 as a catalyst and 2 M K2CO3 as a base.
SYNTHESIS 2004, No. 15, pp 2535–2539
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x.
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x
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0
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Advanced online publication: 23.08.2004
DOI: 10.1055/s-2004-831194; Art ID: F07904SS
© Georg Thieme Verlag Stuttgart · New York

2536
L. Mao et al.
PAPER
Table 2 Synthesis of Unsymmetrical 2,3-Disubstituted Quinoxa-
lines by Two-Step Coupling Reactions
reaction if more than two reacting points with similar re-
activity are present.11
Ar1
Cl
N
Cl
Cl
Ar1
N
Ar2
N
110 mol% Ar1B(OH)2
1.5 mol% Pd2(dba)3
110 mol% Ar2B(OH)2
3 mol% Pd(PPh3)4
When 2,3-dichloroquinoxaline reacted with 1.1 molar
amounts of phenylboronic acid in the presence of 3 mol%
Pd(PPh3)4 and 2 M K2CO3, unfortunately, the desired 2-
chloro-3-phenylquinoxaline was isolated in only 33%
yield. The main side product was 2,3-diphenylquinoxa-
line. Lowering the reaction rate and increasing the steric
repulsion among the substituents in a quinoxaline-palladi-
um intermediate are considered to allow the selective for-
mation of the mono-substituted quinoxaline. Therefore,
the ligand effect was mainly investigated. After the survey
of various reaction conditions such as palladium sources,
ligands, bases, and solvents, Pd2(dba)3/Cy3P catalyst
system with Cs2CO3 as a base in dioxane was found to un-
dergo selective mono-substitution of 2,3-dichloroquinox-
aline. For example, 2-chloro-3-phenylquinoxaline was
isolated in 69% yield under the optimum conditions. Fur-
thermore, the yield was increased to 85% when the same
procedure was applied to the coupling of bulky o-tolylbo-
ronic acid or o-methoxylphenyl boronic acid as shown in
Table 2.
N
N
N
3.6 mol% Cy3P
200 mol% Cs2CO3
dioxane, 85 °C, 24 h
2M K2CO3
toluene – ethanol
reflux, 48 h
2a–c
3a–g
Entry Ar1
Yield of 2 Ar2
Yield of 3
(%)
(%)
1
2
3
4
5
6
7
Ph
2a (69)
2a (69)
2b (85)
2b (85)
2b (85)
2b (85)
2c (85)
4-MeC6H4
3a (93)
3b (88)
3c (96)
3d (91)
3e (90)
3f (95)
3g (91)
Ph
4-MeOC6H4
Ph
2-MeC6H4
2-MeC6H4
2-MeC6H4
2-MeC6H4
2-MeOC6H4
4-MeC6H4
4-MeOC6H4
2-MeOC6H4
4-MeC6H4
Table 3 Absorption, Emission, and Redox Properties of Quinoxa-
line Derivatives 1 and 3
With these mono-substituted quinoxaline derivatives in
hand, further conversion to unsymmetrical 2,3-disubsti-
tuted quinoxalines was carried out by the further coupling.
When 2-chloro-3-phenylquinoxaline reacted with 1.1 mo-
lar amounts of 4-methylphenylboronic acid in the pres-
ence of 3 mol% Pd(PPh3)4 and 2 M K2CO3, the desired 2-
phenyl-3-(4-methylphenyl)quinoxaline was obtained in
93% yield after refluxing for 48 hours. Using the same
protocol and changing the combination of various boronic
acids, a wide variety of unsymmetrical 2,3-disubstituted
quinoxalines were prepared in good yields (Table 2). To
the best of our knowledge, only a few of these unsymmet-
rical quinoxaline derivatives have appeared in the litera-
ture.12,13 It may be possibly due to the unavailability of the
corresponding unsymmetrical a-dicarbonyl compounds.
However, the two-step Suzuki–Miyaura coupling provid-
ed a versatile approach to these unsymmetrical quinoxa-
lines.
Compound Absorbance
Emission Redox (V)
lmax [nm)] E1/2
red
l [nm] (log e)
1a
1b
1c
1d
1e
1f
233 (6.0), 258 (5.7), 282 (5.6),
322 (5.3)
350
351
355
351
348
347
348
–2.04
–2.07
–2.09
–2.10
–2.12
–1.99
–2.02
233 (6.1), 259 (5.7), 283 (5.6),
322 (5.3)
233 (6.0), 258 (5.6), 282 (5.6),
321 (5.2)
232 (5.6), 258 (5.3), 281 (5.2),
321 (5.0)
234 (5.2), 262 (5.1), 282 (5.0),
330 (4.5)
232 (5.8), 259 (5.5), 282 (5.4),
321 (5.0)
Photophysical and electrochemical properties of thus-ob-
tained symmetrical and unsymmetrical 2,3-diarylquinox-
alines were next investigated. Table 3 lists the absorption,
emission, and redox potential data for all these com-
pounds. In general, these quinoxaline derivatives exhibit
similar absorption and emission wavelengths as well as
redox potentials. However, the minute difference in UV
absorption intensity was observed due to the change of
various substituents in the position and nature. Of all sym-
metrical 2,3-diarylquinoxalines, for example, the com-
pound 1b bearing 4-methylphenyl group showed the
highest absorption intensity at around 233 nm. In contrast,
the compound 1e bearing 2-methoxyphenyl group indi-
cates the lowest absorption intensity at almost the same
wavelength under the identical measurement conditions.
This may be ascribed to the steric and electronic effect of
different substituents in the quinoxaline ring.
1g
230 (5.7), 257 (5.3), 287 (5.2),
323 (4.8)
3a
3b
230 (5.8), 262 (5.4), 332 (4.7)
347
349
–2.06
–2.06
230 (5.5), 268 (5.1), 331 (4.4),
360 (4.3)
3c
241 (4.9), 262 (4.8), 334 (4.4)
347
348
–2.06
–2.07
3d
237 (5.6), 260 (5.3), 324 (4.9),
360 (4.4)
3e
237 (5.5), 259 (5.3), 280 (5.2),
322 (5.0)
349
–2.08
3f
237 (5.1), 322 (4.6)
295
294
–2.12
–2.10
3g
236 (5.8), 258 (5.7), 280 (5.6),
306 (5.5)
Synthesis 2004, No. 15, 2535–2539 © Thieme Stuttgart · New York

PAPER
Facile Synthesis of 2,3-Disubstituted Quinoxalines by Suzuki–Miyaura Coupling
2537
IR (KBr): 3068, 1977, 1952, 1843, 1725, 1647, 1606, 1579, 1560,
1479, 1446, 1346, 1308, 1270, 1146, 1065, 1033, 979, 961, 809,
771, 693, 648, 612, 584, 373, 407 cm–1.
1H NMR (CDCl3): d = 8.20 (dd, J = 6.5, 3.5 Hz, 2 H), 7.86 (dd, J =
6.5, 3.5 Hz, 2 H), 7.76 (dd, J = 8.0, 0.8 Hz, 2 H), 7.34–7.46 (m, 4
H), 7.20 (d, J = 7.5 Hz, 2 H).
In summary, the present transformation provides a con-
venient and efficient method for the synthesis of both
symmetrical and unsymmetrical 2,3-disubstituted quinox-
alines from 2,3-dichloroquinoxaline.14 Further efforts will
be directed to the utilization of these quinoxaline deriva-
tives for the development of novel electrical/photochemi-
cal materials.
13C NMR (CDCl3): d = 131.1, 130.7, 129.3, 129.0, 128.7, 127.0,
126.9, 125.8, 122.1.
EIMS: m/z = 418 [M+].
All reagents and solvents were purchased from commercial sources
and were further purified by the standard methods, if necessary.
Melting points were determined on a Yanagimoto Micromelting
Point apparatus and are uncorrected. IR spectra were obtained with
Anal. Calcd for C22H12F6N2: C, 63.16; H, 2.89; N, 6.70. Found: C,
63.15; H, 2.91; N, 6.63.
1
2,3-Bis(1-naphthyl)quinoxaline (1g)
Colorless; mp 208–209 °C.
a JASCO FT/IR-480 plus spectrometer. The H NMR (300 MHz)
and 13C NMR (75 MHz) spectra were recorded on a Varian MER-
CURY 300 (300 MHz) spectrometer. Mass spectra were run on a
JEOL JMS-DX303HF mass spectrometer. UV–visible spectra were
obtained by using a Hitachi U-3500 spectrophotometer at 1.0 ×
10–6 M concentration in CH2Cl2 at 298 K. Emission spectra were
taken on a Shimadzu RF-5300PC spectrofluorophotometer at 1.0 ×
10–6 M concentration in CH2Cl2 at 298 K. The cyclic voltammetry
measurement was performed on a BAS CV-50 W voltammetry an-
alyzer in deaerated MeCN containing 0.1 M Bu4NPF6 as a support-
ing electrolyte at 298 K with a three-electrode system consisting of
a stationary platinum working electrode (BAS), a platinum auxilia-
ry electrode (BAS), and an Ag/AgCl (0.01 M) reference electrode
(BAS) at 100 mV/s scan rate. Redox potentials are given vs Fc/Fc+.
IR (KBr): 3057, 1943, 1824, 1592, 1559, 1535, 1507, 1475, 1318,
1248, 1176, 1113, 973, 947, 865, 801, 766, 657, 610, 563, 538, 476,
461, 425 cm–1.
1H NMR (CDCl3): d = 8.31 (dd, J = 6.5, 3.5 Hz, 2 H), 7.90 (dd, J =
6.5, 3.5 Hz, 2 H), 7.87 (d, J = 7.2 Hz, 2 H), 7.77 (d, J = 7.5 Hz, 2
H), 7.69 (d, J = 7.8 Hz, 2 H), 7.32–7.44 (m, 4 H), 7.12–7.24 (m, 4
H).
13C NMR (CDCl3): d = 150.5, 136.6, 131.3, 129.0, 127.1, 125.9,
124.9, 124.4, 123.8, 123.2, 121.9, 121.3, 120.9, 120.1.
EIMS: m/z = 382 [M+].
Anal. Calcd for C28H18N2: C, 87.93; H, 4.74; N, 7.32. Found: C,
87.66; H, 4.82; N, 7.30.
Synthesis of Symmetrical 2,3-Disubstituted Quinoxalines (Ta-
ble 1); General Procedure
Synthesis of Unsymmetrical 2,3-Disubstituted Quinoxalines
(Table 2); General Procedure
A two-neck flask was charged with 2,3-dichloroquinoxaline (199.0
mg, 1.0 mmol), boronic acid (2.2 mmol), and Pd(PPh3)4 (69.3 mg,
6 mol%) under an Ar atmosphere. Toluene (5 mL), EtOH (0.7 mL),
and K2CO3 (2.0 M in water, 2.2 mL) were added using the syringe
through a rubber septum. The reaction mixture was stirred and heat-
ed under reflux for 48 h. It was then cooled, diluted with CH2Cl2,
and poured into a separatory funnel. The organic layer was separat-
ed and the aqueous phase was extracted with CH2Cl2 twice. The
combined organic extracts were washed with water, dried over an-
hyd MgSO4, filtered, and concentrated in vacuo. The residue was
purified by chromatography on silica gel (hexane–EtOAc, 10:1) to
give the desired product 1.
2,3-Diphenylquinoxaline (1a),15 2,3-bis(4-methylphenyl)quinoxa-
line (1b),16 2,3-bis(4-methoxyphenyl)quinoxaline (1c),7c and 2,3-
bis(2-methoxyphenyl)quinoxaline (1e)17 were reported in the liter-
ature as known compounds, and their spectral data are in good
agreement with those of authentic samples.
A two-neck flask was charged with 2,3-dichloroquinoxaline (398.1
mg, 2.0 mmol), boronic acid (2.2 mmol), Pd2(dba)3 (27.5 mg, 1.5
mol%), Cy3P (20.2 mg, 3.6 mol%), and Cs2CO3 (1303.3 mg, 4.0
mmol) under an Ar atmosphere. After dioxane (5 mL) was added
using a syringe, the reaction mixture was stirred and heated to 85 °C
for 24 h. Then, it was cooled to r.t., diluted with CH2Cl2, and filtered
through a pad of Celite. The filtrate was evaporated to dryness and
the column chromatography of the residue afforded the desired
product 2. A two-neck flask was charged with 2 (1.0 mmol), boronic
acid (1.1 mmol), and Pd(PPh3)4 (34.7 mg, 3.0 mol%) under an Ar
atmosphere, and then toluene (2.5 mL), EtOH (0.35 mL), and
K2CO3 (2.0 M in water, 1.1 mL) were added using the syringe
through a rubber septum. The reaction mixture was stirred and heat-
ed under reflux for 48 h. It was then cooled, diluted with CH2Cl2,
and poured into a separatory funnel. The organic layer was separat-
ed and the aqueous phase was extracted with CH2Cl2 twice. The
combined organic extracts were washed with water, dried over an-
hyd MgSO4, filtered, and concentrated in vacuo. The residue was
purified by chromatography on silica gel (hexane–EtOAc, 10:1) to
give the desired product 3.
2,3-Bis(2-methylphenyl)quinoxaline (1d)
Colorless; mp 132–133 °C.
IR (KBr): 3057, 3023, 2924, 1603, 1559, 1493, 1477, 1455, 1376,
1341, 1324, 1213, 1129, 1055, 1032, 976, 871, 818, 784, 763, 746,
732, 606, 588, 567, 471, 454 cm–1.
1H NMR (CDCl3): d = 8.20 (dd, J = 6.3, 3.6 Hz, 2 H), 7.82 (dd, J =
6.3, 3.6 Hz, 2 H), 7.16–7.24 (m, 4 H), 7.04–7.13 (m, 4 H), 2.21 (s,
6 H).
2-Chloro-3-phenylquinoxaline (2a),18 2-(4-methylphenyl)-3-phen-
ylquinoxaline (3a),12 and 2-(4-methoxyphenyl)-3-phenylquinoxa-
line (3b)13 are reported in the literature as known compounds and
their spectral data are in good agreement with those of authentic
samples.
13C NMR (CDCl3): d = 154.9, 140.8, 137.9, 136.1, 130.4, 129.90,
2-Chloro-3-(2-methylphenyl)quinoxaline (2b)
Colorless; mp 119–120 °C.
129.87, 129.1, 128.4, 125.2, 20.0.
EIMS: m/z = 310 [M+].
IR (KBr): 3061, 3034, 1684, 1653, 1559, 1539, 1482, 1456, 1331,
1293, 1276, 1153, 1130, 1086, 981, 775, 760, 723, 601 cm–1.
1H NMR (CDCl3): d = 8.14–8.17 (m, 1 H), 8.08–8.12 (m, 1 H),
7.79–7.86 (m, 2 H), 7.40–7.45 (m, 2 H), 7.34–7.38 (m, 2 H), 2.23
(s, 3 H).
Anal. Calcd for C22H18N2: C, 85.13; H, 5.85; N, 9.03. Found: C,
84.84; H, 5.87; N, 8.94.
2,3-Bis(2-trifluoromethylphenyl)quinoxaline (1f)
Colorless; mp 140–141 °C.
Synthesis 2004, No. 15, 2535–2539 © Thieme Stuttgart · New York

2538
L. Mao et al.
PAPER
13C NMR (CDCl3): d = 154.3, 153.0, 147.2, 141.2, 140.6, 136.6,
13C NMR (CDCl3): d = 160.1, 154.2, 153.0, 141.5, 140.6, 139.2,
135.7, 130.9, 130.8, 130.4, 129.81, 129.75, 129.4, 129.04, 129.01,
128.6, 126.0, 113.5, 55.3, 19.7.
136.2, 130.8, 130.3, 129.4, 129.1, 128.8, 128.1, 125.8, 19.7.
EIMS: m/z = 254 [M+].
EIMS: m/z = 326 [M+].
Anal. Calcd for C15H11ClN2: C, 70.73; H, 4.35; N, 11.00; Cl, 13.92.
Found: C, 70.58; H, 4.39; N, 11.00; Cl, 13.80.
Anal. Calcd for C22H18N2O: C, 80.96; H, 5.56; N, 8.58. Found: C,
80.87; H, 5.70; N, 8.45.
2-Chloro-3-(2-methoxyphenyl)quinoxaline (2c)
Colorless; mp 134–135 °C.
2-(2-Methoxyphenyl)-3-(2-methylphenyl)quinoxaline (3f)
Colorless; mp 122–123 °C.
IR (KBr): 3033, 2828, 1601, 1585, 1559, 1495, 1465, 1433, 1386,
1335, 1303, 1269, 1251, 1118, 1089, 1047, 1027, 983, 935, 849,
771, 755, 687, 601, 544, 501, 431 cm–1.
1H NMR (CDCl3): d = 8.13–8.18 (m, 1 H), 8.05–8.10 (m, 1 H),
7.75–7.82 (m, 2 H), 7.50 (ddd, J = 7.8, 7.8, 1.6 Hz, 1 H), 7.43 (dd,
J = 7.8, 1.6 Hz, 1 H), 7.13 (ddd, J = 7.8, 7.8, 0.8 Hz, 1 H), 7.04 (dd,
J = 7.8, 0.8 Hz, 1 H), 3.82 (s, 3 H).
13C NMR (CDCl3): d = 157.1, 152.5, 148.0, 141.0, 140.8, 139.7,
131.1, 130.6, 130.1, 130.0, 129.1, 128.1, 120.8, 111.0, 55.6.
EIMS: m/z = 270 [M+].
IR (KBr): 3068, 3007, 2965, 2934, 2834, 1600, 1582, 1559, 1493,
1477, 1461, 1433, 1391, 1340, 1328, 1276, 1252, 1114, 1057, 1037,
1021, 977, 816, 766, 749, 692, 609, 549, 497 cm–1.
1H NMR (CDCl3): d = 8.16–8.23 (m, 2 H), 7.76–7.81 (m, 2 H), 7.54
(dd, J = 7.5, 1.5 Hz, 1 H), 7.26–7.33 (m, 1 H), 7.16–7.18 (m, 2 H),
7.00–7.07 (m, 3 H), 6.65 (d, J = 8.4 Hz, 1 H), 3.36 (s, 3 H), 2.26 (s,
3 H).
13C NMR (CDCl3): d = 156.2, 155.6, 153.2, 141.1, 140.8, 138.3,
136.4, 131.0, 130.4, 130.1, 129.6, 129.5, 129.3, 129.2, 129.1, 128.2,
128.0, 124.5, 120.7, 110.4, 54.6, 20.0.
Anal. Calcd for C15H11ClN2O: C, 66.55; H, 4.10; N, 10.35; Cl,
13.10. Found: C, 66.44; H, 4.19; N, 10.30; Cl, 12.88.
EIMS: m/z = 326 [M+].
Anal. Calcd for C22H18N2O: C, 80.96; H, 5.56; N, 8.58. Found: C,
80.95; H, 5.72; N, 8.54.
2-(2-Methylphenyl)-3-phenylquinoxaline (3c)
Colorless; mp 109–110 °C.
2-(2-Methoxyphenyl)-3-(4-methylphenyl)quinoxaline (3g)
Colorless; mp 137–138 °C.
IR (KBr): 3056, 3022, 2925, 1602, 1559, 1544, 1495, 1478, 1457,
1442, 1394, 1379, 1345, 1247, 1219, 1129, 1077, 1056, 1026, 977,
924, 764, 725, 695, 603, 565, 553, 454 cm–1.
1H NMR (CDCl3): d = 8.16–8.24 (m, 2 H), 7.78–7.82 (m, 2 H),
7.48–7.52 (m, 2 H), 7.15–7.34 (m, 7 H), 2.01 (s, 3 H).
13C NMR (CDCl3): d = 154.3, 153.5, 141.4, 140.8, 138.8, 138.4,
135.8, 130.4, 129.91, 129.86, 129.79, 129.5, 129.2, 129.1, 128.72,
128.64, 127.9, 125.9, 19.8.
IR (KBr): 3058, 2998, 2932, 2831, 1598, 1583, 1493, 1463, 1434,
1394, 1346, 1278, 1251, 1163, 1119, 1062, 1020, 979, 827, 804,
764, 687, 610, 602, 545, 523, 486 cm–1.
1H NMR (CDCl3): d = 8.15–8.20 (m, 2 H), 7.72–7.78 (m, 2 H), 7.63
(dd, J = 7.5, 1.8 Hz, 1 H), 7.35–7.41 (m, 3 H), 7.06–7.15 (m, 3 H),
6.73 (d, J = 8.1 Hz, 1 H), 3.25 (s, 3 H), 2.32 (s, 3 H).
13C NMR (CDCl3): d = 156.3, 154.6, 152.2, 141.3, 141.0, 138.2,
136.6, 130.8, 130.4, 129.5, 129.2, 129.1, 128.5, 128.3, 121.1, 111.1,
54.9, 21.3.
EIMS: m/z = 296 [M+].
Anal. Calcd for C21H16N2: C, 85.11; H, 5.44; N, 9.45. Found: C,
85.14; H, 5.60; N, 9.40.
EIMS: m/z 326 [M+].
2-(2-Methylphenyl)-3-(4-methylphenyl)quinoxaline (3d)
Colorless; mp 121–122 °C.
Anal. Calcd for C22H18N2O: C, 80.96; H, 5.56; N, 8.58. Found: C,
80.75; H, 5.60; N, 8.52.
IR (KBr): 3060, 3018, 2960, 2924, 1614, 1557, 1539, 1513, 1476,
1457, 1392, 1381, 1342, 1248, 1213, 1184, 1127, 1056, 1039, 1021,
978, 847, 832, 805, 767, 728, 601, 555, 509, 463 cm–1.
Acknowledgment
The use of the facilities of the Analytical Center, Graduate School
of Engineering, Osaka University is acknowledged. The discussion
with Mr. Hiroyuki Fujii, Material and Devices Development Cen-
ter, Sanyo Electric Co., Ltd., is acknowledged. We also thank Ms.
Kana Nakamoto and Ms. Shoko Wakatsuki for the help of UV, PL
and CV measurement.
1H NMR (CDCl3): d = 8.15–8.22 (m, 2 H), 7.76–7.80 (m, 2 H),
7.16–7.41 (m, 6 H), 7.08 (d, J = 8.4 Hz, 2 H), 2.33 (s, 3 H), 2.01 (s,
3 H).
13C NMR (CDCl3): d = 154.3, 153.5, 141.4, 140.7, 139.1, 138.8,
135.8, 135.6, 130.4, 129.81, 129.80, 129.6, 129.4, 129.1, 129.0,
128.7, 128.6, 125.9, 21.4, 19.8.
EIMS: m/z = 310 [M+].
References
Anal. Calcd for C22H18N2: C, 85.13; H, 5.85; N, 9.03. Found: C,
84.93; H, 6.04; N, 8.86.
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2-(4-Methoxyphenyl)-3-(2-methylphenyl)quinoxaline (3e)
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1392, 1341, 1294, 1250, 1174, 1143, 1028, 976, 838, 809, 768, 730,
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Facile Synthesis of 2,3-Disubstituted Quinoxalines by Suzuki–Miyaura Coupling
2539
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Synthesis 2004, No. 15, 2535–2539 © Thieme Stuttgart · New York