A highly efficient and aerobic protocol for the synthesis of N-heteroaryl substituted 9-arylcarbazolyl derivatives via a palladium-catalyzed ligand-free Suzuki reaction

Article abstract of DOI:10.1039/c2ob26119g

A palladium-catalyzed aerobic and ligand-free Suzuki reaction in aqueous ethanol has been developed for the synthesis of N-heteroaryl substituted 9-arylcarbazolyl derivatives. A number of N-heteroaryl halides, namely 2-halogenated pyridines, 2-bromoquinoline, 5-bromopyrimidine and 2-chloropyrazine, were coupled with 4-(9H-carbazol-9-yl)phenylboronic acid (CPBA) or 9-phenyl-9H-carbazol-3-ylboronic acid (PCBA) efficiently to afford good to excellent yields in a short reaction time. Moreover, the catalytic system of Pd(OAc)₂-EtOH/H₂O-K₂CO₃ was successfully extended to the cross-couplings of N-heteroaryl halides with various arylboronic acids. The results demonstrated that the cross-coupling reaction in the present protocol was promoted by oxygen.

Full text of DOI:10.1039/c2ob26119g

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Volume 10 | Number 39 | 21 October 2012 | Pages 7849–8028
ISSN 1477-0520
PAPER
Chun Liu et al.
A highly efficient and aerobic protocol for the synthesis of N-heteroaryl
substituted 9-arylcarbazolyl derivatives via a palladium-catalyzed ligand-free
Suzuki reaction
1477-0520(2012)10:39;1-5

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PAPER
A highly efficient and aerobic protocol for the synthesis of N-heteroaryl
substituted 9-arylcarbazolyl derivatives via a palladium-catalyzed ligand-free
Suzuki reaction†
Xiaofeng Rao, Chun Liu,* Jieshan Qiu and Zilin Jin
Received 11th June 2012, Accepted 19th July 2012
DOI: 10.1039/c2ob26119g
A palladium-catalyzed aerobic and ligand-free Suzuki reaction in aqueous ethanol has been developed for
the synthesis of N-heteroaryl substituted 9-arylcarbazolyl derivatives. A number of N-heteroaryl halides,
namely 2-halogenated pyridines, 2-bromoquinoline, 5-bromopyrimidine and 2-chloropyrazine, were
coupled with 4-(9H-carbazol-9-yl)phenylboronic acid (CPBA) or 9-phenyl-9H-carbazol-3-ylboronic acid
(PCBA) efficiently to afford good to excellent yields in a short reaction time. Moreover, the catalytic
system of Pd(OAc)2–EtOH/H2O–K2CO3 was successfully extended to the cross-couplings of N-heteroaryl
halides with various arylboronic acids. The results demonstrated that the cross-coupling reaction in the
present protocol was promoted by oxygen.
developed in the past decades.7 However, these methods, as
described in the literature, are always combined with toxic sol-
Introduction
Natural carbazole moieties have drawn a wide range of interest
due to their being an important pharmacophore in various bio-
logical compounds as well as for their intriguing physical pro-
perties.1 In recent years, carbazole derivatives have been
extensively used as functional building blocks for the synthesis
of small molecules, oligomers or polymers.2 As is well known,
carbazole derivatives with their associated ready functionaliza-
tion at the 3-, 6-, or 9-position can be used as the hole-transport-
ing components in the construction of numerous photo- and
electroluminescent devices and photorefractive materials.3
Small-molecule iridium complexes derived from carbazole units
have been reported by Wong and co-workers.4 They showed
that carbazole moieties played a crucial role in alleviating
the self-quenching of the luminophores and consequently
increased the emission efficiency. Carbazole derivatives have
also attracted interest in the field of dye-sensitized solar cells
(DSSCs) for their strong electron donating nature.5 Chen et al.
prepared two ruthenium-based dyes modified with a carbazole
unit, which provided a high solar energy conversion efficiency
(η) of up to 9.72%.6
vents, harsh conditions, long reaction times and low yields. Thus
far, a more effective method for synthesizing this important type
of compound is still missing from the chemist’s toolbox.
The palladium-catalyzed Suzuki reaction of aryl boronic acids
with aryl halides is one of the most versatile and powerful tools
for the construction of biaryls.8 This reaction has been widely
used to synthesize pharmaceuticals, fine chemicals and advanced
materials. Generally, the Suzuki reaction is carried out in the
presence of a ligand, in particular phosphine,9 N-heterocyclic
carbene10 or palladacyclic complexes.11 However, if the cross-
coupling could be performed under air and ligand-free con-
ditions, it would be considerably cheaper, safer, and more envir-
onmentally friendly. In recent years, significant progress has
been made in this area, which enables this transformation to be
performed in the absence of a ligand.12 Our laboratory has docu-
mented a series of ligand-free protocols for the palladium-cata-
lyzed Suzuki reaction over the last few years, including the
activation of challenging aryl chlorides.13
In this paper, we report a fast and efficient ligand-free protocol
for the synthesis of N-heteroaryl substituted 9-arylcarbazolyl
derivatives under aerobic and aqueous conditions (Scheme 1).
Numerous synthetic methodologies for the construction of
N-heteroaryl substituted 9-arylcarbazolyl derivatives have been
Results and discussion
State Key Laboratory of Fine Chemicals, Dalian University of
Technology, Linggong Road 2, Dalian, 116024, China.
E-mail: chunliu70@ yahoo.com; Fax: (+86) 411-8498-6812;
Tel: (+86) 411-8498-6182
†Electronic supplementary information (ESI) available: Experimental
details and characterization of cross-coupling products. See DOI:
10.1039/c2ob26119g
Optimization of reaction conditions
In accordance with the literature reports, a suitable amount of
water is important for the efficiency of the palladium-catalyzed
ligand-free Suzuki reaction.14 Therefore, we initially investigated
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Table 2 Effect of precatalyst and temperature on the Suzuki reactiona
Entry
Precatalyst
Temp./°C
Time/min
Yieldb [%]
1
2
3
4
5
6
7
8
—
Pd(OAc)2
PdCl2
Pd2(dba)3
5% Pd/C
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
80
80
80
80
80
80
50
25
15
15
40
40
40
15
15
15
No reaction
99
83
58
71
60c
30
Scheme 1 Ligand-free protocol for the synthesis of N-heteroaryl sub-
stituted 9-arylcarbazolyl derivatives.
Trace
a Reaction conditions: 2-bromopyridine (0.25 mmol), CPBA
(0.375 mmol), palladium loading (1.5 mol%), K2CO3 (0.5 mmol),
EtOH–H2O (3 mL–1 mL), under air. The reaction was monitored by
TLC. b Isolated yields. c Pd(OAc)2 (0.5 mol%).
Table 1 Effect of solvent and base on the Suzuki reactiona
We next studied the effects of different bases on the same
model reaction. The use of inorganic bases, such as K2CO3,
K3PO4·7H2O, or Na2CO3, delivered the desired product in high
yields (Table 1, entries 4, 11 and 12). On the other hand, an
organic base, such as Et3N and 1,4-diazabicyclo-[2,2,2]octane
(DABCO), gave disappointing results in the catalytic system
(Table 1, entries 15 and 16). The results reveal that an inorganic
base is better than an organic base in this catalytic system. We
chose K2CO3 as the optimal base for further study.
The next investigation was carried out to screen palladium
species. The results are illustrated in Table 2. It is clear that the
reaction could not occur without palladium (Table 2, entry 1).
Palladium(II) salts such as Pd(OAc)2 and PdCl2 exhibited high
catalytic activity, respectively (Table 2, entries 2 and 3).
However, the activity was decreased when palladium(II) salt was
replaced with zero-valent palladium such as Pd2(dba)3 or Pd/C
(Table 2, entries 4 and 5), which is consistent with both our
recent results15 and Li and Venkatraman’s report.16 Among the
palladium species screened, Pd(OAc)2 is the preferred catalyst
in the reaction system. However, decreasing the loading of
Pd(OAc)2 from 1.5 mol% to 0.5 mol% led to the desired product
in 60% isolated yield (Table 2, entry 6). In addition, the effect of
temperature on the reaction was observed. When the temperature
was dropped to 50 °C, only 30% isolated yield was obtained and
it was difficult for the reaction to proceed at room temperature
(Table 2, entries 7 and 8). Therefore, the optimized conditions
for the cross-couplings of N-heteroaryl halides with CPBA were
1.5 mol% Pd(OAc)2, K2CO3 as a base at 80 °C under air.
Entry Solvent (v/v)
Base
Time/min Yieldb [%]
1
2
3
4
5
6
Pure water
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
20
20
20
15
20
20
20
20
20
20
Trace
33
75
99
92
51
74
58
52
39
98
95
84
79
48
35
EtOH–H2O (1 : 1)
EtOH–H2O (2 : 1)
EtOH–H2O (3 : 1)
EtOH–H2O (4 : 1)
Neat EtOH
7
8
9
10
11
12
13
14
15
16
i-PrOH–H2O (3 : 1) K2CO3
DMF–H2O (3 : 1)
EG–H2O (3 : 1)
Neat EG
EtOH–H2O (3 : 1)
EtOH–H2O (3 : 1)
EtOH–H2O (3 : 1)
EtOH–H2O (3 : 1)
EtOH–H2O (3 : 1)
EtOH–H2O (3 : 1)
K2CO3
K2CO3
K2CO3
K3PO4·7H2O 20
Na2CO3
NaOH
EtONa
Et3N
20
40
40
40
40
DABCO
a Reaction conditions: 2-bromopyridine (0.25 mmol), CPBA
(0.375 mmol), Pd(OAc)2 (1.5 mol%), solvent (4 mL), base (0.5 mmol),
80 °C, under air. The reaction was monitored by TLC. b Isolated yields.
the effect of the water content on the reaction. The cross-coup-
ling reaction of 2-bromopyridine (0.25 mmol) with CPBA
(0.375 mmol) using Pd(OAc)2 (1.5 mol%) and K2CO3
(0.5 mmol) at 80 °C under air, was chosen as a model reaction.
As is evidenced from Table 1, the reaction in pure water was
sluggish (Table 1, entry 1). However, the addition of an incre-
mental amount of ethanol led to a very rapid increase in the reac-
tivity, and a nearly quantitative isolated yield was obtained when
the volume ratio of ethanol to water was 3 : 1 within 15 min
(Table 1, entry 4). While further increasing the amount of
ethanol, the isolated yield of the cross-coupling product
decreased a little and only a 51% yield was obtained when the
reaction was carried out in neat ethanol (Table 1, entries 5 and
6). These results show that the volume ratio of ethanol and water
plays a crucial role in the cross-coupling reaction. We also inves-
tigated the effect of different solvents on the cross-coupling reac-
tion. The use of i-PrOH, ethylene glycol (EG) or N,N-
dimethylformamide (DMF) as co-solvents gave moderate to
good yields (Table 1, entries 7–9). Although the Pd(OAc)2–
ethylene glycol system could activate a wide range of N-hetero-
aryl halides for the Suzuki reaction in the absence of a ligand,13c
only a 39% yield was obtained in 20 min (Table 1, entry 10).
Scope and limitations of substrates
Under the optimal conditions, the scope and limitations of
various N-heteroaryl halides were investigated. The results are
summarized in Table 3. A quantitative yield of product 1 was
obtained within 15 min in 75% aqueous ethanol (Table 3,
entry 1). Compared with the reported methods,4d,7a operational
simplicity, a short reaction time and good yield are the key
advantages of this protocol. A wide range of 2-halogenated pyri-
dines bearing either an electron-donating group or an electron-
withdrawing group performed well and delivered the desired pro-
ducts in high yields. These results illustrate that the electronic
nature of the substituent group has a small influence on the
reactivity.
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Table 3 Suzuki reactions of N-heteroaryl halides with CPBAa
Table 3 (Contd.)
Entry Heteroaryl-X Product
16
Time/min Yieldb [%]
Entry Heteroaryl-X Product
1
Time/min Yieldb [%]
15
38c
15
99
2
3
4
5
6
20
99
a Reaction conditions: N-heteroaryl halide (0.25 mmol), CPBA
(0.375 mmol), Pd(OAc)2 (1.5 mol%), K2CO3 (0.5 mmol), EtOH–H2O
(3 mL–1 mL), 80 °C, under air. The reaction was monitored by TLC.
b Isolated
yields.
c Reaction
conditions:
2,6-dibromopyridine
10
20
5
91
93
99
96
(0.25 mmol), CPBA (0.75 mmol), Pd(OAc)2 (3.0 mol%), K2CO3
(1.0 mmol), EtOH–H2O (3 mL–1 mL), 80 °C, under air.
As shown in Table 3, the coupling of 2-bromo-5-methyl-pyri-
dine with CPBA gave the product 2 in 99% yield after 20 min
(Table 3, entry 2), showing high efficiency. Moreover, 2-bromo-
5-fluoropyridine and 2-bromo-5-nitropyridine underwent the
cross-coupling smoothly and afforded the desired products in
91% and 93% yields, respectively (Table 3, entries 3 and 4). It is
noteworthy that the cross-coupling between 2-bromo-6-methyl-
pyridine and CPBA could be conducted with a 99% yield after
5 min, resulting in a TOF up to 792 h−1 (Table 3, entry 5). The
reaction system exhibited similar high reactivity for the coup-
lings of CPBA with 2-bromo-6-methoxylpyridine or 1-(6-bro-
mopyridin-2-yl)ethanone (Table 3, entries 7 and 9). In addition
to 2-halogenated pyridines, other 2-halogenated heteroarenes as
one of the cross-coupling partners also performed well and
afforded good to excellent yields of the expected products. For
example, 2-bromoquinoline produced the product 11 in a 92%
yield within 40 min (Table 3, entry 11). Noticeably, 5-bromopyr-
imidine was also successfully used in the reaction to afford a
96% yield in 40 min (Table 3, entry 13). In general, N-heteroaryl
chlorides are less reactive than N-heteroaryl bromides and
require drastic reaction conditions for arylation. To our delight,
the coupling of 2-chloropyrazine with CPBA produced the
biaryl 14 in an 81% yield within 40 min (Table 3, entry 14).
However, 3-halogenated heteroarenes were less active and gave
moderate yields (Table 3, entries 12 and 15). More significantly,
2,6-dibromopyridine also delivered the double cross-coupled
product 16 in 38% yield using 3 mol% Pd(OAc)2 and 4 equiv.
of the base (Table 3, entry 16).
In the field of OLEDs, carbazole derivatives with a functional
group at the 3- or 6-position are important building blocks
because of their high triplet energy and good hole-transporting
ability. Organometallic complexes of carbazoles have been
reported as potential luminescent materials, especially carbazoles
containing a 3,6-linkage with heterocycles or diarylamines.4a,17
Encouraged by the successful cross-coupling mentioned-above,
we tried to carry out the Suzuki reaction of N-heteroaryl halides
with PCBA under the same catalytic system (Pd(OAc)2–EtOH/
H2O–K2CO3), and the results are illustrated in Table 4. The
coupling of 2-bromopyridine with PCBA provided the corres-
ponding product 17 in 91% yield within 25 min (Table 4,
10
7
8
5
99
96
20
9
5
98
90
10
15
11
12
13
40
60
40
92
77
96
14
15
40
20
81
74
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Table 4 Suzuki reactions of N-heteroaryl halides with PCBAa
far as we know, the carbazole derivatives with an N-heteroaryl
group on the 3- or 6-position, such as products 17, 18 and 19,
are important ligands for the synthesis of iridium complexes used
in OLEDs.4a,d To the best of our knowledge, the present protocol
for the formation of these carbazole derivatives is simpler and
much more efficient than the reported procedures.4a,d,18 Other
N-heteroaryl halides also exhibited high reactivity in this proto-
col. For example, 2-bromoquinoline produced the expected
biaryl 26 in 72% yield within 60 min (Table 4, entry 10).
Finally, the cross-coupling of 2-chloropyrazine coupled with
PCBA under the reaction conditions afforded a yield of 73% in
60 min (Table 4, entry 12). Thus, this work provides a fast and
very practical method for the synthesis of N-heteroaryl substi-
tuted 9-arylcarbazole derivatives, which are the potential build-
ing blocks for the construction of various intermediates and
advanced functional materials.
To further investigate the scope and limitations of this methodo-
logy, cross-couplings of different aryl boronic acids with N-
heteroaryl halides were carried out. The results are summarized
in Table 5. The coupling of 2-bromopyridine with phenylboronic
acid gave 2-phenylpyridine in a quantitative isolated yield after
10 min (Table 5, entry 1). Even decreasing the catalyst loading
to 0.25 mol%, the cross-coupling was completed in 60 min
(Table 5, entry 2). As far as we know, this is the most efficient
catalytic system for such a transformation under ligand-free con-
ditions.13b,19 Both electron-rich and electron-poor aryl boronic
acids proceeded smoothly. For example, using 4-methylphenyl
boronic acid instead of phenyl boronic acid, the coupling was
completed in 5 min (Table 5, entry 4), resulting in a TOF of
784 h−1. In addition, 4-methoxyphenyl boronic acid was
coupled with 2-bromopyridine giving the product 32 in 92%
yield for 10 min (Table 5, entry 5). Moreover, electron-poor
4-fluorophenyl boronic acid afforded the target product 33 in
95% for 30 min (Table 5, entry 6). While increasing the steric
hindrance of arylboronic acid, the reactivity decreased (Table 5,
entries 8 and 9). Note that a nearly quantitative yield of product
37 was obtained when using 4-(diphenylamino)phenylboronic
acid as a coupling partner in 10 min (Table 5, entry 10). To the
best of our knowledge, the present protocol for the formation of
product 37 is simpler and more efficient than the methods
described in the literature.13f,20 Moreover, 2-chloropyrazine is a
good coupling partner in the catalytic system (Table 5, entries
11 and 12).
Entry Heteroaryl-X Product
1
Time/min Yieldb [%]
25
91
2
3
4
5
20
15
40
40
84
71
81
90
6
40
89
7
30
60
40
60
60
86
75
81
72
75
8
9
10
11
12
60
73
Effect of atmosphere on the Suzuki reaction
a Reaction conditions: N-heteroaryl halide (0.25 mmol), PCBA
(0.375 mmol), Pd(OAc)2 (1.5 mol%), K2CO3 (0.5 mmol), EtOH–H2O
(3 mL–1 mL), 80 °C, under air. The reaction was monitored by TLC.
b Isolated yields.
As we reported previously,13a,b,21 oxygen served as a promoter
in the palladium-catalyzed ligand-free Suzuki reaction, which
inspired us to speculate whether oxygen could also promote the
Suzuki reaction of carbazole boronic acid with N-heteroaryl
halides in the present catalytic system. Consequently, the effects
of different atmospheres on the cross-couplings were investi-
gated. The results are illustrated in Table 6. It is clear that the
couplings gave higher yields under air than in nitrogen (Table 6,
entries 1a–4a vs. 1b–4b). For example, the cross-coupling
between 2-bromopyridine and CPBA in open air resulted in
99% isolated yield in 15 min (Table 6, entry 2a), while the iso-
lated yield was decreased to 51% in nitrogen (Table 6, entry 2b).
entry 1), which indicated that the catalytic system also showed
high activity in the cross-coupling of N-heteroaryl halides with
PCBA. We next explored the reactivity of various N-heteroaryl
halides in the catalytic system. The cross-couplings between
PCBA and 5- or 6-substituted 2-bromopyridines provided the
products in good to excellent yields (Table 4, entries 2–9). As
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Table 5 Suzuki reactions of N-heteroaryl halides with arylboronic
synthesis of N-heteroaryl substituted 9-arylcarbazolyl derivatives
under aerobic and ligand-free conditions. A wide range of N-
heteroaryl halides readily underwent the Suzuki reaction with
CPBA or PCBA to provide good to excellent yields of the
cross-coupled products. Moreover, the present approach was suc-
cessfully extended to the cross-couplings of N-heteroaryl halides
with various arylboronic acids. This aerobic and water-involved
protocol is in accordance with the concept of green chemistry
and is of great interest for the synthesis of advanced functional
materials. Further investigations including photophysical proper-
ties of these N-heteroaryl substituted 9-arylcarbazolyl derivatives
and synthetic applications of this methodology are in progress in
our laboratory.
acidsa
Entry Heteroaryl-X Product
1
Time/min Yieldb [%]
10
60
20
5
99
96c
96
98
92
95
98
2
3
4
5
6
7
Experimental section
General remarks
10
30
10
Unless otherwise noted, all the reactions were carried out in air.
All N-heteroaryl halides were purchased from Alfa Aesar or
Avocado. 4-(9H-carbazol-9-yl)phenylboronic acid (CPBA) and
9-phenyl-9H-carbazol-3-ylboronic acid (PCBA) were purchased
from Trusyn Chem-Tech Co., Ltd, China. Other chemicals were
purchased from commercial sources and used without further
purification. NMR spectra were recorded on a Brucker Advance
II 400 spectrometer using TMS as internal standard (400 MHz
8
9
180
120
60
81
1
for H NMR and 100 MHz for 13C NMR). Mass spectroscopy
data of the products were collected with a MS-EI instrument. All
products were isolated by short chromatography on a silica gel
(200–300 mesh) column using petroleum ether (60–90 °C).
Compounds described in the literature were characterized by
1H NMR spectra compared to reported data.
10
11
12
10
30
30
97
94
90
General procedure for the Suzuki cross-coupling of N-hetero-
aryl halides with CPBA or PCBA. A mixture of N-heteroaryl
halide (0.25 mmol), CPBA or PCBA (0.375 mmol), K2CO3
(0.5 mmol), Pd(OAc)2 (0.00375 mmol), distilled water (1 mL)
and ethanol (3 mL) was stirred at 80 °C in air for the indicated
time. The reaction mixture was added to brine (15 mL) and
extracted with ethyl acetate (4 × 15 mL). The solvent was con-
centrated under vacuum, and the product was isolated by short-
column chromatography on silica gel (200–300 mesh).
a Reaction conditions: N-heteroaryl halide (0.25 mmol), arylboronic acid
(0.375 mmol), Pd(OAc)2 (1.5 mol%), K2CO3 (0.5 mmol), EtOH–H2O
(3 mL–1 mL), 80 °C, under air. The reaction was monitored by TLC.
b Isolated yields. c Pd(OAc)2 (0.25 mol%).
General procedure for the Suzuki cross-coupling of N-hetero-
aryl halides with arylboronic acids. A mixture of N-heteroaryl
halide (0.25 mmol), arylboronic acid (0.375 mmol), K2CO3
(0.5 mmol), Pd(OAc)2 (0.00375 mmol), distilled water (1 mL)
and ethanol (3 mL) was stirred at 80 °C in air for the indicated
time. The reaction mixture was added to brine (15 mL) and
extracted with ethyl acetate (4 × 15 mL). The solvent was con-
centrated under vacuum, and the product was isolated by short-
column chromatography on silica gel (200–300 mesh).
Gratifyingly, it took only 9 min to complete the same reaction in
oxygen (Table 6, entry 2c). Using PCBA instead of CPBA, it
took 15 min to complete the coupling in oxygen (Table 6, entry
4c), faster than that in nitrogen (Table 6, entry 4b). Therefore,
we can conclude that oxygen serves as a promoter in the
Pd(OAc)2-catalyzed ligand-free Suzuki reaction in EtOH–H2O.
It is proposed that a peroxo-palladium complex might be formed
in the presence of oxygen,22 which accelerates the oxidative
addition step due to the enhanced electron density of the palla-
dium. However, the details of the mechanism are ambiguous at
present and will be the subject of the further study.
9-(4-(5-Methylpyridin-2-yl)phenyl)-9H-carbazole (2). Yield:
99%; white solid, m.p. 212–213 °C. 1H NMR (400 MHz,
CDCl3, 25 °C): δ = 8.58 (s, 1H), 8.20 (d, J = 8.0 Hz, 2H),
8.15 (d, J = 8.0 Hz, 2H), 7.73 (d, J = 8.0 Hz, 1H), 7.67 (d, J =
8.0 Hz, 2H), 7.62 (m, 1H), 7.47 (d, J = 8.0 Hz, 2H), 7.42 (t, J =
8.0 Hz, 2H), 7.30 (t, J = 8.0 Hz, 2H), 2.42 (s, 3H) ppm. 13C NMR
(100 MHz, CDCl3, 25 °C): δ = 153.93, 150.29, 140.80, 138.48,
Conclusions
In summary, we have developed a very fast and highly efficient
catalytic system of Pd(OAc)2–EtOH/H2O–K2CO3 for the
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Table 6 Effect of atmosphere on the Suzuki reactiona
Entry
Ar-B(OH)2
Product
Atmosphere
Time/min
Yieldb [%]
1a
1b
1c
Open air
N2
O2 balloon
10
10
8
99
76
98
2a
2b
2c
Open air
N2
O2 balloon
15
15
9
99
51
99
3a
3b
3c
Open air
N2
O2 balloon
20
20
12
99
73
99
4a
4b
4c
Open air
N2
O2 balloon
25
25
15
91
77
92
a Reaction conditions: N-heteroaryl bromide (0.25 mmol), arylboronic acid (0.375 mmol), Pd(OAc)2 (1.5 mol%), K2CO3 (0.5 mmol), EtOH–H2O
(3 mL–1 mL), 80 °C. The reaction was monitored by TLC. b Isolated yields.
138.05, 137.50, 132.01, 128.18, 127.21, 126.01, 123.50, 120.33,
155.45, 155.31, 141.90, 141.82, 140.66, 139.01, 136.47,
128.48, 127.51, 127.18, 126.09, 123.62, 120.40, 120.23, 120.13,
117.35, 117.31, 109.84, 108.25, 107.87 ppm. MS (EI): m/z =
338.1222 [M]+.
120.04, 109.88, 18.23 ppm. MS (EI): m/z = 334.1467 [M]+.
9-(4-(5-Fluoropyridin-2-yl)phenyl)-9H-carbazole (3). Yield:
91%; white solid, m.p. 210–211 °C. 1H NMR (400 MHz,
CDCl3, 25 °C): δ = 8.60 (d, J = 2.8 Hz, 1H), 8.19–8.15 (m, 4H),
7.83–7.81 (m, 1H), 7.70–7.68 (m, 2H), 7.56–7.51 (m, 1H), 7.47
(d, J = 8.0 Hz, 2H), 7.45–7.40 (m, 2H), 7.32–7.28 (m, 2H) ppm.
13C NMR (100 MHz, CDCl3, 25 °C): δ = 160.28, 157.72,
152.88, 152.84, 140.75, 138.42, 138.12, 137.88, 137.38, 128.29,
127.28, 126.05, 123.82, 123.64, 123.58, 121.35, 121.31, 120.37,
120.14, 109.83 ppm. MS (EI): m/z = 338.1223 [M]+.
1-(6-(4-(9H-Carbazol-9-yl)phenyl)pyridin-2-yl)ethanone (7).
1
Yield: 99%; white solid, m.p. 161–162 °C. H NMR (400 MHz,
CDCl3, 25 °C): δ = 8.36–8.34 (m, 2H), 8.17 (d, J = 8.0 Hz, 2H),
8.05–8.02 (m, 2H), 7.96 (t, J = 7.6 Hz, 1H), 7.74 (d, J = 8.8 Hz,
2H), 7.51 (d, J = 8.0 Hz, 2H), 7.46–7.42 (m, 2H), 7.32
(t, J = 8.0 Hz, 2H), 2.87 (s, 3H) ppm. 13C NMR (100 MHz,
CDCl3, 25 °C):
δ = 200.40, 155.60, 153.59, 140.69,
138.93, 137.89, 137.33, 128.42, 127.28, 126.07, 123.61, 123.46,
120.41, 120.21, 120.09, 109.83, 25.81 ppm. MS (EI): m/z =
362.1428 [M]+.
9-(4-(5-Nitropyridin-2-yl)phenyl)-9H-carbazole
(4). Yield:
1
93%; light-yellow solid, m.p. 266–267 °C. H NMR (400 MHz,
CDCl3, 25 °C): δ = 9.55 (d, J = 2.4 Hz, 1H), 8.61–8.58 (m, 1H),
8.36–8.34 (m, 2H), 8.16 (d, J = 7.6 Hz, 2H), 8.01 (d, J =
8.4 Hz, 1H), 7.79–7.76 (m, 2H), 7.51 (d, J = 8.4 Hz, 2H),
7.46–7.42 (m, 2H), 7.34–7.30 (m, 2H) ppm. 13C NMR
(100 MHz, CDCl3, 25 °C): δ = 161.44, 145.45, 143.01, 140.44,
140.33, 135.70, 132.15, 129.28, 127.29, 126.17, 123.77, 120.47,
119.99, 109.78 ppm. MS (EI): m/z = 365.1167 [M]+.
6-(4-(9H-Carbazol-9-yl)phenyl)picolinaldehyde
(8). Yield:
96%; white solid, m.p. 141–142 °C. 1H NMR (400 MHz,
CDCl3, 25 °C): δ = 10.22 (s, 1H), 8.34 (d, J = 8.4 Hz, 2H), 8.16
(d, J = 7.6 Hz, 2H), 8.06 (d, J = 7.6 Hz, 1H), 8.03–7.96 (m,
2H), 7.75 (d, J = 8.4 Hz, 2H), 7.50 (d, J = 8.0 Hz, 2H), 7.44 (t,
J = 7.6 Hz, 2H), 7.32 (t, J = 7.6 Hz, 2H) ppm. 13C NMR
(100 MHz, CDCl3, 25 °C): δ = 193.78, 157.02, 152.89, 140.65,
139.12, 138.05, 137.02, 128.58, 127.34, 126.12, 124.44, 123.63,
120.44, 120.27, 120.05, 109.83 ppm. MS (EI): m/z = 348.1268
[M]+.
9-(4-(6-Methylpyridin-2-yl)phenyl)-9H-carbazole (5). Yield:
99%; white solid, m.p. 201–202 °C. 1H NMR (400 MHz,
CDCl3, 25 °C): δ = 8.23–8.21 (m, 2H), 8.16 (d, J = 7.6 Hz, 2H),
7.72–7.66 (m, 3H), 7.61 (d, J = 8.0 Hz, 1H), 7.48 (d, J =
8.4 Hz, 2H), 7.45–7.41 (m, 2H), 7.32–7.28 (m, 2H), 7.16 (d, J =
7.6 Hz, 1H), 2.68 (s, 3H) ppm. 13C NMR (100 MHz, CDCl3,
25 °C): δ = 158.64, 156.07, 140.85, 138.84, 138.21, 137.12,
128.55, 127.22, 126.02, 123.53, 121.95, 120.34, 120.05, 117.68,
109.88, 24.76 ppm. MS (EI): m/z = 334.1470 [M]+.
9-(4-(6-Methoxypyridin-2-yl)phenyl)-9H-carbazole (9). Yield:
98%; white solid, m.p. 140–141 °C. 1H NMR (400 MHz,
CDCl3, 25 °C): δ = 8.28 (d, J = 8.4 Hz, 2H), 8.16 (d, J = 8.0
Hz, 2H), 7.71–7.65 (m, 3H), 7.48 (d, J = 8.4 Hz, 2H), 7.42 (t,
J = 7.2 Hz, 3H), 7.30 (t, J = 8.0 Hz, 2H), 6.75 (d, J = 8.4 Hz,
1H), 4.09 (s, 3H) ppm. 13C NMR (100 MHz, CDCl3, 25 °C): δ
= 163.94, 153.77, 140.81, 139.35, 138.24, 138.11, 128.18,
127.09, 126.03, 123.54, 120.37, 120.09, 112.89, 109.91, 109.72,
53.31 ppm. MS (EI): m/z = 350.1422 [M]+.
9-(4-(6-Fluoropyridin-2-yl)phenyl)-9H-carbazole (6). Yield:
96%; white solid, m.p. 137–138 °C. 1H NMR (400 MHz,
CDCl3, 25 °C): δ = 8.25–8.23 (m, 2H), 8.15 (d, J = 8.0 Hz, 2H),
7.93–7.88 (m, 1H), 7.73–7.68 (m, 3H), 7.48 (d, J = 8.0 Hz, 2H),
7.45–7.41 (m, 2H), 7.32–7.29 (m, 2H), 6.94–6.91 (m, 1H) ppm.
13C NMR (100 MHz, CDCl3, 25 °C): δ = 164.72, 162.34,
6-(4-(9H-Carbazol-9-yl)phenyl)picolinonitrile (10). Yield: 90%;
white solid, m.p. 180–181 °C. 1H NMR (400 MHz,
7880 | Org. Biomol. Chem., 2012, 10, 7875–7883
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2,6-Bis(4-(9H-carbazol-9-yl)phenyl)pyridine (16). Yield: 38%;
white solid, m.p. 253–254 °C. 1H NMR (400 MHz, CDCl3,
25 °C): δ = 8.43 (d, J = 8.4 Hz, 4H), 8.17 (d, J = 7.6 Hz, 4H),
7.96 (t, J = 8.0 Hz, 1H), 7.85 (d, J = 7.6 Hz, 2H), 7.74 (d, J =
8.8 Hz, 4H), 7.52 (d, J = 8.0 Hz, 4H), 7.46–7.42 (m, 4H), 7.31
(t, J = 7.2 Hz, 4H) ppm. 13C NMR (100 MHz, CDCl3, 25 °C):
δ = 156.15, 140.75, 138.74, 138.25, 137.88, 128.70, 127.21,
126.06, 123.59, 120.37, 120.15, 119.21, 109.89 ppm. MS (EI):
m/z = 561.2205 [M]+.
CDCl3, 25 °C): δ = 8.28 (d, J = 8.8 Hz, 2H), 8.16 (d, J =
7.6 Hz, 2H), 8.04 (d, J = 7.6 Hz, 1H), 7.95 (t, J = 7.2 Hz, 1H),
7.74 (d, J = 8.4 Hz, 2H), 7.68 (d, J = 7.6 Hz, 1H), 7.49 (d, J =
8.0 Hz, 2H), 7.43 (t, J = 7.2 Hz, 2H), 7.32 (t, J = 7.6 Hz, 2H)
ppm. 13C NMR (100 MHz, CDCl3, 25 °C): δ = 158.07, 140.56,
139.65, 137.95, 135.98, 134.07, 128.64, 127.31, 126.79, 126.12,
123.68, 123.40, 120.42, 120.33, 117.32, 109.78 ppm. MS (EI):
m/z = 345.1269 [M]+.
9-(4-(Quinolin-2-yl)phenyl)-9H-carbazole (11). Yield: 92%;
white solid, m.p. 155–156 °C. 1H NMR (400 MHz, CDCl3,
25 °C): δ = 8.41 (d, J = 8.4 Hz, 2H), 8.30 (d, J = 8.8 Hz, 1H),
8.22 (d, J = 8.8 Hz, 1H), 8.17 (d, J = 7.6 Hz, 2H), 7.98 (d, J =
8.4 Hz, 1H), 7.88 (d, J = 8.4 Hz, 1H), 7.79–7.74 (m, 3H), 7.58
(t, J = 8.8 Hz, 1H), 7.51 (d, J = 8.0 Hz, 2H), 7.44 (t, J = 7.6 Hz,
2H), 7.31 (t, J = 7.2 Hz, 2H) ppm. 13C NMR (100 MHz, CDCl3,
25 °C): δ = 156.44, 148.39, 140.77, 138.78, 138.72, 137.05,
129.89, 129.80, 129.10, 127.54, 127.30, 126.54, 126.05,
123.58, 120.36, 120.13, 118.85, 109.88 ppm. MS (EI): m/z =
370.1479 [M]+.
3-(5-Methylpyridin-2-yl)-9-phenyl-9H-carbazole (18). Yield:
1
84%; colorless oil. H NMR (400 MHz, CDCl3, 25 °C): δ =
8.78 (d, J = 1.2 Hz, 1H), 8.55 (s, 1H), 8.22 (d, J = 7.6 Hz, 1H),
8.03–8.01 (m, 1H), 7.74 (d, J = 8.0 Hz, 1H), 7.63–7.55 (m, 5H),
7.49–7.44 (m, 2H), 7.41 (d, J = 4.0 Hz, 2H), 7.32–7.29 (m, 1H),
2.38 (s, 3H) ppm. 13C NMR (100 MHz, CDCl3, 25 °C): δ =
155.47, 149.93, 141.48, 141.31, 137.64, 137.42, 131.61, 130.75,
129.93, 127.56, 127.09, 126.15, 124.95, 123.91, 123.74, 120.61,
120.23, 119.86, 118.81, 109.95, 109.89, 18.15 ppm. MS (EI):
m/z = 334.1466 [M]+.
3-(5-Nitropyridin-2-yl)-9-phenyl-9H-carbazole
(20). Yield:
9-(4-(Quinolin-3-yl)phenyl)-9H-carbazole (12). Yield: 77%;
white solid, m.p. 261–262 °C. 1H NMR (400 MHz, CDCl3,
25 °C): δ = 9.30 (d, J = 2.0 Hz, 1H), 8.42 (d, J = 2.0 Hz, 1H),
8.18 (t, J = 7.6 Hz, 3H), 7.95 (t, J = 8.0 Hz, 3H), 7.79–7.74
(m, 3H), 7.63 (t, J = 7.6 Hz, 1H), 7.51 (d, J = 8.4 Hz, 2H), 7.45
(t, J = 7.2 Hz, 2H), 7.32 (t, J = 7.6 Hz, 2H) ppm. 13C NMR
(100 MHz, CDCl3, 25 °C): δ = 149.72, 147.56, 140.76, 137.79,
136.93, 133.37, 132.98, 129.68, 129.37, 128.87, 128.09, 128.03,
127.72, 127.24, 126.08, 123.57, 120.42, 120.19, 109.79 ppm.
MS (EI): m/z = 370.1476 [M]+.
81%; yellow solid, m.p. 196–197 °C. 1H NMR (400 MHz,
CDCl3, 25 °C): δ = 9.52 (d, J = 2.4 Hz, 1H), 8.94 (d, J = 1.6 Hz,
1H), 8.54–8.51 (m, 1H), 8.25 (d, J = 7.6 Hz, 1H), 8.18–8.15 (m,
1H), 8.02 (d, J = 8.8 Hz, 1H), 7.67–7.63 (m, 2H), 7.60–7.78 (m,
2H), 7.55–7.42 (m, 4H), 7.38–7.34 (m, 1H) ppm. 13C NMR
(100 MHz, CDCl3, 25 °C): δ = 163.06, 145.38, 142.52, 142.17,
141.68, 137.08, 131.86, 130.09, 128.99, 128.01, 127.09, 126.73,
125.71, 124.13, 123.38, 120.79, 120.64, 120.38, 119.37, 110.34,
110.26 ppm. MS (EI): m/z = 365.1159 [M]+.
9-(4-(Pyrimidin-5-yl)phenyl)-9H-carbazole (13). Yield: 96%;
white solid, m.p. 188–189 °C. 1H NMR (400 MHz, CDCl3,
25 °C): δ = 9.27 (s, 1H), 9.07 (s, 2H), 8.17 (d, J = 7.6 Hz, 2H),
7.83 (d, J = 8.4 Hz, 2H), 7.76 (d, J = 8.4 Hz, 2H), 7.49–7.42
(m, 4H), 7.34–7.30 (m, 2H) ppm. 13C NMR (100 MHz, CDCl3,
25 °C): δ = 157.78, 154.91, 140.60, 138.75, 133.60, 133.17,
128.51, 127.91, 126.14, 123.66, 120.46, 120.36, 109.67 ppm.
MS (EI): m/z = 321.1257 [M]+.
3-(6-Methylpyridin-2-yl)-9-phenyl-9H-carbazole (21). Yield:
90%; colorless oil. H NMR (400 MHz, CDCl3, 25 °C): δ =
1
8.79 (d, J = 1.6 Hz, 1H), 8.23 (d, J = 8.0 Hz, 1H), 8.06–8.04
(m, 1H), 7.64–7.63 (m, 2H), 7.61–7.57 (m, 4H), 7.49–7.45 (m,
2H), 7.42–7.41 (m, 2H), 7.33–7.30 (m, 1H), 7.08–7.06 (m, 1H),
2.67 (s, 3H) ppm. 13C NMR (100 MHz, CDCl3, 25 °C): δ =
158.29, 157.65, 141.45, 141.37, 137.64, 136.90, 132.03, 129.93,
127.55, 127.09, 126.10, 125.28, 123.85, 123.75, 120.87, 120.66,
120.18, 119.17, 117.45, 109.93, 109.90, 24.89 ppm. MS (EI):
m/z = 334.1464 [M]+.
9-(4-(Pyrazin-2-yl)phenyl)-9H-carbazole (14). Yield: 81%;
white solid, m.p. 146–147 °C. 1H NMR (400 MHz, CDCl3,
25 °C): δ = 9.14 (d, J = 1.6 Hz, 1H), 8.71–8.69 (m, 1H), 8.57
(d, J = 2.4 Hz, 1H), 8.28–8.26 (m, 2H), 8.16 (d, J = 8.0 Hz,
2H), 7.77–7.73 (m, 2H), 7.49 (d, J = 8.0 Hz, 2H), 7.45–7.42 (m,
2H), 7.33–7.29 (m, 2H) ppm. 13C NMR (100 MHz, CDCl3,
25 °C): δ = 152.06, 144.38, 143.04, 142.01, 140.59, 139.47,
135.13, 128.50, 127.43, 126.11, 123.67, 120.42, 120.31,
109.79 ppm. MS (EI): m/z = 321.1267 [M]+.
3-(6-Fluoropyridin-2-yl)-9-phenyl-9H-carbazole (22). Yield:
1
89%; colorless oil. H NMR (400 MHz, CDCl3, 25 °C): δ =
8.84 (d, J = 1.6 Hz, 1H), 8.23 (d, J = 8.0 Hz, 1H), 8.07–8.05
(m, 1H), 7.88–7.82 (m, 1H), 7.75–7.72 (m, 1H), 7.65–7.61 (m,
2H), 7.59–7.57 (m, 2H), 7.51–7.47 (m, 1H), 7.46–7.40 (m, 3H),
7.35–7.31 (m, 1H), 6.84–6.82 (m, 1H) ppm. 13C NMR
(100 MHz, CDCl3, 25 °C): δ = 164.70, 162.34, 157.14, 157.00,
141.78, 141.62, 141.54, 137.42, 130.00, 129.68, 127.73, 127.07,
126.39, 125.04, 123.91, 123.59, 120.67, 120.47, 119.32, 116.93,
116.89, 110.06, 109.96, 106.72, 106.34 ppm. MS (EI): m/z =
338.1217 [M]+.
9-(4-(6-Methoxypyridin-3-yl)phenyl)-9H-carbazole (15). Yield:
74%; white solid, m.p. 157–158 °C. 1H NMR (400 MHz,
CDCl3, 25 °C): δ = 8.50 (d, J = 2.4 Hz, 1H), 8.16 (d, J =
7.6 Hz, 2H), 7.91–7.88 (m, 1H), 7.76–7.74 (m, 2H), 7.65 (d, J =
7.6 Hz, 2H), 7.48 (d, J = 8.0 Hz, 2H), 7.45–7.41 (m, 2H),
7.33–7.29 (m, 2H), 6.89 (d, J = 8.4 Hz, 1H), 4.02 (s, 3H) ppm.
13C NMR (100 MHz, CDCl3, 25 °C): δ = 163.88, 145.10,
140.83, 137.42, 137.02, 136.97, 129.24, 128.05, 127.58, 126.04,
123.49, 120.39, 120.09, 111.09, 109.82, 53.68 ppm. MS (EI):
m/z = 350.1418 [M]+.
1-(6-(9-Phenyl-9H-carbazol-3-yl)pyridin-2-yl)ethanone (23).
Yield: 86%; colorless oil. 1H NMR (400 MHz, CDCl3, 25 °C): δ
= 8.86 (d, J = 1.6 Hz, 1H), 8.25 (d, J = 7.6 Hz, 1H), 8.20 (d, J =
7.6 Hz, 1H), 8.04 (d, J = 7.6 Hz, 1H), 7.95 (d, J = 7.2 Hz, 1H),
7.89 (t, J = 7.6 Hz, 1H), 7.66–7.58 (m, 4H), 7.52–7.47 (m, 2H),
7.45–7.42 (m, 2H), 7.36–7.32 (m, 1H), 2.89 (s, 3H) ppm.
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13C NMR (100 MHz, CDCl3, 25 °C): δ = 200.88, 157.21,
153.39, 141.73, 141.53, 137.55, 137.44, 130.64, 130.00, 127.74,
127.09, 126.39, 125.15, 123.88, 123.55, 123.21, 120.49, 120.39,
119.00, 110.11, 25.93 ppm. MS (EI): m/z = 362.1415 [M]+.
Acknowledgements
The authors thank the financial support from the National
Natural Science Foundation of China (21076034, 20923006,
20836002), the Fundamental Research Funds for the Central
Universities (DUT11LK15), and the Ministry of Education
(the Program for New Century Excellent Talents in University).
3-(6-Methoxypyridin-2-yl)-9-phenyl-9H-carbazole (24). Yield:
1
75%; colorless oil. H NMR (400 MHz, CDCl3, 25 °C): δ =
8.82 (d, J = 1.2 Hz, 1H), 8.24–8.22 (m, 1H), 8.15–8.12 (m, 1H),
7.67–7.57 (m, 5H), 7.50–7.46 (m, 2H), 7.45–7.44 (m, 1H),
7.42 (d, J = 4.0 Hz, 2H), 7.35–7.29 (m, 1H), 6.68–6.66 (m, 1H),
4.10 (s, 3H) ppm. 13C NMR (100 MHz, CDCl3, 25 °C): δ =
163.81, 155.56, 141.47, 139.24, 137.61, 131.42, 129.96, 127.61,
127.10, 126.18, 125.12, 123.75, 123.72, 120.51, 120.24, 118.81,
112.52, 110.00, 109.83, 108.11, 53.32 ppm. MS (EI): m/z =
350.1419 [M]+.
Notes and references
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6-(9-Phenyl-9H-carbazol-3-yl)picolinonitrile (25). Yield: 81%;
white solid, m.p. 192–193 °C. 1H NMR (400 MHz, CDCl3,
25 °C): δ = 8.85 (d, J = 1.2 Hz, 1H), 8.25 (d, J = 8.0 Hz, 1H),
8.11–8.06 (m, 2H), 7.88 (t, J = 7.6 Hz, 1H), 7.64 (t, J = 8.0 Hz,
2H), 7.60–7.57 (m, 3H), 7.53–7.42 (m, 4H), 7.37–7.33 (m, 1H)
ppm. 13C NMR (100 MHz, CDCl3, 25 °C): δ = 159.58, 142.04,
141.57, 137.54, 137.25, 133.70, 130.02, 129.20, 127.84, 127.07,
126.53, 125.75, 125.04, 123.96, 123.43, 123.16, 120.63,
120.56, 119.47, 117.73, 110.16, 110.12 ppm. MS (EI): m/z =
345.1261 [M]+.
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9-Phenyl-3-(quinolin-2-yl)-9H-carbazole (26). Yield: 72%;
yellow oil. 1H NMR (400 MHz, CDCl3, 25 °C): δ = 8.99 (d, J =
1.6 Hz, 1H), 8.29–8.21 (m, 4H), 8.04 (d, J = 8.4 Hz, 1H), 7.84
(d, J = 8.0 Hz, 1H), 7.76–7.72 (m, 1H), 7.67–7.61 (m, 4H), 7.53
(d, J = 8.4 Hz, 2H), 7.51–7.48 (m, 1H), 7.45–7.43 (m, 2H),
7.36–7.32 (m, 1H) ppm. 13C NMR (100 MHz, CDCl3, 25 °C):
δ = 157.95, 148.48, 141.75, 141.55, 137.54, 136.69, 131.80,
129.99, 129.64, 129.57, 127.67, 127.54, 127.11, 126.99, 126.29,
125.89, 125.83, 124.00, 123.75, 120.72, 120.38, 119.87, 119.15,
110.09, 110.05 ppm. MS (EI): m/z = 370.1471 [M]+.
9-Phenyl-3-(pyrimidin-5-yl)-9H-carbazole (27). Yield: 75%;
white solid, m.p. 173–174 °C. 1H NMR (400 MHz, CDCl3,
25 °C): δ = 9.20 (s, 1H), 9.08 (s, 2H), 8.35 (d, J = 1.6 Hz, 1H),
8.21 (d, J = 7.6 Hz, 1H), 7.66–7.57 (m, 5H), 7.54–7.50 (m, 2H),
7.49–7.43 (m, 2H), 7.37–7.33 (m, 1H) ppm. 13C NMR
(100 MHz, CDCl3, 25 °C): δ = 156.79, 154.90, 141.51, 141.17,
137.24, 135.12, 130.06, 127.90, 127.10, 126.73, 126.00, 124.81,
124.33, 122.99, 120.53, 120.50, 118.89, 110.81, 110.18 ppm.
MS (EI): m/z = 321.1265 [M]+.
9-Phenyl-3-(pyrazin-2-yl)-9H-carbazole (28). Yield: 73%;
brown solid, m.p. 156–157 °C. 1H NMR (400 MHz, CDCl3,
25 °C): δ = 9.16 (d, J = 1.2 Hz, 1H), 8.84 (d, J = 1.6 Hz, 1H),
8.65 (t, J = 2.0 Hz, 1H), 8.48 (d, J = 2.8 Hz, 1H), 8.24 (d, J =
8.0 Hz, 1H), 8.10–8.07 (m, 1H), 7.64 (t, J = 8.0 Hz, 2H), 7.59
(d, J = 7.2 Hz, 2H), 7.53–7.50 (m, 2H), 7.47–7.42 (m, 2H),
7.36–7.32 (m, 1H) ppm. 13C NMR (100 MHz, CDCl3, 25 °C):
δ = 153.58, 144.07, 142.13, 142.00, 141.94, 141.57, 137.32,
130.02, 128.31, 127.83, 127.12, 126.52, 124.87, 124.10,
123.42, 120.62, 120.53, 119.28, 110.32, 110.11 ppm. MS (EI):
m/z = 321.1256 [M]+.
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