N-Arylation of carbazole by microwave-assisted ligand-free catalytic CuI reaction

Article abstract of DOI:10.1016/j.tet.2011.05.022

N-Arylation of carbazole has been achieved in high yields within 1 h using a microwave-assisted catalytic CuI reaction with no organic ligand. The N-arylation can be performed by various arylhalides, such as phenyl, pyridine, thiophene, and thiazole moieties. Specifically, N-arylated bromocarbazoles were converted into useful synthetic intermediates for functionalized carbazole materials.

Full text of DOI:10.1016/j.tet.2011.05.022

Tetrahedron 67 (2011) 4820e4825
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
N-Arylation of carbazole by microwave-assisted ligand-free catalytic CuI reaction
*
Jae Kwan Kwon, Joong Hyun Cho, Young-Sil Ryu, Se Hwan Oh, Eul Kgun Yum
Department of Chemistry, Chungnam National University, Yusung, Daejon 305-764, South Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
N-Arylation of carbazole has been achieved in high yields within 1 h using a microwave-assisted catalytic
CuI reaction with no organic ligand. The N-arylation can be performed by various arylhalides, such as
phenyl, pyridine, thiophene, and thiazole moieties. Specifically, N-arylated bromocarbazoles were con-
verted into useful synthetic intermediates for functionalized carbazole materials.
Ó 2011 Elsevier Ltd. All rights reserved.
Received 3 March 2011
Received in revised form 6 May 2011
Accepted 7 May 2011
Available online 13 May 2011
Keywords:
Carbazole
Microwave
N-Arylation
Catalytic
CuI
1. Introduction
times, and strong bases.10d,11b,13 Although several papers
have reported N-arylation of carbazoles synthesized by catalytic
High-speed synthesis using microwave technology has attracted
considerable attention in organic chemistry because it can accel-
erate slow thermal reactions.1 Microwave irradiation provides
advantages over conventional heating in chemical transformations,
such as accelerated reaction rates, significant energy savings, high
chemical yields, and cleaner reactions.2 Recently, microwave-
assisted copper (Cu)-catalyzed CeN-arylation has been shown
to efficiently synthesize indoles,3 imidazoles,4 amines,5 and
benzothiadiazines.6
Cu-mediated reactions, these results show only one or several ex-
amples with long reaction times.13,14
As part of our continuing organometallic research regarding
heterocycles, such as indoles,15 azaindoles,16 and quinolines,17 we
examined microwave-assisted catalytic Cu-mediated N-arylation of
carbazoles with our previously reported N-arylation conditions.16f
2. Results and discussion
Natural carbazole moieties have interesting biological activities,
such as protein kinase inhibition and antibacterial, anti-
inflammatory, and antitumor properies.7,8 Other synthetic carba-
zole derivatives have been used widely as functional building
blocks for optoelectronic applications.9 In the field of organic light-
emitting devices (OLEDs), organometallic complexes of carbazoles
have been reported as potential luminescent materials,10 especially
carbazole molecules containing a 2,7-linkage with heterocycles or
diarylamine.11 Polymeric carbazole derivatives have attracted in-
terest as solid-state dye-sensitized solar cells.12
Initially, we examined the thermal catalytic N-arylation of car-
bazole using arylhalides (X¼I, Br, Cl) under optimized reaction
conditions for imidazoles,18 alkylamine,19 and azaindoles16f with
a ligand-free catalytic CuI reaction. The results are presented in
Scheme 1.
X
20 mol % CuI, 2 eq Base
+
1.5
Additive, DMF, 150 oC, 48 h
N
Ph
N
H
N-Arylated carbazoles are important moieties for material sci-
ence. The typical preparation of N-arylated carbazoles has been the
traditional Ullmann-type CeN coupling reaction, which requires
stoichiometric amounts of copper, harsh conditions, long reaction
X = I
Base
X = Br
Base
Isolated yield
LiCl
1 eq
-
Isolated yield
LiCl
1 eq
-
K3PO4
87
85
90
85
K3PO4
21
19
"
"
Cs2CO3
1 eq
-
1 eq
-
Cs2CO3
25
19
"
"
* Corresponding author. Tel.: þ82 428215474; fax: þ82 428218896; e-mail
Scheme 1. N-Arylation of carbazole by thermal reaction conditions.
address: ekyum@cnu.ac.kr (E.K. Yum).
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.05.022

J.K. Kwon et al. / Tetrahedron 67 (2011) 4820e4825
4821
The reaction using iodobenzene provided high yields of
N-phenylcarbazole, but the reaction with bromobenzene provided
low yields of the desired product with large amounts of starting
materials left. However, chlorobenzene did not react with carbazole
under the reaction conditions used. The results showed that the
arylhalide and heterocyclic substrates were very sensitive to the N-
arylation reaction conditions. Many microwave-assisted reactions
have shown advantages over conventional heating for slow organic
reactions.2 Specifically, in a previous report on microwave-assisted
Cu-free N-arylation of indole with nitrobenzene containing halides
(X¼I, Br, Cl, and F), the reaction was efficient with F, but inefficient
for I, Br, and Cl.20 We applied the microwave-assisted Cu-free
N-arylation of carbazole with variation of the arylhalide at 220 ꢀC
for 1 h, but the reaction using arylhalide (X¼I, Br, Cl) afforded no
N-arylated product. Hence, we investigated microwave-assisted
Cu-mediated N-arylation of carbazole with bromobenzene to
optimize the N-arylation of carbazole in a short reaction time. The
results are summarized in Table 1.
for N-arylation of carbazoles were 1 equiv Cs2CO3, 10 mol % CuI,
and DMF at 220 ꢀC. N-Arylation was examined using various
aryliodides or bromides under optimal reaction conditions to di-
versify the N-arylated carbazole products. The results are sum-
marized in Table 2. The reaction using substituted iodobenzene
produced high yields of N-arylated carbazoles (Table 2, entries
1e4). Specifically, the reaction using 1-bromo-4-iodobenzene
produced N-substituted 4-bromophenyl carbazole with excellent
selectivity for the iodo substituent (Table 2, entry 2). Additionally,
reactions using heteroaryl bromides, such as pyridine, thiophene,
and thiazole, produced reasonable yields of N-heteroarylated
carbazoles (Table 2, entries 5e8). These results indicate that re-
actions using nitrogen-containing heterocycles produced the
same reactivity of the benzene ring, but reactions using diheter-
oarylbromide produced lower yields of the desired product. The
optimized reaction conditions were applied for the diversification
of substituted carbazoles using substituted aryliodides (Table 2,
entries 10e13). Good yields of N-arylated carbazole were obtained
Table 1
Table 2
Optimization of conditions for Cu-catalyzed N-arylation of carbazoles
N-Arylation of carbazoles with arylhalides
Br
5
4
10 mol % Cu
3
6
1 eq Base, 220 oC
10 % CuI, 1 eq Cs2CO3
Mw, DMF, 220 o
+
2
R1
7
+
X-Ar
9
N
H
N
Ph
Microwave , 1 h
R2
R1
C
R2
1
N
N
Ar
2
8
H
1
Entrya,b
Cu Source
Additive
Base
Solvent
Yield (%)
Entrya,b
R1
R2
XAr
Time
(min)
Product
Yield
(%)
1
2
3
4
5
6
7
8
CuI
CuI
CuI
CuI
CuI
CuI
CuI
CuI
LiCl
d
K2CO3
K2CO3
Cs2CO3
Cs2CO3
K3PO4
K3PO4
DBU
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMA
NMP
DMF
DMF
DMF
57
62
75
85
52
61
48
65
58
70
70
72
LiCl
d
1
2
3
4
H
H
H
H
H
H
H
H
20
30
40
40
2a
2b
2c
2d
96
79
85
91
LiCl
d
d
d
9
CuI
d
10
11
12
CuBr
CuCl
Cu(OAc)2
d
d
d
a
All reactions were conducted on a 1.0-mmol scale under 2 mL of solvent in
a Biotage 5-mL vial sealed crimp cap using an initiator instrument (EXP EU, Biotage,
400 W, 2450 MHz).
b
5
6
H
H
H
H
40
40
2e
2f
82
61
Vapor pressure of the reaction mixture in the vial was monitored as 5e7 bar at
220 ꢀC.
Reactions carried out at 210 ꢀC usually required twice the time
to reach completion, compared with reactions at 220 ꢀC. Yields
were higher when no chloride source was used than when LiCl
was added (Table 1, entries 1e6). We also examined the effects of
several Cu species that are used frequently for Cu-coupling re-
actions. N-Arylation of carbazoles using CuI produced higher
yields of the desired product compared to the reactions using
other copper sources (Table 1, entries 4 and 10e12). The yields
were slightly lower with the use of alternative Cu species, such as
CuBr, CuCl, and Cu(OAc)2. Reactions using Cs2CO3 as a base also
produced good yields of the desired product. However, reactions
using K2CO3, K3PO4, and 1,8-diazabicyclo(5.4.0)undec-7-ene
(DBU) as bases only produced moderate yields of the desired
product (Table 1, entries 1e7). We also investigated the effect of
different solvents under the same temperature conditions (Table
1, entries 4 and 8e9). The reaction using DMF as the solvent
produced good yields of the desired product, but the yields
changed from slightly to dramatically lower in different solvents.
The vapor pressure of the reaction mixture in the vial was moni-
tored as 5e7 bar using an online programmed Biotage microwave
reactor at 220 ꢀC. The results showed that the optimal conditions
7
8
H
H
H
H
40
40
2g
2h
89
44
9
2-Ph
2-Ph
2-Ph
H
H
H
30
30
30
2i
76
77
82
10
11
2j
2k
12
13
2-Br
2-Br
H
H
30
30
2l
82
85
2m
(continued on next page)

4822
J.K. Kwon et al. / Tetrahedron 67 (2011) 4820e4825
Table 2 (continued)
dibromocarbazole intermediates for possible applications in ma-
terial science.12a,21
Time
(min)
Yield
(%)
Entrya,b
14
R1
R2
XAr
Product
4. Experimental
3-Br
6-Br
30
30
2n
75
79
4.1. Instrumentation and analysis
15
16
3-Br
3-Br
6-Br
6-Br
2o
2p
All 1H and 13C NMR spectra were recorded on a Jeol 400 MHz
spectrometer, and chemical shifts were referenced to tetrame-
thylsilane (TMS) as an internal standard. The GCeMS spectra were
obtained using a Shimadzu QP 1000 GC-MS. Elemental analyses were
carried out by Chungnam National University using an elemental
analyzer (EA-1110). Microwave-assisted reactions were performed
with an initiator instrument (EXP EU, Biotage, 400 W, 2450 MHz).
Each reaction was carried out in a 5-mm-thickness Biotage 5-mL vial
sealed with a crimp cap. Reaction temperatures were measured
using infrared sensors on the outer surface of the reaction vial.
Products were purified by flash chromatography on 230e400-mesh
ASTM 60 silica gel. All base and Cu species were purchased from
SigmaeAldrich Chemical Co. Chemicals were used directly as
obtained from commercial sources unless otherwise noted.
30
82
17
18
2-Br
2-Br
7-Br
7-Br
30
30
2q
2r
80
88
19
2-Br
7-Br
30
2s
78
a
All reactions were conducted on a 1.0-mmol scale under 2 mL of solvent in
a Biotage 5-mL vial sealed crimp cap using an initiator instrument (EXP EU, Biotage,
400 W, 2450 MHz).
4.2. General experimental procedure for microwave-assisted
N-arylation of carbazoles
with substituent variations. N-Arylation of 2,7- and 3,6-dibro-
mocarbazole were also examined using aryliodo compounds.
The reactions produced N-arylated dibromocarbazoles in good-to-
excellent yields (Table 2, entries 14e19). However, N-arylation of
dibromocarbazole with arylbromide produced low yields of the
desired product due to nonselective Cu-catalyst reactivity for
arylbromide and bromocarbazole.
The N-arylated bromocarbazoles could be converted into useful
OLED or solar-cell intermediates by conventional palladium-
catalyzed Heck-, Suzuki-, and Stille-coupling reaction conditions
(Scheme 2).
9H-Carbazole (1.0 mmol), Cs2CO3 (1.0 mmol), iodobenzene
(1.1 mmol), CuI (0.1 mmol), and DMF (2 mL) were added to a 5-mL
vial. The vial was sealed with a crimp cap and placed in a Biotage
initiator microwave cavity. After irradiation at 220 ꢀC for the ap-
propriate time and subsequent cooling, the reaction mixture was
diluted with saturated aqueous ammonium chloride. Products
were isolated by extraction into ethyl acetate. The organic layer was
dried over anhydrous magnesium sulfate, filtered, and concen-
trated. Products were purified by silica gel column chromatography
using a hexane/ethyl acetate solvent. N-Phenyl-carbazole (2a)22
was obtained (96% yield) as a white solid. Mp 86e87 ꢀC; 1H NMR
(400 MHz, CDCl3)
d
8.18 (d, 2H, J¼7.6 Hz), 7.61 (m, 4H), 7.50 (t, 1H),
7.44 (d, 4H, J¼7.6 Hz), 7.32 (m, 2H); 13C NMR (100 MHz, CDCl3)
d
107.6, 104.5, 96.6, 94.2, 93.9, 92.7, 90.1, 87.0, 86.6, 76.5; MS (m/z,
relative intensity): 243 (Mþ, 100), 140 (11), 120 (16); Anal. Calcd for
C18H13N1: C, 88.89; H, 5.35; N, 5.76. Found: C, 88.73; H, 5.29, N, 5.98.
The following compounds (2bes) were prepared with
microwave-assisted general experimental procedures.
N
N
3a
3b
Sn(Bu)3
Pd(PPh3)4
Pd(PPh3)2Cl2
82%
80 %
Br
4.2.1. 9-(4-Bromophenyl)-9H-carbazole (2b)23. The product (2b)
was obtained as a white solid in 79% isolated yield from 9H-car-
bazole and 1-bromo-4-iodobenzene. Mp 142e143 ꢀC; 1H NMR
N
Pd(PPh3
)
Pd(PPh3
)
4
4
B(OH)2
Sn(Bu)3
(400 MHz, CDCl3)
d
8.12 (d, 2H, J¼4.4 Hz), 7.89 (d,1H, J¼4.4 Hz), 7.70
N
(d, 1H, J¼8.4 Hz), 7.40 (m, 5H), 7.29 (m, 3H); 13C NMR (100 MHz,
CDCl3)
d 140.6, 139.1, 133.1, 128.9, 128.7, 126.1, 123.5, 120.4, 120.2,
N
N
N
109.5; MS (m/z, relative intensity): 322 (Mþ, 100), 321 (97), 241
c
3
3d
(75), 121 (20).
88%
80%
4.2.2. 9-(4-Methoxyphenyl)-9H-carbazole (2c). Product (2c) was
obtained as a white solid in 85% isolated yield from 9H-carbazole
Scheme 2. Functionalization of N-arylated bromocarbazole by palladium-catalyzed
coupling reactions.
and 4-bromoanisole. 1H NMR (400 MHz, CDCl3)
d 8.12 (d, 2H,
J¼7.6 Hz), 7.44 (m, 4H), 7.14 (m, 6H), 3.83 (s, 3H); 13C NMR
3. Conclusions
(100 MHz, CDCl3) d 160.8, 140.8, 138.8, 130.5, 125.9, 123.3, 120.2,
119.9, 119.3, 113.2, 112.6, 109.9, 55.4; MS (m/z, relative intensity):
273 (Mþ, 77), 230 (12), 228 (10), 182 (21), 181 (100), 180 (77), 152
(17); Anal. Calcd for C19H15N1: C, 88.71; H, 5.84; N, 5.45. Found: C,
88.73; H, 5.79, N, 5.48.
Simple and efficient N-arylation of carbazoles was achieved
using microwave-assisted catalytic CuI reactions without an or-
ganic ligand in a short reaction time. The selective reactivity of
arylhalide could be extended to various halocarbazoles. N-Ary-
lated halocarbazoles gave promising results for the functionali-
zation of carbazole moieties with palladium-catalyzed coupling
reactions. We will examine the synthesized N-arylated
4.2.3. 9-(Pyridin-2-yl)-9H-carbazole (2d). Product (2d) was
obtained as a white solid in 91% isolated yield from 9H-carbazole
and 2-bromopyridine. Mp 89e91 ꢀC; 1H NMR (400 MHz, CDCl3)

J.K. Kwon et al. / Tetrahedron 67 (2011) 4820e4825
4823
d
8.71 (d, 1H, J¼7.6 Hz), 8.11 (d, 2H, J¼7.6 Hz), 7.89 (d, 1H, J¼7.6,
120.6,109.3,107.7,100.1; MS (m/z, relative intensity): 364 (Mþ,100),
318 (45), 241 (17).
1.6 Hz), 7.82 (d, 2H, J¼4.4 Hz), 7.61 (d, 1H, J¼4.4 Hz), 7.42 (t, 2H,
J¼7.2 Hz), 7.29 (m, 3H); 13C NMR (100 MHz, CDCl3)
d 151.8, 149.6,
139.5, 138.5, 126.2, 124.3, 121.2, 120.9, 120.2, 119.1, 111.1; MS (m/z,
relative intensity): 244 (Mþ, 100), 243 (73), 242 (10), 121 (13); Anal.
Calcd for C17H12N2: C, 83.58; H, 4.95; N, 11.47. Found: C, 83.52; H,
4.96; N, 11.52.
4.2.10. 9-(4-(Benzyloxy)phenyl)-2-phenyl-9H-carbazole (2k). The
product (2k) was obtained as a white solid in 82% isolated yield
from 2-phenyl-9H-carbazole and 1-(benzyloxy)-4-iodobenzene.
Mp 125e127 ꢀC; 1H NMR (400 MHz, CDCl3)
d
8.12 (d, 2H, J¼8.4 Hz),
7.6 (d, 2H, J¼8.4 Hz), 7.2e7.5 (m, 15H), 7.12 (d, 2H, J¼8.4 Hz), 5.08 (s,
2H); 13C NMR (100 MHz, CDCl3)
158.1, 141.9, 139.3, 136.6, 130.3,
4.2.4. 9-(Pyridin-3-yl)-9H-carbazole (2e). The product (2e) was
obtained as a white solid in 82% isolated yield from 9H-carbazole
and 3-bromopyridine. Mp 109e111 ꢀC; 1H NMR (400 MHz, CDCl3)
d
128.7, 128.1, 127.9, 127.5, 127.0, 125.9, 122.9, 122.3, 120.9, 120.5,
120.3, 116.0, 114.8, 109.7, 108.2, 70.3; MS (m/z, relative intensity):
425 (Mþ, 50), 334 (100), 304 (19), 91 (55).
d
8.89 (s, 1H), 8.72 (d, 1H, J¼4.4 Hz), 8.14 (d, 2H, J¼7.6 Hz), 7.91 (d,
1H, J¼8.0 Hz), 7.56 (dd, 1H, J¼8.0, 4.8 Hz), 7.35 (m, 6H); 13C NMR
(100 MHz, CDCl3)
d
148.6, 148.5, 140.6, 134.6, 134.5, 126.2, 124.4,
4.2.11. 2-Bromo-9-(4-bromophenyl)-9H-carbazole (2l). The product
(2l) was obtained as a white solid in 82% isolated yield from 2-
bromo-9H-carbazole and 1-bromo-4-iodobenzene. Mp 128e
123.7, 120.5, 120.5, 109.3; MS (m/z, relative intensity): 244 (Mþ,
100), 243 (43), 242 (16), 121 (13); Anal. Calcd for C17H12N2: C, 83.58;
H, 4.95; N, 11.47. Found: C, 83.54; H, 4.97; N, 11.49.
130 ꢀC; 1H NMR (400 MHz, CDCl3)
d
8.08 (d, 1H, J¼8.0 Hz), 7.93 (d,
1H, J¼8.0 Hz), 7.72 (d, 1H, J¼8.0 Hz), 7.47 (d, 1H, J¼1.6 Hz), 7.39 (m,
4H), 7.30 (m, 3H); 13C NMR (100 MHz, CDCl3)
141.2, 140.6, 139.1,
4.2.5. 9-(Pyrimidin-2-yl)-9H-carbazole (2f). The product (2f) was
obtained as a white solid in 61% isolated yield from 9H-carbazole
and 2-bromopyrimidine. Mp 112 ꢀC; 1H NMR (400 MHz, CDCl3)
d
135.9, 133.1, 128.7, 128.5, 126.3, 123.2, 122.6, 122.2, 121.2, 120.5,
120.2, 119.4, 112.4, 109.5; MS (m/z, relative intensity): 403 (Mþ2,
50), 401 (Mþ, 100), 399 (Mꢁ2, 50), 241 (91), 121 (35).
d
8.83 (m, 4H), 8.06 (d, 2H, J¼7.6 Hz), 7.50 (t, 2H, J¼7.6 Hz), 7.36 (t,
2H, J¼7.6 Hz), 7.08 (t, 1H, J¼4.8 Hz); 13C NMR (100 MHz, CDCl3)
d
157.9, 139.1, 126.6, 125.8, 122.3, 119.5, 116.2, 116.0; Anal. Calcd for
4.2.12. 2-Bromo-9-(3-nitrophenyl)-9H-carbazole (2m). The product
(2m) was obtained as a yellow solid in 85% isolated yield from 2-
bromo-9H-carbazole and 1-iodo-3-nitrobenzene. Mp 136e138 ꢀC;
C17H12N3: C, 78.37; H, 4.49; N, 17.14. Found: C, 78.32; H, 4.47;
N, 17.21.
1H NMR (400 MHz, CDCl3)
d
8.51 (d, 1H, J¼8.0 Hz), 8.12 (d, 1H,
4.2.6. 9-(Thiophen-2-yl)-9H-carbazole (2g). The product (2g) was
obtained as a yellow oil in 89% isolated yield from 9H-carbazole and
J¼8.0 Hz), 7.89 (m, 2H), 7.4 (m, 4H), 7.24 (m, 3H); 13C NMR
(100 MHz, CDCl3)
d 149.1, 143.2, 138.1, 132.6, 132.1, 130.8, 130.4,
2-bromothiophene. 1H NMR (400 MHz, CDCl3)
d
8.13 (dd, 2H, J¼7.6,
0.8 Hz), 7.47 (m, 4H), 7.55 (dd, 1H, J¼7.6, 0.8 Hz) 7.33 (m, 2H) 7.21
(m, 2H); 13C NMR (100 MHz, CDCl3)
142.0, 138.7, 126.2, 126.1,
126.6, 123.8, 122.4, 121.7, 121.5, 121.1, 120.3, 112.1, 109.2; MS (m/z ,
relative intensity): 368 (Mþ2, 98), 366 (Mþ,100), 241
(50),120 (35).
d
124.8, 124.2, 123.4, 120.5, 120.2, 110.2; MS (m/z, relative intensity):
250 (Mþ1, 38), 249 (Mþ, 100), 248 (12), 247 (10), 204 (40); Anal.
Calcd for C16H11N1S1: C, 77.11; H, 4.44; N, 5.62. Found: C, 77.08;
H, 4.46; N, 5.58.
4.2.13. 3,6-Dibromo-9-(4-bromophenyl)-9H-carbazole (2n). The
product (2n) was obtained as a white solid in 75% isolated yield
from 3,6-dibromo-9H-carbazole and 1-bromo-4-iodobenzene. Mp
181e183 ꢀC; 1H NMR (400 MHz, CDCl3)
d
8.13 (d, 2H, J¼8.4 Hz), 7.71
4.2.7. 2-(9H-Carbazol-9-yl)thiazole (2h). The product (2h) was
obtained as a white solid in 44% isolated yield from the CuI-
mediated reaction of 9H-carbazole and 2-bromothiazole. Mp
(d, 2H, J¼8.4 Hz), 7.47 (dd, 2H, J¼8.4, 1.6 Hz), 7.34 (m, 4H); 13C NMR
(400 MHz, CDCl3)
d 137.6, 131.6, 127.7, 126.9, 126.7, 122.2, 121.5,
111.6, 109.4; MS (m/z, relative intensity): 483 (Mþ4, 36), 481 (Mþ2,
83e85 ꢀC; 1H NMR (400 MHz, CDCl3)
d
8.22 (d, 2H, J¼7.6 Hz),
98), 479 (Mþ, 88), 477 (Mꢁ2, 36), 239 (100).
8.06 (d, 2H, J¼7.6 Hz), 7.75 (d, 1H, J¼2.8 Hz), 7.49 (t, 2H,
J¼7.6 Hz), 7.35 (t, 2H, J¼7.6 Hz), 7.21 (t, 2H, J¼2.8 Hz); 13C NMR
4.2.14. 3,6-Dibromo-9-(3-nitrophenyl)-9H-carbazole
(2o). The
(100 MHz, CDCl3)
d
159.0, 139.8, 139.3, 126.8, 124.7, 122.1, 120.1,
product (2o) was obtained as a yellow solid in 79% isolated yield
from 3,6-dibromo-9H-carbazole and 1-iodo-3-nitrobenzene. Mp
114.5, 112.8; MS (m/z, relative intensity): 250 (Mþ, 100), 249
(12), 224 (13), 191 (13), 125 (12), 58 (14); Anal. Calcd for C15
H10N2S1: C, 71.97; H, 4.06; N, 11.17. Found: C, 71.95; H, 4.03;
N, 11.20.
173e174 ꢀC; 1H NMR (400 MHz, CDCl3)
d 8.13 (s, 2H), 7.71 (d, 2H,
J¼8.0 Hz), 7.47 (dd, 2H, J¼8.0, 1.2 Hz), 7.34 (m, 4H); 13C NMR
(100 MHz, CDCl3)
d 131.2, 130.9, 129.2, 128.4, 122.0, 121.2, 120.3,
109.5, 108.6; MS (m/z, relative intensity): 448 (Mþ2, 34), 446 (Mþ,
61), 444 (Mꢁ2, 32), 321 (61), 239 (100).
4.2.8. 9-(4-Bromophenyl)-2-phenyl-9H-carbazole (2i). The product
(2i) was obtained as a white solid in 76% isolated yield from
2-phenyl-9H-carbazole
and
1-bromo-4-iodobenzene.
Mp
4.2.15. Methyl 4-(3, 6-dibromo-9H-carbazol-9-yl)benzoate (2p). The
product (2p) was obtained as a white solid in 82% isolated yield
from 3,6-dibromo-9H-carbazole and methyl 4-iodobenzoate. Mp
120e122 ꢀC; 1H NMR (400 MHz, CDCl3)
d
8.19 (t, 2H, J¼8.0 Hz), 7.76
(d, 2H, J¼8.0 Hz), 7.67 (d, 2H, J¼7.2 Hz), 7.30 (m, 10H); 13C NMR
(100 MHz, CDCl3)
d
141.7, 141.1, 141.0, 139.5, 139.0, 137.3, 136.6, 133.1,
125e126 ꢀC; 1H NMR (400 MHz, CDCl3)
d
8.38 (dd,1H, J¼8.4,1.6 Hz),
128.8, 128.7, 127.1, 126.0, 120.9, 120.6, 120.4, 119.8, 109.5, 107.9; MS
(m/z, relative intensity): 399 (Mþ2, 98), 397 (Mþ, 100), 317 (26),
241 (12).
8.14 (d, 1H, J¼1.6 Hz), 8.05 (d, 1H, J¼1.6 Hz), 7.68 (t, 1H, J¼7.4 Hz),
7.53 (m, 3H), 7.27 (m, 3H), 4.57 (s, 3H); 13C NMR (100 MHz, CDCl3)
d
165.3, 130.7, 128.7, 128.1, 125.4, 122.2, 110.5, 109.2, 51.5; MS (m/z,
relative intensity): 461 (Mþ2, 57), 459 (Mþ, 100), 457 (Mꢁ2, 48),
4.2.9. 9-(3-Nitrophenyl)-2-phenyl-9H-carbazole (2j). The product
(2j) was obtained in 77% isolated yield from 2-phenyl-9H-carbazole
and 1-iodo-3-nitrobenzene. Mp 118e120 ꢀC; 1H NMR (400 MHz,
321 (40), 239 (97).
4.2.16. 2,7-Dibromo-9-(4-bromophenyl)-9H-carbazole (2q). The
product (2q) was obtained as a white solid in 80% isolated yield
from 2,7-dibromo-9H-carbazole and 1-bromo-4-iodo- benzene.
CDCl3)
7.91 (t, 1H, J¼7.8 Hz), 7.75 (d, 1H, J¼8.4 Hz), 7.45e7.60 (m, 4H),
7.25e7.40 (m, 6H); 13C NMR (100 MHz, CDCl3)
133.0, 130.9, 128.8,
127.5, 127.3, 126.4, 124.8, 124.2, 123..9, 123.1, 122.1, 121.0, 120.8,
d
8.45 (s, 1H), 8.27 (d, 1H, J¼7.2 Hz), 8.12 (t, 2H, J¼7.8 Hz),
d
Mp 134e136 ꢀC; 1H NMR (400 MHz, CDCl3)
d
7.93 (d, 2H, J¼8.8 Hz),
7.75 (d, 2H, J¼8.8 Hz), 7.40 (m, 6H); 13C NMR (100 MHz, CDCl3)

4824
J.K. Kwon et al. / Tetrahedron 67 (2011) 4820e4825
d
137.2, 131.3, 126.4, 126.4, 121.6, 119.5, 119.3, 117.4, 116.4, 110.5; MS
magnesium sulfate, filtered, and concentrated. Product (3c) was
obtained as a white solid in 88% isolated yield by silica gel col-
umn chromatography using a hexane/ethyl acetate solvent. Mp
(m/z, relative intensity): 483 (Mþ4, 30), 481 (Mþ2, 98), 479 (Mþ,
98), 477 (Mꢁ2, 30), 239 (100).
128e130 ꢀC; 1H NMR (400 MHz, CDCl3)
d
8.01 (dd, 2H, J¼8.0,
1.2 Hz), 7.61 (d, 2H, J¼8.0 Hz), 7.54 (d, 2H, J¼1.2 Hz), 7.40 (m, 3H),
7.32 (m, 8H); 13C NMR (100 MHz, CDCl3)
141.7, 141.1, 141.0,
4.2.17. 2,7-Dibromo-9-(3-nitrophenyl)-9H-carbazole
(2r). The
product (2r) was obtained as a yellow solid in 88% isolated yield
from 2,7-dibromo-9H-carbazole and 1-iodo-3-nitrobenzene. Mp
d
139.5, 139.0, 137.3, 136.6, 133.1, 128.9, 128.7, 127.1, 126.0, 120.9,
120.6, 120.4, 119.8, 109.5, 107.9; MS (m/z, relative intensity): 319
(Mþ, 100).
126e128 ꢀC; 1H NMR (400 MHz, CDCl3)
d
8.39 (d, 1H, J¼8.4 Hz),
8.22 (d, 1H, J¼8.4 Hz), 7.94 (d, 1H, J¼1.6 Hz), 7.67 (m, 3H), 7.54 (m,
4H); 13C NMR (100 MHz, CDCl3)
134.6, 131.4, 129.3, 125.1, 124.6,
d
123.5, 122.8, 121.8, 112.6; MS (m/z, relative intensity): 448 (Mþ2,
4.3.4. 9-Phenyl-2-(pyridin-2-yl)-9H-carbazole (3d). Pd(PPh3)4 (60 mg,
0.05 mmol), 2-bromo-9-phenyl-carbazole (321 mg, 1 mmol), and
2-(tributylstannyl)pyridine (552 mg, 1.5 mmol) were dissolved in
3 mL of 1,4-dioxane in 10 mL vial with screw cap. The reaction was
stirred at 100 ꢀC in oil bath for 5 h. The reaction mixture was diluted
with saturated aqueous ammonium chloride. Products were isolated
by extraction into ethyl acetate. The organic layer was dried over
anhydrous magnesium sulfate, filtered, and concentrated. The prod-
uct (3c) was obtained as a white solid in 80% isolated yield. Mp
52), 446 (Mþ, 100), 444 (Mꢁ2, 50), 319 (41), 239 (58).
4.2.18. 4-(2,7-Dibromo-9H-carbazol-9-yl)aniline (2s)21. The prod-
uct (2s) was obtained as a white solid in 78% isolated yield from 2,7-
dibromo-9H-carbazole and 4-iodoaniline. Mp 185e187 ꢀC; 1H NMR
(400 MHz, CDCl3)
d
7.91 (d, 2H, J¼8.0 Hz), 7.36 (m, 4H), 7.18 (d, 2H,
J¼8.0 Hz), 6.81 (d, 2H, J¼8.0 Hz); 13C NMR (100 MHz, CDCl3)
d 147.1,
142.9, 128.5, 127.0, 123.2, 121.4, 117.3, 116.0, 113.1; MS (m/z, relative
intensity): 418 (Mþ2, 52), 416 (Mþ, 100), 414 (Mꢁ2, 50), 256 (70).
88e90 ꢀC; 1H NMR (400 MHz, CDCl3)
2H, J¼8.0, 1.2 Hz), 8.04 (s, 1H), 7.87 (d, 1H, J¼8.4 Hz), 7.72 (q, 2H), 7.58
(m, 4H), 7.27 (m, 5H); 13C NMR (100 MHz, CDCl3)
157.1, 148.6, 140.7,
d
8.63 (d,1H, J¼8.0 Hz), 8.17 (dd,
4.3. Functionalization of 2-bromo-9-phenyl-carbazole by
palladium-catalyzed coupling reactions
d
140.4, 136.5, 136.5, 135.1, 128.9, 126.6, 125.3, 123.0, 122.0, 120.8, 120.0,
119.5, 118.1, 108.9, 107.3; MS (m/z, relative intensity): 320 (Mþ, 100),
319 (Mꢁ1, 69).
4.3.1. 9-Phenyl-2-vinyl-9H-carbazole (3a). Pd(PPh3)4 (60 mg,
0.05 mmol), 2-bromo-9-phenylcarbazole (321 mg, 1 mmol), and
tributyl(vinyl)stannane (475 mg, 1.5 mmol) were dissolved in 3 mL
of 1,4-dioxane in a 10-mL vial with a screw cap. The reaction was
stirred at 100 ꢀC in oil bath for 6 h, the reaction mixture was di-
luted with saturated aqueous ammonium chloride, and the
products were isolated by extraction into ethyl acetate. The or-
ganic layer was dried over anhydrous magnesium sulfate, filtered,
and concentrated. Product (3a) was obtained as a white solid in
82% isolated yield by silica gel column chromatography using
a hexane/ethyl acetate solvent. Mp 81e83 ꢀC; 1H NMR (400 MHz,
Acknowledgements
This work was supported by a grant from the Fundamental R&D
Program for Core Technology of Materials funded by the Ministry of
Knowledge Economy, Republic of Korea.
References and notes
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J¼8.4, 1.6 Hz), 7.57 (s, 1H), 7.51 (m, 5H), 7.48 (t, 2H, J¼7.4 Hz), 7.34
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d 8.07 (dd, 2H,
d
129.3,127.7,127.5,126.5,125.8,123.0,122.8,122.3,119.9,119.7,119.6,
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4.3.3. 2,9-Diphenyl-9H-carbazole
(3c). Pd(PPh3)4
(60
mg,
0.05 mmol), 2-bromo-9-phenyl-carbazole (231 mg, 1 mmol),
phenylboronic acid (181 mg, 1.5 mmol), and K2CO3 (2 mmol)
were dissolved in 3 mL of toluene in 10 mL vial sealed with
screw cap. The reaction mixture was stirred at 100 ꢀC in oil bath
for 6 h. The reaction mixture was diluted with saturated aqueous
ammonium chloride. Products were isolated by extraction into
ethyl acetate. The organic layer was dried over anhydrous

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