MCM-41-immobilized bidentate nitrogen copper(I) complex: A highly efficient and recyclable catalyst for Buchwald N-arylation of indoles

Article abstract of DOI:10.1016/j.tet.2013.04.106

The heterogeneous N-arylation reaction of indoles with aryl halides was achieved in toluene at 110 C by using 4 mol % MCM-41-immobilized bidentate nitrogen copper(I) complex [MCM-41-2N-CuI] as catalyst and K₃PO ₄ as base, yielding a variety of N-arylindoles in good to excellent yields. The heterogeneous copper catalyst exhibited as high activity as homogeneous CuI/diamine catalytic system and can be easily prepared by a simple two-step procedure from commercially available and cheap reagents and recovered by a simple filtration of the reaction solution and reused for 10 cycles with almost consistent activity.

Full text of DOI:10.1016/j.tet.2013.04.106

Tetrahedron xxx (2013) 1e7
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
MCM-41-immobilized bidentate nitrogen copper(I) complex:
a highly efficient and recyclable catalyst for Buchwald N-arylation
of indoles
,
a,
Ruian Xiao a, Hong Zhao b , Mingzhong Cai
*
*
a Key Laboratory of Functional Small Organic Molecule, Ministry of Education and Department of Chemistry, Jiangxi Normal University,
Nanchang 330022, PR China
b School of Chemistry and Chemical Engineering, Guangdong Pharmaceutical University, Guangzhou 510006, PR China
a r t i c l e i n f o
a b s t r a c t
The heterogeneous N-arylation reaction of indoles with aryl halides was achieved in toluene at 110 ꢀC by
using 4 mol % MCM-41-immobilized bidentate nitrogen copper(I) complex [MCM-41e2N-CuI] as catalyst
and K3PO4 as base, yielding a variety of N-arylindoles in good to excellent yields. The heterogeneous
copper catalyst exhibited as high activity as homogeneous CuI/diamine catalytic system and can be easily
prepared by a simple two-step procedure from commercially available and cheap reagents and recovered
by a simple filtration of the reaction solution and reused for 10 cycles with almost consistent activity.
Ó 2013 Published by Elsevier Ltd.
Article history:
Received 4 February 2013
Received in revised form 14 April 2013
Accepted 23 April 2013
Available online xxx
Keywords:
Immobilized catalyst
Bidentate nitrogen copper(I) complex
N-Arylation
Indole
Heterogeneous catalysis
1. Introduction
to promote copper-catalyzed N-arylation of indoles and other
heterocycles.
The N-aryl nitrogen heterocycle motif is present in numerous
natural products and biologically active pharmaceutical products.1
Various strategies have been developed for the N-arylation of het-
erocycles. The Ullmann-type coupling of aryl halides with nitrogen
heterocycles represents a straightforward, inexpensive approach to
N-aryl nitrogen heterocycles.2 These copper-catalyzed reactions
usually suffer from several limitations such as high reaction tem-
peratures, generally 140 ꢀC or more, use of stoichiometric amounts
of copper reagents, long reaction times, and low yields. The
palladium-catalyzed N-arylation of heterocycles is an alternative
method under mild reaction conditions.3 However, use of expensive
palladium limits the attractiveness of this method for industrial
applications. The efficiency of copper-catalyzed Ullmann reactions
has been improved by the correct choice of copper sources, bases,
ligands, and other additives in the past few years, several mild and
efficient methods havebeen reported for the N-arylation of indoles.4
Ligands based on diamines,5 oximeephosphine oxide,6 amino-
acids,7 phosphoramidite,8 proline,9 and diimines10 have been used
Although these copper-catalyzed N-arylations of indoles or
other heterocycles are highly efficient, the problem with homoge-
neous catalysis is the difficulty to separate the catalyst from the
reaction mixture and the impossibility to reuse it in consecutive
reactions. In addition, homogeneous catalysis might result in un-
acceptable copper contamination of the desired isolated product,
which is a particularly significant drawback for its application in the
pharmaceutical industry. To overcome these problems, the de-
velopment of highly efficient and recyclable heterogeneous cata-
lysts, such as immobilization of catalytically active species, i.e.,
organometallic complexes, onto a solid support to produce a mo-
lecular heterogeneous catalyst is essential.11 Heterogeneous catal-
ysis also helps to minimize wastes derived from reaction workup,
contributing to the development of green chemical processes.12 In
spite of tremendous effort dedicated to the immobilization of ho-
mogeneous palladium complexes over the last two decades,13 very
few examples of carbonecarbon or carboneheteroatom bond for-
mation reactions catalyzed by heterogeneous copper catalysts have
appeared.14 Therefore, the development of a stable heterogeneous
copper catalyst that allows for highly efficient N-arylation of a wide
range of substrates (indoles and aryl halides) is worthwhile.
* Corresponding authors. Fax: þ86 791 8812 0388; e-mail addresses: zhao-
hong1001@sina.com (H. Zhao), mzcai@jxnu.edu.cn (M. Cai).
0040-4020/$ e see front matter Ó 2013 Published by Elsevier Ltd.
http://dx.doi.org/10.1016/j.tet.2013.04.106
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2
R. Xiao et al. / Tetrahedron xxx (2013) 1e7
Developments on the mesoporous material MCM-41 provided
be the most effective (Table 1, entry 7), DMF and NMP also afforded
good yields (Table 1, entries 12 and 14). While other solvents such as
xylene, DCE, and benzene were substantially less effective (Table 1,
entries 13, 15, and 16). The effect of reaction temperature and time
on the reaction was also investigated. It was found that the reaction
was accomplished when it was carried out in toluene at 110 ꢀC for
24 h. Reducing the reaction temperature resulted in a decrease in
yield (Table 1, entries 17 and 18). Finally, the amount of supported
copper catalyst was also screened, and 4.0 mol % loading of copper
was found to be optimal, a lower yield was observed when the
amount of the catalyst was decreased (Table 1, entry 19). Increasing
the amount of copper catalyst could shorten the reaction time, but
did not increase the yield of N-phenylindole (Table 1, entry 20). The
N-arylation reaction did not take place in the absence of the catalyst
(Table 1, entry 21). Thus, the optimized reaction conditions for this
N-arylation reaction of indole are the MCM-41e2N-CuI (4.0 mol %)
in toluene using K3PO4 as base at 110 ꢀC under Ar for 24 h (Table 1,
entry 7).
With this promising result in hand, we started to investigate the
scope of this reaction under the optimized conditions. The scope of
both indoles and aryl halides was explored, and the results are
summarized in Table 2. As shown in Table 2, the N-arylation reaction
of indole with a variety of aryl iodides proceeded smoothly under
mild conditions affording the corresponding N-arylindoles 3aeo in
good to excellent yields (entries 1e15). Various electron-donating
and electron-withdrawing substituents such as eCH3, eOCH3,
eNH2, eCl, eF, eCF3, eCN, eCO2CH3, eCOCH3, and eNO2 on aryl
iodides were well tolerated. The reactivity of aryl iodides having
electron-withdrawing groups was higher than that of aryl iodides
having electron-donating groups. The reactions of sterically hin-
dered aryl iodides such as 2-iodotoluene and 2-iodoanisole with
indole also provided good yields of the desired N-arylindoles 3b and
3e under the optimized reaction conditions, respectively (entries 2
and 5). The N-arylation of heteroaryl iodides such as 2-
iodothiophene and 3-iodopyridine with indole gave the corre-
sponding N-heteroarylindoles 3p and 3q in 90 and 94% yields, re-
spectively (entries 16 and 17). The bulky 1-iodonaphthalene also
a new possible candidate for a solid support for immobilization of
homogeneous catalysts.15 MCM-41 has a regular pore diameter of
ca.5 nm and a specific surface area >700 m2 gꢁ116 Its large pore size
.
allows passage of large molecules such as organic reactants and
metal complexes through the pores to reach to the surface of the
channel.17 To date, some palladium and rhodium complexes on
functionalized MCM-41 support have been prepared and success-
fully used in organic reactions.11b,18 Very recently, we reported the
synthesis of the first MCM-41-immobilized bidentate nitrogen
copper(I) complex and found that it is a highly efficient and re-
cyclable heterogeneous catalyst for the homo- and heterocoupling
of terminal alkynes.14d However, to the best of our knowledge, no
N-arylation of indoles catalyzed by immobilization of copper in
MCM-41 has been described in the open literature. In continuing
our efforts to develop greener synthetic pathways for organic
transformations, herein we wish to report a highly efficient, het-
erogeneous N-arylation of indoles with aryl halides catalyzed by an
MCM-41-immobilized bidentate nitrogen copper(I) complex under
mild reaction conditions.
2. Results and discussion
The MCM-41-immobilized bidentate nitrogen copper(I) com-
plex (MCM-41e2N-CuI) was conveniently prepared starting from
commercially available and inexpensive 3-(2-aminoethylamino)
propyltrimethoxysilane and CuI according to our previous pro-
cedure14d (Scheme 1). Firstly, the mesoporous material MCM-41
reacted with 3-(2-aminoethylamino)propyltrimethoxysilane in
toluene at 100 ꢀC for 24 h, followed by the silylation with Me3SiCl in
toluene at room temperature for 24
h to generate 3-(2-
aminoethylamino)propyl-functionalized MCM-41 (MCM-41e2N).
The latter was subsequently treated with CuI in DMF at room
temperature for 7 h to generate the MCM-41-immobilized biden-
tate nitrogen copper(I) complex (MCM-41e2N-CuI) as a pale blue
powder, the copper content of the complex was found to be
0.45 mmol gꢁ1 according to the ICP-AES measurements.
Scheme 1.
In our initial screening experiments, the N-arylation reaction of
indole with iodobenzene was investigated to optimize the reaction
conditions, and the results are summarized in Table 1. At first, the
base effect was examined, and a significant base effect was observed.
It is evident that good to high yields were obtained when Bu3N,
Na2CO3, Cs2CO3, K2CO3, K3PO4, and Et3N were used as the base (Table
1, entries 1e3, 6e8), whereas DBU, t-BuOK, and CsF afforded low to
moderate yields (Table 1, entries 5, 9, 10) and KF was ineffective
(Table 1, entry 4), so K3PO4 was finally selected as the base for the
reaction. The N-arylation reaction did not occur without base (Table
1, entry 11). Our next studies focused on the effect of solvent on the
model reaction. Among the solvents examined, toluene was found to
reacted effectively with indole to afford the desired N-(1-naphthyl)
indole (3r) in good yield (entry 18). This heterogeneous copper
catalyst exhibited as high activity as homogeneous CuI/diamine
catalytic system. For example, the N-arylation reaction of 4-
iodonitrobenzene (1.2 equiv) with indole in the presence of
4 mol % of MCM-41e2N-CuI in toluene using K3PO4 (2.0 equiv) as
base at 110 ꢀC for 24 h gave a 98% yield of the N-arylated product 3m
(entry 13), the same reaction of indole (1.2 equiv) with 4-
iodonitrobenzene in the presence of 1 mol % of CuI and 10 mol % of
racemic trans-1,2-cyclohexanediamine in dioxane using K3PO4
(2.1 equiv) as base at 110 ꢀC for 24 h gave 3m in 99% yield.5a Com-
parison with homogeneous analogous catalysts such as CuI/
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R. Xiao et al. / Tetrahedron xxx (2013) 1e7
3
Table 1
Reaction condition screening for the N-arylation of indole with iodobenzenea
Entry
Base
Solvent
Temp (ꢀC)
Time (h)
Yieldb (%)
1
2
3
4
5
6
7
8
Bu3N
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
DMF
Xylene
NMP
DCE
Benzene
Toluene
Toluene
Toluene
Toluene
Toluene
110
110
110
110
110
110
110
110
110
110
110
140
130
110
80
24
24
24
24
24
24
24
24
24
24
48
24
24
24
36
36
30
48
48
15
48
81
79
70
Trace
37
75
92
77
57
30
0
81
52
82
67
72
85
76
81
91
0
Na2CO3
Cs2CO3
KF
t-BuOK
K2CO3
K3PO4
Et3N
9
DBU
CsF
10
11
12
13
14
15
16
17
18
19c
20d
21e
None
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
80
100
80
110
110
110
a
Reaction conditions: indole (1.0 mmol), iodobenzene (1.2 mmol), copper catalyst (4.0 mol %), base (2.0 mmol), solvent (2.0 mL).
Isolated yield.
Copper catalyst (2.0 mol %) was used.
Copper catalyst (8.0 mol %) was used.
No copper catalyst.
b
c
d
e
Table 2
Heterogeneous copper-catalyzed N-arylation of indoles with aryl halidesa
Entry
R
Ar/X
Product
Yieldb (%)
1
2
3
4
5
6
7
8
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Ph/I
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
3p
3q
3r
92
83
92
91
79
90
93
89
96
94
91
95
98
96
95
90
94
79
87
90
92
94
89
91
78
83
88
59
57
0
2-CH3C6H4/I
3-CH3C6H4/I
4-CH3C6H4/I
2-CH3OC6H4/I
4-CH3OC6H4/I
3-CF3C6H4/I
4-NH2C6H4/I
4-CH3OCOC6H4/I
4-ClC6H4/I
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25c
26c
27c
28c
29c
30c
4-FC6H4/I
3-O2NC6H4/I
4-O2NC6H4/I
4-CH3COC6H4/I
4-NCC6H4/I
2-Thienyl/I
H
H
3-Pyridinyl/I
1-Naphthyl/I
4-ClC6H4/I
3-Pyridinyl/I
4-ClC6H4/I
2-CH3
2-CH3
5-CH3
5-CH3
5-CHO
5-CHO
H
H
H
H
H
3s
3t
3u
3v
3w
3x
3y
3n
3m
3h
3m
3h
3-Pyridinyl/I
4-ClC6H4/I
3-Pyridinyl/I
4-PhenylC6H4/Br
4-CH3COC6H4/Br
4-O2NC6H4/Br
4-NH2C6H4/Br
4-O2NC6H4/Cl
4-NH2C6H4/Cl
H
a
Reaction conditions: indole (1.0 mmol), aryl halide (1.2 mmol), MCM-41e2N-CuI (4.0 mol %), K3PO4 (2.0 mmol), toluene (2.0 mL) at 110 ꢀC for 24 h.
Isolated yield.
For 48 h.
b
c
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4
R. Xiao et al. / Tetrahedron xxx (2013) 1e7
H2N(CH2)2NH2 was also made in order to assess the immobilization
effect on activity. When 4 mol % of CuI and 10 mol % of H2N(CH2)2NH2
were used as the catalytic system, the N-arylation reaction of 4-
iodonitrobenzene (1.2 equiv) with indole in toluene using K3PO4
(2.0 equiv) as base at 110 ꢀC for 24 h afforded 3m in 85% yield.
The optimized reaction conditions were also applied to the N-
ether. After being air-dried, it can be reused directly without further
purification. The recovered copper catalyst was used in the next
run, and almost consistent activity was observed for 10 consecutive
cycles (Table 3, entries 1e10). In addition, copper leaching in the
immobilized catalyst was also determined. The copper content of
the catalyst was found by ICP analysis to be 0.43 mmol gꢁ1 after 10
Table 3
N-Arylation reaction of indole with 4-nitroiodobenzene catalyzed by the recycled catalysta
Cycle
Yieldb (%)
Cycle
Yieldb (%)
1
3
5
7
9
98
98
97
95
95
2
4
6
8
10
97
97
96
96
95
a
Reaction was carried out with indole (1 mmol), 4-nitroiodobenzene (1.2 mmol), MCM-41e2N-CuI (4.0 mol %), K3PO4 (2.0 mmol), toluene (2.0 mL) at 110 ꢀC for 24 h.
Isolated yield.
b
arylation reactions of a variety of substituted indoles such as 2-
consecutive runs, only 4.4% of copper had been lost from the MCM-
41 support. The high stability and excellent reusability of the cat-
alyst should result from the chelating action of bidentate 2-
aminoethylamino ligand on copper and the mesoporous structure
of the MCM-41 support. The result is important from a practical
point of view. The high catalytic activity, excellent reusability, and
the easy accessibility of the MCM-41e2N-CuI make it a highly at-
tractive heterogeneous copper catalyst for the parallel solution
phase synthesis of diverse libraries of compounds.
methylindole, 5-methylindole, and indole-5-carboxaldehyde with
various aryl iodides, the results are also summarized in Table 2. As
shown in Table 2, the reactions of a variety of substituted indoles
having either electron-donating or electron-withdrawing groups
with aryl iodides also proceeded smoothly to give the corre-
sponding N-arylated indoles 3sex in high yields (entries 19e24).
The reactivity of 2-methylindole was slightly lower than that of 5-
methyl-indole due to the steric effect. The method provides a quite
general route for the synthesis of N-arylindoles having various
functionalities. The results above prompted us to investigate the
reaction of indole with aryl bromides or chlorides. The reactions of
indole with various aryl bromides could proceed efficiently under
the optimized reaction conditions to afford the desired N-arylated
indoles in moderate to good yields on longer reaction times (entries
25e28). The reactivity of aryl chlorides was obviously lower than
that of aryl bromides, the reaction of only 4-nitrochlorobenzene
with indole could give a moderate yield of desired product 3m
after 48 h (entry 29).
In order to determine whether the catalysis was due to the
MCM-41e2N-CuI complex or to a homogeneous copper complex
that comes off the support during the reaction and then returns to
the support at the end, we performed the hot filtration test.19 We
focused on the N-arylation reaction of indole with iodobenzene. We
filtered off the MCM-41e2N-CuI complex after 5 h of reaction time
and the filtered solution was concentrated under reduced pressure.
To the residue were added 10 mol % of racemic trans-1,2-
cyclohexanediamine in dioxane (2 mL) and K3PO4 (2.0 mmol) and
the mixture was stirred at 110 ꢀC under Ar for 24 h to give 3a in 41%
yield. The catalyst filtration was performed at the reaction tem-
perature (110 ꢀC) in order to avoid possible recoordination or pre-
cipitation of soluble copper upon cooling. The reaction of indole
with iodobenzene at 110 ꢀC for 5 h before the hot filtration could
afford 3a in 42% yield. We found that, after this hot filtration, no
further reaction was observed. This result suggests that the copper
catalyst remains on the MCM-41 support at elevated temperatures
during the reaction and points to a process of heterogeneous nature.
For a heterogeneous transition-metal catalyst, it is important to
examine its ease of separation, recoverability, and reusability. We
also investigated the recyclability of the MCM-41e2N-CuI by using
the N-arylation reaction of indole with 4-nitroiodobenzene. After
carrying out the reaction, the catalyst was separated by simple
filtration and washed with distilled water, ethanol, and diethyl
3. Conclusions
In summary, we have developed a novel, practical, and envi-
ronmentally friendly method for the synthesis of N-arylindoles
through the reaction of indoles with aryl halides by using an MCM-
41-immobilized bidentate nitrogen copper complex as catalyst
under mild reaction conditions. The reactions generated the cor-
responding N-arylindoles in good to excellent yields and were ap-
plicable to various indoles and a variety of aryl iodides or bromides.
This heterogeneous copper catalyst can be very conveniently pre-
pared by a simple two-step procedure from commercially available
and cheap reagents. In addition, this methodology offers the
competitiveness of recyclability of the catalyst without significant
loss of catalytic activity, and the catalyst could be easily recovered
and reused for at least 10 cycles, thus making this procedure en-
vironmentally more acceptable.
4. Experimental
4.1. Physical measurements and materials
All chemicals were reagent grade and used as purchased. All
solvents were dried and distilled before use. The products were
purified by flash chromatography on silica gel and a mixture of
EtOAc and petroleum ether was generally used as eluent. IR spectra
were determined on a PerkineElmer 683 instrument. 1H NMR
spectra (400 MHz) were recorded on a Bruker Avance 400 MHz
spectrometer with TMS as an internal standard in CDCl3 as solvent.
13C NMR spectra (100 MHz) were recorded on a Bruker Avance
400 MHz spectrometer in CDCl3 as solvent. Microanalyses were
measured by using a Yanaco MT-3 CHN microelemental analyzer.
The MCM-41e2N-CuI complex was prepared according to our
previous procedure, the copper content was 0.45 mmol gꢁ114d
.
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R. Xiao et al. / Tetrahedron xxx (2013) 1e7
5
4.2. Typical experimental procedure for the synthesis of N-
arylindoles
(m, 2H), 7.53 (d, J¼8.0 Hz,1H), 7.30 (d, J¼3.2 Hz,1H), 7.24 (t, J¼7.6 Hz,
1H), 7.19 (t, J¼7.6 Hz, 1H), 6.70 (d, J¼3.2 Hz, 1H). 13C NMR (100 MHz,
2
CDCl3):
d
¼140.3, 135.6, 132.2 (q, JCF¼33.0 Hz), 130.3, 129.5, 127.5,
To a resealable Schlenk tube were added indole (1.0 mmol),
K3PO4 (0.424 g, 2.0 mmol), and MCM-41e2N-CuI (88 mg,
0.04 mmol), and the reaction vessel was fitted with a rubber sep-
tum. The vessel was evacuated and back-filled with argon and this
evacuation/back-fill procedure was repeated one additional time.
The aryl halide (1.2 mmol) and toluene (2 mL) were then added
under a stream of argon. The reaction tube was quickly sealed and
the contents were stirred while heating in an oil bath at 110 ꢀC for
24e48 h. After completion of the reaction, the reaction mixture was
cooled to room temperature, diluted with ethyl acetate (5 mL), and
filtered. The MCM-41e2N-CuI complex was washed with distilled
water (2ꢂ5 mL), ethanol (2ꢂ5 mL), and Et2O (2ꢂ5 mL) and reused
in the next run. The filtrate was concentrated under reduced
pressure and the residue was purified by flash column chroma-
tography on silica gel (petroleum/ethyl acetate¼50:1 to 4:1) to
provide the desired product.
127.3, 123.7 (q, 1JCF¼271.0 Hz), 122.9 (q, 3JCF¼4.0 Hz), 121.4, 120.9 (q,
3JCF¼4.0 Hz), 110.1, 104.7. IR (film, cmꢁ1): 1596, 1520, 1496, 1463,
1321, 1130, 1068, 742.
4.2.8. N-(4-Aminophenyl)indole (3h). Colorless oil. 1H NMR
(400 MHz, CDCl3):
d
¼7.67 (d, J¼7.2 Hz, 1H), 7.43 (d, J¼7.6 Hz, 1H),
7.24e7.11 (m, 5H), 6.72 (d, J¼8.4 Hz, 2H), 6.62 (d, J¼3.2 Hz, 1H), 3.71 (s,
2H). 13C NMR (100 MHz, CDCl3):
d¼145.3, 136.5, 130.9, 128.9, 128.5,
126.1, 122.0, 121.0, 119.9, 115.7, 110.5, 102.5. IR (film, cmꢁ1): 3455, 3371,
1622, 1520, 1458, 1282, 1135, 832, 743. Anal. Calcd for C14H12N2: C,
80.75; H, 5.81; N, 13.45. Found: C, 80.52; H, 5.54; N, 13.53.
4.2.9. N-(4-Methoxycarbonylphenyl)indole (3i). White solid.5d 1H
NMR (400 MHz, CDCl3):
d
¼8.17 (d, J¼8.4 Hz, 2H), 7.68 (d, J¼7.6 Hz,
1H), 7.62 (d, J¼8.0 Hz, 1H), 7.56 (d, J¼8.4 Hz, 2H), 7.35 (d, J¼3.2 Hz,
1H), 7.27e7.18 (m, 2H), 6.71 (d, J¼3.2 Hz, 1H), 3.94 (s, 3H). 13C NMR
(100 MHz, CDCl3):
d
¼166.5, 143.8, 135.4, 131.3, 129.8, 127.6, 127.5,
4.2.1. N-Phenylindole (3a). Colorless oil.20 1H NMR (400 MHz, CDCl3):
123.3,122.9,121.5,121.0,110.6,105.0, 52.3. IR (KBr, cmꢁ1): 1710,1639,
1617, 1457, 1285, 1135, 1069, 953, 861.
d
¼7.68 (d, J¼8.0 Hz, 1H), 7.55 (d, J¼8.0 Hz, 1H), 7.50e7.47 (m, 4H),
7.35e7.31 (m, 2H), 7.21 (t, J¼7.2 Hz, 1H), 7.16 (t, J¼7.2 Hz, 1H), 6.67 (d,
J¼¼2.8 Hz, 1H). 13C NMR (100 MHz, CDCl3):
d¼139.8, 135.8, 129.6,
4.2.10. N-(4-Chlorophenyl)indole (3j). Colorless oil.21 1H NMR
129.3, 127.9, 126.4, 124.3, 122.3, 121.1, 120.3, 110.5, 103.5. IR (film,
(400 MHz, CDCl3):
d
¼7.68 (d, J¼8.0 Hz, 1H), 7.51e7.41 (m, 5H), 7.27
cmꢁ1): 2924, 1596, 1502, 1138, 745, 688.
(d, J¼3.2 Hz, 1H), 7.25e7.17 (m, 2H), 6.68 (d, J¼3.6 Hz, 1H). 13C NMR
(100 MHz, CDCl3):
d
¼138.2, 135.6, 131.8, 129.7, 129.3, 127.6, 125.4,
4.2.2. N-(2-Methylphenyl)indole (3b). Colorless oil.21 1H NMR
122.6,121.2,120.6,110.2,104.0. IR (film, cmꢁ1): 1641,1567,1517,1495,
(400 MHz, CDCl3):
d
¼7.71e7.69 (m, 1H), 7.37e7.31 (m, 4H), 7.18e7.13
1455, 1333, 1134, 1089, 954, 831, 739.
(m, 3H), 7.06e7.03 (m, 1H), 6.67 (d, J¼3.2 Hz, 1H), 2.07 (s, 3H). 13
C
NMR (100 MHz, CDCl3):
d¼138.3, 137.0, 135.9, 131.2, 128.7, 128.3,
4.2.11. N-(4-Fluorophenyl)indole (3k). Colorless oil.22 1H NMR
128.2, 128.1, 126.8, 122.0, 120.9, 119.9, 110.6, 102.5, 17.7. IR (film,
(400 MHz, CDCl3):
d
¼7.65 (d, J¼8.0 Hz, 1H), 7.41 (d, J¼8.0 Hz, 1H),
cmꢁ1): 2924, 1583, 1512, 1496, 1462, 1331, 1235, 742.
7.34e7.30 (m, 2H), 7.19e7.06 (m, 4H), 6.62 (d, J¼3.2 Hz, 1H). 13C NMR
1
(100 MHz, CDCl3):
d
¼161.2 (d, JCF¼245.0 Hz) 136.3, 136.0 (d,
4.2.3. N-(3-Methylphenyl)indole (3c). Colorless oil.20 1H NMR
(400 MHz, CDCl3):
4JCF¼3.0 Hz), 129.4, 128.2, 126.3 (d, JCF¼8.0 Hz), 122.7, 121.4, 120.7,
116.6 (d, 2JCF¼23.0 Hz), 110.4, 103.8. IR (film, cmꢁ1): 1515, 1458, 1334,
1213, 1135, 838, 742.
3
d¼7.67 (d, J¼7.6 Hz, 1H), 7.55 (d, J¼8.0 Hz, 1H), 7.34
(t, J¼7.6 Hz, 1H), 7.29e7.26 (m, 3H), 7.22e7.11 (m, 3H), 6.64 (d,
J¼2.8 Hz, 1H), 2.40 (s, 3H). 13C NMR (100 MHz, CDCl3):
¼139.8, 139.7,
d
135.9, 129.5, 129.4, 128.1, 127.3, 125.1, 122.4, 121.5, 121.2, 120.4, 110.7,
103.5, 21.6. IR (film, cmꢁ1): 2920, 1608, 1590, 1515, 1494, 1459, 1335,
1215, 741, 698.
4.2.12. N-(3-Nitrophenyl)indole (3l). Pale yellow solid.5c 1H NMR
(400 MHz, CDCl3):
d
¼8.39 (t, J¼4.0 Hz, 1H), 8.19 (d, J¼8.0 Hz, 1H),
7.87 (d, J¼8.0 Hz, 1H), 7.71 (t, J¼8.0 Hz, 2H), 7.59 (d, J¼8.0 Hz, 1H),
7.37 (d, J¼3.2 Hz,1H), 7.29 (t, J¼7.4 Hz,1H), 7.23 (t, J¼7.6 Hz,1H), 6.76
4.2.4. N-(4-Methylphenyl)indole (3d). Colorless oil.5d 1H NMR
(400 MHz, CDCl3):
(d, J¼3.2 Hz, 1H). 13C NMR (100 MHz, CDCl3):
¼149.1, 140.9, 135.4,
d
d¼7.67 (d, J¼7.6 Hz, 1H), 7.51 (d, J¼8.0 Hz, 1H), 7.35
130.6, 129.7, 129.6, 127.3, 123.3, 121.6, 121.3, 120.8, 118.7, 110.1, 105.4.
IR (KBr, cmꢁ1): 1638, 1618, 1537, 1348, 1068, 984, 864, 728.
(d, J¼8.4 Hz, 2H), 7.28e7.26 (m, 3H), 7.21e7.12 (m, 2H), 6.64 (d,
J¼3.2 Hz, 1H), 2.39 (s, 3H). 13C NMR (100 MHz, CDCl3):
¼137.4, 136.4,
d
136.1, 130.3, 129.3, 128.2, 124.4, 122.3, 121.2, 120.3, 110.6, 103.3, 21.2. IR
4.2.13. N-(4-Nitrophenyl)indole (3m). Pale yellow solid.5d 1H NMR
(film, cmꢁ1): 2921, 1608, 1519, 1457, 1333, 1213, 821, 740.
(400 MHz, CDCl3):
d
¼8.40 (d, J¼8.8 Hz, 2H), 7.72e7.64 (m, 4H), 7.38
(d, J¼2.8 Hz, 1H), 7.32e7.24 (m, 2H), 6.78 (d, J¼2.8 Hz, 1H). 13C NMR
4.2.5. N-(2-Methoxyphenyl)indole (3e). Colorless oil.5d 1H NMR
(100 MHz, CDCl3):
d
¼145.3, 145.1, 135.3, 130.1, 127.1, 125.6, 123.4,
(400 MHz, CDCl3):
d¼7.66 (d, J¼8.0 Hz, 1H), 7.38e7.32 (m, 2H),
123.3,121.7,121.6, 110.5,106.2. IR (KBr, cmꢁ1): 1641,1594,1566, 1505,
1456, 1326, 1137, 1069, 953, 854.
7.27e7.02 (m, 6H), 6.64 (d, J¼3.2 Hz, 1H), 3.71 (s, 3H). 13C NMR
(100 MHz, CDCl3):
d
¼154.6, 136.9, 129.5, 128.7, 128.6, 128.3, 128.2,
122.6, 122.0, 120.9, 120.0, 112.6, 110.9, 102.6, 55.8. IR (film, cmꢁ1):
4.2.14. N-(4-Acetylphenyl)indole (3n). White solid.5d 1H NMR
2926, 1578, 1249, 1112, 1013, 822, 789.
(400 MHz, CDCl3):
d
¼8.09 (d, J¼8.4 Hz, 2H), 7.69 (d, J¼7.6 Hz, 1H),
7.64 (d, J¼8.0 Hz, 1H), 7.58 (d, J¼8.4 Hz, 2H), 7.36 (d, J¼1.6 Hz, 1H),
7.26 (t, J¼7.2 Hz, 1H), 7.20 (t, J¼7.2 Hz, 1H), 6.72 (s, 1H), 2.64 (s, 3H).
4.2.6. N-(4-Methoxyphenyl)indole (3f). Colorless oil.5d 1H NMR
(400 MHz, CDCl3):
d
¼7.68 (d, J¼7.6 Hz, 1H), 7.45 (d, J¼8.4 Hz, 1H), 7.40
13C NMR (100 MHz, CDCl3):
d¼197.0, 143.8, 135.4, 134.5, 130.1, 129.9,
(d, J¼8.8 Hz, 2H), 7.27 (d, J¼3.2 Hz, 1H), 7.20 (t, J¼7.6 Hz, 1H), 7.15 (t,
J¼7.6 Hz, 1H), 7.03 (d, J¼8.8 Hz, 2H), 6.65 (d, J¼3.2 Hz, 1H), 3.87 (s, 3H).
127.4, 123.3, 123.0, 121.5, 121.1, 110.6, 105.1, 26.7. IR (KBr, cmꢁ1): 1673,
1600, 1516, 1458, 1357, 1163, 1075, 952, 860, 732.
13C NMR (100 MHz, CDCl3):
d¼158.2, 136.3, 132.8, 129.0, 128.3, 126.0,
122.2, 121.0, 120.1, 114.7, 110.4, 102.9, 55.6. IR (film, cmꢁ1): 2925, 1641,
4.2.15. N-(4-Cyanophenyl)indole (3o). White solid.23 1H NMR
1565, 1519, 1458, 1249, 1163, 1075, 836, 747.
(400 MHz, CDCl3):
d
¼7.73 (d, J¼8.4 Hz, 2H), 7.67 (d, J¼7.6 Hz, 1H),
7.58e7.54 (m, 3H), 7.29 (d, J¼3.6 Hz, 1H), 7.25 (t, J¼7.6 Hz, 1H), 7.20
4.2.7. N-(3-Trifluoromethylphenyl)indole (3g). Colorless oil.22 1H
(d, J¼7.2 Hz, 1H), 6.72 (d, J¼3.2 Hz, 1H). 13C NMR (100 MHz, CDCl3):
NMR (400 MHz, CDCl3):
d¼7.76 (s, 1H), 7.69e7.65 (m, 2H), 7.62e7.58
d¼143.6, 135.3, 133.8, 130.0, 127.1, 123.9, 123.3, 121.7, 121.4, 118.5,
Please cite this article in press as: Xiao, R.; et al., Tetrahedron (2013), http://dx.doi.org/10.1016/j.tet.2013.04.106

6
R. Xiao et al. / Tetrahedron xxx (2013) 1e7
110.4, 109.4, 105.8. IR (KBr, cmꢁ1): 2221, 1604, 1512, 1456, 1134, 1068,
953, 839, 732.
1069, 954, 864. Anal. Calcd for C15H10NOCl: C, 70.45; H, 3.94; N, 5.47.
Found: C, 70.21; H, 4.07; N, 5.22.
4.2.16. N-(2-Thienyl)indole (3p). Colorless oil.22 1H NMR (400 MHz,
4.2.24. N-(3-Pyridinyl)indole-5-carboxaldehyde (3x). White solid. 1H
CDCl3):
d
¼7.64 (d, J¼8.0 Hz, 1H), 7.57 (d, J¼8.4 Hz, 1H), 7.26e7.10 (m,
NMR (400 MHz, CDCl3):
d
¼10.1 (s, 1H), 8.85 (s, 1H), 8.70 (d, J¼4.0 Hz,
4H), 7.04e6.98 (m, 2H), 6.63 (d, J¼2.8 Hz, 1H). 13C NMR (100 MHz,
1H), 8.24 (s, 1H), 7.88e7.81 (m, 2H), 7.58e7.52 (m, 2H), 7.43 (d,
CDCl3):
d
¼141.6, 137.0, 129.2, 128.9, 126.0, 122.8, 121.5, 121.0, 120.8,
J¼3.6 Hz, 1H), 6.90 (d, J¼3.2 Hz, 1H). 13C NMR (100 MHz, CDCl3):
120.3, 110.6, 104.1. IR (film, cmꢁ1): 1611, 1551, 1460, 1312, 1227, 1202,
d
¼192.1, 148.5, 146.0, 139.1, 135.7, 131.9, 130.5, 129.5, 129.3, 126.4,
841, 742.
124.3,123.3, 110.6,106.3. IR (KBr, cmꢁ1): 1681, 1640, 1564, 1417, 1259,
1122, 1069, 954, 864. Anal. Calcd for C14H10N2O: C, 75.67; H, 4.54; N,
12.60. Found: C, 75.39; H, 4.61, N, 12.42.
4.2.17. N-(3-Pyridinyl)indole (3q). Colorless oil.5d 1H NMR (400 MHz,
CDCl3):
d
¼8.80 (s, 1H), 8.56 (d, J¼4.0 Hz, 1H), 7.76 (d, J¼7.2 Hz, 1H),
7.68 (d, J¼7.2 Hz, 1H), 7.49 (d, J¼8.0 Hz, 1H), 7.40e7.37 (m, 1H), 7.27
4.2.25. N-(4-Biphenyl)indole (3y). White solid.22 1H NMR (400 MHz,
(d, J¼3.2 Hz, 1H), 7.25e7.16 (m, 2H), 6.70 (d, J¼2.4 Hz, 1H). 13C NMR
CDCl3):
d
¼7.74e7.69 (m, 3H), 7.65e7.56 (m, 5H), 7.48 (t, J¼7.6 Hz,
(100 MHz, CDCl3):
d¼147.4, 145.5, 136.3, 135.6, 131.2, 129.4, 127.3,
2H), 7.41e7.37 (m, 2H), 7.25e7.18 (m, 2H), 6.70 (d, J¼3.2 Hz, 1H). 13
C
124.0, 122.8, 121.3, 120.8, 109.9, 104.7. IR (film, cmꢁ1): 1722, 1584,
NMR (100 MHz, CDCl3):
d¼139.8, 138.9, 138.5, 135.4, 128.9, 128.5,
1518, 1487, 1456, 1334, 1214, 809, 742.
127.8, 127.4, 127.1, 126.6, 124.1, 122.0, 120.7, 120.0, 110.1, 103.3. IR (KBr,
cmꢁ1): 1642, 1567, 1486, 1458, 1135, 1070, 954, 862, 753.
4.2.18. N-(1-Naphthyl)indole (3r). White solid.24 1H NMR (400 MHz,
CDCl3):
d
¼7.93 (d, J¼7.6 Hz, 2H), 7.74 (d, J¼7.6 Hz, 1H), 7.56e7.43 (m,
Acknowledgements
3H), 7.37 (d, J¼8.0 Hz, 1H), 7.34e7.32 (m, 2H), 7.18e7.09 (m, 2H), 7.02
(d, J¼8.0 Hz, 1H), 6.75 (d, J¼2.8 Hz, 1H). 13C NMR (100 MHz, CDCl3):
We thank the National Natural Science Foundation of China (no.
21272044) and Key Laboratory of Functional Small Organic Mole-
cule, Ministry of Education (no. KLFS-KF-201213) for financial
support.
d
¼137.9, 136.0, 134.4, 130.5, 129.7, 128.4, 128.2, 126.9, 126.6, 125.4,
125.1, 123.3, 122.1, 120.9, 120.1, 110.8, 102.9. IR (KBr, cmꢁ1): 1640,
1594, 1567, 1454, 1404, 1141, 1071, 954, 778.
4.2.19. N-(4-Chlorophenyl)-2-methylindole(3s). White solid.1H NMR
References and notes
(400 MHz, CDCl3):
d
¼7.58 (d, J¼8.4 Hz, 1H), 7.49 (d, J¼8.8 Hz, 2H),
7.27 (d, J¼8.8 Hz, 2H), 7.14e7.06 (m, 3H), 6.41 (s, 1H), 2.29 (s, 3H). 13
C
1. (a) Comprehensive Heterocyclic Chemistry II; Katritzky, A. R., Rees, C. W., Eds.;
Elsevier: Oxford, UK, 1996; (b) Craig, P. N. In Comprehensive Medicinal Chemistry;
Drayton, C. J., Ed.; Pergamon: New York, NY, 1991; Vol. 8.
2. (a) Ullmann, F. Ber. Dtsch. Chem. Ges. 1903, 36, 2382e2384; (b) Ullmann, F. Ber.
Dtsch. Chem. Ges. 1904, 37, 853e854; (c) Lindley, J. Tetrahedron 1984, 40,
1433e1456; (d) Unangst, P. C.; Connor, D. T.; Stabler, S. R.; Weikert, R. J. J.
Heterocycl. Chem. 1987, 24, 811e816; (e) Kato, Y.; Conn, M. M.; Rebek, J. J. Am.
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K. H.; Alcazar-Roman, L. M. J. Org. Chem. 1999, 64, 5575e5580; (c) Old, D. W.;
Harris, M. C.; Buchwald, S. L. Org. Lett. 2000, 2, 1403e1406; (d) Watanabe, M.;
Nishiyama, M.; Yamamoto, T.; Koie, Y. Tetrahedron Lett. 2000, 41, 481e483; (e)
Grasa, G. A.; Viciu, M. S.; Huang, J.; Nolan, S. P. J. Org. Chem. 2001, 66, 7729e7737.
4. (a) Kunz, K.; Scholz, U.; Ganzer, D. Synlett 2003, 2428e2439; (b) Beletskaya, I. P.;
Cheprakov, A. V. Coord. Chem. Rev. 2004, 248, 2337e2364; (c) Corbet, J.-P.;
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NMR (100 MHz, CDCl3):
d¼138.1, 136.8, 136.6, 133.5, 129.8, 129.3,
128.3,121.4,120.4,119.8,109.9,101.8,13.4. IR (KBr, cmꢁ1): 2919,1593,
1557, 1493, 1458, 1322, 1088, 1013, 823, 738. Anal. Calcd for
C15H12NCl: C, 74.52; H, 5.00; N, 5.79. Found: C, 74.31; H, 5.11; N, 5.58.
4.2.20. 2-Methyl-N-(3-pyridinyl)indole (3t). White solid. 1H NMR
(400 MHz, CDCl3): ¼8.67e8.65 (m, 2H), 7.67e7.64 (m, 1H), 7.56 (d,
J¼8.4 Hz, 1H), 7.46e7.42 (m, 1H), 7.13e7.05 (m, 3H), 6.43 (s, 1H), 2.29
(s, 3H). 13C NMR (100 MHz, CDCl3):
d
d¼149.1, 148.7, 138.1, 136.6, 135.2,
134.6, 128.4, 124.0, 121.6, 120.6, 119.8, 109.5, 102.4, 13.3. IR (KBr,
cmꢁ1): 2920, 1610, 1585, 1557, 1483, 1458, 1425, 1318, 781, 747. Anal.
Calcd for C14H11N2: C, 80.75; H, 5.81; N, 13.45. Found: C, 80.81; H,
5.64; N, 13.32.
4.2.21. N-(4-Chlorophenyl)-5-methylindole (3u). White solid. 1H
NMR (400 MHz, CDCl3):
d
¼7.45e7.36 (m, 6H), 7.21 (d, J¼3.2 Hz, 1H),
7.04 (d, J¼8.4 Hz, 1H), 6.58 (d, J¼3.2 Hz, 1H), 2.45 (s, 3H). 13C NMR
(100 MHz, CDCl3):
d¼138.6, 134.1, 131.7, 130.0, 129.8, 129.7, 127.7,
125.3, 124.3, 121.0, 110.0, 103.7, 21.4. IR (KBr, cmꢁ1): IR (film, cmꢁ1):
2919, 1596, 1497, 1333, 1221, 1091, 834, 794, 717. Anal. Calcd for
C15H12NCl: C, 74.52; H, 5.00; N, 5.79. Found: C, 74.28; H, 4.77; N, 5.54.
4.2.22. 5-Methyl-N-(3-pyridinyl)indole (3v). White solid. 1H NMR
(400 MHz, CDCl3):
d
¼8.80 (s, 1H), 8.56 (d, J¼4.0 Hz, 1H), 7.77 (d,
J¼8.0 Hz, 1H), 7.46 (s, 1H), 7.41e7.38 (m, 2H), 7.25 (d, J¼2.8 Hz, 1H),
7.06 (d, J¼8.4 Hz, 1H), 6.63 (d, J¼2.8 Hz, 1H), 2.45 (s, 3H). 13C NMR
(100 MHz, CDCl3):
d
¼147.3, 145.4, 136.6, 134.1, 131.1, 130.3, 129.9,
127.4, 124.5, 124.1, 121.1, 109.8, 104.5, 21.4. IR (KBr, cmꢁ1): 2919, 1585,
1490, 1429, 1222, 1159, 909, 794, 711. Anal. Calcd for C14H12N2: C,
80.75; H, 5.81; N, 13.45. Found: C, 80.49; H, 5.59; N, 13.21.
4.2.23. N-(4-Chlorophenyl)indole-5-carboxaldehyde
solid. 1H NMR (400 MHz, CDCl3):
(3w). White
¼10.1 (s, 1H), 8.22 (d, J¼0.8 Hz,
d
15. Kresge, C. T.; Leonowicz, M. E.; Roth, W. J.; Vartuli, J. C.; Beck, J. S. Nature 1992,
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16. Beck, J. S.; Vartuli, J. C.; Roth, W. J.; Leonowicz, M. E.; Kresge, C. T.; Schmitt, K. D.;
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Schlenker, J. L. J. Am. Chem. Soc. 1992, 114, 10834e10843.
1H), 7.82e7.79 (m,1H), 7.57e7.53 (m, 3H), 7.45 (d, J¼8.8 Hz, 2H), 7.39
(d, J¼3.6 Hz, 1H), 6.85 (d, J¼2.8 Hz, 1H). 13C NMR (100 MHz, CDCl3):
d
¼192.2, 139.1, 137.5, 133.1, 130.3, 130.1, 129.8, 129.1, 126.4, 125.9,
122.9, 110.9, 105.6. IR (KBr, cmꢁ1): 1683, 1640, 1607, 1564, 1492, 1137,
Please cite this article in press as: Xiao, R.; et al., Tetrahedron (2013), http://dx.doi.org/10.1016/j.tet.2013.04.106

R. Xiao et al. / Tetrahedron xxx (2013) 1e7
7
17. (a) Zhou, W.; Thomas, J. M.; Shephard, D. S.; Johnson, B. F. G.; Ozkaya, D.;
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Please cite this article in press as: Xiao, R.; et al., Tetrahedron (2013), http://dx.doi.org/10.1016/j.tet.2013.04.106