Sc(OTf) 3 -Catalyzed Oligomerization of Indole: One-Pot Synthesis of 2-[2,2-Bis(indol-3-yl)ethyl]anilines and 3-(Indolin-2-yl)indoles

Article abstract of DOI:10.1055/s-0036-1588181

Oligomerization of substituted indoles and N -methylindoles was investigated in the presence of catalytic amounts of scandium triflate in dichloromethane. Two types of indole oligomer, 2-[2,2-bis(indol-3-yl)ethyl]anilines and 3-(indolin-2-yl)indoles were obtained based on the substituent on indole ring. This study constitutes the first example of Sc(OTf) ₃ -catalyzed oligomerization of indoles and gave good yield of 2-[2,2-bis(indol-3-yl)ethyl]anilines and 3-(indolin-2-yl)indoles..

Full text of DOI:10.1055/s-0036-1588181

SYNTHESIS
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© Georg Thieme Verlag Stuttgart · New York
2017, 49, A–F
paper
A
en
G. M. Shelke, A. Kumar
Paper
Synthesis
Sc(OTf)3-Catalyzed Oligomerization of Indole: One-Pot Synthesis
of 2-[2,2-Bis(indol-3-yl)ethyl]anilines and 3-(Indolin-2-yl)indoles
Ganesh M. Shelke
R
R
Anil Kumar*
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0
0
0
0-
0
0
3
4-
6
9
9
3-
1
7
8
R1
N
R
Department of Chemistry, Birla Institute of Technology
and Science, Pilani, Rajasthan 333031, India
anilkumar@pilani.bits-pilani.ac.in
R1HN
R
N
Sc(OTf)3 (15 mol%)
CH2Cl2, 40 °C, 24 h
or
R1
R
N
R
R1
N
N
R1
R1 = H, Me
R = F, Cl, Br, Me, OMe, CO2Me
R1
2 examples
10 examples
Received: 11.05.2017
Accepted after revision: 12.05.2017
Published online: 01.08.2017
H
N
H
NMe
DOI: 10.1055/s-0036-1588181; Art ID: ss-2017-z0186-op
HN
NH
arundine
CH3
Abstract Oligomerization of substituted indoles and N-methylindoles
was investigated in the presence of catalytic amounts of scandium tri-
flate in dichloromethane. Two types of indole oligomer, 2-[2,2-bis(in-
dol-3-yl)ethyl]anilines and 3-(indolin-2-yl)indoles were obtained based
on the substituent on indole ring. This study constitutes the first exam-
ple of Sc(OTf)3-catalyzed oligomerization of indoles and gave good yield
of 2-[2,2-bis(indol-3-yl)ethyl]anilines and 3-(indolin-2-yl)indoles.
N
N
H
Me
H
HN
NH
chimonanthine
NH
vibrindole A
Key words oligomerization, scandium triflate, bis(indolyl)methanes,
indole, dimer, trimer
NH
N
NH
N
N
H
Indole is a ubiquitous heterocycle that is found in natu-
ral products, pharmaceuticals, agrochemicals and other
synthetic organic compounds.1 Given their diverse biologi-
cal properties, structural modification of the indole nucleus
has attracted the attention of many synthetic organic
chemists in recent years. A large number of naturally isolat-
ed alkaloids with a dimeric indole scaffold and synthetically
prepared bis(indolyl) compounds have been found to exhib-
it a wide range of biological activities, including antibiotic,
antitumor, antiviral, diuretic, and anticancer action (Figure
1).2 Thus, several methods have been developed for their
synthesis using different catalysts.3
On the other hand, indole itself polymerizes to polyin-
dole (dimer or trimer) under acidic conditions (Scheme 1).4
Geller5 reported the first acid-catalyzed self-addition prod-
uct of indole as a trimer, which was further studied by
Smith6 and it was found to have the structure of indole-
3,3′-trimer 2. Later, the Ishii group reported a new indole-
2,3′-trimer 3 formed by the self-addition of indole in the
diuretic agent
1,1,3-tris(3-indolyl)butane
Figure 1 Structures of some bioactive indole dimers and trimers
presence of p-toluenesulfonic acid (p-TSA) in benzene at re-
flux.7 When indole was treated with 98% formic acid, indole
trimer 2 and dimer 4 were obtained in 30 and 32% yields,
respectively.8 A mixture of indole trimers 2 and 3 and dimer
4 and was obtained by the reaction of 3-bromoindole and
indole in the presence of trifluoroacetic acid (TFA) in di-
chloromethane at room temperature.9 These reactions were
catalyzed by Brønsted acids and required a stoichiometric
amount of catalyst. Pal et al. reported InCl3-mediated oligo-
merization of indole in which indole 3,3′-trimer 2 was ob-
tained in 46% yield along with unexpected 3-acetylindole.10
Thus, indole oligomerization is sensitive to the substituent
on the indole ring, acid concentration, temperature, and the
nature of both the solvent and the acid.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2017, 49, A–F

B
G. M. Shelke, A. Kumar
Paper
Synthesis
H2N
H2N
H
HN
N
NH
acid catalyst
N
other
products
+
+
+
HN
H
HN
N
H
1
2
3
4
6
-
-
2%
39%
8%
6%
CF3CO2H/CH2Cl2
p-TSA7
-
-
HCH2Cl2H8
30%
32%
-
-
10
-
46%
-
InCl3
40%
Scheme 1 Acid-catalyzed oligomerization of indole
Over the past decade, rare-earth triflates have drawn
the attention of chemists as water-compatible, environ-
ment friendly, noncorrosive and reusable Lewis acids for a
variety of organic transformations.11 Among these metal
triflates, Sc(OTf)3 shows high catalytic activities even com-
pared with lanthanide triflate in some cases.12 The unique
properties of Sc(OTf)3 and differential behavior of indole
with different acids prompted us to investigate indole oligo-
merization using Sc(OTf)3.
To evaluate metal triflate catalyzed oligomerization of
indole, unsubstituted indole (1a) was chosen as a model
substrate. Reaction of 1a with Sc(OTf)3 (10 mol%) at 40 °C in
CH2Cl2 after 24 hours resulted in formation of a new prod-
uct along with unreacted 1a. The product was isolated by
column chromatography and characterized by NMR and
mass analysis. The spectral data were consistent with the
reported data for 2a.13 Bisai et al. also observed formation of
indole-3,3′-trimer 2a during his work on Friedel–Crafts al-
kylations of 3-hydroxy-3-methyl-2-oxindole with indole
(1a) in the presence of In(OTf)3.14
To increase the yield of the product 2a, we further
screened solvents using Sc(OTf)3 (10 mol%) as catalyst (Ta-
ble 1, entry 1–5). Nonpolar solvents gave better yield as
compared with polar solvents and the best yield was ob-
tained in CH2Cl2 (60%). In acetonitrile and 1,4-dioxane the
yield of 2a was poor and 3-(indolin-2-yl)-1H-indole 4a
(<5%) was also obtained along with 2a. Thus, we selected
CH2Cl2 as the solvent of choice for further study.
Table 1 Optimization of Reaction Conditions for Formation of 2aa
We then studied the effect of different metal triflates
such as Sc(OTf)3, Bi(OTf)3, AgOTf, Ce(OTf)3, In(OTf)3,
Eu(OTf)3, and La(OTf)3, as catalysts in CH2Cl2 (Table 1, en-
Entry
Catalyst (mol%)
Solvent
Yield (%)b
2a
3a
a
1
2
Sc(OTf)3 (10)
Sc(OTf)3 (10)
Sc(OTf)3 (10)
Sc(OTf)3 (10)
Sc(OTf)3 (10)
Sc(OTf)3 (5)
Sc(OTf)3 (15)
Bi(OTf)3 (10)
AgOTf (10)
CH2Cl2
DCE
60
48
27
19
10
49
66
32
18
12
55
16
14
0
Table 2 Trimerization of Substituted Indoles Using Sc(OTf)3
0
0
H2N
R
3
CHCl3
R
R
4
toluene
MeCN
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
<5c
<5c
0
Sc(OTf)3 (15 mol%)
CH2Cl2, 40 °C, 24 h
R
N
5
H
HN
6
1
2
N
H
7
0
8
0
Entry
R
Yield (%)b
Entry
R
Yield (%)b
9
<5c
<5c
0
a
b
c
H
66
54
52
51
52
f
6-CO2Me
5-CN
45
–
10
11
12
13
Ce(OTf)3 (10)
In(OTf)3 (10)
Eu(OTf)3 (10)
La(OTf)3 (10)
5-Cl
5-Br
5-F
g
h
i
5-OMe
5-Me
76
74
<5c
<5c
d
e
6-Cl
a General reaction conditions: Indole 1a (1.0 mmol), M(OTf)n (x mol%), sol-
vent (5 mL), 40 °C, 24 h.
a General reaction conditions: indole 1a (1.0 mmol), Sc(OTf)3 (15 mol%),
CH2Cl2 (5 mL), 40 °C, 24 h.
b Isolated yield after column chromatography.
c Based on TLC, product was not isolated.
b Isolated yield after column chromatography.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2017, 49, A–F

C
G. M. Shelke, A. Kumar
Paper
Synthesis
tries 1 and 8–13). Among the metal triflates screened,
In(OTf)3 and Sc(OTf)3 gave 2a in 55 and 60% isolated yield,
respectively. After performing solvent and catalyst study,
we standardized catalyst loading, reaction time and tem-
perature. The yield of 2a increased from 49 to 66% on in-
creasing Sc(OTf)3 loading from 5 to 15 mol% (entries 6 and
7). Further increase in catalyst loading did not improve the
yield but resulted in sluggish reaction with a mixture of
products 2a and 4a. Increasing the reaction time from 24 to
72 hours did not result in an increase in yield. Increasing re-
action temperature from 40 to 80 °C resulted in the disap-
pearance of 2a. Thus, Sc(OTf)3 (15 mol%) in dichlorometh-
ane was selected as the reaction conditions to study the
oligomerization of indoles.
Substituted indoles 1a–i were treated with Sc(OTf)3 (15
mol%) in dichloromethane at 40 °C for 24 hours and the
products formed were analyzed. The results are shown in
Table 2. It was observed that indoles with electron-with-
drawing groups at C-5 and C-6 positions (1b–f) afforded
lower yields of the corresponding indole 3,3′-trimer (2b–f),
compared with indoles with electron-donating groups. In-
dole derivatives with strong electron-withdrawing groups
such as a cyano group at the C-5 position (1g) did not react
under these conditions. Azaindole and 3-substituted in-
doles also did not undergo oligomerization under these
conditions.
We then turned our attention towards the 1-methylin-
dole derivatives (Table 3). N-Methylindole (1j) and 5-bro-
mo-N-methylindole (1k), on treatment with Sc(OTf)3 under
the optimized reaction conditions, gave the corresponding
a
Table 3 Oligomerization of N-Methylindoles using Sc(OTf)3
MeHN
R
R
R
R
R
Sc(OTf)3 (15 mol%)
R
or
N
N
CH2Cl2, 40 °C, 24 h
N
N
Me
H
Me
N
Me
1
2
4
Me
Entry
R
Yield (%)b
2
4
j
H
54
50
0
0
0
k
l
5-Br
5-Me
5-OMe
56
58
m
0
a General reaction conditions: Indole 1a (1.0 mmol), Sc(OTf)3 (15 mol%), CH2Cl2 (5 mL), 40 °C, 24 h.
b Isolated yield after column chromatography.
H
N
Sc(OTf)3
H
Sc(OTf)3
(TfO)3ScHN
HN
N
H
N
H
N
1
A
N
H
N
H
H
1
B
4
H2N
NH
H
NH
HN
NH
N
H
(TfO)3Sc
C
2
Scheme 2 Proposed mechanism for the formation of indole dimer 4 and trimers 2
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2017, 49, A–F

D
G. M. Shelke, A. Kumar
Paper
Synthesis
indole-3,3′-trimers 2j and 2k in 54 and 50% yields, respec-
tively. However, 5-methyl-N-methylindole (1l) and 5-meth-
oxy-N-methylindole (1m) afforded the corresponding in-
dole-2,3′-dimers 4l and 4m instead of indole-3,3′-trimers,
in 56 and 58% yields, respectively.
Dimer 4 is possibly formed through generation of indo-
linium cation A by coordination of Sc(OTf)3 at the C-3 posi-
tion followed by nucleophilic attack by a second indole at
the electrophilic C-2 position of A (Scheme 2). This pathway
is consistent with previous reports14,15 and with the substit-
uent effect observed on the yield. Lower yields were ob-
tained from indoles with electron-withdrawing groups
compared with indoles with electron-donating groups. Di-
mer 4 was then converted into intermediate B, which acts
as a Michael acceptor to react with a third molecule of in-
dole 1 to furnish the indole-3,3′-trimer 2.
13C NMR (75 MHz, DMSO-d6): δ = 146.7, 136.9, 129.6, 127.1, 126.5,
125.1, 122.7, 120.9, 119.5, 119.1, 118.3, 116.6, 115.1, 111.7, 36.3, 32.9.
ESI-TOF: m/z [M + H]+ calcd for C24H22N3+: 352.1808; found: 352.1861.
2-[2,2-Bis(5-chloro-1H-indol-3-yl)ethyl]-4-chloroaniline (2b)
Yield: 54% (82 mg); brown solid; mp 104−106 °C.
FTIR (KBr): 3441, 2932, 1620, 1458, 1273, 1095, 802, 741 cm–1
.
1H NMR (400 MHz, DMSO-d6): δ = 11.00 (s, 2 H), 7.48 (dd, J = 17.9,
1.9 Hz, 2 H), 7.31 (d, J = 8.6 Hz, 2 H), 6.98 (dd, J = 8.6, 1.9 Hz, 2 H), 6.90
(d, J = 2.3 Hz, 1 H), 6.82 (dd, J = 8.5, 2.4 Hz, 1 H), 6.59 (d, J = 8.5 Hz,
1 H), 5.05 (s, 2 H), 4.87 (t, J = 7.6 Hz, 1 H), 3.31 (d, J = 7.6 Hz, 2 H).
13C NMR (100 MHz, DMSO-d6): δ = 145.9, 135.3, 129.2, 128.1, 126.5,
126.3, 124.7, 123.1, 121.1, 119.6, 118.7, 118.4, 116.4, 113.3, 35.7,
32.1.
ESI-TOF: m/z [M + H]+ calcd for C24H19Cl3N3+: 454.0639; found:
454.0642.
In conclusion, we have described oligomerization of in-
dole catalyzed by scandium triflate, a water-compatible, re-
usable Lewis acid, in dichloromethane. The product forma-
tion is found to be dependent on the substituent present on
the indole ring. This is the first report on the oligomeriza-
tion of indole using metal triflate, and provides a one-pot
method for the preparation of 2-[2,2-bis(indol-3-yl)eth-
yl]anilines and 3-(indolin-2-yl)indoles.
2-[2,2-Bis(5-bromo-1H-indol-3-yl)ethyl]-4-bromoaniline (2c)
Yield: 52% (102 mg); brown solid; mp 194−196 °C.
FTIR (KBr): 3441, 2924, 1497, 1450, 1242, 1080, 795, 733 cm–1
.
1H NMR (400 MHz, DMSO-d6): δ = 11.02 (s, 2 H), 7.64 (d, J = 1.2 Hz,
2 H), 7.44 (d, J = 2.0 Hz, 2 H), 7.26 (d, J = 8.6 Hz, 1 H), 7.09 (dd, J = 8.6,
1.7 Hz, 1 H), 7.02 (d, J = 2.0 Hz, 1 H), 6.93 (dd, J = 8.5, 2.1 Hz, 1 H), 6.54
(d, J = 8.5 Hz, 1 H), 5.07 (s, 1 H), 4.86 (t, J = 7.6 Hz, 1 H), 3.29 (d,
J = 7.6 Hz, 2 H).
13C NMR (100 MHz, DMSO-d6): δ = 146.3, 135.5, 132.0, 129.2, 128.8,
127.0, 124.6, 123.6, 121.7, 118.4, 116.9, 113.8, 111.2, 107.2, 35.8, 32.1.
ESI-TOF: m/z [M + H]+ calcd for C24H19Br3N3+: 585.9124; found:
585.9132.
Indoles and metal triflates were purchased from Sigma–Aldrich, India.
Melting points were determined by the open capillary tube method
with a melting point apparatus (EZ-Melt) and are uncorrected. IR
spectra were recorded with an FTIR spectrometer and the values are
expressed in cm–1. The 1H and 13C NMR spectra were recorded with a
Bruker (300 and 400 MHz) NMR spectrometer. High-resolution mass
spectra (HRMS) were obtained with a quadrupole time of flight
(qTOF) mass spectrometer. Thin-layer chromatography (TLC) was per-
formed on pre-coated alumina sheets and detected under UV light.
Silica gel (100–200 mesh) was used for column chromatography.
2-[2,2-Bis(5-fluoro-1H-indol-3-yl)ethyl]-4-fluoroaniline (2d)
Yield: 51% (69 mg); brown solid; mp 164−166 °C.
FTIR (KBr): 3464, 2924, 1628, 1489, 1265, 1026, 856, 741 cm–1
.
1H NMR (400 MHz, DMSO-d6): δ = 10.86 (s, 2 H), 7.45 (d, J = 1.8 Hz,
2 H), 7.26 (dd, J = 8.7, 4.5 Hz, 3 H), 7.22 (d, J = 2.1 Hz, 1 H), 6.82 (td,
J = 9.2, 2.3 Hz, 2 H), 6.69 (dd, J = 10.3, 2.6 Hz, 1 H), 6.62 (td, J = 8.5,
2.8 Hz, 1 H), 6.56 (dd, J = 8.5, 5.4 Hz, 1 H), 4.81 (t, J = 7.6 Hz, 1 H), 4.72
(s, 2 H), 3.32 (d, J = 7.7 Hz, 2 H).
Oligomerization of Indole; General Procedure
A mixture of indole 1a–n (1.0 mmol), dichloromethane (5.0 mL) and
Sc(OTf)3 (74 mg, 15 mol%) in a round-bottom flask of 10 mL was
stirred for 24 h at reflux. The progress of the reaction was monitored
by TLC (EtOAc–hexane, 6:4 v/v). After completion of the reaction, the
mixture was diluted with water (5 mL) and extracted with dichloro-
methane (2 × 10 mL). The combined organic phases were dried over
anhydrous Na2SO4 and evaporated under vacuum. The residue was
purified by column chromatography on silica gel (100–200 mesh) to
afford the pure product 2 or 4.
13C NMR (100 MHz, DMSO-d6): δ = 156.7 (d, J = 230.2 Hz), 153.6,
143.2, 133.5, 127.2 (d, J = 9.7 Hz), 126.5 (d, J = 6.5 Hz), 124.9, 118.8 (d,
J = 4.6 Hz), 115.9, 115.6 (d, J = 9.1 Hz), 112.8 (s), 112.5 (d, J = 9.8 Hz),
109.1 (d, J = 26.0 Hz), 104.1 (d, J = 23.1 Hz), 35.7, 32.3.
ESI-TOF: m/z [M + H]+ calcd for C24H19F3N3+: 406.1526; found:
406.1524.
2-[2,2-Bis(6-chloro-1H-indol-3-yl)ethyl]-5-chloroaniline (2e)
Yield: 52% (79 mg); brown solid; mp 232−234 °C.
2-[2,2-Di(1H-indol-3-yl)ethyl]aniline (2a)
Yield: 66% (77 mg); brown solid; mp 169−170 °C (lit.9,16 167–169 °C).
FT-IR (KBr): 3441, 3387, 3063, 2924, 1620, 1450, 1095, 849, 802 cm–1
.
1H NMR (400 MHz, DMSO-d6): δ = 10.91 (s, 2 H), 7.44 (d, J = 8.4 Hz,
2 H), 7.32 (s, 4 H), 6.85 (d, J = 8.1 Hz, 2 H), 6.73 (d, J = 8.0 Hz, 1 H), 6.61
(s, 1 H), 6.29 (d, J = 7.2 Hz, 1 H), 5.14 (s, 2 H), 4.80 (t, J = 7.3 Hz, 1 H),
3.31 (d, J = 7.3 Hz, 2 H).
13C NMR (100 MHz, DMSO-d6): δ = 148.5, 137.2, 131.2, 130.9, 125.9,
125.8, 123.9, 123.3, 120.8, 118.9, 118.7, 115.6, 114.0, 111.4, 35.6, 32.4.
FTIR (KBr): 3433, 3333, 3209, 3055, 2932, 1620, 1450, 1250, 802,
748 cm–1
.
1H NMR (300 MHz, DMSO-d6): δ = 10.68 (s, 2 H), 7.52 (d, J = 7.9 Hz,
2 H), 7.30–7.22 (m, 4 H), 6.97 (t, J = 7.1 Hz, 2 H), 6.90–6.73 (m, 4 H),
6.56 (d, J = 6.9 Hz, 1 H), 6.33 (t, J = 6.8 Hz, 1 H), 4.85 (t, J = 7.5 Hz, 1 H),
4.67 (s, 2 H), 3.35 (d, J = 6.4 Hz, 2 H).
ESI-TOF: m/z [M + H]+ calcd for C24H19Cl3N3+: 454.0639; found:
454.0640.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2017, 49, A–F

E
G. M. Shelke, A. Kumar
Paper
Synthesis
Dimethyl 3,3′-{2-[2-Amino-4-(methoxycarbonyl)phenyl]ethane-
1,1-diyl}bis(1H-indole-6-carboxylate) (2f)
2-[2,2-Bis(5-bromo-1-methyl-1H-indol-3-yl)ethyl]-4-bromo-N-
methylaniline (2k)
Yield: 45% (79 mg); brown solid; mp 213−214 °C.
Yield: 50% (105 mg); white solid; mp 220−221 °C.
FTIR (KBr): 3364, 3286, 2924, 1697, 1620, 1435, 1296, 1250, 825,
FTIR (KBr): 3441, 2924, 1504, 1474, 1288, 1049, 795, 733 cm–1
.
771 cm–1
.
1H NMR (400 MHz, DMSO-d6): δ = 7.63 (d, J = 1.8 Hz, 2 H), 7.34 (s,
1 H), 7.32 (s, 1 H), 7.29 (s, 2 H), 7.19 (d, J = 1.9 Hz, 1 H), 7.17 (d,
J = 1.9 Hz, 1 H), 7.06 (dd, J = 8.6, 2.4 Hz, 1 H), 6.95 (d, J = 2.4 Hz, 1 H),
6.36 (d, J = 8.7 Hz, 1 H), 5.25 (d, J = 4.9 Hz, 1 H), 4.87 (t, J = 7.6 Hz, 1 H),
3.71 (s, 6 H), 3.23 (d, J = 7.6 Hz, 2 H), 2.64 (d, J = 4.8 Hz, 3 H).
1H NMR (400 MHz, DMSO-d6): δ = 11.22 (s, 2 H), 7.96 (s, 2 H), 7.57 (d,
J = 7.7 Hz, 4 H), 7.47 (d, J = 8.5 Hz, 2 H), 7.23 (s, 1 H), 6.89 (q,
J = 7.8 Hz, 2 H), 5.18 (s, 2 H), 4.98 (t, J = 7.6 Hz, 1 H), 3.81 (s, 6 H), 3.74
(s, 3 H), 3.43 (d, J = 7.6 Hz, 2 H).
13C NMR (100 MHz, DMSO-d6): δ = 167.7, 167.2, 147.2, 136.0, 130.5,
130.0, 129.9, 128.1, 127.0, 122.1, 119.3, 119.2, 119.1, 117.1, 115.5,
113.8, 55.4, 52.2, 36.4, 32.1.
13C NMR (100 MHz, DMSO-d6): δ = 147.2, 135.9, 131.5, 129.5, 129.0,
128.8, 127.2, 123.8, 121.8, 117.8, 112.1, 111.5, 111.2, 106.9, 36.3, 33.0,
31.3, 30.7.
ESI-TOF: m/z [M + H]+ calcd for C30H28N3O6+: 526.1973; found:
ESI-TOF: m/z [M + H]+ calcd for C27H25Br3N3+: 627.9593; found:
526.1970.
627.9598.
2-[2,2-Bis(5-methoxy-1H-indol-3-yl)ethyl]-4-methoxyaniline (2h)
Yield: 76% (112 mg); brown solid; mp 119−120 °C [Lit.10 117–119 °C].
3-(1,5-Dimethylindolin-2-yl)-1,5-dimethyl-1H-indole (4l)
Yield: 56% (81 mg); white solid; mp 142−144 °C.
FTIR (KBr): 3450, 3418, 3050, 2924, 1620, 1428, 795, 741 cm–1
.
FTIR (KBr): 3047, 2908, 2854, 1612, 1489, 1327, 1265, 795 cm–1
.
1H NMR (400 MHz, DMSO-d6): δ = 10.57 (s, 2 H), 7.25 (d, J = 2.3 Hz,
2 H), 7.19 (s, 1 H), 7.16 (s, 1 H), 7.02 (d, J = 2.4 Hz, 2 H), 6.66 (d,
J = 2.4 Hz, 1 H), 6.64 (d, J = 2.4 Hz, 1 H), 6.52 (t, J = 5.3 Hz, 2 H), 6.42
(dd, J = 8.5, 2.9 Hz, 1 H), 4.75 (t, J = 7.5 Hz, 1 H), 4.38 (s, 2 H), 3.67 (s,
6 H), 3.42 (s, 3 H), 3.32 (d, J = 7.5 Hz, 2 H).
13C NMR (100 MHz, DMSO-d6): δ = 152.9, 151.2, 140.4, 132.1, 127.5,
127.0, 123.5, 118.9, 116.1, 116.0, 112.2, 111.9, 110.8, 101.8, 55.7, 55.3,
36.5, 32.9.
1H NMR (400 MHz, DMSO-d6): δ = 7.31 (d, J = 12.6 Hz, 3 H), 6.98 (d,
J = 8.1 Hz, 1 H), 6.88 (d, J = 9.5 Hz, 2 H), 6.46 (d, J = 7.6 Hz, 1 H), 4.48–
4.37 (m, 1 H), 3.74 (s, 3 H), 3.36 (s, 3 H), 3.18 (dd, J = 15.3, 8.6 Hz, 1 H),
3.10–2.93 (m, 1 H), 2.33 (s, 3 H), 2.22 (s, 3 H).
13C NMR (100 MHz, DMSO-d6): δ = 151.6, 136.2, 129.5, 128.7, 127.9,
127.4, 127.0, 126.6, 125.2, 123.3, 119.6, 113.6, 110.1, 107.7, 65.3, 37.4,
34.9, 32.8, 21.7, 21.0.
ESI-TOF: m/z [M + H]+ calcd for C20H23N2+: 291.1856; found: 291.1860.
ESI-TOF: m/z [M + H]+ calcd for C27H28N3O3+: 442.2125; found:
442.2129.
5-Methoxy-3-(5-methoxy-1-methylindolin-2-yl)-1-methyl-1H-in-
dole (4m)
2-[2,2-Bis(5-methyl-1H-indol-3-yl)ethyl]-4-methylaniline (2i)
Yield: 74% (97 mg); brown solid; mp 178−179 °C.
Yield: 58% (94 mg); white solid; mp 104−105 °C.
FTIR (KBr): 2947, 2831, 1620, 1490, 1242, 1026, 802 cm–1
1H NMR (400 MHz, DMSO-d6): δ = 7.31 (d, J = 9.9 Hz, 2 H), 6.97 (d,
J = 2.2 Hz, 1 H), 6.83–6.74 (m, 2 H), 6.66 (dd, J = 8.3, 2.0 Hz, 1 H), 6.48
(d, J = 8.4 Hz, 1 H), 4.48–4.38 (m, 1 H), 3.73 (s, 3 H), 3.68 (s, 3 H), 3.67
(s, 3 H), 3.37 (s, 3 H), 3.23 (dd, J = 15.5, 8.4 Hz, 1 H), 2.98 (dd, J = 15.1,
11.2 Hz, 1 H).
.
FTIR (KBr): 3464, 3418, 3055, 2924, 1628, 1420, 795, 741 cm–1
.
1H NMR (400 MHz, DMSO-d6): δ = 10.57 (s, 2 H), 7.30 (s, 2 H), 7.17 (d,
J = 7.0 Hz, 4 H), 6.82 (d, J = 7.8 Hz, 3 H), 6.62 (d, J = 7.5 Hz, 1 H), 6.48
(d, J = 7.6 Hz, 1 H), 4.78 (t, J = 6.2 Hz, 1 H), 4.46 (s, 2 H), 3.26 (d,
J = 6.7 Hz, 2 H), 2.30 (s, 6 H), 2.00 (s, 3 H).
13C NMR (100 MHz, DMSO-d6): δ = 144.2, 135.3, 130.2, 127.4, 127.0,
126.5, 125.5, 124.8, 122.8, 122.6, 119.1, 118.7, 115.4, 111.4, 36.5, 33.3,
21.8, 20.8.
13C NMR (100 MHz, DMSO-d6): δ = 153.5, 153.0, 148.0, 132.9, 130.9,
129.0, 127.2, 113.8, 112.2, 111.7, 111.5, 111.0, 108.0, 102.0, 65.3, 55.9,
55.8, 37.5, 35.3, 33.0.
ESI-TOF: m/z [M + H]+ calcd for C27H28N3+: 394.2278; found: 394.2282.
ESI-TOF: m/z [M + H]+ calcd for C20H23N2O2+: 323.1754; found:
323.1758.
2-[2,2-Bis(1-methyl-1H-indol-3-yl)ethyl]-N-methylaniline (2j)
Yield: 54% (71 mg); colorless solid; mp 135−136 °C [Lit.10 135–
137 °C].
Funding Information
FTIR (KBr): 3433, 3055, 2924, 1605, 1512, 1474, 1065, 820, 741 cm–1
.
The authors are grateful to Council of Scientific and Industrial Re-
search (CSIR), New Delhi for financial support [01(2214)/08/EMR-II]
1H NMR (400 MHz, DMSO-d6): δ = 7.53 (d, J = 7.9 Hz, 2 H), 7.32 (d,
J = 8.2 Hz, 2 H), 7.22 (s, 2 H), 7.07 (t, J = 7.5 Hz, 2 H), 6.92 (dt, J = 17.9,
5.4 Hz, 4 H), 6.44 (d, J = 8.0 Hz, 1 H), 6.36 (t, J = 7.3 Hz, 1 H), 4.95–4.89
(m, 1 H), 4.87 (d, J = 7.4 Hz, 1 H), 3.69 (s, 6 H), 3.34 (d, J = 7.4 Hz, 2 H),
2.63 (d, J = 4.6 Hz, 3 H).
and GMS thanks CSIR for the award of a senior research fellowship.
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Supporting Information
13C NMR (100 MHz, DMSO-d6): δ = 148.0, 137.2, 128.9, 127.4, 127.1,
127.0, 125.1, 121.2, 119.6, 118.6, 118.5, 115.9, 109.9, 109.3, 36.4, 32.7,
32.2, 30.8.
Supporting information for this article is available online at
https://doi.org/10.1055/s-0036-1588181.
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ESI-TOF: m/z [M + H]+ calcd for C27H28N3+: 394.2278; found: 394.2274.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2017, 49, A–F

F
G. M. Shelke, A. Kumar
Paper
Synthesis
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© Georg Thieme Verlag Stuttgart · New York — Synthesis 2017, 49, A–F