A distinct novel approach for the synthesis of 3-indolyl-methanamines starting from indoles, aldehydes and nitrobenzenes in water

Article abstract of DOI:10.1039/c3ra41131a

3-Indolyl-methanamines have efficiently been synthesized by the treatment of indoles with aldehydes and nitrobenzenes using indium in aqueous HCl at room temperature. The products are formed in excellent yields (91-98%) within a short period of time (30-45 min). Bisindolyl methanes have not been obtained under the present reaction conditions. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c3ra41131a

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A distinct novel approach for the synthesis of 3-indolyl-
methanamines starting from indoles, aldehydes and
nitrobenzenes in water3{
Cite this: RSC Advances, 2013, 3,
14308
Biswanath Das,* Jayprakash Narayan Kumar, Avula Satya Kumar,
Gandham Satyalakshmi and Digambar Balaji Shinde
Received 8th March 2013,
Accepted 10th June 2013
3-Indolyl-methanamines have efficiently been synthesized by the treatment of indoles with aldehydes and
nitrobenzenes using indium in aqueous HCl at room temperature. The products are formed in excellent
yields (91–98%) within a short period of time (30–45 min). Bisindolyl methanes have not been obtained
under the present reaction conditions.
DOI: 10.1039/c3ra41131a
www.rsc.org/advances
have also been utilized as catalysts to accomplish different
organic reactions.11
Introduction
In continuation of our work12 on the development of useful
synthetic methodologies in water we have observed that the
treatment of indoles (1) with aldehydes (2) and nitrobenzenes
(3) using indium in aqueous HCl afforded the corresponding
3-indolyl-methanamines (4) at room temperature (Scheme 1).
Indole derivatives have attracted much attention due to their
interesting biological properties.1 They are known to inhibit
colon cancer cell and tumour growths.2 They also act as non-
steroidal aromatase inhibitors against breast cancer3 and HIV-
1 integrase inhibitors.4 Various indole derivatives possess
antibacterial, antioxidant and insecticidal properties.1,5 Some
of them are utilized as antibiotics.1 The indole moiety is also
found in several bioactive metabolites of terrestrial and
marine organisms.6 Among various indole derivatives, 3-sub-
stituted indoles are most important and many different
syntheses of these compounds have been reported.1a,7 Here
we would like to report a distinct approach for the synthesis of
3-indolyl-methanamines in water.
Organic reactions in water are of great current interest,
because water is an easily available, economical, safe, and
environmentally benign solvent.8 The development of efficient
and convenient synthetic methodologies in water is of
paramount significance in recent organic chemistry. Metallic
indium in water has now been utilized to carry out various
organic transformations.9 Indium is unreactive towards air
and water as well as non-toxic compared to other metals. Its
first ionisation potential (5.8 eV) is lower than that of other
reducing metals such as zinc (9.4 eV) and tin (7.3 eV) and is
close to that of an alkali metal such as sodium (5.1 eV). As a
result it can readily participate in single electron transfer
processes. The important application of the metal is to reduce
the nitro compounds in acidic media.10 Different indium salts
Results and discussion
Initially the reaction of indole, benzaldehyde and nitroben-
zene was carried out using different metals such as Zn, In, Fe
and Sn in aqueous HCl at room temperature (Table 1).
Considering the reaction time and yield indium was found
to be the most effective. Subsequently this metal was applied
to prepare various 3-indolyl-methanamines from different
indoles, aldehydes and nitrobenzenes following the above
multicomponent reaction (Scheme 1, Table 2).
The products were derived from aromatic, heteroaromatic
as well as aliphatic aldehydes. The aromatic aldehydes
contained both electron-donating and electron-withdrawing
groups. An acid sensitive aldehyde such as furfuraldehyde
(Table 2, entry B) furnished the desired product conveniently.
3-Indolyl-methanamines (4) were formed in excellent yields
(91–98%) within 30–45 min. However, with aliphatic nitro
Division of Natural Products Chemistry, CSIR-Indian Institute of Chemical
Technology, Hyderabad, 500 607, India. E-mail: biswanathdas@yahoo.com;
Fax: +91-40-27193198
Electronic supplementary information (ESI) available: Copies of 1H and 13C
3
NMR spectrum of products. See DOI: 10.1039/c3ra41131a
Scheme 1 Synthesis of 3-indolyl-methanamines.
{ Part 236 in the series ‘‘Studies on novel synthetic methodologies’’.
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Table 1 Synthesis of 3-indolyl-methanamine using different metalsa
methanes were not obtained here. Possibly, under the present
reaction conditions, the aldehydes react more quickly with the
amines to form the imines than with the indoles to produce
bisindolyl methanes.
Entry
Metal
Time (h)
Yield (%)b
1
2
3
4
Zn
Sn
Fe
In
5
6
4
1
52
61
45
96
Conclusions
a
Reaction Conditions: Nitrobenzene (1.0 mmol), 1 N aqueous HCl (1
mL), benzaldehyde (1.0 mmol), indole (1.0 mmol) and water (5 mL)
at room temperature. Yields of isolated pure compound after
column chromatography.
In conclusion, we have developed a novel efficient one-pot
b
synthesis of 3-indolyl-methanamines through
a distinct
approach involving the multicomponent reaction of indoles,
aldehydes and nitrobenzenes using indium in dilute aqueous
HCl at room temperature. The application of water as a
reaction medium, direct utilization of nitro compounds, mild
reaction conditions, formation of only the desired products,
rapid conversion and excellent yields are the advantages of the
present method.
compounds a mixtures of products were obtained. The
structures of 4 were established from their spectral (1H, 13C
NMR, ESIMS, HRESIMS) data. The compounds 4Aa13 (Table 2,
entry a) and 4Af13 (Table 2, entry f) are known.
Organic reactions in water have been highly attractive in
recent years due to economic benefits. The present conversion
has efficiently been carried out in water. The conversion
consists of three steps in one pot. Initially the nitrobenzenes
upon treatment with In/HCl are reduced to amines which
upon reaction with aldehydes form the corresponding imines.
Finally, indoles undergoes an electrophilic substitution reac-
tion with these imines to produce 3-indolyl-methanamines.
When amines (instead of nitro compounds) or imines were
used earlier for the preparation of 3-indolyl-methanamines,
bisindolyl methanes were also formed in several cases.7b,d,e,f
However, under the present reaction conditions bisindolyl
Experimental section
General experimental procedure
To a mixture of a nitro compound (1.0 mmol), indium powder
(325 mesh, 2.0 mmol), 1 N aqueous HCl (1 mL) and an
aldehyde (1.0 mmol) were added indole (1.0 mmol) and water
(5 mL). The mixture was stirred at room temperature and the
reaction was monitored by TLC. After completion, the reaction
mixture was washed with saturated NaHCO3 solution (3 6 5
Table 2 Synthesis of 3-indolyl-methanamine using indium in dilute aqueous HCl at room temperaturea
Entry
A.
Aldehyde
Nitrobenzene (ArNO2)
Indole
Time (min)
Yieldb (%)
a
b
c
d
e
f
g
h
i
Z = H
Z = 4-CH3
Z = 4-isopropyl
Z = 3,4-di-OMe
Z = 3,4,5-tri-OMe
Z = 4-Cl
Z = 4-F
Z = 4-CN
Z = 4-isopropyl
Y = H
Y = H
Y = H
Y = H
Y = H
Y = H
Y = H
Y = H
Y = 3-OMe
Y = H
X = H
X = H
X = H
X = H
X = H
X = H
X = H
X = H
X = 5-OMe
X = H
40
40
45
45
45
40
40
30
40
35
96
96
94
94
93
96
97
98
92
97
B.
C.
Y = H
X = H
40
97
D.
E.
Y = H
Y = H
X = H
X = H
45
35
93
92
a
b
The structures of the products were settled from their spectral (IR, 1H, 13C NMR and MS) data. Yields of isolated pure compounds after
column chromatography.
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mL) and water (3 6 5 mL) and was extracted with EtOAc (3 6 5
mL). The extract was concentrated and the residue was
subjected to column chromatography (silica gel, hexane–
EtOAc) to obtained the pure 3-indolyl-methanamine.
N-((1H-indole-3-yl)(phenylamino)methyl)benzonitrile (4Ah)
Violet solid; m.p. 133–135 uC; IR vmax (neat)/cm21 3414, 2216,
1620, 1513, 1424, 1342, 1215 cm21; 1H NMR (200 MHz, CDCl3):
d 10.38 (1H, brs), 7.72–7.58 (4H, m), 7.56–7.42 (2H, m), 7.37–
7.20 (4H, m), 7.11–7.02 (2H, m), 6.89 (1H, m), 6.78–6.62 (2H,
m), 5.91 (1H, brs); 13C NMR (50 MHz, CDCl3): d 150.2, 136.5,
131.5, 129.1, 127.9, 126.1, 123.5, 120.8 118.6, 118.5, 118.1,
116.5, 111.2, 108.9, 39.8; ESIMS: m/z 346 [M + Na]+; HRESIMS:
m/z 346.1321 Anal. Cald. for C21H17N2FNa: m/z 346.1315.
N-((1H-indole-3-yl)(p-tolyl)methyl)benzenamine (4Ab)
Violet solid; m.p. 132–134 uC; IR vmax (neat)/cm21 3407, 1663,
1613, 1457, 1335 cm21; 1H NMR (200 MHz, CDCl3): d 7.36 (1H,
brs), 7.24 (2H, d, J = 8.0 Hz), 7.11–7.01 (7H, m), 6.99 (2H, t, J =
8.0 Hz), 6.85 (2H, t, J = 8.0 Hz), 6.32 (2H, brs), 5.71 (1H, brs),
2.26 (3H, s); 13C NMR (50 MHz, CDCl3): d 141.1, 136.1, 135.2,
129.0, 128.8, 127.0, 123.2, 121.5, 119.8, 119.6, 118.5, 110.5,
39.2, 21.1; ESIMS: m/z 335 [M + Na]+; HRESIMS: m/z 335.1526,
Anal. Cald. for C22H20N2Na: m/z 335.1524.
N-((4-isopropylphenyl)(5-methoxy-1H-indole-3-yl) methyl)-3-
methoxybenzenamine (4Ai)
Violet solid; m.p. 139–140 uC; IR vmax (neat)/cm21 3413, 1622,
1587, 1482, 1451, 1211 cm21 1H NMR (200 MHz, CDCl3): d
;
7.68 (1H, brs), 7.25–7.03 (7H, m), 6.73 (2H, dd, J = 8.0, 2.0 Hz),
6.71 (2H, d, J = 2.0 Hz), 6.58 (2H, brs), 5.66 (1H, brs), 3.62 (6H,
s), 2.83 (1H, m), 1.2 (6H, d, J = 7.0 Hz); 13C NMR (50 MHz,
CDCl3): d 154.0, 146.2, 141.1, 131.3, 128.9, 127.8, 126.4, 124.2,
119.2, 111.3, 111.2, 55.8, 39.9, 33.7, 24.1; ESIMS: m/z 423, [M +
Na]+; HRESIMS: m/z 423.2047 Anal. Cald. for C21H17N2FNa: m/z
423.2043.
N-((1H-indol-3-yl)(4-isopropylphenyl)methyl)aniline (4Ac)
Violet solid; m.p. 130–133 uC; IR vmax (neat)/cm21 3412, 1662,
1599, 1458, 1363 cm21; 1H NMR (200 MHz, CDCl3): d 7.41 (1H,
brs), 7.25 (2H, d, J = 8.0 Hz), 7.21–7.01 (9H, m), 6.88 (2H, t, J =
8.0 Hz), 6.32 (2H, brs), 5.73 (1H, brs), 2.82 (1H, m), 1.15 (6H, d,
J = 7.0 Hz); 13C NMR (50 MHz, CDCl3): d 146.5, 141.1, 136.2,
128.9, 127.3, 126.0, 123.1, 121.5, 120.1, 119.0, 110.4, 39.2, 32.8,
23.0; ESIMS: m/z 363 [M + Na]+; HRESIMS: m/z 363.1844, Anal.
Cald. for C24H24N2Na: m/z 363.1837.
N-(furan-2-yl(1H-indole-3-yl)methyl)benzenamine (4B)
Violet solid; m.p. 141–142 uC; IR vmax (neat)/cm21 3403, 1599,
1497, 1456, 1340 cm21; 1H NMR (200 MHz, CDCl3): d 7.78 (1H,
brs), 7.40 (2H, d, J = 8.0 Hz), 7.30 (1H, m), 7.21 (2H, dd, J = 8.0,
2.0 Hz), 7.10 (3H, t, J = 8.0 Hz), 6.99 (2H, t, J = 8.0 Hz), 6.73–
6.69 (2H, m), 6.22 (1H, m), 6.17 (1H, m), 5.82 (1H, brs); 13C
NMR (50 MHz, CDCl3): d 157.0, 141.1, 136.2, 129.2, 126.7,
123.0, 122.2 119.4, 119.1, 117.1, 111.2, 110.3, 106.7, 33.2;
ESIMS: m/z 311 [M + Na]+; HRESIMS: m/z 311.1174 Anal. Cald.
for C19H16N2ONa: m/z 311.1160.
N-((3,4-dimethoxyphenyl)(1H-indole-3-yl)methyl)benzenamine
(4Ad)
Light red solid; m.p. 129–131 uC; IR vmax (neat)/cm21 3373,
1
1666, 1615, 1511, 1459, 1419, 1266 cm21; H NMR (200 MHz,
CDCl3): d 7.62 (1H, brs), 7.29 (2H, d, J = 8.0 Hz), 7.14–7.00 (5H,
m), 6.90 (2H, t, J = 8.0 Hz), 6.80 (1H, d, J = 1.5 Hz), 6.70 (1H, dd,
J = 8.0, 1.5 Hz), 6.57 (1H, d, J = 8.0 Hz), 6.32 (2H, brs), 5.70 (1H,
brs), 3.71 (3H, s), 3.59 (3H, s); 13C NMR (50 MHz, CDCl3): d
148.9, 147.8, 138.0, 127.2, 123.7, 121.5, 120.4 119.7, 119.1,
112.1, 110.5, 110.3, 56.0, 39.9; ESIMS: m/z 381 [M + Na]+;
HRESIMS: m/z 381.1575, Anal. Cald. for C23H22N2O2Na: m/z
381.1578.
N-((1H-indole-3-yl)(thiophen-2-yl)methyl) benzenamine (4C)
Violet solid; m.p. 145–147 uC; IR vmax (neat)/cm21 3408, 1602,
1592, 1487, 1356 cm21; 1H NMR (200 MHz, CDCl3): d 7.66 (1H,
brs), 7.38 (3H, d, J = 8.0 Hz), 7.21 (1H, m), 7.20 (1H, d, J = 8.0),
7.08 (3H, t, J = 8.0 Hz), 6.95 (2H, t, J = 8.0 Hz), 6.88–6.80 (2H,
m), 6.61 (2H, brs), 6.02 (1H, brs); 13C NMR (50 MHz, CDCl3): d
149.1, 136.9, 129.2, 127.2, 126.5, 125.1, 123.7, 123.2, 121.9,
120.0, 119.3, 111.3, 35.7; ESIMS: m/z 327 [M + Na]+; HRESIMS:
m/z 327.0922 Anal. Cald. for C19H16N2SNa: m/z 327.0931.
N-((1H-indole-3-yl)(3,4,5trimethoxyphenyl)methyl)benzenamine
(4Ae)
Light red solid; m.p. 126–129 uC; IR vmax (neat)/cm21 3382,
1670, 1604, 1528, 1432, 1262 cm21; 1H NMR (200 MHz, CDCl3):
d 7.86 (1H, brs), 7.36 (2H, d, J = 8.0 Hz), 7.31 (2H, d, J = 8.0 Hz),
7.13 (2H, t, J = 8.0 Hz), 6.99 (3H, t, J = 8.0 Hz), 6.62 (2H, brs),
6.51 (2H, s), 5.76 (1H, brs), 3.80 (3H, s), 3.71 (6H, s); 13C NMR
(50 MHz, CDCl3): d 152.0, 140.2, 136.2, 134.9, 127.1, 123.3,
120.5 118.8, 117.9, 117.8, 110.2, 106.1, 60.0, 55.0, 39.2; ESIMS:
m/z 411 [M + Na]+; HRESIMS: m/z 411.1695, Anal. Cald. for
C23H22N2O2Na: m/z 411.1684.
N-(1-(1H-indol-3-yl)hexyl)aniline (4D)
Violet solid; m.p. 102–104 uC; IR vmax (neat)/cm21 3410, 1585,
1478, 1373, 1219 cm21; 1H NMR (200 MHz, CDCl3): d 7.55 (2H,
d, J = 8.0 Hz), 7.38–7.30 (2H, m), 7.09–6.98 (6H, m), 6.70–6.62
(2H, m), 4.35 (H, t, J = 7.0 Hz), 2.15–2.05 (2H, m), 1.41–1.15
(6H, m), 0.83 (3H, t, J = 7.0 Hz); 13C NMR (50 MHz, CDCl3): d
135.6, 128.0, 121.7, 121.5, 120.0, 119.5, 119.0, 110.1, 40.5, 32.5,
29.0, 24.7, 21.6, 14.1; ESIMS: m/z 315 [M + Na]+; HRESIMS: m/z
315.1415 Anal. Cald. for C20H24N2Na: m/z 315.1419.
N-((4-fluorophenyl)methyl)(1H-indole-3-yl)benzenamine (4Ag)
Violet solid; m.p. 121–123 uC; IR vmax (neat)/cm21 3412, 1605,
1504, 1456, 1417, 1339, 1217 cm21; 1H NMR (200 MHz, CDCl3):
d 7.81 (1H, brs), 7.31–7.22 (7H, m), 7.11 (2H, t, J = 8.0 Hz),
7.00–6.90 (4H, m), 6.57 (2H, brs), 5.80 (1H, brs); 13C NMR (50
MHz, CDCl3): d 162.9, 160.0, 139.2, 136.5, 130.0, 127.1, 123.2,
121.3 119.8, 119.1, 119.0, 114.6 (d, J = 10.0), 110.4, 39.2; ESIMS:
m/z 339, [M + Na]+; HRESIMS: m/z 339.1285 Anal. Cald. for
C21H17N2FNa: m/z 339.1273.
N-(1-(1H-indole-3-yl)-2-methylpropyl)benzenamine (4E)
Violet solid; m.p. 108–110 uC; IR vmax (neat)/cm21 3402, 1598,
1468, 1373, 1227 cm21; 1H NMR (200 MHz, CDCl3): d 7.55 (2H,
d, J = 8.0 Hz), 7.38–7.30 (2H, m), 7.09–6.98 (6H, m), 6.70–6.62
(2H, m), 4.09 (1H, m), 2.51 (1H, m), 0.92 (6H, d, J = 7.0 Hz); 13
C
NMR (50 MHz, CDCl3): d 135.8, 127.9, 121.9, 121.4, 119.8,
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119.7, 118.9, 111.2, 41.0, 32.8, 21.7; ESIMS: m/z 287 [M + Na]+;
HRESIMS: m/z 287.1514 Anal. Cald. for C18H20N2Na: m/z
287.1519.
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The authors thanks CSIR and UGC, New Delhi for financial
assistance. They are also thankful to the NMR, Mass and IR
Divisions of IICT for spectral recording.
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