Synthesis of 3-substituted indoles promoted by pulverization-activation method catalyzed by Bi(NO3)3·5H2O

Article abstract of DOI:10.1002/jhet.5570450213

(Chemical Equation Presented) A new, facile, efficient, "green" and chemoselective procedure for the synthesis of indole derivatives has been developed with pulverization-activation method catalyzed by Bi(NO ₃)₃·5H₂O (PAMC- Bi(NO₃) ₃·5H₂O) through grinding of indoles with aldehydes or Michael acceptors in the presence of catalytic amounts of Bi(NO ₃)₃·5H₂O under solvent-free conditions.

Full text of DOI:10.1002/jhet.5570450213

Mar-Apr 2008
377
Synthesis of 3-Substituted Indoles Promoted by Pulverization-
Activation Method Catalyzed by Bi(NO3)3·5H2O
Mohammad M. Khodaeia, *, Iraj Mohammadpoor-Baltorkb, Hamid R. Memarianb,
Ahmad R. Khosropourb, Kobra Nikoofarb and Parvin Ghanbarya
aDepartment of Chemistry, Faculty of Science, Razi University, Kermanshah 67149, Iran
bCatalysis Division, Department of Chemistry, University of Isfahan, Isfahan 81746-73441, Iran.
Received April 15, 2007
R
.
Bi(NO3)3 5H2O
+
RCHO
grinding
N
H
N
H
N
H
R3
R4
Bi(NO3)3. 5H2O
grinding
R2
R2
+
R3CH=CHR4
N
N
R1
R1
A new, facile, efficient, “green” and chemoselective procedure for the synthesis of indole derivatives has
been developed with pulverization-activation method catalyzed by Bi(NO3)3·5H2O (PAMC- Bi(NO3)3
·5H2O) through grinding of indoles with aldehydes or Michael acceptors in the presence of catalytic
amounts of Bi(NO3)3·5H2O under solvent-free conditions.
J. Heterocyclic Chem., 45, 377 (2008).
INTRODUCTION
low selectivity [17] or applicable only for aryl aldehydes
[22]. Furthermore, some of these methods require strictly
anhydrous conditions [23,24]. Consequently, there is a need
for a greener catalytically efficient method for these
transformations, which might work under mild and more
economical conditions. As a part of our ongoing research
program to develop new synthetic methodologies [25-27],
we found that Bi(NO3)3· 5H2O as a non-toxic, inexpensive
and readily available Lewis acid, catalyzes bis(indolyl)-
methanes synthesis, efficiently with grinding of indole with
aldehydes (Scheme I).
Indole derivatives are widely distributed in nature and
are known to possess broad spectrum of biological and
pharmaceutical activities [1]. In particular, 3-substituted
indoles have received much attention in previous years [2].
Such compounds are prone to develop interesting
bioactivity and could be used as antibacterial [3] and anti-
tumor agents [4]. Moreover, some alkaloids containing
indole unit have been isolated from marine sources like
Hapalosiphon fontinalis (a blue-green algae) [5]. The scope
of this has been further increased by the identification of
the tri- or tetracyclic skeleton derivatives called hapal-
indole, as a biogenetic precursor [6]. Thus, the development
of facile and environmentally friendly synthetic methods
for the preparation of these compounds constitutes an
active area of investigation in pharmaceutical and organic
synthesis. The principal approach for the synthesis of these
3-substituted indoles involve, condensation reaction of
indoles with various aldehydes or ketones or Friedel-Crafts-
type conjugated additions of indoles with α,β-unsaturated
compounds in the presence of protic or Lewis acids [7,8].
Although a variety of different catalytic systems for the
synthesis of 3-substiuted indoles has been developed, there
is a growing interest in the search for new efficient catalysts
for this concern. However, some of these methods are
associated with certain drawbacks such as the use of
expensive catalyst [9-14] or less easily available reagents
[15-17] use of toxic solvents [18,19] prolonged reaction
times [20] (e.g. 10 days), tedious manipulations in the
isolation of the pure products [21], unsatisfactory yields [3],
Scheme I
R
.
Bi(NO3)3 5H2O
RCHO
+
grinding
N
H
N
H
N
H
RESULTS AND DISCUSSION
First, we investigated the influence of the different
catalysts in this transformation. 4-Chlorobenzaldehyde
was employed as a model compound and various catalysts
were tested under pulverization-activation method. As
shown in Table 1, the best conversion was observed when
the reaction performed in the presence of 1 mol% of
Bi(NO3)3·5H2O for 5 min. Therefore, a series of aromatic
and aliphatic aldehydes reacted with indole smoothly to
afford the corresponding bis(indolyl)methanes in good to
excellent yields (Table 2).

378
M. M. Khodaei, I. Mohammadpoor-Baltork, H. R. Memarian,
A. R. Khosropour, K. Nikoofar and P. Ghanbary
Vol 45
Table 1
Table 2 (continued)
Synthesis of 3,3'-bis(indolyl)-4-chlorophenylmethane with grinding
of 4-chlorobenzaldehyde with indole in the presence of various
catalysts under solid-state conditions.
References
for Known
Compounds
Time
(min)
Yield
(%)a,b
Entry
R
Catalysta
Time
(min)
Yield
(%)b
14c
15
16
17
18
19
20d
21d
22e
2,4-(CH3O)2C6H3
2,5-(CH3O)2C6H3
2-furyl
4
6
3
8
10
6
6
10
13
84
85
29
29
10e
22
10d
10b
30
22
29
94
56
50
83
80
70
79
ZrCl4
BiCl3
Ce(NO3)3·6H2O
FeCl3
p-TSOH
5
5
5
5
5
55
60
25
45
50
2-OHC6H4
3-CH3O-4-OHC6H3
C6H5CH=CH
C6H5CH2CH2
CH3CH=CH
Bi(NO3)3·5H2O
5
87
CH3(CH3)CHCH2
[a]1 mol%. [b] Isolated yield.
CH3
15
62
29
H3C
H3C
23f
The presence of electron-donating and electron-
withdrawing groups on the aromatic ring of aldehydes,
irrespective to their positions in the ring, did not make any
obvious difference in this condensation reaction (Table 2,
entries 1-16). Interestingly we found that under the reaction
conditions, only one of the carbonyl groups of terepht-
halaldehyde participated in this reaction (Table 2, entry 8).
[a] Products were characterized by 1H NMR, 13C NMR, IR and
comparison with reported data; [b] Isolated yields; [c] In the
presence of 2 mol% of Bi(NO3)3·5H2O; [d] In the presence of 5
mol% of Bi(NO3)3·5H2O; [e] In the presence of 3 mol% of
Bi(NO3)3·5H2O; [f] In the presence of 4 mol% of Bi(NO3)3·5H2O.
Phenolic aldehydes such as salicylaldehyde and
vaniline (Table 2, entries 17,18) afforded the corre-
sponding products in 56 and 50% yields respectively.
Aliphatic aldehydes as well as α,β-unsaturated ones, also
gave the corresponding bis(indolyl)methanes in good to
high yields under similar reaction conditions (Table 2,
entries 19-23). However, aliphatic or aromatic ketones
were unaffected even the reaction mixtures were ground
for 15 min, and the starting materials were quantita-
tively recovered.
The reaction conditions are mild enough not to induce
any isomerization for furfural and conjugated aldeydes
(Table 2, entries 16 and 19) or damage to moieties such as
methoxy, which often undergo cleavage in strongly acidic
reaction media (Table 2, entries 13-15 and 18). On the
other hand, no side products were observed in the course
of the reactions we studied. The chemoselectivity of the
present method is also demonstrated by competitive
Table 2
.
Synthesis of bis(indolyl)methanes catalyzed with Bi(NO3)3 5H2O
under solid-state conditions at room temperature.
References
for Known
Compounds
Time
(min)
Yield
(%)a,b
Entry
R
1
2
3
4
5
6
7
8
C6H5
5
7
4
5
4
5
4
7
5
5
9
8
6
85
15a
10e
10e
15b
10a
10e
29
29
29
10d
29
4-NO2C6H4
3-NO2C6H4
4-ClC6H4
2-ClC6H4
4-BrC6H4
92
91
87
88
90
89
92
89
85
86
75
90
3-BrC6H4
4-CHOC6H4
4-CNC6H4
4-CH3C6H4
4-PhC6H4
2,4-(CH3)2C6H3
2-CH3OC6H4
9
10
11
12c
13
10e
10b
Scheme II
NO2
CHO
indole (2.1 mmol)
CHO
+
+
Bi(NO3)3. 5H2O (0.01 mmol)
grinding (8 min)
O2N
N
H
N
H
N
H
N
H
79%
12%
1 mmol
1 mmol
O2N
Br
Br
CHO
COCH3
CH3
indole (2.1 mmol)
+
O2N
Bi(NO3)3. 5H2O (0.01 mmol)
grinding (4 min)
+
N
H
N
H
N
H
N
H

Mar-Apr 2008
Synthesis of 3-Substitated Indoles Promoted by Pulverization-Activation Method
379
reactions of indole with arylaldehydes in the presence of
aliphatic ones and ketones. For example, when a mixture
of 4-nitrobenzaldeyde and 3-methylbutyraldehyde was
allowed to react with two equivalents of indole in the
presence of 1 mol% of Bi(NO3)3·5H2O for 8 min, the aryl-
aldehyde was chemoselectively converted to the
corresponding bis(indolyl)methane but the aliphatic ones
converted slightly (Scheme II). Also in an equimolar
mixture of arylaldehyde and ketone, only arylaldehyde
converted to the corresponding bis(indolyl)methane,
whereas, ketone remained intact (Scheme II).
In continuation of our investigation, we also found that
PAMC-Bi(NO3)3·5H2O can also act as an efficient
procedure for the Michael addition of indoles. Recently,
Srivastava, et. al. carried out these conjugate addition
reactions in the presence of Bi(NO3)3·5H2O in solvent at
prolonged reaction times (10-15h) [30]. In preliminary
investigation on this transformation with PAMC-
Bi(NO3)3·5H2O, we found that the reaction time reduced
surprisingly (3-10 min). Then we decided to expand this
protocol to carry out this transformation (Scheme III).
Table 3
Effect of Bi(NO3)3·5H2O amount on the reaction of indole with
β-nitrostyrene.
Entry
Mole % of catalyst
Time (min)
Yield (%)
1
2
3
4
5
1
3
5
10
20
20
13
7
7
7
35
65
93
93
93
The reaction is fairly general, clean, rapid and efficient.
Unlike previously reported methods, the present method
does not require toxic or anhydrous organic solvents. All
the products were characterized by NMR, IR and mass
spectroscopy and also by comparison with authentic
samples. Under the optimized reaction conditions, a wide
range of structurally divers Michael acceptors reacted
with indoles to afford the corresponding products in good
to excellent yields (Table 4). As presented in Table 4, the
yields of Michael addition for 1-methylindole in the
reaction conditions were less than 30% (Table 4, entries
13-15). To increase the yields, 50 mg of silica gel was
added to the reaction mixture. In this case the yields were
60-95%. As a control the same amount of silica gel was
used in the reaction of indole and β-nitrostyrene and it
was found that silica gel addition didn't have any catalytic
influence on the time and yield of the reaction. The
promoting role, although not well understood, could be
explained through the absorption of 1-methylindole with
Michael acceptors that come into closer contact with each
other on silica surface. We also examined the chemo-
selectivity of the present method in this transformation. It
is noteworthy that Michael acceptors are transformed to
their corresponding 3-substituated indoles in the presence
Scheme III
R3
R4
Bi(NO )3. 5H2O
3
R2 + R3CH=CHR4
R2
grinding
N
N
R1
R1
First, we investigated the influence of the amount of
catalyst on the reaction using indole and β-nitrostyrene as a
model system. As shown in Table 3, 5 mol% of Bi(NO3)3
·5H2O was the optimum amount for this transformation.
Scheme IV
Bi(NO3)3. 5H2O (0.05 mmol)
O
O
O
O
+
CH2=CHCOCH3
PhCH=CHC-
Ph
PhCH=CHC–
Ph
+
+
grinding (3 min)
N
O
N
H
H
100%
95%
Bi(NO3)3. 5H2O (0.05 mmol)
grinding (5 min)
O
CH3
PhCH=CH-CH OTHP
CH =CHCOCH
2
+
+
CH3 +
PhCH=CH-CH2OTHP
3
2
N
N
H
H
92%
100%
O
Ph
OTMS
OTMS
Ph
Bi(NO3)3. 5H2O (0.05 mmol)
+
CH3 + PhCH=CHCOPh
+
CH3
grinding (8 min)
N
N
H
H
CH3
CH3
100%
90%

380
M. M. Khodaei, I. Mohammadpoor-Baltork, H. R. Memarian,
A. R. Khosropour, K. Nikoofar and P. Ghanbary
Vol 45
analyses were carried out using a Perkin-Elmer elemental
analyzer 2400CHN. All the chemicals were purchased from
Aldrich or Merck chemical companies and used without further
purification.
Typical Procedure for the Preparation of Bis(indolyl)-
methanes. A mixture of indole (117 mg, 2.1 mmol), terephthal-
dialdehyde (134 mg, 1 mmol) and Bi(NO3)3.5H2O (4.85 mg,
of acid sensitive groups such as acetals, THP and TMS
ethers with excellent chemoselectivity (Scheme IV).
It is also observed that only one of the unsaturated
groups of bis(benzylidene)acetone participated in the
Michael addition reaction with indole and the amounts of
indole and catalyst did not affect the result (Scheme V).
Scheme V
O
COCH=CHPh
Ph
Ph
Ph
Bi(NO3)3. 5H2O (5 mol %)
+
+ PhCH=CHCOCH=CHPh
grinding, 7 min
N
H
N
H
N
N
H
H
1 mmol
95 %
0 %
2.2 mmol
0.01 mmol) was ground with a pestle in a mortar for 7 min.
After completion of the reaction as indicated by TLC, EtOH (5
ml) was added and filtered. The solvent was evaporated under
reduced pressure. Column chromatography of the crude residue
on silica gel using n-heptane/ethyl acetate (4/1) as eluent gave
the pure product in 92% yield. (Table 2, Entry 8) Pink colored
solid, mp 190-192 °; ir (KBr): 3400, 2900, 1680, 1600, 1200,
In conclusion, in this study a new, simple, efficient and
eco-friendly procedure is described for the chemo-
selective synthesis of bis(indolyl)methanes and 3-
substituated indole derivatives using catalytic amounts of
Bi(NO3)3·5H2O as a cheap and non-toxic catalyst with
pulverization-activation method. In addition, efficiency,
simplicity and chemoselectivity of this protocol provide a
very fast, “green” and low cost procedure for the
synthesis of these products.
1
740 cm-1; H nmr (200 MHz, CDCl3): δ 10 (s, 1H), 8.21 (br, s
2H), 7.85-6.95 (m, 12H), 6.7 (s, 2H), 6.06 (s, 1H); δC (50 MHz,
CDCl3) 40.9, 111.6, 118.9, 119.9, 120, 122.6, 124.1, 127, 129.8,
130.4, 200.8. Anal. Calcd. for C24H18N2O: C, 82.26; H, 5.18; N,
7.99. Found: C, 82.23; H, 5.19; N, 8.01.
EXPERIMENTAL
Typical Procedure for the Preparation of Michael Adduct.
A mixture of ethyl indole-2-carboxylate (208 mg, 1.1 mmol),
methyl vinyl ketone (70 mg, 1 mmol) and Bi(NO3)3·5H2O (26
mg, 0.05 mmol) was ground with pestle in a mortar for 15 min.
After completion of the reaction monitored by TLC, the residue
was diluted with water (10 ml), extracted with ethyl acetate
(3×10 ml) and then dried over MgSO4. The crude product was
purified by chromatography on silica gel using n-hexane/ethyl
acetate (9/1) as eluent to afford pure product in 85% yield.
(Table 4, entry 7) Pale yellow solid; mp 116-117 °; ir
General. All products were identified by comparison of their
physical and spectral data with those of authentic samples.
Melting points were determined using a Stuart Scientific
apparatus and are uncorrected. IR spectra were run on a
Shimadzu IR-435 spectrophotometer. 1H NMR spectra were
recorded in CDCl3 solvent on a Brucker 500 or 200 MHz
spectrometer. Mass spectra were obtained on Platform II
spectrometer from Micromass; EI mode at 70 eV. Elemental
Table 4
Condensation reaction of indoles with Michael acceptors in the presence of 5 mol% of Bi(NO3)3·5H2O
under solid phase conditions at room temperature.
References for
Known
Entry
R1
R2
R3
R4
Time (min)
Yield (%)a
Compounds
1
2
3
4
5
6
7
8
H
H
H
H
H
H
H
H
H
H
H
H
CH3
CH3
CH3
H
H
H
H
H
H
CO2Et
CH3
CH3
CH3
CH3
CH3
H
H
CH3CO
NO2
CH3CO
C6H5CO
C6H5CH=CHCO
CN
CH3CO
CH3CO
NO2
CH3CO
C6H5CO
C6H5CH=CHCO
CH3CO
NO2
3
7
96
93
85
86
95
80
85
97
97
92
95
95
95
60
75
12
11
11
26c
14
31
-
26b
32
18
10b
-
C6H5
C6H5
C6H5
C6H5
H
10
10
7
35
15
5
10
10
8
10
8
H
H
9
C6H5
C6H5
C6H5
C6H5
H
10
11
12
13b
14b
15b
11
32
11
H
H
C6H5
C6H5
20
40
CH3CO
[a] Isolated yields. [b] 50 % of silica gel is added; in the absence of silica gel the yields are very low (less than 30%).

Mar-Apr 2008
Synthesis of 3-Substitated Indoles Promoted by Pulverization-Activation Method
381
(KBr): 3291, 2979, 1689, 1544, 1254, 1023, 738 cm-1; 1H
nmr (500 MHz, CDCl3): δ 1.39 (t, J = 7.12 Hz, 3H), 2.13
(s, 3H), 2.79 (t, J = 7.86 Hz, 2H), 3.34 (t, J = 7.83 Hz,
2H), 4.40 (q, J = 7.01 Hz, 2H), 7.13 (t, J = 7.47 Hz, 1H),
7.30 (t, J = 7.07 Hz, 1H), 7.35 (d, J = 8.26 Hz, 1H), 7.68
(d, J = 8.16 Hz, 1H), 8.81 (br, s 1H); ms: m/z 259 (M+),
216, 202, 189, 186.
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Marinelli, F. Synlett 2004, 944.
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1229.
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(Table 4, entry 12) white solid; mp 104-105 °C; ir (KBr):
1
3409, 3022, 2902, 1606, 1461, 1300, 1093, 733 cm-1; H nmr
(500 MHz, CDCl3): δ 2.45 (s, 3H), 3.56 (dd, J = 15.35, 8.70 Hz
6.61 (d, J = 16.19 Hz, 1H), 7.06 (t, J = 7.48 Hz, 1H), 7.13 (t, J =
7.51 Hz, 1H), 7.21 (t, J = 7.28 Hz, 2H), 7.28 (d, J = 11.32 Hz,
1H), 7.31-7.44 (m, 8H), 7.52 (d, J = 7.83 Hz, 2H), 7.87 (br, s
1H); ms: m/z 365 (M+), 234, 220, 204, 145, 131.
Acknowledgement. We are thankful to Center of Excellence
of Chemistry (Catalyst and Fuel Cell), University of Isfahan”
(CECUI), Research Council of University of Isfahan and also
Razi University Research Councils for their financial support.
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