Micelle promoted synthesis of bis-(indolyl)methanes

Article abstract of DOI:10.2174/157017812800233679

Abstract: Bis-(indolyl)methanes were synthesized by a simple, clean and highly efficient Tween-20 micelle promoted reaction of indole with aldehydes in water by the single step reaction. The absence of electrical double layer in the nonionic surfactant mi

Full text of DOI:10.2174/157017812800233679

294
Letters in Organic Chemistry, 2012, 9, 294-299
Micelle Promoted Synthesis of Bis-(indolyl)methanes
Krishnammagari S. Kumar, Chinnapareddy B. Reddy, Balam S. Krishna, Kambam Srinivasulu and
Cirandur S. Reddy*
Department of Chemistry, Sri Venkateswara University, Tirupati-517502, India
Received October 11, 2011: Revised February 01, 2012: Accepted February 01, 2012
Abstract: Bis-(indolyl)methanes were synthesized by a simple, clean and highly efficient Tween-20 micelle promoted
reaction of indole with aldehydes in water by the single step reaction. The absence of electrical double layer in the non-
ionic surfactant micelles makes them as potential model adsorbent in the interfacial processes. This approach had explored
the present synthesis of bis-(indolyl)methanes.
Keywords: Aldehydes, bis-indolylmethanes, green chemistry, indoles, non-ionic surfactants, tween-20.
INTRODUCTION
micellar and vesicle forming surfactants as catalysts in water
is widespread and has been studied for a number of different
synthetic transformations/ multicomponent reactions in
water [33]. Surfactant-type catalyzed organic reaction had
motivated the organic synthesis in aqueous medium [33] like
synthesis of benzylamino coumarins [34], Betti base [35].
Based on this back ground here in is reported a highly
efficient green procedure for the preparation of bis-
(indolyl)methane derivatives.
Indole moiety is a major constituent in a wide variety of
pharmaceuticals [1]. Many bis-indole alkaloids are
recognized as one of the major groups of sponge metabolites
because of their broad spectrum of biological properties [2-
7]. Bis-indolylmethanes are obtained by the reaction of
indole with aldehydes through the azafulvanium salts as
intermediate in their synthesis [8]. Several other methods are
available for the preparation of bis-indolylmethanes using
protic [9-15], and Lewis acids [16-20]. Also other reagents,
such as P2O5/ SiO2 [21], and heteropolyacids [22-24] were
used for their synthesis. Ionic liquids in conjugation with
In(OTf)3 or FeCl3.6H2O [25] were acted as media for their
synthesis. Recently oxalic acid [26, 27], as solid supported
catalyst [28, 29] had also been successfully exploited for the
preparation of bis-indolylmethanes. The Lewis and Brønsted
acid surfactant catalyzed synthetic reactions are known for
them [30]. But majority of the available methods suffer from
several setbacks such as requirement of stoichiometric
amount of the Lewis acids, generation harmful wastes,
posing environmental problem and long reaction times
associated with poor product yields.
RESULTS AND DISCUSSION
The highly efficient green procedure for the preparation
of bis-indolylmethane derivatives (3a-r) proceeds by the
single step reaction of two moles of indole (1) with one mole
of aldehyde (2) using non-ionic surfactant Tween-20 as
catalyst in aqueous media (Scheme 1). The absence of
electrical double layer in the non-ionic surfactant micelles
makes them as potential model adsorbent in the interfacial
processes [36]. This property of non-ionic surfactant was
explored in the present synthesis of bis-indolylmethanes
from the reaction of indole with aldehydes. Tween-20 is also
commonly used non-ionic detergent in water as solubilizer
with a wide range of applications in biological systems [37,
38]. Solubilization of lipid membranes triggered by Tween-
20 as a well-described phenomenon to use as an emulsifier
and complexing agent in both aqueous and non-aqueous
media is well known.
As the use of environmentally friendly reaction medium
is one of the fundamental principles of green chemistry. In
reactions such water as a reaction solvent had received much
attention in the synthesis of organic compounds, because it
would be considerably safe, non-toxic, environmentally
friendly, and cheap as compared to organic solvents [31].
However, water is rarely considered as a solvent for organic
reactions based on the reason of limited solubility of most
organic compounds in water. As the solubility is important
for good reactivity, alternatives for improving the solubility
of organic substrates in water will ultimately expand the
scope of water-based organic synthesis [32]. Incorporation of
surface-active agents (surfactants) in aqueous media has
proved to enhance the reactivity of water mediated reactions
via the formation of micelles or vesicular cavities. The use of
In the selection of catalyst, several surfactants and boric
acid catalysts in water medium were attempted for
optimization of reaction between indole and benzaldehyde
(Table 2, entry 1). The non-ionic surfactant catalysts like
Triton CF-10, [benzyl-polyethylene glycol (1,1,3,3-tetra
methylbutylphenyl) ether], Triton X-100 (t-octyl phenoxy-
polyethoxy-ethanol) and Tween-20 (t-octylphenoxypol-
yethoxyethanol) were found to be very effective promoters
of the reaction, require a less reaction time and almost
quantitative product yield of them Tween-20 drives the
reaction very fast and affords the product in 98% yield.
*Address correspondence to this author at the Department of Chemistry, Sri
Venkateswara University, Tirupati-517502, India; Mobile: +91-
9849694958; Fax: +91-877 2289555; E-mail: csrsvu@gmail.com
Among the ionic surfactant catalysts the anionic
surfactants Sodium dodecyl sulfate (SDS) and 4-dodecylben-
1875-6255/12 $58.00+.00
© 2012 Bentham Science Publishers

Micelle Promoted Synthesis of Bis-(indolyl)methanes
Letters in Organic Chemistry, 2012, Vol. 9, No. 4
295
R
H
O
2a-r
+
H
R
Tween-20
Water, 70-80 oC
N
N
H
H
N
H
N
H
1
3a-r
Scheme 1. Synthesis of bis-indolylmethanes using Tween-20 surfactant in water.
Table 1. Screening of various types of catalysts for the synthesis of bis-indolylmethanes
Entry
Catalysta
Time (h)
Yield (%)b
1
2
3
4
5
6
7
Boric acid
SDS
5.5
4.0
4.5
4.5
4.2
4.0
5.0
40
60
70
90
84
98
20
SDBS
Triton X-100
Triton CF-10
Tween-20
CTAB
aReaction were carried out at 60-70 ºC for 4-5.5 h with aldehyde (1.0 mmol) and Indole (2.0 mmol) in a solution of catalyst (5 mol %) and water (2 mL).
bIsolated yield.
zenesulfonic acid (SDBS) were slightly less effective than
the cationic surfactant cetyltrimethylammonium bromide
(CTAB). The simple boric acid also catalyzes the reaction at
a slow rate and affords the product in poor yield (Table 1).
The necessity of catalyst in this reaction is proved by the fact
that when the reaction is run without it, the starting materials
are recovered even after running the reaction for a long time.
way chemical membrane. This seems to protect water liable
zwitterion intermediates 5 from hydrolytic decomposition.
At the same time it allows transfer of water molecule formed
during the reaction to the surrounding aqueous environment
(Fig. 1). This reaction situation acts favorably for the
accelerated rate of electrophilic substitution of the carbonyl
carbon of 2 on the C3 atom of Indole 1 regiospecifically
leading to the coupling of two indole 1 moieties with a
substituted methylene bridge.
The aqueous reaction medium turns turbid during the
reaction due to precipitation of reactants encapsulated in
non-ionic surfactant micelles 4. The amphiphilic surfactant
molecule assemblies of the micelles 4 being sufficiently
hydrophobic render the organic substances and reagents
more soluble in the aqueous medium [39-42], bring them in
close proximity and enhance chemical reaction between
them. The boundary of the micelle 4 acts as a kind of one
EXPERIMENTAL
Chemicals were procured from Sigma-Aldrich and
Merck, used without further purification. All solvents used
for the spectroscopic and other physical studies were reagent
O
OH
H
-H2O
N
H
R
H
H
N
R
N
R
H
H
O
O
R
H
R
H
H
N
N
NH
H
N
H
N
N
H
H
HO
R
H
R
OH
N
N
H
4
5
Fig. (1). Schematic representation of micelle promoted bis-indolylmethanes synthesis.

296 Letters in Organic Chemistry, 2012, Vol. 9, No. 4
Kumar et al.
Table 2. Synthesis of bis-indolylmethanes by using tween-20
Melting point (ᵒC)
Entry
3a
Aldehyde
Time (h)
Yield (%)
Literature
Found
CHO
4
5
98
96
125-127
124-126 24,26
104-106 26
3b
102-104
72-74
Cl
CHO
CHO
3c
3d
3e
3f
5
4
93
98
93
91
95
73-75 26
220-222 26
265-266 24,26
96-98 24,26
Cl
221-223
264-226
97-99
O2N
CHO
CHO
4.5
6
NO2
H3C
CHO
H3CO
CHO
OCH3
3g
6
191-193
191-193 24,26
CHO
OCH3
3h
3i
5.5
5.5
4.5
96
91
83
133-135
195-197
125-127
134-136 26
197-199 44
126-127 9
H3CO
H3CO
CHO
H3CO
HO
3j
CHO
Cl
3k
4
87
218-220
------
CHO
OH
Br
3l
CHO
4.25
90
90
228-230
102-104
228-230 4
OH
Cl
CHO
3m
4
103-105 26
Cl

Micelle Promoted Synthesis of Bis-(indolyl)methanes
Letters in Organic Chemistry, 2012, Vol. 9, No. 4
297
(Table 2). Contd…..
Melting point (ᵒC)
Entry
3n
Aldehyde
Time (h)
Yield (%)
Literature
Found
Cl
CHO
4
5
88
92
93
152-154
153-154 44
210-212 26
------
Cl
3o
208-210
264-266
96-98
N
CHO
CHO
OCH2C6H5
3p
4.5
3q
5
95
96
98-100 21,26
CHO
3r
4.5
150-152
------
CHO
NO2
aIsolated yield.
grade and further purified by literature methods [43]. The
melting points (mp) were determined in open capillary tubes
on a Mel-Temp apparatus (Tempo Instruments and Equip
Pvt. Ltd., Mumbai, India), expressed in degrees centigrade
(oC) and were uncorrected. Infrared (IR) Spectra were
obtained on a Nicolet (San Diego, CA, USA) 380 Fourier
transform infrared (FT-IR) spectrophotometer at the
Environmental Engineering Laboratory, Sri Venkateswara
University, Tirupati, India and samples were analyzed as
potassium bromide (KBr) disks and absorptions (νmax) were
reported in wave numbers (cm-1). The 1H, 13C, and 31P-NMR
spectra were recorded on a Bruker (Ettlingen, Germany)
AMX 400 MHz nuclear magnetic resonance (NMR)
extracted thrice with ethyl acetate (3 X10 mL). The
combined organic extracts were dried over anhydrous
Na2SO4, filtered, and concentrated under reduced pressure.
The crude product was further purified by silica gel column
chromatography using hexane/ethylacetate mixture as an
eluent.
The same experimental procedure was adopted for the
synthesis of all the Bis-(indolyl)methanes 3a-r and their
structural moieties are tabulated in Table 2 above. The
spectral data of some of the representative compounds are
given below.
1
spectrometer operating at 400 MHz for H-NMR, 100.57
Spectral Data of the Selected Compounds
3,3'-(phenylmethylene)bis(1H-indole) (3a)
MHz for 13C-NMR, and 161.9 MHz for 31P-NMR
respectively and expressed in parts per million (ppm). All
compounds were dissolved in DMSO-d6 and chemical shifts
were referenced to TMS in 1H-NMR and 13C-NMR and 85%
H3PO4 in 31P NMR. Mass spectra were recorded on a Jeol
SX 102DA/600 (Tokyo, Japan) mass spectrometer using
argon/xenon (6 keV, 10 mA) as the FAB gas. Microanalysis
was performed with a Thermo Finnigan (Courtaboeuf,
France) Flash EA 1112 I instrument at University of
Hyderabad, Hyderabad, India. The purity of all the products
was accomplished by TLC on silica gel polygram SIL G/UV
254 plates.
Solid; mp 124-126 °C; IR (KBr, cm-1): 3415 (NH), 3055,
1
1620, 1600, 1455, 1095, 750; H NMR (400 MHz, DMSO-
d6): δ 7.95 (br s, 2H, NH), 7.35 (m, 6H), 7.30 (m, 2H), 7.22
(m, 3H), 7.00 (t, 2H, J= 7.0), 6.65 (s, 2H), 5.90 (s, IH, Ar-
CH); Anal. Calc. for C23H18N2 (322.14): C, 85.7; H, 5.6; N,
8.7 %; Found: C, 85.8; H, 5.5; N, 8.6 %.
3,3'-((4-chlorophenyl)methylene)bis(1H-indole) (3b)
Solid; mp 104-106 °C; IR (KBr, cm-1): 3415 (NH), 3055,
1
1490, 1450, 1090; H NMR (400 MHz, DMSO-d6): δ 7.95
(br s, 2H, NH), 7.35-7.25 (m, 8H), 7.15 (t, 2H, J= 7.9), 7.05
(t, 2H, J= 8.3), 6.65 (s, 2H), 5.80 (s, I H, Ar-CH).
General Experimental Procedure for the Synthesis of
Bis-(indolyl)methanes
3,3'-((2-chlorophenyl)methylene)bis(1H-indole) (3c)
Solid; mp 73-75 °C; IR (KBr, cm-1): 3410 (NH), 3050,
The aldehyde (1 mmol) and indole (2 mmol) were added
to a solution of Tween-20 (5 mol %) and water (2 mL) in a
round bottomed flask. The reaction mixture was
1
1620, 1455, 1415, 1340, 1095, 1045, 1015; H NMR (400
MHz, DMSO-d6): δ 7.97 (brs, 2H, NH), 7.41-7.35 (m, 4H),
7.20-7.10 (m, 6H), 7.05 (t, 2H), 6.70 (s, 2H), 6.30 (s, 1H, Ar-
CH).
o
continuously stirred at 70-80 C. After completion of the
reaction as indicated by TLC, the reaction mixture was

298 Letters in Organic Chemistry, 2012, Vol. 9, No. 4
Kumar et al.
3,3'-(3-phenylprop-2-ene-1,1-diyl)bis(1H-indole) (3q)
3,3'-((4-nitrophenyl)methylene)bis(1H-indole) (3d)
Semisolid; IR (KBr, cm-1): 3450 (NH), 3110, 2960, 1595,
1475, 1050, 990, 765; 1H NMR (500 MHz, DMSO-d6): 7.95
(br s, 2H, NH), 7.75 (d, 1H, J= 16.0), 7.55 (m, 2H), 7.40 (m,
3H), 7.30 (m, 4H), 7.15 (t, 2H, J= 8.0), 7.05 (t, 2H, J= 8.0),
6.65 (d, 2H, J= 2.2), 6.42 (d, 1H, J= 16.0), 5.95 (s, 1H);
LCMS m/z: 346 (M+).
Solid; rnp 220-222 °C; IR (KBr, cm-1): 3420 (NH), 3050,
1595, 1510, 1455, 1340; H NMR (400 MHz, DMSO-d6): δ
8.15 (d, 2H, J= 8.8). 8.05 (brs, 2H, NH), 7.50 (d, 2H, J= 8.8),
7.40 (d, 2H, J= 8.2), 7.35 (d, 3H, J= 8.0), 7.05-7.00 (m, 3H),
6.70 (s, 2H), 5.98 (s, IH, Ar-CH); Anal. Calc. for
C23H17N3O2 (367.40): C, 75.2; H, 4.7; N, 11.4 %; Found: C,
75.3; H, 4.5; N, 11.6 %.
1
3,3'-(3-(2-nitrophenyl)prop-2-ene-1,1-diyl)bis(1H-indole)
(3r)
3,3'-(p-tolylmethylene)bis(1H-indole) (3f)
Solid; mp 150-152 ºC; 1H NMR (500 MHz, DMSO-d6): δ
8.02 (brs, 2H, NH), 7.91 (dd, 1H, J= 8 & 1.5 Hz,), 7.66-7.00
(m, 14H, Ar-H & one =CH), 6.77 (dd, J= 15.5 & 7.5 Hz, 1H,
=CH-C), 5.48 (d, 1H, J= 7.5 Hz, Ar-CH); 13C NMR (125
MHz, DMSO-d6): δ 147.7, 137.7, 136.7, 133.7, 132.9, 129.0,
127.5, 126.8, 125.8, 124.4, 122.7, 122.0, 119.8, 119.3, 117.6,
111.1, 37.7; Anal. Calcd. for C15H20NO7P: C, 50.42; H, 5.60;
N, 3.92 %. Found: C, 50.38; H, 5.67; N, 3.99%; LCMS m/z:
394.
Solid; mp 96-98 °C; IR (KBr, cm-1): 3415 (NH), 3040,
2930, 1610, 1515, 1220, 1055, 775; H NMR (400 MHz,
DMSO-d6): δ 7.98 (brs, 2H, NH), 7.5 (d, 17.6, 2H), 7.29-
7.25 (rn, 6H), 7.1 (d, 2H, J= 7.6), 7.05 (t, 2H, J= 7.2), 6.70
(s, 2H), 5.85 (s, 1H, Ar-CH), 2.35 (s, 3H, Ar-CH3); Anal.
Calc. for C24H20N2 (349.45): C, 85.7; H, 6.0; N, 8.3 %;
Found: C, 85.4; H, 5.9; N, 8.0 %.
1
3,3'-((4-methoxyphenyl)methylene)bis(1H-indole) (3g)
Solid; mp 191-193 °C; IR (KBr, cm-1): 3415 (NH), 2930,
1610, 1505, 1455, 1240, 1220; 1H NMR (400 MHz, DMSO-
d6): δ 3.75 (s, 3H, CH3), 5.80 (s, 1H, Ar-CH), 6.65 (s, 2H),
6.80 (d, 2H, J= 8.2), 7.05 (t, 2H, J= 7.2), 7.15 (t, 2H, J= 7.2),
7.20 (s, 2H), 7.35-7.40 (m, 4H), 7.98 (brs, 2H, NH). Anal.
Calc. for C24H20N2O (352.43): C, 81.8; H, 5.7; N 8.0 %;
Found: C, 81.7; H, 5.8; N, 8.0 %.
CONCLUSION
In summary, a simple, highly efficient and eco-friendly
Tween-20 micelle promoted procedure for the preparation of
bis-(indolyl)methanes by the reaction of indoles with
aldehydes in aqueous medium is reported. The significance
is that it serves as a versatile method for coupling two indole
moieties at their C3-position with a substituted methylene
bridge.
3,3'-((3,4-dimethoxyphenyl)methylene)bis(1H-indole) (3i)
Solid; mp 197-199 °C; IR (KBr, cm-1): 3445 (NH), 3060,
1
2980, 1620, 1495, 1235, 1005, 765; H NMR (400 MHz,
DMSO-d6): δ 10.45 (br s, 2H, NH), 7.35 (t, 4H, J= 8.2), 7.05
(t, 2H, J= 8.0), 6.90 (d, 2H, J= 8.2), 6.85 (s, 1H), 3.75 (s,
3H), 6.80 (d, 2H, J= 8.2), 6.72 (d, 2H, J= 2.4), 5.75 (s, 1H),
3.82 (s, 3H).
CONFLICT OF INTEREST
The authors have declared no conflict of interest.
ACKNOWLEDGEMENTS
3,3'-((5-chloro-2-hydroxyphenyl)methylene)bis(1H-indole)
(3k)
This work was financially supported by the Council of
Scientific and Industrial Research Project (01/2347/09/EMR-
II) CSIR, New Delhi, India.
Solid; mp 218-220 ºC; 1H NMR (500 MHz, DMSO-d6): δ
10.80 (brs, 2H, NH), 9.60 (s, 1H, OH), 7.50-6.70 (m, 13H,
Ar-H), 6.25 (s, 1H, Ar-CH), 5.14 (s, 2H, O-CH2); 13C NMR
(125 MHz, DMSO-d6): δ 157.2, 139.4, 134.2, 131.5, 129.5,
127.5, 126.6, 125.3, 124.6, 120.2, 119.8, 118.2, 112.7, 111.8,
43.4; Anal. Calc. for C23H17ClN2O: C, 74.09; H, 4.60; N,
7.51; Found: C, 73.96; H, 4.56; N, 7.45; LCMS m/z: 373.
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