Green synthesis of bis(indolyl)methane derivatives using PEG-400

Article abstract of DOI:10.14233/ajchem.2018.21261

Polyethylene glycol (PEG-400) has been considered as an effective and eco-friendly solvent cum activator for the one-pot coupling of indole and aldehydes to produce indole derivatives. The reaction was performed under mild conditions and the versatility o

Full text of DOI:10.14233/ajchem.2018.21261

Asian Journal of Chemistry; Vol. 30, No. 6 (2018), 1369-1373
A
SIAN
J
OURNAL OF HEMISTRY
C
https://doi.org/10.14233/ajchem.2018.21261
Green Synthesis of Bis(indolyl)methane Derivatives using PEG-400
1
2
2,*
RAJU GURRAPU , RAMESH POSHALA and BHASKAR KUTHATI
1Organic and Bio molecular Chemistry Division, CSIR-Indian Institute of Chemical Technology, Hyderabad-500 007, India
2Department of Chemistry, Osmania University, Hyderabad-500 007, India
*Corresponding author: E-mail: kuthatibhaskar@gmail.com
Received: 30 January 2018;
Accepted: 15 March 2018;
Published online: 30 April 2018;
AJC-18896
Polyethylene glycol (PEG-400) has been considered as an effective and eco-friendly solvent cum activator for the one-pot coupling of
indole and aldehydes to produce indole derivatives. The reaction was performed under mild conditions and the versatility of one-pot
reaction was confirmed.
Keywords: 3,3'-(Phenylmethylene)bis(1H-indole), Indole, Aldehyde, Polyethylene glycol, Catalyst-free conditions.
glycerol and CeCl3 [30], B(C6F5)3 [31], H6P2W18O6 [2,32]
phosphated zirconia [33], Ph3CCl [34] have also been utilized
for the synthesis of bis(indolyl)methanes. These methods
involves certain drawbacks, such as expensive catalysts, long
reaction times, a harsh reaction conditions (e.g., high tempe-
ratures, pressure vessels), tedious work-up, high amount of
catalyst loading and poor yield of desired product [35-37]. In
this scenario, the necessity of an efficient and green reaction
medium for the synthesis of bis(indolyl)methanes is highly
desirable.
As we know that the inherent properties of polyethylene
glycol (PEG) such as inexpensive, thermally stability, recycl-
ability and non-toxic nature, in addition to them the high solub-
ility in water and organic solvents alcohol and acetone [38]
and insoluble in less polar solvents such as hexane makes it
easy to recover [2,39-41]. Therefore from the past decade, the
usage of PEG for various organic transformations is an area
of growing interest. To the best of our knowledge, there is no
report for the synthesis of bis(indolyl)methanes using PEG as
a recyclable and mild reaction medium. Hence, as a part of our
ongoing research in the field of PEG-mediated and catalyst free
synthesis of heterocyclic compounds [42-44]. Herein, we report
an green, simple and efficient method for the synthesis of bis-
(indolyl)methanes using PEG-400 as recyclable medium.
INTRODUCTION
Green chemistry relates to the design of a process that mini-
mizes the use and generation of hazardous substances. Green
catalysis is one of the key areas of green chemistry. Now a days,
the environmentally friendly solvents such as ionic liquids,
super critical fluids and polyethylene glycol have been gaining
importance as green reaction media in view of environmental
regulations [1]. In this connection, polyethylene glycol (PEG)
attain much more importance as an alternative reaction media
to perform most of the organic reactions, because of its character-
istic advantages such as recyclable, non-toxic in nature, thermally
stable, inexpensive and easy to handle over the conventional
solvents. Further, PEG also emerged as a powerful phase transfer
catalyst and used in many organic transformations. In this
perspective, PEG has been played a key role in the practice of
green chemistry [2].
There are various methods for the synthesis of bis(indolyl)-
methanes available in literature. However, most of the methods
involves protic acids and Lewis acids as catalysts to promote
nucleophilic substitution reaction on various aldehydes and
carbonyl compounds with indoles [3]. Further there are other
acidic catalysts such as H-Y zeolite [4], sulfamidic acid [5],
metaltriflates [6], LiClO4 [7], bis(cyclopentadienyl) ZrCl2 [8],
CuBr2 [9], ZrCl4 [10] Zn(HSO4)2 [11], CAN [12] polyindole
salt [13], N-tert ion exchange resin [14], butanesulfinyl
aldimines [15], AcOH [16], InCl3 [17], InF3 [18], Ln(OTf)3
[19], Dy(OTf)3 [3c], FeCl3·6H2O [20], V(HSO4)3 [21], SBA-
15/SO3H [22], TBBDA [23], oxalic acid [24], silica bonded
S-sulfonic acid [25], Bi(NO3)3 [26], Cu(BF4)2·SiO2 [27], vana-
dium molybdophosphoric acid [28], Ph-PMO-SO3H [29],
EXPERIMENTAL
All the chemicals were purchased from Sigma Aldrich
with purity not less than 99.9%.Analytical thin layer chromato-
graphy (TLC) was carried out by using silica gel 60 F254 pre-
coated plates. Visualization was accomplished with UV lamp

1370 Gurrapu et al.
Asian J. Chem.
of I2 stain. All the products were characterized by their NMR
and HRMS spectra. 1H NMR and 13C NMR were recorded on
400 or 100 MHz, in CDCl3 and the chemical shifts were reported
in parts per million (ppm, δ) downfield from the tetramethylsilane.
General procedure for the synthesis of bis(indolyl)
methane by using PEG as reaction medium: A mixture of
the requisite aldehyde (2 mmol), indole (1.0 mmol) was taken
in PEG (5 mL) and stirred at 85 ºC for the appropriate time.
After completion of the reaction, as monitored by TLC, the
reaction mixture was poured into water and extracted with ethyl
acetate. The organic layer was removed under reduced pressure
and the crude product was purified by column chromatography.
The recovered PEG could be reused for a number of cycles with-
out significant loss of activity (Scheme-I).
H
N
CHO
PEG-400(5mL)
85 oC, 8h
+
N
R
H
NH
R= CH3, Br, Cl, F, NO2
R
1
2a-o
3a-o
H
H
N
H
H
N
N
N
NH
NH
Br
NH
NH
NO2
Br
3c
3a
3b
3d
H
N
H
H
H
N
N
N
NH
NH
NH
NH
O2N
Br
NO2
3e
3f
3g
3h
H
H
N
H
H
N
N
N
Cl
F
NH
NH
NH
NH
Cl
Cl
3i
3j
3k
3l
H
N
H
N
H
N
NH
NH
F
NH
F
3n
3m
3o
Scheme-I: PEG-400 mediated synthesis of bis(indolyl)methane derivatives

Vol. 30, No. 6 (2018)
Green Synthesis of Bis(indolyl)methane Derivatives using PEG-400 1371
Spectral data
m.p. 217-218 ºC; Reported: 219 ºC [46]. Elemental analysis:
Calcd. (found): C 75.19 (75.22), H 4.66 (4.68), N 11.44 (11.41);
IR (KBr, νmax, cm-1): 7835, 802, 1009, 1340, 1458, 1510, 1593,
1706, 1727, 2848, 2920, 2956, 3411. 1H NMR (400 MHz, CDCl3):
δ 6.18 (s, 1H), 6.76 (s, 2H), 7.0-7.05 (m, 3H), 7.42 (d, 3H, J =
7.8 Hz), 7.4 (d, 2H, J = 7.9 Hz), 7.49 (d, 2H, J = 8.6 Hz), 7.97
(br, 2H), 8.00 (d, 2H, J = 8.3 Hz). 13C NMR (DMSO): δ 29.3,
111.4, 116.9, 118.5, 118.9, 121.1, 123.9, 126.4, 129.3, 136.7.
MS: m/z 366 (M+).
3,3′-Bis(indolyl)-4-(bromophenyl)methane (3g): Red
colour solid, m.f. C23H17N2Br, m.w. 400.06, yield 70 %; m.p.
108-110ºC;Reported:108-111 ºC [47]. Elementalanalysis:Calcd.
(found): C 68.84 (68.82), H 4.27 (4.26), N 6.98 (6.99), Br 19.91
(19.89); IR (KBr, νmax, cm-1): 740, 1004, 1086, 1417, 1458,
1484, 2848, 2920, 2956, 3406. 1H NMR (400 MHz CDCl3): δ
7.78 (1H, s, NH), 7.39 (2H, m, H-5 and H-11), 7.33 (1H, d, J =
8.8 Hz, H-8), 7.20 (2H, t, H-6, H-12, J = 8.2 Hz), 7.04 (1H, t, H-7,
J = 8.2 Hz), 6.56 (1H, s, H-2), 5.85 (1H, s, H-3′). 13C NMR (100
MHz (CDCl3): δ 111.1, 119.1, 119.6, 119.8, 122.0, 126.8, 130.5,
131.2, 136.7, 143.1. MS: m/z 400 (M+).
3,3′-(Phenylmethylene)bis(1H-indole) (3a): Red colour
solid, m.f. C23H18N2, m.w. 322.15, yield 90 %; m.p. 152 ºC;
Reported: 150-152 ºC [45]. Elemental analysis: Calcd. (found):
C 85.68 (85.62), H 5.63 (5.62), N 8.69 (8.65); IR (KBr, νmax
,
cm-1): 704, 740, 1004, 1086, 1216, 1262, 1340, 1417, 1453,
1
1494, 1593, 1624, 2848, 2924, 3054, 3416, 3416. H NMR
(400 MHz, CDCl3): δ 5.85 (s, 1H), 6.72 (s, 2H), 7.02 (t, 2H, J
= 6.7 Hz), 7.12-7.20 (m, 3H), 7.25-7.30 (m, 2H), 7.34-7.40
(m, 6H), 7.90 (br, 2H).13C NMR (DMSO): δ 46.1, 111.0, 119.2,
119.7, 119.9, 121.9, 123.6, 126.1, 127.1, 128.2, 128.7, 136.7,
144.0. MS: m/z 321 (M+).
3,3′-[(2-Bromophenyl)methylene]bis(1H-indole) (3b):
Red colour solid, m.f. C23H17N2Br, m.w. 400.06, yield 70 %;
m.p. 76-77 ºC [46]. Elemental analysis: Calcd. (found): C 68.84
(68.81), H 4.27 (4.22), N 6.98 (6.91), Br 19.91 (19.91); IR(KBr,
ν
max, cm-1): 740, 792, 1024, 1024, 1097, 1216, 1257, 1334,
1412, 1453, 1567, 1582, 2848, 2920, 2977, 3054, 3411; 1H NMR
(400 MHz, CDCl3): δ 7.88 (s, 2H), 7.46-7.27 (m, 5H), 7.19 (s,
1H), 7.15 (d, J = 5.8 Hz, 1H), 7.13-7.06 (m, 2H), 7.05-7.00 (m,
1H), 6.95 (t, J = 7.5 Hz, 2H), 6.56 (s, 2H), 6.27 (s, 1H); 13C NMR
(DMSO): δ 111.3, 118.1, 119.2, 119.8, 121.9, 124.1, 127.0,
127.3, 130.6, 132.8, 136.8, 143.2. MS: m/z 400 (M+).
3,3′-[(4-Nitrophenyl)methylene]bis(1H-indole) (3h):
Red colour solid, m.f. C23H17N3O2, m.w. 367.13, yield 85 %;
m.p, 219-220 ºC [46]. Elemental analysis: Calcd. (found): C
75.19 (75.21), H 4.66 (4.64), N 11.44 (11.41); IR (KBr, νmax
,
3,3′-[(3-Bromophenyl)methylene]bis(1H-indole) (3c):
Red colour solid, m.f. C23H17N2Br, m.w. 400.06, yield 70 %;
m.p.: 104-106 ºC [46]. Elemental analysis: Calcd. (found): C
68.84 (68.82), H 4.27 (4.25), N 6.98 (6.96), Br 19.91 (19.96);
IR (KBr, νmax, cm-1): 740, 792, 1014, 1097, 1216, 1272, 1334,
1417, 1458, 1567, 1587, 1618, 2925, 2972, 3054, 3416; 1H NMR
(400 MHz, CDCl3): δ 7.97 (s, 2H), 7.49 (s, 1H), 7.41-7.34 (m,
5H), 7.31 (d, J = 21.5 Hz, 1H), 7.22-7.11 (m, 3H), 7.02 (t, J =
7.5 Hz, 2H), 6.65 (s, 2H), 5.85 (s, 1H); 13C NMR (DMSO): δ
39.7, 111.1, 119.1, 119.3, 119.8, 119.9, 122.0, 123.6, 126.8,
130.5, 131.3, 136.7, 143.1 MS: m/z 435 (M+).
3,3′-((2-Nitrophenyl)methylene)bis(1H-indole) (3d):
Red colour solid, mf. C23H17N3O2, m.w. 367.13, yield 85 %;
m.p. 140-142 ºC [46]. Elemental analysis: Calcd. (found): C 75.19
(75.15), H 4.66 (4.61), N 11.44 (11.42); IR (KBr, νmax, cm-1):
735, 1092, 1340, 1453, 1515, 1593, 1711, 2848, 2920, 2956,
3426; 1H NMR (400 MHz, DMSO): δ 10.93 (s, 2H), 7.88 (d, J
= 7.9 Hz, 1H), 7.56 (t, J = 7.5 Hz, 1H), 7.46 (t, J = 7.3 Hz,
1H), 7.40 (d, J = 7.7 Hz, 1H), 7.36 (d, J = 8.1 Hz, 2H), 7.21
(d, J = 8.0 Hz, 2H), 7.06 (t, J = 7.5 Hz, 2H), 6.89 (t, J = 7.4 Hz,
cm-1): 740, 1340, 1453, 1505, 1598, 1727, 2848, 2920, 2956,
3406. 1H NMR (400 MHz, DMSO): δ 10.95 (s, 2H), 8.15 (d, J
= 8.7 Hz, 2H), 7.61 (d, J = 8.7 Hz, 2H), 7.38 (d, J = 8.1 Hz,
2H), 7.30 (d, J = 7.9 Hz, 2H), 7.06 (t, J = 7.5 Hz, 2H), 6.96-6.78
(m, 4H), 6.04 (s, 1H); 13C NMR (100 MHz, DMSO): δ 29.3,
111.4, 116.9, 118.5, 118.9, 121.2, 123.1, 123.9, 126.4, 129.3,
136.7; MS: m/z 366 (M+).
3,3′-(3-Chlorophenyl)methylen)bis(1H-indole) (3i): Red
colour solid, yield 85 %; m.f. C23H17N2Cl, m.w. 356.11, m.p. 77
ºC; Reported: 76-77 ºC. Elemental analysis: Calcd. (found): C
77.41 (77.34), H 4.80 (4.83), N 7.85 (7.81), Cl 9.97 (9.96); IR
(KBr, νmax, cm-1): 740, 797, 1004, 1035, 1086, 1210, 1267, 1334,
1412, 1453, 1613, 2848, 2920, 3054, 3411. 1H NMR (400 MHz,
CDCl3): δ 6.02 (s, 1H), 6.67 (s, 2H), 7.12 (t, 3H, J = 8.5 Hz),
7.20 (t, 2H, J = 7.9 Hz), 7.27-7.40 (m, 8H), 7.97 (br, 2H). 13C
NMR (DMSO): δ111.1, 118.3, 119.3, 119.8, 122.0, 123.8, 126.6,
127.0, 127.5, 129.5, 130.3, 134.0, 136.7, 141.3. MS: m/z 355
(M+).
3,3′-(4-Chlorophenyl)methylene)bis(1H-indole) (3j):
Red colour solid; m.f. C23H17N2Cl, m.w. 356.11, yield 85 %;
m.p. 77 ºC; Reported: 76-77 ºC [46].Elemental analysis: Calcd.
(found): C 77.41 (77.35), H 4.80 (4.82), N 7.85 (7.87), Cl 9.97
(9.90); IR (KBr, νmax, cm-1): 740, 797, 1004, 1035, 1086, 1210,
1267, 1334, 1412, 1453, 1613, 2848, 2920, 3054, 3411. 1H NMR
(400 MHz, CDCl3): δ 6.02 (s, 1H), 6.67 (s, 2H), 7.12 (t, 3H, J
= 8.5 Hz), 7.20 (t, 2H, J = 7.9 Hz), 7.27-7.40 (m, 8H), 7.97
(br, 2H). 13C NMR (DMSO): δ 111.1, 118.3, 119.3, 119.8,
122.0, 123.8, 126.6, 127.0, 127.5, 129.5, 130.3, 134.0, 136.7,
141.3. MS: m/z 355 (M+).
13
2H), 6.78 (s, 2H), 6.40 (s, 1H). C NMR (DMSO): δ 111.4,
116.9, 118.5, 118.9, 121.2, 123.1, 123.9, 126.4, 129.3, 126.4,
129.3, 136.7. MS: m/z 366 (M+).
3,3′-(p-Tolylmethylene)bis(1H-indole) (3e): Dark pink
colour solid, m.f. C24H20N2, m.w. 336.16, yield 92 %; m.p. 94-
95 ºC; Reported: 94-96 ºC [45]. Elemental analysis: Calcd.
(found): C 85.68 (85.64), H 5.99 (5.97), N 8.33 (8.23); IR (KBr,
ν
max, cm-1): 740, 808, 952, 1045, 1159, 1200, 1340, 1453, 1515,
1608, 2853, 2920, 3411. 1H NMR (400 MHz, CDCl3): δ 2.38
(s, 3H), 5.82 (s, 1H), 6.65 (s, 2H), 6.97 (t, 2H, J = 7.5Hz), 7.2 (d,
2H, J = 7.3 Hz), 7.19-7.26 (m, 6H), 7.2 (d, 2H, J = 7.3 Hz), 7.91
(br, 2H). 13C NMR (DMSO): δ 110.9, 119.2, 119.9, 121.8,
123.5, 127.1, 128.5, 128.9, 135.4, 136.7, 141.0. MS: m/z 335 (M+).
3,3′-(3-Nitrophenyl)methylene)bis(1H-indole) (3f):
Brown colour solid, m.f. C23H17N3O2, m.w. 367.13, yield 85 %;
3,3′-[(2-Chlorophenyl)methylene]bis(1H-indole) (3k):
Red colur solid, m.f. C23H17N2Cl, m.w. 356.11, yield 82 %; m.p.
71-72 ºC [46]. Elemental analysis: Calcd. (found): C 77.41
(77.35), H 4.80 (4.82), N 7.85 (7.87), Cl 9.97 (9.90); IR (KBr,
νmax, cm-1):735, 792, 906, 1009, 1035, 1092, 1128, 1210, 1262,

1372 Gurrapu et al.
Asian J. Chem.
1
1334, 1412, 1453, 1613, 2848, 2915, 3049, 3400; H NMR
(400 MHz, CDCl3): δ 7.93 (s, 2H), 7.64 (d, J = 7.8 Hz, 1H),
7.44 (d, J = 7.9 Hz, 2H), 7.38 (d, J = 8.1 Hz, 2H), 7.23 (s, 1H),
7.21 (s, 1H), 7.17 (s, 2H), 7.14-7.10 (m, 1H), 7.06 (d, J = 15.0
Hz, 2H), 6.62 (s, 2H), 6.34 (s, 1H). 13C NMR (100 MHz, CDCl3):
δ 111.1, 118.3, 119.3, 119.8, 122.0, 123.8, 126.6, 127.0, 127.7,
129.5, 130.3, 134.0, 136.7, 141.3. MS: m/z 355 (M+).
rich aldehydes that are aldehydes with electron donating groups
reacted efficiently and with less reaction time whereas aldehydes
with electron withdrawing groups takes slighter more reaction
time. The structures of all the final compounds were confirmed
by their analytical and spectroscopic data and also comparing
with already available reported values.
Conclusion
3,3′-(3-Flurophenyl)methylene)bis(1H-indole) (3l): Red
colour solid, m.f. C23H17N2F, m.w. 340.14, yield 80 %; m.p. 73
ºC; Reported: 74 ºC. Elemental analysis: Calcd. (found): C 81.16
(81.02), H 5.03 (4.97), N 8.23 (8.20), F 5.58 (5.60); IR (KBr,
An efficient, inexpensive, high yielding and green synth-
etic method of bis(indolyl)methane derivatives from various
aldehydes and indole under mild reaction conditions using
PEG-400 is reported.
ν
max, cm-1): 740, 777, 875, 937, 1014, 1086, 1128, 1221, 1247,
1334, 1417, 1453, 1484, 1587, 1613, 2848, 2920, 3054, 3411.
1H NMR (400 MHz, CDCl3): δ 6.12 (s, 1H), 6.71 (s, 2H), 7.16
(t, 3H, J = 8.7 Hz), 7.22 (t, 2H, J = 8.0 Hz), 7.32-7.43 (m, 8H),
8.0 (br, 2H). 13C NMR (DMSO): δ40.0, 111.1, 113.0, 113.1, 115.5,
115.6, 119.0, 119.3, 119.8, 122.0, 123.6, 124.4, 124.4, 126.9,
129.5, 129.6, 136.7, 146.8, 146.8, 162.0, 164.0. MS: m/z 339 (M+).
3,3′-(4-Flurophenyl)methylene)bis(1H-indole) (3m):
Red colour solid, m.f. C23H17N2F, m.w. 340.14, yield 85 %;
m.p. 77 ºC; yield 88 %; m.p. 77 ºC; Reported: 76-77 ºC [45].
Elemental analysis: Calcd. (found): C 81.16 (81.01), H 5.03
(4.99), N 8.23 (8.21), F 5.58 (5.56); IR (KBr, νmax, cm-1): 735,
849, 1009, 1086, 1159, 1210, 1267, 1340, 1417, 1453, 1500,
1598, 2848, 2920, 2956, 3054, 3406. 1H NMR (400 MHz, CDCl3):
δ 6.02 (s, 1H), 6.67 (s, 2H), 7.12 (t, 3H, J = 8.5 Hz), 7.20 (t, 2H,
J= 7.9 Hz), 7.27-7.40 (m, 8H), 7.97 (br, 2H). 13C NMR (DMSO):
δ 111.0, 114.8, 115.0, 119.3, 119.6, 119.8, 122.0, 123.5, 126.9,
130.0, 130.1, 136.7. MS: m/z 339 (M+).
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Red colour solid, m.f. C23H17N2F, m.w. 340.14, yield 85 %;
m.p. 77 ºC; Reported: 76-77 ºC. Elemental analysis: Calcd.
(found): C 81.16 (81.02), H 5.03 (4.97), N 8.23 (8.20), F 5.58
(5.60); IR (KBr, νmax, cm-1): 736, 850, 1010, 1088, 1161, 1211,
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3407. H NMR (400 MHz, CDCl3): δ 6.02 (s, 1H), 6.67 (s,
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2H), 7.12 (t, 3H, J = 8.5 Hz), 7.20 (t, 2H, J = 7.9 Hz), 7.27-
7.40 (m, 8H), 7.97 (br, 2H). 13C NMR (DMSO): δ 111.1, 114.9,
1151, 119.4, 119.7, 119.6, 122.1, 123.6, 126.9, 130.0, 130.0,
136.8. MS: m/z 339 (M+).
3,3′-((2-Methylphenyl)methylene)bis(1H-indole) (3o):
Dark pink colour solid, m.f. C24H17N2, m.w. 336.16, yield 80
%; m.p. 94-95 ºC; Reported: 94-96 ºC. Elemental analysis:
Calcd. (found): C 85.68 (85.62), H 5.99 (5.97), N 8.33 (8.30);
IR (KBr, νmax, cm-1): 741, 809, 953, 1046, 1160, 1201, 1341,
1454, 1516, 1609, 2855, 2921, 3412. 1H NMR (400 MHz, CDCl3):
δ 2.38 (s, 3H), 5.82 (s, 1H), 6.65 (s, 2H), 6.97 (t, 2H, J = 7.5
Hz), 7.2 (d, 2H, J = 7.3 Hz), 7.19-7.26 (m, 6H), 7.2 (d, 2H, J
= 7.3 Hz), 7.91 (br, 2H). 13C NMR (DMSO): δ 110.9, 119.3,
119.8, 121.9, 123.6, 127.2, 128.6, 128.9, 135.5, 136.8, 142.0.
MS: m/z 335 (M+).
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with various aldehydes are smoothly going and good yielding
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