Novel multicomponent synthesis of 2,9-dihydro-9-methyl-2-oxo-4-aryl-1H- pyrido[2,3-b]indole-3-carbonitrile compounds

Article abstract of DOI:10.1007/s12039-013-0369-y

Novel multicomponent approach for the synthesis of 2,9-dihydro-2-oxo-4- aryl-1H-pyrido[2,3-b]indole-3-carbonitrile derivatives via one-pot cyclocondensation reaction of substituted (triethoxymethyl)arene, 1-methyl-1H-indol-2-ol and cyanoacetamide in the presence of silica supported ionic liquid [pmim]HSO_{4 SiO2} (silica-supported 1-methyl-3- (triethoxysilylpropyl)imidazolium hydrogensulphate) has been reported.

Full text of DOI:10.1007/s12039-013-0369-y

c
J. Chem. Sci. Vol. 125, No. 1, January 2013, pp. 95–100. ꢀ Indian Academy of Sciences.
Novel multicomponent synthesis of 2,9-dihydro-9-methyl-2-oxo-4-aryl-
1H-pyrido[2,3-b]indole-3-carbonitrile compounds
SAMAN DAMAVANDI1,∗ and REZA SANDAROOS2
1Young Researchers Club, Sarvestan Branch, Islamic Azad University, Sarvestan, Iran
2Department of Chemistry, Faculty of Science, University of Birjand, Birjand, Iran
e-mail: Saman_Damavandi@yahoo.com; R_Sandaroos@yahoo.com
MS received 31 December 2011; revised 13 June 2012; accepted 10 July 2012
Abstract. Novel multicomponent approach for the synthesis of 2,9-dihydro-2-oxo-4-aryl-1H-
pyrido[2,3-b]indole-3-carbonitrile derivatives via one-pot cyclocondensation reaction of substituted (tri-
ethoxymethyl)arene, 1-methyl-1H-indol-2-ol and cyanoacetamide in the presence of silica supported ionic
liquid [pmim]HSO4 SiO2 (silica-supported 1-methyl-3-(triethoxysilylpropyl)imidazolium hydrogensulphate)
has been reported.
Keywords. Pyrido[2,3-b]indole; multicomponent; silica supported ionic liquid.
1. Introduction
these, ionic liquids possessing HSO4 as a counteran-
ion find a broad application in organic synthesis, act-
ing as both solvents and catalysts. Recently, immo-
bilization processes involving acidic ionic liquids on
solids supports have been designed.18–20 The hetero-
genization of catalysts and reagents can offer impor-
tant advantages in handling, separation and reuse pro-
cedures. Based on economic criteria, it is desirable to
minimize the amount of ionic liquid utilized in a poten-
tial process. Immobilized acidic ionic liquids have been
used as novel solid catalysts for a wide spectrum of
reactions.21,22
Following the discovery of α-carboline structure and
its cytotoxic activity toward L1210 leukemia cells,1
in the recent years, there has been interest in the
synthesis of functionalized pyrido[2,3-b]indoles. Syn-
thetic α-carboline compounds have also been found to
exhibit antiviral and antitumour activities.2–4 Moreover,
pyrido[2,3-b]indoles have been known as the biologi-
cal control agent for receptor research on bio-enzyme
inhibitors, such as the inhibition of HLE (human leuko-
cyte elastase).5–8
Synthetic approaches for this class of compounds
mostly involve construction of either pyridine ring from
2-amino-3-substituted indole derivatives9,10 or synthe-
sis of pyrrole ring via cross coupling between an appro-
priately substituted pyridine and aniline derivatives.11,12
In addition, synthesis of pyrido[2,3-b]indole derivatives
via condensation of 3-substituted indole-2(3H)-one
derivatives and enamines followed by thermal cycliza-
tion with ammonium acetate has been reported.13,14
Other approaches involve intramolecular Diels–Alder
reaction of 2(1H)-pyrazinones and conjugated carbodi-
imides.15,16
In continuation of our ongoing research in devel-
oping new multicomponent synthetic approach,23–27
we considered it to be of interest to devise a facile,
efficient, versatile and one-pot synthetic method for
construction of pyrido[2,3-b]indoles utilizing easily
accessible 1-methyl-1H-indol-2-ol, substituted (tri-
ethoxymethyl)arene, and cyanoacetamide in the pre-
sence of immobilized [pmim]HSO4 SiO2 being a silica-
supported ionic liquid with acidic counteranion of
HSO−4 (figures 1 and 2). Here, we report the details of
this study.
In the recent years, ionic liquids have become a
powerful alternative to conventional molecular organic
solvents due to their particular properties, such as
undetectable vapour pressure and the ability to dis-
solve many organic and inorganic substances.17 Among
2. Experimental
2.1 General
All Chemicals and accessible ionic liquids were pur-
chased from Merck, Fluka and Aldrich Chemical
∗For correspondence
95

96
Saman Damavandi and Reza Sandaroos
O
OEt
O
O
O
NH2
NH2
CN
O
[pmim] HSO4 SiO2
O
OH
+
NC
+
+
O
NH2
NH
N
N
N
A
B
time (h)
3.0
5.0
8.0
1.5
B:A ratio
10:0
10:0
10:0
8:2
MeOH, 70 o
C
DMF, 110 oC,
2.0
6:4
4.0
1:9
5.0
1:9
Figure 1. One-pot synthesis of pyrido[2,3-b]indoles.
Companies. All yields refer to isolated products. The 1-methyl-1H-indol-2-ol (1 mmol) and ionic liquid
products were characterized by their spectral data. IR catalyst (0.15 mmol) in appropriate solvent (DMF or
spectra were recorded on a Shimadzu-IR 470 spec- methanol) (6 mL) was stirred for requisite time. The
1
trophotometer. H NMR spectra were recorded on a reaction was monitored by TLC, and after completion
Bruker 100-MHz spectrometer in chloroform as the sol- of the reaction, the catalyst was simply recovered by
vent and TMS as internal standard. Elemental analy- filtration and washed by dichloromethane. The solvent
sis (C, H, N %) was carried out by Perkin-Elmer 2400 was removed from filtrate by distillation and crude
series-II elemental analyzer. [pmim]HSO4 SiO2 (extent of product was purified by column chromatography on
labelling 0.25 mol/g loading) was prepared according silica gel.
to the literature.28
2.2a 2-Amino-4-ethoxy-4,9-dihydro-9-methyl-4-
phenylpyrano[2,3-b]indole-3-carboxamide (III): IR
2.2 General procedure for synthesis of compounds
IV(a–k) and III
(KBr, νmax, cm−1): 3260, 3144, 2979, 2835, 1660,
1
1578, 1462, 1220 cm−1. H-NMR (400 MHz, DMSO-
A mixture of substituted (triethoxymethyl)arene (1 mmol),
3-hydroxyindole and cyanoacetamide (1.1 mmol),
d6): δ = 3.55 (3H, s, indole), 10.85 (1H, s, -NHCO-),
7.65 (1H, d, J = 7.2 Hz, ArH), 7.36 (1H, d, J = 7.2 Hz,
OEt
EtO
OEt
EtO
OEt
CN
CN
OEt
OEt
H+
H
NH2
NH2
OEt
H
H
..
OH
OH
..
O
O
O
N
N
N
X
CN
NH
H
CN
NH
EtO
H+
OEt
CN
O
a
H
O
Thermodynamic pathway
O
H
b
N
OH
NH2
..
N
O
a
N
Y
IV
b
II
O
O
O
NH2
N
NH2
NH
NH2
H
EtO
EtO
EtO
NH2
H+
..
O
O
O
N
H
N
N
III
Kinetic pathway
Figure 2. Proposed mechanism for one-pot three-component synthesis of
pyrido[2,3-b]indole derivatives catalysed by [pmim] HSO4 SiO2
.

MCR synthesis of functionalized pyridoindole
97
ArH), 7.30–7.15 (8H, m, ArH), 7.05 (2H, d, J = 7.4 Hz, d, J = 6.4 Hz, ArH), 7.80 (2H, d, J = 6.4 Hz, ArH),
ArH), 3.73 (q, J = 12.5 Hz, O-CH2-), 1.35 (t, J = 3.55 (s, -CH3, indole). 13C-NMR (250 MHz, DMSO-
12.5 Hz, -CH3). Anal. Calcd for C21H21N3O3: C, 69.41; d6): δ = 168.5, 160.7, 139.2, 132.3, 129.5, 128.3,
H, 5.82; N, 11.56%. Found: C, 69.22; H, 5.79; N, 127.9, 124.8, 124.1, 122.6, 121.8, 121.6, 117.3, 116.5,
11.55%.
111.3, 96.6, 32.7. Anal. Calcd for C19H12BrN3O: C,
60.34; H, 3.20; N, 11.11%. Found: C, 60.21; H, 3.14;
N, 11.05%.
2.2b 2,9-Dihydro-4-(4-methoxyphenyl)-9-methyl-2-
oxo-1H-pyrido[2,3-b]indole-3-carbonitrile
(IV–a):
IR (KBr, νmax, cm−1): 3255, 3110, 2955, 2830, 2235, 2.2f 4-(2-Bromophenyl)-2,5-dihydro-9-methy-2-oxo-
1
1645, 1555, 1440, 1133 cm−1. H NMR (400 MHz, 1H-pyrido[3,2-b]indole-3-carbonitrile
(IV–e): IR
DMSO-d6): δ = 10.85 (1H, s, -NHCO-), 7.60–7.35 (KBr, νmax, cm−1): 3255, 3134, 2991, 2806, 2228, 1650,
(2H, m, ArH), 7.28 (2H, d, J = 7.1 Hz, ArH), 7.12 1544, 1487 cm−1. H NMR (400 MHz, DMSO-d6):
1
(2H, d, J = 7.4 Hz, ArH), 6.95 (2H, d, J = 7.1 Hz, δ = 10.57 (1H, s, -NHCO-), 7.60 (1H, d, J = 7.0 Hz,
ArH), 3.80 (s, OCH3), 3.65 (3H, s, indole). 13C-NMR ArH), 7.45–7.37 (2H, m, ArH), 7.22–7.14 (5H, m,
(250 MHz, DMSO-d6): δ = 165.8, 155.1, 150.4, 135.8, ArH), 3.63 (s, -CH3, indole). 13C-NMR (250 MHz,
128.2, 126.3, 124.6, 124.4, 124.2, 122.1, 121.4, 119.6, DMSO-d6): δ = 163.3, 155.2, 139.7, 135.5, 132.1,
115.3, 111.9, 112.6, 99.8, 55.8, 35.2. Anal. Calcd for 129.8, 125.9, 125.2, 124.6, 123.3, 121.9, 121.0, 118.8,
C20H15N3O2: C, 72.94; H, 4.59; N, 12.76%. Found: C, 118.6, 118.1, 115.7, 94.1, 31.6. Anal. Calcd for
72.56; H, 4.55; N, 12.73%.
C19H12BrN3O: C, 60.34; H, 3.20; N, 11.11%. Found:
C, 60.27; H, 3.13 N, 11.07%.
2.2c 2,9-Dihydro-9-methyl-2-oxo-4-phenyl-1H-
pyrido[2,3-b]indole-3-carbonitrile (IV–b): IR (KBr, 2.2g 4-(4-Chlorophenyl)-2,9-dihydro-9-methyl-2-oxo-
νmax, cm−1): 3250, 3120, 2965, 2833, 2230, 1642, 1551, 1H-pyrido[2,3-b]indole-3-carbonitrile
(IV–f): IR
1431 cm−1. 1H NMR (400 MHz, DMSO-d6): δ = 11.02 (KBr, νmax, cm−1): 3263, 3115, 2980, 2802, 2212, 1652,
1
(1H, s, -NHCO-), 7.55 (1H, d, J = 6.3 Hz, ArH), 7.43 1535, 1470 cm−1. H NMR (400 MHz, DMSO-d6):
(1H, d, J = 6.3 Hz, ArH), 7.33–7.15 (7H, m, ArH), δ = 11.02 (1H, s, -NHCO-), 7.55 (1H, d, J = 7.5 Hz,
3.62 (3H, s, indole). 13C-NMR (250 MHz, DMSO-d6): ArH), 7.46 (1H, d, J = 7.7 Hz, ArH), 7.25–7.18 (4H,
δ = 169.3, 155.2, 138.5, 129.2, 125.5, 124.2, 123.7, m, ArH), 7.04 (2H, d, J = 7.7 Hz, ArH), 3.55 (s, -CH3,
13
122.47 120.4, 118.5, 118.0, 117.5, 116.1, 114.6, 110.8, indole). C-NMR (250 MHz, DMSO-d6): δ = 166.4,
96.2, 34.5. Anal. Calcd for C19H13N3O: C, 76.24; H, 161.1, 138.9, 135.3, 129.7, 127.4, 124.93, 124.7, 123.6,
4.38; N, 14.04%. Found: C, 75.90; H, 4.34; N, 14.42%. 122.1, 121.5, 120.5, 118.8, 116.7, 111.1, 93.6, 33.1.
Anal. Calcd for C19H12ClN3O: C, 68.37; H, 3.62; N,
12.59%. Found: C, 67.91; H, 3.53; N, 12.51%.
2.2d 2,9-Dihydro-9-methyl-2-oxo-4-p-tolyl-1H-
pyrido[2,3-b]indole-3-carbonitrile (IV–c): IR (KBr,
νmax, cm−1): 3254, 3119, 2976, 2835, 2218, 1647, 2.2h 4-(2-Chlorophenyl)-2,9-dihydro-9-methyl-2-oxo-
1
1551, 1422 cm−1. H NMR (400 MHz, DMSO-d6): 1H-pyrido[2,3-b]indole-3-carbonitrile
(IV–g): IR
δ = 10.80 (1H, s, -NHCO-), 7.46 (1H, d, J = 7.1 Hz, (KBr, νmax, cm−1): 3250, 3142, 2997, 2812, 2211, 1667,
ArH), 7.57 (1H, d, J = 7.1 Hz, ArH), 7.30–7.12 (6H, 1553, 1465 cm−1. H NMR (400 MHz, DMSO-d6):
1
m, ArH), 3.52 (s, -CH3, indole), 2.12 (s, -CH3). 13C- δ = 10.92 (1H, s, -NHCO-), 7.50 (1H, d, J = 6.5 Hz,
NMR (250 MHz, DMSO-d6): δ = 161.9, 156.1, 139.6, ArH), 7.43 (1H, d, J = 6.5 Hz, ArH), 7.30–7.24
135.5, 129.3, 128.7, 127.1, 125.9, 125.3, 124.0, 121.8, (2H, m, ArH), 7.20–7.05 (4H, m, ArH), 3.60 (s, -CH3,
13
120.1, 117.8, 115.1, 112.9, 95.2, 34.6, 24.9. Anal. indole). C-NMR (250 MHz, DMSO-d6): δ = 169.5,
Calcd for C20H15N3O: C, 76.66; H, 4.82; N, 13.41%. 158.4, 139.7, 134.4, 131.1, 128.9, 125.5, 124.2, 122.9,
Found: C, 76.49; H, 4.78; N, 13.38%.
122.1, 120.8, 120.1, 118.9, 118.7, 116.9, 116.3, 98.5,
34.5. Anal. Calcd for C19H12ClN3O: C, 68.37; H, 3.62;
N, 12.59%. Found: C, 67.84; H, 3.55; N, 12.49%.
2.2e 4-(4-Bromophenyl)-2,5-dihydro-9-methy-2-oxo-
1H-pyrido[3,2-b]indole-3-carbonitrile
(IV–d): IR
(KBr, νmax, cm−1): 3246, 3125, 2983, 2826, 2217, 2.2i 2,9-Dihydro-9-methyl-4-(4-nitrophenyl)-2-oxo-1H-
1
1656, 1509, 1452 cm−1. H NMR (400 MHz, DMSO- pyrido[2,3-b]indole-3-carbonitrile (IV–i): IR (KBr,
d6): δ = 10.90 (1H, s, -NHCO-), 7.57 (1H, d, νmax, cm−1): 3255, 3175, 2995, 2810, 2217, 1637,
J = 6.2 Hz, ArH), 7.40–7.30 (3H, m, ArH), 7.15 (2H, 1552, 1516, 1481, 1345 cm−1. H-NMR (400 MHz,
1

98
Saman Damavandi and Reza Sandaroos
DMSO-d6): δ = 10.85 (1H, s, -NHCO-), 8.09 (2H, d, 96.7, 32.8. Anal. Calcd for C19H12FN3O: C, 71.92; H,
J = 7.2 Hz, ArH), 7.65–7.50 (3H, m, ArH), 7.40 (1H, 3.81; N, 13.24%. Found: C, 71.38; H, 3.73; N, 13.18%.
d, J = 7.5 Hz, ArH), 7.10 (2H, d, J = 7.7 Hz, ArH),
3.62 (s, -CH3, indole). 13C-NMR (250 MHz, DMSO-
2.2k 2,9-Dihydro-9-methyl-4-(naphthalen-1-yl)-2-
d6): δ = 167.7, 159.2, 154.1, 148.3, 144.4, 129.9,
oxo-1H-pyrido[2,3-b]indole-3-carbonitrile
(IV–k):
127.4, 125.9, 125.2, 123.3, 122.1, 121.7, 120.4, 119.5,
115.6, 114.1, 95.5, 34.6. Anal. Calcd for C19H12N4O3:
C, 66.28; H, 3.51; N, 16.27%. Found: C, 66.01; H,
3.42; N, 16.16%.
IR (KBr, νmax, cm−1): 3265, 3140, 2990, 2866,
1
2234, 1651, 1568, 14545 cm−1. H NMR (400 MHz,
DMSO-d6): δ = 10.80 (1H, s, -NHCO-), 7.65–7.50
(4H, m, ArH), 7.40–7.25 (5H, m, ArH), 7.05 (2H, d,
J = 7.4 Hz, ArH), 3.45 (s, -CH3, indole). 13C-NMR
(250 MHz, DMSO-d6): δ = 169.6, 159.5, 141.4, 133.1,
128.2, 128.0, 126.3, 125.1, 124.6, 124.4, 124.6, 124.2,
123.7, 122.1, 121.4, 119.6, 115.3, 111.9, 112.6, 99.8,
32.9. Anal. Calcd for C23H15N3O: C, 79.07; H, 4.33; N,
12.03%. Found: C, 78.91; H, 4.26; N, 11.95%.
2.2j 4-(4-Fluorophenyl)-2,9-dihydro-9-methyl-2-oxo-
1H-pyrido[2,3-b]indole-3-carbonitrile
(IV–j): IR
(KBr, νmax, cm−1): 3240, 3155, 2985, 2795, 2236, 1656,
1
1540, 1477 cm−1. H NMR (400 MHz, DMSO-d6):
δ = 11.12 (1H, s, -NHCO-), 7.60 (1H, d, J = 6.9 Hz,
ArH), 7.52 (1H, d, J = 7.1 Hz, ArH), 7.44 (2H, d,
J = 6.9 Hz, ArH), 7.20–6.95 (4H, m, ArH), 3.54
(s, -CH3, indole). 13C NMR (250 MHz, DMSO-d6):
δ = 168.67 164.6, 140.1, 135.6, 129.5, 127.2, 124.9,
122.7, 122.1, 121.8, 1205, 120.2, 119.4, 117.4, 114.2,
3. Results and discussion
In order to study the feasibility of the synthesis of
pyrido[2,3-b]indoles, a 15% mol of the immobilized
Table 1. Results of one-pot three component synthesis of pyrido[2,3-b]indoles.a
Entry
(triethoxymethyl)arene
Productb
Time (h)
Yield (%)c
OMe
OMe
1
2
73
CN
O
C(OMe)3
N
N
N
H
CN
O
2
3
65
C(OMe)3
N
H
CN
O
3
4
3
4
65
61
C(OMe)3
Br
N
N
H
Br
CN
O
C(OMe)3
N
N
H

MCR synthesis of functionalized pyridoindole
99
Table 1. (continued).
Entry
(triethoxymethyl)arene
Productb
Time (h)
4
Yield (%)c
56
5
Br
Br
CN
C(OMe)3
N
N
H
O
Cl
Cl
6
7
6
6
61
55
CN
O
C(OMe)3
N
N
N
H
Cl
Cl
CN
C(OMe)3
N
H
O
NO2
NO2
8
11
42
CN
O
C(OMe)3
F
N
N
H
F
9
7
2
53
61
CN
O
C(OMe)3
C(OMe)3
N
N
H
10
CN
O
N
N
H
aReaction conditions: 1.0 equiv. of 1-methyl-1H-indol-2-ol, 1.0 equiv. of substituted (triethoxymethyl)arene, 1.1 equiv. of
b
cyanoacetamide, 15 mol% of [pmim] HSO4 SiO2, 6 mL of DMF as solvent and at 100◦C. The products were identified by
NMR and IR spectrometer. cIsolated yields
catalyst of [pmim]HSO4 Sio2 along with a mixture of under reflux condition. Surprisingly, pyrano[2,3-b]indole
(triethoxymethyl)benzene, 1-methyl-1H-indol-2-ol and (B) was produced as the main product. Moreover, when
cyanoacetamide were chosen as the model reaction and the reaction mixture was refluxed in ethanol, A:B molar
examined for the synthesis of 2,9-dihydro-9-methyl- ratio was independent on reaction time and B was the
2-oxo-4-phenyl-1H-pyrido[2,3-b]indole-3-carbonitrile single product. Next, we carried out the model reaction
(A) (figure 1). The reaction was carried out in methanol in different solvent having higher boiling points to

100
Saman Damavandi and Reza Sandaroos
synthesis pyrido[2,3-b]indole and DMF was found to References
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A was enhanced as reaction time became longer. We
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the reaction might be controlled by either kinetic or
thermodynamic factors. It sounds that conversion of
intermediate (II) (figure 2) to A is more rapid than B.
We proposed a three-step mechanism for one-pot
synthesis of pyrido[3,2-b]indole derivatives (figure 2).
Cross coupling between 3-hydroxyindole and (tri-
ethoxymethyl)benzene results in α,β-unsaturated com-
pound (X), possessing ethoxy substituent on its β posi-
tion which can act as leaving group when needed.
Nucleophilic attack of cyanoacetamide on β-position
of intermediate (X) generates the key intermediate
(II) which can proceed the reaction through either
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ethoxymethyl)arene influenced the reaction times and
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