Montmorillonite K-1O clay catalyzed solvent-free synthesis of bis-indolylindane1,3-dione, 2-(1′,3′-dihydro-1 H-[2,3′] biindolyl-2-ylidene)-indan-1,3-dione and bisindolylindeno[ 1,2-b]quinoxaline under microwave irradiation

Article abstract of DOI:10.1016/j.tet.2010.04.084

An environmentally benign protocol has been described for the synthesis of novel 2-(1′,3′-dihydro-IH-12,3′ I biindolyl-2′-ylidene)- indan-1,3-diones/bis-indolylindane-1,3-diones from ninhydrin and 3-substituted/unsubstituted indoles. It uses montmorillonite K-10 as catalyst in a solvent-free condition under microwave irradiation. The method was also used for the synthesis of novel bisindolylindenoll,2-bIquinoxaline derivatives.

Full text of DOI:10.1016/j.tet.2010.04.084

Tetrahedron 66 (2010) 5196e5203
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Montmorillonite K-10 clay catalyzed solvent-free synthesis of bis-indolylindane-
1,3-dione, 2-(10,30-dihydro-1H-[2,30]biindolyl-20-ylidene)-indan-1,3-dione and
bisindolylindeno[1,2-b]quinoxaline under microwave irradiation
Subhendu Naskar a, Priyankar Paira a, Rupankar Paira a, Shyamal Mondal a, Arindam Maitya,
Abhijit Hazra a, Krishnendu B. Sahu a, Pritam Saha a, Sukdeb Banerjee a, Peter Luger b,
,
Manuela Webe b, Nirup B. Mondal a
*
a Department of Chemistry, Indian Institute of Chemical Biology, Council of Scientific & Industrial Research, 4 Raja S.C. Mullick Road, Jadavpur, Kolkata 700 032, West Bengal, India
b
€
Freie Universitat Berlin, Institut für Chemie und Biochemie/Kristallographie, Fabeckstr. 36a, D-14195 Berlin, Germany
a r t i c l e i n f o
a b s t r a c t
An environmentally benign protocol has been described for the synthesis of novel 2-(10,30-dihydro-1H-[2,30]
biindolyl-20-ylidene)-indan-1,3-diones/bis-indolylindane-1,3-diones from ninhydrin and 3-substituted/
unsubstituted indoles. It uses montmorillonite K-10 as catalyst in a solvent-free condition under microwave
irradiation. The method was also used for the synthesis of novel bisindolylindeno[1,2-b]quinoxaline
derivatives.
Article history:
Received 17 March 2010
Received in revised form 20 April 2010
Accepted 21 April 2010
Available online 20 May 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Montmorillonite K-10
Ninhydrin
Indole
Microwave
Solvent-free condition
1. Introduction
the availability of ample range of reactions that facilitate
subtle structural modifications in heterocyclic compounds.18e20
In recent years growing interest is being observed in the use of
solid acidic catalysts in acid dependent organic syntheses.1,2 This
interest is likely to increase with demanding environmental legis-
lation, public and corporate pressure, and drive toward clean
technology. In this perspective, montmorillonite K-10 Clay (Mont.
K-10), known to behave both as protic and Bronsted acid,3 is
a widely studied catalyst found useful in many organic reactions,
Since indole and its derivatives possess various biological activi-
ties,21 development of new methodologies for the synthesis of
indole derivatives, which will yield subsets of heterocycles having
potentiality to serve as templates for new biologically active mol-
ecules, is of great importance.
In this context, we wish to describe a convenient and simple
methodology for the synthesis of 2-(10,30-dihydro-1H-[2,30]biin-
dolyl-20-ylidene)-indan-1,3-diones/bis-indolylindane-1,3-diones
(by reacting ninhydrin with 3-substituted/unsubstituted indoles)
and also bisindolylindeno[1,2-b]quinoxalines (from the reaction of
ninhydrin, 1,2-phenylenediamine, and indole). The reactions were
carried out using montmorillonite K-10 as solid acidic catalyst in
solvent-free condition under microwave irradiation. The novelty of
the methodology lies in its eco-friendly operation, formation of
structurally unique molecules, short reaction time, and excellent
yield.
viz., synthesis of
g
-lactones,4 synthesis of fused heterocycles,5
FriedeleCrafts reaction,6 synthesis of biomarkers,7 oxidative
demethylation of methylphenols to benzoquinones,8 (2,5) intra-
molecular ene cyclization,9 Michael addition,10 Boc group removal
from aromatic amines,11 DielseAlder reaction12 and so on. It has
also been used in many microwave reactions both in liquid phase as
well as solvent-free conditions.13e16
Important pharmaceuticals often possess heterocyclic moieties
as their building blocks.17 The extensive use of heterocyclic com-
pounds in the pharmaceutical industry is perhaps attributable to
2. Results and discussion
Initially, 1 mmol ninhydrin (2) and 2 mmol indole (1a) were
added to the montmorillonite K-10 (0.5 g) in a mortar and mixed
* Corresponding author. Tel.: þ91 33 2473 3491; fax: þ91 33 2473 5197; e-mail
address: nirup@iicb.res.in (N.B. Mondal).
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.04.084

S. Naskar et al. / Tetrahedron 66 (2010) 5196e5203
5197
thoroughly. The resulting mixture was transferred into a beaker
and exposed to microwave irradiation at 130 ꢀC for 5 min to afford
2,2-bis-(1H-indol-3-yl)-indan-1,3-dione (3a) in excellent yield
(Scheme 1).
was unequivocally established as 2-(3,30-dimethyl-10,30-dihydro-
1H-[2,30]biindolyl-20-ylidene)-indan-1,3-dione.
The structure of 3g and 3h could thereafter be determined from
IR, NMR, and mass spectral correlations. In case of 3h, the reaction
Scheme 1. Montmorillonite K-10 catalyzed solvent-free synthesis of 3aee.
Thereafter, differently substituted indole derivatives (1beh)
were reacted with ninhydrin (2). Of these, 5-bromo (1b), 2-methyl
(1c), 5-methoxy (1d), and 1-methyl (1e) indoles reacted smoothly
to produce novel bis-indolylindane-1,3-diones (3bee) in high yield
(Table 1, entries 2e5). The characteristic quaternary carbon signal
had proceeded further as the eCOOH group of one indole moiety
was in close proximity to the nitrogen atom of the other indole unit
to form a spiro fused six-membered lactam.
The plausible mechanism for the formation of 2-(10,30-dihydro-
1H-[2,30]biindolyl-20-ylidene)-indan-1,3-dione derivatives (3feh)
is depicted in Scheme 2.
displayed at
d
59e60 in the 13C NMR spectrum of the products
(3aee) clearly indicates the attachment of two indole moieties at C-
2 of ninhydrin. Finally, single crystal X-ray crystallographic analysis
of 3d led to confirmation of the assumed structure (Fig. 1).
Ninhydrin is in equilibrium with indane-1,2,3-trione (2a). The
electrophilic substitution at C-2 of indole, possibly via 1,2-migra-
tion after an initial attack at C-3 of indole,22,23 produced carboca-
tion intermediate 2b, which was attacked by another indole moiety
to form intermediate 2c. Finally, intermediate 2c after dehydration
formed the 2-(10,30-dihydro-1H-[2,30]biindolyl-20-ylidene)-indan-
With 3-substituted indoles viz., 3-methylindole (1f), indole-3-
acetic acid (1g), and indole-3-propionic acid (1h), the coupling with
ninhydrin was smooth but yielded somewhat different products
(3feh) with high yield and selectivity (Table 1, entries 6e8). The
spectroscopic data (HRMS and NMR) of 3feh strongly indicated the
involvement of 2 mol of indole in the formation of the products.
Though the spectral characteristics of 3g were very close to those of
3f, the data appeared to be inadequate for unambiguous de-
termination of the structures. Eventually this was elucidated by
single crystal X-ray analysis of 3f. ORTEP representation of the
molecular structure of 3f, showing also the atomic numbering, is
given in Figure 2. Thus, the complete structure of the compound
Table 1
Montmorillonite K-10 catalyzed solvent-free synthesis of 3aeh and 5aei
Entry
Indole
Other substrate
Producta
Timeb (min)
Yieldc (%)
1
2
3
4
5
6
7
8
1a
1b
1c
1d
1e
1f
1g
1h
1a
1b
1d
1e
1a
1c
1d
1e
1e
2
2
2
2
2
2
2
2
3a
3b
3c
3d
3e
3f
3g
3h
5a
5b
5c
5d
5e
5f
5
5
5
6
5
5
6
6
5
5
5
6
6
5
6
5
6
95
94
94
96
92
96
92
90
94
96
92
94
95
94
92
94
92
9
2þ4a
2þ4a
2þ4a
2þ4a
2þ4b
2þ4b
2þ4b
2þ4b
2þ4c
10
11
12
13
14
15
16
17
5g
5h
5i
a
All the products were characterized by IR, NMR, and Mass spectroscopy.
Extension of the reaction does not improve the products yield.
Yield refers to pure products after crystallization.
b
c
Figure 1. ORTEP representation of 3d.

5198
S. Naskar et al. / Tetrahedron 66 (2010) 5196e5203
Institute of Chemical Biology, Kolkata). The NMR spectra were
taken on a BRUKER 300/600 DPX spectrometer operating at 300/
600 MHz for 1H and 75/150 MHz for 13C, respectively, with tetra-
methylsilane (TMS) as an internal standard and the chemical shifts
are reported in
d units. Microwave irradiation was performed by
using a mono-mode Discover microwave reactor (CEM Corp.,
Matthews, NC, USA). Ninhydrin, montmorillonite K-10, ortho-phe-
nylenediamine and indole derivatives were purchased from Aldrich
Chemical Ltd (USA). Thin layer chromatography was performed on
pre-coated silica gel 60 F254 aluminum sheets (E. Merck, Germany)
using different solvent system.
4.2. General reaction procedure for the synthesis of bis-
indolylindane-1,3-dione, 2-(10,30-dihydro-1H-[2,30]biindolyl-
20-ylidene)-indan-1,3-dione and bisindolylindeno[1,2-b]
quinoxaline derivatives
Montmorillonite K-10 (0.5 g) was placed in a mortar followed by
either 1 mmol ninhydrin (2) and 2 mmol indole derivative (1aeh)
[for the synthesis 3aeh] or 1 mmol ninhydrin (2), 1 mmol 1,2-
phenylenediamine derivative (4aec), and 2 mmol indole derivative
(1aee) [for the synthesis 5aei]. The reactants were mixed well for
5 min using a pestle. The homogenized mixture was placed in
a beaker, preheated in a microwave oven for 2 min at 130 ꢀC
(250 W) and the heating was continued for 5e6 min to complete
the reaction (monitored by TLC). The contents were cooled to room
temperature and mixed thoroughly with 10 mL of acetone. The
solid inorganic material was filtered off and the filtrate was evap-
orated to dryness. The residue was crystallized from chloroform/
hexane or chloroform/methanol mixture to afford pure 3aeh or
5aei. All the products were identified by spectroscopic analysis (IR,
NMR, and MS). The recovered catalyst was washed by acetone
(4ꢁ5 mL), activated by keeping in oven for 3 h at 120 ꢀC, and di-
rectly used in the next experiment without any loss of activity.
Figure 2. ORTEP representation of 3f.
1,3-diones (3feh). It was noted that in case of indoles having
electron withdrawing groups at 3-position, viz., 3-cyanoindole,
indole-3-carboxaldehyde, indole-3-carboxylic acid, failed to react
as anticipated.
However, when the reaction was performed following the same
protocol using 1 equiv of indoles (1i and 1j), exclusively 2-hydroxy-
2-(1H-indol-3-yl)-indan-1,3-dione (3i) and 2-hydroxy-2-(1H-
indol-2-yl)-indan-1,3-dione (3j) derivatives were formed (Scheme
3) with excellent yields (95%), which appears similar to the ear-
lier report.24
Next, we attempted to synthesize novel bisindolylindeno[1,2-b]
quinoxalines from the reaction of ninhydrin (2) with 1,2-phenyl-
enediamine (4aec) and indole (1aee) derivatives under the same
reaction condition (Scheme 4).
In this case, initially the condensation of ninhydrin (2) and 1,2-
phenylenediamine (4aec) took place to produce the intermediate
A, which reacted with 2 mol of indoles (1aee) via the intermediate
A to generate 5aei in high yield (Table 1, entries 9e17). All the
structures were established by mass, 1H and 13C NMR spectral
analysis. Single crystal X-ray crystallographic analysis of 5b was
also carried out for unambiguous determination of its structure
(Fig. 3).
4.2.1. 2,2-Bis-(1H-indol-3-yl)-indan-1,3-dione (3a). Yellow prisms
(95% yield), mp 208e210 ꢀC; Rf (ethyl acetate/petroleum ether 1:1)
0.28; IR (KBr, cmꢂ1
300 MHz)
7.20 (d, 2H, J¼7.8 Hz), 7.38 (d, 2H, J¼8.1 Hz), 8.09 (m, 4H), 11.17 (s,
2H, eNH); 13C NMR (DMSO-d6, 75 MHz)
) n
3399, 1702, 1246, 747; 1H NMR (DMSO-d6,
d
6.84 (t, 2H, J¼7.5 Hz), 6.96 (s, 2H), 7.05 (t, 2H, J¼7.2 Hz),
d
59.6 (C), 110.7 (2ꢁCH),
112.2 (2ꢁC), 119.2 (4ꢁCH), 120.5 (2ꢁCH), 121.7 (2ꢁCH), 124.2
(2ꢁCH), 125.9 (2ꢁCH), 137.1 (2ꢁC), 137.3 (2ꢁC), 140.1 (2ꢁC), 199.6
(2ꢁCO); MS: (ESI-MS, positive mode) m/z 377 [MþH]þ, 399
[MþNa]þ. HRMS (ESI) m/z calcd for C25H16N2O2Na: 399.1109;
found: 399.1096.
4.2.2. 2,2-Bis-(5-bromo-1H-indol-3-yl)-indan-1,3-dione (3b). Yel-
low prisms (94% yield), mp 104e106 ꢀC; Rf (ethyl acetate/petroleum
3. Conclusion
ether 1:1) 0.20; IR (KBr, cmꢂ1 3445, 1702, 1457, 1239; 1H NMR
) n
(pyridine-d5, 300 MHz)
7.41 (s, 2H), 7.65 (m, 1H), 7.74 (m, 1H), 8.09 (m, 1H), 8.29 (m, 1H),
12.70 (s, 2H, eNH); 13C NMR (pyridine-d5, 75 MHz)
60.0 (C), 111.4
(2ꢁC), 113.1 (2ꢁC), 114.1 (2ꢁCH), 124.3 (2ꢁCH), 125.0 (4ꢁCH), 127.9
(2ꢁCH), 128.6 (2ꢁC), 136.7 (2ꢁCH), 136.9 (2ꢁC), 140.6 (2ꢁC), 199.7
(2ꢁCO); MS: (ESI-MS, positive mode) m/z 555 (MþþNa, 30), 557
(Mþþ2þNa, 100), 559 (Mþþ4þNa, 35). HRMS (ESI) calcd for
C25H14Br2N2O2Na: 554.9320; found: 554.9313.
d 7.32 (s, 2H), 7.35 (m, 2H), 7.39 (m, 2H,),
In summary, we have developed an eco-friendly methodology
for the solvent-free synthesis of bis-indolylindane-1,3-dione, 2-
(10,30-dihydro-1H-[2,30]biindolyl-20-ylidene)-indan-1,3-dione, and
bisindolylindeno[1,2-b]quinoxaline using montmorillonite K-10 as
solid catalyst under microwave irradiation. Bio-evaluation of the
synthesized compounds is in progress in our laboratory.
d
4. Experimental section
4.1. General experimental
4.2.3. 2,2-Bis-(2-methyl-1H-indol-3-yl)-indan-1,3-dione (3c). Yel-
low needles (94% yield), mp 108e110 ꢀC; Rf (ethyl acetate/petro-
leum ether 1:1) 0.24; IR (KBr, cmꢂ1
)
n
3369, 1706, 1459, 1256, 738;
2.38 (s, 6H, 2ꢁMe), 6.98 (m, 2H),
7.13 (m, 4H,), 7.33 (s, 2H), 7.48 (d, 1H, J¼8.0 Hz), 7.75 (m, 2H), 8.21
(m, 1H), 12.14 (s, 2H, eNH); 13C NMR (pyridine-d5, 75 MHz)
13.9
(2ꢁCH3), 59.2 (C), 107.7 (2ꢁC), 111.3 (2ꢁCH), 119.5 (2ꢁCH), 120.7
Melting points were determined with a capillary melting point
apparatus and are uncorrected. IR spectra were recorded on
a JASCO FTIR (model 410) in KBr pellets. ESI-MS (positive) was
conducted using LC-ESI-Q-TOF micro Mass spectrometer (Indian
1H NMR (pyridine-d5, 300 MHz)
d
d

S. Naskar et al. / Tetrahedron 66 (2010) 5196e5203
5199
Scheme 2. Plausible mechanism for the formation of 3feh.
(2ꢁCH), 121.0 (2ꢁCH), 124.3 (CH), 128.7 (CH), 135.7 (2ꢁC), 136.3
(DMSO-d6, 300 MHz)
d
3.36 (s, 3H), 3.51 (s, 3H), 6.65 (s, 2H), 6.73 (d,
(2ꢁCH), 136.5 (4ꢁC), 142.6 (2ꢁC), 199.6 (2ꢁCO); MS: (ESI-MS,
positive mode) m/z 427 [MþNa]þ. HRMS (ESI) m/z calcd for
C27H20N2O2Na: 427.1422; found: 427.1416.
2H, J¼8.7 Hz), 6.94 (s, 2H), 7.28 (d, 2H, J¼8.7 Hz), 8.10 (m, 4H), 11.01
(s, 2H, eNH); 13C NMR (DMSO-d6, 75 MHz)
d
55.1 (2ꢁCH3), 59.2 (C),
102.7 (2ꢁCH), 109.7 (2ꢁC), 110.9 (2ꢁCH), 112.5 (2ꢁCH), 123.8
(2ꢁCH),126.0 (2ꢁC),126.3 (2ꢁCH),132.1 (2ꢁC),137.0 (2ꢁCH),139.8
(2ꢁC), 152.9 (2ꢁC), 199.4 (2ꢁCO); MS: (ESI-MS, positive mode) m/z
459 [MþNa]þ. HRMS (ESI) calcd for C27H20N2O4Na: 459.1321;
found: 459.1342.
4.2.4. 2,2-Bis-(5-methoxy-1H-indol-3-yl)-indan-1,3-dione (3d). Yel-
low prisms (96% yield), mp 114e116 ꢀC; Rf (ethyl acetate/petroleum
ether 1:1) 0.22; IR (KBr, cmꢂ1 3392, 1702, 1483, 1213; 1H NMR
) n

5200
S. Naskar et al. / Tetrahedron 66 (2010) 5196e5203
Scheme 3. Montmorillonite K-10 catalyzed condensation of ninhydrin with 1 equiv of indole derivative.
4.2.5. 2,2-Bis-(1-methyl-1H-indol-3-yl)-indan-1,3-dione(3e). Yellow
prisms (92% yield), mp 232e234 ꢀC; Rf (ethyl acetate/petroleum
(CH), 119.8 (CH), 120.4 (CH), 122.8 (CH), 123.3 (CH), 125.1 (C), 126.4
(2ꢁCH), 130.0 (2ꢁCH), 134.6 (CH), 134.7 (C), 134.9 (CH), 137.7 (C),
140.2 (C), 141.5 (C), 142.1(C), 142.7 (C), 173.1 (C), 189.5 (CO), 194.9
(CO); MS: (ESI-MS, positive mode) m/z 405 [MþH]þ, 427 [MþNa]þ.
HRMS (ESI) calcd for C27H20N2O2Na: 427.1422; found: 427.1414.
ether 1:2) 0.55; IR (KBr, cmꢂ1 1710, 1256, 740; 1H NMR (CDCl3,
) n
300 MHz)
(m, 2H), 7.23 (d, 2H, J¼8.1 Hz), 7.43 (d, 2H, J¼8.0 Hz), 7.82 (m, 2H),
8.04 (m, 2H); 13C NMR (CDCl3, 75 MHz)
d
3.62 (s, 6H, CH3), 6.87 (s, 2H), 6.97 (t, 2H, J¼7.4 Hz), 7.15
d
32.7 (2ꢁCH3), 59.5 (C),
109.3 (2ꢁCH), 110.1 (2ꢁC), 119.4 (2ꢁCH), 121.0 (2ꢁCH), 121.8
(2ꢁCH), 124.0 (2ꢁCH), 126.1 (2ꢁC), 129.6 (2ꢁCH), 135.9 (2ꢁCH),
137.5 (2ꢁC), 140.4 (2ꢁC), 199.6 (2ꢁCO); MS: (ESI-MS, positive
mode) m/z 405 [MþH]þ. HRMS (ESI) m/z calcd for C27H20N2O2Na:
427.1422; found: 427.1416.
4.2.7. [30-Carboxymethyl-20-(1,3-dioxo-indan-2-ylidene)-20,30-dihy-
dro-1H,10H-[2,30]biindolyl-3-yl]-acetic acid (3g). Yellow needles
(92% yield), mp >300 ꢀC; Rf (methanol/chloroform 1:4) 0.64; IR
(KBr, cmꢂ1 3377, 1713, 1552, 1221; 1H NMR (DMSO-d6, 300 MHz)
) n
d
2.83 (m, 1H), 3.09 (m, 1H), 3.17 (s, 1H, COOH), 3.51 (m, 1H), 3.92
(m, 1H), 4.11 (s, 1H, COOH), 7.11 (m, 1H,), 7.27 (m, 1H), 7.42 (m, 4H),
4.2.6. 2-(3,30-Dimethyl-10,30-dihydro-1H-[2,30]biindolyl-20-ylidene)-
7.52 (m, 1H), 7.63 (m, 4H), 8.10 (d, 1H, J¼7.8 Hz), 12.01 (s, 1H, eNH),
indan-1,3-dione (3f). Yellow prisms (96% yield), mp 284e286 ꢀC; Rf
12.35 (s, 1H, eNH); 13C NMR (DMSO-d6, 75 MHz)
d 28.4 (CH2), 47.6
(ethyl acetate/petroleum ether 1:2) 0.53; IR (KBr, cmꢂ1
)
n
3321,
(CH2), 51.6 (C), 102.1 (C), 106.3 (C), 113.2 (CH), 113.3 (CH), 120.1 (CH),
121.1 (CH), 121.6 (CH), 123.1 (CH), 123.6 (CH), 123.9 (CH), 124.9 (CH),
129.2 (2ꢁCH), 129.7 (C), 133.6 (CH), 134.2 (C), 134.7 (C), 139.4 (C),
139.6 (C), 140.1 (C), 141.5 (C), 165.5 (C), 169.2 (C), 170.6 (C), 188.0
(CO), 191.3 (CO). MS: (ESI-MS, positive mode) m/z 515 [MþNa]þ.
HRMS (ESI) calcd for C29H20N2O6Na: 515.1219; found: 515.1219.
1642, 1563, 747; 1H NMR (pyridine-d5, 600 MHz)
d 1.92 (s, 3H), 2.55
(s, 3H), 7.15 (m, 2H), 7.23 (m, 1H), 7.29 (d, 1H, J¼7.8), 7.33 (m, 1H),
7.40 (m, 1H), 7.46 (m, 2H), 7.57 (m, 3H), 7.83 (d, 1H, J¼7.2 Hz), 12.32
(s, 1H, eNH), 12.95 (s, 1H, eNH); 13C NMR (pyridine-d5, 75 MHz)
d
9.8 (CH3), 23.8 (CH3), 55.4 (C), 104.3 (C), 108.5 (C), 113.1 (CH), 114.0
Scheme 4. Montmorillonite K-10 catalyzed solvent-free synthesis of 5aei.

S. Naskar et al. / Tetrahedron 66 (2010) 5196e5203
5201
J¼8.9 Hz),11.0 (s, 2H, eNH); 13C NMR (DMSO-d6, 75 MHz)
d
53.1 (C),
111.7 (2ꢁCH), 115.6 (2ꢁC), 118.3 (2ꢁCH), 120.8 (CH), 121.0 (CH),
122.1 (2ꢁCH), 124.7 (2ꢁCH), 125.8 (2ꢁC), 126.4 (CH), 128.6 (CH),
128.8 (CH), 129.1 (CH), 129.2 (CH), 129.5 (CH), 131.9 (2ꢁCH), 135.3
(C), 137.0 (C), 140.7 (C), 141.6 (C), 152.7 (2ꢁC), 153.3 (C), 165.5 (C);
MS: (ESI-MS, positive mode) m/z 449 [MþH]þ, 471 [MþNa]þ. HRMS
(ESI) calcd for C31H20N4Na: 471.1586; found 471.1586.
4.2.12. 11,11-Bis-(5-bromo-1H-indol-3-yl)-11H-indeno[1,2-b]qui-
noxaline (5b). Yellow prisms (96% yield), mp 274e276 ꢀC; Rf (ethyl
acetate/petroleum ether 1:1) 0.24; IR (KBr, cmꢂ1
)
n
3421,1456,1104,
760; 1H NMR (pyridine-d5, 300 MHz)
d 7.17 (s, 2H), 7.29 (m, 2H),
7.48 (m, 6H), 7.89 (d, 1H, J¼7.5 Hz), 8.11 (d, 1H, J¼8.4 Hz), 8.16 (s,
2H), 8.27 (d, 1H, J¼8.4 Hz), 8.52 (d, 1H, J¼7.2 Hz), 12.47 (2H, eNH);
13C NMR (pyridine-d5, 75 MHz)
d
54.0 (C), 112.6 (2ꢁC), 114.0
(2ꢁCH), 116.8 (2ꢁC), 122.9 (2ꢁCH), 124.4 (CH), 124.7 (CH), 127.0
(CH), 127.1 (CH), 129.0 (2ꢁC), 129.1 (CH), 129.2 (CH), 129.5 (CH),
129.7 (CH), 130.0 (2ꢁCH), 132.2 (2ꢁCH), 136.6 (C), 137.2 (C), 141.9
(C), 142.9 (C), 152.9 (2ꢁC), 154.0 (C), 165.8 (C); MS: (ESI-MS, positive
mode) m/z 627 (MþþNa, 40), 629 (Mþþ2þNa, 82), 631 (Mþþ4þNa,
45). HRMS (ESI) calcd for C31H18Br2N4Na: 626.9796; found
626.9796.
Figure 3. ORTEP representation of 5b.
4.2.8. Compound 3h. Green needles (90% yield), mp 290e292 ꢀC; Rf
(methanol/chloroform 1:9) 0.77; IR (KBr, cmꢂ1
)
n
3253, 1701, 1562,
4.2.13. 11,11-Bis-(5-methoxy-1H-indol-3-yl)-11H-indeno[1,2-b]qui-
1216; 1H NMR (DMSO-d6, 300 MHz)
d
1.60 (m, 1H), 1.76 (m, 1H),
noxaline (5c). Brown needles (92% yield), mp 212e214 ꢀC; Rf (ethyl
1.92 (1H, m), 2.27 (2H, m), 2.89 (1H, m), 3.20 (m, 2H), 7.10 (m, 1H),
7.22 (m, 1H), 7.38 (m, 3H), 7.51 (m, 2H), 7.70 (m, 4H), 8.53 (d, 1H,
J¼8.1 Hz), 11.93 (s, 1H, eNH), 12.50 (s, 1H, eNH); 13C NMR (DMSO-
acetate/petroleum ether 1:1) 0.22; IR (KBr, cmꢂ1
)
n
3411, 1479, 1213,
762; 1H NMR (DMSO-d6, 300 MHz)
d 3.42 (s, 6H), 6.56 (s, 2H), 6.68
(m, 2H), 6.95 (m, 2H), 7.27 (d, 2H, J¼8.8 Hz), 7.72 (m, 5H), 7.95 (d,
d6, 75 MHz)
d 19.0 (CH2), 30.4 (CH2), 31.1 (CH2), 32.4 (CH2), 52.3
1H, J¼7.9 Hz), 8.19 (m, 1H), 8.32 (m, 1H), 10.87 (s, 2H); 13C NMR
(C), 101.5 (C), 114.5 (CH), 115.8 (C), 116.6 (CH), 119.0 (CH), 121.5
(CH), 122.0 (CH), 123.9 (CH), 124.1 (CH), 125.0 (CH), 129.5 (2ꢁCH),
129.8 (C), 132.2 (C), 134.3 (2ꢁCH), 134.6 (C), 135.6 (C), 139.4 (C),
139.9 (C), 141.3 (C), 168.4 (C), 169.6 (C), 173.4 (C), 187.9 (CO), 191.9
(CO); MS: (ESI-MS, positive mode) m/z 503 [MþH]þ, 525
[MþNa]þ. HRMS (ESI) calcd for C31H22N2O5Na: 525.1426; found:
525.1405.
(DMSO-d6, 75 MHz)
d
53.1 (C), 55.0 (2ꢁCH3), 103.1 (2ꢁCH), 110.6
(2ꢁCH), 112.2 (2ꢁCH), 115.0 (2ꢁC), 122.0 (2ꢁCH), 125.5 (CH), 126.2
(2ꢁC), 126.5 (CH), 128.7 (CH), 128.8 (CH), 129.2 (CH), 129.6 (CH),
132.0 (2ꢁCH), 132.2 (C), 135.4 (2ꢁC), 140.7 (C), 141.6 (C), 152.4
(2ꢁC),152.7 (C),153.3 (C), 164.6 (C); MS: (ESI-MS, positive mode) m/
z 509 [MþH]þ, 531 [MþNa]þ. HRMS (ESI) calcd for C33H24N4O2Na:
531.1797; found 531.1819.
4.2.9. 3-(2-Hydroxy-1,3-dioxo-indan-2-yl)-1H-indole-2-carboxylic
4.2.14. 11,11-Bis-(1-methyl-1H-indol-3-yl)-11H-indeno[1,2-b]qui-
acid (3i). Green needles (90% yield), mp 274e276 ꢀC; Rf (methanol/
noxaline (5d). Green prisms (94% yield), mp 182e184 ꢀC; Rf (ethyl
chloroform 1:4) 0.65; IR (KBr, cmꢂ1
)
n
3421, 1456, 1104, 760; 1H
acetate/petroleum ether 1:2) 0.66; IR (KBr, cmꢂ1
)
n
3052, 1469, 744;
NMR (DMSO-d6, 300 MHz)
J¼7.5 Hz), 6.99 (m, 1H), 7.37 (d, 1H, J¼8.1 Hz), 8.10 (m, 5H), 11.18 (s,
1H), 13.68 (br s, 1H); 13C NMR (pyridine-d5, 75 MHz)
81.1 (C), 114.7
d
6.38 (d, 1H, J¼7.8 Hz), 6.64 (t, 1H,
1H NMR (CDCl3, 300 MHz)
d 3.62 (s, 6H, CH3), 6.78 (s, 2H), 6.84 (t,
2H, J¼7.5 Hz), 7.10 (t, 2H, J¼7.2 Hz), 7.23 (m, 4H), 7.44 (t, 1H,
J¼7.2 Hz), 7.54 (m, 2H), 7.65 (m, 2H), 7.98 (d, 1H, J¼8.1 Hz), 8.13 (d,
1H, J¼8.4 Hz), 8.34 (d, 1H, J¼7.5 Hz); 13C NMR (CDCl3, 75 MHz)
d
(2ꢁCH), 119.5 (C), 122.0 (2ꢁCH), 126.5 (2ꢁCH), 126.6 (2ꢁCH), 129.3
(C), 131.5 (C), 136.9 (C), 139.4 (C), 143.4 (C), 166.7 (C), 200.6 (2ꢁCO);
MS: (ESI-MS, positive mode) m/z 322 [MþH]þ. HRMS (ESI) m/z
calcd for C18H11NO5Na: 344.0535; found: 344.0535.
d
31.5 (CH3), 32.7 (CH3), 53.3 (C), 109.1 (2ꢁCH), 115.7 (2ꢁC), 118.7
(2ꢁCH), 121.4 (2ꢁCH), 122.0 (2ꢁCH), 122.4 (2ꢁCH), 126.4 (C), 126.6
(CH), 128.4 (CH), 128.7 (CH), 128.8 (CH), 129.0 (C), 129.9 (2ꢁCH),
131.6 (C), 136.0 (C), 137.7 (2ꢁCH), 141.7 (C), 142.2 (C), 152.9 (2ꢁC),
153.7 (C), 165.4 (C); MS: (ESI-MS, positive mode) m/z 477 [MþH]þ,
499 [MþNa]þ. HRMS (ESI) calcd for C33H25N4 [MþH]þ: 477.2079;
found 477.2077.
4.2.10. 2-(1,3-Dimethyl-1H-indol-2-yl)-2-hydroxy-indan-1,3-dione
(3j). Yellow needles (92% yield), mp 185e188 ꢀC; Rf (ethyl acetate/
petroleum ether 1:2) 0.57; IR (KBr, cmꢂ1
)
n
3365, 3054, 1710, 1254;
1.84 (s, 3H), 4.13 (s, 3H), 7.00 (m,
1H,), 7.18 (t,1H, J¼7.5 Hz), 7.31 (s,1H), 7.41 (d, 2H, J¼8.1 Hz), 8.10 (m,
4H); 13C NMR (DMSO-d6, 75 MHz)
9.80 (CH3), 32.9 (CH3), 77.4 (C),
1H NMR (DMSO-d6, 300 MHz)
d
4.2.15. 11,11-Bis-(1H-indol-3-yl)-7,8-dimethyl-11H-indeno[1,2-b]qui-
d
noxaline (5e). Yellow prisms (95% yield), mp 218e220 ꢀC; Rf (ethyl
108.6 (C), 109.3 (CH), 118.5 (CH), 118.9 (CH), 122.6 (CH), 124.1
(2ꢁCH), 127.5 (C), 128.2 (C), 137.4 (2ꢁCH), 137.5 (2ꢁC), 140.1 (C),
197.4 (2ꢁCO); MS: (ESI-MS, positive mode) m/z 306 [MþH]þ, 328
[MþNa]þ. HRMS (ESI) calcd for C19H15NO3Na: 328.0950; found
328.0944.
acetate/petroleum ether 1:1) 0.30; IR (KBr, cmꢂ1
)
n
3414, 1335, 747;
1H NMR (DMSO-d6, 300 MHz)
d 2.34 (s, 3H, CH3), 2.39 (s, 3H, CH3),
6.77 (m, 2H), 6.93 (s, 2H), 7.02 (t, 2H, J¼7.2 Hz), 7.12 (d, 2H,
J¼7.8 Hz), 7.39 (d, 2H, J¼7.8 Hz), 7.53 (m, 2H), 7.68 (d, 1H, J¼9.6 Hz),
7.92 (s, 1H), 8.25 (d, 1H, J¼6.6 Hz), 8.33 (s, 1H), 11.0 (s, 2H, eNH); 13C
NMR (DMSO-d6, 75 MHz)
d 19.6 (CH3), 19.7 (CH3), 53.1 (C), 111.7
4.2.11. 11,11-Bis-(1H-indol-3-yl)-11H-indeno[1,2-b]quinoxaline
(2ꢁCH), 116.0 (2ꢁCH), 118.3 (2ꢁCH), 121.0 (CH), 121.8 (CH), 124.6
(2ꢁCH), 125.9 (2ꢁC), 126.3 (CH), 127.9 (CH), 128.4 (CH), 128.5 (CH),
131.4 (2ꢁCH), 135.7 (C), 137.0 (C), 139.2 (C), 139.5 (C), 139.6 (2ꢁC),
140.4 (2ꢁC), 152.3 (2ꢁC), 152.5 (C), 164.6 (C); MS: (ESI-MS, positive
mode) m/z 477 [MþH]þ, 499 [MþNa]þ. HRMS (ESI) calcd for
C33H24N4Na: 499.1899, found 499.1882.
(5a). Yellow prisms (94% yield), mp 276e278 ꢀC; Rf (ethyl acetate/
petroleum ether 1:1) 0.25; IR (KBr, cmꢂ1 3414,1336, 750; 1H NMR
) n
(DMSO-d6, 300 MHz)
J¼7.5 Hz), 7.08 (d, 2H, J¼7.8 Hz), 7.36 (d, 2H, J¼8.1 Hz), 7.64 (m, 4H),
7.76 (m, 1H), 7.91 (d, 1H, J¼8.1 Hz), 8.16 (d,1H, J¼8.1 Hz), 8.30 (d,1H,
d
6.74 (t, 2H, J¼7.5 Hz), 6.91 (s, 2H), 6.99 (t, 2H,

5202
S. Naskar et al. / Tetrahedron 66 (2010) 5196e5203
ꢀ
4.2.16. 7,8-Dimethyl-11,11-bis-(2-methyl-1H-indol-3-yl)-11H-indeno
were measured with Mo Ka (0.71073 A) radiation at 296 K using
[1,2-b]quinoxaline (5f). Brown needles (94% yield), mp 204e206 ꢀC;
Kappa Apex 2. The structure was solved by direct methods using the
SHELXL-97 program. Refinements of F2 were carried out against all
reflection using SHELXL-97. The non-hydrogen atoms were refined
with anisotropic thermal parameters. The hydrogen atoms were in-
cluded in geometric position and given thermal parameters equiva-
lent to 1.2 times those of the atom to which they were attached. The
final R-values were R1 0.0382, and wR2 0.1028.
Rf (ethyl acetate/petroleum ether 1:1) 0.72; IR (KBr, cmꢂ1
)
n
3403,
1455, 745; 1H NMR (DMSO-d6, 300 MHz)
d 1.68 (s, 3H, CH3), 1.97 (s,
3H, CH3), 2.40 (s, 3H, CH3), 2.50 (s, 3H, CH3), 6.46 (m, 2H), 6.60 (t, 1H,
J¼7.5 Hz), 6.85 (m, 2H), 7.20 (m, 2H), 7.48 (m, 1H), 7.58 (m, 1H), 7.63
(m, 2H), 7.91 (s, 1H), 8.17 (d, 1H, J¼7.5 Hz), 8.32 (s, 1H), 10.85 (s, 1H,
-NH), 10.92 (s, 1H, eNH); 13C NMR (DMSO-d6, 75 MHz)
d 13.7 (CH3),
13.8 (CH3), 19.6 (CH3), 19.8 (CH3), 53.2 (C), 110.5 (2ꢁCH), 110.9 (C),
111.8 (C), 117.9 (CH), 118.0 (CH), 119.5 (CH), 119.8 (CH), 121.6 (2ꢁCH),
127.0 (CH), 127.8 (C), 127.9 (CH), 128.5 (2ꢁCH), 131.4 (2ꢁCH), 132.1
(C), 134.3 (C), 134.9 (C), 135.1 (C), 139.3 (C), 139.6 (C), 139.7 (C), 140.3
(2ꢁC), 152.5 (2ꢁC), 153.0 (C), 165.4 (C); MS: (ESI-MS, positive mode)
m/z 505 [MþH]þ, 527 [MþNa]þ. HRMS (ESI) calcd for C35H28N4Na:
527.2212; found 527.2198.
4.3.2. Crystal data for 3f. X-ray data collection for 3f was carried
out on a Huber four circle diffractometer (Mo K
a
radiation,
ꢀ
l
¼0.7107 A, graphite monochromator) equipped with a Bruker
APEX CCD area detector. A total of 28,379 reflections (2
q
ꢃ54ꢀ) were
measured in three runs, each with 1150 frames in
4 increments of
0.3ꢀ. Integration and merging with SAINT and XPREP.25 Structure
solution (SHELXS)26 and refinement (SHELXL)26 ran routinely. C, N,
and O atoms were refined anisotropically, isotropic displacement
parameters were assigned to the hydrogens, which were located
from difference syntheses. The asymmetric unit consists of one
molecule of the title compound, C27H20N2O2.
4.2.17. 11,11-Bis-(5-methoxy-1H-indol-3-yl)-7,8-dimethyl-11H-in-
deno[1,2-b]quinoxaline (5g). Brown needles (92% yield), mp
216e218 ꢀC; Rf (ethyl acetate/petroleum ether 1:1) 0.25; IR (KBr,
cmꢂ1 3372, 1482, 1214, 796; 1H NMR (DMSO-d6, 300 MHz)
) n d 2.34
(s, 3H), 2.45 (s, 3H), 3.42 (s, 6H), 6.48 (s, 2H), 6.64 (d, 2H, J¼8.4 Hz),
C27H20N2O2, Mr¼404.45, yellow block shaped crystals were
grown from chloroform/methanol. Dimensions of the specimen
used for X-ray experiments 0.54ꢁ0.40ꢁ0.15 mm. Space group
6.87 (s, 2H), 7.22 (d, 2H, J¼8.7 Hz), 7.59 (m, 3H), 7.66 (s, 1H), 7.94 (s,
1H), 8.24 (m, 1H), 10.80 (s, 2H); 13C NMR (DMSO-d6, 75 MHz)
d 19.6
ꢀ
ꢀ
(CH3),19.7 (CH3), 52.1 (C), 55.0 (2ꢁCH3),103.2 (2ꢁCH),110.5 (2ꢁCH),
112.1 (2ꢁCH), 115.2 (2ꢁC), 121.7 (2ꢁCH), 125.4 (CH), 126.2 (2ꢁC),
126.4 (CH), 127.9 (CH), 128.3 (CH), 128.5 (CH), 131.4 (CH), 132.2 (C),
135.7 (2ꢁC), 139.3 (C), 139.5 (C), 140.4 (2ꢁC), 152.3 (4ꢁC), 164.6 (C);
MS: (ESI-MS, positive mode) m/z 537 [MþH]þ, 559 [MþNa]þ. HRMS
(ESI) calcd for C35H28N4O2Na: 559.2110; found 559.2128.
monoclinic C2/c. Lattice constants a¼27.645(6) A, b¼7.886(2) A,
3
ꢀ ꢀ
ꢀ
c¼19.100(4) A,
b
¼91.82(3) , cell volume V¼4162.(2) A , formula
units/cell Z¼8, X-ray density rx¼1.291 g cmꢂ3, 2qmax¼54ꢀ. Number
of independent reflections were 4521, observed (Fo>4s(Fo)) 3989,
linear absorption coeff.
m
¼8.2 cmꢂ1, Rint¼0.030, Rs¼0.018. After
convergence of refinements R1¼0.055, Rw¼0.146, GoF¼1.06.
4.2.18. 7,8-Dimethyl-11,11-bis-(1-methyl-1H-indol-3-yl)-11H-indeno
4.3.3. Crystal data for 5b. X-ray data collection for 5b was carried
[1,2-b]quinoxaline (5h). Green needles (94% yield), mp 170e172 ꢀC;
out on a Huber four circle diffractometer (Mo K
a
radiation,
Rf (ethyl acetate/petroleum ether 1:2) 0.72; IR (KBr, cmꢂ1
)
n
3049,
l¼0.7107 A, graphite monochromator) equipped with a Bruker
ꢀ
1469, 740; 1H NMR (CDCl3, 300 MHz)
d
2.38 (s, 3H, CH3), 2.46 (s, 3H,
APEX CCD area detector. A total of 34,576 reflections (2
q
ꢃ54ꢀ) were
CH3), 3.65 (s, 6H, CH3), 6.78 (s, 2H), 6.84 (m, 2H), 7.10 (m, 2H), 7.22
measured in three runs, each with 1150 frames in 4 increments of
(m, 4H), 7.42 (m,1H), 7.52 (m,1H), 7.69 (d,1H, J¼7.5 Hz), 7.75 (s,1H),
0.3ꢀ. Integration and merging with SAINT and XPREP.25 Structure
solution (SHELXS)26 and refinement (SHELXL)26 ran routinely. C, N,
O, and Br atoms were refined anisotropically, isotropic displace-
ment parameters were assigned to the hydrogens, which were lo-
cated from difference syntheses. The asymmetric unit consists of
one molecule of the title compound, C31H18N4Br2. Absorption cor-
rection was made with SADABS.
7.89 (s, 1H), 8.31 (d, 1H, J¼7.5 Hz); 13C NMR (CDCl3, 75 MHz)
d 20.0
(CH3), 20.2 (CH3), 32.7 (2ꢁCH3), 53.3 (C), 109.1 (2ꢁCH), 115.9 (2ꢁC),
118.6 (2ꢁCH), 121.3 (2ꢁCH), 122.0 (CH), 122.1 (CH), 126.4 (2ꢁCH),
126.6 (2ꢁC), 128.0 (CH), 128.2 (CH), 128.8 (CH), 129.1 (CH), 131.1
(2ꢁCH), 136.3 (C), 137.7 (C), 138.6 (C), 139.2 (C), 140.5 (C), 141.0 (C),
152.7 (2ꢁC), 152.8 (C), 164.5 (C); MS: (ESI-MS, positive mode) m/z
505 [MþH]þ, 527 [MþNa]þ. HRMS (ESI) calcd for C35H28N4Na:
527.2212; found 527.2224.
C31H18N4Br2, Mr¼606.3, yellow block shaped crystals were
grown from chloroform/hexane. Dimensions of the specimen used
for X-ray experiments 0.50ꢁ0.46ꢁ0.40 mm. Space group mono-
ꢀ
ꢀ
4.2.19. 7,8-Dichloro-11,11-bis-(1-methyl-1H-indol-3-yl)-11H-indeno
clinic C2/c. Lattice constants a¼21.996(5) A, b¼19.218(4) A,
3
ꢀ ꢀ
[1,2-b]quinoxaline (5i). Green prisms (92% yield), mp 186e188 ꢀC;
c¼14.002(3) A, ¼121.19(3) , cell volume V¼5063.(2) A , formula
b
ꢀ
Rf (ethylacetate/petroleumether1:2)0.68;IR(KBr, cmꢂ1
)
n
3047,1470,
units/cell Z¼8, X-ray density rx¼1.591 g cmꢂ3, 2qmax¼54ꢀ. Number
742; 1H NMR(CDCl3, 300 MHz)
d
3.66(s, 6H, CH3), 6.76 (s, 2H), 6.86 (m,
of independent reflections were 5491, observed (Fo>4s(Fo)) 4653,
2H), 7.13 (m, 2H), 7.23 (m, 4H), 7.53 (m, 2H), 7.65 (1H, d, J¼7.5 Hz), 8.08
linear absorption coeff.
m
¼32.3 cmꢂ1, Rint¼0.027, Rs¼0.019. After
(s, 1H), 8.23 (s, 1H), 8.30 (1H, d, J¼7.5 Hz); 13C NMR (CDCl3, 75 MHz)
convergence of refinements R1¼0.050, Rw¼0.121, GoF¼1.08.
d
32.8(2ꢁCH3), 53.4 (C),109.3 (2ꢁCH),115.3(2ꢁC),118.9 (2ꢁCH),121.6
(CH),121.9 (CH),122.7 (2ꢁCH),126.5 (2ꢁC),126.6 (2ꢁCH),128.6 (CH),
128.9 (CH), 129.4 (CH), 130.5 (CH), 132.2 (2ꢁCH), 132.5 (C), 133.2 (C),
135.4 (C),137.7 (C),140.4 (C),141.2 (C),153.0 (2ꢁC),154.8 (C),166.6 (C);
MS: (ESI-MS, positive mode) m/z 545 [MþH]þ, 547 [Mþ2þH]þ, 549
[Mþ4þH]þ, 567 [MþNa]þ, 569 [Mþ2þNa]þ, 571 [Mþ4þNa]þ. HRMS
(ESI) calcd for C33H22Cl2N4Na: 567.1119; found 567.1104.
Acknowledgements
We are thankful to the Director, IICB for laboratory facilities, and
the Council of Scientific and Industrial Research (CSIR) for fellow-
ships to S.N., P.P., P.S., R.P., S.M., A.M., A.H., and K.B.S. We are also
thankful to Professor B. Achari, Emeritus Scientist, CSIR, for his
valuable suggestions and Dr. B.C. Ranu of IACS, Kolkata for his
generous cooperation in utilizing the MW instrument.
4.3. X-ray experiments, structure determination, and
refinements
Supplementary data
4.3.1. Crystal data for 3d. Single crystal data for compound 3d:
C27H20N2O4 436.14, triclinic, space group P-1, unit cell parameters:
1H and 13C NMR spectra and crystallographic data of all com-
pounds. Crystallographic data in CIF format are available free of
charge via the internet. CCDC 752085/734164/734165 contains the
¼115.209(8)ꢀ,
ꢀ
ꢀ
ꢀ
a¼10.4755(11) A, b¼11.2253(11) A, c¼11.3541(19) A,
a
b
¼107.583(8)ꢀ,
g
¼102.220(6)ꢀ; dcalcd¼1.418 g cmꢂ3. Diffraction data

S. Naskar et al. / Tetrahedron 66 (2010) 5196e5203
5203
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supplementary crystallographic data for this paper. These data can
be obtainedfreeofchargeviawww.ccdc.cam.ac.uk/conts/retrieving.
html (or from the Cambridge Crystallographic Data Centre,12 Union
Road, Cambridge CB2 1EZ, UK; fax: þ44 1223 336033; or depos-
it@ccdc.cam.ac.uk). Supplementary data associated with this article
can be found in the online version, at doi:10.1016/j.tet.2010.04.084.
These data include MOL files and InChiKeys of the most important
compounds described in this article.
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