An efficient, simple, and scaleable domino reaction to diverse N -(1-oxo-1H-inden-2-yl)benzamides catalyzed by HPW@nano-SiO2 under microwave irradiation

Article abstract of DOI:10.1055/s-0030-1260938

A facile, efficient, and large-scale strategy for the synthesis of N-(1-oxo-1H-inden-2-yl)benzamide derivatives via domino reaction between aryl aldehydes, hippuric acid, and acetic anhydride catalyzed by HPW@nano-SiO ₂ was accomplished under m

Full text of DOI:10.1055/s-0030-1260938

LETTER
1677
An Efficient, Simple, and Scaleable Domino Reaction to Diverse
N-(1-Oxo-1H-inden-2-yl)benzamides Catalyzed by HPW@nano-SiO2 under
Microwave Irradiation
D
omino
R
eaction toD
a
iverse
N
-(1
h
H
-
ind
b
en-2-yl)benz
o
amides ubeh Rostami, Ahmad R. Khosropour,* Valiollah Mirkhani,* Iraj Mohammadpoor-Baltork,
Majid Moghadam, Shahram Tangestaninejad
Catalysis Division, Department of Chemistry, Faculty of Science, University of Isfahan, Isfahan 81746-7344, Iran
Fax +98(311)6689732; E-mail: Khosropour@chem.ui.ac.ir
Received 31 January 2011
amidoindenone by Awad et al.5 Recently, this transforma-
tion was modified by Kangani et al. through IFC reaction
of 2-benzylamino-3-phenylacrylic acid using cyanuric
chloride, pyridine, and AlCl3.6 However, one of the chal-
Abstract: A facile, efficient, and large-scale strategy for the syn-
thesis of N-(1-oxo-1H-inden-2-yl)benzamide derivatives via domi-
no reaction between aryl aldehydes, hippuric acid, and acetic
anhydride catalyzed by HPW@nano-SiO2 was accomplished under
microwave irradiation. The reaction conditions are very simple and lenging problems in such processes is the introduction of
offer easy isolation of the product. Moreover, the catalyst can be re-
appropriate substituents during cyclization because, in
used up to five times in 86% average yield after simple filtration.
some cases, the presence of functionality often hinders the
Keywords: tandem reaction, indenones, heterogeneous catalyst,
microwave irradiation, nanosilica, heteropoly acid
desired IFC reaction.
Recently, applications of heteropoly acids (HPA) in syn-
thesis have grown tremendously due to the potential for
green benefits.7 Among the HPA, H3PW12O40 (HPW) is
usually the catalyst of choice owing to its stronger Brøn-
sted acidity and higher thermal stability compared to other
HPA.8 Furthermore, modifications to the activity of HPW
have been performed by supporting on solids such as sili-
ca.9
The presence of indenone skeleta in a number of naturally
occurring compounds and synthetic materials, coupled
with their role in biological systems, underpins the devel-
opment of new methods for the preparation and function-
alization of these compounds. For instance, euplectin (I,
Figure 1), is a natural product with an indenone moiety,
reported to exhibit cytotoxicity against the growth of mu-
rine P-815 mastocytoma cells.1 Furthermore, indenone
derivatives have been used as starting materials in the syn-
thesis of kinamycin antibiotics, which show excellent ac-
tivity against gram-positive bacteria.2 On the other hand,
growing efforts have been directed toward the develop-
ment of new indenone-based structures as ligands in orga-
nometallic chemistry (II, Figure 1).3
Recent examination of functionalized silica nano particles
(nano-SiO2) and applications in organic synthesis have
shown unusual behaviors.10 To achieve an effective and
new solid-acid catalytic system for organic synthesis, we
decided to concentrate our attention on HPW supported
on nanosilica as a powerful solid Brønsted acid which
could be prepared easily by impregnating nano-SiO2 with
aqueous HPW solution.11 This procedure yielded a white
solid which could be stored at room temperature for
months in a desiccator without loss of activity.
HO
O
In continuation of our recent investigation on nano
catalysts12 and also fine chemicals,13 we herein report a
new, efficient, simple, and green domino reaction for the
synthesis of N-(1-oxo-1H-inden-2-yl)benzamide cata-
lyzed by HPW@nano-SiO2 (200 mg, 4 mol%) with aryl
aldehydes, hippuric acid, and acetic anhydride as sub-
strates under microwave irradiation (Scheme 1).14
O
Ph
O
O
OH
II
I
Figure 1 Structure of euplectin (I) and indenone-based ligand II
Recently, Murakami et al. reported that 2-alkynylbenzoyl
cyanides can react with carboxylic acids via a cyclic
allene intermediate to produce 2-acylamino-3-acylin-
denones after heating for 24 hours in p-xylene.4 The in-
tramolecular Friedel–Crafts (IFC) reaction is an attractive
method for the formation of these types of compounds.
This method was established for the synthesis of 2-benz-
R2
R1
CHO
R3
Ph
HN
O
R4
HPW@nano-SiO2
MW
O
R4
+
R3
R1
NH
Ph
O
R2
OH
O
Ac2O
Scheme 1 Synthesis of N-(1-oxo-1H-inden-2-yl)benzamides
SYNLETT 2011, No. 12, pp 1677–1682
x
x
.x
x
.2
0
1
1
Advanced online publication: 05.07.2011
DOI: 10.1055/s-0030-1260938; Art ID: D03211ST
© Georg Thieme Verlag Stuttgart · New York

1678
M. Rostami et al.
LETTER
At the outset, 4-chlorobenzaldehyde (1 mmol), hippuric conditions, showing the highest catalytic activity for
acid (1 mmol), and acetic anhydride (2 mmol) in the pres- HPW@nano-SiO2 (Table 1, entries 1, 8–17). No reaction
ence of HPW@nano-SiO2 (200 mg, 4 mol%) was selected occurred in the absence of a catalyst (Table 1, entry 5) and
as a model system to investigate solvent and temperature no useful conversion was obtained in the presence of
effects under conventional heating (Table 1, entries 1–5). nano-SiO2, SiO2, or Al2O3 without HPW (Table 1, entries
6–8). In contrast, using HPW on solid supports such as
Al2O3 or SiO2 instead of nano-SiO2 gave the product, but
in lower yields (Table 1, entries 9 and 10). Homogeneous
Brønsted acids such as H2SO4, ionic liquids such as 1-
butyl-3-methyl-imidazolium hexafluorophosphate, and
Lewis acids such as BiCl3, Bi(NO3)3·5H2O, AlCl3,
Zn(OTf)2, and even polyoxometalates such as
K5CoW12O40 gave 2b in very poor yields (0–37%) with
large amounts of side products (Table 1, entries 11–17).
Table 1 The Effect of Catalysts on the Yield of 2b Using Micro-
wave Energya
Cl
CHO
Figure 2 Solvent and temperature effects. Reagents and conditions:
4-chlorobenzaldehyde (1 mmol), hippuric acid (1 mmol), Ac2O (2
mmol), HPW@nano-SiO2 (200 mg, 4 mol%), solvent (2 mL), 1.5 h.
The reaction was conducted under reflux conditions (in solvent).
Ph
O
cat.
O
+
+
Ac2O
HN
MW
O
OH
NH
Cl
As shown in Figure 2, the desired product was obtained in
dichloromethane in very low yield (<10%), while the con-
version of 2b was 28% in 1,2-dichloroethane. The corre-
sponding product in polar solvents such as acetonitrile or
N,N-dimethylformamide was produced in unsatisfactory
conversion (35% and 46%, respectively). A large im-
provement in the conversion (62%) was achieved for the
reaction under solvent-free conditions at 100 °C. Higher
reaction temperature (120 °C) makes an obvious differ-
ence in the yield of products (73%) but using lower reac-
tion temperature (80 °C), sharply decreased the
conversion to about 50% even with prolonged reaction
times. Accordingly, performing the reaction under sol-
vent-free microwave irradiation conditions at 120 °C was
deemed to be optimal for the domino reaction.
1b
O
Ph
2b
Entry Catalyst
Temp
Yield
(%)b
(°C)
120
80
1
2
HPW@nano-SiO2 (200 mg, 4 mol%)
HPW@nano-SiO2 (200 mg, 4 mol%)
HPW@nano-SiO2 (200 mg, 4 mol%)
HPW@nano-SiO2 (150 mg, 4 mol%)
–
93
74
84
75
n.r.
35
30
20
87
83
37
10
20
18
34
5
3
100
120
120
120
120
120
120
120
120
120
120
120
120
120
120
4
5
6
nano-SiO2 (200 mg)
7
SiO2 (200 mg)
In order to show the effect of microwave irradiation, we
performed the reaction using conventional heating and
compared it with the data obtained in the microwave-
assisted procedure. With standard heating a 73% yield
was obtained after 1.5 hours; however, prolonged reaction
time did not give any improvement in the yield. We then
investigated the reaction under microwave irradiation
with a temperature-controlled program. During irradia-
tion, the temperature was monitored by an IR sensor
which controlled microwave power levels. At 80 °C only
74% of conversion was registered after 35 minutes
(Table 1, entry 2). However, surprisingly, by increasing
the temperature up to 120 °C, quantitative conversion was
registered after 35 minutes, and 93% of the domino adduct
2b was isolated (Table 1, entry 1). Notably, lower yields
were obtained when the same reaction was carried out
with a lesser amount of catalyst (Table 1, entry 4).
8
alumina (200 mg)
9
HPW@SiO2 (200 mg, 4 mol%)
HPW@Al2O3 (200 mg, 4 mol%)
H2SO4 (concd) (4 mol%)
[bmim]PF6 (4 mol%)
10
11
12
13
14
15
16
17
BiCl3 (4 mol%)
Bi(NO3)3·5H2O (4 mol%)
AlCl3 (4 mol%)
Zn(OTf)2 (4 mol%)
K5CoW12O40 (4mol%)
–
a Reaction conditions: 4-chlorobenzaldehyde (1 mmol), hippuric acid
(1 mmol), Ac2O (2 mmol), and catalyst after 35 min under microwave
irradiation (650 W).
A comparison of catalytic activity between homogeneous
Brønsted acids, Lewis acids, or other solid acids was ex-
amined in the model reaction under the optimal reaction
b Isolated yield.
Synlett 2011, No. 12, 1677–1682 © Thieme Stuttgart · New York

LETTER
Domino Reaction to Diverse N-(1-Oxo-1H-inden-2-yl)benzamides
1679
The high catalytic performance of HPW@nano-SiO2 was electron-withdrawing groups also afforded indenone de-
also confirmed for the scale-up reaction of 1b (50 mmol) rivatives in high to excellent isolated yields. With aryl
with hippuric acid (50 mmol), and acetic anhydride (75 dicarbaldehydes such as terephthalaldehyde the corre-
mmol) in the presence of 400 mg of HPW@nano-SiO2 in sponding product was also obtained in high yield
50 minutes. After the reaction was completed, the used (Table 2, 2j). Moreover, this reaction works well with het-
catalyst was easily separated by filtration from the reac- eroaromatic carbaldehydes such as 5-methylthiophene-2-
tion mixture, and 2b was obtained in 91% yield after re- carbaldehyde (Table 2, entry 11) or indole-3-carbalde-
crystallization from hot ethanol.
hyde (Table 2, entry 12). indicating that the domino reac-
tion is general for this transformation.
After successful generation of 2b, we considered intro-
duction of more diversity into the N-(1-oxo-1H-inden-2- The recovered HPW@nano-SiO2 could also be reused
yl)benzamide scaffold via this domino reaction. With the without any significant lessening of its catalytic perfor-
optimized reaction conditions in hand, we examined sev- mance. The catalyst was separated by filtration, washed
eral aryl aldehydes and found that HPW@nano-SiO2 is an with ethanol, and activated at 80 °C under reduced pres-
efficient catalyst for the synthesis of a large spectrum of sure. In this way, HPW@nano-SiO2 retained its activity
N-(1-oxo-1H-inden-2-yl)benzamides through this proto- after five consecutive runs.
col (Table 2).
A plausible rationalization for the formation of N-(1-oxo-
It was generally observed that high to excellent yields of 1H-inden-2-yl)benzamides is shown in Scheme 2. Initial-
the products were obtained in all cases, irrespective of the ly, a HPW@nano-SiO2-catalyzed azlactone A as an inter-
kind of substituent present in the aromatic ring of the aryl mediate would be obtained. Subsequently, A undergoes
aldehyde, and the indene derivatives 2a–m were obtained IFC reaction and subsequent rearrangement to an amide,
exclusively (Table 2). It was found that aryl aldehydes which is converted into the corresponding product.
carrying electron-donating groups could be smoothly con-
verted into the desired products (87–94% yields, Table 2,
entries 7–9). The coupling of aryl aldehydes containing
Table 2 Synthesis of N-(1-Oxo-1H-inden-2-yl)benzamide Catalyzed by HPW@nano-SiO2 via Domino Reaction of Aryl Aldehydes, Hippu-
ric Acid, and Acetic Anhydride under Solvent-free Microwave Conditions
R1
CHO
O
Ph
R2
R3
R4
R3
HPW@nano-SiO2
MW
O
+
+
Ac2O
HN
NH
O
R1
Ph
O
OH
R2
R4
1
2
Entry
1
Substrate
Product
Time (min)
40
Yield (%)a
85
O
2a
CHO
NHCOPh
O
Cl
Cl
2
3
2b
2c
35
38
93
82
Cl
Cl
CHO
NHCOPh
NHCOPh
O
Cl
CHO
CHO
Cl
O
Br
4
5
2d
2e
28
35
95
85
Br
Br
NHCOPh
Br
O
CHO
NHCOPh
Synlett 2011, No. 12, 1677–1682 © Thieme Stuttgart · New York

1680
M. Rostami et al.
LETTER
Table 2 Synthesis of N-(1-Oxo-1H-inden-2-yl)benzamide Catalyzed by HPW@nano-SiO2 via Domino Reaction of Aryl Aldehydes, Hippu-
ric Acid, and Acetic Anhydride under Solvent-free Microwave Conditions (continued)
R1
CHO
O
Ph
R2
R3
R4
R3
HPW@nano-SiO2
MW
O
+
+
Ac2O
HN
NH
O
R1
Ph
O
OH
R2
R4
1
2
Entry
6
Substrate
Product
Time (min)
45
Yield (%)a
90
O
O2N
2f
O2N
CHO
NHCOPh
NHCOPh
NHCOPh
O
MeO
7
8
2g
2h
35
32
94
90
MeO
CHO
CHO
O
Me2N
Me2N
MeO
HO
OMe
HO
O
9
2i
35
87
CHO
NHCOPh
O
MeO
MeO
10
11
12
2j
2k
2l
45
35
43
83
87
85
OHC
CHO
PhOCHN
O
NHCOPh
O
Me
S
CHO
Me
NHCOPh
NHCOPh
S
O
CHO
H
N
N
H
O
CHO
13
NHCOPh
2m
29
90
a Isolated Yield
To confirm this mechanism we also isolated the interme- a wide spectrum of these indenone derivatives, scalable
diate A and, after irradiation in the microwave oven in the synthesis of the indenone derivatives, and the recycling of
presence of the catalyst, the corresponding product was the catalyst. We believe that the protocol described herein
afforded quantitatively.
represents a new and efficient way for the large-scale syn-
thesis of N-(1-oxo-1H-inden-2-yl)benzamides. Further re-
search in this field is in progress.
In conclusion, we have demonstrated a practical and con-
cise synthesis of structurally diverse N-(1-oxo-1H-inden-
2-yl)benzamides via the domino microwave-assisted re-
action. In this flexible and straightforward synthetic route,
HPW@nano-SiO2 was found to be a powerful catalyst
which was capable of reuse without loss of efficiency for
at least five runs. Notable features of our approach are the
use of simple precursors, applicability of this procedure to
Acknowledgment
The authors are grateful to the Center of Excellence of Chemistry of
University of Isfahan (CECUI) and also the Research Council of the
University of Isfahan for financial support of this work.
Synlett 2011, No. 12, 1677–1682 © Thieme Stuttgart · New York

LETTER
Domino Reaction to Diverse N-(1-Oxo-1H-inden-2-yl)benzamides
1681
hippuric acid (0.179 g, 1 mmol), Ac2O (0.204 g, 2 mmol),
and PW@nano-SiO2 (200 mg, 4 mol%) was submitted to
microwave irradiation at 120 °C (650 W) using a Micro-
SYNTH labstation reactor for 28–45 min. During this time,
the power was modulated automatically to hold the reaction
mixture at 120 °C. After the reaction was complete
(monitoring by TLC), the reaction mixture was cooled to r.t.,
filtered, washed with a hot mixture of EtOAc–EtOH (10:1, 2
× 10 mL) and concentrated in vacuo to give crude 2, which
was purified as appropriate by recrystallization with EtOH
(95%).
CHO
O
+
Ac2O
OH
OH
O
NH
Ph
O
H
O
N
Ph
H2O
N-(6-Chloro-1-oxo-1H-inden-2-yl)benzamide (2b)
FTIR (KBr, solid): 3235, 1698, 1644, 1470, 1423, 1311,
1277, 1088, 910, 699, 524 cm–1. 1H NMR (500 MHz,
DMSO): d = 9.54 (s, 1 H), 7.88–7.89 (d, J = 7.55 Hz, 2 H),
7.54–7.56 (t, J = 7.80 Hz, 1 H), 7.47–7.50 (t, J = 7.80 Hz, 2
H), 7.34–7.35 (d, J = 8.10 Hz, 1 H), 7.28–7.29 (d, J = 8.10
Hz, 2 H), 7.16 (s, 1 H). 13C NMR (125 MHz, DMSO):
d = 167.6, 163.5, 149.5, 137.1, 135.8, 134.7, 131.4, 130.9,
130.4, 128.4, 127.6, 127.3, 124.2, 122.9. MS (EI): m/z =
149.94 [M + 2], 104.87, 76.86, 50.9.
O
O
NHCOPh
O
N
A
IFC reaction
Ph
N-(6-Bromo-1-oxo-1H-inden-2-yl)benzamide (2d)
FTIR (KBr, solid): 3235.97, 1696, 1644.98, 1477, 1438,
1314, 1279, 1072, 913, 693, 528 cm–1. 1H NMR (500 MHz,
DMSO): d = 9.92 (s, 1 H), 7.94–7.95 (d, J = 7.35 Hz, 2 H),
= HPW@nano-SiO2
7.58–7.60 (m, 4 H), 7.49–7.55 (m, 2 H), 7.37 (s, 1 H). 13
NMR (125 MHz, DMSO): d = 166.15, 165.83, 149.35,
133.48, 133.17, 131.76, 131.46, 130.98, 130.94, 128.41,
128.22, 127.62, 122.30. MS (EI): m/z = 195.96 [M + 2],
C
Scheme 2 Plausible mechanism
References and Notes
104.98, 76.97, 51. Anal. Calcd for C16H10BrNO2: C, 58.56;
H, 3.07; N, 4.27. Found: C, 58.02; H, 3.56; N, 4.07.
N-(6-Nitro-1-oxo-1H-inden-2-yl)benzamide (2f)
FTIR (KBr, solid): 3216, 1699, 1651, 1518, 1478, 1432,
1343, 1272, 1109, 691, 326 cm–1. 1H NMR (400 MHz,
DMSO): d = 9.66 (s, 1 H), 7.88–7.90 (d, J = 7.61 Hz, 1 H),
7.56–7.57 (d, J = 6.40 Hz, 1 H), 7.49–7.52 (t, J = 7.20 Hz, 2
H), 7.36–7.38 (d, J = 8.00 Hz, 2 H), 7.29–7.31 (d, J = 7.22
Hz, 2 H), 7.10 (s, 1 H). 13C NMR (125 MHz, DMSO):
d = 166.14, 165.83, 149.35, 133.48, 133.18, 131.76, 131.48,
131.47, 130.98, 130.94, 128.41, 128.22, 127.62, 122.29. MS
(EI): m/z = 294.01, 104.98, 77.03, 55.66.
(1) Russell, M. A.; Chai, C. L. L.; Wardlaw, J. H.; Elix, J. A.
J. Nat. Prod. 2000, 63, 129.
(2) Kitani, Y.; Morita, A.; Kumamoto, T.; Ishikawa, T. Helv.
Chim. Acta 2002, 85, 1186.
(3) Kim, D. H.; Son, S. U.; Chung, Y. K. Org. Lett. 2003, 5,
3151.
(4) Shimizu, H.; Murakami, M. Synlett 2008, 1817.
(5) Awad, W. I.; Hafez, M. S. J. Org. Chem. 1961, 26, 2055.
(6) Kangani, C. O.; Day, B. W. Org. Lett. 2008, 10, 2645.
(7) (a) Kozhevnikov, I. V. Catalysis by Polyoxometalates, In
Catalysts for Fine Chemical Synthesis, Vol. 2; J. Wiley and
Sons: Chichester, 2002, 216. (b) Costa, V. V.;
da Silva Rocha, K. A.; Kozhevnikov, I. V.; Gusevskaya,
E. V. Appl. Catal., A 2010, 383, 217.
(8) Kozhevnikov, I. V. J. Mol. Catal. A: Chem. 2009, 305, 104.
(9) Alsalme, A. M.; Wiper, P. V.; Khimyak, Y. Z.;
Kozhevnikova, E. F.; Kozhevnikov, I. V. J. Catal. 2010,
276, 181.
(10) (a) Zou, H.; Wu, S.; Shen, J. Chem. Rev. 2008, 108, 3893.
(b) Roelofs, K. S.; Hirth, T.; Schiestel, T. J. Membr. Sci.
2010, 346, 215.
(11) The supported H3PW12O40 on nano-SiO2 was prepared by
the method of incipient wetness. In a typical process,
H3PW12O40 (400 mg) was dissolved in deionized water and
impregnated dropwise onto nano-SiO2 (1600 mg) with
constant agitation. The resulting paste was dried for 8 h at
120 °C and calcined for 4 h at 250 °C.
N-(6-Methoxy-1-oxo-1H-inden-2-yl)benzamide (2g)
FTIR (KBr, solid): 3386, 2929, 2839, 1690, 1653, 1439,
1079, 980, 896, 811, 516 cm–1. 1H NMR (500 MHz, DMSO):
d = 9.42 (s, 1 H), 7.48–7.57 (m, 5 H), 7.36–7.38 (d, J = 8.20
Hz, 2 H), 6.83–6.85 (d, J = 8.41 Hz, 1 H), 6.78–6.80 (d,
J = 8.00 Hz, 1 H), 3.73 (s, 3 H). 13C NMR (125 MHz,
DMSO): d = 166.54, 165.82, 158.85, 145.98, 133.47,
133.17, 131.76, 131.5, 131.45, 130.98, 130.94, 128.4,
128.22, 122.3, 55.98. MS (EI): m/z = 264.08 [M – 15],
105.06, 77.03, 55.12. Anal. Calcd for C17H13NO3: C, 73.11;
H, 4.69; N, 5.02. Found: C, 72.99; H, 5.00; N, 4.89.
N,N¢-(1,5-Dioxo-1,5-dihydros-indacene-2,6-
diyl)dibenzamide (2j)
FTIR (KBr, solid): 3374, 1703, 1610, 1569, 1437, 1266,
1026, 675, 589 cm–1.1H NMR (400 MHz, DMSO): d = 9.7
(s, 2 H), 7.94–7.95 (d, J = 7.10 Hz, 2 H), 7.84–7.85 (d,
J = 7.10 Hz, 2 H), 7.66 (br s, 2 H), 7.49–7.51 (t, J = 8.40 Hz,
4 H), 7.41–7.44 (t, J = 8.35 Hz, 4 H). 13C NMR (300 MHz,
DMSO): d = 167, 165.93, 152.17, 142.38, 133.22, 131.76,
131.48, 128.41, 127.63, 126.40, 121.48. MS (EI): m/z =
420.19, 105.01, 77.02, 55.04.
N-(2-Methyl-4-oxo-4H-cyclopenta[b]thiophen-5-
yl)benzamide (2k)
FTIR (KBr, solid): 3395, 1695, 1610, 1539, 1448, 1028, 670,
469 cm–1. 1H NMR (400 MHz, DMSO): d = 9.3 (s, 1 H), 7.99
(s, 2 H), 7.33–7.68 (m, 3 H), 7.01 (s, 1 H), 6.71 (s, 1 H), 2.35
(12) Khorsandi, Z.; Khosropour, A. R.; Mirkhani, V.;
Mohammadpoor-Baltork, I.; Moghadam, M.;
Tangestaninejad, S. Tetrahedron Lett. 2011, 52, 1213.
(13) Rostami, M.; Khosropour, A. R.; Mirkhani, V.; Moghadam,
M.; Tangestaninejad, S.; Mohammadpoor-Baltork, I. Appl.
Catal., A 2011, 397, 27.
(14) General Procedure for Synthesis of N-(1-oxo-1H-inden-
2-yl)benzamides
In a high-pressure Teflon reactor equipped with a magnetic
stir bar and an IR sensor (for controlling of reaction
temperature), a mixture of aryl aldehyde 1 (1 mmol),
Synlett 2011, No. 12, 1677–1682 © Thieme Stuttgart · New York

1682
M. Rostami et al.
LETTER
(s, 3 H). 13C NMR (125 MHz, DMSO): d = 166.09, 163.80,
149.89, 144.12, 141.57, 135.82, 130.91, 130.4, 128.46,
127.65, 127.32, 121.99, 17.21. MS (EI): m/z = 148.96 (M-
120), 104.94, 76.95, 57.04. Anal. Calcd for C15H11NO2S: C,
66.89; H, 4.12; N, 5.20. Found: C, 66.45; H, 4.40; N, 5.09.
N-(3,4-Dihydro-3-oxocyclopenta[b]indol-2-yl)benz-
amide (2l)
(s, 1 H), 9.98 (s, 1 H), 7.83–7.85 (d, J = 5.58 Hz, 2 H), 7.65
(br s, 3 H), 7.48–7.49 (d, J = 4.40 Hz, 2 H), 7.40–7.43 (t,
J = 4.70 Hz, 2 H), 7.30 (s, 1 H). 13C NMR (125 MHz,
DMSO): d = 166.15, 163.73, 149.35, 137.98, 133.48,
133.18, 131.76, 131.47, 131.46, 130.97, 130.84, 128.41,
128.22, 127.63, 122.29, 117.99. MS (EI): m/z = 167.07 [M –
120], 149, 71, 57. Anal. Calcd for C18H12N2O2: C, 74.99; H,
4.20; N, 9.72. Found: C, 74.85; H, 4.68; N, 9.01.
FTIR (KBr, solid): 3364, 3343, 1698, 1644, 1539, 1079, 962,
889, 792, 437 cm–1. 1H NMR (300 MHz, DMSO): d = 10.31
Synlett 2011, No. 12, 1677–1682 © Thieme Stuttgart · New York

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