Furan ring opening-indole ring closure: Recyclization of 2-(2-aminophenyl)furans into 2-(2-oxoalkyl)indoles

Article abstract of DOI:10.1016/j.tet.2011.10.114

The acid-catalyzed rearrangement of 5-alkyl-2-[2-(sulfonylamino)phenyl] furans into 2-(2-oxoalkyl)indoles is described. When the N-sulfonyl group in the starting compounds was displaced by an N-acyl group, the corresponding indoles were not formed under t

Full text of DOI:10.1016/j.tet.2011.10.114

Tetrahedron 68 (2012) 619e627
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Furan ring openingeindole ring closure: recyclization of 2-(2-aminophenyl)furans
into 2-(2-oxoalkyl)indoles
,
Arkady S. Pilipenko a, Vladimir V. Mel’chin a, Igor V. Trushkov b c, Dmitry A. Cheshkov d,
,e,
Alexander V. Butin a
*
a Research Institute of Heterocyclic Compounds Chemistry, Kuban State Technological University, Moskovskaya 2, Krasnodar 350072, Russian Federation
b M.V. Lomonosov Moscow State University, Department of Chemistry, Leninskie Gory 1/3, Moscow 119991, Russian Federation
c Federal Research Center of Pediatric Hematology, Oncology and Immunology, Laboratory of Chemical Synthesis, Leninskii av. 117/2, Moscow 117997. Russian Federation
d State Scientific Research Institute of Chemistry and Technology of Organoelement Compounds, Entuziastov shosse 38, Moscow 111123, Russian Federation
e Perm State University, Bukireva 15, Perm 614990, Russian Federation
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 25 July 2011
Received in revised form 10 October 2011
Accepted 31 October 2011
Available online 6 November 2011
The acid-catalyzed rearrangement of 5-alkyl-2-[2-(sulfonylamino)phenyl]furans into 2-(2-oxoalkyl)in-
doles is described. When the N-sulfonyl group in the starting compounds was displaced by an N-acyl
group, the corresponding indoles were not formed under the same reaction conditions due to the in situ
indole deacylation and decomposition. The presence of an alkyl group at the C5 position of the furan ring
is also crucial for the efficiency of the process. The discussed rearrangement provides a simple and ef-
ficient approach to 2-(2-oxoalkyl)indoles.
Keywords:
Furans
Ó 2011 Elsevier Ltd. All rights reserved.
Recyclization
Indoles
Heterocycles
Acid catalysis
Synthetic methods
1. Introduction
In recent years we have investigated acid-catalyzed furan
recyclizations as a general method for the synthesis of a broad
For many years indoles have been among the most studied
compounds due to their significant role in biology and medicine as
well as high reactivity in various chemical reactions.1 There are
thousands of natural and synthetic physiologically active com-
pounds containing the indole scaffold.2 Many indole derivatives,
such as indomethacin, vinblastine, indoramin, pindolol, etc., are
commercial medicines. The broad application of various indoles
stimulates organic chemists to develop novel methodologies for
indole core formation and functionalization. One of the approaches
toward synthesis of indoles possessing the required pharmaco-
phores and/or functional groups involves the modification of the
pre-existing indole core. Alternatively, these indoles can be as-
sembled from the appropriately functionalized starting materials.
The last approach is realized, for example, when indoles are pre-
pared by recyclization of other heterocyclic compounds. It allows
for selective introduction of various functional groups at the defi-
nite positions.3
range of heterocycles.4 In these recyclizations, furans can be con-
sidered as synthetic equivalents of dicarbonyl synthons. One of the
latent carbonyl groups participates in the formation of the new
heterocycle, while the second one is transformed from the latent
form into its genuine entity. Alternatively, it can further react with
the appropriate functional group if it is present in the started
compound. In particular, we used this approach to synthesize 2-(3-
oxoalkyl)indoles 2 (reaction a in Fig. 1),5 2-(2-acylvinyl)indoles 4
(reaction b),6 3-(2-acylvinyl)indoles 6 (reaction c),7 and 2-(2-
oxoalkyl)indoles 8 (reaction d)8 from the corresponding furans 1,
3, 5, 7, respectively.
The processes a and d seem to be very similar but they have two
principal distinctions. Firstly, in reaction a furan provided only one
out of four carbon atoms of the furan ring and is incorporated into
the formed pyrrole ring of the indole. In contrast, in process d, the
furan ring provides two carbon atoms for the indole ring formation
(Fig. 1). Secondly, in the recyclization of 2-(2-aminobenzyl)furans
the furan ring reacts as a synthetic equivalent of 1,4-diketone
(Fig. 2), which is a typical behavior for furans in ring-opening
transformations. On the other hand, in recyclization of 2-(2-
aminophenyl)furans, the furan ring can be considered as
* Corresponding author. Tel.: þ7 861 255 9556; fax: þ7 861 259 6592; e-mail
address: alexander_butin@mail.ru (A.V. Butin).
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.10.114

620
A.S. Pilipenko et al. / Tetrahedron 68 (2012) 619e627
Table 1
Ts
NH
Ts
N
Synthesis of sulfonamides 7aem
H+
R1
R1
NO2
NH2
O
Path a
Path b
Path c
O
O
.
NH2NH2 H2O
O
O
X
X
Raney Ni, EtOH
R
2
R
1
O
R2
R1
R2
Ts
NH
9a-m
10a-m
Ts
N
H+
-TsNH2
NHR
O
NHTs
X
X
X
X
RCl
pyridine
R
4
R
3
H
N
R2
7a-m
NH2
H+
R
RCHO
+
Entry
R
R1
R2
Yield [%]
O
10
7
6
5
a
b
c
d
e
f
g
h
i
Ts
Ts
Ts
Ts
Ts
Ts
Ts
Ts
Ts
Ts
Ts
Ts
Ms
CH3
CH3O
Cl
Cl
H
H
H
H
H
H
Cl
CH3
CH3
CH3
CH3
CH3
C2H5
CH3
C2H5
Bn
4-CH3C6H4CH2
CO2C2H5
H
89
82
82
90
85
83
89
89
80
85
77
80
89
65
57
69
73
65
68
72
78
75
70
62
64
55
O
Ts
NH
Ts
N
H+
Path d
R
X
X
O
O
R
7
8
j
k
l
CH2CH2CO2CH3
CH2CH2CO2CH3
CH3
Fig. 1. Furans into indoles recyclizations.
m
R 1
NH
R 1
NH
R1
N
O
R
O
O
R
R
Furan
O
1,4-Diketone
R 1
NH
R1
N
R 1
NH
O
O
R
R
O
Furan
R
O
1,3-Diketone
Fig. 2. Furans as synthetic equivalents of 1,4- and 1,3-diketones in the indole synthesis.
a synthetic equivalent of 1,3-diketone. Indeed, reaction d is quite
similar to the indole synthesis from 1-(2-aminobenzyl)-1,3-
diketones, which is generated by reduction of the corresponding
nitrobenzenes (Fig. 2).9
This unusual reactivity of 2-(2-aminophenyl)furans stimulated
us to study their transformations in more depth. Herein, we report
more detailed study of this promising recyclization reaction.
recyclization of 2-[2-(tosylamino)benzyl]furans 1 into 2-(3-
oxoalkyl)indoles 2. This process was found to efficiently proceed
when 1 was heated to reflux in ethanolic HCl solution for
10e40 min.5b However, under the same reaction conditions, the
conversion of 7 was incomplete even after prolonged heating
producing indoles 8 in low yields only. Thus, when 7aec were
2. Results and discussion
R
O
NH2
O
NH
The parent sulfonamides 7aem were synthesized by reduction
of the corresponding 2-(2-nitrophenyl)furans 9 with hydrazine
hydrate in the presence of Raney nickel, followed by treatment of
the formed anilines 10 with sulfonyl chlorides (Table 1). Treatment
of the aniline 10a with acyl chloride in benzene afforded amides
7n,o (Scheme 1).
RCOCl
NaHCO3
C6H6, rt
O
10a
7n R = Me (52%)
7o R = Ph (68%)
Initially, we started our investigation of the title recyclization by
testing the reaction conditions, which were earlier applied for the
Scheme 1. Synthesis of N-acylanilides 7n,o.

A.S. Pilipenko et al. / Tetrahedron 68 (2012) 619e627
621
refluxed in saturated ethanolic HCl for 6 h, the target products 8aec
were obtained in 27, 42, and 30% yields, respectively. Along with
8aec, the side-products, diketones 11aec, were isolated in 43, 32,
and 25% yields, respectively (Scheme 2). The unreacted starting
compounds 7aec were also found in the reaction mixtures.
a direct precursor of the target indole 2, in the reaction mixture is
sufficient enough, thus providing high efficiency of recyclization of
benzylfurans 1. Moreover, both C and D can be transformed under
the reaction conditions into the diketone 12, which undergoes cy-
clization into indole 2 (Scheme 3).
Ts
NH
Ts
NH
1
R
1
R
H+, - H2O
O
R2
H2O, - H+
O
H
H
+
H2O,
- H+
O
11
R2
H+,
- H2O
Ts
NH
Ts
Ts
NH
1
R
1
R
1
NH
R
- H+
H+
H+
..
- H+
+
+
O
O
O
H
A
B
7
R2
R2
R2
Ts
N
Ts
N
1
R
1
R
Ts
N
1
R
H
- H+
R2
R2
R2
H
O
HO
O
H+
8
Scheme 2. Plausible mechanism for recyclization of arylfurans 7.
The differences in behavior of 7 and 1 could be understood by
comparison of mechanistic schemes for these two recyclizations.
Both reactions proceed via protonation of the furan ring leading to
cations A and B in reactions of arylfurans 7 (Scheme 2) and cations
C and D in reactions of benzylfurans 1 (Scheme 3). Most likely, the
stabilities of the cations C and D are very similar, which originate
In contrast, the benzylic cation A, which is formed by protonation
of 2-[2-(tosylamino)aryl]-5-alkylfuran 7 at C(5) position, is much
more stable than the cation B. Thus, the concentration of B in re-
action mixture is low. It leads to the low yield of the product and
a significant decrease of reaction rate as this cation is a direct pre-
cursor of indole 8. At the same time, under used reaction conditions
both A and B are transformed into diketone 11, formation of which
was observed in our experiments. In the presence of acid, this side-
product cyclizes slowly into furan 7, as the furan ring opening into
1,4-diketone is a reversible process. Therefore, a small concentration
of cation B should be permanently present under equilibrium con-
ditions, what allows for the smooth formation of indole 8. Therefore,
it is possible to suppose that the formation of 8 should be more ef-
ficient if harsher reaction conditions were used, at which equilib-
rium between furan 7 and diketone 11 could be achieved.
Indeed, treatment of furan 7a solution in glacial acetic acid with
70% HClO4 under reflux allowed us to both increase significantly
indole yield and decrease reaction time. The best yield of indole 8a
was obtained when the ratio of perchloric and acetic acids was 1:10
and reaction time was 10e15 min. Furthermore, a decrease of the
process duration, as well as utilization of a lower loading of HClO4
afforded the target indole 8a together with diketone 11a. The control
experiments showed that treatment of diketones 11aec under these
reaction conditions afforded indoles 8aec in high yields.
from the protonation of both
a-positions in benzylfurans 1, are
quite similar. Therefore, the concentration of the cation D, which is
Ts
NH
Ts
NH
X
X
H2O, - H+
H+, - H2O
O
+
- H2O
O
H
R
C
R
12
O
Ts
N
X
H+,
- H2O
- H+
O
H2O,
- H+
H+
R
2
Ts
NH
Ts
NH
X
X
H+
H
+
- H+
O
O
R
R
1
D
Next, the scope of this recyclization using a series of furans 7
under the optimized reaction conditions was studied (Table 2).
Formation of the indole 8 was found to be efficient for the
Scheme 3. The proposed mechanism for recyclization of benzylfurans 1.

622
A.S. Pilipenko et al. / Tetrahedron 68 (2012) 619e627
Table 2
Ts
NH
Ts
N
1
1
Recyclization of 2-[2-(tosylamino)phenyl]furans 7 into indoles 8
R
R
HClO4
AcOH
Ts
N
Ts
NH
1
1
R
HClO4
R
COOH
O
O
AcOH,
reflux
2
R
O
7k,l
13a R1 = Cl (45%)
O
13b R1 = CH3 (43%)
COOCH3
2
R
8a-h
7a-j
Scheme 4. Recyclization of 3-{5-[2-(tosylamino)phenyl]-2-furyl}propionates 7k,l.
Entry
R1
R2
Yield of 8 [%]
a
b
c
d
e
f
g
h
i
CH3
CH3O
Cl
Cl
H
H
H
H
H
CH3
75
64
85
73
83
80
56
60
d
benzoyl-2-(2-furyl)anilines 7n,o in both HClO4/AcOH mixture and
ethanolic HCl solution resulted in total decomposition of the
starting materials only. We believe that indoles formed from these
substrates, undergo fast deacylation leading to N-unsubstituted
derivatives, which are unstable under these reaction conditions.5b,d
CH3
CH3
C2H5
CH3
C2H5
Bn
4-CH3C6H4CH2
CO2C2H5
H
Ms
Ms
HClO4
AcOH
NH
j
H
d
N
O
O
substrates containing various substituents at the aniline moiety
and alkyl groups at C(5) position of the furan ring. However, the
attempts of recyclization of furans 7i,j into the corresponding in-
doles were not successful. In reaction of 7i, the starting furan stayed
intact after refluxing for 40 min. The possible reason for the low
reactivity of 7i toward protonation is its deactivation by the
electron-withdrawing ester group. Oppositely, protonation at the
unsubstituted C(5) position of the furan ring in 7j is too fast, leading
to full destruction of the substrate in 5 min.
7m
14 (68%)
Scheme 5. Recyclization of mesylate 7m.
3. Conclusion
In summary, we have developed a simple and efficient approach
to 2-(2-oxoalkyl)indoles by acid-catalyzed recyclization of 2-(2-
aminophenyl)furans. This method was shown to be efficient for 2-
furylanilines containing alkyl substituent at the C(5) position of the
furan ring and sulfonyl group at the nitrogen atom of aniline moiety.
The obtained 2-(2-oxoalkyl)indoles are interesting both themselves
and as potent precursors in syntheses of the more complex indole
derivatives,10 such as alkaloids vindorosine,11 ibogain, and iso-
ibogain.12 Nevertheless, there are only a few investigations of 2-(2-
oxoalkyl)indoles nowadays due to, mainly, the absence of the gen-
eral approaches to these compounds.13e16 So, we believe that the
method described herein would be useful for organic chemists as
a simple and convenient route to these ketoindoles.
Structures of indoles 8 were determined using 1H and 13C NMR,
mass spectrometry, and elemental analysis data. For compound 8e
it was unambiguously proved by single-crystal X-ray diffraction
data (Fig. 3).
4. Experimental section
4.1. General
Melting points are uncorrected. 1H NMR and 13C NMR spectra
were recorded on Bruker DPX 300 and Bruker AM 360 spectrom-
eters at room temperature; the chemical shifts
d were measured in
parts per million with respect to the solvent (CDCl3, 1H:
d
¼7.26 ppm, 13C:
d
¼77.0 ppm; DMSO-d6, 1H:
d
¼2.50 ppm, 13C:
d¼39.5 ppm). Coupling constants (J) are given in hertz. Splitting
patterns of an apparent multiplet associated with an averaged
coupling constants were designed as s (singlet), d (doublet), t
(triplet), q (quartet), m (multiplet), dd (doublet of doublets) and br
(broadened). IR spectra were measured as KBr plates on InfraLUM
FT-02 and InfraLUM FT-801 instruments. Mass spectra were
recorded on a Kratos MS-30 instrument with 70 eV electron impact
ionization at 200 ꢀC. Column chromatography was performed on
Fig. 3. Single-crystal X-ray structure of 8e.
It was found that recyclization of 3-{5-[2-(tosylamino)phenyl]-
2-furyl}propionates 7k,l into indoles is accompanied by hydrolysis
of the ester moiety furnishing 6-(2-indolyl)-4-oxopentanoic acids
13a,b in moderate yields (Scheme 4).
At last, we investigated the effect of the N-protecting group on
the efficiency of recyclization reaction. We found that 2-furyl-N-
mesyl aniline 7m was smoothly rearranged into the corresponding
N-mesylindole (Scheme 5). In contrast, heating N-acetyl- and N-
silica gel KSK (50e160 mm, LTD Sorbpolymer). The synthesis of
compounds 9 is described in Supplementary data. All the reactions
were carried out using freshly distilled and dry solvents from sol-
vent stills. Crystallographic data (excluding structure factors) for
compound 8e have been deposited with the Cambridge Crystallo-
graphic Data Center as supplementary publication number CCDC
832947. Copies of the data can be obtained, free of charge, on

A.S. Pilipenko et al. / Tetrahedron 68 (2012) 619e627
623
application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [fax:
þ44 (0)1223 336033 or e-mail: deposit@ccdc.cam.ac.uk].
C
19H18ClNO3S requires C, 60.71; H, 4.83; N, 3.73%. Rf¼0.62 (CH2Cl2/
acetone/petroleum ether¼1:1:2); nmax (KBr) 3315, 1573, 1491, 1399,
1339, 1160, 1090, 1038, 935, 906, 870, 818 cmꢁ1
dH (300 MHz,
;
4.2. Synthesis of 2-[2-(tosylamino)phenyl]furans 7ael
CDCl3) 7.91 (1H, br s, NH), 7.53 (1H, d, J 2.1 Hz, HAr), 7.41 (2H, d, J
8.4 Hz, HTs), 7.13 (1H, d, J 8.7 Hz, HAr), 7.02 (2H, d, J 8.4 Hz, HTs), 6.94
(1H, dd, J 8.7, 2.1 Hz, HAr), 6.15 (1H, d, J 3.3 Hz, HFur), 5.91 (1H, d, J
3.3 Hz, HFur), 2.61 (2H, q, J 7.5 Hz, CH2), 2.22 (3H, s, CH3),1.20 (3H, t, J
7.5 Hz, CH3); dC (75 MHz, CDCl3) 158.2, 148.9, 143.9, 135.6, 133.7,
133.6, 129.5 (2C), 128.0, 126.9 (2C), 125.3, 122.7, 120.9, 109.1, 106.3,
21.5, 21.4, 12.2; m/z (EI, 70 eV) 377/375 (Mþ, 9/27), 222/220 (33/
100), 193 (25), 192 (87), 177 (30), 163 (27), 157 (65), 128 (20), 91
(36), 65 (20), 59 (15%).
Hydrazine hydrate (10 mL) and Raney nickel (4 g) were added
to solution of nitroarene 9 (38 mmol) in ethanol (100 mL). Mixture
was refluxed for 2 h (TLC monitoring). Nickel was filtered off.
Evaporation of filtrate afforded 2-(2-aminophenyl)furan 10. This
product (13 mmol) was dissolved in pyridine (15 mL) and cooled
to 0 ꢀC. Then TsCl (5 g, 26 mmol) was added. The reaction mixture
was stirred at room temperature for 12 h (TLC monitoring) and
poured into 6 M HCl (200 mL). Residue was filtered, washed with
water, and air-dried. Product was purified by column chromatog-
raphy on silica gel using benzene/petroleum ether (1:3) mixture as
an eluent.
4.2.5. 4-Methyl-N-[2-(5-methyl-2-furyl)phenyl]benzenesulfonamide
(7e). White solid; yield 65% (2.76 g); mp 88e89 ꢀC (benzene/pe-
troleum ether). Found: C, 66.13; H, 5.27; N, 4.15. C18H17NO3S re-
quires C, 66.03; H, 5.23; N, 4.28%. Rf¼0.65 (CH2Cl2/acetone/
petroleum ether¼1:1:2); nmax (KBr) 3312, 1597, 1577, 1445, 1415,
4.2.1. 4-Methyl-N-[5-methyl-2-(5-methyl-2-furyl)phenyl]benzene-
sulfonamide (7a). White solid; yield 65% (2.88 g); mp 92e93 ꢀC
(benzene/petroleum ether). Found: C, 67.09; H, 5.74; N, 3.96.
C19H19NO3S requires C, 66.84; H, 5.61; N, 4.10%. Rf¼0.61 (CH2Cl2/
acetone/petroleum ether¼1:1:2); nmax (KBr) 3271, 1572, 1493,
1334, 1304, 1218, 1167, 1091, 1024, 896, 818 cmꢁ1
; dH (360 MHz,
CDCl3) 7.85 (1H, br s, NH), 7.62e7.60 (1H, m, HAr), 7.46 (2H, d, J
8.3 Hz, HTs), 7.35e7.30 (1H, m, HAr), 7.24e7.19 (1H, m, HAr),
7.12e7.07 (3H, m, HArþ2HTs), 6.21 (1H, d, J 3.2 Hz, HFur), 5.98 (1H,
d, J 3.2 Hz, HFur), 2.36 (3H, s, CH3), 2.30 (3H, s, CH3); dC (90 MHz,
CDCl3) 152.3, 150.0, 143.5, 136.0, 132.7, 129.3 (2C), 128.3, 127.2,
126.9 (2C), 125.4, 123.7, 123.0, 109.0, 107.7, 21.4, 13.7; m/z (EI,
70 eV) 327 (Mþ, 97), 172 (100), 144 (90), 129 (23), 115 (17), 91 (34),
77 (17), 43 (25%).
1397, 1336, 1172, 1092, 1024, 896, 816 cmꢁ1
; dH (360 MHz, CDCl3)
7.79 (1H, br s, NH), 7.47e7.44 (3H, m, HArþ2HTs), 7.18 (1H, d, J
8.3 Hz, HAr), 7.07 (2H, d, J 8.0 Hz, HTs), 6.90 (1H, d, J 8.3 Hz, HAr),
6.12 (1H, d, J 3.2 Hz, HFur), 5.95 (1H, d, J 3.2 Hz, HFur), 2.34 (3H, s,
CH3), 2.32 (3H, s, CH3), 2.30 (3H, s, CH3); dC (90 MHz, CDCl3)
151.9, 150.2, 143.4, 138.6, 136.0, 132.5, 129.2 (2C), 127.1, 126.9
(2C), 126.3, 124.2, 120.3, 108.3, 107.5, 21.4, 21.2, 13.6; m/z (EI,
70 eV) 341 (Mþ, 100), 186 (78), 171 (14), 158 (29), 143 (19), 91
(32), 43 (20%).
4.2.6. 4-Methyl-N-[2-(5-ethyl-2-furyl)phenyl]benzenesulfonamide
(7f). White solid; yield 68% (3.01 g); mp 89e90 ꢀC (benzene/pe-
troleum ether). Found: C, 66.99; H, 5.73; N, 4.00. C19H19NO3S re-
quires C, 66.84; H, 5.61; N, 4.10%. Rf¼0.65 (CH2Cl2/acetone/
petroleum ether¼1:1:2); nmax (KBr) 3253, 1593, 1538, 1488, 1392,
4.2.2. 4-Methyl-N-[5-methoxy-2-(5-methyl-2-furyl)phenyl]benzene-
sulfonamide (7b). White solid; yield 57% (2.65 g); mp 82e83 ꢀC
(benzene/petroleum ether). Found: C, 64.13; H, 5.50; N, 3.82.
C19H19NO4S requires C, 63.85; H, 5.36; N, 3.92%. Rf¼0.58 (CH2Cl2/
acetone/petroleum ether¼1:1:2); nmax (KBr) 3324, 1583, 1502,
1328,1154,1091,1017, 905, 763 cmꢁ1
; dH (360 MHz, CDCl3) 7.94 (1H,
br s, NH), 7.63e7.61 (1H, m, HAr), 7.46 (2H, d, J 8.3 Hz, HTs),
7.33e7.30 (1H, m, HAr), 7.24e7.19 (1H, m, HAr), 7.11e7.06 (3H, m,
HArþ2HTs), 6.22 (1H, d, J 3.3 Hz, HFur), 6.00 (1H, d, J 3.3 Hz, HFur),
2.70 (2H, q, J 7.6 Hz, CH2), 2.30 (3H, s, CH3),1.30 (3H, t, J 7.6 Hz, CH3);
dC (90 MHz, CDCl3) 157.9, 150.0, 143.5, 136.0, 132.7, 129.3 (2C), 128.3,
127.2, 126.9 (2C), 125.3, 123.4, 122.9, 108.8, 106.1, 21.4 (2C), 12.3; m/z
(EI, 70 eV) 341 (Mþ, 36), 186 (70), 158 (100), 143 (18), 130 (21), 129
(35), 91 (36), 43 (34%).
1449, 1336, 1238, 1160, 1090, 1029, 972, 894 cmꢁ1
; dH (360 MHz,
CDCl3) 7.87 (1H, br s, NH), 7.51 (2H, d, J 8.3 Hz, HTs), 7.20 (1H, d, J
8.7 Hz, HAr), 7.17 (1H, d, J 2.5 Hz, HAr), 7.09 (2H, d, J 8.3 Hz, HTs), 6.62
(1H, dd, J 8.7, 2.5 Hz, HAr), 6.08 (1H, d, J 3.2 Hz, HFur), 5.96 (1H, d, J
3.2 Hz, HFur), 3.79 (3H, s, OCH3), 2.34 (3H, s, CH3), 2.30 (3H, s, CH3);
dC (90 MHz, CDCl3) 159.6, 151.6, 149.9, 143.6, 136.0, 134.0, 129.3 (2C),
128.5, 127.0 (2C), 115.5, 111.7, 107.7, 107.6, 107.4, 55.4, 21.4, 13.6; m/z
(EI, 70 eV) 357 (Mþ, 65), 202 (100), 187 (22), 174 (33), 171 (32), 170
(25),162 (18),159 (27),131 (17),116 (17), 91 (29), 65 (24), 59 (20), 43
(18%).
4.2.7. 4-Methyl-N-[2-(5-benzyl-2-furyl)phenyl]benzenesulfonamide
(7g). White solid; yield 72% (3.78 g); mp 108e109 ꢀC (benzene/
petroleum ether). Found: C, 71.12; H, 5.19; N, 3.36. C24H21NO3S
requires C, 71.44; H, 5.25; N, 3.47%. Rf¼0.63 (CH2Cl2/acetone/
petroleum ether¼1:1:2); nmax (KBr) 3364, 3315, 1580, 1537, 1490,
4.2.3. 4-Methyl-N-[5-chloro-2-(5-methyl-2-furyl)phenyl]benzene-
sulfonamide (7c). White solid; yield 69% (3.24 g); mp 131e132 ꢀC
(benzene/petroleum ether). Found: C, 60.02; H, 4.45; N, 3.77.
C18H16ClNO3S requires C, 59.75; H, 4.46; N, 3.87%. Rf¼0.60 (CH2Cl2/
acetone/petroleum ether¼1:1:2); nmax (KBr) 3332, 1595, 1574, 1490,
1420, 1336, 1302, 1224, 1161, 1089, 1030, 908 cmꢁ1
; dH (300 MHz,
CDCl3) 7.92 (1H, br s, NH), 7.66e7.63 (1H, m, HAr), 7.44e7.19 (9H,
m, 7HArþ2HTs), 7.11e7.06 (1H, m, HAr), 6.97 (2H, d, J 8.1 Hz, HTs),
6.25 (1H, d, J 3.0 Hz, HFur), 6.08 (1H, d, J 3.0 Hz, HFur), 4.02 (2H, s,
CH2), 2.27 (3H, s, CH3); dC (75 MHz, CDCl3) 154.6, 150.7, 143.3,
137.3, 135.6, 132.5, 129.2 (2C), 128.8 (2C), 128.6 (2C), 128.3, 128.2,
127.1, 126.7 (2C), 125.2, 123.4, 122.5, 108.6, 108.0, 34.6, 21.3; m/z
(EI, 70 eV) 403 (Mþ, 14), 248 (22), 220 (38), 91 (100), 65 (25), 39
(17%).
1397, 1334, 1294, 1154, 1091, 1032, 940, 869, 820, 782 cmꢁ1
; dH
(360 MHz, CDCl3) 7.88 (1H, br s, NH), 7.63 (1H, d, J 2.2 Hz, HAr), 7.52
(2H, d, J 8.3 Hz, HTs), 7.23 (1H, d, J 8.3 Hz, HAr), 7.12 (2H, d, J 8.3 Hz,
HTs), 7.04 (1H, dd, J 8.3, 2.2 Hz, HAr), 6.23 (1H, d, J 3.6 Hz, HFur), 6.00
(1H, d, J 3.6 Hz, HFur), 2.36 (3H, s, CH3), 2.32 (3H, s, CH3); dC (90 MHz,
CDCl3) 152.6, 149.1, 143.9, 135.8, 133.8, 133.7, 129.5 (2C), 128.1, 127.0
(2C), 125.4, 123.0, 121.0, 109.4, 107.8, 21.4, 13.7; m/z (EI, 70 eV) 363/
361 (Mþ, 24/72), 208/206 (33/100), 191 (38), 178 (63), 171 (56), 163
(40), 143 (71), 91 (86), 69 (35), 57 (37), 43 (47%).
4.2.8. 4-Methyl-N-{2-[5-(4-methylbenzyl)-2-furyl]phenyl}benzene-
sulfonamide (7h). White solid; yield 78% (4.23 g); mp 76e77 ꢀC
(benzene/petroleum ether). Found: C, 72.24; H, 5.65; N, 3.29.
C25H23NO3S requires C, 71.92; H, 5.55; N, 3.35%. Rf¼0.64 (CH2Cl2/
acetone/petroleum ether¼1:1:2); nmax (KBr) 3368, 3344, 1600,
4.2.4. 4-Methyl-N-[5-chloro-2-(5-ethyl-2-furyl)phenyl]benzenesulfo-
namide (7d). White solid; yield 73% (3.56 g); mp 132e134 ꢀC
(benzene/petroleum ether). Found: C, 60.68; H, 4.71; N, 3.76.
1488, 1346, 1336, 1164, 1092, 1024, 892, 800 cmꢁ1
; dH (300 MHz,
CDCl3) 7.92 (1H, br s, NH), 7.66e7.63 (1H, m, HAr), 7.33e7.30 (3H, m,
HArþ2HTs), 7.24e7.19 (5H, m, HAr), 7.11e7.06 (1H, m, HAr), 6.99 (2H,

624
A.S. Pilipenko et al. / Tetrahedron 68 (2012) 619e627
d, J 8.1 Hz, HTs), 6.25 (1H, d, J 3.3 Hz, HFur), 6.06 (1H, d, J 3.3 Hz, HFur),
3.98 (2H, s, CH2), 2.36 (3H, s, CH3), 2.29 (3H, s, CH3); dC (75 MHz,
CDCl3) 155.0, 150.6, 143.3, 136.3, 135.7, 134.2, 132.6, 129.5 (2C),129.2
(2C), 128.5 (2C), 128.3, 127.1, 126.8 (2C), 125.2, 123.4, 122.5, 108.6,
107.8, 34.2, 21.3, 20.9; m/z (EI, 70 eV) 417 (Mþ, 18), 262 (64), 234
(27), 145 (28), 105 (100), 91 (22), 59 (21), 43 (27%).
(EI, 70 eV) 413 (Mþ, 4), 258 (100), 226 (13), 198 (18), 184 (15), 170
(20), 144 (16), 91 (29), 65 (15%).
4.3. N-[5-Methyl-2-(5-methyl-2-furyl)phenyl]
methanesulfonamide (7m)
This compound was synthesized from 9a and methanesulfonyl
chloride using procedure described in Section 4.2. White solid; yield
55% (1.90 g); mp 71e72 ꢀC (benzene/petroleum ether). Found: C,
59.09; H, 5.58; N, 5.32. C13H15NO3S requires C, 58.85;H, 5.70;N, 5.28%.
Rf¼0.54 (CH2Cl2/acetone/petroleum ether¼1:1:2); nmax (KBr) 3336,
4.2.9. Ethyl 5-(4-methyl-2-{[(4-methylphenyl)sulfonyl]amino}phe-
nyl)-2-furoate (7i). White solid; yield 75% (3.75 g); mp 108e109 ꢀC
(benzene/petroleum ether). Found: C, 62.22; H, 4.83; N, 3.43.
C20H19NO5S requires C, 62.32; H, 4.97; N, 3.63%. Rf¼0.52 (CH2Cl2/
acetone/petroleum ether¼1:1:2); nmax (KBr) 3247, 1720, 1485, 1442,
1612,1576,1396,1336,1328,1152,1132,1036,976,900,808,800 cmꢁ1
;
1385, 1335, 1298, 1213, 1157, 1020, 813 cmꢁ1
;
dH (300 MHz, CDCl3)
dH (300 MHz, CDCl3) 7.62 (1H, br s, NH), 7.43 (1H, d, J 0.9 Hz, HAr), 7.38
(1H, d, J 8.1 Hz,HAr), 6.98 (1H, dd, J 8.1, 0.9 Hz,HAr), 6.49 (1H, d, J 3.3 Hz,
HFur), 6.10 (1H, d, J 3.3 Hz, HFur), 2.87(3H, s, CH3), 2.38(3H, s, CH3), 2.36
(3H, s, CH3); dC (75 MHz, CDCl3) 152.3,150.1, 139.0,132.4,127.4,126.4,
123.2, 119.8,108.9,107.8, 39.0, 21.2, 13.6; m/z (EI, 70 eV) 265 (Mþ, 57),
186 (100), 171 (32), 158 (68), 143 (49), 115 (22), 43 (44%).
7.96 (1H, br s NH), 7.66e7.63 (1H, m, HAr), 7.50 (2H, d, J 8.4 Hz, HTs),
7.42e7.39 (1H, m, HAr), 7.33e7.28 (1H, m, HAr), 7.16e7.13 (1H, m,
HAr), 7.12 (1H, d, J 3.9 Hz, HFur), 7.04 (2H, d, J 8.4 Hz, HTs), 6.45 (1H, d,
J 3.9 Hz, HFur), 4.40 (2H, q, J 7.1 Hz, CH2), 2.28 (3H, s, CH3), 1.43 (3H, t,
J 7.1 Hz, CH3); dC (75 MHz, CDCl3) 158.1, 154.9, 143.9, 143.6, 135.7,
133.4, 130.1, 129.3 (2C), 127.9, 126.9 (2C), 125.7, 124.7, 121.5, 119.0,
109.5, 61.2, 21.4, 14.3; m/z (EI, 70 eV) 385 (Mþ, 2), 202 (43), 178 (21),
155(44), 156 (45), 129 (57), 114 (28), 102 (34), 91 (100), 77 (43), 65
(44), 51 (27), 39 (31%).
4.4. General procedure for synthesis of N-acyl-5-methyl-2-(5-
methyl-2-furyl)anilines 7n,o
Solution of acyl chloride (15 mmol) in benzene (25 mL) was
added under stirring to solution of aniline 10a (1.87 g, 10 mmol) in
benzene (30 mL). The reaction mixture was stirred at room tem-
perature for 1 h (TLC control), poured into cold water (100 mL), and
neutralized with NaHCO3. The mixture was kept for 2 h, then or-
ganic layer was separated and aqueous layer was extracted with
ethyl acetate (2ꢂ30 mL). The combined organic fractions were
dried with anhydrous Na2SO4 and filtered. Solvent was evaporated
to dryness under reduced pressure. Residue was purified by chro-
matography on silica gel using benzene/petroleum ether (1:3)
mixture as an eluent.
4.2.10. N-[2-(2-Furyl)phenyl]-4-methylbenzenesulfonamide
(7j). White solid; yield 70% (2.85 g); mp 130e131 ꢀC (benzene/
petroleum ether). Found: C, 65.41; H, 4.91; N, 4.37. C17H15NO3S
requires C, 65.16; H, 4.82; N, 4.47%. Rf¼0.59 (CH2Cl2/acetone/pe-
troleum ether¼1:1:2); nmax (KBr) 3339, 1593, 1507, 1458, 1417,
1336, 1291, 1167, 1089, 1006, 890, 809 cmꢁ1
; dH (300 MHz, CDCl3)
7.88 (1H, br s, NH), 7.64e7.61 (1H, m, HAr), 7.48e7.44 (3H, m,
HFurþ2HTs), 7.36e7.33 (1H, m, HAr), 7.28e7.23 (1H, m, HAr),
7.14e7.09 (1H, m, HAr), 7.07 (2H, d, J 8.3 Hz, HTs), 6.41 (1H, dd, J 3.2,
1.8 Hz, HFur), 6.32 (1H, dd, J 3.2, 0.7 Hz, HFur), 2.31 (3H, s, CH3); dC
(75 MHz, CDCl3) 151.9, 143.5, 142.3, 136.0, 133.1, 129.4 (2C), 128.9,
127.7, 126.9 (2C), 125.4, 123.7, 122.6, 111.6, 108.0, 21.4; m/z (EI,
70 eV) 313 (Mþ, 19), 158 (70), 130 (100), 102 (13), 91 (27), 77 (17),
43 (14%).
4.4.1. N-[5-Methyl-2-(5-methyl-2-furyl)phenyl]acetamide
(7n). White solid; yield 52% (1.19 g); mp 148e149 ꢀC (benzene/
petroleum ether). Found: C, 73.29; H, 6.71; N, 6.06. C14H15NO2 re-
quires C, 73.34; H, 6.59; N, 6.11%. Rf¼0.47 (CH2Cl2/acetone/petro-
leum ether¼1:1:2); nmax (KBr) 3225, 1656, 1576, 1536, 1028,
4.2.11. Methyl 3-[5-(4-chloro-2-{[(4-methylphenyl)sulfonyl]amino}
phenyl)-2-furyl]propanoate (7k). White solid; yield 62% (3.49 g);
mp 75e76 ꢀC (benzene/petroleum ether). Found: C, 58.07; H, 4.42;
N, 3.39. C21H20ClNO5S requires C, 58.13; H, 4.65; N, 3.23%. Rf¼0.52
(CH2Cl2/acetone/petroleum ether¼1:1:2); nmax (KBr) 3240, 1736,
820 cmꢁ1
; dH (300 MHz, CDCl3) 8.42 (1H, br s, NH), 8.10 (1H, s, HAr),
7.37 (1H, d, J 8.1 Hz, HAr), 6.92 (1H, d, J 8.1 Hz, HAr), 6.42 (1H, d, J
3.0 Hz, HFur), 6.09 (1H, d, J 3.0 Hz, HFur), 2.38 (3H, s, CH3), 2.35 (3H, s,
CH3), 2.18 (3H, s, CH3); dC (75 MHz, CDCl3) 168.1, 151.7, 150.7, 138.4,
133.7, 126.9, 125.1, 122.5, 118.0, 108.3, 107.6, 24.9, 21.4, 13.6; m/z (EI,
70 eV) 229 (Mþ, 47), 187 (26), 144 (63), 115 (12), 43 (100%).
1332, 1160, 828 cmꢁ1
; dH (300 MHz, CDCl3) 7.86 (1H, br s, NH), 7.62
(1H, d, J 2.1 Hz, HAr), 7.53 (2H, d, J 8.1 Hz, HTs), 7.23 (1H, d, J 8.7 Hz,
HAr), 7.13 (2H, d, J 8.1 Hz, HTs), 7.05 (1H, dd, J 8.7, 2.1 Hz, HAr), 6.23
(1H, d, J 3.3 Hz, HFur), 6.07 (1H, d, J 3.3 Hz, HFur), 3.72 (3H, s, OCH3),
3.04e3.00 (2H, m, CH2), 2.73e2.68 (2H, m, CH2), 2.33 (3H, s, CH3);
dC (75 MHz, CDCl3) 172.6, 154.7, 143.9, 135.7, 134.0, 133.8, 129.5 (2C),
128.3, 126.9 (2C), 125.4 (2C), 122.9, 120.8, 109.2, 107.7, 51.9, 32.2,
23.4, 21.5; m/z (EI, 70 eV) 435/433 (Mþ, 2/6), 280/278 (33/100), 91
(20%).
4.4.2. N-[5-Methyl-2-(5-methyl-2-furyl)phenyl]benzamide
(7o). Beige solid; yield 68% (1.99 g); mp 104e105 ꢀC (benzene/pe-
troleum ether). Found: C, 78.56; H, 5.72; N, 4.64. C19H17NO2 re-
quires C, 78.33; H, 5.88; N, 4.81%. Rf¼0.63 (CH2Cl2/acetone/
petroleum ether¼1:1:2); nmax (KBr) 3420, 3400, 1684, 1576, 1544,
1420, 1304, 1036, 800 cmꢁ1
; dH (300 MHz, CDCl3) 9.63 (1H, br s,
NH), 8.45 (1H, d, J 0.9 Hz, HAr), 7.97e7.93 (2H, m, HAr), 7.58e7.46
(3H, m, HAr), 7.42 (1H, d, J 8.1 Hz, HAr), 6.95 (1H, dd, J 8.1, 0.9 Hz,
HAr), 6.48 (1H, d, J 3.3 Hz, HFur), 6.12 (1H, d, J 3.3 Hz, HFur), 2.41 (3H,
s, CH3), 2.40 (3H, s, CH3); dC (75 MHz, CDCl3) 165.0, 151.5, 151.3,
138.5, 135.2, 134.0, 131.7, 128.6 (2C), 126.9 (2C), 126.8, 125.0, 121.9,
117.6, 108.3, 107.9, 21.5, 13.6; m/z (EI, 70 eV) 291 (Mþ, 31), 143 (12),
105 (100), 77 (79)51 (33), 43 (19%).
4.2.12. Methyl 3-[5-(4-methyl-2-{[(4-methylphenyl)sulfonyl]amino}
phenyl)-2-furyl]propanoate (7l). White solid; yield 64% (3.44 g); mp
81e82 ꢀC (benzene/petroleum ether). Found: C, 64.29; H, 5.82; N,
3.37. C22H23NO5S requires C, 63.91; H, 5.61; N, 3.39%. Rf¼0.53
(CH2Cl2/acetone/petroleum ether¼1:1:2); nmax (KBr) 3180, 1712,
1360, 1284, 1256, 1172, 1140, 1084, 1052, 828 cmꢁ1
; dH (300 MHz,
CDCl3) 7.75 (1H, br s, NH), 7.44 (2H, d, J 8.1 Hz, HTs), 7.41 (1H, d, J
1.2 Hz, HAr), 7.16 (1H, d, J 7.8 Hz, HAr), 7.06 (2H, d, J 8.1 Hz, HTs), 6.89
(1H, dd, J 7.8, 1.2 Hz, HAr), 6.11 (1H, d, J 3.3 Hz, HFur), 6.00 (1H, d, J
3.3 Hz, HFur), 3.69 (3H, s, OCH3), 3.00e2.96 (2H, m, CH2), 2.70e2.65
(2H, m, CH2), 2.30 (3H, s, CH3), 2.28 (3H, s, CH3); dC (75 MHz, CDCl3)
172.6, 153.9, 150.5, 143.4, 138.8, 136.0, 132.5, 129.3 (2C), 127.2, 126.8
(2C), 126.4, 124.3, 120.3, 108.1, 107.4, 51.8, 32.3, 23.4, 21.4, 21.2; m/z
4.5. Recyclization of 2-[2-(tosylamino)phenyl]furans 7 into
indoles 8, 13, 14
To the refluxing solution of compound 7 (9 mmol) in acetic acid
(30 mL) was added 70% HClO4 (3 mL). The reaction mixture was
refluxed for 10e15 min (TLC control) and poured into cold water

A.S. Pilipenko et al. / Tetrahedron 68 (2012) 619e627
625
(300 mL). The formed precipitate was filtered off, washed sub-
1121, 1053, 814 cmꢁ1
;
dH (300 MHz, CDCl3) 7.94e7.91 (1H, m, HAr),
sequently with NaHCO3 solution and water, air-dried, and purified
by column chromatography on silica gel using benzene/petroleum
ether (1:3) mixture as an eluent.
7.67 (2H, d, J 8.4 Hz, HTs), 7.46e7.43 (1H, m, HAr), 7.27e7.16 (4H, m,
2HArþ2HTs), 6.51 (1H, s, HInd), 4.13 (2H, s, CH2), 2.32 (3H, s, CH3),
2.30 (3H, s, CH3); dC (75 MHz, CDCl3) 204.3, 144.9, 136.5, 135.7,
134.0, 129.8 (2C), 129.1, 126.6 (2C), 124.3, 123.4, 120.6, 114.3, 112.3,
43.6, 29.6, 21.5; m/z (EI, 70 eV) 327 (Mþ,100), 284 (82), 220 (54),172
(26), 130 (57), 91 (47%).
4.5.1. 1-{6-Methyl-1-[(4-methylphenyl)sulfonyl]-1H-indol-2-yl}ace-
tone (8a). White solid; yield 75% (2.30 g); mp 119e120 ꢀC (ben-
zene/petroleum ether). Found: C, 67.02; H, 5.90; N, 4.02.
C19H19NO3S requires C, 66.84; H, 5.61; N, 4.10%. Rf¼0.52 (CH2Cl2/
acetone/petroleum ether¼1:1:2); nmax (KBr) 1720, 1424, 1364,1263,
4.5.6. 1-{1-[(4-Methylphenyl)sulfonyl]-1H-indol-2-yl}butan-2-one
(8f). White solid; yield 80% (2.46 g); mp 111e112 ꢀC (benzene/pe-
troleum ether). Found: C, 67.02; H, 5.67; N, 3.94. C19H19NO3S re-
quires C, 66.84; H, 5.61; N, 4.10%. Rf¼0.60 (CH2Cl2/acetone/
petroleum ether¼1:1:2); nmax (KBr) 1715, 1594, 1450, 1366, 1172,
1172, 1135, 1050, 826 cmꢁ1
; dH (300 MHz, CDCl3) 7.76 (1H, d, J
1.2 Hz, HAr), 7.64 (2H, d, J 8.4 Hz, HTs), 7.32 (1H, d, J 7.8 Hz, HAr), 7.19
(2H, d, J 8.4 Hz, HTs), 7.02 (1H, dd, J 7.8, 1.2 Hz, HAr), 6.45 (1H, s, HInd),
4.07 (2H, s, CH2), 2.43 (3H, s, CH3), 2.33 (3H, s, CH3), 2.28 (3H, s,
CH3); dC (75 MHz, CDCl3) 204.4, 144.8, 137.0, 135.9, 134.4, 133.3,
129.8 (2C), 126.9, 126.5 (2C), 125.0, 120.1, 114.5, 112.2, 43.6, 29.5,
22.0, 21.5; m/z (EI, 70 eV) 341 (Mþ, 70), 298 (77), 234 (73),144 (100),
143 (69), 91 (56), 65 (14), 43 (14%).
1111, 809 cmꢁ1
; dH (300 MHz, CDCl3) 7.95e7.92 (1H, m, HAr), 7.66
(2H, d, J 8.4 Hz, HTs), 7.46e7.43 (1H, m, HAr), 7.26e7.16 (4H, m,
2HArþ2HTs), 6.50 (1H, s, HInd), 4.10 (2H, s, CH2), 2.60 (2H, q, J 7.4 Hz,
CH2), 2.32 (3H, s, CH3), 1.10 (3H, t, J 7.4 Hz, CH3); dC (75 MHz, CDCl3)
206.7, 144.8, 136.5, 135.7, 134.1, 129.7 (2C), 129.2, 126.5 (2C), 124.2,
123.4, 120.5, 114.3, 112.2, 42.6, 35.4, 21.5, 7.6; m/z (EI, 70 eV) 341
(Mþ, 94), 285 (47), 284 (76), 220 (100), 186 (30), 130 (79), 129 (25),
91 (29), 57 (24), 43 (28%).
4.5.2. 1-{6-Methoxy-1-[(4-methylphenyl)sulfonyl]-1H-indol-2-yl}ac-
etone (8b). White solid; yield 64% (2.06 g); mp 176e177 ꢀC (ben-
zene/petroleum ether). Found: C, 64.19; H, 5.34; N, 3.91.
C19H19NO4S requires C, 63.85; H, 5.36; N, 3.92%. Rf¼0.48 (CH2Cl2/
acetone/petroleum ether¼1:1:2); nmax (KBr) 1720, 1616, 1490, 1364,
4.5.7. 1-{1-[(4-Methylphenyl)sulfonyl]-1H-indol-2-yl}-3-phenylace-
tone (8g). White solid; yield 56% (2.03 g); mp 115e116 ꢀC (ben-
zene/petroleum ether). Found: C, 71.22; H, 5.21; N, 3.44.
C24H21NO3S requires C, 71.44; H, 5.25; N, 3.47%. Rf¼0.61 (CH2Cl2/
acetone/petroleum ether¼1:1:2); nmax (KBr) 1730, 1452, 1358, 1172,
1280, 1173, 1055, 972, 819 cmꢁ1
; dH (300 MHz, CDCl3) 7.65 (2H, d, J
8.4 Hz, HTs), 7.47 (1H, d, J 2.4 Hz, HAr), 7.31 (1H, d, J 8.7 Hz, HAr), 7.20
(2H, d, J 8.4 Hz, HTs), 6.82 (1H, dd, J 8.7, 2.4 Hz, HAr), 6.42 (1H, s,
HInd), 4.06 (2H, s, CH2), 3.82 (3H, s, OCH3), 2.33 (3H, s, CH3), 2.28
(3H, s, CH3); dC (75 MHz, CDCl3) 204.6, 157.6, 144.9, 137.6, 135.7,
132.7, 129.8 (2C), 126.5 (2C), 122.9, 121.0, 112.5, 112.1, 98.9, 55.6,
43.7, 29.5, 21.5; m/z (EI, 70 eV) 357 (Mþ, 47), 315 (23), 314 (92), 250
(21), 160 (100), 144 (39), 117 (19), 91 (31), 43 (19%).
1088, 1051 cmꢁ1
; dH (300 MHz, CDCl3) 7.96e7.93 (1H, m, HAr), 7.64
(2H, d, J 8.4 Hz, HTs), 7.45e7.42 (1H, m, HAr), 7.39e7.16 (9H, m,
7HArþ2HTs), 6.46 (1H, s, HInd), 4.11 (2H, s, CH2), 3.90 (2H, s, CH2),
2.31 (3H, s, CH3); dC (75 MHz, CDCl3) 203.7,144.9,136.6,135.8,133.9,
133.8, 129.8 (2C), 129.7 (2C), 129.2, 128.7 (2C), 127.1, 126.6 (2C),
124.3, 123.4, 120.6, 114.3, 112.4, 49.6, 42.2, 21.5; m/z (EI, 70 eV) (%)
403 (Mþ, 21), 284 (49), 220 (71), 205 (21), 130 (89), 102 (22), 91
(100), 77 (17), 65 (66%).
4.5.3. 1-{6-Chloro-1-[(4-methylphenyl)sulfonyl]-1H-indol-2-yl}ace-
tone (8c). White solid; yield 85% (2.76 g); mp 117e118 ꢀC (benzene/
petroleum ether). Found: C, 60.04; H, 4.28; N, 3.88. C18H16ClNO3S
requires C, 59.75; H, 4.46; N, 3.87%. Rf¼0.49 (CH2Cl2/acetone/pe-
troleum ether¼1:1:2); nmax (KBr) 1721, 1592, 1457, 1424, 1372, 1328,
4.5.8. 1-(4-Methylphenyl)-3-{1-[(4-methylphenyl)sulfonyl]-1H-in-
dol-2-yl}acetone (8h). White solid; yield 60% (2.25 g); mp
109e110 ꢀC (benzene/petroleum ether). Found: C, 72.03; H, 5.63; N,
3.25. C25H23NO3S requires C, 71.92; H, 5.55; N, 3.35%. Rf¼0.63
(CH2Cl2/acetone/petroleum ether¼1:1:2); nmax (KBr) 1724, 1456,
1273, 1173, 1091, 1048, 948, 830 cmꢁ1
; dH (300 MHz, CDCl3) 7.96
(1H, d, J 1.8 Hz, HAr), 7.65 (2H, d, J 8.4 Hz, HTs), 7.34 (1H, d, J 8.1 Hz,
HAr), 7.23 (2H, d, J 8.4 Hz, HTs), 7.17 (1H, dd, J 8.1, 1.8 Hz, HAr), 6.47
(1H, s, HInd), 4.10 (2H, s, CH2), 2.35 (3H, s, CH3), 2.29 (3H, s, CH3); dC
(75 MHz, CDCl3) 203.9, 145.3, 136.9, 135.4, 134.7, 130.3, 130.0 (2C),
127.6, 126.6 (2C), 124.1, 121.3, 114.5, 111.8, 43.5, 29.6, 21.6; m/z (EI,
70 eV) 363/361 (Mþ, 20/60), 320/318 (33/100), 256/254 (18/56), 219
(17), 206 (22), 166 (28), 164 (58), 91 (54), 43 (16%).
1386, 1256, 1192, 1180, 1088, 1068, 1052, 808 cmꢁ1
; dH (300 MHz,
CDCl3) 7.98e7.95 (1H, m, HAr), 7.66 (2H, d, J 8.1 Hz, HTs), 7.46e7.43
(1H, m, HAr), 7.28e7.16 (8H, m, 6HArþ2HTs), 6.46 (1H, s, HInd), 4.13
(2H, s, CH2), 3.88 (2H, s, CH2), 2.36 (3H, s, CH3), 2.31 (3H, s, CH3); dC
(75 MHz, CDCl3) 203.9, 144.8, 136.6, 136.5, 135.8, 133.9, 130.8, 129.7
(2C), 129.5 (2C), 129.3 (2C), 129.1, 126.6 (2C), 124.2, 123.4, 120.5,
114.2, 112.4, 49.2, 42.1, 21.5, 21.0; m/z (EI, 70 eV) 417 (Mþ, 13), 284
(57), 220 (70), 130 (71), 105 (100), 91 (62), 77(26), 65 (21%).
4.5.4. 1-{6-Chloro-1-[(4-methylphenyl)sulfonyl]-1H-indol-2-yl}bu-
tan-2-one (8d). White solid; yield 73% (2.46 g); mp 131e132 ꢀC
(benzene/petroleum ether). Found: C, 60.52; H, 4.78; N, 3.72.
C19H18ClNO3S requires C, 60.71; H, 4.83; N, 3.73%. Rf¼0.55 (CH2Cl2/
acetone/petroleum ether¼1:1:2); nmax (KBr) 1721, 1454, 1365, 1168,
4.5.9. 5-{6-Chloro-1-[(4-methylphenyl)sulfonyl]-1H-indol-2-yl}-4-
oxopentanoic acid (13a). White solid; yield 45% (1.70 g); mp
147e148 ꢀC (benzene/petroleum ether). Found: C, 56.84; H, 4.15; N,
3.13. C20H18ClNO5S requires C, 57.21; H, 4.32; N, 3.34%. Rf¼0.02
(CH2Cl2/acetone/petroleum ether¼1:1:2); nmax (KBr) 3430, 1712,
1092,1050, 952, 816 cmꢁ1
; dH (300 MHz, CDCl3) 7.97 (1H, d, J 1.8 Hz,
HAr), 7.65 (2H, d, J 8.4 Hz, HTs), 7.33 (1H, d, J 8.4 Hz, HAr), 7.22 (2H, d, J
8.4 Hz, HTs), 7.17 (1H, dd, J 8.4, 1.8 Hz, HAr), 6.46 (1H, s, HInd), 4.07
(2H, s, CH2), 2.59 (2H, q, J 7.5 Hz, CH2), 2.35 (3H, s, CH3), 1.10 (3H, t, J
7.5 Hz, CH3); dC (75 MHz, CDCl3) 206.4, 145.3, 136.9, 135.5, 134.8,
130.2, 129.9 (2C), 127.7, 126.6 (2C), 124.1, 121.2, 114.5, 111.8, 42.5,
35.5, 21.5, 7.6; m/z (EI, 70 eV) 377/375 (Mþ, 11/33), 320/318 (12/36),
254 (64), 219 (27), 164 (57), 128 (22), 91 (50), 57 (100%).
1424, 1360, 1276, 1260, 1172, 1088, 948 cmꢁ1
; dH (300 MHz, CDCl3)
9.92 (1H, br s, OH), 7.97 (1H, s, HAr), 7.63 (2H, d, J 8.2 Hz, HTs),
7.34e7.14 (4H, m, 2HArþ2HTs), 6.49 (1H, s, HInd), 4.11 (2H, s, CH2),
2.89e2.87 (2H, m, CH2), 2.69e2.66 (2H, m, CH2), 2.33 (3H, s, CH3);
dC (75 MHz, CDCl3) 203.9, 178.5, 145.3, 136.9, 135.4, 134.2, 130.3,
130.0 (2C), 127.6, 126.5 (2C), 124.2, 121.3, 114.5, 112.2, 42.7, 36.4,
27.8, 21.5; m/z (EI, 70 eV) 421/419 (Mþ, 2/6), 319 (33), 164 (100),
155(18), 101 (27), 91 (84) 65 (44%).
4.5.5. 1-{1-[(4-Methylphenyl)sulfonyl]-1H-indol-2-yl}acetone
(8e). White solid; yield 83% (2.44 g); mp 97e98 ꢀC (benzene/pe-
troleum ether). Found: C, 66.38; H, 5.11; N, 4.18. C18H17NO3S re-
quires C, 66.03; H, 5.23; N, 4.28%. Rf¼0.56 (CH2Cl2/acetone/
petroleum ether¼1:1:2); nmax (KBr) 1722, 1452, 1361, 1250, 1170,
4.5.10. 5-{6-Methyl-1-[(4-methylphenyl)sulfonyl]-1H-indol-2-yl}-4-
oxopentanoic acid (13b). White solid; yield 43% (1.54 g); mp

626
A.S. Pilipenko et al. / Tetrahedron 68 (2012) 619e627
170e171 ꢀC (benzene/petroleum ether). Found: C, 63.28; H, 5.20; N,
3.36. C21H21NO5S requires C, 63.14; H, 5.30; N, 3.51%. Rf¼0.02
(CH2Cl2/acetone/petroleum ether¼1:1:2); nmax (KBr) 3472, 1712,
102.6, 55.5, 36.7, 32.9, 30.1, 21.5; m/z (EI, 70 eV) 375 (Mþ, 52), 304
(83), 239 (90), 220 (34), 176 (100), 149 (46), 91 (56), 43 (53%).
1360, 1264, 1224, 1172, 1140, 1084, 1052, 828 cmꢁ1
;
dH (300 MHz,
4.6.3. N-[5-Chloro-2-(4-oxopentanoyl)phenyl]-4-methylbenzenesul-
fonamide (11c). White solid; yield 25% (0.28 g); mp 115e116 ꢀC
(AcOEt/petroleum ether). Found: C, 56.72; H, 4.61; N, 3.49.
C18H18ClNO4S requires C, 56.92; H, 4.78; N, 3.69. Rf¼0.05 (AcOEt/
petroleum ether¼1:4); nmax (KBr) 3113, 1716, 1649, 1616, 1397, 1158,
CDCl3) 9.98 (1H, br s, OH), 7.77 (1H, s, HAr), 7.62 (2H, d, J 8.4 Hz, HTs),
7.31 (1H, d, J 7.8 Hz, HAr), 7.19 (2H, d, J 8.4 Hz, HTs), 7.02 (1H, d, J
7.8 Hz, HAr), 6.48 (1H, s, HInd), 4.09 (2H, s, CH2), 2.89e2.86 (2H, m,
CH2), 2.68e2.65 (2H, m, CH2), 2.43 (3H, s, CH3), 2.32 (3H, s, CH3); dC
(75 MHz, CDCl3) 204.3, 178.2, 144.8, 137.2, 135.9, 134.5, 132.8, 129.8
(2C),126.9,126.5 (2C),125.0,120.2,114.6,112.6, 42.9, 36.3, 27.8, 21.9,
21.5; m/z (EI, 70 eV) 399 (Mþ, 3), 299 (12), 234 (13), 144 (100), 115
(10), 91 (31), 65 (17%).
906, 818 cmꢁ1
; dH (300 MHz, CDCl3) 11.47 (1H, br s, NH), 7.80 (1H, d,
J 8.4 Hz, HAr), 7.72 (2H, d, J 8.4 Hz, HTs), 7.66 (1H, d, J 1.8 Hz, HAr),
7.26 (2H, d, J 8.4 Hz, HTs), 6.99 (1H, dd, J 8.4, 1.8 Hz, HAr), 3.20e3.16
(2H, m, CH2), 2.83e2.79 (2H, m, CH2), 2.37 (3H, s, CH3), 2.26 (3H, s,
CH3); dC (75 MHz, CDCl3) 206.8, 201.5, 144.2, 141.0, 140.9, 136.0,
132.1, 129.8 (2C), 127.2 (2C), 122.6, 119.8, 118.3, 36.6, 33.3, 30.0, 21.5;
m/z (EI, 70 eV) 381/379 (Mþ, 12/36), 338/336 (6/18), 310/308 (24/
72), 243 (28), 224 (57),182 (30),180 (44), 155 (52), 91 (100), 65 (32),
55 (31), 43 (32%).
4.5.11. 1-(1-Methanesulfonyl-6-methyl-1H-indol-2-yl)acetone
(14). White solid; yield 68% (1.62 g); mp 159e160 ꢀC (benzene/
petroleum ether). Found: C, 59.08; H, 5.66; N, 5.32. C13H15NO3S
requires C, 58.85; H, 5.70; N, 5.28%. Rf¼0.51 (CH2Cl2/acetone/pe-
troleum ether¼1:1:2); nmax (KBr) 1720, 1452, 1423, 1354, 1330,
1268, 1167, 1060, 974, 810 cmꢁ1
; dH (300 MHz, CDCl3) 7.39 (1H, d, J
Acknowledgements
8.1 Hz, HAr), 7.18 (1H, d, J 0.9 Hz, HAr), 7.08 (1H, dd, J 8.1, 0.9 Hz, HAr),
6.41 (1H, s, HInd), 4.10 (2H, s, CH2), 3.11 (3H, s, CH3), 2.48 (3H, s, CH3),
2.29 (3H, s, CH3); dC NMR (75 MHz, CDCl3) 205.5, 136.7, 134.6, 133.3,
126.7, 124.9, 120.3, 113.6, 111.3, 43.6, 39.1, 29.5, 21.9; m/z (EI, 70 eV)
265 (Mþ, 2), 222 (26),142 (49), 143 (74), 115 (22), 43 (100), 39 (20%).
Financial support was provided by Russian Foundation of Basic
Research (grant 10-03-00254-a) and Ministry of Education and
Science of the Russian Federation (grant 2.1.1/4628). The authors
would like to emphasis their special thanks to Dr. V.E. Zavodnik for
the accomplishment of X-ray analysis.
4.6. Transformation of 2-[2-(tosylamino)phenyl]furans 7aec
induced by ethanolic HCl
Supplementary data
Compound 7 (3 mmol) was added to HCl ethanolic solution
(20 mL) prepared by dissolution of 100 g of gaseous HCl in 200 g of
ethanol. The reaction mixture was refluxed for 6 h. Then it was
poured into cold water. The formed precipitate was filtered off,
washed subsequently with NaHCO3 solution and water, air-dried.
Residue was purified by column chromatography on silica gel us-
ing AcOEt/petroleum ether (1:4) mixture as an eluent affording
compounds 8 and 11. Reaction of 7a (Rf¼0.34) affords 27% 8a
(Rf¼0.16) and 43% 11a (Rf¼0.05); 7b (Rf¼0.29) gives 42% 8b
(Rf¼0.14) and 32% 11b (Rf¼0.04); 7c (Rf¼0.29) gives 30% 8c
(Rf¼0.09) and 25% 11c (Rf¼0.05).
Supplementary data associated with this article can be found in
online version, at doi:10.1016/j.tet.2011.10.114.
References and notes
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fonamide (11a). White solid; yield 43% (0.46 g); mp 111e112 ꢀC
(AcOEt/petroleum ether). Found: C, 63.78; H, 6.11; N, 3.83.
C19H21NO4S requires C, 63.49; H, 5.89; N, 3.90%. Rf¼0.05 (AcOEt/
petroleum ether¼1:4); nmax (KBr) 3089, 1716, 1652, 1596, 1494,
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1402, 1163, 931, 874, 820 cmꢁ1
; dH (300 MHz, CDCl3) 11.42 (1H, br s,
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NH), 7.73 (1H, d, J 8.1 Hz, HAr), 7.69 (2H, d, J 8.1 Hz, HTs), 7.43 (1H, d, J
1.2 Hz, HAr), 7.21 (2H, d, J 8.1 Hz, HTs), 6.83 (1H, dd, J 8.1, 1.2 Hz, HAr),
3.20e3.16 (2H, m, CH2), 2.80e2.76 (2H, m, CH2), 2.35 (3H, s, CH3),
2.30 (3H, s, CH3), 2.26 (3H, s, CH3); dC (75 MHz, CDCl3) 207.1, 201.8,
146.2, 143.8, 140.0, 136.4, 130.9, 129.6 (2C), 127.2 (2C), 123.5, 119.4,
119.1, 36.7, 33.1, 30.1, 22.0, 21.5; m/z (EI, 70 eV) 359 (Mþ, 33), 288
(65), 223 (40), 204 (26), 161 (70), 134 (57), 91 (100), 77 (32), 65 (33),
59 (47), 43(27%).
4.6.2. N-[5-Methoxy-2-(4-oxopentanoyl)phenyl]-4-methylbenzene-
sulfonamide (11b). White solid; yield 32% (0.36 g); mp 114e115 ꢀC
(AcOEt/petroleum ether). Found: C, 60.88; H, 5.63; N, 3.69.
C19H21NO5S requires C, 60.78; H, 5.64; N, 3.73%. Rf¼0.04 (AcOEt/
petroleum ether¼1:4); nmax (KBr) 3402, 1719, 1635,1571, 1510, 1158,
898 cmꢁ1 1H NMR (300 MHz, CDCl3)
; d 11.80 (1H, br s, NH), 7.79
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(1H, d, J 9.0 Hz, HAr), 7.71 (2H, d, J 8.4 Hz, HTs), 7.23 (2H, d, J 8.4 Hz,
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A.S. Pilipenko et al. / Tetrahedron 68 (2012) 619e627
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627
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