Synthesis of polysubstituted pyrroles in aqueous medium directly from nitro compounds

Article abstract of DOI:10.1134/S1070363215010272

A novel approach for the synthesis of polysubstituted pyrroles has been followed through multicomponent reaction of nitro compounds, phenacyl bromide or its derivatives and dialkyl acetylene dicarboxylates using indium in dilute aqueous HCl at room temperature. The products are formed in high yields (75-87%) in 10-16 h.

Full text of DOI:10.1134/S1070363215010272

ISSN 1070-3632, Russian Journal of General Chemistry, 2015, Vol. 85, No. 1, pp. 155–161. © Pleiades Publishing, Ltd., 2015.
Synthesis of Polysubstituted Pyrroles in Aqueous Medium
Directly From Nitro Compounds1
L. Madhava Reddy, P. Chandrashekar, A. R. Reddy, and C. K. Reddy
Department of Chemistry, University College of Science, Osmania University, Hyderabad, 500007 India
e-mail: krreddych@gmail.com
Received September 5, 2014
Abstract—A novel approach for the synthesis of polysubstituted pyrroles has been followed through multicom-
ponent reaction of nitro compounds, phenacyl bromide or its derivatives and dialkyl acetylene dicarboxylates
using indium in dilute aqueous HCl at room temperature. The products are formed in high yields (75–87%) in
10–16 h.
Keywords: polysubstituted pyrrole, three component reaction, In/HCl, nitro compounds
DOI: 10.1134/S1070363215010272
INTRODUCTION
RESULTS AND DISCUSSION
Pyrroles are valuable and important heterocyclic
compounds. They were found in different natural
bioactive molecules [1], including drugs like atrovastin
calcium, and pharmaceutical agents [2]. They are also
versatile synthetic intermediates in organic synthesis
[3]. Some of the pyrrole derivatives are widely applied
in material science [4]. A number of procedures have
been developed for the synthesis of pyrrole-containing
new heterocyclic molecules because of their biological
activity and synthetic utility. One of the simplest
syntheses is the Paal-Knorr synthesis which involves
condensation of 1,4-dicarbonyl compounds with
primary amines in the presence of acids/metal catalysts
[5]. Later, high atom economy multicomponent pro-
tocols have been developed for the synthesis of
pyrroles [6]. However, many of the developed methods
suffer from various drawbacks such as harsh reaction
conditions, tedious experimental procedure, unsatis-
factory yields and long reaction time [7]. Herein, we
describe an efficient new multicomponent reaction for
the synthesis of the polysubstituted pyrroles starting
from nitro compounds in aqueous medium.
Initially, the reaction of nitro compounds, phenacyl
bromide, and dialkyl acetylene dicarboxylate was
conducted using different metals such as Fe, Zn, Sn,
and In in aqueous HCl at room temperature (Table 1).
Considering the reaction time and the yield of the
prepared pyrrole, indium was found to be most
effective. Subsequently, it was applied to prepare a
series of pyrroles from phenacyl bromide or its
derivatives, dialkyl acetylene dicarboxylates and
different nitro compounds (Table 2). The reaction was
complete within 10–16 h and the products were formed
in good yields (75–87%). The derivatives of phenacyl
bromide containing electron withdrawing groups also
afforded the products smoothly. Dimethyl as well as
diethyl acetylene dicarboxylate were applied to prepare
Table 1. Synthesis of polysubstituted pyrroles using different
metalsa
Run no.
Metala
Zn
Time, h
24
Yield, %b
1
2
3
4
59
61
65
87
Sn
24
Polysubstituted pyrroles were directly obtained by
the multicomponent reaction of nitro compounds, phe-
nacyl bromide or its derivatives and dialkyl acetylene-
dicarboxylates by using indium metal powder in dilute
aqueous HCl at room temperature (Scheme 1).
Fe
24
In
10
a
Reaction conditions: nitrobenzene (1 mmol), 1 N aqueous HCl
(1 mL), metal (2 mmol), dimethyl acetylene dicarboxylate
(1 mmol), phenacyl bromide (1.1 mmol), and 5 mL of water at
b
room temperature. Yields of isolated pure compound after
1 The text was submitted by the authors in English.
column chromatography.
155

156
MADHAVA REDDY et al.
Scheme 1.
COOR1
COOR1
COOR1
O
In/HCl
H2O
R
NO2
Ar
Br
RT, 10−16 h
Ar
N
COOR1
R
IV
I
II
III
(75−87%)
I: R = Aryl, Alkyl, II: Ar = Phenyl, III, IV: R1 = Me, Et.
Scheme 2.
COOR1
O
Ar
InCl3
In/HCl
Ar
COOR1
COOR1
COOR1
COOR1
COOR1
Br
RNO2
RNH2
II
III
O
I
−HBr
NH
H2N
R
R
A
B
InCl3
COOR1
COOR1
HO
Ar
−H2O
Ar
COOR1
COOR1
N
R
N
R
the pyrrole derivatives. The structure of the products
CDCl3; δ, ppm; internal standard – Me4Si, J,n Hz. ESI-
MS: Finnigan MAT 1020 mass spectrometer.
1
was established by IR, H and 13C NMR spectroscopy
and mass spectrometry.
General procedure. To a mixture of nitro
compound I (1.0 mmol) were added indium metal
powder (325 mesh, 2 mmol), 1 N aqueous HCl (1 mL),
dialkyl acetylene dicarboxylate (1.0 mmol). After
5 min, phenacyl bromide or its derivative (1.1 mmol)
was added. The reaction mixture was stirred at room
temperature for 10–16 h and monitored by TLC. After
completion, the reaction mixture was washed with
saturated NaHCO3 solution (3 × 5 mL) and water (3 ×
5 mL) and extracted with EtOAc (3 × 5 mL). The
extract was concentrated and the residue was subjected
to column chromatography (silica gel, hexane/EtOAc)
to obtain pure product.
The present synthesis of polysubstituted pyrroles
consists of three steps in one pot. Initially, the nitro
compounds I on treatment with In/HCl are reduced to
amines, which then react with dialkyl acetylene
dicarboxylate III to form zwitter-ion A [8] and the
reaction of the latter with phenacyl bromide II to
produce intermediate B. Cyclisation of B followed by
aromatization afforded the polysubstituted pyrroles IV
(Scheme 2).
EXPERIMENTAL
TLC: Precoated silica-gel plates (60 F254, 0.2-mm
layer, E. Merck). Column chromatography: Silica gel,
60–120 mesh. mp: Fischer-Johns apparatus; uncor-
rected. IR Spectra: Thermo Nicolet Nexus 670 FT-IR
1
The IR, H and 13C NMR and mass spectra and
analytical data of the products are given below.
Dimethyl 1,5-diphenyl-1H-pyrrole-2,3-dicarboxylate
(IVa). IR spectrum, ν, cm–1: 1727, 1498, 1447, 1255.
1H NMR spectrum: δ, ppm: 7.52–7.21 m (10H), 6.98 s
1
spectrophotometer; in KBr. H and 13C NMR spectra:
Bruker Avance 300 and Innova 75 MHz instrument, in
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SYNTHESIS OF POLYSUBSTITUTED PYRROLES IN AQUEOUS MEDIUM
157
Table 2. Synthesis of polysubstituted pyrroles using indium metal in aqueous HCl at room temperature
Comp.
no.
Nitro
compounds
Dialkyl acetylene
dicarboxylate
Polysubstituted
pyrrole
Isolated
yield, %
Phenacyl bromide
Time, h
10
COOMe
IVa
87
NO2
COOMe
COOMe
COOMe
O
N
Br
IVb
10
13
86
85
COOEt
NO2
COOEt
COOEt
COOEt
O
N
Br
COOMe
IVc
NO2
COOMe
COOMe
COOMe
O
N
Br
Br
Br
COOEt
IVd
13
84
NO2
COOEt
O
COOEt
COOEt
Br
N
Br
Br
COOMe
IVe
16
75
COOMe
COOMe
COOMe
NO2
O
O2N
N
Br
O2N
COOMe
IVf
12
81
NO2
COOMe
COOMe
COOMe
O
N
Br
F
F
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MADHAVA REDDY et al.
Dialkyl
Table 2. (Contd.)
Comp.
no.
Nitro
compounds
Polysubstituted
pyrrole
Time, Isolated
Phenacyl bromide
acetylene
h
yield, %
dicarboxylate
IVg
12
75
COOEt
NO2
COOEt
O
COOEt
COOEt
N
O2N
Br
F
F
O2N
IVh
12
82
COOMe
NO2
COOMe
COOMe
COOMe
O
N
Br
CH3
NO2
CH3
IVi
12
82
COOEt
COOEt
O
COOEt
COOEt
Br
N
CH3
NO2
CH3
IVj
16
80
COOMe
O
COOMe
COOMe
COOMe
Br
N
O2N
CH3
CH3
O2N
COOMe
COOMe
IVk H3C–NO2
10
85
O
COOMe
COOMe
N
Br
CH3
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SYNTHESIS OF POLYSUBSTITUTED PYRROLES IN AQUEOUS MEDIUM
159
Table 2. (Contd.)
Dialkyl
acetylene
dicarboxylate
Comp.
no.
Nitro
compounds
Polysubstituted
Time, Isolated
Phenacyl bromide
pyrrole
h
yield, %
O
COOEt
IVl
H3CH2C–NO2
COOMe
10
83
COOEt
Br
COOMe
N
CH2CH3
(1H), 3.81 s (3H); 3.69 s (3H). 13C NMR spectrum: δ,
ppm: 167.1, 160.8, 139.6, 133.3, 128.8, 128.2, 127.9,
127.0, 126.1, 126.0 125.1, 123.2, 122.4, 117.1, 52.4,
52.0. ESI-MS: m/z 336 [M + H]+; Calculated, %: C
71.64; H 5.08; N 4.18. C20H17NO4. Found, %: C 71.58;
H 5.12; N 4.22.
Calculated, %: C 60.00; H 4.55; N 3.18. C22H20BrNO4.
Found, %: C 60.21; H 4.62; N 3.12.
Dimethyl 5-(4-nitrophenyl)-1-phenyl-1H-pyrrole-
2,3-dicarboxylate (IVe). IR spectrum, ν, cm–1: 1712,
1
1600, 1511, 1443. H NMR spectrum, δ, ppm: 8.22 d
(2H, J = 8.0 Hz), 7.58 d (2H, J = 8.0 Hz); 7.51–7.41 s
(3H); 7.39–7.32 m (2H); 7.02 s (1H); 3.82 s (3H); 3.71
s (3H). 13C NMR spectrum, δ, ppm: 166.2, 160.1,
146.5, 139.9, 138.2, 129.6, 129.0, 128.2, 126.1, 126.0,
125.2, 123.8, 122.0, 120.5, 52.1, 52.0; ESI-MS: m/z
381 [M + H]+. Calculated, %: C 63.17, H 4.21, N 7.37.
C20H16N2O6. Found, %: C 63.23, H 4.26, N 7.31.
Diethyl 1,5-diphenyl-1H-pyrrole-2,3-dicarboxylate
(IVb). IR spectrum, ν, cm–1: 1720, 1598, 1502, 1413,
1
1240. H NMR spectrum, δ, ppm: 7.49–7.20 m (10H),
6.93 s (1H), 4.28 q (2H, J = 7.0 Hz), 4.16 q (2H, J =
7.0 Hz), 1.24 t (3H, J = 7.0 Hz), 1.12 t (3H, J = 7.0 Hz).
13C NMR spectrum, δ, ppm: 166.4, 160.1, 146.5,
140.0, 133.1, 128.8, 128.2, 127.9, 127.1, 126.4, 125.9,
124.4, 123.2, 122.2, 61.5, 61.0, 14.0, 13.9. ESI-MS: m/
z 364 [M + H]+; Calculated, %: C22H21NO4: C 72.73; H
5.79; N 3.86%. Found, %: C 72.85; H 5.72; N 3.82%.
Dimethyl 1-(4-fluorophenyl)-5-phenyl-1H-pyrrole-
2,3-dicarboxylate (IVf). IR spectrum, ν, cm–1: 1714,
1
1451, 1415. H NMR spectrum, δ, ppm: 7.50–7.29 m
(7H), 7.12 t (2H, J = 7.0 Hz), 6.98 s (1H), 3.83 s (3H),
3.71 s (3H). 13C NMR spectrum, δ, ppm: 166.0 d (J =
280 Hz), 161.1, 160.1, 146.9, 141.0, 138.3, 132.5,
129.2, 129.0, 127.8, 127.2, 126.7, 125.5, 121.2, 115.2,
115.0 d (J = 30 Hz), 52.2, 51.7. ESI-MS: m/z 354 [M +
H]+; Calculated, %: C 67.99; H 4.53; N 3.97.
C22H16FNO4. Found, %: C 67.89; H 4.56; N 3.91.
Dimethyl 5-(4-bromophenyl)-1-phenyl-1H-pyrrole-
2,3-dicarboxylate (IVc). IR spectrum, ν, cm–1: 1716,
1
1450, 1412. H NMR spectrum, δ, ppm: 7.52–7.41 m
(5H), 7.38–7.21 m (4H), 6.92 s (1H), 3.81 s (3H), 3.69
s (3H). 13C NMR spectrum, δ, ppm: 166.6, 160.4,
140.0, 139.2, 132.2, 131.1, 130.8, 129.0, 128.5, 126.0,
125.2, 124.2, 123.5, 120.2, 52.2, 52.0. ESI-MS: m/z
414, 416 [M + H]+; Calculated, %: C 57.97; H 3.86.
C20H16BrNO4. Found, %: C 57.91; H 3.82; N 3.41.
Diethyl 1-(4-fluorophenyl)-5-(4-nitrophenyl)-1H-
pyrrole-2,3-dicarboxylate (IVg). IR spectrum, ν, cm–1:
1
1721, 1600, 1515. H NMR spectrum, δ, ppm: 8.22 d
(2H, J = 8.0 Hz), 7.59 d (2H, J = 8.0 Hz), 7.35 t (2H,
J = 8.0 Hz), 7.12 t (2H, J = 8.0 Hz), 7.00 s (1H), 4.30 q
(2H, J = 7.0 Hz), 4.15 q (2H, J = 7.0 Hz), 1.20 t (3H,
J = 7.0 Hz), 0.88 t (3H, J = 7.0 Hz); 13C NMR
spectrum, δ, ppm: 168.1 d (J = 280 Hz), 164.9, 161.4,
147.0, 140.1, 135.8, 130.9, 129.1, 129.0, 128.9, 125.1,
123.5, 122.2, 121.1, 115.6, 115.0 d (J = 30 Hz), 61.2,
60.8, 13.0, 12.9. ESI-MS: m/z 449 [M + Na]+;
Calculated, %: C 72.21; H 5.44; N 4.01. C21H19NO4.
Found, %: C 72.28; H 5.40; N 4.07.
Diethyl 5-(4-bromophenyl)-1-phenyl-1H-pyrrole-
2,3-dicarboxylate (IVd). IR spectrum, ν, cm–1: 1716,
1452, 1403. 1H NMR spectrum, δ, ppm: 7.52–7.38 m
(6H), 7.40–7.25 m (3H), 6.91 s (1H), 4.25 q (2H, J =
7.0 Hz), 4.12 q (2H, J = 7.0 Hz), 1.22 t (3H, J =
7.0 Hz), 1.11 t (3H, J = 7.0 Hz). 13C NMR spectrum, δ,
ppm: 166.1, 160.2, 141.3, 139.2, 132.1, 131.8, 129.2,
129.0, 128.2, 126.1, 125.6, 124.6, 123.4, 121.0, 61.2,
61.0, 13.9, 13.2. ESI-MS: m/z 444, 442 [M + H]+;
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MADHAVA REDDY et al.
Dimethyl 5-phenyl-1-p-tolyl-1H-pyrrole-2,3-di-
127.2, 126.4, 123.9, 123.2, 122.0, 120.1, 61.0, 60.3,
44.5, 17.0, 13.7 (2Me). ESI-MS: m/z 316 [M + H]+;
Calculated, %: C 68.57; H 6.67; N 4.44. C18H21NO4.
Found, %: C 68.69; H 6.61; N 4.40.
carboxylate (IVh). IR spectrum, ν, cm–1: 1720, 1659,
1
1451, 1415. H NMR spectrum, δ, ppm: 7.43–7.31 m
(3H), 7.30–7.20 m (4H), 7.19–7.02 m (2H), 6.95 s
(1H), 3.81 s (3H), 3.70 s (3H), 2.41 s (3H); 13C NMR
spectrum, δ, ppm: 167.1, 161.1, 142.1, 138.7, 136.3,
133.3, 131.2, 129.2, 128.6, 128.4, 128.2, 128.0, 127.2,
125.6, 51.8, 51.2, 22.0. ESI-MS: m/z 350 [M + H]+;
Calculated, %: C 72.21, H 5.44; N 4.01. C21H19NO4.
Found, %: C 72.28; H 5.40; N 4.07.
CONCLUSIONS
We have developed a novel efficient method for the
one pot synthesis of polysubstituted pyrroles involving
the reaction of nitro compounds, phenacyl bromide and
dialkyl acetylene dicarboxylate with indium metal in
dilute aqueous HCl at room temperature. The direct
application of nitro compounds, reaction in water, mild
experimental conditions, smooth conversion, and
impressive yields are the advantages of the present
method.
Diethyl
5-phenyl-1-p-tolyl-1H-pyrrole-2,3-di-
carboxylate (IVi). IR spectrum, ν, cm–1: 1720, 1601,
1
1519, 1460. H NMR spectrum, δ, ppm: 7.42 d (2H,
J = 8.0 Hz), 7.33 t (2H, J = 8.0 Hz), 7.30–7.21 m (5H),
6.94 s (1H), 4.30 q (2H, J = 7.0 Hz), 4.15 t (2H, J =
7.0 Hz), 2.41 s (3H), 1.31 t (3H, J = 7.0 Hz), 1.18 t
(3H, J = 8.0 Hz). 13C NMR spectrum, δ, ppm: 166.7,
160.1, 138.9, 137.1, 133.8, 131.1, 129.8, 128.5, 127.8,
127.0, 126.1, 126.0, 124.6, 121.4, 61.2, 61.0, 21.0,
13.6, 13.5. ESI-MS: m/z 378 [M + H]+; Calculated, %:
C 73.21; H 6.10; N 3.71. C23H23NO4. Found, %: C
73.29; H 6.15; N 3.78.
ACKNOWLEDGMENTS
The authors are thankful to CSIR and UGC New
Delhi for financial assistance.
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SYNTHESIS OF POLYSUBSTITUTED PYRROLES IN AQUEOUS MEDIUM
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