PEG-mediated catalyst-free expeditious synthesis of polysubstituted anilines and benzenes via the reaction of malononitrile and β-ketoester derivatives in the presence of activated acetylenes

Article abstract of DOI:10.2174/138620712801619195

Poly(ethylene glycol) (PEG) has been used as a sustainable, non-volatile, and environmentally friendly reaction solvent for synthesis of functionalized anilines and benzenes via the reaction of malononitrile and β-ketoester derivatives in the presence of activated acetylenes at 80o C. No additional solvent and catalyst are required.

Full text of DOI:10.2174/138620712801619195

Combinatorial Chemistry & High Throughput Screening, 2012, 15, 571-575
571
PEG-Mediated Catalyst-Free Expeditious Synthesis of Polysubstituted
Anilines and Benzenes via the Reaction of Malononitrile and ꢀ-Ketoester
Derivatives in the Presence of Activated Acetylenes
Mohammad Piltan*,1, Loghman Moradi2, Hiwa Salimi1, Kiomars Zargoosh3 and Seyed Amir Zarei1
1Department of Chemistry, Sanandaj Branch, Islamic Azad University, Sanandaj, Iran
2Department of Chemistry, Faculty of Science, University of Kurdistan, Sanandaj, Iran
3Department of Chemistry, Isfahan University of Technology, Isfahan, Iran
Abstract: Poly(ethylene glycol) (PEG) has been used as a sustainable, non-volatile, and environmentally friendly reaction
solvent for synthesis of functionalized anilines and benzenes via the reaction of malononitrile and ꢀ-ketoester derivatives
in the presence of activated acetylenes at 80o C. No additional solvent and catalyst are required.
NH2
CO2R
RO2C
R'
R"
R'
R"
CN
2
2
+
R'
CO2R
1
3
R= Me, Et, iPr
i
R'=H, CO2Me, CO2Et, CO2 Pr
R"=CN, CO2Et
Keywords: Activated acetylenes, functionalized anilines and benzenes, malononitrile, PEG, ꢀ-ketoester.
1. INTRODUCTION
and many other industrially relevant materials. The amino
function can be introduced into the benzene ring by a wide
variety of methods, i.e., by the reduction of a nitro moiety,
by the replacement of a halogen atom, by rearrangement
reactions, etc. [7, 8]. Different anilines have also been
obtained by the amination of arenes with azodicarboxylates,
followed by the reduction of the primary-formed hydrazino
intermediates [9, 10], by the Buchwald-Hartwig cross-
coupling reaction [11-13], by the microwave-assisted
replacement of a halogen atom with the amino moiety [14],
etc. Numerous approaches for the synthesis of aromatic
compounds from acyclic precursors have received growing
interest due to their short synthetic steps and the avoidance
of regioisomeric problems.
The concept of “green chemistry” has been widely
adopted to meet the fundamental scientific challenges of
protecting human health and the environment while
simultaneously achieving commercial viability. One of the
thrust areas for achieving this target is to explore alternative
reaction conditions and reaction media to accomplish the
desired chemical transformations with minimum byproducts
and waste generation, as well as eliminating the use of
volatile and toxic organic solvents [1].
Volatile, toxic and hazardous organic solvents are
continuously being replaced either by the use of solvent-free
techniques [2], or by using ionic liquids [3], water [4] or
phase-transfer catalysts [5].
According to the literature, cyanoanilines are the building
blocks of artificial photosynthetic systems [15]. Due to their
semiconducting or nonlinear optical properties [16], these
compounds are useful in fabrication of molecular electronic
devices [17].
Recently PEG is found to be an interesting solvent
system. The important difference between using PEG and
other neoteric solvents is that all of the toxicological
properties, the short and long-term hazards, and the
biodegradability, etc., are established and known. The
application of PEG as a reaction medium is highly beneficial
as the system remains neutral, which helps in maintaining a
wide variety of functional groups unchanged that are either
acid or base susceptible [6].
Recently a green one-pot multicomponent synthesis of
polysubstituted
aniline
derivatives
of
biological,
pharmacological, and optical applications using silica
nanoparticles as reusable catalyst has been reported by
Banerjee et al. [18].
Aromatic amines are very important compounds, being
the structural units of some medicinally important molecules
2. RESULTS AND DISCUSSION
As part of our current studies on the development of new
routes to heterocyclic systems [19-23], we now report the
results of our studies involving the reactions of activated
*Address correspondence to this author at the Department of Chemistry,
Sanandaj Branch, Islamic Azad University, Sanandaj, Iran; Fax: +98-871-
6662740; E-mail: mohammadpiltan@yahoo.com
1875-631X/12 $58.00+.00
© 2012 Bentham Science Publishers

572 Combinatorial Chemistry & High Throughput Screening, 2012, Vol. 15, No. 7
Piltan et al.
acetylenes (1) and malononitrile derivatives (2) in PEG at
800C which led to high polysubstituted aniline derivatives
(3) in the absence catalyst (Scheme 1).
The structures of compounds 4a-4c were assigned based
1
on their IR, H-NMR and 13C-NMR spectral data. In the IR
spectrum of (4a) observed characteristic ester carbonyl
bands. In the 1H-NMR spectrum of (4a), the methoxy
NH2
1
protons resonated at (ꢀ= 3.46, 3.89 and 3.92 ppm). The H
CO2R
RO2C
R'
R"
R'
decoupled 13C-NMR spectrum of (4a) showed 23 distinct
resonances which further confirmed the proposed structure.
The 1H NMR and 13C NMR spectra of (4a–c) were similar to
those for (4a) except for the ester moieties, which exhibited
characteristic resonances in appropriate regions of the
spectrum. The abovementioned reactions in PEG run in the
absence catalyst and products obtained with good yields. It
seems the high viscosity of PEG can increase the contact
surface between the reagents and generate the adequate
position for the reactions to occure.
R"
PEG-400
800C
2
+
CN
R'
CO2R
1
2
3
Scheme 1. Synthesis of high polysubstituted aniline derivatives.
The choice of an appropriate reaction medium is of
crucial importance for successful synthesis. Different
solvents, such as methanol, ethanol, acetonitrile, and
tetrahydrofuran (THF) were explored. The results are
summarized in Table 1.
Although the mechanistic details of the reaction are not
known, a plausible rationalization maybe advanced to
explain the product formation (Scheme 2).
Table 1. Synthetic Results of 3a Under Different Reactions
Conditions
Presumably, the intermediate (5) formed from
malononitrile and dimethylacetylenedicarboxylate attacks to
another
dimethylacetylenedicarboxylate
to
furnish
Entry
Solvent
Temp/°C Time/h
Isolated Yield (%)
intermediate (6), which is converted to heterocyclic
compound (7). Intermediate (7) then undergoes a proton-
transfer reaction to generate product (3a). In summary, we
1
2
3
4
5
PEG-400
Methanol
Ethanol
80
18
20
24
20
20
90
-
Reflux
Reflux
Reflux
Reflux
have reported
a
transformation involving activated
-
acetylenes (1a-e) and malononitrile and ꢀ-ketoester
deravatives (2a-c) in PEG, which leads to the regioselective
synthesis of polysubstituted anilines and benzenes.
THF
-
Acetonitrile
-
3. CONCLUSION
As can be seen from Table 1, the best results were
obtained by heating the reaction mixture in PEG-400 at
800C, which yielded product 3a in high yield (Table 1, entry
1). Encouraged by this success we investigated the scope of
the reaction activated acetylenic compounds (1a-g) with
malononitrile derivatives (2a–b) in PEG-400 at
In conclusion, we have described a convenient route to
polysubstituted anilines and benzenes from malononitrile
and ꢀ-ketoester derivatives and activated acetylenes. The
polysubstituted anilines and benzenes reported in this work
may be considered as potentially useful synthetic
intermediates because they possess atoms with different
oxidation states. The advantage of the present procedure is
that the reaction is performed under neutral conditions by
simple mixing of the starting materials. No additional
solvent and catalyst are required. The simplicity of the
present procedure makes it an interesting alternative to other
approaches.
0
80 C which led to high polysubstituted aniline derivatives
(3a–g) in 32-90% yields (Table 2). The reaction proceeded
smoothly in Poly (ethylene glycol) (PEG) and was complete
within 18 h at 800C.
1
The H and 13C NMR spectra of the crude products
clearly indicated the formation of high functionalized aniline
derivatives (3a–g). The structures of compounds (3a-g) were
deduced from their elemental analyses and their IR, 1H NMR
and 13C NMR analyses. For example, the 1H NMR spectrum
of (3a) exhibited four singlets identified (ꢀ= 3.84, 3.91, 3.92
and 4.00 ppm) as methoxy groups and a broad signal for
Material and Methods
IR Spectra: Shimadzu IR-460 spectrometer. 1H- and 13C-
NMR spectra: Bruker DRX-500 AVANCE instrument; in
CDCl3 at 500.1 and 125.7 MHz, resp.; ꢀ in ppm, J in Hz. EI-
MS (70 eV): Finnigan-MAT-8430 mass spectrometer, in
m/z. Elemental analyses (C, H, N) were performed with a
Heraeus CHN-O-Rapid analyzer. All chemicals were used
as-received from the appropriate suppliers.
1
aniline protons. The H decoupled 13C NMR spectrum of
(3a) showed 15 distinct resonances which further confirmed
the proposed structure. The IR spectrum of (3a) displayed
1
characteristic ester carbonyl bands. The H NMR and 13C
NMR spectra of (3b–g) were similar to those for (3a) except
for the ester moieties, which exhibited characteristic
resonances in appropriate regions of the spectrum.
General Procedure
The reaction of ꢀ-ketoesters with activated acetylenes in
PEG-400 also was investigated at 800C for 12 h that lead to
functionalized benzenes in good yields. The results are
summarized in Table 3.
General procedure for the preparation of compounds 3
and 4: To a stirred solution of 2 (2 mmol) in 1 mL of PEG-
400 was added activated acetylenes (4 mmol) at room
temperature. The reaction mixture was heated at 800C for 12
or 18 h. the product was extracted from the mixture with
diethyl ether (3 ꢁ 4 ml) to afford pure title compound.

Synthesis of Polysubstituted Anilines and Benzenes
Combinatorial Chemistry & High Throughput Screening, 2012, Vol. 15, No. 7 573
Table 2. Reaction of Activated Acetylenic Compounds and Malononitrile Deravatives in PEG-400 at 80 0C
Entry
a
Activated Acetylene
Malononitrile Derivative
Product
Yield%
90
NH2
MeO2C
MeO2C
CN
NC
2a
CN
MeO2C
CO2Me
1a
CO2Me
CO2Me
3a
NH2
MeO2C
CN
H
H
CO2Me
1b
b
c
d
e
f
2a
88
84
81
72
35
H
3b
CO2Me
NH2
EtO2C
CN
EtO2C
CO2Et
2a
2a
2a
1c
EtO2C
CO2Et
CO2Et
3c
NH2
EtO2C
CN
H
H
CO2Et
1d
H
CO2Et
NH2
3d
PrO2iC
CN
PrO2iC
MeO2C
CO2iPr
1e
PrO2iC
CO2iPr
CO2iPr
3e
NH2
O
MeO2C
CO2Et
CO2Me
NC
OEt
1a
MeO2C
CO2Me
CO2Me
2b
3f
NH2
EtO2C
CO2Et
CO2Et
EtO2C
CO2Et
g
2b
32
1c
EtO2C
CO2Et
3g
Table 3. PEG-400 Catalyzed Reaction of ꢀ-Ketoesters with
Tetramethyl 5-amino-6-cyano-1,2,3,4-benzenete tetraca-
rboxylate (3a)
Activated Acetyls
E
E
Yield: 0.31 g (90%), yellow oil. IR (KBr) (vmax/cm-1):
3386, 3332 (NH2), 2351(CN), 1734, 1726, 1720, 1713,
(C=O), 1282 (C–O) cm-1.1H NMR: 3.84 (s, 3H, OCH3), 3.91
(s, 3H, OCH3), 3.92 (s, 3H, OCH3), 4.00 (s, 3H, OCH3) 6.89
(broad, 2H, NH2).13C NMR: 53.0 (OCH3), 53.1 (OCH3), 53.2
(OCH3), 53.6 (OCH3), 97.6 (C), 111.1 (C), 113.7 (C), 123.4
(C), 124.3 (C), 128.8 (C), 152.5 (C), 165.2, 165.5, 166.8,
167.8 (4 C=O, ester). EI-MS: 350 (M+, 6), 114 (34), 59
(100). Anal. Calcd for C15H14N2O8 (350.28): C, 51.43; H,
4.03; N, 8.00. Found: C, 51.48; H, 4.01; N, 7.91.
E
O
O
PEG
80 0
E
R1
+
OR2
C
E
E
R2O2C
R1
2c
4
4
R1
R2
E
Yield%
a
b
c
H
H
Et
Et
CO2Me
CO2Et
95
92
93
Dimethyl 4-amino-5-cyano isophthalate (3b)
Yield: 0.20 g (88%), yellow oil. IR (KBr) (vmax/cm-1):
3412, 3342 (NH2), 2341(CN), 1732, 1717, (C=O), 1261
Br
Me
CO2Me

574 Combinatorial Chemistry & High Throughput Screening, 2012, Vol. 15, No. 7
Piltan et al.
N
N
CO2Me
CO2Me
CO2Me
CO2Me
N
H
H
NC
NC
PEG
PEG
CO2Me
CO2Me
CO2Me
+
+
NC
NC
CO2Me
N
5
H
N
NH2
NH
MeO2C
MeO2C
CN
NC
CO2Me
CO2Me
CO2Me
H shift
NC
H
CO2Me
CO2Me
MeO2C
CO2Me
CO2Me
MeO2C
CO2Me
3a
7
6
Scheme 2. Proposed mechanism for the formation of compound 3a.
(C–O) cm-1.1H NMR: 3.81 (s, 3H, OCH3), 3.85.( s, 3H,
OCH3), 6.77 (broad, 2H, NH2), 8.52(s, 1H, CH), 8.85(s, 1H,
CH) 13C NMR: 53.1 (OCH3), 53.3 (OCH3), 98.2 (C), 114.1
(C), 116.7 (C), 123.4 (C), 128.6 (CH), 132.3 (CH), 151.2
(C), 164.2, 165.5, (2 C=O, ester). EI-MS: 234 (M+, 5), 116
(48), 59 (100). Anal. Calcd for C11H10N2O4 (234.21): C,
56.41; H, 4.30; N, 11.96. Found: C, 56.45; H, 4.38; N, 11.90.
(CHMe2), 67.8 (CHMe2), 68.1 (CHMe2), 98.1 (C), 115.3 (C),
117.1 (C), 125.2 (C), 127.8 (C), 128.3 (C), 153.0 (C), 164.6,
165.1, 165.4, 166.3 (4 C=O, ester). EI-MS: 462 (M+, 7), 114
(60), 87 (100). Anal. Calcd for C23H30N2O8 (462.49): C,
59.73; H, 6.54; N, 6.06. Found: C, 59.70; H, 6.59; N, 6.12.
1-ethyl
2,3,4,5-tetramethyl
6-amino-1,2,3,4,5-benzene
pentacarboxylate (3f)
Tetraethyl 5-amino-6-cyano-1,2,3,4-benzenete tetracar-
boxylate (3c)
Yield: 0.14 g (35%), yellow oil. IR (KBr) (vmax/cm-1):
3462, 3409 (NH2), 1734, 1723, 1716, 1710, 1704, (C=O),
Yield: 0.34 g (84%), yellow oil. IR (KBr) (vmax/cm-1):
3512, 3435 (NH2), 2289(CN), 1728, 1722, 1720, 1714,
1250 (C–O) cm-1.1H NMR: 1.32 (t, J = 7.0 Hz, 3H, CH3),
3
3.82 (s, 3H, OCH3), 3.83 (s, 3H, OCH3), 3.85 (s, 3H, OCH3),
3.87 (s, 3H, OCH3), 4.31 (q, 3J = 7.0 Hz, 2H, OCH2), 6.41
(broad, 2H, NH2).13C NMR: 13.5 (CH3), 51.8 (OCH3), 51.9
(OCH3), 52.0 (OCH3), 52.4 (OCH3), 62.8 (OCH2), 119.5 (C),
120.1 (C), 126.7 (C), 140.4 (C), 141.8 (C), 151.2 (C), 155.5,
159.2, 161.5, 165.8, 167.8 (5C=O). EI-MS: 397 (M+, 7), 88
(56), 73 (40), 59 (100). Anal. Calcd for C17H19NO10 (397.33): C,
51.39; H, 4.82; N, 3.53. Found: C, 51.42; H, 4.85; N, 3.63.
1
(C=O), 1251 (C–O) cm-1. H NMR: 1.17-1.46 (m, 12H,
3
CH3), 3.47 (q, J = 7.0 Hz, 2H, OCH2), 3.70 (q, 3J = 6.9 Hz,
2H, OCH2), 4.22-4.32 (m, 4H, OCH2), 6.79 (broad, 2H,
NH2). 13C NMR (75.5 MHz, CDCl3): ꢀ 14.2 (Me), 14.3
(Me), 15.4 (Me), 15.6 (Me), 62.5 (OCH2), 62.6 (OCH2), 63.0
(OCH2), 63.4 (OCH2), 97.8 (C), 111.9 (C), 114.2 (C), 119.1
(C), 142.1 (C), 144.1 (C), 152.7 (C), 164.5, 165.0, 165.7,
166.6 (4 C=O, ester). EI-MS: 406 (M+, 9), 114 (52), 73
(100). Anal. Calcd for C19H22N2O8 (406.39): C, 56.15; H,
5.46; N, 6.89. Found: C, 56.20; H, 5.40; N, 6.83.
Pentaethyl 6-amino-1,2,3,4,5-benzene pentacarboxylate (3g)
Yield: 0.14 g (32%), yellow oil. IR (KBr) (vmax/cm-1): 3446,
3361 (NH2), 1729, 1722, 1716, 1711 1705 (C=O), 1278 (C–O)
Diethyl 4-amino-5-cyano isophthalate (3d)
1
cm-1. H NMR: 1.32-1.42 (m, 15H, CH3), 4.30-4.38 (m, 4H,
Yield: 0.21 g (81%), yellow oil. IR (KBr) (vmax/cm-1):
3487, 3451 (NH2), 2355(CN), 1728, 1718, (C=O), 1241 (C–
O) cm-1. 1H NMR: 1.22 (t, 3J = 6.9 Hz, 3H, CH3), 1.44 (t, 3J =
7.1 Hz, 3H, CH3), 3.48 (q, 3J = 6.9 Hz,2H, OCH2), 4.45 (q, 3J
= 7.1 Hz, 2H, OCH2), 6.67 (broad, 2H, NH2), 8.37(s, 1H,
CH), 8.73 (s, 1H, CH). 13C NMR: 14.7 (Me), 14.9 (Me), 62.1
(OCH2), 62.3 (OCH2), 97.1 (C), 112.5 (C), 115.2 (C), 121.3
(C), 131.0 (CH), 134.8 (CH), 145.7 (C), 165.5, 165.9, (2
C=O, ester). Anal. Calcd for C13H14N2O4 (262.26): C, 59.54;
H, 5.38; N, 10.68. Found: C, 59.50; H, 5.42; N, 10.65.
2OCH2), 4.42-4.48 (m, 4H, 2OCH2), 4.45 (q, 3J = 7.01 Hz, 2H,
OCH2), 6.35 (broad, 2H, NH2). 13C NMR: 13.5 (Me), 14.2
(Me), 14.3 (Me), 14.4 (Me), 15.2 (Me), 60.5 (OCH2), 61.6
(OCH2), 62.6 (OCH2), 63.0 (OCH2), 63.4 (OCH2), 119.6 (C),
122.6 (C), 125.6 (C), 140.5 (C), 146.6 (C), 151.2 (C), 163.2,
164.5, 165.0, 165.7,166.6 (5C=O). MS (EI, 70 eV): EI-MS: 453
(M+, 8), 88 (51), 73 (100). Anal. Calcd for C21H27NO10
(453.44): C, 55.6; H, 6.00; N, 3.09. Found: C, 55.7; H, 5.96; N,
3.12.
Biphenyl-2,3,4,5,6-pentacarboxylic acid 6-ethyl ester 2,3, 4,5-
tetramethyl ester (4a)
Tetraisopropyl 5-amino-6-cyano-1,2,3,4-benzenete tetra-
carboxylate (3e)
Yield 0.43g (95%). Colorless crystalline solid, mp 125–
127oC. IR (KBr) (vmax/cm-1): 1738, 1725, 1723, 1712, 1708
(C=O), 1251 (C–O) cm-1. 1H NMR: 0.89 (m, 3H, CH3), 3.46 (s,
3H, OCH3 ), 3.89 (s, 6H, 2OCH3 ), 3.92 (s, 3H, OCH3), 3.95–
3.99 (m, 2H, OCH2), 7.21–7.40 (m, 5H, 5CH). 13C NMR: 13.8,
52.3, 53.4, 54.5, 55.7, 66.1, 127.6, 127.9 (2CH), 128.4 (2CH),
131.1, 131.4, 132.1, 135.9, 136.4, 136.6, 140.3, 165.2, 165.3,
165.7, 165.8, 166.2. Anal. Calcd for C23H22O10 (458.41): C,
60.26; H, 4.84. Found: C, 60.18; H, 4.80.
Yield: 0.33 g (72%), yellow oil. IR (KBr) (vmax/cm-1):
3436, 3379 (NH2), 2286(CN), 1731, 1724, 1713, 1696,
1
3
(C=O), 1267 (C–O) cm-1. H NMR: 1.32 (d, J = 7.0 Hz, 6
H, CHMe2), 1.37 (d, 3J = 7.0 Hz, 6 H, CHMe2), 1.42 (d, 3J =
3
7.0 Hz, 6 H, CHMe2), 1.48 (d, J = 7.0 Hz, 6 H, CHMe2),
5.01–5.12 (m, 2H, 2CHMe2), 5.23–5.34 (m, 2H, 2CHMe2),
6.75 (broad, 2H, NH2). 13C NMR: 21.
(CHMe2), 214
(CHMe2), 21.6 (Cꢁꢀe2), 21.8 (Cꢁꢀe2), 67.3 (CHMe2), 67.5

Synthesis of Polysubstituted Anilines and Benzenes
Combinatorial Chemistry & High Throughput Screening, 2012, Vol. 15, No. 7 575
[11]
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a) Fox, M. A.; Chanon, M. Eds. Photoinduced Electron Transfer;
Elsevier: Amsterdam, 1988. b) Kurreck, H.; Huber M. Model reactions
for photosynthesis-photoinduced charge and energy-transfer between
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a) Prasad, P. N.; Williams, D. J. Introduction to Nonlinear Optical
Effects in Molecules and Polymers; Wiley: New York, 1991. (b) Nalwa,
H. S. Organic materials for third-order nonlinear optics. Adv. Mater.,
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Biphenyl-2,3,4,5,6-pentacarboxylic acid pentaethyl ester (4b)
Yield 0.47g (92%). Colorless crystalline solid, mp 122–124
oC. IR (KBr) (vmax/cm-1): 1738, 1725, 1718 (C=O), 1259 (C–O)
cm-1. 1H NMR: 0.89-1.04 (m, 15H, 5 CH3), 3.91–4.30 (m, 10H,
5OCH2), 7.20–7.38 (m, 5H, 5CH). 13C NMR: 13.2, 13.5, 13.6,
62.1, 62.2, 62.4, 126.6, 128.3, 128.2, 131.2, 132.2, 135.8, 136.3,
140.2, 165.4, 165.8, 166.3. Anal. Calcd for C27H30O10 (514.52):
C, 63.03; H, 5.88. Found: C, 63.11; H, 5.83.
4'-Bromo-biphenyl-2,3,4,5,6-pentacarboxylic acid penta-
methyl ester (4c)
Yield 0.50g (93%). Colorless crystalline solid, mp 147–148
oC. IR (KBr) (vmax/cm-1): 1742, 1731, 1724 (C=O), 1252 (C–O)
cm-1. 1H NMR: 3.51 (s, 6H, 2 OCH3), 3.85 (s, 3H, OCH3), 3.90
(s, 6H, 2 OCH3), 7.07 (2H, d, 3J= 8.2 Hz, 2CH), 7.49 (d, 2H, 3J=
8.3 Hz, 2CH). 13C NMR: 52.3, 53.5, 53.6, 123.1, 130.2, 131.6,
131.7, 133.1, 134.3, 135.9, 138.2, 165.3, 165.8, 166.2. Anal.
Calcd for C22H19BrO10 (537.31): C, 50.50; H, 3.66. Found: C,
50.61; H, 3.68.
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Received: June 3, 2011
Revised: November 24, 2011
Accepted: January 26, 2012