Leucoemeraldine-Base-Catalyzed Knoevenagel Condensation

Article abstract of DOI:10.1080/00397910902730853

A facile method for Knoevenagel condensation has been developed by using Leucoemeraldine base as catalyst to give substituted alkenes in excellent yields. The recycling of the solid catalyst was investigated.

Full text of DOI:10.1080/00397910902730853

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Leucoemeraldine-Base-
Catalyzed Knoevenagel
Condensation
a
a
a
Ai-Qin Zhang , Ning Zhang , Sanguo Hong & Ming
b
Zhang
a
Department of Chemistry, Nanchang University,
Nanchang, China
b
Chemistry College, Jiangxi Normal University,
Nanchang, Jiangxi, China
Published online: 03 Aug 2009.
To cite this article: Ai-Qin Zhang , Ning Zhang , Sanguo Hong & Ming Zhang
(2009) Leucoemeraldine-Base-Catalyzed Knoevenagel Condensation, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 39:17, 3024-3030
To link to this article: http://dx.doi.org/10.1080/00397910902730853
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1
Synthetic Communications , 39: 3024–3030, 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910902730853
Leucoemeraldine-Base-Catalyzed
Knoevenagel Condensation
1
Ai-Qin Zhang, Ning Zhang, Sanguo Hong, and Ming Zhang
Department of Chemistry, Nanchang University, Nanchang, China
Chemistry College, Jiangxi Normal University, Nanchang, Jiangxi, China
1
1
2
1
2
Abstract: A facile method for Knoevenagel condensation has been developed by
using Leucoemeraldine base as catalyst to give substituted alkenes in excellent
yields. The recycling of the solid catalyst was investigated.
Keywords: Catalysis, Knoevenagel condensation, Leucoemeraldine base
INTRODUCTION
The Knoevenagel condensation, named after Emil Knoevenagel, is one of
the most important reactions in organic synthesis for carbon–carbon
bond formation. There are many reports of this type of reaction. The
Knoevenagel condensation is a base- or acid-catalyzed reaction. It may
be performed either in homogeneous or heterogeneous phase. The usual
[1]
[2]
base catalysts are ethylenediamine, piperidine, its corresponding
[3]
ammonium salts, dimethylaminopyridine, or amino acids such as gly-
[
4]
[5]
[6]
cine, alanine, and L-proline. However, many of the methods suffer
from generality and use of expensive or toxic reagents, and catalysts can-
not be reused. Therefore, the development of a new, efficient, and envir-
onmentally benign protocol for the condensation is still needed. To our
Received September 4, 2008.
Address correspondence to Ming Zhang, Chemistry College, Jiangxi Normal
University, 99 Ziyangdadao, Nanchang, Jiangxi 330022, China. E-mail: zmchem@
163.com
3
024

Leucoemeraldine-Base-Catalyzed Condensation
3025
knowledge, there are no reports for Knoevenagel condensation using leu-
coemeraldine base, Herein, we report the use of Leucoemeraldine base
[
25233-30-1] as a novel and reusable catalyst for the Knoevenagel con-
7]
[
densation.
RESULTS AND DISCUSSION
Leucoemeraldine base is a light purple powder prepared from aniline
(Scheme 1); because it is insoluble in ethanol and isopropyl alcohol, it
can be used as a reusable solid base.
The results are listed in Table 1. They show that Leucoemeraldine
base is an efficient catalyst for Knoevenagel condensation (Scheme 2).
Moreover, it is cheap, and the protocol is an environmentally benign
method.
The rate of reaction of malononitrile and aldehyde is faster than
that of ethyl cyanoacetiate and the same aldehyde. The separation
of the products is simple: only filtration, not recrystallization, is
necessary.
CONCLUSIONS
In conclusion, we have developed a convenient method for Knoevenagel
condensation. The procedure offers several advantages, including opera-
tional simplicity and inexpensive reagents, and it is an environmentally
benign method.
Scheme 1. Preparation of Leucoemeraldine base.

3026
A.-Q. Zhang et al.
a
Table 1. Catalyzed Knoevenagel condensation
Entry substrate
1
R
Product
Reaction time (h)
2
Yield (%)
b
COOEt
88 (87, 86, 86)
2
3
4
5
CN
1
2
1
2
93
83
88
86
COOEt
CN
COOEt
6
7
CN
1
2
90
85
COOEt
8
9
CN
1
2
1
90
86
90
COOEt
CN
1
0
1
1
1
2
COOEt
CN
2
1
87
91
a
All the products gave melting points and spectral data consistent with the
8,9]
[
reported data.
b
Isolated yield after recycling of catalyst.

Leucoemeraldine-Base-Catalyzed Condensation
3027
Scheme 2. The Knoevenagel condensation.
EXPERIMENTAL
General Procedures
Melting points were determined in open capillaries and are uncorrected.
1
H NMR was measured on a Bruker 400 MHz spectrometer with
tetramethylsilane (TMS) as internal standard. Infrared (IR) spectra were
measured on a Nicolet Magna-IR550 spectrometer.
Preparation of Leucoemeraldine Base
Under an N atmosphere, aniline (2.4 g), concentrated hydrochloric acid
2
(
solution, and then a solution of ammonium peroxydisulfate (4.5 g) in
2.5 mL), and distilled water (33 mL) were mixed to be a homogeneous
ꢀ
distilled water (10 mL) was added slowly to the solution at 25 C to ini-
tiate the polymerization of aniline. Afer 10 h, the solid product was col-
lected and rinsed with distilled water and then with ethanol to give the
Emeraldine salt. The Emeraldine salt was then dispersed in ammonium
hydroxide (40 mL, 10%) to give the Emeraldine base form of polyaniline
(
PEM). PEM (1 g) was dispersed in dimethylformamide (DMF) (40 mL),
phenylhydrazine (20 mL) was added and reacted for 8 h, and the powder
was collected by filtration, washed with ethanol (80 mL), and dried
under vacuum to give the Leucoemeraldine-base form of polyaniline
(
PLM).
General Synthetic Procedure
Leucoemeraldine base (0.1 g) was added to a mixture of aldehyde
(
(
10 mmol) and active methylene compound (10 mmol) in ethanol
10 ml). The solution was stirred for a specified time at reflux. Leuco-
emeraldine base was removed by filtration, water (100 ml) was
added to the filtrate, and the mixture was stirred for a moment, then
filtered. The product is pure enough, and recrystallization is not
necessary.

3028
A.-Q. Zhang et al.
Selected Data
Ethyl (E)-2-Cyano-3-phenyl-2-propenoate (a)
ꢀ
Mp 50–51 C. IR (KBr): t 3030, 2984, 2225, 1721, 1601, 1441, 1257, 1201,
ꢁ
1 1
1
089, 769 cm . H NMR (400 MHz, CDCl ): d 1.41 (t, J ¼ 7.2 Hz, 3H),
3
4
.39 (q, J ¼ 7.2 Hz, 2H), 7.49–7.59 (M, 3H), 7.99 (d, J ¼ 7.6 Hz, 2H), 8.26
(s, 1H).
2
-(Phenylmethylene) Malononitrile (b)
ꢀ
ꢁ1
.
Mp 83–84 C. IR (KBr): t 3033, 2223, 1591, 1257, 1568, 1491, 1450 cm
1
H NMR (400 MHz, CDCl ): d 7.55 (t, J ¼ 8 Hz, 2H), 7.64 (t, J ¼ 7.6 Hz,
3
1
H), 7.78 (s, 1H), 7.91 (d, J ¼ 7.6 Hz, 2H).
Ethyl (E)-2-Cyano-3-(2-chloro phenyl)-2-propenoate (c)
ꢀ
Mp 51–52 C. IR (KBr): t 2992, 2225, 1729, 1609, 1465, 1265, 1201,
ꢁ
1
1
7
53 cm . H NMR (400 MHz, CDCl ): d 1.42 (t, J ¼ 7.2 Hz, 3H), 4.41
3
(
(
q, J ¼ 7.2 Hz, 2H), 7.40–7.53 (m, 3H), 8.24 (d, J ¼ 7.6 Hz, 1H), 8.70
s, 1H).
2
-(2-Chlorophenylmethylene)malononitrile (d)
ꢀ
ꢁ1
.
Mp 95–96 C. IR (KBr): t 3050, 2231, 1509, 1609, 1464, 1441, 758 cm
1
H NMR (400 MHz, CDCl ): d 7.46 (m, 1H), 7.55 (d, J ¼ 3.6 Hz, 2H),
3
8
.20 (d, J ¼ 8 Hz, 1H), 8.28 (s, 1H).
Ethyl (E)-2-Cyano-3-(4-hydroxy phenyl)-2-propenoate (e)
ꢀ
Mp 172–173 C. IR (KBr): t 3320, 2993, 2225, 1713, 1585, 1521, 1441,
ꢁ
1 1
1
281, 1169, 841 cm . H NMR (400 MHz, CDCl ): d 1.40 (t, J ¼ 7.2 Hz,
3
3
(
H), 4.37 (q, J ¼ 7.2 Hz, 2H), 6.27 (s, 1H), 6.96 (d, J ¼ 8.8 Hz, 2H), 7.95
d, J ¼ 8.8 Hz, 2H), 8.19 (s, 1H).
2
-(4-Hydroxyphenylmethylene) Malononitrile (f)
ꢀ
Mp 188–189 C. IR (KBr): t 3400, 3030, 2929, 2231, 1611, 1586, 1567,
ꢁ
1
1
1
520, 1444 cm . H NMR (400 MHz, CDCl ). d 6.00 (s, 1H), 6.95
3
(d, J ¼ 8.4 Hz, 2H), 7.65 (s, 1H), 7.87 (d, J ¼ 8.8 Hz, 2H).

Leucoemeraldine-Base-Catalyzed Condensation
3029
Ethyl (E)-2-Cyano-3-(4-methoxy phenyl)-2-propenoate (g)
ꢀ
Mp 82–83 C. IR (KBr): t 3017, 2992, 2216, 1721, 1577, 1513, 1185,
ꢁ
1
1
8
33 cm . H NMR (400 MHz, CDCl ): d 1.39 (t, J ¼ 7.2 Hz, 3H), 3.90
3
(
(
s, 3H), 4.38 (q, J ¼ 7.2 Hz, 2H), 6.99 (d, J ¼ 8.8 Hz, 2H), 8.00
d, J ¼ 8.8 Hz, 2H), 8.18 (s, 1H).
2
-(4-Methoxyphenylmethylene) Malononitrile (h)
ꢀ
ꢁ
Mp 114–115 C. IR (KBr): t 2852, 2223, 1605, 1571, 1513, 1184, 1154,
1
1
9
37, 834 cm
.
H NMR (400 MHz, CDCl ): d 3.92 (s, 3H), 7.01
3
(
d, J ¼ 8.8 Hz, 2H), 7.66 (s, 1H), 7.90 (d, J ¼ 8.8 Hz, 2H).
Ethyl (E)-2-Cyano-3-(4-dimethylaminophenyl)-2-propenoate (i)
ꢀ
Mp 124–125 C. IR (KBr): t 2913, 2209, 1665, 1601, 1529, 1369, 1161,
ꢁ
1 1
8
17 cm . H NMR (400 MHz, CDCl ): d 1.38 (t, J ¼ 7.2 Hz, 3H), 3.12
3
(
(
s, 6H), 4.33 (q, J ¼ 7.2 Hz, 2H), 6.75 (d, J ¼ 9.2 Hz, 2H), 7.94
d, J ¼ 9.2 Hz, 2H), 8.09 (s, 1H).
2
-(4-Dimethylaminophenyllmethylene) Malononitrile (j)
ꢀ
ꢁ1
1
Mp 179–180 C. IR (KBr): t 3010, 2220, 1601, 1521, 1160, 818 cm . H
NMR (400 MHz, CDCl ). d 3.14 (s, 6H), 6.70 (d, J ¼ 8.8 Hz, 2H), 7.47
3
(
s, 1H), 7.81 (d, J ¼ 8.4 Hz, 2H).
Ethyl (E)-2-Cyano-3-(2-furyl)-2-propenoate (k)
ꢀ
Mp 92–93 C. IR (KBr): t 3120, 3040, 2917, 2225, 1713, 1617, 1465, 1369,
ꢁ
1 1
1
3
1
265, 1209, 761 cm . H NMR (400 MHz, CDCl ): d 1.39 (t, J ¼ 7.2 Hz,
3
H), 4.36 (q, J ¼ 7.2 Hz, 2H), 6.66 (q, J ¼ 1.2 Hz, 1H), 7.39 (d, J ¼ 3.6 Hz,
H), 7.75 (d, J ¼ 1.6 Hz, 1H), 8.02 (s, 1H).
2
-(Furyllmethylene) Malononitrile (l)
ꢀ
Mp 72–73 C. IR (KBr): t 3125, 3042, 2225, 1608, 1509, 1457, 1395,
ꢁ
1 1
1
1
1
152, 1022, 936, 767 cm . H NMR (400 MHz, CDCl ): d 6.72 (q, J ¼
3
.6 Hz, 1H), 7.36 (d, J ¼ 3.6 Hz,1H), 7.52 (s, 1H), 7.81 (d, J ¼
.2 Hz, 1H).

3030
A.-Q. Zhang et al.
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