Zeolite (ZSM-5) as a highly efficient and heterogeneous catalyst for the synthesis of β-Enaminones and β-Enamino esters

Article abstract of DOI:10.1155/2011/176829

Several β-enaminones and β-enaminoesters have been synthesized in high yields from amine and β-diketone in the presence of Zeolite (ZSM-5) as a catalyst. This method is applicable to both cyclic and acyclic ketones with aromatic and aliphatic amines. Copyright E-Journal of Chemistry 2004-2011.

Full text of DOI:10.1155/2011/176829

ISSN: 0973-4945; CODEN ECJHAO
E-Journal of Chemistry
2011, 8(4), 1632-1637
http://www.e-journals.net
Zeolite (ZSM-5) as a Highly Efficient and
Heterogeneous Catalyst for the Synthesis of
β-Enaminones and β-Enamino Esters
*
AMIYA SHEKHAR and DEVENDRA DEO PATHAK
Department of Applied Chemistry
Indian School of Mines, Dhanbad-826004, Jharkhand, India
ddpathak@yahoo.com
Received 28 December 2010; Accepted 28 February 2011
Abstract: Several β-enaminones and β-enaminoesters have been synthesized
in high yields from amine and β-diketone in the presence of Zeolite (ZSM-5)
as a catalyst. This method is applicable to both cyclic and acyclic ketones with
aromatic and aliphatic amines.
Keywords: β-Enaminones, β-Enamino Esters, ZSM-5
Introduction
β-enaminones and β-enamino esters have been used as synthons for the synthesis of a variety
of bioactive heterocycles and pharmaceuticals displaying anti-inflammatory antitumor ,
1-3
4
5
6
antibacterial , anti-epileptic , anti-convulsant and other therapeutic properties . These
7-8
9
10,11
1
2-14
compounds also serve as key intermediates in organic synthesis
and their chemistry has
undergone a renaissance of interest . The most common and widely employed protocol
involves direct condensation of -dicarbonyl compounds with amines in aromatic
15
β
1
6
hydrocarbon solvents under reflux with azeotropical removal of water . Subsequently the
reaction procedure has been modified with the use of several catalysts such a molecular
1
7
iodine , Bi(TFA)
18
19
20
ZrOCl .8H O , ionic liquid [EtNH ]NO3
21
,
HClO .SiO , silica chloride , ceric(IV)ammonium nitrate . Sc(OTf) and Yb(OTf)3
NaAuClO4
23
,
,
.
3
2
2
3
2
2
24
25
26
4
2
3
Some other routes to the synthesis of β-Enaminones include condensation of methyl ketones
with dimethylformamide dimethylacetals , aminolysis of dithioacetals mediated by copper
2
7
2
8
29
acetate , reductive cleavage of isoxazoles , cyclization of aminoacids and substitution of
30
31
the imidoylbenzotriazoles with trimethylsilyl enol ethers . Out of these methods, most of
them suffer from various disadvantages such as long reaction time and unspecified yields,
use of expensive reagents, tedious work-up and lack of general applicability etc. The
reaction has recently been reported to be catalysed by heterogeneous catalysts such as silica
3
2
33
sulfuric acid and silica-supported LiHSO
.
4

1
633
D. DEO PATHAK et al.
Keeping in view the importance of these compounds, it is desirable to find out more
efficient, environmental friendly, cheap and readily available catalysts for synthesis of
β-enaminones and β-enamino esters. During the last few years, there has been a spurt in the
owing to their
34-36
use of inorganic solid acids, particularly zeolites, in organic reactions
varied lewis and bronsted acidity, thermal stability, low cost and ease of separation.
Prompted by these reports, we herein report a zeolite (ZSM-5) catalysed synthesis of various
β-enaminones and β-enamino esters (Scheme 1).
NH2
ZSM-5
O
O
∆
, EtOH, 30 min
+
N
H
O
Scheme 1
Experimental
1
All the isolated compounds were characterized by IR, H NMR, mass spectroscopy and
-
1
melting point. The IR spectra were recorded in the range of 4000-400 cm FT-IR
spectrophotometer using KBr disk. Melting points were taken in open capillary tubes and
therefore uncorrected. Purity of the compounds was checked on silica gel alumina sheet
using n-hexane and ethylacetate as eluent. The visualization of spot was carried out in UV
1
chamber. The H NMR were recorded on Brucker 400 MHz spectrometer in CDCl using
3
TMS as an internal standard. The catalyst ZSM-5 (SAR-100) was purchased from ranbaxy
(
India) and used as received.
General procedure for the synthesis of β-enaminones and β-enamino esters
derivatives
A mixture of amine (1 mmol), β-carbonyl compound (1 mmol) and zeolite (0.04 g) was
placed in a 25 mL two-necked round-bottomed flask fitted with a reflux condenser. Ethanol
(
2 mL) was added to the mixture and the contents were heated under reflux till the
completion of the reaction as monitored by TLC. After completion, the reaction was cooled
to room temperature, solvent removed under reduced pressure and the crude product isolated
with EtOAc (2x10 mL). The combined portions were filtered, dried under vacuum. The
crude product was recrystallised from EtOH/H O.
2
Spectral data of the product
5
,5-Dimethyl-3-(phenylamino)cyclohex-2-enone ( Table 3, entry 1)
-
Pale yellow solid; IR( KBr): 3236, 2958, 1720, 1573, 1244, 708 cm ; H NMR (CDCl 400
1 1
3,
MHz): δ 1.12 (s, 6H, 2x CH ), 2.23 (s, 2H, 2x CH ), 2.34 (s, 2H, CH ), 5.59 (s, 1H, =CH),
3
2
2
6
data for C H NO: m/z [M H] 216.299. Found 216.278.
.01 (br.,1H, -NH), 7.15-7.18 (m, 3H, ArH), 7.32-7.36 (m, 2H, ArH); LCMS: Calculated
+
+
1
4
17
The spectral data of rest of the products were matching to the literature value.
Results and Discussion
First of all, in order to screen the catalytic activity of the catalyst, i.e., ZSM-5, the reaction
of aniline (1 mmol) with dimedone (1 mmol) was selected. Various reactions in the presence
of different amount of catalyst in ethanol at room temperature and under reflux were carried
out in order to optimize the reaction conditions (Table 1). It is clear from the Table 1 that the
best results (maximum yields and minimum time) were obtained with 0.04 g of the catalyst
in EtOH under reflux.

Zeolite (ZSM-5) as a Highly Efficient and Heterogeneous Catalyst
1634
Table 1. Effect of catalyst loading and temperature on the reaction of aniline with dimedone
o
Temperature, C
a
Yield , %
Amount of Zeolite, g
Time, min
120
120
120
110
100
90
0
0
0
0
0
0
0
0
0
0
.01
.02
.04
.04
.04
.01
.02
.03
.04
.05
25
25
25
60
70
80
80
80
80
80
5
8
14
40
55
50
62
75
93
93
65
45
30
25
a
Isolated yield
After optimization of the catalyst concentration and temperature, the reaction was
performed in various other solvents (Table 2) in order to study solvents effects. The best
results were obtained using EtOH (2 mL) under reflux, though the reaction had also taken
place in other solvents but with poor yields (Table 2).
Table 2. Study of solvent effects on the reaction of dimedone with aniline in the presence of ZSM-5
a
Solvent
THF
CH CN
CHCl3
MeOH
EtOH,2 mL
EtOH, 5 mL
EtOH, 10 mL
Temperature condition
Reflux
Reflux
Time, min
% Yield
39
48
60
60
60
60
60
60
60
3
Reflux
Reflux
Reflux
Reflux
53
61
93
85
Reflux
a
80
Isolated yields
The products, after work up and recrystallization, were isolated either as off-white
solids (Entry 1-8, Table 3) or as viscous liquids (Entry 9 and 10, Table 3). The products
1
obtained were characterized by H NMR and Mass spectrum, and comparing the data with
1
the literature values. The H NMR spectrum obtained on the product 5,5-dimethyl-3-
(
phenylamino)cyclohex-2-enone (Table 3, entry 1) is shown in Figure 1.
Table 3. Synthesis of β-enaminones and β-enamino esters using ZSM-5 as a catalyst
Entry
Product
O
Time, min Yield, %
M. P.˚C, Lit.
3
7
1
1
82-184(185)
1
30
30
25
90
86
92
N
H
O
Me
2
3
187-189
N
H
O
37
MeO
94-196(195)
N
H
Contd…

1
635
D. DEO PATHAK et al.
O
38
1
30-132(129-131)
4
40
87
N
H
OMe
O
Br
3
3
9
9
5
6
7
40
40
30
89
90
92
218-219(219-220)
222-224(225-227)
N
H
O
AcO
N
H
O
39
1
22-124(125)
N
H
O
33
1
15-117(117-119)
8
40
86
N
H
4
4
0
0
9
NH
O
60
65
82
83
Oil(Oil)
Oil(Oil)
OEt
NH
O
1
0
OEt
1
Figure 1. The H NMR spectra of 5,5-dimethyl-3-(phenylamino)cyclohex-2-enone

Zeolite (ZSM-5) as a Highly Efficient and Heterogeneous Catalyst
1636
The methyl protons (2x CH ) were observed at δ 1.12, methylene protons (2x CH ) at
3
2
δ 2.33 and 2.34 as singlets. The sharp singlets at δ 5.59 and 6.01 were assigned to
olefinic(=CH) proton and (-NH) proton, respectively. The aromatic protons were obtained as
a complex multiplet ranging from δ 7.12 to 7.36. The rest of the products were characterized
by comparing the data with the literature values. It has been observed that the presence of
electron withdrawing groups leads to slightly decreased yields and prolonged reaction time.
In summary, we have demonstrated that zeolite (ZSM-5) is an efficient, easily available
and environmental friendly, heterogeneous catalyst for the synthesis of a number of
β-enaminones and β-enamino esters. The catalyst works well with both aromatic and
aliphatic amines and the corresponding cyclic or acyclic ketones to afford the desired
product in good to excellent yields.
Acknowledgment
One of the Author (AS) would like to thank the Director of Indian School of Mines,
Dhanbad for the award of ISM Junior Research Fellowship and Head, Department of
Applied Chemistry for providing research facilities.
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