K7[PW11CoO40]: Efficient and ecofriendly catalyst for the enamination of β-dicarbonyl compounds

Article abstract of DOI:10.1080/00397910701860968

Condensation of a variety of β-dicarbonyl compounds with primary and secondary amines carried out in the presence of catalytic amounts of K7[PW11CoO40]. From this reaction N-substituted β-enamino esters and ketones were obtained in high yields. Copyright

Full text of DOI:10.1080/00397910701860968

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K7[PW11CoO40]: Efficient and
Ecofriendly Catalyst for the
Enamination of β-Dicarbonyl
Compounds
Hossein A. Oskooie a , Majid M. Heravi a , Negar
M. Javadi a , Khadijeh Bakhtiari a & Fatemeh F.
Bamoharram b
a Department of Chemistry, School of Sciences,
Azzahra University, Vanak, Tehran, Iran
b Department of Chemistry, Azad University of
Mashad, Mashad, Iran
Published online: 28 Aug 2008.
To cite this article: Hossein A. Oskooie , Majid M. Heravi , Negar M. Javadi , Khadijeh
Bakhtiari & Fatemeh F. Bamoharram (2008) K7[PW11CoO40]: Efficient and Ecofriendly
Catalyst for the Enamination of β-Dicarbonyl Compounds, Synthetic Communications:
An International Journal for Rapid Communication of Synthetic Organic Chemistry,
38:17, 2864-2869, DOI: 10.1080/00397910701860968
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Synthetic Communications1, 38: 2864–2869, 2008
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910701860968
K7[PW11CoO40]: Efficient and Ecofriendly
Catalyst for the Enamination of
b-Dicarbonyl Compounds
Hossein A. Oskooie,1 Majid M. Heravi,1 Negar M. Javadi,1
Khadijeh Bakhtiari,1 and Fatemeh F. Bamoharram2
1Department of Chemistry, School of Sciences, Azzahra University,
Vanak, Tehran, Iran
2Department of Chemistry, Azad University of Mashad, Mashad, Iran
Abstract: Condensation of a variety of b-dicarbonyl compounds with primary
and secondary amines carried out in the presence of catalytic amounts of
K7[PW11CoO40]. From this reaction N-substituted b-enamino esters and ketones
were obtained in high yields.
Keywords: Amines, b-dicarbonyl compounds, enamination, heteropolyacid,
Keggin-type, K7[PW11CoO40]
b-Enamino esters are an important class of functionalized building
blocks. They are valuable intermediates for the synthesis of biologically
active compounds such as a[1] and b-amino acids,[2] c-aminols,[3] alka-
loids,[4–6] peptides,[7] and heterocyclic derivatives.[8–11] There are many
routes for the preparation of these compounds including addition of met-
allic ester or amide enolates to nitriles,[12,13] tosyl imines,[14] and imidoly
halides.[15,16] Moreover, b-enamino esters can be successfully obtained
from direct condensation of b-keto esters with amines.[17–19] Recently,
the enamination of b-dicarbonyl compounds in the presence of Bi(TFA)3
in aqueous media.[20] Bi(TFA)3 immobilized on molten TBAB,[21] and
Bi(TFA)3 immobilized on Zn(ClO4)2 ꢀ 6H2O[22] are reported. Nevertheless,
Received in the U.K. June 12, 2006.
Address correspondence to Majid M. Heravi, Department of Chemistry,
School of Sciences, Azzahra University, Vanak, Tehran, Iran. E-mail:
mmh1331@yahoo.com
2864

Efficient and Ecofriendly Catalyst for b-Dicarbonyl Compounds
2865
most of the approaches currently available suffer from some drawbacks
such as low chemical yields and lack of general applicabililty.
Heteropolyacids (HPAs) have many advantages that make them
economical and environmentally attractive in both academic and indus-
trial settings; they are useful acids and oxidation catalysts in various reac-
tions because their catalytic features can be varied at a molecular
level.[23,24] Among them, the Keggin-type HPAs have long been known
to be good catalysts for oxidation reactions.[25,26] They exhibit many
advantages: for example, their catalytic properties can be tuned by chan-
ging the identity of charge-compensating counter cations, heteroatoms,
and framework metal atoms.[23]
To the best of our knowledge, there are no example of the use of
HPAs as catalysts for the enamination reaction. In continuation of our
investigations on the use of HPAs as catalysts for chemical prep-
aration[27–33] and our interest in green chemistry,[34,35] herein we report
the condensation of b-dicarbonyl compounds with amines in the presence
of a catalytic amount of K7[PW11CoO40], PW11Co, as an inexpensive,
ecofriendly, recyclable, and reusable catalyst.
The model reaction was carried out simply by mixing 4-bromo aniline
(1 mmol), acetyl acetone (1 mmol), and PW11Co (0.03 g, 1 mol%) in acetic
acid (5 mL) and refluxing the resulting mixture for 70 min (Scheme 1). The
corresponding enaminoketone was obtained in high yield (90%).
This methodology was applied to a variety of b-dicarbonyl com-
pounds and amines. The results are summarized in Table 1. In all cases,
good yields were obtained. In the case of unsymmetrical compounds, the
regio-chemistry is controlled by the more reactive carbonyl group, which
undergoes the attack of the amine.
In summary, we reported the condensation of amines with b-dicarbonyl
compounds in the presence of an HPA as a clean, general, and inexpensive
reaction. Relatively short reaction times, very simple performance and
workup procedure, high chemoselectivity, and high yields are some of the
advantages of this procedure. The catalyst is recyclable and could be reused
without significant loss of activity. Even after five runs of the reaction, the
catalytic activity of K7[PW11CoO40] was almost the same as that of fresh
catalyst. The results are summarized in Table 2.
Scheme 1.

2866
H. A. Oskooie et al.
Table 1. Synthesis of N-substituted b-enamino esters ketones via condensation of
b-dicarbonyl compounds with amines in the presence of a Keggin structure
heteropolyacid
Time
Product (min)
Mp
(ꢁC)
Yield
(%)a
Entry
R1
R2
R3
R4
1
2
3
4
5
6
7
8
9
Me
Me
Me
Me
Me
Me
Me
Me
C3H7
C3H7
C3H7
C3H7
H
H
H
H
H
H
H
H
H
H
H
H
Me
Me
Me
Me
OMe
OMe
OMe
p-Br-Ph
Ph
3-NO2-Ph
2,6-Dimethyl-Ph
p-Br-Ph
2a
2b
2c
2d
2e
2f
70
70
60
75
70
75
60
60
70
60
60
60
48–50
45–56
76–77
48–49
48–50
59–60
76–77
50–51
37–38
62–63
78–79
37–38
90
85
90
80
80
83
90
85
84
80
90
83
Ph
3-NO2-Ph
2g
2h
2i
OMe 2,6-Dimethyl-Ph
OEt
OEt
OEt
p-Br-Ph
Ph
3-NO2-Ph
10
11
12
2j
2k
2l
OEt 2,6-Dimethyl-Ph
aYields refer to isolated products.
K7[PW11CoO40] is noncorrosive and environmentally benign and
presents few disposal problems. The use of this solid acid catalyst allows
replacement of the usual soluble inorganic acids, contributing in this way
to reduction of wastes.
EXPERIMENTAL
All products were identified by their spectral and physical data. Melting
points were measured with a Bamstead Electrothermal apparatus and are
uncorrected. IR spectra were recorded as KBr discs on the FT-IR Brucker
Table 2. Reuse of the catalyst for synthesis of (z)-4-(4-
bromo ani-line)-3-pentene-2-one (entry 1. Table 1)
Entry
Yield (%)a
1
2
3
4
5
90
88
83
80
79
aYields refer to isolated product.

Efficient and Ecofriendly Catalyst for b-Dicarbonyl Compounds
2867
Tensor 27. Mass spetra were recorded on an MS 5973 network mass selec-
tive detector. All the yields were calculated from isolated products, and gas
chromatography (GC) was used to confirm their purities.
Enamination of b-Dicarbonyl Compounds: Typical Procedure
Heteropolyacid (0.03 g), 4-bromo-aniline (1 mmol), and acetyl acetone
(1 mmol) in acetic acid (5 mL) were refluxed for 70 min. The progress
of the reaction was monitored by thin-layer chromatography (TLC) using
petroleum ether-ethyl acetate (2:1) as eluent. After completion of the
reaction, the catalyst was removed by filtration and washed with HOAc.
Et2O was added to the solution. Then the filtrate was washed with 5%
NaHCO3 (5 mL) and brine (2 ꢂ 5 mL) successively, and the organic layer
was dried over MgSO4. The solvent was evaporated under reduced pres-
sure. The crude product was purified by recrystallization from ethanol.
Physical and Spectral Data for Selected Compounds
Compound 2a: mp 48–50 ꢁC. IR (KBr, cmꢃ1) nmax: 3280, 3067, 2991, 1604,
1562, 1475, 1358, 914, 839. MS: m=z (%) ¼ 253, 238, 210, 196, 159, 131,
117, 104, 91, 76, 63, 43.
Compound 2d: mp 48–49 ꢁC. IR (KBr, cmꢃ1) nmax: 3280, 3016, 2991, 1611,
1559, 1497, 1356, 916, 826. MS: m=z (%) ¼ 203, 188, 146, 131, 91, 77.
Compound 2f: mp 59–60 ꢁC. IR (KBr, cmꢃ1) nmax: 3250, 3057, 2991, 1608,
1588, 1484, 1356, 910, 823. MS: m=z (%) ¼ 191, 176, 160, 144, 130, 118,
91, 77, 65, 51.
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