Cadmium chloride (CdCl2): An efficient catalyst for conjugate addition of amines to electron-poor alkenes

Article abstract of DOI:10.1080/00397910601055115

Electron-deficient olefins undergo rapid Aza-Michael reaction with a wide range of amines catalyzed by cadmium chloride at room temperature. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910601055115

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Cadmium Chloride (CdCl ): An Efficient
2
Catalyst for Conjugate Addition of Amines to
Electron‐Poor Alkenes
a
a
a
Medamoni Vijender , P. Kishore & B. Satyanarayana
a
Department of Chemistry , University College of Engineering, Osmania
University , Tarnaka, Hyderabad, India
Published online: 05 Mar 2007.
To cite this article: Medamoni Vijender , P. Kishore & B. Satyanarayana (2007) Cadmium Chloride (CdCl ):
2
An Efficient Catalyst for Conjugate Addition of Amines to Electron‐Poor Alkenes, Synthetic Communications:
An International Journal for Rapid Communication of Synthetic Organic Chemistry, 37:4, 589-592, DOI:
10.1080/00397910601055115
To link to this article: http://dx.doi.org/10.1080/00397910601055115
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Synthetic Communications , 37: 589–592, 2007
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910601055115
Cadmium Chloride (CdCl ): An Efficient
2
Catalyst for Conjugate Addition of Amines
to Electron-Poor Alkenes
Medamoni Vijender, P. Kishore, and B. Satyanarayana
Department of Chemistry, University College of Engineering, Osmania
University, Tarnaka, Hyderabad, India
Abstract: Electron-deficient olefins undergo rapid Aza–Michael reaction with a wide
range of amines catalyzed by cadmium chloride at room temperature.
Keywords: amines, Aza–Michael additions, Lewis acid b-amino compounds, olefins
The Aza–Michael reaction is widely recognized as one of the most important
[1]
carbon–nitrogen bond-forming reactions in organic synthesis. The obtained
-amino compounds are versatile intermediates for the synthesis of various
complex natural products (Taxol), antibiotics (b-lactams), and chiral auxili-
2
[2]
aries.
The most common method for the preparation of 2-amino
compounds is the conjugate addition of amines (nucleophiles) to the a,b-unsa-
[3]
turated systems. These methods generally require basic or acidic activators.
In recent years, various Lewis acid–induced reactions have been reported.
However, many of these procedures often require large excesses of reagents,
[4]
[5]
long reaction times, and drastic reaction conditions. The development of
simple, more convenient, and ecofriendly approaches are encouraged.
Cadmiun chloride is known for various organic transformations in the litera-
[6]
ture as a mild, inexpensive, and moisture-stable Lewis acid.
Received July 12, 2006
Address correspondence to B. Satyanarayana, Department of Chemistry, University
College of Engineering, Osmania University, Tarnaka, Hyderabad 500 007, India.
E-mail: ursvijender@rediffmail.com
5
89

590
M. Vijender, P. Kishore, and B. Satyanarayana
Table 1. Conjugate addition of amines to ethylenic compounds catalyzed by CdCl
2
Amines
(1)
Ethylenic
compound (2)
Product
(3)
Reaction Yield
(%)
Entry
A
hours
3.0
93
87
B
2.5
C
D
3.0
2.5
89
92
E
F
4.0
2.5
80
88
G
3.0
93
H
I
4.0
3.5
89
84
J
2.5
4.0
87
82
K
L
3.0
90
(
continued)

Cadmium Chloride as Catalyst
591
Table 1. Continued
Amines
(1)
Ethylenic
compound (2)
Product
(3)
Reaction Yield
hours
Entry
M
(%)
3.5
86
N
O
3.0
3.5
99
90
In a typical experiment, the conjugate addition of benzyl amine to ethy-
lacrylate in dichloromethane was carried out in the presence of cadmium
chloride (CdCl ) to afford the corresponding ethyl-3-benzylamino propionate
2
in 93% yield. The reaction proceeds rapidly at room temperature with
2
0 mol% of catalyst and completes within 3 h of reaction time (entry a). In
a similar manner, various amines such as phenyl ethyl amine, n-phenyl piper-
azine, morpholine, diisopropyl amine, and aniline were reacted with a variety
of ethylenic corresponds such as ethylacrylate, acrylnitrile, nitrostyrene, and
methyl cinnamate to afford the corresponding 1,4-addition of Aza–Michael
products in very good to excellent yields. Primary amines and alicyclic
amines were reacted faster when compared with aniline. All the reactions
were completed within 2.5 to 4 h. The obtained yields of Aza–Michael
1
products were 80–93%. All the products were confirmed by H NMR, IR,
and mass spectroscopy, and the data were compared with literature reports.
The scope and generality of this protocol is illustrated with respect to
various /,b-ethylenic compounds and amines, and the results are summarized
in Table 1.
In conclusion, we have demonstrated a new method for accelerating the
Michael addition of amines with electron-deficient olefins using the inexpen-
sive catalyst cadmium chloride (Scheme 1). All the reactions were carried out
at room temperature in dichloromethane solvent. The present procedure
Scheme 1. R ¼ H, Ph; EWG ¼ Co Et, CN, No .
2
2
2

592
M. Vijender, P. Kishore, and B. Satyanarayana
provides an efficient and general protocol for the preparation of b-amino
compounds in excellent yields.
EXPERIMENTAL
General Procedure
To a mixture of amine (2 mmol) and acryl compound (2.2 mmol) in dichlor-
omethane (10 ml), cadmium chloride (0.4 mol%) was added. The resulting
reaction mixture was stirred at room temperature for a specified period
(
Table 1). After completion of the reaction (confirmed by thin-layer chromato-
graphy), dichloromethane (20 ml) was added and the reaction mixture was
washed with water. The organic layer was dried over Na SO and concen-
2
4
trated under reduced pressure. The obtained crude products were purified by
column chromatography on silica gel (60–120 mesh) by eluting with ethyl
1
acetate and petroleum ether. All the products were confirmed by H NMR,
IR, and mass spectroscopy, and data were compared with literature reports.
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