Complex containing a Lewis acid and Bronsted acid for the catalytic reactions of aza-Michael addition

Article abstract of DOI:10.1134/S0023158411030207

The novel efficient complex catalyst containing a Lewis acid and a Bronsted acid have been prepared by the reaction of proline ion liquid and cuprous iodide. The catalyst was characterized by FT-IR techniques using pyridine as probe molecule. A fast, mild, and quantitative procedure for aza-Michael addition reactions between various amines and α,β- unsaturated carbonyl compounds and nitriles has been developed using the novel complex catalyst. The results showed that the novel catalyst owned high activities for the reactions with excellent yields within 1 min.

Full text of DOI:10.1134/S0023158411030207

ISSN 0023ꢀ1584, Kinetics and Catalysis, 2011, Vol. 52, No. 4, pp. 525–528. © Pleiades Publishing, Ltd., 2011.
Complex Containing a Lewis Acid and Brønsted Acid
for the Catalytic Reactions of AzaꢀMichael Addition1
Xinꢀxin Mao, Jiao Wang, Qunꢀhua Xia, and Yongꢀmiao Shen
Department of Chemistry, Shaoxing University, Shaoxing, China
eꢀmail: shenyongmiao@usx.edu.cn
Received September 7, 2010
Abstract—The novel efficient complex catalyst containing a Lewis acid and a Brønsted acid have been preꢀ
pared by the reaction of proline ion liquid and cuprous iodide. The catalyst was characterized by FTꢀIR techꢀ
niques using pyridine as probe molecule. A fast, mild, and quantitative procedure for azaꢀMichael addition
reactions between various amines and
α
,βꢀunsaturated carbonyl compounds and nitriles has been developed
using the novel complex catalyst. The results showed that the novel catalyst owned high activities for the reacꢀ
tions with excellent yields within 1 min.
DOI: 10.1134/S0023158411030207
The azaꢀMichael reaction is an important reaction hazardous organic solvents. Hence, the development
since it provides an easy route for obtaining ꢀamino
β
of less expensive, simpler, “greener” procedures for
the reactions are still highly desirable. Aiming to these
advantages, we developed a novel solventꢀfree proceꢀ
dure for the azaꢀMichael addition of amines to elecꢀ
tron deficient alkenes at room temperature (r.t.) using
the proline cuprous iodide complex containing a
Lewis acid and a Brønsted acid as catalyst [13]
(Scheme 1). The results showed that the catalyst is very
efficient for the reactions with high yields, and very
carbonyl derivatives [1, 2], especially for the synthesis
of C–N heterocycles [3]. It is a straightforward
approach for the synthesis of substituted amines and
their derivatives with 100% atom efficiency and withꢀ
out any byꢀproduct formation [4]. A number of alterꢀ
native procedures have been reported recently using a
variety of reagents such as Pd compounds [5], Lewis
acids [6–8], clay [9], silica gel [10], lipase [11], ion liqꢀ
uid [12] etc. However, despite satisfactory results,
many of these methods used heavy metal salts and short reaction time.
O
O
O
O
CuI
CuIBr22–
+
2
+
+
+ HBr
,
N
H
N
N
N
H
H2Br–
H2Br–
OH
OH
OH
OH
2
Scheme 1. The synthesis of the proline cuprous iodide complex catalyst.
EXPERIMENTAL . Then, the water was removed under reduced
25°C
pressure and a light yellow ionic liquid was formed. It
was used without further purification. A mixture of
synthesized ionic liquid (20 mmol) and cuprous iodide
(10 mmol) were placed in vacuum drying oven for 1 h.
All organic reagents were commercial products of
the highest purity available (>98%) and used for the
reaction without further purification. Proline, cuprous
iodide, acrylonitrile, butyl acrylate, methyl acrylate,
methyl methacrylate, piperidine, diethylamine, morꢀ
pholine, isopropylamine, cyclohexanamine were purꢀ
chased from Shanghai Chemicals Co.
Catalytic Procedure for the AzaꢀMichael Addition
Typical procedure for the conjugate addition of
amines was the next. A mixture of amine (4 mmol),
alkene (4.8 mmol) and the catalyst (15 mg) was stirred
at room temperature for 1 min. The residue was filꢀ
tered and condensed under reduced pressure. The
process of the reaction was monitored by GC analysis.
Synthesis of the Catalyst
Proline and equimolar hydrobromic acid were
mixed together and stirred magnetically for 2 h at
1
The article is published in the original.
525

526
XINꢀXIN MAO et al.
The azaꢀMichael additions of various amines with alkenes*
R2
R1
H
N
EWG
cat (1 mol %)
1 min, r.t.
N
+
R2
R1
EWG
Entry
1
Amines
NH
Alkenes
Yield, %
98.4
Entry
9
Amines
Alkenes
Yield, %
99.7
NH2
COOCH3
COOC4H9
O
COOCH3
COOCH3
COOCH3
COOCH3
COOC4H9
N
H
2
3
4
5
6
7
8
99.7
99.7
95.7
99.9**
99.9
98.7
98.2
10
11
12
13
14
15
93.7
99.9
99.4
99.6
98.9
99.7**
NH2
CN
HN
O
NH
NH2
CN
N
H
CN
NH2
HN
NH2
COOC4H9
COOC4H9
COOC4H9
CN
O
NH
CN
N
H
NH2
HN
* The reaction conditions: amine 4 mmol, alkenes 4.8 mmol, catalyst 15 mg, r.t. (25°C), reaction time 1 min. The yield was estimated by
GC analysis.
** Reaction time 2 min.
RESULTS AND DISCUSSION
two bands at 1460–1445 and 1610–1600 cm–1 whereas
Brønsted acid sites (BꢀPy) are usually observed at 1540
and 1640–1630 cm–1 [14, 15]. The IR spectrum corꢀ
responding to pyridine adsorbed on the proline
cuprous iodide complex is shown on Fig. 1. We can see
Characterization of Catalyst
FTꢀIR absorption spectra of pyridine adsorbed on
metal oxides have been widely described in the literature
[13]. Pyridine adsorbed on Lewis acid sites (LꢀPy), yields that coordinated pyridine on Lewis acid sites is
KINETICS AND CATALYSIS Vol. 52
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2011

COMPLEX CONTAINING A LEWIS ACID AND BRØNSTED ACID
527
100
80
1640
1630
1460
60
40
20
0
1
2
3
4
5
6
7
Number of cycle
8
9 10 11
2000 1800 1600 1400 1200 1000 800
Wavenumber, cm–1
Fig. 1. FTꢀIR spectrum of pyridine adsorbed on proline
cuprous iodide complex.
Fig. 2. The reuse of the proline cuprous iodide complex
catalyst.
observed at 1460 cm–1, and the presence of stretching
mode at 1630 and 1640 cm–1 were assigned to Brønꢀ
sted acid sites.
The Reuse of the Catalyst
The catalyst has been used in the heterogeneous
catalytic process. Thus, recovery of the catalyst is very
convenient. After reactions, the reaction mixture was
filtered, and the catalyst was washed with acetone
(5 ml) and dried. The complex catalyst could be
reused without any further disposal. The recovered
activities were investigated through the reaction of
diethylamine and methyl acrylate carefully (Fig. 2).
The yield remained unchanged even after the catalyst
had been recycled for ten times.
Catalytic Procedure for the AzaꢀMichael Addition
The azaꢀMichael additions of various amines with
alkenes under solventꢀfree condition were investigated
(table). The results showed that the reactions underꢀ
went smoothly at room temperature just within one or
two minutes. The cyclohexanamine showed a low
activity for all kinds of electron deficient alkenes with
2 min reaction time (entries 5, 15). The primary
amines underwent the single substitution reaction
under the reaction condition. The reaction conditions
are mild and not sufficient enough to cause double
substitution reaction. The multiꢀsubstitution reactions
could also be activated when more alkenes (2.4 equiv)
The Selectivity of the Catalyst
It is noteworthy that aromatic amines could not be
transformed to the corresponding products under the
same reaction conditions (Scheme 2). This result indiꢀ
cated that the present protocol could be applicable to
the selective addition of aliphatic amines in the presꢀ
ence of aromatic amines.
and high temperature (80
substituted products were obtained with high yields
(88%) after 2 h. As to the alkenes, the reactivity was
affected by the electronic withdrawing groups (EWG
°C) applied, then the double
)
and the steric hindrance around the double bond also
had the certain effect on the reaction.
NH2
H
N
COOCH3
10 mmol
NH2
COOCH3
12 mmol
cat, r.t.
1 min
99.3%
+
NH2
10 mmol
Scheme 2. The selectivity of the proline cuprous iodide complex catalyst.
KINETICS AND CATALYSIS Vol. 52
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2011

528
XINꢀXIN MAO et al.
It was also found that methyl methacrylate greatly influenced by the steric hindrance of the
could not be transformed to the corresponding methyl at the double bond of the methyl methacryꢀ
products (Scheme 3). The reaction activity was late.
COOCH3
12 mmol
N
COOCH3
97.8%
N
H
cat, r.t.
1 min
+
COOCH3
10 mmol
COOCH3
CH3
CH3
12 mmol
Scheme 3. The selectivity of the proline cuprous iodide complex catalyst.
5. Miao, T. and Wang, L., Tetrahedron Lett., 2008, vol. 49,
In conclusion, a novel efficient catalyst has been
p. 2173.
prepared for the azaꢀMichael addition of amines to
electron deficient alkenes. FTꢀIR spectra indicated
that the new catalyst contains both a Lewis acid site
and a Brønsted acid site. The novel efficient procedure
has been developed. Low cost and possibility of reuse
of the catalyst, excellent selectivity, high yields are the
key features of this methodology.
6. Attanasi, O., Favi, G., Filippone, P., Golobic, A., Perꢀ
rulli, F., Stanovnik, B., and Svete, J., Synlett, 2007,
vol. 19, p. 2971.
7. Micheletti, G., Pollicino, S., Ricci, A., Berionni, G.,
and Cahiez, G., Synlett, 2007, vol. 18, p. 2829.
8. Esteban, J., Costa, A., Gomez, A., and Vilarrasa, J.,
This work was supported by the Excellent Young
Teachers Program of Zhejiang province and Underꢀ
graduate in Science and technology innovation proꢀ
gram of Zhejiang Province “Emerging Talent Proꢀ
gram”.
Org. Lett., 2008, vol. 10, p. 65.
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2008, vol. 49, p. 1249.
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2011