A simple, efficient and green procedure for Michael addition catalyzed by [C4dabco]OH ionic liquid

Article abstract of DOI:10.1016/j.cclet.2014.01.032

A dabco-based basic ionic liquid, 1-butyl-4-aza-1-azaniabicyclo[2.2.2] octane hydroxide, has been developed as a catalyst for a convenient and rapid method for the Michael addition of active methylene compounds to α,β-unsaturated carboxylic esters and nitriles. The method is very simple, and the yields are very high. The catalyst can be recycled several times without much loss of activity.

Full text of DOI:10.1016/j.cclet.2014.01.032

G Model
CCLET-2856; No. of Pages 4
Chinese Chemical Letters xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Chinese Chemical Letters
journal homepage: www.elsevier.com/locate/cclet
Original article
A simple, efficient and green procedure for Michael addition catalyzed
by [C4dabco]OH ionic liquid
*
Sanjoy Keithellakpam, Warjeet S. Laitonjam
Department of Chemistry, Manipur University, Canchipur, Imphal 795003, India
A R T I C L E I N F O
A B S T R A C T
Article history:
A dabco-based basic ionic liquid, 1-butyl-4-aza-1-azaniabicyclo[2.2.2]octane hydroxide, has been
developed as a catalyst for a convenient and rapid method for the Michael addition of active methylene
Received 28 November 2013
Received in revised form 19 December 2013
Accepted 30 December 2013
Available online xxx
compounds to a,b-unsaturated carboxylic esters and nitriles. The method is very simple, and the yields
are very high. The catalyst can be recycled several times without much loss of activity.
ß 2014 Warjeet S. Laitonjam. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights
reserved.
Keywords:
Dabco-based
Ionic liquid
Michael addition
Recyclable
1. Introduction
ketones, carboxylic esters, and nitriles [1]. However, a large
amount of catalyst was necessary to obtain high yield. Recently,
In the last two decades, ionic liquids (ILs) have emerged as
potential ‘greener’ alternatives to volatile organic solvents, and
they have been used as environmentally friendly media for many
important organic reactions [1]. A number of ionic liquids have
been developed and used as catalysts for different reactions. Some
acidic ionic liquids have been utilized to catalyze Friedel Crafts
acylation [2], Knoevenagel condensation [3], esterification reaction
[4], and cleavages of ether [5]. Basic ionic liquids have aroused
unprecedented interest because they show more advantages, such
as catalytic efficiency and recycling of the ionic liquid, which
cannot be provided by the combination of inorganic base and ionic
liquid for base catalyzed processes [6].
another basic ionic liquid, [Bmim]OAc, was also used to catalyze
the Michael addition of active methylene to -unsaturated
carboxylic esters and nitriles [11]. However, in this protocol,
volatile and toxic organic solvents were used in order to achieve
a,b
high yields. Recently, Xiaoming Feng et al. used
a chiral
organocatalyst in the Michael reaction [12]. In this letter, we
report dabco-based basic ionic liquids (Fig. 1) as highly efficient
and environmentally friendly catalysts for Michael addition of
active methylene compounds to a,b-unsaturated carboxylic esters
and nitriles at room temperature under solvent free conditions,
providing excellent yields. The catalysts can be recycled many
times without much loss of activity.
The Michael addition is one of the most important carbon–
carbon bond forming reactions and is widely applied in organic
syntheses [7]. This reaction is usually performed in organic solvent
and is catalyzed by strong bases and Lewis acids that lead to
undesirable side reactions [8]. Many catalysts have been developed
to solve the above problems [9]. However, these catalysts have
some limitations, such as long reaction time [9a,b,d–f,h], high
reaction temperature [9c,f], use of large amount of catalysts
[9g,10], and low yields [9b,c,e,f,h]. A task specific ionic liquid,
[Bmim]OH, was applied as a catalyst and reaction medium in
Michael addition of active methylene compounds to conjugated
2. Experimental
All the reagents were commercial reagents of A.R. grade and
were used without further purification. All the commercial
solvents were used after distillation. Melting points were
determined by using a Veego melting point apparatus-I and were
uncorrected. IR spectra were taken using KBr pellets for solids and
thin films for liquids on a Shimadzo 8400S FTIR spectrophotome-
ter. 1H NMR and 13C NMR spectra were recorded on a Bruker AV III
500 MHz, Varian 400 MHz, or Varian 300 MHz spectrometer in
CDCl3 or D2O. 1H NMR and 13C NMR chemical shifts (
d) in ppm are
down field from tetramethylsilane. Elemental analyses were done
in a Perkin Elmer CHNS/O Analyzer 2400.
*
Corresponding author.
E-mail address: warjeet@yahoo.com (W.S. Laitonjam).
1001-8417/$ – see front matter ß 2014 Warjeet S. Laitonjam. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
http://dx.doi.org/10.1016/j.cclet.2014.01.032
Please cite this article in press as: S. Keithellakpam, W.S. Laitonjam, A simple, efficient and green procedure for Michael addition
catalyzed by [C4dabco]OH ionic liquid, Chin. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.cclet.2014.01.032

G Model
CCLET-2856; No. of Pages 4
2
S. Keithellakpam, W.S. Laitonjam / Chinese Chemical Letters xxx (2014) xxx–xxx
1370; 1H NMR (300 MHz, CDCl3):
d
4.13 (q, 2H), 3.6 (s, 6H), 2.2–2.0
204.0,
172.8, 171.3, 61.6, 61.6, 51.7, 28.7, 26.6, 26.4, 13.9. Anal. Calcd. for
(m, 11H), 1.2 (t, 3H, J = 7.2 Hz); 13C NMR (75 MHz, CDCl3):
d
n
N
N
C
14H22O7: C, 55.62; H, 7.33. Found: C, 55.50; H, 7.36.
Triethyl-3-acetylpentane-1,3,5-tricarboxylate (3i): Light yel-
n = 4 to 9,
A
low oil; IR (KBr, cmÀ1):
n
2984, 1741, 1712, 1550, 1456, 1371, 1188,
1095, 1024, 860, 783; 1H NMR (400 MHz, CDCl3):
4.2 (q, 2H,
J = 7.2 Hz), 4.1 (q, 4H, J = 7.2 Hz), 2.3–2.1 (m, 11H), 1.3–1.2 (m, 9H).
13C NMR (100 MHz, CDCl3):
172.6, 171.1, 61.5, 51.6, 28.6, 26.5,
A= Cl, OH
d
Fig. 1. Structure of dabco-based ionic liquids.
d
26.1, 13.9. Anal. Calcd. for C16H2678: C, 58.17; H, 7.93. Found: C,
58.0; H, 7.80.
Diethyl-4,4-diacetylheptanedioate (3l): White solid, mp 63–
64 8C; IR (KBr, cmÀ1): 2982, 1732, 1689, 1367; 1H NMR (400 MHz,
n
General procedure for synthesis of catalyst: The catalyst was
prepared with modification according to the procedures reported
previously [13]. To a solution of 1-butyl-1,4-diazabicyclo[2.2.2]oc-
tan-1-ium chloride (5.4 g, 26.37 mmol) in dry acetonitrile, solid
KOH (1.45 g, 26.37 mmol) was added, and the mixture was stirred
vigorously at room temperature for 15 h. The precipitate, KCl, was
removed by filtration, and the resulting filtrate was evaporated at
reduced pressure. The viscous liquid obtained was washed with
diethyl ether (20 mL Â 3) and dried to give pure ionic liquid,
CDCl3):
2.13 (t, 4H, J = 7.2 Hz), 1.3 (t, 6H, J = 7.2 Hz). 13C NMR (100 MHz,
CDCl3): 203.9, 172.1, 68.4, 58.6, 29.8, 24.6, 23.3, 13.2. Anal. Calcd.
d 4.1 (q, 4H, J = 7.2 Hz), 2.2 (t, 4H, J = 7.2 Hz), 2.14 (s, 6H),
d
for C15H24O6: C, 59.98; H, 8.05. Found: C, 59.90; H, 8.10.
Dimethyl-4,4-dicyanoheptanedioate (3o): White solid, mp 64–
65 8C; IR (KBr, cmÀ1):
n
2963, 2253, 1732, 1456, 1375; 1H NMR
[C4dabco]OH (4.56 g, 92.87%). 1H NMR (500 MHz, D2O):
d
3.3 (t, 6H,
(400 MHz, CDCl3):
d
3.7 (s, 6H), 2.7 (t, 4H, J = 7.2 Hz), 2.3 (t, 4H,
171.2, 115.1, 62.9, 27.8,
J = 7.0 Hz), 3.1 (t, 2H, J = 9.0 Hz), 3.0 (t, 6H, J = 8.0 Hz), 1.6 (quintet,
2H, J = 8.5 Hz), 1.3–1.2 (m, 2H), 0.8 (t, 3H, J = 7.5 Hz); 13C NMR
J = 8.4 Hz). 13C NMR (100 MHz, CDCl3):
d
25.9, 24.0, 13.9. Anal. Calcd. for C11H12N2O4: C, 58.63; H, 6.81; N,
10.52. Found: C, 58.53; H, 6.85; N, 10.39.
(100 MHz, D2O):
10H22N2O: C, 64.47; H, 11.90; N, 15.04. Found: C, 64.37; H, 11.78;
N, 14.91.
d 64.4, 52.0, 44.2, 23.1, 19.1, 12.8. Anal. Calcd. for:
C
Ethyl-2,4-dicyano-2-(2-cyanoethyl)butanoate (3q): Colourless
liquid; 1H NMR (300 MHz, CDCl3):
d
4.3 (q, J = 7.2 Hz, 2H), 2.7–2.5
(m, 4H), 2.5–2.3 (m, 2H), 2.2–2.0 (m, 2H), 1.3 (t, J = 7.2 Hz, 3H); 13
NMR (75 MHz, CDCl3): 166.2, 117.5, 116.4, 64.4, 47.8, 32.2, 14.2,
General procedure for Michael addition: To a well stirred
mixture of active methylene compound 1 (1 mmol) and ionic
C
d
liquid [C4dabco]OH (19.5 mg, 5 mol% of the substrate),
a
,
b
-
13.8. Anal. Calcd. for C13H19NO6: C, 54.73; H, 6.71; N, 4.91. Found:
C, 54.58; H, 6.80; N, 4.79.
unsaturated carboxylic ester or nitrile 2 (2.1 mmol) was added
and the reaction mixture was stirred at room temperature. The
formation of the products was monitored by TLC. After completion
of the reaction, water (2.0 mL) was poured to the reaction mixture,
which was then filtered and dried to obtain the products. In
general, no further purification was required to obtain the solid
product. However, for the liquid mixture, ethyl acetate (2.0 mL)
was added to the water extract of the reaction mixture. The organic
phase was dried with anhydrous MgSO4 and evaporated. In some
cases, the crude product was purified by column chromatography
over silica gel to afford the pure product. All of the products were
previously reported and were characterized by melting point
determination, IR, and 1H NMR and 13C NMR spectroscopy. The
ionic liquid catalyst was recovered from water and reused for the
subsequent reactions. Selected data for typical compounds are
given below.
3-Ethyl-1,5-dimethyl-3-cyanopentane-1,3,5-tricarboxylate
(3r): Colourless liquid; 1H NMR (300 MHz, CDCl3):
d
4.2 (q, 2H,
J = 7.2 Hz), 3.6 (s, 6H), 2.6–2.0 (m, 8H), 1.3 (t, 3H, J = 7.2 Hz); 13C
NMR (75 MHz, CDCl3): 171.7, 167.6, 117.8, 63.1, 51.8, 47.9, 31.8,
d
29.8, 13.9. Anal. Calcd. for C15H23NO6: C, 57.50; H, 7.40; N, 4.47.
Found: C, 57.43; H, 7.45; N, 4.39.
3. Results and discussion
For optimization of the reaction conditions: first, the Michael
addition of dimethylmalonate (1a) and acrylonitrile (2a) was
carried out under solvent free conditions, in the presence of
[C4dabco]OH as the catalyst. The reaction was very fast and the
reaction mixture solidified as soon as the catalyst was added (entry
1, Table 1). The effect of the concentration of the catalyst was also
studied (entries 1–3, Table 1). When the amount of the catalyst
used was changed, we found that 5 mol% of the catalyst gave
quantitative yield of the product (entry 3, Table 1). When the
amount of the catalyst, [C4dabco]OH was further reduced to 1.0
and 0.5 mol%, the reaction required more time to complete;
however, the yields were still very high. Next, the Michael addition
reactions of 1a and 2a were studied by using various catalysts, such
as, [C5dabco]OH, [C6dabco]OH, [C7dabco]OH, [C8dabco]OH,
[C9dabco]OH and [C4dabco]Cl. It was found that the reaction
proceeded efficiently, resulting in near a quantitative yield of the
product and a slight change in reaction time (entries 4–9, Table 1).
Thus, [C4dabco]OH (5 mol%) was taken as the catalyst of choice for
the Michael addition reactions.
Dimethyl-2,2-bis(2-cyanoethyl)malonate (3a): White solid, mp
141–142 8C; IR (KBr, cmÀ1):
n
2969, 2253, 1734, 1466, 1431, 1205;
3.8 (s, 6H), 2.4 (t, 4H, J = 7.5 Hz), 2.3 (t,
4H, J = 7.5 Hz); 13C NMR (75 MHz, CDCl3):
169.5, 118.4, 55.6, 53.3,
1H NMR (300 MHz, CDCl3):
d
d
29.8, 13.1. Anal. Calcd. for C11H14N2O4: C, 55.46; H, 5.92; N, 11.76.
Found: C, 55.42; H, 5.98; N, 11.61.
Diethyl bis(2-cyanoethyl)malonate (3d): White solid, mp 80–
81 8C; IR (KBr, cmÀ1):
n
2969, 2253, 1734, 1468, 1323, 1209; 1H
NMR (400 MHz, CDCl3):
J = 7.6 Hz), 2.2 (t, 4H, J = 7.6 Hz), 1.3 (t, 6H, J = 7.2 Hz). 13C NMR
(100 MHz, CDCl3): 170.0, 119.0, 58.6, 54.6, 28.3, 22.8, 13.7. Anal.
d 4.2 (q, 4H, J = 6.8 Hz), 2.4 (t, 4H,
d
Calcd. for C13H18N2O4: C, 58.63; H, 6.81; N, 10.52. Found: C, 58.47;
H, 6.68; N, 10.31.
3,3-Diethyl-1,5-dimethylpentane-1,3,3,5-tetracarboxylate
The Michael addition reactions of various active methylene
compounds to a,b-unsaturated carboxylic esters and nitriles were
(3e): Colourless crystal, mp 40 8C; IR (KBr, cmÀ1):
n
2992, 1730,
1443, 1384, 1304, 1202, 748; 1H NMR (400 MHz, CDCl3):
4.2 (q,
4H, J = 7.6 Hz), 3.6 (s, 6H), 2.3 (t, 4H, J = 8 Hz), 2.2 (t, 4H, J = 8 Hz),
1.2 (t, 6H, J = 7.6 Hz). 13C NMR (100 MHz, CDCl3):
203.8, 172.6,
d
examined in the presence of [C4dabco]OH (5 mol%) under solvent
free conditions, and the products were isolated with excellent
yields (Table 2). All of the reactions given in Table 2 underwent bis-
addition in one stroke within a very short duration with excellent
yields. The formation of bis-adducts between different active
d
171.1, 61.5, 61.4, 51.5, 28.5, 26.4, 26.2, 13.5. Anal. Calcd. for
C15H24O8: C, 54.21; H, 7.28. Found: C, 54.10; H, 7.12.
3-Ethyl-1,5-dimethyl-3-acetylpentane-1,3,5-tricarboxylate
methylene compounds and
presence of several catalysts has been reported [9h,10,11].
a,b-unsaturated compounds in the
(3h): Colourless liquid; IR (KBr, cmÀ1):
n 2995, 1730, 1712, 1453,
Please cite this article in press as: S. Keithellakpam, W.S. Laitonjam, A simple, efficient and green procedure for Michael addition
catalyzed by [C4dabco]OH ionic liquid, Chin. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.cclet.2014.01.032

G Model
CCLET-2856; No. of Pages 4
S. Keithellakpam, W.S. Laitonjam / Chinese Chemical Letters xxx (2014) xxx–xxx
3
Table 1
Table 3
Michael addition of dimethylmalonate to acrylonitrile catalized by dabco-based
ionic liquids.a
Recycling of the catalyst [C4dabco]OH in the Michael addition of dimethylmalonate
to acrylonitrile.a
CN
CN
MeO2C
Run
Time (s)
Yield (%)b
MeO2C
MeO2C
Catalyst 1
stir, r.t.
CN
1
2
3
4
5
6
<60
65
100
97
97
94
95
92
MeO2C
1a
2a
3a
72
87
.
94
Entry
Catalyst
Time (s)
3a (%)e
120
[C4dabco]OHb
[C4dabco]OHc
[C4dabco]OHd
[C5dabco]OHb
[C6dabco]OHb
[C7dabco]OHb
[C8dabco]OHb
[C9dabco]OHb
[C4dabco]Clb
3
85
89
100
87
92
89
95
90
96
a
1
2
3
4
5
6
7
8
9
Reaction conditions: 1a (1.0 mmol), 2a (2.1 mmol), catalyst ([C4dabco]OH,
10
<60
7
5 mol%), room temperature.
b
Isolated yield of 3a.
12
17
28
34
24
However, the result obtained from combination of the catalysts
was not better than the use of [C4dabco]OH alone.
a
The recyclability of the catalyst was also examined (Table 3).
Once product 3a had been filtered from the reaction mixture after
addition of water (2.0 mL), excess water from the ionic liquid was
evaporated under reduced pressure, and the catalyst was reused
for the same reaction. The catalyst did not show much reduction of
activity even after the sixth run. All reactions were completed in 1–
2 min affording 92%–100% yields.
Reaction conditions: 1a (1.0 mmol), 2a (2.1 mmol), catalyst [C4dabco]OH, room
temperature;
b
catalyst 15 mol%;
c
catalyst 10 mol%;
d
e
catalyst 5 mol%;
isolated yield of the product.
However, there were some drawbacks of using these catalysts for
the formation of bis-adducts in one step, such as, long reaction
time [9h] low yields [9h] high reaction temperature [9h] large
amount of catalyst [10], and use of volatile and toxic organic
solvents [11]. Michael addition of acrylonitrile to different active
methylene compounds in the presence of the catalyst [C4dabco]OH
were faster than methylacrylate and ethylacrylate. This is because
of the strong electron withdrawing nature of the cyano group
compared to the carboxylic ester group. The product, which
solidified from the reaction mixture in a few minutes, was filtered
after the addition of water (2.0 mL), and no further purification was
needed (entries 1,4,7,10,13,16, Table 2).
4. Conclusion
In conclusion, we have demonstrated that readily available
DABCO-based ionic liquids behave as recyclable catalysts for the
Michael addition of a broad range of active methylene compounds
with
a,b-unsaturated carboxylic esters and nitriles, offering
excellent yields in short durations. The reactions, without
hazardous organic solvents, allowed Michael addition reactions
to be performed in a simple, clean, and green manner. Most of the
products required no further purification. In this process, after
stirring for a few minutes, the product was isolated in pure form
for both solid and liquid products. The catalyst was easily
recovered and could be reused more than five times without much
loss of activity. What is more, only bis-addition products were
detected. The procedure can be applied for large-scale syntheses
also. Thus, we have developed an improved process which offers
several advantages over other processes. We believe that this new
synthetic method will greatly contribute to environmentally
greener and safer processes.
We also investigated the catalytic activities of [C4dabco]Cl
alone and
a combination of [C4dabco]Cl and [C4dabco]OH.
Table 2
Michael addition catalyzed by [C4DABCO]OHa
Michael addition catalyzed by [C4DABCO]OHa
W
R1
R1
[C4dabco]OH
W
5 mol%
R2
W
R2
1
2
3
.
Acknowledgments
Entry
1
W
Product
Time (min)
Yield (%)b
Sanjoy Keithellakpam gratefully acknowledge the University
Grants Commission, New Delhi for BSR-fellowship; and the
authors acknowledge Guwahati University, the SAIF, IIT Madras
and the CIF, IIT Guwahati, India for the spectral data.
1
MeO2CCH2COOMe
MeO2CCH2COOMe
MeO2CCH2COOMe
EtO2CCH2COOEt
EtO2CCH2COOEt
EtO2CCH2COOEt
MeO2CCH2COOEt
MeO2CCH2COOEt
MeO2CCH2COOEt
MeO2CCH2COOMe
MeO2CCH2COOMe
MeO2CCH2COOMe
NCCH2CN
CN
3a
3b
3c
3d
3e
3f
<1
15
20
30
50
55
10
20
30
10
25
30
1
100
97
99
98
97
98
99
96
98
99
99
98
100
96
99
98
98
98
2
CO2Me
CO2Et
CN
3
4
5
CO2Me
CO2Et
CN
6
References
7
3g
3h
3i
8
CO2Me
CO2Et
CN
[1] (a) T. Welton, Room-temperature ionic liquids. Solvents for synthesis and catal-
ysis, Chem. Rev. 99 (1999) 2071–2084;
9
10
11
12
13
14
15
16
17
18
3j
(b) P. Wassercheid, W. Keim, Ionic liquids-new ‘‘solutions’’ for transition metal
catalysis, Angew. Chem. Int. Ed. 39 (2000) 3772–3789;
(c) R. Sheldon, Catalytic reactions in ionic liquids, Chem. Commun. (2001)
2399–2407;
(d) J. Dupont, R.F. de Souza, P.A.Z. Suarez, Ionic liquid (molten salt) phase
organometallic catalysis, Chem. Rev. 102 (2002) 3667–3692;
(e) P. Wassercheid, T. Welton, Ionic Liquids in Synthesis, Wiley-VCH, Weinheim,
2002.
CO2Me
CO2Et
CN
3k
3l
3m
3n
3o
3p
3q
3r
NCCH2CN
CO2Me
CO2Et
CN
10
15
5
NCCH2CN
NCCH2COOEt
NCCH2COOEt
CO2Me
CO2Et
5
[2] J.A. Boon, J.A. Levisky, J.L. Pflug, J.S. Wilkes, Friedel–Crafts reactions in ambient-
temperature molten salts, J. Org. Chem. 51 (1986) 480–483.
[3] J.R. Harjani, S.J. Nara, M.M. Salunkhe, Lewis acidic ionic liquids for the synthesis of
electrophilic alkenes via the Knoevenagel condensation, Tetrahedron Lett. 43
(2002) 1127–1130.
NCCH2COOEt
20
a
Reaction conditions: 1 (1 mmol), 2 (2.1 mmol), catalyst [C4dabco]OH (5 mol%),
room temperature;
b
Isolated yield of the product.
Please cite this article in press as: S. Keithellakpam, W.S. Laitonjam, A simple, efficient and green procedure for Michael addition
catalyzed by [C4dabco]OH ionic liquid, Chin. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.cclet.2014.01.032

G Model
CCLET-2856; No. of Pages 4
4
S. Keithellakpam, W.S. Laitonjam / Chinese Chemical Letters xxx (2014) xxx–xxx
[4] (a) J. Fraga-Dubreuil, K. Bourahla, M. Rahmouni, J.P. Bazureau, J. Hamelin, Cat-
alysed esterifications in room temperature ionic liquids with acidic counteranion
as recyclable reaction media, Catal. Commun. 3 (2002) 185–190;
(b) H. Xing, T. Wang, Z.H. Zhou, Y. Dai, Novel Brønsted-acidic ionic liquids for
esterifications, Ind. Eng. Chem. Res. 44 (2005) 4147–4150;
[9] (a) L. Yang, L.W. Xu, C.G. Xia, Highly efficient KF/Al2O3-catalyzed versatile hetero-
Michael addition of nitrogen, oxygen, and sulfur nucleophiles to a,b-ethylenic
compounds, Tetrahedron Lett. 46 (2005) 3279–3282;
(b) D.Y. Kim, S.C. Huh, S.M. Kim, Enantioselective Michael reaction of malonates
and chalcones by phase-transfer catalysis using chiral quaternary ammonium
salt, Tetrahedron Lett. 42 (2001) 6299–6301;
(c) A. Horvath, Catalysis and regioselectivity in the Michael addition of azoles.
Kinetics vs. thermodynamic control, Tetrahedron Lett. 37 (1996) 4423–4426;
(d) K. Shimizu, M. Miyagi, T. Kan-no, T. Kodama, Y. Kitayama, Fe3+-exchanged
fluorotetrasilicic mica as an active and reusable catalyst for Michael reaction,
Tetrahedron Lett. 44 (2003) 7421–7424;
(e) B. Ni, Q. Zhang, A.D. Headley, Functionalized chiral ionic liquid as recyclable
organocatalyst for asymmetric Michael addition to nitrostyrenes, Green Chem. 9
(2007) 737–739;
(f) M.M. Dell’Anna, V. Gallo, P. Mastrorilli, et al., Metal catalysed Michael addi-
tions in ionic liquids, Chem. Commun. (2002) 434–435;
(c) J. Gui, X. Cong, D. Liu, et al., Novel brønsted acidic ionic liquid as efficient
and reusable catalyst system for esterification, Catal. Commun. 5 (2004) 473–477;
(d) H.P. Zhu, F. Yang, J. Tang, M.Y. He, Brønsted acidic ionic liquid 1-methylimi-
dazolium tetrafluoroborate: a green catalyst and recyclable medium for esterifi-
cation, Green Chem. 5 (2003) 38–39.
[5] (a) G. Driver, K.E. Johnson, 3-Methylimidazolium bromohydrogenates(I): a room-
temperature ionic liquid for ether cleavage, Green Chem. 5 (2003) 163–169;
(b) G.J. Kemperman, T.A. Roeters, P.W. Hilberink, Cleavage of aromatic methyl
ethers by chloroaluminate ionic liquid reagents, Eur. J. Org. Chem. 9 (2003)
1681–1686.
[6] (a) P. Formentin, H. Garcia, A. Leyva, Assessment of the suitability of imidazolium
ionic liquids as reaction medium for base-catalysed reactions: case of Knoeve-
nagel and Claisen–Schmidt reactions, J. Mol. Catal. A: Chem. 214 (2004) 137–142;
(b) H. Chen, D.R. Justes, R.G. Cooks, Proton affinities of N-heterocyclic carbene
super bases, Org. Lett. 7 (2005) 3949–3952.
(g) X. Xin, X. Guo, H.F. Duan, Y. Lin, H. Sun, Efficient Knoevenagel condensation
catalyzed by cyclic guanidinium lactate ionic liquid as medium, Catal. Commun. 8
(2007) 115–117;
(h) G.A. Salvador, S. Hasegawa, M. Hirano, S. Komiya, Michael reaction promoted
by h1-o-enolatoruthenium(II) complexes derived from Ru(cod)(cot), diphosphine,
and dimethyl malonate, Tetrahedron Lett. 39 (1998) 5209–5212.
[10] B.C. Ranu, B. Subhash, Ionic liquid as catalyst and reaction medium. The dramatic
influence of a task-specific ionic liquid, [bmIm]OH, in Michael addition of active
methylene compounds to conjugated ketones, carboxylic esters, and nitriles, Org.
Lett. 7 (2005) 3049–3052.
[7] (a) J.K. Myers, E.N. Jacobsen, Asymmetric synthesis of b-amino acid derivatives
via catalytic conjugate addition of hydrazoic acid to unsaturated imides, J. Am.
Chem. Soc. 121 (1999) 8959–8960;
(b) J.S. Yadav, B.V.S. Reddy, G. Baishya, Green protocol for conjugate addition of
thiols to a,b-unsaturated ketones using a [Bmim]PF6/H2O system, J. Org. Chem.
68 (2003) 7098–7100;
(c) N. Azizi, M.R. Saidi, LiClO4 accelerated Michael addition of amines to a,
b-unsaturated olefins under solvent-free conditions, Tetrahedron 60 (2004)
383–387.
[11] Y. Yu, L.B. Wang, Z. Zhang, et al., [Bmim]OAc catalyzed Michael addition of active
methylene to a,b-unsaturated carboxylic esters and nitriles, Chem. Res. Chin.
Univ. 26 (2010) 554–557.
[8] (a) E.D. Bergmann, D. Ginsburg, R. Pappo, Organic Reactions, vol. 10, John Wiley &
Sons, New York, 1959p. 179;
[12] Y. Yang, S.X. Dong, X.H. Liu, L.L. Lin, X.M. Feng, Chiral guanidine-catalyzed
asymmetric direct vinylogous Michael reaction of a, b-unsaturated g-butyro-
lactams with alkylidene malonates, Chem. Commun. 48 (2012) 5040–5042.
[13] Z.Z. Yang, L.N. He, X.Y. Dou, S. Chanfreau, Dimethyl carbonate synthesis catalyzed
by DABCO-derived basic ionic liquids via transesterification of ethylene carbonate
with methanol, Tetrahedron Lett. 51 (2010) 2931–2934.
(b) S. Kobayashi, Rare earth metal trifluoromethanesulfonates as water-tolerant
Lewis acid catalysts in organic synthesis, Synlett 9 (1994) 689–701;
(c) N. Srivastava, B.K. Banik, Bismuth nitrate-catalyzed versatile Michael reac-
tions, J. Org. Chem. 68 (2003) 2109–2114.
Please cite this article in press as: S. Keithellakpam, W.S. Laitonjam, A simple, efficient and green procedure for Michael addition
catalyzed by [C4dabco]OH ionic liquid, Chin. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.cclet.2014.01.032