Basic-functionalized recyclable ionic liquid catalyst: A solvent-free approach for Michael addition of 1,3-dicarbonyl compounds to nitroalkenes under ultrasound irradiation

Article abstract of DOI:10.1016/j.ultsonch.2012.11.002

A task-specific ionic liquid (TSIL) has been introduced as a recyclable catalyst in Michael addition. A series of nitroalkenes and various C-based nucleophiles were reacted in the presence of 30 mol% of recyclable basic-functionalized ionic liquid. Good t

Full text of DOI:10.1016/j.ultsonch.2012.11.002

Ultrasonics Sonochemistry xxx (2012) xxx–xxx
Contents lists available at SciVerse ScienceDirect
Ultrasonics Sonochemistry
journal homepage: www.elsevier.com/locate/ultson
Short Communication
Basic-functionalized recyclable ionic liquid catalyst: A solvent-free approach
for Michael addition of 1,3-dicarbonyl compounds to nitroalkenes under
ultrasound irradiation
⇑
Senthil Narayanaperumal , Rodrigo César da Silva, Karla Santos Feu, Alexander Fernández de la Torre,
⇑
Arlene G. Corrêa, Márcio Weber Paixão
Departamento de Química, Universidade Federal de São Carlos, 13565-905 São Carlos, SP, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
A task-specific ionic liquid (TSIL) has been introduced as a recyclable catalyst in Michael addition. A series of
nitroalkenes and various C-based nucleophiles were reacted in the presence of 30 mol% of recyclable basic-
functionalized ionic liquid. Good to excellent yields were obtained in 30 min under ultrasound irradiation.
Ó 2012 Elsevier B.V. All rights reserved.
Received 14 September 2012
Received in revised form 22 October 2012
Accepted 3 November 2012
Available online xxxx
Keywords:
Task specific ionic liquids
Michael addition
Recyclability
Ultrasonication
1,3-Dicarbonyl compounds
1. Introduction
as Al2O3, K2CO3, rhodium and ruthenium complex, clay-supported
nickel bromide, quaternary ammonium salt, and N-phenyl-
Ionic liquids (IL’s) are emerging solvents of interest as greener
alternatives to conventional organic solvents aimed at facilitating
sustainable chemistry. As a consequence of their unusual physical
properties, reusability, and eco-friendly nature, ionic liquids have
attracted the attention of chemists [1].
tris(dimethylamino)imino-phosphorane immobilized on polysty-
rene resin have been developed over the past few years [7].
Moreover, room temperature ionic liquids, particularly BMIM-BF4,
have been used as alternative green solvents to carry out the Mi-
chael addition using Ni(acac)2 and Cu(II) triflate as catalysts [8].
Recent development of IL’s turned on designing suitable ionic
liquids with specific application repetition of ILs many times that
can be used both as catalysts/promoters and solvents [9]. Several
innovative synthetic procedures on this task lead to successful re-
sults and emerge as a new field in task specific ionic liquids (TSIL’s).
In this way, TSIL’s were utilized in many chemical transformations
and especially the Michael addition reaction have much paid
attention due to the formation of C–C bond [10]. For example, Ranu
et al. explored the influence of a new tailor-made, task-specific io-
nic liquid BMIM-OH on Michael addition reactions. The BMIM-OH
was used in quantitative amount which would function as solvent
and catalyst [11].
A pressing challenge for organic chemists is to develop new cat-
alytic processes that are not only efficient, byproduct free, and high
yielding but also eco-compatible [12]. On account of these factors,
here in we report the solvent free Michael addition of 1,3-dicar-
bonyl compounds to nitroalkenes under ultrasound irradiation
using catalytic amount of basic-functionalized ionic liquid as a
recyclable catalyst (Fig. 1).
It is becoming evident from the increasing number of reports on
the use of ionic liquids as solvents, catalysts, and reagents in organic
synthesis that they are not totally inert under many reaction
conditions [2]. While in some cases, their unexpected reactivity
has proven fortuitous and in others, it is imperative that when
selecting an ionic liquid for a particular synthetic application, atten-
tion must be paid to its compatibility with the reaction conditions.
The Michael addition is a powerful reaction for the formation of
carbon–carbon bonds [3]. Moreover, the addition products are
important synthetic intermediate, which can be further manipu-
lated into a range of different classes of biologically active com-
pounds [4]. This type of reaction is traditionally promoted by
quantitative amount of strong bases that often lead to undesirable
side reactions [5]. On the other hand, a range of Lewis acids are
found to catalyze this reaction, and these procedures are also not
free from disadvantages [6]. Thus, a number of milder reagents such
⇑
Corresponding authors. Tel./fax: +55 16 33519781.
E-mail address: mwpaixao@ufscar.br (M.W. Paixão).
1350-4177/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ultsonch.2012.11.002
Please cite this article in press as: S. Narayanaperumal et al., Basic-functionalized recyclable ionic liquid catalyst: A solvent-free approach for Michael addi-
tion of 1,3-dicarbonyl compounds to nitroalkenes under ultrasound irradiation, Ultrason. Sonochem. (2012), http://dx.doi.org/10.1016/
j.ultsonch.2012.11.002

2
S. Narayanaperumal et al. / Ultrasonics Sonochemistry xxx (2012) xxx–xxx
Cl
N
N
N
O
R
O
O
O
IL-1 (30 mol%)
30 min
ultrasonication
R1
R2
NO2
R
NO2
R1
R2
Solvent-free
Short reaction time
Eco-fridendly process
Recyclable ionic liquid
High yield
Low catalyst loading
Fig. 1. Michael addition reactions of 1,3-dicarbonyl compounds to nitroalkenes.
2. Results and discussion
Table 1
Screening of reaction: ionic liquid, catalyst loading, and reaction time.
The efficacy of this protocol was initially evaluated by the
reaction of 2,4-pentanedione (2 equivalents) to trans-b-nitrosty-
rene (1 equivalent) in the presence of 30 mol% of five different
ionic liquids under sonication for 30 min. In the initial experiment,
a range of ionic liquids were screened for the Michael addition
(Table 1, entries 1–5). The result for IL-1 significantly better as
compared with other ionic liquids (entry 1, Table 1) [13]. After
selecting the appropriate ionic liquid, the amount of ionic liquid re-
quired to promote the completion of the reaction was also evalu-
ated. Reactions with 20 and 10 mol% of IL-1 showed significant
decrease in yields (Table 1, entries 1 vs 6 and 7). A decrease in yield
was observed when the reaction time was reduced from 30 to
15 min (Table 1, entry 1 vs entry 8). In the absence of ultrasonica-
tion, the conjugate adduct was obtained in only 73% of yield in
120 min reaction time at room temperature under magnetic stir-
ring (entry 9). No product was formed in the absence of IL-1 (entry
10).
Entry
TSIL’s
IL (% mol)
Time (min)
Yield (%)a,b
1
2
3
4
5
6
7
8
IL-1
IL-2
IL-3
IL-4
IL-5
IL-1
IL-1
IL-1
IL-1
–
30
30
30
30
30
20
10
30
30
–
30
30
30
30
30
30
30
15
120
30
98
42
10
23
16
81
66
88
73
–
Therefore, an optimum combination for the conjugate addition
of nitroalkenes with 1,3-dicarbonyl compounds is using 30 mol% of
IL-1 catalyst under 30 min ultrasonication under solvent free
conditions.
9c
10d
The results of the optimization process to decode the scope and
applicability of reactions are summarized in Tables 2 and 3. The
Michael addition of 2,4-pentanedione to a variety of nitroalkenes
was examined considering the usefulness and versatility of
adducts in organic synthesis [14]. It is apparent from results that
all reactions of nitroalkenes proceeded smoothly affording the
desired products with good to excellent yields. Electronic effects
had small influence on the reaction course, with electron-with-
drawing groups attached to the aromatic ring of b-nitrostyrenes
afforded the products with good to excellent yield (Table 2, entries
2–5 and 8–9). By using 30 mol% IL-1, the reactions of nitrostyrenes,
bearing ortho or para electron donating substituent, with 2,4-pen-
tanedione proceeded smoothly, and afforded the corresponding
Michael adducts in 99% yield (Table 2, entries 6 and 7). We also
employed other nitrostyrene in this reaction, e.g. heterocyclic.
For instance, 2-(2-nitrovinyl) thiophene reacted with 2,4-pentane-
dione, allowing the conjugate adduct in 76% yield (Table 2, entry
10).
Next, the scope of the reaction was investigated with different
nucleophilic species. As shown in Table 3, various ketoesters effec-
tively reacted with trans-b-nitrostyrene in the presence of 30 mol%
IL-1 (Table 3, entries 1–3). An important feature of our methodol-
ogy is the use of different nucleophiles, such as cyclic-b-ketoester,
giving the corresponding products in good yields (Table 3, entries
4–6). This result demonstrates the potential wide ranging utility
of this methodology by the preparation of various conjugate
adducts.
a
Unless otherwise specified, the reactions were performed using trans-b-nitro-
styrene (0.25 mmol), 2,4-pentanedione (0.5 mmol), and ionic liquid (30 mol%)
under ultrasonication for 30 min.
b
Isolated yield.
c
Reaction was performed without ultrasonication under room temperature for
2 h.
d
Reaction was performed without ionic liquid.
Hence, we attempted to reuse the ionic liquid/catalyst, which was
one of the prime objectives in our quest. In this regard, we per-
formed a set of experiments to explore whether the ionic liquid
can be reused for further reactions (Fig. 2). After completion of
the reaction, task-specific ionic liquid catalyst was recovered and
subjected to another run, affording the product in 98% yield. This
process was repeated four more times, affording the desired prod-
uct in excellent yields. The simple experimental and product isola-
tion procedures combined with the ease of recovery and reuse of
the reaction medium is expected to contribute to the development
of a green strategy for the Michael addition reactions.
3. Experimental section
For visualization, TLC plates were either placed under ultravio-
let light, or stained with iodine vapor, or acidic vanillin. All solvents
were used as purchased unless otherwise noted. Purification of
products was carried out by flash chromatography on silica gel.
Although steps toward sustainability can be made by reusing
solvents, recycling is rarely accomplished with complete efficiency.
Please cite this article in press as: S. Narayanaperumal et al., Basic-functionalized recyclable ionic liquid catalyst: A solvent-free approach for Michael addi-
tion of 1,3-dicarbonyl compounds to nitroalkenes under ultrasound irradiation, Ultrason. Sonochem. (2012), http://dx.doi.org/10.1016/
j.ultsonch.2012.11.002

S. Narayanaperumal et al. / Ultrasonics Sonochemistry xxx (2012) xxx–xxx
3
Table 2
Michael addition reactions of 2,4-pentanedione to nitroalkenes.
a,b
Entry
1
Substrate
Product
Yield
98
2
52
3
4
5
6
7
8
9
71
74
99
99
99
>99
81
10
61(76)c
a
Unless otherwise specified, the reactions were performed using nitrostyrene (0.25 mmol), 2,4-pentanedione (0.5 mmol)
and ionic liquid (30 mol%) under ultrasonication for 30 min at room temperature.
b
Isolated yield.
c
Yield in parenthesis refer to 1 h reaction time under ultrasonication.
Chemical yields refer to pure isolated substances. 1H and 13C NMR
3.1. 1General synthetic procedure of ionic liquid
spectra were obtained using deuterated solvents (CDCl3 and
DMSO-d6) in a Bruker Avance III spectrometer. Chemical shifts
are reported in ppm from tetramethylsilane with the solvent as
the internal standard. All ionic liquids were prepared according lit-
erature procedure [13]. 1H and 13C NMR spectral data of the com-
pounds are identical to those reported.
3.1.1. Synthesis of-1-methyl-3-(2-(piperidin-1-yl)ethyl)-1H-imidazol-
3-ium-chloride (IL-1)
In a two neck 100 mL round-bottomed flask equipped with re-
flux condenser and magnetic stirrer, N-methyl imidazole (1.025 g,
12.5 mmol), 1-(2-chloroethyl)piperidine hydrochloride (1.84 g,
Please cite this article in press as: S. Narayanaperumal et al., Basic-functionalized recyclable ionic liquid catalyst: A solvent-free approach for Michael addi-
tion of 1,3-dicarbonyl compounds to nitroalkenes under ultrasound irradiation, Ultrason. Sonochem. (2012), http://dx.doi.org/10.1016/
j.ultsonch.2012.11.002

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S. Narayanaperumal et al. / Ultrasonics Sonochemistry xxx (2012) xxx–xxx
Table 3
Variation of nucleophiles in reaction with trans-b-nitrostyrene catalyzed byIL-1.
Entrya
1
Nucleophile
Product
Yieldb,c
92
2
3
83(1:1)
80(1:1)
4
5
6
62(8:2)
>99(7:3)
89(7:3)
a
Unless otherwise specified, the reactions were performed using trans-b-nitrostyrene (0.25 mmol),
nucleophile (0.5 mmol), and ionic liquid (30 mol%) under ultrasonication.
b
Isolated yield.
d.r. (in parenthesis) was determined by NMR analysis.
c
Fig. 2. Recyclability of ionic liquid for the conjugate addition.
Please cite this article in press as: S. Narayanaperumal et al., Basic-functionalized recyclable ionic liquid catalyst: A solvent-free approach for Michael addi-
tion of 1,3-dicarbonyl compounds to nitroalkenes under ultrasound irradiation, Ultrason. Sonochem. (2012), http://dx.doi.org/10.1016/
j.ultsonch.2012.11.002

S. Narayanaperumal et al. / Ultrasonics Sonochemistry xxx (2012) xxx–xxx
5
10 mmol) and absolute ethanol (10 mL) were added. The mixture
was refluxed for 24 h. After the reaction, the solvent was removed
under vacuum, the residue was washed with dichloromethane
and dried at 70 °C under vacuum. The white solid was dissolved
in the mixture of ethanol (5 mL) and water (5 mL), and neutralized
by NaOH (0.4 g, 10 mmol). After removal of solvents, the product
was extracted with dichloromethane, dried at 70 °C under vacuum
for 10 h. Pale yellow oily liquid was obtained in 90% yield. 1H NMR
(400 MHz, DMSO-d6) d: 1.52–1.37 (m, 6 H), 2.53–2.59 (m, 4 H),
2.90–2.94 (m, 2 H), 3.86 (s, 3 H), 4.42–4.47 (m, 2 H), 7.76 (s, 1 H),
7.86 (s, 1H), 9.41 (s, 1H) ppm. 13C NMR (100 MHz, DMSO-d6) d:
23.1, 24.4, 35.7, 45.0, 53.2, 56.5, 122.5, 123.2, 137.0 ppm.
(d, J = 7,6 Hz, 2H), 8.33 (d, J = 7.8 Hz, 2H) ppm. 13C NMR
(100 MHz, DMSO-d6) d: 13.9, 25.4, 28.4, 28.7, 28.8, 28.9, 29.0
(2C), 31.3, 39.7, 56.6, 107.6, 142.0, 155.8 ppm.
3.2. General procedure for the synthesis of Michael adduct
In
a
vial, ionic liquid (30 mol%), trans-b-nitrostyrene
(0.25 mmol) and 1,3-dicarbonyl compound (0.5 mmol) was added
and the reaction mixture was allowed under ultrasonication for
30 min. After completion of the reaction (monitored by TLC), the
reaction mixture was washed with Et2O (3 Â 5 mL) and dried over
Na2SO4. The crude was purified by silica column chromatography
affording the corresponding pure Michael adducts. The NMR data’s
of products were in accordance with literature data [15].
3.1.2. Synthesis of 1-butyl-4-(dimethylamino)pyridinium bromide (IL-
2)
A mixture of 4-dimethylaminopyridine (5 mmol) and butyl bro-
mide (6 mmol) and MeCN (10 mL) was allowed to stir 24 h at 70 °C.
The resulting mixture was then evaporated affording the yellow
crystals. The resulting crystalline mass was washed twice with
ether (20 mL) and, after vacuum drying, a pale yellow crystals
was obtained in 95% yield. 1H NMR (400 MHz, DMSO-d6) d: 0.88
(t, J = 7.3 Hz, 3 H), 1.27–1.16 (m, 2 H), 1.76–1.68 (m, 2 H), 3.17 (s,
6 H), 4.17 (t, J = 7.3 Hz, 2 H), 7.03 (d, J = 7.8 Hz, 2 H), 8.34 (d,
J = 7.7 Hz, 2 H) ppm. 13C NMR (100 MHz, DMSO-d6) d: 13.3, 18.7,
32.3, 39.7, 56.3 (2C), 107.7, 142.0, 155.8 ppm.
3.3. General procedure for ionic liquid recycle experiments
Following extraction with diethyl ether, the ionic liquid solution
was subjected to vacuum to remove traces of diethyl ether, flushed
with inert gas and charged with further portions of trans-b-nitro-
styrene (1 eq) and 2,4-pentanedione (2 eq) at room temperature.
4. Conclusions
In conclusion, we have developed an efficient solvent free con-
jugate Michael addition of 1,3-dicarbonyl compounds to various
nitroalkenes in the presence of catalytic amount of base-behavior
ionic liquid under ultrasonication providing the desired conjugate
adducts in good to excellent yields. The versatility, economic and
high yield of this method, in addition to the shorter reaction time
and low loading of catalyst/ionic liquid, highlights the potential for
the use of this developed method in large scale library synthesis
involving carbon–carbon bond formation. Most importantly, the
recovery and recycling of the ionic liquid in further reactions was
successfully achieved and can be reused for at least four successive
runs without observing significant decrease in yield.
We believe that the ionic liquids which enable the easy recy-
cling in organic reactions will have great synthetic value and
potentially find wide applications in organic synthesis. Further
investigations to clarify the mechanism and explore applications
in asymmetric transformations are currently underway in our
laboratory.
3.1.3. Synthesis of 1-butyl-4-(dimethylamino)pyridinium
tetrafluoroborate (IL-3)
A mixture of 1-butyl-4-(dimethylamino)pyridinium bromide
(5 mmol), sodium tetrafluoroborate (6 mmol) and distilled water
(1 mL) was vigorously stirred for 60 min. The lower aqueous phase
was separated and discarded and, to the remaining liquid, dichlo-
romethane (20 mL) was added. The organic phase was separated
and solvent evaporation afforded the desired 1-butyl-3-methylimi-
dazolium tetrafluoroborate in quantitative yield. 1H NMR
(400 MHz, DMSO-d6) d: 0.88 (t, J = 7.3 Hz, 3 H), 1.27–1.16 (m, 2
H), 1.76–1.68 (m, 2 H), 3.17 (s, 6 H), 4.17 (t, J = 7.3 Hz, 2 H), 7.03
(d, J = 7.8 Hz, 2 H), 8.34 (d, J = 7.7 Hz, 2 H) ppm. 13C NMR
(100 MHz, DMSO-d6) d: 13.3, 18.7, 32.3, 39.7, 56.3 (2C), 107.7,
142.0, 155.8 ppm.
3.1.4. Synthesis of 4-(dimethylamino)-1-dodecylpyridinium bromide
(IL-4)
A mixture of 4-dimethylaminopyridine (5 mmol) and dodecyl
bromide (6 mmol) and MeCN (10 mL) was allowed to stir 24 h at
70 °C. The resulting mixture was then evaporated affording the yel-
low crystals. The resulting crystalline mass was washed twice with
ether (20 mL) and, after vacuum drying, pale yellow crystals was
obtained in 99% yield. 1H NMR (400 MHz, DMSO-d6) d: 0.83 (t,
J = 7.25 Hz, 3 H), 1.30–1.13 (m, 18 H), 1.78–1.69 (m, 2 H), 3.17 (s,
6 H), 4.16 (t, J = 7,2 Hz, 2H), 7.03 (d, J = 7,6 Hz, 2H), 8.33 (d,
J = 7.8 Hz, 2H) ppm. 13C NMR (100 MHz, DMSO-d6) d: 13.9, 25.4,
28.4, 28.7, 28.8, 28.9, 29.0 (2C), 31.3, 39.7, 56.6, 107.6, 142.0,
155.8 ppm.
Acknowledgements
Senthil Narayanaperumal thanks FAPESP (2011/01055-8) for
postdoctoral fellowship, while R.C.S, A.F.D.L.T and K.S.F are CNPq
and CAPES fellowship holders for the Ph.D., and cordially
acknowledge their financial support. We are also obliged to CNPq
(INCT-Catálise) and FAPESP (2009/07281-0) for their financial
support.
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Please cite this article in press as: S. Narayanaperumal et al., Basic-functionalized recyclable ionic liquid catalyst: A solvent-free approach for Michael addi-
tion of 1,3-dicarbonyl compounds to nitroalkenes under ultrasound irradiation, Ultrason. Sonochem. (2012), http://dx.doi.org/10.1016/
j.ultsonch.2012.11.002