Amino Acid Amide based Ionic Liquid as an Efficient Organo-Catalyst for Solvent-free Knoevenagel Condensation at Room Temperature

Article abstract of DOI:10.1007/s10562-019-02840-5

Abstract: Ionic liquids of amino acid amide were synthesized and used as an efficient catalyst for solvent-free Knoevenagel condensation. Synthesized ionic liquids are an environmentally benign, inexpensive, metal free and plays the dual role of solvent as well as an efficient catalyst for Knoevenagel condensation. A wide range of aliphatic, aromatic and heteroaromatic aldehydes easily undergo condensation with malononitrile and ethyl cyanoacetate. The reaction proceeds at room temperature without using any organic solvent and is very fast with good to excellent yield. Additionally, the catalyst is easily separable and recyclable without loss of activity. Graphic Abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s10562-019-02840-5

Catalysis Letters
https://doi.org/10.1007/s10562-019-02840-5
Amino Acid Amide based Ionic Liquid as an Efcient Organo‑Catalyst
for Solvent‑free Knoevenagel Condensation at Room Temperature
Pralhad A. Burate1,2 · Balasaheb R. Javle1,2 · Pranjal H. Desale1 · Anil K. Kinage1,2
Received: 16 January 2019 / Accepted: 19 May 2019
© Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
Ionic liquids of amino acid amide were synthesized and used as an efcient catalyst for solvent-free Knoevenagel condensa-
tion. Synthesized ionic liquids are an environmentally benign, inexpensive, metal free and plays the dual role of solvent as
well as an efcient catalyst for Knoevenagel condensation. A wide range of aliphatic, aromatic and heteroaromatic aldehydes
easily undergo condensation with malononitrile and ethyl cyanoacetate. The reaction proceeds at room temperature without
using any organic solvent and is very fast with good to excellent yield. Additionally, the catalyst is easily separable and
recyclable without loss of activity.
Graphic Abstract
O
R
NC
CN
H
CN
NC
R
Cl
O
Me
Cl
N
H
O
NH2
Me
N
H
+
NH3
ClO4
HClO4
Ionic Liquid
Keywords Ionic liquid · Amino acid amide · Knoevenagel condensation · Solvent-free · Acrylonitrile · Cyanoacrylate
1 Introduction
Knoevenagel condensation is a versatile C–C bond forming
reaction between carbonyl compounds and active methylene
compounds to form electrophilic alkenes in organic synthe-
sis [1]. This reaction found many applications such as, in
the synthesis of intermediate of fne chemicals [2–4], in the
synthesis of intermediates like Quinoline, Imidazopyridines,
Coumarin, Benzofuran and Iminocoumarin derivatives of bio-
logical important compounds [5–10]. The methods reported
so far requires long reaction time and is usually catalyzed by
acid or base at high temperature [11] or it needed other special
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s10562-019-02840-5) contains
supplementary material, which is available to authorized users.
* Anil K. Kinage
ak.kinage@ncl.res.in
1
Chemical Engineering & Process Development Division,
CSIR-National Chemical Laboratory, Pune 411008, India
2
Academy of Scientifc & Innovative Research (AcSIR),
New Delhi 110025, India
Vol.:(0123456789)
1 3

P. A. Burate et al.
conditions, such as microwave irradiation [12]. Also in some
reactions the catalyst cannot be recycled [13].
round bottom fask equipped with magnetic stir bar, a mix-
ture of l-alanine (11.2 mmol) in pyridine (15 ml) was stirred
at room temperature (25–30 °C) for 10 min. Then dichlo-
rodimethyl silane (11.2 mmol) was added drop by drop to
the reaction mixture and reaction was further stirred till the
clear solution was obtained. To this reaction mixture aniline
(45 mmol) was added and continued stirring. After com-
pletion of reaction (monitored by TLC) saturated solution
of NaHCO3 was added to quench the pyridine as well as
silane and the ethyl acetate was added to form two separate
layers. Two layers were separated by using separating fun-
nel. Organic layer was washed with saturated solution of
NaHCO3 (three times) and dried over Na2SO4. The organic
layer was then concentrated in vaccuo and pure compounds
were isolated by column chromatography. The isolated pure
products were then confrmed by 1H, 13C NMR and HRMS
analysis.
Solvent-free organic synthesis has been receiving consider-
able attention because of growing worldwide concerns over
chemical wastes and future resources as well as for the require-
ments of green chemistry [14]. In such means, scientists are
concentrating more on the development of environmentally
friendly organic synthesis through the use of metal-free cata-
lysts, eco-friendly solvents, renewable resources, and waste
reduction. The utilization of reusable catalysts and solvent-
free media for organic synthesis has been recently developed,
and relates with the green chemistry protocols. During last
decade ionic liquids (ILs) have emerged as a very potential
green alternative to volatile and hazardous organic solvents
and are being used as efcient and recyclable reaction media
for a variety of important reactions [15, 16]. Importantly, they
have been introduced as alternative green reaction media due
to their unique chemical and physical properties such as low
vapour pressure, high thermal, and chemical stability [17–23].
Moreover, they have also been used as catalyst due to its good
activity, selectivity, controlled miscibility and ease of recy-
clability [24, 25]. In recent years, many functional ILs have
been synthesized and developed further as catalyst, playing a
remarkable role in various organic reactions like Henry reac-
tion [26], Mannich reaction [27], Friedel–Crafts alkylation
[28]. A variety of ILs have been employed for Knoevenagel
condensation reaction too, such as [C6-mim]PF6 [29] [bmim]
Cl.xAlCl3, [bpy]Cl.xAlCl3 [30] [bmim]BF4 [31] [bmIm]OH
[32], [MmIm][MSO4] [33], [MeOEt-MIm]+[CF3COO]− [34],
guanidinium lactate ILs [35], ethylammonium nitrate [36],
HMTA-AcOH-H2O [37], 2-hydroxyethylammonium formate
[38], [C4-choline][Ac] [39], glycine in ILs [40], Ether- and
alcohol-functionalized ILs [41], N-methyl morpholine (Nmm)
based ILs [42], [Et3NH][HSO4] [5], [C4dabco][BF4] [43],
amino acid ILs [44], etc.
2.2 General Procedure for the Synthesis of ILs
(5d–5f)
We have synthesized ILs from amino acid amide of l-alanine
by the treatment of HClO4 in dichloromethane at 5–10 °C
temperature for 30 min. (Table 1) by using the procedure
reported in the literature [49]. In detail procedure, a mix-
ture of amino acid amide (0.5 mmol) in dichloromethane
(5 ml) was taken in an oven dried 50 ml round bottom fask
equipped with a magnetic stir bar in an ice bath. To this
reaction mixture perchloric acid (0.5 mmol) was added drop
by drop and the reaction was stirred at room temperature for
30 min. After completion of reaction the dichloromethane
was removed under reduced pressure to aford pure IL. The
quantitative yield is provided in Table 1. The products were
1
then confrmed by H, 13C NMR and by HRMS analysis.
The 5f was also characterized by TGA, DTA and DSC and
spectral data is presented in Supporting Information Fig-
ures S3–S5. From DSC spectra glass transition temperature
of the IL was observed around at 68.4 °C. From TGA and
DTA it was observed that the IL completely decomposed
between temperature 120–180 °C.
Recently, ILs made from amino acid have attracted sig-
nifcant attention in many chemical and biochemical trans-
formations [45–48]. In this context, the amino acid amides
were synthesised from amino acids and ILs of these amino
acid amides were prepared by using a simple reaction pro-
cess and we, herein report ILs of amino acid amides as an
acidic Brønsted ILs as an environmentally benign, efcient
and recyclable catalyst for Knoevenagel condensation in
solvent-free media at room temperature.
2.3 General Procedure for the Synthesis
of Acrylonitrile’s and Cyanoacrylates
In an oven dried clean 10 ml round bottom fask equipped
with a magnetic stir bar, benzaldehyde (0.9 mmol) and (5f)
(30 mol%) were taken and stirred for 10 min. Under the
stirring condition, active methylene compound (0.9 mmol)
was added to the reaction mixture and allowed the reac-
tion mixture to stir at room temperature for 30 min. Upon
completion of reaction (monitored by TLC), 5 ml of ethyl
acetate and water was added to the reaction mixture. Two
layers formed were separated by using separating funnel.
2 Experimental
2.1 General Procedure for the Synthesis of Amino
Acid Amides (5a–5c)
At frst, amino acid amides were synthesised by using pro-
cedure described earlier in the literature [49]. In a 100 ml
1 3

Amino Acid Amide based Ionic Liquid as an Efcient Organo‑Catalyst for Solvent‑free Knoevenagel…
Table 1 Synthesise of ILs of
Sr. no.
1
Amino acid amide
Acid
Product
Isolated
yield %
amino acid amides
HClO4
99
OMe
OMe
O
O
(5d)
N
H
N
H
NH2
NH3
ClO4
(5a)
2
3
HClO4
HClO4
99
Br
Br
O
O
(5e)
N
H
N
H
NH2
NH3
ClO4
(5b)
99
Cl
Cl
O
O
(5f)
N
H
N
H
NH2
NH3
ClO4
(5c)
Reaction conditions: Amino acid amide (0.1 mmol), Acid (0.1 mmol), DCM, 5–10 °C for 30 min
Table 2 Screening of catalytic activity of ILs for Knoevenagel condensation
O
IL
(30 mol%)
CN
CN
NC
CN
H
CH
80oC
3OH,
12h
Sr. no.
Ionic liquid
Isolated yield %
1
2
3
4
5
6
5a
5b
5c
5d
5e
5f
trace
trace
trace
27
34
42
Reaction conditions: Benzaldehyde (0.9 mmol), malononitrile (0.9 mmol), IL (30 mol %), methanol (5 ml)
The aqueous layer was washed with ethyl acetate (5 ml×3
times). The organic layer was dried over anhydrous Na2SO4,
fltered and concentrated in vacuo. The residue was sub-
jected to column chromatography to obtain the correspond-
ing product. The products were confrmed by 1H, 13C NMR
and HRMS analysis.
has no activity in Knoevenagel condensation and IL (5f)
shows good catalytic activity for Knoevenagel condensation
in methanol. On the basis of these results we, herein wish to
report ILs of amino acid amide 1-((4-chlorophenyl) amino)-
1-oxopropan-2-aminium perchlorate (5f) an acidic Brønsted
IL as an environmentally benign, efcient and recyclable
catalyst for Knoevenagel condensation in solvent-free media
at room temperature.
3 Results and Discussion
In further experiments, we investigated the optimi-
zation of reaction conditions regarding the catalyst and
solvent of the reaction. For this purpose, benzaldehyde 1
(0.9 mmol) and malononitrile 2 (0.9 mmol) were chosen
as model substrate and 30 mol % of catalyst for the synthe-
sis of representative compound 3a at 80 °C. Initially, we
carried out the reaction in the absence of catalyst; only a
We examine the catalytic activity of these synthesised amino
acid amides and ILs for the Knoevenagel condensation of
Benzaldehyde and malononitrile in methanol at 80 °C. The
results obtained were summarised in Table 2. From results,
it is observed that amino acid amides without protonation
1 3

P. A. Burate et al.
Table 3 Optimization of reaction conditions for Knoevenagel condensation
O
Catalyst
(30 mol%)
CN
CN
NC
CN
H
1
2
3a
Entry
Solvent
Temp. (oC)
Time (h)
Isolated
yield
(%)
1a
2b
3c
4
5
6
7
8
9
10
11
12
13
14
15d
16e
17f
DMF
DMF
DMF
DMF
Dioxane
DMSO
CH3CN
THF
CH3OH
C6H5H3
H2O
–
80
80
80
80
80
80
80
80
80
80
80
80
80
RT
RT
RT
RT
24
24
24
12
12
12
12
12
12
12
6
trace
trace
trace
43
43
27
24
22
42
18
71
92
86
97
73
57
34
1
–
–
–
–
0.5
0.5
0.5
0.5
0.5
–
aNo catalyst
bCatalyst-alanine
cCatalyst-amino acid amide
Catalyst concentration d20 mol%
e10 mol%
f5 mol%
trace amounts of the product was formed even after 24 h
in DMF (Table 3 entry 1). Next, we carried out reactions
using alanine (an amino acid precursor for amidation) and
amino acid amide without protonation, trace amount of
product was formed after 24 h (Table 3 Entry 2 & 3). It
was then clear that amino acid amide without protonation
has no activity in Knoevenagel condensation. Therefore,
we used protonated amino acid amide (IL) for Knoeve-
nagel condensation for further studies. Next, to investigate
the solvent efect, we performed the reaction in diferent
organic solvents. The desired product was obtained in
moderate to good yield within 12 h (Table 3 entry 4–10).
This is because of poor solubility of IL in organic solvents.
When water was used as a solvent, the yield of the reac-
tion was signifcantly increased to 71% in 6 h (Table 3
entry 11). Further, we carried out the solvent-free reac-
tion and observed a drastic change in the yield of product.
(Table 3 entry 12). Then we carried out the same reac-
tion at room temperature and surprisingly, the yield of the
reaction was increased to 97% in 30 min. (Table 3 entry
13). We observed that 86% yield of the isolated product
was obtained after 30 min and 92% yield of the isolated
product was obtained after 1 h. the result was added in
Table 3 entry no. 13). At high temperature CN group of
one reactant may form acryl amide as by-product due to
hydration reaction, hence yield of desired product is less.
Then we investigated the efect of substrate to catalyst
ratio (Table 3 Entry 14–17) the yield of the product was
decresed buy decreseing catalyst substrat to catalyst ratio.
The highest yield of product was obtained at 30 mol% of
catalyst. Thus, it is concluded that 30 mol% of IL is an
ideal concentration for the best results. Therefore, all fur-
ther reactions were carried out by using 30 mol% of the
catalyst at room temperature under solvent-free conditions.
1 3

Amino Acid Amide based Ionic Liquid as an Efcient Organo‑Catalyst for Solvent‑free Knoevenagel…
Table 4 Solvent-free Knoevenagel condensation reaction of diferent aldehydes with active methylene compounds over IL (5f)
X
O
(5f)
(30 mo%)
30
R
X
NC
R
H
CN
3a-z
min.
rt,
Entry
R
X
Product
Isolated
yield %
1
2
3
4
5
6
7
8
C6H5
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
CN
3a
3b
3c
3d
3e
3f
3 g
3 h
3i
3 J
3 k
3 l
3 m
3n
3o
3p
3q
3r
97
96
93
94
87
92
88
91
98
84
86
72
95
91
94
89
84
87
92
96
90
93
83
81
71
82
4-MeO–C6H4
2-Cl–C6H4
4-C2H5–C6H4
3-Br–C6H4
4-F–C6H4
4-Cl–C6H4
2-MeO–C6H4
4-Me–C6H4
1-C10H7
2,5-(Me)2–C6H3
3-CN–C6H4
C6H5
4-MeO–C6H4
2-Cl–C6H4
4-C2H5–C6H4
3-Br–C6H4
4-F–C6H4
4-Cl–C6H4
2-MeO–C6H4
4-Me–C6H4
2-Me–C6H4
2,5-(Me)2–C6H3
3-CN–C6H4
4-OH–C6H4
2-Me–C6H4
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
3 s
3t
3u
3v
3w
3x
3y
3z
CO2Et
Using these optimized reaction conditions, the scope and
efciency of this approach were explored for the synthesis
of other acrylonitrile and cyanoacrylate derivatives and the
obtained results were summarized in Table 4. As illustrated
in Table 4, various aromatic aldehydes with electronic donat-
ing groups (–Me, –OMe, –Et, –OH, etc.) and electronic with-
drawing groups (–Cl, –F, –Br,–CN) at o-, m-, p-positions of
aromatic ring, were reacted efectively with active methylene
compounds like malononitrile and ethyl cyanoacetate. The
good to excellent yields of acrylonitrile and cyanoacrylate
derivatives were obtained over IL. From these results, it was
observed that less yield of product was obtained when alde-
hydes with an electron withdrawing group compare to the
aldehydes with electron donating groups.
(Table 5). Results show that (Table 5), cyclic ketones can
also undergo reaction under optimized reaction conditions
to give moderate to a good yield of products (Table 5 entry
1–4). Notably, condensation of aliphatic aldehydes with
ethyl cyanoacetate accomplished with moderate to good
yield (Table 5 entry 5 & 6). The heteroaromatic aldehydes
such as Thiophene-2-carboxaldehyde and Furan-2-car-
boxaldehyde gave a good yield of corresponding products
(Table 5 entry 7–10). Surprisingly, α, β-unsaturated alde-
hyde like Cinnamaldehyde and di-Substituted aldehyde like
3-hydroxy, 4-methoxy benzaldehyde also easily undergo
reaction under optimized reaction condition with ethyl
cyanoacetate to aford respective products in very good yield
(Table 5 entry 11 & 12).
Next, we explored the feasibility of this protocol with var-
ious cyclic ketones and aliphatic, heteroaromatic aldehydes
The reusability of the catalyst is a signifcant advantage,
particularly for commercial applications. Thus, the recovery
1 3

P. A. Burate et al.
Table 5 Solvent-free Konevenagel condensation of cyclic ketones,
Table 6 Reusability of catalyst (5f) for model reaction
aliphatic, heteroaromatics and unsaturated aldehyde
Entry
Run
Time (min)
Isolated yield
(%)
CN
(5f)
(30 mol%)
30
1
2
3
4
5
6
1
2
3
4
5
6
30
30
30
30
30
30
97
96
96
95
95
93
R
X
NC
1a
X
min.
rt,
R'
4a-l
Entry
1a
X
Product
Isolated
yield
(%)
1
2
CN
CN
4a
4b
54
67
O
O
repeated six times and results show that there is no signif-
cant change in yield of Knoevenagel condensation product.
These results show that the IL can be easily separable and
reuse for Knoevenagel condensation reaction more than six
times without loss of its activity. The fresh and after 6th
recycled catalyst was characterized by FTIR and 1H NMR
data shows almost no change after 6th recycling (Supporting
Information, Figures S1 and S2).
3
4
CO2Et
CO2Et
4c
4d
53
58
O
O
O
H
5
6
7
CO2Et
CO2Et
CN
4e
4f
58
53
68
Next, we performed the model reaction on 2 g scale and
2.8 g of 3a was prepared in 95% yield. Therefore, it is a sim-
ple route to solvent-free gram scale synthesis of substituted
electrophilic alkenes using amino acid amide based ILs as
a catalyst. Moreover, only the E-isomers of cyanoacrylates
were detected and confrmed by NOESY NMR analysis of
3m. (Supporting information Figure-S1).
Me
Me
H
Me
O
O
4 g
O
H
We have compared the catalytic activity of ILs of amino
acid amides (5f) with the other ILs reported in the literature
for Knoevenagel condensation. It have been observed that
most of catalysts exhibit considerable catalytic performance
in the reaction. However, in some cases, extra base is needed
along with ILs [29, 31, 33, 44], special equipment’s like
glow box is required [30]. However, the ILs reported here is
metal free, easy to prepared and recyclable without loss in
catalytic performance (Table 7).
O
8
CN
4 h
4i
62
66
60
73
S
O
S
H
O
9
CO2Et
CO2Et
CO2Et
H
O
10
11
4j
H
O
4 k
H
On the basis of the above results and previous related
studies, a plausible reaction mechanism of Knoevenagel con-
densation catalyzed by IL for the synthesis of acrylonitrile
and cyanoacrylate is shown in Scheme 1. As IL used here
is a protic Brønsted acidic IL initially, the aldehyde is acti-
vated by partial bond formation between the aldehyde and
the acidic proton of IL to form reactive intermediate-(I). It
facilitated the nucleophilic attack of the active methylene
compound for C–C bond formation to form intermediate-
(II). The final Knoevenagel condensation product was
formed by the elimination of water molecule and an IL is
regenerated, which continue the reaction cycle.
O
12
CO2Et
4 l
77
H
MeO
OH
and reusability of IL were also investigated and results were
shown in Table 6. After the completion of the reaction, ethyl
acetate and water was added to the reaction mixture. The
two separate layers were formed. The aqueous layer was
separated by using separating funnel. The aqueous layer was
washed with ethyl acetate three times. The IL was recovered
from the aqueous layer by removing water under reduced
pressure and was reused for a fresh batch. The reaction was
1 3

Amino Acid Amide based Ionic Liquid as an Efcient Organo‑Catalyst for Solvent‑free Knoevenagel…
Table 7 Comparison of catalytic performance of IL (5f) and reported ILs for Knoevenagel condensation
Sr. no. Catalyst
Solvent
Temp. Reaction time min/h Yield % Ref. no.
1
2
3
4
5
6
7
8
Glycine
[bmim]Cl·AlCl3
Piperidine
[bmIm]OH
Glycine
[6-mim] PF6
Solvent-free (In glove box)
[bmim]BF4
Solvent-free
[mmIm][mSO4]
Solvent-free
Guanidinium lactate ILs
H2O
2-hydroxyethylammonium formate
RT
RT
RT
RT
RT
RT
RT
22 h
5 min
10 h
10–30 min
70 min
40 min
1–7 min
77
87
94
96
98
98
93
96
88
93
91
99
100
92
95
97
[29]
[30]
[31]
[32]
[33]
[34]
[35]
[37]
[38]
[40]
[41]
[42]
[43]
[44]
[45]
This work
[MeOEt-MIm]+[CF3COO]−
Guanidinium lactate ILs
HMTA-AcOH-H2O
2-hydroxyethylammonium formate
40 °C 20 min
RT 5 h
40 °C 20 min
9
10
11
12
13
14
15
16
Tetrabutylphosphonium amino acid ILs Solvent-free
3-Hydroxypropanaminium Acetate
N-methyl morpholine (Nmm) based ILs H2O
[C4dabco][BF4]
DABCO
Tricationic ILs of pyridine
ILs of amino acid amides
Solvent-free (Pulverized in a mortar) RT 5 min
RT
RT
7 min
1–5 min
H2O
[HyEtPy] Cl
H2O
50 °C 20 min
RT
RT
10 min
30 min
Solvent-free
Cl
X
References
O
O
Me
ClO4
N
H
CN
H
O
NH3
Cl
1. Jones G (1967) Org React 15:204–599
2. Freeman F (1980) Chem Rev 80:329–350
3. Tietze LF (1996) Chem Rev 96:115–136
H
2O
H
Me
N
H
N
OH
ClO4
O
H
H
H
4. Kim I, Kim SG, Choi J, Lee GH (2008) Tetrahedron 64:664–671
5. Siddique ZN, Khan K (2014) ACS Sustain Chem Eng
2:1187–1194
X
NC
H
(I)
Cl
O
Me
H
N
H
6. Pandey K, Rangan K, Kumar A (2018) J Org Chem 83:8026–8035
7. Chavan HV, Bandgar BP (2013) ACS Sustain Chem Eng
1:929–936
ClO4
N
H
H
O
CN
H
H
CN
X
8. Weclawski MK, Meiling TT, Leniak A, Cywinski PJ, Gryko DT
(2015) Org Lett 17:4252–4255
X
9. Riveira MJ, Marcarino MO, La-Venia A (2018) Org Lett
20:4000–4004
(II)
10. Chang M-Y, Chen H-Y, Chen Y-H (2017) J Org Chem
82:12631–12639
Scheme 1 Plausible reaction mechanism of Knoevenagel condensa-
11. Sonawane YA, Phadtare SB, Borse BN, Jagtap AR, Shankarling
GS (2010) Org Lett 12(7):1456–1459
tion reaction
12. Devi I, Bhuyan PJ (2004) Tetrahedron Lett 45:8625–8627
13. Lu J, Toy PH (2011) Synlett 12:1723–1726
14. Tanaka K, Toda F (2000) Chem Rev 100:1025–1074
15. Welton T (1999) Chem Rev 99:2071–2083
16. Lei Z, Chen B, Koo Y-M, MacFarlane DR (2017) Chem Rev
117:6633–6635
4 Conclusions
In conclusion, we have demonstrated that ionic liquid of
amino acid amide is used as an efcient and recyclable
catalyst for Knoevenagel condensation in the solvent-free
medium. A present protocol using IL provides a very ef-
cient and convenient method for room temperature Knoev-
enagel condensation of cyclic ketones, aliphatic, aromatic
and heteroaromatic aldehydes with diferent active methyl-
ene compounds. The attractive feature of this methodology
is IL used here is easily recovered and recyclable without
loss of its activity.
17. Amarasekara AS (2016) Chem Rev 116:6133–6183
18. Azov VA, Egorova KS, Seitkalieva MM, Kashin AS, Ananikov
VP (2018) Chem Soc Rev 47:1250–1284
19. Petkovic M, Seddon KR, Rebelo LPN, Pereira CS (2011) Chem
Soc Rev 40:1383–1403
20. Lv S, Li Y, Yao T, Yu X, Zhang C, Hai L, Wu Y (2018) Org Lett
20:4994–4997
21. Chen J, Xie F, Li X, Chen L (2018) Green Chem 20:4169–4200
22. Wang R, Twamley B, Shreeve JM (2006) J Org Chem 71:426–429
23. Guo H-M, Cun L-F, Gong L-Z, Mi A-Q, Jiang Y-Z (2005) Chem
Commun 11:1450–1452
24. Alvim HGO, Correa JR, Assumpcao JAF, da Silva WA, Rodrigues
MO, de Macedo JL, Fioramonte M, Gozzo FC, Gatto CC, Neto
BAD (2018) J Org Chem 83:4044–4053
Acknowledgements PAB and BRJ acknowledge to CSIR, New Delhi,
for Research Fellowship.
1 3

P. A. Burate et al.
25. Weng J, Wang C, Li H, Wang Y (2006) Green Chem 8:96–99
26. Grobeheilmann J, Bandomir J, Kragl U (2015) Chem Eur J
21:18957–18960
39. Zhu A, Bai S, Jin W, Liu R, Li L, Zhao Y, Wang J (2014) RSC
Adv 4:36031–36035
40. Fang D-W, Tong J, Guan W, Wang H, Yang J-Z (2010) J Phys
Chem B 114:13808–13814
27. Feng L-C, Sun Y-W, Tang W-J, Xu L-J, Lam K-L, Zhou Z, Chan
ASC (2010) Green Chem 12:949–952
41. Tang S, Baker GA, Zhao H (2012) Chem Soc Rev 41:4030–4066
42. Xu H, Pan L, Fang X, Liu B, Zhang W, Lu M, Xu Y, Ding T,
Chang H (2017) Tetrahedron Lett 58:2360–2365
28. Taheri A, Lai B, Cheng C, Gu Y (2015) Green Chem 17:812–816
29. Morrison DW, Forbes DC, Davis JH (2001) Tetrahedron Lett
42:6053–6055
43. Xu D-Z, Liu Y, Shi S, Wang Y (2010) Green Chem 12:514–517
44. Ouyang F, Zhou Y, Li Z-M, Hu N, Tao D-J (2014) Korean J Chem
Eng 31:1377–1383
30. Harjani JR, Nara SJ, Salunkhe MM (2002) Tetrahedron Lett
43:1127–1130
31. Tahmassebi D, Wilson LJA, Kieser JM (2009) Synth Commun
39:2605–2613
45. Chen F-F, Huang K, Zhou Y, Tian Z-Q, Zhu X, Tao D-J, Jiang D,
Dai S (2016) Angew Chem Int Ed 55:7166–7170
32. Ranu BC, Jana R (2006) Eur J Org Chem 16:3767–3770
33. Santamarta F, Verdia P, Tojo E (2008) Catal Commun
9:1779–1781
46. Chen F-F, Huang K, Fan J-P, Tao D-J (2018) AIChE J 64:632–639
47. del Hierro I, Perez Y, Fajardo M (2018) Mol Catal 450:112–120
48. Ossowicz P, Rozwadowski Z, Gano M, Janus E (2016) Pol J Chem
Technol 18(1):90–95
34. Hu X, Ngwa C, Zheng Q (2016) Curr Org Synth 13:101–110
35. Xin X, Guo X, Duan H, Lin Y, Sun H (2007) Catal Commun
8:115–117
49. Javle BR, Kinage AK (2018) Chem Sel 3:2623–2625
36. Mulla SAR, Sudalai A, Pathan MY, Siddique SA, Inamdar SM,
Chavan SS, Reddy RS (2012) RSC Adv 2:3525–3529
37. Zhao S, Wang X, Zhang L (2013) RSC Adv 3:11691–11696
38. Ying A, Liang H, Zheng R, Ge C, Jiang H, Wu C (2011) Res
Chem Intermed 37:579–585
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