Functionalized Polystyrene Supported Copper(I) Complex as an Effective and Reusable Catalyst for Propargylamines Synthesis in Aqueous Medium

Article abstract of DOI:10.1007/s10562-016-1728-3

Abstract: An efficient procedure for the one-pot synthesis of propargylamines is A³ coupling in which an alkyne, an aldehyde, and an amine are coupled together. Here, we report that polystyrene supported Cu(I) catalyst is excellent for A³ coupling in water without using any additives or hazardous organic solvents. The polystyrene supported Cu(I) catalyst was synthesized and its catalytic activity was also evaluated in the synthesis of propargylamines in oxidative A³-coupling reaction with benzyl alcohols instead of their aldehydes in water. This protocol offers several advantages such as high yields of the desired product, reaction in aqueous medium and recyclability of the catalyst. It gives well to excellent yields for a variety of substrates. As it acts as heterogeneous catalyst, it can be easily separated from the reaction mixture and reused without appreciable loss of activity. Graphical Abstract: Polymer supported copper catalyst, Cu-PS-ala, acts as a heterogeneous catalyst for the one pot synthesis of propargylamines via A³ coupling reaction in water using aldehydes or alcohols, amines and alkynes.[Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-016-1728-3

Catal Lett
DOI 10.1007/s10562-016-1728-3
Functionalized Polystyrene Supported Copper(I) Complex
as an Effective and Reusable Catalyst for Propargylamines
Synthesis in Aqueous Medium
1
1,2
1
Md. Mominul Islam
•
Anupam Singha Roy
•
Sk. Manirul Islam
Received: 29 February 2016 / Accepted: 10 March 2016
Ó Springer Science+Business Media New York 2016
Abstract An efficient procedure for the one-pot synthesis
3
of propargylamines is A coupling in which an alkyne, an
aldehyde, and an amine are coupled together. Here, we
report that polystyrene supported Cu(I) catalyst is excellent
3
for A coupling in water without using any additives or
hazardous organic solvents. The polystyrene supported
Cu(I) catalyst was synthesized and its catalytic activity was
also evaluated in the synthesis of propargylamines in
3
oxidative A -coupling reaction with benzyl alcohols
instead of their aldehydes in water. This protocol offers
several advantages such as high yields of the desired pro-
duct, reaction in aqueous medium and recyclability of the
catalyst. It gives well to excellent yields for a variety of
substrates. As it acts as heterogeneous catalyst, it can be
easily separated from the reaction mixture and reused
without appreciable loss of activity.
Graphical Abstract Polymer supported copper catalyst,
Cu-PS-ala, acts as a heterogeneous catalyst for the one pot
3
synthesis of propargylamines via A coupling reaction in
water using aldehydes or alcohols, amines and alkynes.
Keywords Polymer supported Cu(I) catalyst Á One-pot
3
synthesis Á Propargylamines Á A coupling Á C–H activation
Md. Mominul Islam and Anupam Singha Roy have contributed
equally to this manuscript.
1
Introduction
Electronic supplementary material The online version of this
article (doi:10.1007/s10562-016-1728-3) contains supplementary
material, which is available to authorized users.
The efforts from the last century have resulted in the devel-
opment of a number of synthetic pathways. However, the
exceedingly high cost of chemicals and the increasing
awareness on their potential environment hazards have per-
suadedafreshlookatdevisingmoreefficient and eco-friendly
alternate ways for chemical synthesis [1, 2]. The one-pot
multi-component reaction (MCR) is one of the best useful
synthetic routes to generate complex structures with greater
structural and skeletal diversity [3, 4]. Generally, these MCRs
take place in one-pot and show a higher economy of atom and
&
Sk. Manirul Islam
manir65@rediffmail.com
1
2
Department of Chemistry, University of Kalyani, Nadia,
Kalyani, W.B. 741235, India
Department of Chemical Sciences, Indian Institute of Science
Education and Research (IISER) Kolkata, Mohanpur 741246,
India
123

Md. M. Islam et al.
steps and also the selectivity. Besides, they are easy to per-
form and also lower the cost, time and energy. A three com-
ponent coupling of carbonyl compounds-amines-alkynes is
one of the bestreported processes for C–C bond formation [5–
catalyst have been studied. This catalyst could be easily
separated from the reaction mixture by filtration and reused
several times without significant degradation in activity.
7] and has received much more attention in recent years. The
resultant propargylamines, obtained from the above coupling
reaction, are synthetically versatile key intermediates [8, 9]
for the preparation of natural products and a large number of
nitrogen containing biologically active compounds such as
conformationally restricted peptide isosteres, oxotremorine
analogues, and b-lactams. The conventional methods for the
preparation of the propargylamine moiety have usually fol-
lowed direct amination of propargyl halides [10], phosphates,
triflates [11] or acetates [12] or utilized the high acidity of
terminal alkynic C–H bond to form alkynyl-metal reagents by
reaction with strong bases [13–15]. But unfortunately, the
reagents, used in these processes, have to take in stoichio-
metric ratios, and are highly sensitive to moisture and also
require strictly controlled reaction conditions. So an easy and
efficientsyntheticroute isrequired, whichisapplicableforthe
synthesis of the wide range of propargylamines [16–18]. In
recent years, a huge progress on an alternative atom-eco-
nomical nucleophilic addition of in situ generated metal-
acetylides to imines and enamines has been made by C–H
activation, where water is the only by-product [19]. The
alkynic C–H bond can be activated by using various homo-
geneous or heterogeneous catalysts containing transition
metal ions such as gold [20], zinc [21], iron [22], silver [23],
indium [24], iridium [25, 26], mercury [27], ruthenium [28]
and copper [29–33] etc. Among these transition metals, we
turned our attention to the use of copper because it is an
efficient, cheap and non-toxic element and can be used for the
synthesis of many organic compounds [34]. Commonly, the
reported copper catalysts are homogeneous and the main
drawbacks of these complexes are the chance of metal con-
tamination with the final product and the difficulty to recover
and reuse these catalysts for subsequent reactions. To over-
come these drawbacks, copper was immobilised on various
supports to form the corresponding heterogeneous catalysts
which have received considerable attention in recent years
2
Experimental
2.1 Materials and Instruments
Chloromethylated polystyrene (5.5 mmol Cl/gm of resin)
was purchased from Sigma-Aldrich. All other chemicals
used for this investigation purposes were purchased from
commercial sources and were used without purification.
Before use, all solvents were distilled and dried following
the standard process.
A PerkinElmer 2400 C elemental analyzer was used to
collect micro-analytical data (C, H and N). The FT-IR
spectra of the samples were recorded from 400 to
-
1
4000 cm on a PerkinElmer FT-IR 783 spectrophotome-
ter. A Mettler Toledo TGA/SDTA 851 instrument was used
for TGA. The morphology of the functionalized poly-
styrene and complex was analyzed using a scanning elec-
tron microscope (Zeiss EVO40, UK) equipped with EDX
facility. The copper content in the catalyst was determined
using a Varian AA240 atomic absorption spectropho-
tometer. NMR spectra were monitored on a Bruker AMX-
1
00 NMR spectrophotometer (400 MHz for H NMR)
4
using tetramethylsilane as internal standard.
2.2 Synthesis of Polymer Supported Ligand
Chloromethylated polystyrene beads (1) were functionalized
with aldehyde group according to a literature procedure [43].
Then b-alanine (0.4 gm) was added to the stirred aldehyde-
bearing polymer beads (2) (1 gm) in methanol (25 mL) and
refluxed for next 20 h. After filtration and washing with
absolute methanol, the polymeric ligand (3) was obtained.
2.3 Loading of Metal on to the Polymeric Ligand
[35–39]. Several methods for the preparation of propargy-
lamines in water were reported [40–42], some of them
required highly expensive Au [41] or Ag [42]. These infor-
mation’spromptedustopresent ourresults forthe preparation
of propargylamines using polymer supported copper(I) cata-
lyst in water.
Polymeric ligand (3) (1 gm) was stirred for 20 h with CuI
(0.07 gm) in acetonitrile (20 mL) under refluxing condi-
tion. At the end of the reaction, the resulting metal-loaded
polymer (4) was filtered, washed with acetonitrile, metha-
nol and finally dried under vacuum for 6 h at 90 °C.
To the best of our knowledge, there is currently no report
3
of employing polystyrene supported Cu(I) catalyst in A -
3
2.4 General Procedure for the A -Coupling
Reaction in Water-Medium
coupling reactions. Herein, we report that polymer supported
3
Cu(I) catalyst is an efficient catalyst in the A coupling
reactions of aldehydes, amines and alkynes under aerobic
conditions in aqueous medium. Moreover, the effects of
solvent and temperature, and the recycling potential of the
A mixture of polymer supported Cu(I) catalyst, Cu-PS-ala
(0.010 g), aldehyde(1 mmol), phenylacetylene (1 mmol) and
amine(1.2 mmol)in5 mLwaterwasplacedina10 mLround
1
23

Functionalized Polystyrene Supported Copper(I) Complex as an Effective and Reusable Catalyst…
Scheme 1 Outline for the synthesis of polymer supported copper(I) catalyst
bottom flask and stirred at reflux condition. The reaction was
monitored by TLC. After the given reaction time the catalyst
was removed by simple filtration. The filtrate was concen-
trated under reduced pressure and extracted with ethyl acetate
from water. The desired product was isolated from the
extracted organic part by column chromatography. The
Table 1 Chemical composition of polymer supported ligand (3) and
Cu-PS-ala catalyst (4)
Compound
C %
H %
N %
Cu %
3
74.96
72.01
6.36
6.03
4.61
4.45
a
Cu-PS-ala (4)
3.98 (3.96)
1
a
known products were characterized by comparison of their H
Copper content of recycled catalyst after 6th cycles
NMR data with the data already described in the literature.
3
Results and Discussion
3
.1 Characterization of Polymer Supported
Copper(I) Complex
The first step in the accomplishment of this goal was the
preparation of polymer supported Cu(I) catalyst
(
Scheme 1). The catalyst was prepared by stirring polymer
supported ligand (3) in acetonitrile solution of CuI for 20 h.
The catalyst was separated by simple filtration and dried
under vacuum at 90 °C for 6 h.
Elemental analysis data for polymer supported ligand
and copper catalyst are given in Table 1. Amount of copper
metal was determined by using atomic absorption spec-
trophotometer. Copper content in the catalyst is 3.98 wt%.
Copper content remained almost unchanged even after
recycling the catalyst for six cycles.
Fig. 1 FT-IR spectra of a aldehyde functionalized polymer, b poly-
mer supported Schiff base ligand and c polymer supported Cu(I) cat-
alyst Cu-PS-ala
stretching vibration of the –CHO group. In the aldehyde
functionalized polymer (2) the C–Cl peak due to –CH Cl
2
-
1
group at 1264 cm was absent [44]. In the polymeric
-
1
3
.1.1 IR Spectral Study
support (3) a new peak at 1633 cm is observed which
indicted the formation of C=N bond (Fig. 1b). This band
shifted to lower wave numbers after complexation with
copper. It suggested the coordination of the Schiff base to
In the FT-IR spectrum (Fig. 1a) a new peak appeared at
-
703 cm which was assigned to carbonyl C=O bond
1
1
123

Md. M. Islam et al.
the copper through the azomethine nitrogen. The phenolic
3.1.2 DRS-UV Spectroscopy
(
C–O) stretching frequency was observed in the region of
-
262 cm in ligand (3), which shifted to lower frequency
1
1
The electronic spectra of the polymer supported Schiff base
ligand and copper catalyst (Cu-PS-ala) have been recorded
in the diffuse reflectance spectrum mode and given in
Fig. 2. Both in the Schiff base ligand and copper catalyst,
broad bands around 260–350 nm are observed. This
absorption bands may be attributed to p ? p* and n ? p*
transition in phenyl moiety. The bands at 370 nm in Cu-
PS-ala arise due to LMCT.
in the complex, indicating coordination of metal through
the phenolic oxygen (Fig. 1c).
3.1.3 Scanning Electron Micrographs (SEM) and Energy
Dispersive X-ray Analyses (EDX)
The scanning electron micrographs of the polymer sup-
ported b-alanine ligand and copper(I) catalyst are presented
in Fig. 3a and b, respectively. The morphological changes
in the polymer supported ligand and polymer supported
catalyst are quite evident from these images. Quite uniform
and negligible variation in size is observed throughout the
Fig. 2 DRS-UV–Vis spectra of polymer supported Schiff base ligand
(
3) (a) and Cu-PS-ala catalyst (b)
Fig. 3 SEM images of a polymer supported Schiff base ligand and b polymer supported Cu(I) catalyst Cu-PS-ala, c EDAX data of polymer
supported Cu(I) catalyst, Cu-PS-ala, d TGA plots for polymer supported ligand and Cu-PS-ala catalyst
1
23

Functionalized Polystyrene Supported Copper(I) Complex as an Effective and Reusable Catalyst…
specimens. Energy dispersive spectroscopy analysis of
X-rays (EDAX) data for the polymer supported copper
complex is given in Fig. 3c. The EDX data also confirm the
presence of copper on the surface of the polymer matrix.
Table 2 The optimization of amount of catalyst, solvents and tem-
perature in the three-component coupling of benzaldehyde, piperidine
and phenylacetylene
3
.1.4 TGA Studies
TGA curves of both the polymer supported ligand (3) and
catalyst are given in Fig. 3d. The ligand and copper cata-
lyst were stable up to 350–370 °C and above this temper-
ature they decomposed. So, thermogravimetric analysis
suggests that the polymer supported copper complex
degrade at higher temperature.
a
Entry
Catalyst (g)
Solvent
THF
t/h
Yield 4a (%)
1
2
3
4
5
6
7
8
9
–
36
48
6
0
0
–
H
H
H
H
H
H
2
O
2
O
2
O
2
O
2
O
2
O
CuI
80
95
78
95
96
15
58
68
62
46
74
86
0.01
0.005
0.015
0.02
0.005
0.005
0.005
0.005
0.01
0.01
CuI
6
12
6
6
3
.2 Catalytic Activity
DCM
PhMe
THF
12
12
12
12
6
After the successful preparation and characterization of the
polymer supported copper catalyst, we studied its activity
in the coupling of aldehydes, amines, and alkynes. In order
to found the optimum reaction conditions, the activity of
the heterogeneous copper catalyst was examined in a
model reaction using benzaldehyde (1a), piperidine (2a)
and phenylacetylene (3a) under refluxing conditions
1
1
1
1
0
1
2
3
3
CH CN
b
c
d
H
H
H
2
O
2
O
2
O
6
14
6
Benzaldehyde (1 mmol), piperidine (1.2 mmol), phenylacetylene
(1 mmol), solvent (5 mL) Reflux conditions
(
Table 2). A controlled reaction under refluxing conditions
a
-3
Based on isolated yields. CuI = 6.26 9 10 mmol (entries 3 and
4)
in absence of the catalyst gave no expected product even
after 3 days, irrespective of the solvent used (Table 2,
entries 1 and 2). The desired product was generated in
1
b
Reaction carried out at 50 °C
Reaction carried out at 70 °C
Recation carried in presence of CuI and Schiff base ligand derived
c
8
0 % yield when CuI was used (Table 2, entry 3). In
d
comparison, polymer supported copper catalyst, Cu-PS-ala,
gave slightly better yield than CuI. When 0.005 g of Cu-
PS-ala was used, the yield of the product was low even
after long reaction time (Table 2, entry 5) but 0.010 g of
Cu-PS-ala was found to be optimal (Table 2, entry 4).
However, using 0.015 and 0.020 g of Cu-PS-ala catalyst no
improvement of yield was observed (Table 2, entries 6 and
from b-alanine and benzaldehyde
that the best result was achieved with Cu-PS-ala (0.010 g)
under reflux conditions in water.
We have choose a variety of aldehydes and amines to
expand the scope and simplicity of the polymer supported
Cu(I) catalyst, Cu-PS-ala promoted three component cou-
pling reaction under the optimized reaction conditions.
Structurally diverse aldehydes and amines possessing a
wide range of functional groups were employed as reaction
substrates. The results are given in Table 3. Aromatic
aldehydes with electron-donating groups reacted rapidly,
while in case of aldehydes with electron-withdrawing
groups reactivity decreased and required longer reaction
times. In addition, heteroaromatic aldehydes also gave
products (Table 3, entries 9 and 10). To extend the scope of
the reaction, various cyclic and acyclic secondary amines
such as piperidine, morpholine, pyrrolidine, and diethy-
lamine were used and tolerated well (Table 3, entries 11,
12 and 13). To broaden the utility of our catalyst we tested
this three-component coupling with a more challenging
substrate aniline. After a prolonged reaction time, a
7
). To check the effect of solvent, the above reaction was
performed in various solvents like toluene, acetonitrile,
THF, DCM and water. From Table 2, it is evident that
water is the best solvent (Table 2, entry 4). Moderate yields
were obtained when the reaction was performed in toluene,
acetonitrile and THF (Table 2, entries 9, 10 and 11) and a
poor result was observed when the reactions were carried
out in DCM (Table 2, entry 8). Next we examined the
effect of the temperature. The reaction was carried out at
5
0, 70 °C and reflux conditions (entries 4, 12 and 13).
3
Also, we have checked the A coupling reaction between
benzaldehyde, piperidine and phenylacetylene under
refluxing conditions using CuI and Schiff base derived
from b-alanine and benzaldehyde (entry 14). This system
generated slightly lower (86 %) desired product compared
to Cu-PS-ala catalyst. Finally, from Table 2 it can be seen
123

Md. M. Islam et al.
Table 3 One-pot synthesis of
propargylamine derivatives
from aldehydes, amines, and
alkyne, by using Cu-PS-ala as
the catalyst
Entry
1
Aldehyde
Amine
Product
Time (h)
6
Yield
b
(
%)
CHO
95
N
N
H
O
N
CHO
CHO
O
6
91
94
2
N
H
6
6
6
N
3
4
5
N
H
OCH
3
3
H CO
CHO
92
N
N
H
CH
3
H
3
C
C
O
N
CHO
89
O
N
H
CH3
H
3
CHO
6
88
N
6
7
N
H
Cl
Cl
Cl
O
N
CHO
O
6
85
-
N
H
Cl
CHO
16
N
8
9
N
H
NO
2
2
O N
6
87
O
N
CHO
N
H
O
1
23

Functionalized Polystyrene Supported Copper(I) Complex as an Effective and Reusable Catalyst…
Table 3 continued
Entry
Aldehyde
Amine
Product
Time (h)
6
Yield
b
(
%)
84
S
N
1
0
CHO
N
H
S
6
6
84
CHO
N
1
1
2
N
H
80
CHO
N
1
N
H
Cl
Cl
6
6
89
94
CHO
N
N
H
N
1
3
4
CHO
CHO
1
N
H
O
N
6
92
O
1
1
1
5
6
7
N
H
6
6
93
N
HCHO
HCHO
N
H
O
N
90
O
N
H
123

Md. M. Islam et al.
Table 3 continued
Entry
Aldehyde
Amine
Product
Time (h)
6
Yield
b
(
%)
90
N
1
8
CH -CHO
3
N
H
16
49
CHO
NH2
NH
19
CHO
CHO
6
94
67
N
2
0
1
N
H
CH3
16
N
2
N
H
(
CH ) CH
2 5 3
Aldehyde (1 mmol), Amine (1.2 mmol), alkyne (1 mmol), catalyst (0.01 g), water (5 mL) under reflux
conditions
a
Based on isolated yields
Table 4 Oxidative three-component reaction of various benzyl alcohols, secondary amines and phenylacetylene catalyzed by Cu(I)-PS-ala
NR R
2
3
R R NH
2
3
Ph
R1
OH
R1
Ph
a
Entry
R
1
R
2 3
R NH
Yield (%)
1
2
3
4
5
6
Ph
Morpholine
Morpholine
Morpholine
Piperidine
Piperidine
Pyrolidine
76
55
79
58
80
66
4-MeC
6
H
4
4-ClC
6 4
H
4-MeC
H
6 4
4-ClC
4-ClC
6
H
H
4
4
6
2
Alcohols (1 mmol), amine (1.2 mmol), phenylacetylene (1.3 mmol), H O (5 mL), Cu-PS-ala (0.01 g), 6 h, reflux conditions, air
a
Isolated yield
moderate yield of the desired product was obtained
case of aliphatic alkyne, moderate yield of the corre-
sponding propargylamine was obtained after longer reac-
tion time. The results indicated that both aromatic and
aliphatic aldehydes were transformed to the corresponding
propargylamines in excellent yields.
(
Table 3, entry 18). Under the same reaction conditions
several alkynes such as tolyl-substituted ethyne and 1-oc-
tyne can be used to give the corresponding propargy-
lamines. Tolyl-substituted ethyne gave good yields but in
1
23

Functionalized Polystyrene Supported Copper(I) Complex as an Effective and Reusable Catalyst…
To the best of our knowledge, there is currently limited
3
report of employing alcohols instead aldehyde in A -cou-
4 Test for Heterogeneity
pling reactions. We have studied the catalytic activity of
3
the polymer supported copper catalyst in the oxidative A -
To verify the heterogeneity of the catalyst 1 mmol ben-
zaldehyde, 1 mmol phenylacetylene 1.2 mmol piperidine
and 0.01 g catalyst were allowed to stir in 5 mL water under
reflux conditions. This reaction was stopped at 4 h, and the
yield was found to be 65 %. At this time, the catalyst was
separated and the reaction was continued with the filtrate for
next 2 h. After total 6 h the extent of yield was found to
remain almost unchanged (Fig. 4). This information indi-
cates that the reaction followed a heterogeneous pathway.
Further, the leaching of copper from the catalyst was
analyzed from EDX and IR spectra of the used catalyst.
FT-IR spectrum of the reused catalyst was quite similar to
that of the fresh catalyst which indicates the heterogeneous
nature of the catalyst (Fig. 5b). The amount of copper in
the recycled catalyst was determined from AAS and found
that it was remained almost unchanged.
coupling reactions of benzyl alcohols, phenylacetylene and
secondary amines under aerobic conditions in aqueous
media. The scope of various benzyl alcohols, amines and
3
phenylacetylene was examined in the oxidative A reaction
(
Table 4). The benzyl alcohol with an electron-withdraw-
ing group gave a higher yield as compared to that with an
electron donating group (Table 4, entries 2, 3 and 4). In
addition, piperidine or pyrrolidine can also be applied in
3
this A -coupling (Table 4, entries 4, 5, and 6).
Probable reaction mechanism for the one-pot, three
components synthesis of propargylamines catalyzed by
polymer supported Cu(I)-PS-ala under heterogeneous
conditions follow the well established earlier mechanism
[
45–47].
3
Fig. 4 Heterogeneity test in the A coupling of benzaldehyde,
phenylacetylene and piperidine
Fig. 6 Recycling experiment of Cu-PS-ala
Fig. 5 SEM image (a) and FT-IR spectra (b) of recycled catalyst
123

Md. M. Islam et al.
Table 5 Comparison of catalytic activity of Cu-PS-ala with other literature reported methods
3
A coupling
Catalyst
SiO -NH-Cu (2 mol%)
Reaction conditions
Solvent free, r.t
Time (h)/yield (%) [Ref.]
Benzaldehyde ? phenylacetylene ? piperidine
2
24/79 [48]
25/35 [49]
9/90 [21]
5/94 [20]
6/82 [50]
4/95 [51]
6/95*
Cu Zeolites (20 mg)
Zn dust (15 mol%)
CH
CH
CH
3
3
3
CN, 60 °C
CN, reflux
Au nanoparticles, 10 mol%
Nanocrystalline CuO
CN, 75–80 °C
Toluene, 90 °C
Toluene, 111 °C
Water, Reflux
2
NiCl (5 mol%)
Cu-PS-ala
Au@GO-IL
Cu-PS-ala
Benzyl alcohol ? phenylacetylene ? morpholine
(
Water, 100 °C, air
Water, Reflux, air
18/90 [52]
6/76*
3
oxidative A -coupling)
*
Present study
3
5
Recycling of Catalyst
alcohols followed by A -coupling using different combi-
nations of secondary amines and terminal alkynes. The
simple protocol, broad scope of the substrates and recy-
cling of the catalyst permitted us to look forward to a good
future of this process in academic as well as in industry.
After each reaction, the catalyst was separated from the
reaction mixture by filtration. The recovered catalyst was
thoroughly washed with methanol and diethyl ether to
remove organic materials. Then the catalyst was dried at
Acknowledgments SMI acknowledges Department of Science and
Technology (DST-SERB), University Grant Commission (UGC),
New Delhi, India, Council of Scientific and Industrial Research
55 °C for 4 h under vacuum to activate and to use in a new
reaction. It was found that the recovery can be successfully
achieved more than ten successive reaction runs (Fig. 6).
(
CSIR), New Delhi, India and Department of Science and Technol-
ogy, West Bengal (DST-W.B.) for funding. MMI acknowledges Miss
Mita Halder for her entire help and expresses sincere thanks UGC,
New Delhi for his Maulana Azad National Fellowship (F1-17.1/2013-
14/MANF-2013-14-MUS-WES-24492/(SAIII). ASR acknowledges
IISER-Kolkata for his postdoctoral fellowship.
6
Comparative Study
In order to show the importance of this study, we compared
the obtained result with the recently reported results. For
this purpose, reaction between benzaldehyde, pheny-
lacetylene and piperidine were chosen for comparison on
the basis of reaction conditions and yields of the product
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3
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under refluxing condition. Use of water as solvent implies
that the reaction is eco-friendly. The reaction scope was
broad when secondary aliphatic amines were used and
some unprecedented propargylamines have been prepared.
Besides the reported substrates, some explorative experi-
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challenging reactions such as aromatic amines, though the
results in this case are only modest. This catalyst system
shows excellent activity and good yields for a variety of
propargylamine through aerobic oxidation of benzyl
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