Cu(II) salen complex catalyzed synthesis of propargylamines by a three-component coupling reaction

Article abstract of DOI:10.1016/S1872-2067(12)60683-4

A one pot three-component coupling reaction of phenylacetylene, aldehyde, and amine derivatives in the presence of Cu(II) Salen complex as an efficient heterogeneous catalyst under solvent-free conditions is reported. The catalyst displayed high activity

Full text of DOI:10.1016/S1872-2067(12)60683-4

Chinese Journal of Catalysis 34 (2013) 2217–2222
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Article
Cu(ΙI) salen complex catalyzed synthesis of propargylamines by a
three‐component coupling reaction
Mahmood Tajbaksha,*, Maryam Farhang a, Hamid Reza Mardani b, Rahman Hosseinzadeh a,
Yaghoub Sarrafi a
a Faculty of Chemistry, Mazandaran University, Babolsar, 47415, Iran
b Department of Chemistry, Payame Noor University, Iran
A R T I C L E I N F O
A B S T R A C T
Article history:
A one pot three‐component coupling reaction of phenylacetylene, aldehyde, and amine derivatives
in the presence of Cu(II) Salen complex as an efficient heterogeneous catalyst under solvent‐free
conditions is reported. The catalyst displayed high activity and afforded the corresponding propar‐
gylamines in good to excellent yields. This method provides a wide range of substrate applicability.
The catalyst was reused several times without significant loss of its catalytic activity.
© 2013, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Received 10 June 2013
Accepted 20 August 2013
Published 20 December 2013
Keywords:
Propargylamine
Salen
Published by Elsevier B.V. All rights reserved.
Copper
Coupling reaction
Solvent‐free
1. Introduction
tion metals by C–H activation. For example, Ag(Ι) salts [7],
Au(Ι,ΙΙΙ) salts [8],Au(ΙΙΙ) salen complexes [9], Cu(Ι) salts [10],Ir
Propargylamines are important synthetic intermediates for
the synthesis of potential therapeutic drug molecules. Poly‐
functional amino derivatives are versatile building blocks and
are value‐added intermediates in organic synthesis [1]. Tradi‐
tionally, propargylamines have been prepared by the amination
of propargylic halides [2], propargylic phosphates [3], and
propargylic triflates [4] or through the nucleophilic attack of
lithium acetylides and Grignard reagents on imines or their
derivatives [5]. However, these methods suffer from issues
such as moisture sensitivity and the requirement for strictly
controlled reaction conditions. Recently, a three‐component
coupling among aldehyde, alkyne, and amine, commonly re‐
ferred to as A3 coupling, has been reported to be a convenient
and general approach for the preparation of propargylamines
[6]. Generally, the A3 coupling reaction is catalyzed by transi‐
complexes [11], Hg2Cl2 [12],Zn salts [13],InCl3 [14],InBr3 [15],
and the Cu/Ru bimetallic system [16] under homogeneous
conditions. Recently Ag(I) [17] and Cu(I) [18] in ionic liquids
and supported Au(III) [19], Ag(I) [20], and Cu(I) [21] were
successfully used to catalyze three‐component coupling reac‐
tions under heterogeneous conditions with catalyst recycling
and reuse. However, some of these methods require expensive
metal catalysts (Ag, Au, Ir, etc.) [7,8,11], hazardous catalysts
[12], inert conditions [16], harmful solvents [13,15], and long
reaction times [9,21] and catalyst recycling can be difficult
[7–14]. On the other hand, salen complexes are stable solid
compounds that have been used as catalysts for various organic
transformations [22–24]. Herein, we report a high yield syn‐
thesis of propargylamines catalyzed by the Cu(ΙI) salen com‐
plex 1a under solvent‐free conditions at 80 °C (Scheme 1).
* Corresponding author. Fax: +98‐1125242002; E‐mail: Tajbaksh@umz.ac.ir
DOI: 10.1016/S1872‐2067(12)60683‐4 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 34, No. 12, December 2013

Mahmood Tajbaksh et al. / Chinese Journal of Catalysis 34 (2013) 2217–2222
R2 R3
(CDCl3, 400 MHz): δ 7.69–7.61 (s, 2H), 7.56–7.51 (m, 2H),
7.39–7.31 (m, 3H), 4.81 (s, 1H), 3.81–3.65 (m, 4H), 2.77–2.69
(m, 4H); 13C NMR (CDCl3, 100 MHz): δ 137.36, 131.81, 128.50,
128.34, 128.31, 122.90, 88.50, 84.99, 67.17, 61.77, 49.86; MS
(EI, m/z): 476.3 (M+), 390, 304, 200, 152, 86, 56; Anal. Calcd for
C32H34N2O2: C 80.30, H 7.16, N 5.85; Found: C 80. 27, H 7.12, N
5.80.
1a (3 mol%)
N
R2R3NH Ph C CH
R1CHO
R1, R2, R3 = aromatic, aliphatic
Solventless
80 oC
R1
Ph
N
O
N
O
1a M = Cu
1b M = Zn
M
1c M = Mn, [Mn(salen)][ClO4]
1d M = Ni
N‐[1‐(2,4‐Dimethylphenyl)‐3‐phenyl‐2‐propynyl]
piperi‐
dine (Table 2, entry 26). Yellow oil, yield 90%; IR (KBr): 3018,
2934, 2401, 1615, 1492, 1447, 1317, 1216, 771 cm–1; 1H NMR
(CDCl3, 400 MHz): δ 7.62–7.58 (m, 1H), 7.58–7.54 (m, 1H),
7.53(d, J = 2 Hz, 1H), 7.40–7.31 (m, 3H), 7.08–6.98 (m, 2H), 4.83
(s, 1H), 2.65–2.52 (m, 4H), 2.45 (s, 3H), 2.35 (s, 3H), 1.62–1.50
(m, 4H), 1.49–1.40 (m, 2H); 13C NMR (CDCl3, 100 MHz): δ
137.42, 137.03, 133.88, 131.79, 131.45, 128.94, 128.27, 127.91,
125.76, 123.57, 87.84, 86.30, 59.94, 50.53, 26.35, 24.66, 21.05,
19.0; MS (EI, m/z): 302.1 (M+), 219, 203, 115, 84, 55; Anal.
Calcd for C22H25N: C 87.08, H 8.30, N 4.62; Found: C 86.98, H
8.34, N 4.58.
1
Scheme 1. Cu(ΙI) salen complex catalyzed A3‐coupling leading to pro‐
pargylamine.
2. Experimental
2.1. General experimental
All reagents were purchased from Merck and Aldrich and
used without further purification. Melting points were meas‐
ured on an Electrothermal 9100 apparatus. IR spectra were
recorded on a Bruker Vector 22 spectrometer. ¹H and ¹³C NMR
spectra were measured with Bruker DRX‐400 Avance spec‐
trometers. Mass spectra and the purities of volatile compounds
as well as gas chromatography (GC) analyses were recorded on
a FINNIGAN‐MATT 8430 mass spectrometer operating at an
ionization potential of 20 eV. Elemental analyses were per‐
formed using a Perkin‐Elmer 2400(II) CHN/O analyzer. Merck
silica gel 60 (230–400 mesh) was used for column chromatog‐
raphy.
3. Results and discussion
We synthesized the salen complexes 1a–1d and character‐
ized them according to the literature [25,26]. In brief, 1a, 1b,
and 1d were prepared by the treatment of M(OAc)2 (1.2 equiv.)
with N,N‐bis(salicylaldehyde) ethylenediamine as the ligand
(1.2 equiv.) in refluxing ethanol over 2 h.
To determine the catalytic activity of 1a during the prepara‐
tion of propargylamine, a model reaction was conducted by
heating 1a (3 mol%), benzaldehyde (1 mmol), piperidine (1.2
mmol), and phenylacetylene (1.5 mmol) under solvent‐free
conditions at 80 °C for 2.5 h. Work‐up of the reaction mixture
afforded the expected product in 95% isolated yield (Table 1,
entry 1). In the absence of catalyst no conversion was obtained
even after 24 h (Table 1, entry 2). This observation shows the
importance of catalyst 1a in this reaction. To optimize the reac‐
2.2. General procedure for the preparation of propargylamine
derivatives
In a 5‐ml round‐bottomed flask containing Cu(salen) (0.01
g, 3 mol%) in air, aldehyde (1 mmol), amine (1.2 mmol), and
phenylacetylene (1.5 mmol) were added. The flask was then
stoppered and the mixture was stirred at 80 °C (oil bath tem‐
perature). The completion of the reaction was monitored by
TLC or GC. After reaction completion and cooling to room tem‐
perature, diethyl ether (5 ml) was added and the Cu salen was
removed by filtration. The solvent was evaporated under re‐
duced pressure, and the residue was purified by flash column
chromatography on silica gel (eluent: hexane/ethyl acetate =
10) to give the corresponding product. Spectroscopic data for
selected examples are as follows.
Table 1
Reaction conditions and reaction yields for synthesis of progargyla‐
mine.
Isolated
Entry
Catalyst (mol%)
Solvent
t/°C
yield (%)
95
n.r. a
30
1
2
3
4
1a (3)
—
1a (1.5)
1a (5)
—
—
—
80
80
80
—
80
95
1,4‐Bis(3‐phenyl‐1‐(piperidin‐1‐yl)prop‐2‐ynyl)benzene
(Table 2, entry 13). White solid, yield 95%; m.p.: 157–160 °C; IR
(KBr): 3020, 2976, 2361, 1522, 1432, 1216, 772 cm–1; 1H NMR
(CDCl3, 400 MHz): δ 7.67–7.60 (s, 2H), 7.56–7.51 (m, 2H),
7.37–7.31 (m, 3H), 4.83 (s, 1H), 2.68–2.5 (m, 4H), 1.69–1.59 (m,
4H), 1.52–1.44 (m, 2H); 13C NMR (CDCl3, 100 MHz): δ 139.72,
132.81, 128.33, 128.28, 128.05, 122.33, 87.78, 86.13, 62.14,
50.69, 26.15, 24.42; MS (EI, m/z): 471.3 (M+), 388, 300, 232,
204, 130, 102, 77, 57; Anal. Calcd for C34H36N2: C 86.40, H 7.68,
N 5.93; Found: C 86. 37, H 7.69, N 5.89.
5
6
7
8
1a (3)
1a (3)
1a (3)
1a (3)
1a (3)
1a (3)
1d (3)
1b (3)
—
—
25
70
reflux
130
reflux
reflux
15
75
30/75a
tracea
n.r./65a
50c
75
30
5
toluene
DMF
water
MeCN
—
—
—
—
—
9
10
11
12
13
14
15
16
1c (3)
Cu(NO3)2·H2O (3)
Cu(OAC)2·H2O (3)
CuCl (3)
80
80
80
40b,c
35b,c
45 b,c
—
1,4‐Bis(3‐phenyl‐1‐(morpholin‐1‐yl)prop‐2‐ynyl)benzene
(Table 2, entry 23). White solid, yield 95%; m.p.: 150–153 °C;IR
(KBr): 3020, 2974, 2361, 1521, 1420, 1216, 772 cm–1; 1H NMR
Reaction conditions: benzaldehyde 1 mmol, piperidine 1.2 mmol, phe‐
nylacetylene 1.5 mmol, 2.5 h (a 24 h, 12 h). Upon mixing without
solvent, intense heat led to decomposition.
b
c

Mahmood Tajbaksh et al. / Chinese Journal of Catalysis 34 (2013) 2217–2222
tion conditions, a model reaction was carried out under differ‐
showed moderate catalytic activity (Table 1, entry 11), whereas
the Zn(II) and Mn(Ш) salencomplexes 1b and 1c gave a signif‐
icantly lower product yield (Table 1, entries 12 and 13). The
reason for this is not clear, but it is known that Cu ions can form
stronger complexes with acetylenes than nickel [27]. To show
the effect of the salen ligand on catalytic activity, model reac‐
tions were carried out under solvent‐free conditions in the
presence of the Cu(NO3)2, Cu(OAc)2, and CuCl, and the product
yields were 40%, 35%, and 45%, respectively, after 12 h (Table
1, entries 14, 15, and 16). These low yields could be due to de‐
composition because of intense heat evolution upon mixing the
substrates under solvent‐free conditions. However, for the
conversion and yield of the product, a solvent‐free reaction
among an aldehyde, an amine, and phenylacetylene in the
presence of 1a (3 mol%) at 80 °C was performed as a general
procedure for the preparation of propargylamine derivatives.
Subsequently, various aldehydes, secondary amines, and phe‐
nylacetylene were coupled, and the results are summarized in
Table 2. It indicates that aromatic aldehydes with both elec‐
tron‐donating and electron‐withdrawing substituents give high
ent reaction conditions. The results are summarized in Table 1.
To determine the best catalyst loading, the reactions were car‐
ried out with various catalyst concentrations under sol‐
vent‐free conditions (Table 1, entries 1, 3, and 4). Increasing
the catalyst loading of 1a from 3 to 5 mol% did not change the
product yield (Table 1, entry 4), but lowering the catalyst load‐
ing to 1.5 mol% significantly reduced the isolated yield and
only 30% of the product was collected (Table 1, entry 3). Poor
results were obtained when the reaction was conducted at 25
and 70 °C (Table 1, entries 5 and 6).
To investigate the effect of solvents, model reactions were
carried out in toluene, DMF, MeCN, and water under reflux
conditions. All the screened solvents afforded a low product
yield after 2.5 h (Table 1, entries 7–10). The best yield was ob‐
tained under solvent‐free conditions at 80 °C (Table 1, entry 1).
Therefore, solvent‐free conditions were determined to be most
effective for the generation of the desired product. The catalytic
activities of the Zn(ΙI), Mn(III), and Ni(ΙI) salen complexes
1b–1d were also investigated. The Ni(II) salen complex 1d
Table 2
Synthesis of propargylamines using Cu salen (Scheme 1). a
Entry
1
2
3
4
5
6
7
R1
Amine
piperidine
piperidine
piperidine
piperidine
piperidine
piperidine
piperidine
piperidine
piperidine
piperidine
piperidine
piperidine
piperidine
piperidine
piperidine
morpholine
morpholine
morpholine
morpholine
morpholine
morpholine
morpholine
morpholine
piperidine
morpholine
piperidine
morpholine
piperidine
pyrrolidine
pyrrolidine
morpholine
dibenzylamine
diethylamine
diethylamine
Time (h)
2.5
1.45
1.15
2
1.15
2
2
Isolated yield (%)
Ref.
[28]
[29]
[28]
[28]
[21]
[28]
[32]
C6H5
95
100
95
95
90
4‐BrC6H5
4‐MeC6H4
4‐ClC6H4
3‐ClC6H4
4‐MeOC6H4
2‐MeOC6H4
3‐MeOC6H4
2‐BrC6H4
3‐BrC6H4
4‐CNC6H4
2‐OHC6H4
4‐CHOC6H4
Furyl
80
85
8
9
2
80
100
90
[8]
[33]
[32]
[30]
[30]
this work
[29]
[30]
[28]
1.25
0.5
1
1
1
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
85
100
95b
90
85
85
80
85
98
3
Thiophyl
C6H5
4‐CNC6H4
4‐FC6H4
2.75
2.5
1
1.25
1
[30]
[33]
[30]
4‐CF3C6H4
3‐OHC6H4
2‐OHC6H4
3‐BrC6H5
4‐CHOC6H4
2‐Naphthyl
PhCH=CH2
2,4‐DiMeC6H3
CH3CH2CH2
CH3CH2CH2
C6H5
2‐Naphthyl
(CH3)2CH
C6H5
C6H5
4‐FC6H4
1
1
1
85
100
80
95 b
90
100
90
90
95
80
100
100
85
60c
70c
[30]
[30]
[30]
this work
[30]
0.75
1.5
1.25
3
0.45
0.45
2
0.75
0.25
2
[33]
this work
[31]
[31]
[28]
[30]
[30]
[8]
[31]
[31]
2
1
a Aldehyde:phenylacetylene:amine (1:1.5:1.2). b Disubstituted product. c Reaction temperature was 60 °C under N2.

Mahmood Tajbaksh et al. / Chinese Journal of Catalysis 34 (2013) 2217–2222
reactivity and generate the desired products in good yields
model reaction was compared with those reported in the liter‐
ature on the basis of reaction conditions, reaction time, and
percentage yield (Table 3). As shown in Table 3, our method
gives a higher yield of product in a shorter reaction time under
solventless conditions.
The reusability of the catalyst was determined in the reac‐
tion between benzaldehyde, piperidine, and phenylacetylene
under solvent‐free conditions (Table 2, entry 1). After the com‐
pletion of the reaction, which was monitored by TLC, the cata‐
lyst was removed by filtration and washed twice with diethyl
ether (5 ml). It was dried in an oven and reused six times
without any significant loss of activity toward the synthesis of
1‐(1,3‐diphenylprop‐2‐ynyl)piperidine. These results confirm
the practical recyclability of this catalyst and thus confirm its
potential role in modern organic synthesis (Table 4).
Although a similar catalytic reaction has been reported be‐
fore [9], the Cu(II) salen complex has lower cost and higher
catalytic activity and is reusable, and the reaction is not sensi‐
tive to electron‐donating or electron‐withdrawing substituents.
The yields are attractive, and various cyclic and acyclic amines
such as piperidine, morpholine, pyrrolidine, dibenzylamine,
and diethylamine are tolerated. All the obtained results
demonstrate that the Cu(II) salen complex is an efficient cata‐
lyst for the synthesis of propargylamines.
(Table 2, entries 2–13 and 17–23). Similarly, heteroaromatic
aldehydes such as thiophene‐2‐carbaldehyde and furan‐2‐
carbaldehyde participate well in this reaction (Table 2, entries
14 and 15). Aliphatic aldehydes react efficiently and afford ex‐
cellent yields of the corresponding propargylamines (Table 2,
entries 27, 28, and 31). Conjugated aldehydes such as cin‐
namaldehyde react well with morpholine and phenylacetylene,
leading to a high yield of the expected product (Table 2, entry
25).
Interestingly, when the reaction was conducted with ter‐
ephthalaldehyde using 3 equiv. of phenylacetylene and 2.4
equiv of amine piperidine or morpholine (Scheme 2), only di‐
substituted products were obtained in 95% yield without the
formation of any monosubstituted propargylamines (Table 2,
entries 13 and 23).
A tentative mechanism for this reaction is proposed in
Scheme 3 based on previous studies [7,18,34]. It is assumed
that the aldehyde is first condensed in situ with the secondary
amine to give an iminium ion. The Cu(salen) complex activates
the C–H bond of phenylacetylene to generate a copper acetylide
intermediate, which is then added to the iminium ion to afford
propargylamine. Such a coordination/deprotonation/acetylide
formation sequence has been demonstrated for Ag ions [35].
To compare our results with those of other researchers, the
X
N
X
N
CHO
3:1:2.4 yield: 95%
X
1.5:1:1.2 yield: 45%
3 mol% Cu(salen)
Solvent free, 80 oC
N
H
OHC
CHO
X
X = O, CH2
N
Scheme 2. Selective synthesis of disubstituted products from terephthalaldehyde, phenylacetylene, and morpholine or piperidine.
Cu(II)(salen)
N
H
R1
Ph
Ph
-H
R1CHO
Ph
Cu(I)(salen)
N
N
R1
H
H
H2O
Scheme 3. Tentative mechanism of progargylamine synthesis.

Mahmood Tajbaksh et al. / Chinese Journal of Catalysis 34 (2013) 2217–2222
Table 3
Propargylamine formation by Cu(ΙI)salen and other reported catalysts a.
Yield (%)
94
Entry
1
2
Catalyst
Reaction conditions
CH3CN, reflux
Time (h)
Ref.
[28]
[9]
Fe(HSO4)3 (10 mol%)
Gold(III) salen (0.05 mol%)
nano Co3O4 (10 mol%)
SiO2‐Py‐CuI (5 mol%)
Zn(OAC)2·2H2O (10 mol%)
Nafion®NR50 (0.25 g)
NiCl2 (5 mol%)
[Au(C^N)Cl2]b (1mol%)
SiO2‐NH‐Cu, (2 mol%)
FeCl3 (10 mol%)
4
24
15
6
7
5
94
87
H2O, N2, 40 °C
3
4
5
6
7
8
toluene, 130 °C
CH3CN, 90 °C, N2
toluene, reflux
CH3CN, 70–80 °C, N2
toluene, 111 °C
[36]
[37]
[30]
[29]
[38]
[39]
[21]
[40]
[18]
[42]
[41]
this work
90
92
96
95
82
79
8
H2O, N2, 40 °C
24
24
14
5
3
16
2.5
9
solventless, r.t.
52
78
85
75
10
11
13
14
15
solventless, 70 °C
2 ml [bmim][PF6], 100 °C
solventless, 80 °C
toluene, 110 °C
CuI (10 mol%)
CuCl2 (10 mol%)
Fe3O4 nanoparticle (20 mol%)
Cu(ΙI) salen complex (3 mol%)
95
solventless, 80 °C
b
a A3 coupling reaction between benzaldehyde (1 mmol), piperidine (1.2 mmol), and phenylacetylene (1.5 mmol). Gold (III) (C^N) complex
[Au(C^N)Cl2] (N^CH = 2‐phenylpyridine).
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Table 4
5968
Reusability of the catalyst for the synthesis of propargylamine (Table 2,
entry 1).
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Run
Isolated yield (%)
Fresh
95
94
92
92
90
90
1
2
3
4
5
Reaction conditions: benzaldehyde 1 mmol, piperidine 1.2 mmol, phe‐
nylacetylene 1.5 mmol, 80 °C, 2.5 h.
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4. Conclusions
We report an efficient synthesis of propargylamines through
a three‐component coupling between aldehydes, amines, and
phenylacetylene via C–H activation by a Cu(ΙI) salen complex as
a suitable catalyst. Advantages of this method are the recycla‐
bility of the catalyst without a significant loss of catalytic activ‐
ity, an easy procedure and work‐up, broad substrate applica‐
bility, and high yields in short reaction times. Finally, this ap‐
proach could make a valuable contribution to existing process‐
es in the field of propargylamine synthesis.
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Acknowledgments
We are grateful to Mazandaran University for support of our
research.
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Mahmood Tajbaksh et al. / Chinese Journal of Catalysis 34 (2013) 2217–2222
Graphical Abstract
Chin. J. Catal., 2013, 34: 2217–2222 doi: 10.1016/S1872‐2067(12)60683‐4
Cu(ΙI) salen complex catalyzed synthesis of propargylamines by a three‐component coupling reaction
Mahmood Tajbakhsh*, Maryam Farhang, Hamid Reza Mardani, Rahman Hosseinzadeh, Yaghoub Sarrafi
Mazandaran University, Iran; Payame Noor University, Iran
N
O
N
O
M
R2 R3
N
R2R3NH
R1CHO
Ph C CH
R1
Solventless, 80°C
M = (Cu, Zn, Mn, Ni)
Ph
A Cu(ΙI) salen complex showed excellent catalytic activity toward the synthesis of propargylamines through the three‐component cou‐
pling of aldehydes, amines, and phenylacetylene. Highlights are excellent yields, short reaction times, and a recyclable catalyst.
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