Nano copper(I) oxide-zinc oxide catalyzed coupling of aldehydes or ketones, secondary amines, and terminal alkynes in solvent-free conditions

Article abstract of DOI:10.1039/c3nj01146a

A simple, efficient, and environmentally benign method has been described for the synthesis of propargylamines through a one-pot three-component coupling reaction of terminal alkynes, aldehydes or ketones, and secondary amines in excellent isolated yields, under solvent-free conditions, using a catalytic amount of nano Cu₂O-ZnO as the recyclable, and heterogeneous catalyst. The catalyst can be reused in further catalytic reactions, and it was found that its activity remained largely unchanged for ten successive runs. The catalyst was characterized by using powder X-ray diffraction (XRD), a transmission electron microscopy (TEM), a scanning electron microscopy (SEM), BET surface area measurement and FT-IR spectroscopy.

Full text of DOI:10.1039/c3nj01146a

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Nano copper(I) oxide–zinc oxide catalyzed
coupling of aldehydes or ketones, secondary
amines, and terminal alkynes in solvent-free
conditions
Cite this: New J. Chem., 2014,
38, 624
Mona Hosseini-Sarvari* and Fatemeh Moeini
A simple, efficient, and environmentally benign method has been described for the synthesis of
propargylamines through a one-pot three-component coupling reaction of terminal alkynes, aldehydes
or ketones, and secondary amines in excellent isolated yields, under solvent-free conditions, using a
catalytic amount of nano Cu2O–ZnO as the recyclable, and heterogeneous catalyst. The catalyst can be
reused in further catalytic reactions, and it was found that its activity remained largely unchanged for ten
successive runs. The catalyst was characterized by using powder X-ray diffraction (XRD), a transmission
electron microscopy (TEM), a scanning electron microscopy (SEM), BET surface area measurement and
FT-IR spectroscopy.
Received (in Porto Alegre, Brazil)
25th September 2013,
Accepted 25th October 2013
DOI: 10.1039/c3nj01146a
www.rsc.org/njc
and a Cu/RuII bimetallic system.16 Difficulties in recovering
these expensive catalysts from the reaction mixture severely
Introduction
Transition metal catalyzed multicomponent reactions (MCRs) are inhibit their wide use in industry. Recently, different hetero-
a powerful synthetic strategy1 to generate multiple molecular geneous catalysts such as LDH-AuCl4,17 AgI,18a AgTPA,18b Ag
scaffolds and to increase structural, as well as skeletal, diversity nanoparticles,18c Ag nanoparticles supported by Ni,18d CuI
from simple and readily available molecules. Three-component complexes,19a–d CuCl,19e silica-immobilized CuI,19f Ni–Y–zeolite,20
coupling of aldehydes, alkynes, and amines (A3-coupling) is one Zn dust,21 copper ferrite nanoparticles,22a nanocrystalline copperII
of the best examples of such a process, and this transformation oxide,22b copper-nanoparticles,22c Cu/C nanoparticles,22d
has received much more attention in recent years.2 The resultant impregnated copper on magnetite,22e copper–zeolites,22f Fe3O4
propargylamines obtained from A3-coupling reactions are nanoparticles23 and ferric hydrogensulfate24 have been successfully
synthetically versatile and key intermediates for the preparation used to catalyze three-component coupling reactions. In addition,
of many biologically active nitrogen compounds such as con- alternative energy sources like microwaves8,25a and ultrasound25b
formationally restricted peptide isosteres, oxotremorine analogues, have also been used in the presence of CuI to accomplish this
b-lactams, natural products, therapeutic drug molecules and poly- reaction via C–H activation.
functional amino derivatives.3 Traditionally, propargylamines are
For most of the catalysts reported so far, the use of a solvent is
prepared either by the amination of propargylic halides, pro- required, but it is highly desirable to develop a process without a
pargylic phosphonates or propargylic triflates, or by the nucleo- solvent. Recently, the use of nanoparticles as catalysts in organic
philic addition of in situ generated metal acetylides to imines and reactions has attracted much attention,26 because their intri-
enamines.4,5 Unfortunately, these reagents which are used in guing properties are different from those of their corresponding
stoichiometric amounts, are highly moisture sensitive and require bulk materials. Metal and metal oxide nanoparticles characteri-
strictly controlled reaction conditions.
stically have high surface areas that translate into a more active
In recent years, great efforts have been made with the C–H site per unit area, and can maximize the reaction rates while
bond activation reaction of terminal alkynes. The alkyne C–H minimizing the requirement of the catalyst. Because of their easy
bond can be activated by employing various homogeneous preparation and stability in air, the nanoparticles of metal oxides
transition metal catalysts such as AuI/AuIII salts,6 AuIII salen or mixed metal oxides are widely reported, and there are excellent
complexes,7a Au/CeO2,7b CuI salts,8,5c AgI salts,9 FeIII salts,10 Zn examples of their applications as catalysts. In comparison with
salts,11 Hg2Cl2,12 InCl3,13a InBr3,13b NiCl2,14 Ir complexes,15 many examples using various metal oxides or mixed metal oxides
as catalysts, there are only a few reports on the use of Cu2O–ZnO
as a catalyst, and in most cases, Cu2O–ZnO worked as a photo-
catalyst in treating organic dyes.27 Recently, nanoparticles of ZnO
Department of Chemistry, Shiraz University, Shiraz 71454, I. R. Iran.
E-mail: hossaini@shirazu.ac.ir; Fax: +98 711 2284822; Tel: +98 711 2286006
624 | New J. Chem., 2014, 38, 624--635
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Scheme 1 Synthesis of propargylamines catalyzed by Cu2O–ZnO nano-
flakes under solvent-free conditions.
with various morphologies (rods, and flakes) have been used as
good catalysts for various organic transformations such as the
synthesis of quinolines,28 Knoevenagel condensation,29 synthesis of
b-phosphono malonates,30 synthesis of ferrocenyl aminophonates,31
synthesis of chromenes,32 and P–C bond formations.33 Therefore in
continuation of our interest in the preparation of nano metal oxides
and investigation into their catalytic activities in organic synthesis,34
herein we report an efficient, one-pot, three-component coupling
of aldehydes or ketones, terminal alkynes, and amines via C–H
activation, catalyzed by reusable Cu2O–ZnO nanoparticles with-
out any additives or bases under solvent-free reaction conditions
(Scheme 1).
Fig. 2 The SEM image of the Cu2O–ZnO nanoflakes.
peak was selected to calculate the average grain size of Cu2O by
using the Scherrer formula. The average grain size of Cu2O
along the (200) direction and ZnO along the (002) direction in a
Cu2O–ZnO nanoflake is about 21 nm and 30 nm respectively.
The scanning electron micrograph of the synthesized Cu2O–
ZnO particles is shown in Fig. 2. It could be seen that well defined
and discrete Cu2O–ZnO nanoflakes have been formed. The size
and morphology of the Cu2O–ZnO nanoparticles analyzed by
TEM is represented in Fig. 3. This image reveals that the product
consists of flake particles with an average size of 32 nm.
Results and discussion
Characterization of Cu2O–ZnO nanoflakes
In order to evaluate the Cu and Zn contents of the catalyst, it was
treated with concentrated HCl to digest the metal complex and
then analyzed by inductively coupled plasma (ICP) analysis. The
results revealed that, under similar conditions, the contents
of Cu and Zn were 47.01% (w/w) and 21.77% (w/w) respectively
(see experimental section for details).
The FT-IR spectrum of the catalyst in the region of 400–950 cmꢀ1
is shown in Fig. 4. The peak at 624 cmꢀ1 corresponds to the Cu–O
bond,35 and a weak absorption at about 455 cmꢀ1 is attributed to
the characteristic absorption band of the Zn–O bond.36
The crystal structure and composition of the obtained
sample were analyzed by X-ray diffraction. Fig. 1 displays the
XRD pattern of the sample. The XRD pattern of the Cu2O–ZnO
nanoflakes can be indexed with five Cu2O diffraction peaks at
29.51(110), 36.41(111), 42.31(200), 61.61(220), 73.81(311) and six
ZnO diffraction peaks at 31.81(100), 34.51(002), 36.41(101),
47.81(102), 56.71(110), 63.01(103) (JCPDS 78-2076 and 89-1397),
which suggests the presence of Cu2O and ZnO phases in the
sample. Considering the overlapping of a ZnO(101) diffraction
peak with a Cu2O(111) diffraction peak, the Cu2O(200) diffraction
The data obtained by Brunauer–Emmett–Teller (BET) measure-
ments of nano Cu2O–ZnO powder have been given in Table 1.
The BET surface area of the nano Cu2O–ZnO powder was found
to be 14.74 m2 gꢀ1, whereas the Barrett–Joyner–Halenda (BJH)
Fig. 1 The XRD pattern of Cu2O–ZnO nanoflakes.
Fig. 3 The TEM image of the Cu2O–ZnO nanoflakes.
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Scheme 2 Three-component coupling of benzaldehyde, piperidine and
phenylacetylene.
Nano Cu2O–ZnO was found to be the most effective catalyst in
terms of reaction rate and isolated yield of the corresponding
product. Obviously, there was no reaction without the use of
any catalyst (Table 2, entry 9). Using Cu2O and ZnO individually
generated the desired product in 70–80% yield (Table 2,
entries 2–5). In comparison, nanoparticles of Cu2O and ZnO
seemed slightly better than the bulky particles. With respect to
the catalyst loading, 0.010 g of Cu2O–ZnO was found to be
optimal. When 0.0050 g of Cu2O–ZnO was used, the reaction
did not go to completion (Table 2, entry 8). However, no signi-
ficant improvement was observed with 0.020 g and 0.040 g of
Cu2O–ZnO (Table 2, entries 6 and 7).
To check the solvent effect on the outcome of the reaction,
the above model reaction was performed with 0.010 g of Cu2O–
ZnO in various solvents such as toluene, acetonitrile, ethanol,
DMF, DMSO and water at 100 1C (Table 3). From Table 3, it is
evident that toluene is the best solvent (Table 3, entry 1), whereas
acetonitrile afforded a lower yield (Table 3, entry 2). Moderate
yields were obtained when the reaction was performed in
ethanol (Table 3, entry 3) and a poor result was observed when
the reactions were carried out in DMF (Table 3, entry 4). DMSO,
THF, and water did not afford any product (Table 3, entries 5–7).
It is interesting to note that the reaction also took place smoothly
under solvent-free reaction conditions, and generated the corre-
sponding propargylamines in excellent yields. To avoid the use
of volatile solvents and to reduce the environmental pollution,
all the three-component coupling reactions were performed
under solvent-free conditions.
Fig. 4 FT-IR spectrum of the Cu2O–ZnO nanoflakes.
Table 1 Results of BET surface area measurements for Cu2O–ZnO nanoflakes
Surface area
Pore volume
BET surface area (m2 gꢀ1
)
14.74
13.08
BJH adsorption cumulative
surface area of pores (m2 gꢀ1
Single point adsorption total
)
0.07
0.06
pore volume of pores (cm3 gꢀ1
BJH adsorption cumulative
)
volume of pores (cm3 gꢀ1
)
Pore size
Mean pore diameter (nm)
Pore size distribution (nm)
19.54
2.41
adsorption surface area of the pores was 13.08 m2
g
ꢀ1. Tꢀh1e
single point total pore volume was found to be 0.072 cm3 g
and the cumulative adsorption pore volume was 0.063 cm3 gꢀ1
,
.
The pore size distribution was found to be 2.41 nm and the
mean pore diameter was 19.54 nm.
Catalytic application of nano Cu2O–ZnO
After the successful preparation and characterization of the Cu2O–
ZnO nanoflakes, we examined their catalytic activity in the multi-
component coupling of aldehydes, amines, and alkynes. In order to
establish the optimum conditions, the catalytic activities of metal
oxides were examined in a model reaction using benzaldehyde (1a),
piperidine (2a) and phenylacetylene (3a) under solvent-free condi-
tions at 100 1C via a three-component reaction (Table 2, Scheme 2).
Next we examined the effect of the temperature. The process
was carried out at 70, 90, 100, 110, and 130 1C. The results are
shown in Table 4. In order to compare between microwave and
conventional heating procedures, a mixture of the respective
compounds was irradiated under solvent-free conditions at
100 1C and a maximum power of 300 W for 15 min. The desired
propargylamine 4a was isolated in 90% yield (Table 4, entry 6).
Table 2 Investigation of various metal oxides in the three-component
coupling of benzaldehyde, piperidine and phenylacetylenea
Entry
Catalyst (g)
Time (h)
Yieldb (%)
Table 3 The optimization of solventsa
1
2
3
4
5
6
7
8
9
Nano Cu2O–ZnO (0.01)
Nano Cu2Oc (0.01)
Nano ZnOc (0.01)
Bulky Cu2Od (0.01)
Bulky ZnOd (0.01)
Nano Cu2O–ZnO (0.02)
Nano Cu2O–ZnO (0.04)
Nano Cu2O–ZnO(0.005)
None
1
1
1
1
1
1
1
1
24
95
80
78
75
70
95
95
75
0
Entry
Solvent
Time (h)
Yieldb (%)
1
2
3
4
5
6
7
8
Toluene
Acetonitrile
Ethanol
DMF
DMSO
THF
1
2
2
2
2
2
2
1
95
80
50
5
0
0
Water
Neat
0
95
a
Reaction conditions: benzaldehyde (1 mmol), piperidine (1.2 mmol),
phenylacetylene (1.5 mmol), and catalyst (0.010 g) under solvent free
b
c
a
conditions at 100 1C. Isolated yield. Nano Cu2O and ZnO individually,
were prepared according to the experimental section. Cu2O and ZnO phenylacetylene (1.5 mmol), solvent (3 mL), and Cu2O–ZnO nanoflakes
were purchased from Merck.
Reaction conditions: benzaldehyde (1 mmol), piperidine (1.2 mmol),
d
b
(0.010 g), at 100 1C. Isolated yield.
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Table 4 The optimization of temperaturea
Entry
Temperature (1C)
Time (h)
Yieldb (%)
1
2
3
4
5
6
70
90
100
110
130
100c
1
1
1
1
40
70
95
96
96
90
1
15 (min)
a
Reaction conditions: benzaldehyde (1 mmol), piperidine (1.2 mmol),
phenylacetylene (1.5 mmol), and Cu2O–ZnO nanoflakes (0.010 g) under
b
c
solvent-free conditions. Isolated yield. MW irradiation 300 W.
Finally, from Tables 2–4 it can be seen that the best result
was achieved with Cu2O–ZnO nanoparticles (0.010 g) at 100 1C
under solvent-free conditions. To the best of our knowledge,
this is the first example of the use of Cu2O–ZnO nanoparticles
as catalysts for the multicomponent coupling of aldehydes,
amines and alkynes.
Fig. 6 A comparison of the FT-IR spectra of Cu2O–ZnO nanoflakes,
(A) before and (B) after 10 consecutive cycles.
The Cu2O–ZnO catalyst could also be separated from the
reaction mixture and recovered conveniently by centrifugation
by adding the appropriate solvent, and then, new substrates
were added to set up a new reaction. Following this procedure, the
catalyst was recycled effectively ten times without any decrease in
yield or catalytic activity (Fig. 5). After 10 consecutive reactions, the
recovered nano Cu2O–ZnO was found to contain 46.23% (w/w)
of Cu, and 20.58% (w/w) of Zn based on an ICP analysis, which is
comparable to the initial value of Cu 47% (w/w) and Zn 21.77%
(w/w) (see the experimental section for details).
In order to investigate the stability of Cu2O–ZnO nanoparticles
during the 10 consecutive cycles, the XRD patterns and FT-IR
spectra were analyzed before and after recycling 10 times. As
shown in Fig. 6 and 7, no notable changes were detected, which is
indicative of catalyst stability for at least 10 consecutive cycles.
The X-ray diffraction patterns of the reused catalyst were found to
be similar to the fresh sample as illustrated in Fig. 7. The size of
Cu2O along the (200) direction in a Cu2O–ZnO nanoflake is
about 21 nm.
In order to show that Cu2O–ZnO nanoparticles are hetero-
geneous catalysts, a hot filtration test was performed. For this
purpose, we studied the coupling of benzaldehyde, piperidine,
and phenylacetylene in the presence of Cu2O–ZnO nanoparticles.
Fig. 7 The XRD pattern of Cu2O–ZnO nanoflakes: (a) before and (b) after
10 consecutive cycles.
The catalyst was removed from the reaction mixture and heated
to 100 1C after 10 min. The solution was then stirred at the same
temperature and the percent reaction conversions were deter-
mined by gas chromatography (GC). Conversion was found to be
5% at 10 min. Analysis showed no further conversion following
this hot filtration and no Cu or Zn could be detected by ICP
analysis of this hot filtrate.
Using the optimized reaction conditions, a variety of struc-
turally diverse aldehydes and amines possessing a wide range
of functional groups were employed as reaction substrates, to
explore the scope and generality of the nano Cu2O–ZnO pro-
moted three-component coupling reaction. The results are
summarized in Table 5. The results indicated that both aromatic
and aliphatic aldehydes were transformed to the corresponding
propargylamines in excellent yields. Aryl aldehydes with electron-
rich groups reacted rapidly, while substitution of electron-
withdrawing groups on the benzene ring decreased the reactivity,
and required longer reaction times. It is worth noting that
4-nitrobenzaldehyde did not yield the coupled product even
Fig. 5 Recyclability of Cu2O–ZnO nanoparticles for propargylamine synthesis. after long reaction times, which is in accordance with earlier
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Table 5 One-pot synthesis of propargylamine derivatives 4 from aldehydes 1, amines 2, and alkynes 3, by using Cu2O–ZnO nanoparticles as the catalysta
Entry
1
Aldehyde
Amine
Alkyne
Product
Time (min)
Yieldb (%)
Ref.
39
60
95
2
3
4
5
60
55
95
95
90
0
39
39
65
39
120
22b
6
7
70
70
90
87
41
—
8
9
65
60
87
95
39
39
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Table 5 (continued)
Entry
10
Aldehyde
Amine
Alkyne
Product
Time (min)
Yieldb (%)
Ref.
40
60
95
87
95
11
12
65
50
40
19e
13c
50
95
14
14c
15
16
50
60
75
95
90
80
14
19c
—
17
18
80
95
85
80
14
39
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Table 5 (continued)
Entry
19
Aldehyde
Amine
Alkyne
Product
Time (min)
240
Yieldb (%)
Ref.
0
8f
a
Reaction conditions: aldehydes (1 mmol), amines (1.2 mmol), alkynes (1.5 mmol), Cu2O–ZnO nanoflakes (0.010 g) under solvent-free conditions
b
c
at 100 1C. Isolated yield. Under the same conditions, but aqueous formaldehyde (37%, 0.4 mL) was used.
studies18b,19c (Table 5, entry 5). In addition, heteroaromatic have been restricted to aldimines generated in situ. Ketoimines37
aldehydes also gave products (Table 5, entry 8). The reaction of are generally considered to be less reactive towards nucleophilic
aryl aldehydes was also tolerant of ortho substitution and led to additions than aldimines, due to the steric hindrance and
the excellent yield of product (Table 5, entry 6). To extend the electronic effects. Therefore, the utilization of ketoimines
scope of the reaction, various cyclic and acyclic secondary amines generated in situ in the direct alkyne addition reaction still
such as piperidine, morpholine, pyrrolidine, dibutylamine, and remains a significant challenge for chemists. To date, only a
2,20-(azanediylbis(ethane-2,1-diyl))bis(isoindoline-1,3-dione) were few methods have been developed in this field and almost all of
used and tolerated well (Table 5, entries 9–16). Furthermore, by them suffer from limitations,38 such as the generation of the
using various substituted phenylacetylenes with substituents that ketoimine in an intramolecular manner from a preformed
have different electronic properties, different yields of the final precursor containing a ketone moiety and an amine, specific
products were achieved. 4-Methyl-substituted phenylacetylenes reaction conditions, poor substrate scope, low yields, a high
were more reactive compared to 4-fluoro-substituted phenyl- reaction temperature, prolonged reaction times, toxic solvents,
acetylene (Table 5, entries 17 and 18).
and expensive catalysts.
As the Cu2O–ZnO nanoparticles proved to be a good catalyst for
As shown in Table 6, the three-component coupling of
tertiary carbon-containing propargylic amines under the present ketones, amines, and alkynes was completed successfully for
reaction conditions, we set out to prepare quaternary carbon- all the substrates examined, and the desired products were
containing propargylic amines using ketones, amines, and alkynes. isolated in good to excellent yields. Aliphatic ketones, including
Nevertheless, in direct coupling reactions, the CQN electrophiles cyclic ketones, exhibited good reactivity (Table 6, entries 1–7),
Table 6 One-pot synthesis of propargylamine derivatives 6 from ketones 5, amines 2, and alkynes 3, using Cu2O/ZnO nanoparticles as the catalysta
Entry
Ketone
Amine
Alkyne
Product
Time (h)
Yieldb (%)
Ref.
1
2:30
95
—
2
3
2:30
2:30
90
90
—
38d
4
5
2:45
2:45
90
87
42
38d
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Table 6 (continued)
Entry
Ketone
Amine
Alkyne
Product
Time (h)
2:45
Yieldb (%)
Ref.
6
87
85
38d
7
8
4
—
—
24
Tracec
9
24
0
38d
10
24
24
0
0
—
—
11
12
24
3
0
—
—
13
80
a
Reaction conditions: ketones (1.5 mmol), amines (1 mmol), alkynes (1.5 mmol), and Cu2O–ZnO nanoflakes (0.010 g) under solvent-free
b
c
conditions at 100 1C. Isolated yield. Under reflux conditions.
whereas aromatic ketone, such as acetophenone and benzo- terminal alkyne (Table 6, entry 13), the reaction afforded the
phenone, gave none of the desired products (Table 6, entries 9 corresponding propargylamine in good yield.
and 10). In the case of acyclic ketones, such as acetone, only a
trace of the desired product was obtained after a prolonged
period of time (Table 6, entry 8). The methodology was also
applied to the sterically bulky ketones (Table 6, entry 7). To extend
Conclusions
the scope of the reaction, various cyclic secondary amines such as In summary, we have developed a simple and efficient method
piperidine, morpholine, and pyrrolidine, were used. Further, for the synthesis of tertiary or quaternary carbon-containing
some primary amines such as aniline, benzyl amine, were used propargylic amines via C–H activation using nano Cu2O–ZnO as
but unfortunately, no reaction occurred (Table 6, entries 11 the catalyst under mild reaction conditions. The reaction is
and 12). Even when using 4-methylphenylacetylene as the especially effective for both aliphatic and aromatic aldehydes or
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cyclic ketones. No additives and/or toxic reagent(s) are required water bath, products were collected by filtration, washed with
and no laborious purification methods are necessary. deionized water and absolute ethanol several times, and finally
The simple procedure for catalyst preparation, easy recovery dried in air at 60 1C for 3 h. According to the ICP analysis, the
and reusability of the catalyst are expected to contribute to its Cu and Zn content in the catalyst was determined to be 47%
utilization for the development of benign chemical processes (w/w) and 21.77% (w/w) respectively. Therefore, each gram of
and products. These conditions are also cost effective, environ- catalyst includes 7.3 mmol of copper and 3.3 mmol of zinc.
mentally friendly, and possess high generality, which make our
General procedure for the synthesis of nano Cu2O
methodology suitable for industrialization, as a valid contribu-
tion to the existing processes in the field of propargylamine CuSO4 (1 g, 6.26 mmol) was dissolved in 50 mL distilled water to
synthesis and an important building block for organic synthesis. obtain a solution. After stirring, the solution was subsequently
heated to 70 1C in a water bath for 5 min while stirring. Then,
1 mol lꢀ1 N2H4ꢁH2O was slowly added into the suspension until
lots of red-brown precipitate was produced. After stirring for
Experimental section
30 min while in a constant temperature water bath, products
were collected by filtration, washed with deionized water and
absolute ethanol several times, and finally dried in air at 60 1C
for 3 h.
NMR spectra were recorded on a Bruker Avance DPX-250
(1H NMR 250 MHz and 13C NMR 62.9 MHz) in pure deuterated
solvents with tetramethylsilane (TMS) as the internal standard.
Scanning electron micrographs were obtained by SEM instru-
General procedure for the synthesis of nano ZnO
mentation (SEM, XL-30 FEG SEM, Philips, at 20 kV). TEM was
also used for the transmission electron microscopy (Philips CM10)
image. Spectroscopic methods including X-ray diffraction (XRD, D8,
Advance, Bruker, axs) and FT-IR spectroscopy (Shimadzu FT-IR 8300
spectrophotometer) were employed for characterization of the
heterogeneous catalyst. Surface area measurements were con-
ducted according to the BET gas (nitrogen) adsorption method.
The porous structural parameter used in this paper was taken
from the BJH data. Metal contents were obtained by an ICP
analyzer (Varian, vista-pro). Mass spectra were determined on a
Shimadzu GCMS-QP 1000 EX instrument at 70 or 20 eV. Melting
points were determined in open capillary tubes in a Bu¨chi-535
circulating oil melting point apparatus. The purity determination
of the substrates and reaction monitoring were accomplished by
TLC on silica gel PolyGram SILG/UV254 plates or by a Shimadzu
Gas Chromatograph (GC-10A) instrument with a flame ionization
detector using a column of 15% carbowax 20 M chromosorb-w
acid washed 60–80 mesh. Column chromatography was carried
out on short columns of silica gel 60 (70–230 mesh) in glass
columns (2–3 cm diameter), using 15–30 grams of silica gel per
gram of crude mixture. Chemical materials were purchased from
Fluka, Aldrich, Alfa Aesar, and Merck.
First, Zn(OAc)2ꢁ2H2O (as Zn2+ source, 1 g) and PEG 2000 (0.30 g)
were dissolved in water (140 mL). Then, by the dropwise
addition of NH4OH (1.5 mL, 25%) at reflux conditions for 6 h,
2ꢀ
Zn(OH)4 was formed. With the presence of a water-soluble
linear polymer (PEG 2000), ZnO crystals form at the interface
between the substrate and the solution by the dehydration
of Zn(OH)42ꢀ. After that, the product was centrifuged and
washed with deionized water and absolute ethanol. Next, 90 mL
deionized water was added and the mixture was refluxed for 8 h.
It was then cooled under cold water, centrifuged and washed.
Finally, the nano-rod ZnO powder was dried at 100 1C in an oven
to give 0.65 g powder.
General procedure for the three-component synthesis of
propargylamines containing a tertiary carbon centre
A mixture of aldehyde (1 mmol), amine (1.2 mmol), alkyne
(1.5 mmol) and nano Cu2O–ZnO (0.010 g) was stirred in a
round-bottomed flask at 100 1C. For 1 mmol of reactants,
0.073 mmol Cu and 0.033 mmol Zn is needed, which is equal
to 0.01 g of the heterogeneous catalyst according to the ICP
analysis. The progress of the reaction was monitored by TLC and
on completion, the reaction was cooled to the room temperature,
ethyl acetate (2 ꢂ 5 mL) was added and the slurry was stirred at
General procedure for the synthesis of Cu2O–ZnO nanoflakes
CuSO4 (1 g, 6.26 mmol), was dissolved in 50 mL distilled water room temperature to ensure removal of the product from the
to obtain a certain concentration of solution. ZnO (0.51 g, surface of the catalyst. The reaction mixture was centrifuged to
6.26 mmol) was then dispersed in the above solution and separate the catalyst and washed several times with ethyl acetate.
sonicated to obtain a uniform suspension. The suspension The centrifugate was concentrated under reduced pressure to
was vigorously stirred at room temperature for 50 min to ensure afford the crude product, which after chromatography on silica
that enough Cu2+ had been adsorbed on the surface of ZnO. gel (petroleum ether–ethyl acetate 10/1), gave the corresponding
After stirring, in order to dispose of free Cu2+ ions, the mixtures propargylamine derivatives.
were centrifuged and washed alternately with deionized water
and absolute ethanol three times. Then the mixture was added
into 30 mL deionized water to obtain a suspension. The suspen-
General procedure for the three-component synthesis of
propargylamines containing a quaternary carbon centre
sion was subsequently heated to 70 1C in a water bath for 5 min Nano Cu2O–ZnO (0.010 g) was added to a mixture of a ketone
while stirring. Next, 1 mol lꢀ1 N2H4ꢁH2O was slowly added (1.5 mmol), amines (1.0 mmol), and alkynes (1.5 mmol), and
into the suspension until lots of red-brown precipitate was pro- stirred at 100 1C for the appropriate time (Table 6). Progress
duced. After stirring for 30 min while in a constant temperature of the reaction was monitored by TLC or GC. After completion,
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the reaction was cooled to the room temperature, ethyl acetate 7.28–7.25 (m, 3H), 2.80 (br.s, 4H), 2.08–1.99 (m, 2H), 1.93–1.62
(2 ꢂ 5 mL) was added and the slurry was stirred at room (m, 14H). 13C NMR (62.9 MHz, CDCl3): d = 131.7, 128.1, 127.6,
temperature to ensure removal of the product from the surface 123.8, 92.1, 84.6, 62.3, 47.8, 40.1, 28.2, 23.8, 22.1; GC-MS/EI:
of the catalyst. The reaction mixture was centrifuged to separate m/z (%) = 269 (M+ + 2, 3.3), 268 (M+ + 1, 7.9), 267 (M+, 13.1), 238
the catalyst and washed several times with ethyl acetate. The (39.5), 211 (100), 162 (12), 141 (40.1), 115 (35.1), 91 (22.5), 70 (56.6).
centrifugate was concentrated under reduced pressure to afford Anal. calcd for C19H25N (267.41): C, 85.32; H, 9.42; N, 5.24. Found:
the crude product, which after chromatography on silica gel C, 85.38; H, 9.49; N, 5.19.
(petroleum ether–ethyl acetate 10/1), gave the desired products
(Table 6).
1-(1-( p-Tolylethynyl)cyclohexyl)piperidine (6m). Color: yellowish;
Mp: 66–67 1C. IR (KBr): 2931, 2854, 2800, 1504, 1442, 1288,
The known compounds were characterized by comparison 1095 cmꢀ1. 1H NMR (250 MHz, CDCl3): d = 7.33(d, J = 8.25, 2H),
of their physical and spectroscopic data with the data already 7.09 (d, J = 8, 2H), 2.67 (br.t, J = 4.5, 4H), 2.33 (s, 3H), 2.11–2.06
described in the literature.
(m, 2H), 1.73–1.44 (m, 14H). 13C NMR (62.9 MHz, CDCl3): d =
N-[1-(9,10-Dihydroanthracene-9-yl-)-3-phenyl-2-propynyl]- 137.6, 131.6, 128.9, 120.7, 89.9, 86.1, 59.3, 47.1, 35.8, 26.6, 25.8,
piperidine (4g). Color: yellow, Mp: 143–144 1C. IR (KBr): 2931, 24.8, 23.1, 21.4; GC-MS/EI: m/z (%) = 283 (M+ + 2, 17.4),
2854, 1488, 1095, 748, 725 cmꢀ1. 1H NMR (250 MHz, CDCl3): d = 282 (M+ + 1, 28.7), 281 (M+, 30.7), 266 (61.9), 238 (100), 191
8.99 (d, J = 8.75, 2H), 8.44 (s, 1H), 8.01 (d, J = 9, 2H), 7.56–7.44 (21.4), 155 (46.8), 129 (32.5), 105 (18.3), 84 (55.2), 55 (29). Anal.
(m, 4H), 7.33–7.19 (m, 5H), 5.70 (s, 1H), 2.39–2.31 (m, 2H), calcd for C20H27N (281.44): C, 85.35; H, 9.67; N, 4.98. Found: C,
1.56–1.45 (m, 8H). 13C NMR (62.9 MHz, CDCl3): d = 132.2, 132.0, 85.40; H, 9.70; N, 4.90.
131.6, 130.3, 128.9, 128.3, 128.2, 128.1, 127.8, 125.8, 125.2,
124.9, 89.8, 86.6, 56.9, 52.9, 26.2, 24.7; GC-MS/EI: m/z (%) =
378 (M+ + 1, 0.3), 377 (M+ + 1, 3.6), 376 (7.1), 375 (4.3), 291 (100),
199 (15.3), 84 (79.1), 57 (12.1). Anal. calcd for C28H27N (377.52):
C, 89.08; H, 7.21; N, 3.71. Found: C, 89.10; H, 7.26; N, 3.69.
2,20-(((1,3-Diphenyl-2-propynyl)azanediyl)bis(ethan-2,1-diyl))-
bis(isoindolin-1,3-dione) (4p). Color: white, Mp: 151–152 1C. IR
Acknowledgements
We gratefully acknowledge the support of this work by the
Shiraz University. We are also grateful to Mr H. Sajedian Fard
and Mr M. S. Darvish Tafvizi for helpful cooperation and also to
Prof. A. Jarrahpour for editing the English of this paper.
1
(KBr): 2831, 1766, 1712, 1396, 1072, 1033, 717 cmꢀ1. H NMR
(250 MHz, CDCl3): d = 7.72–7.64 (m, 8H), 7.52–7.48 (m, 2H),
7.35–7.26 (m, 5H), 6.99 (t, J = 7.25, 1H), 6.83 (t, J = 7.25, 2H), 5.32
(s, 1H), 4.03–3.92 (m, 2H), 3.65–3.59 (m, 2H), 3.14–3.03 (m, 2H),
2.83–2.77 (m, 2H). 13C NMR (62.9 MHz, CDCl3): d = 168.1, 138.4,
133.5, 132.5, 131.8, 128.3, 128.3, 127.8, 127.2, 122.9, 88.5, 84.5,
56.5, 49.3, 35.7; GC-MS/EI: m/z (%) = 555 (M+ + 2, 0.1), 554 (M+ + 1,
0.3), 553 (M+, 0.6), 379 (9.6), 293 (1), 232 (0.7), 191 (100), 91 (2.4),
57 (3.1). Anal. calcd for C35H27N3O4 (553.61): C, 75.93; H, 4.92; N,
7.59. Found: C, 75.99; H, 4.98; N, 7.51.
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1H NMR (250 MHz, CDCl3): d = 7.44–7.39 (m, 2H), 7.29–7.25 (m, 3H),
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