Propargylamines formed from three-component coupling reactions catalyzed by silver oxide nanoparticles

Article abstract of DOI:10.1039/c2ra22390b

An economic, efficient and green silver oxide nanoparticle catalyzed three-component coupling reaction of aldehydes, amines and alkynes was developed. This method provided various propargylamines in moderate to high yield at room temperature in air. The s

Full text of DOI:10.1039/c2ra22390b

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Propargylamines formed from three-component
coupling reactions catalyzed by silver oxide
Cite this: RSC Advances, 2013, 3, 1732
nanoparticles3
Received 3rd October 2012,
Accepted 3rd December 2012
Xin Zhou, Yi Lu, Ling-Ling Zhai, Yue Zhao, Qing Liu and Wei-Yin Sun*
DOI: 10.1039/c2ra22390b
www.rsc.org/advances
An economic, efficient and green silver oxide nanoparticle
catalyzed three-component coupling reaction of aldehydes,
amines and alkynes was developed. This method provided various
propargylamines in moderate to high yield at room temperature
in air. The silver oxide nanoparticles could be separated simply
and reused without significant decrease of activity.
coupling reaction at room temperature in air without additional
co-catalyst or ligand. Our group has reported silver(I) complex
catalyzed three-component coupling reactions recently.14 Because
of the complicated and time-consuming procedure to prepare the
complex, we attempted to use the silver oxide nanoparticle catalyst
by adopting a much simpler and more direct approach. The silver
oxide nanoparticles were readily prepared according to the
reported procedure,15 and the SEM image of the nanoparticles is
shown in Fig. 1. The size of the silver oxide nanoparticles was
among 1.0 to 2.0 mm with the size distribution as previously
reported.15
Initially, phenylacetylene, cyclohexanecarboxaldehyde and pyr-
rolidine were chosen for the reaction based on the previous
reports. In the presence of 5 mol% of silver oxide nanoparticles,
the A3-coupling reaction was carried out in various solvents at
room temperature in air (Table 1). Among the solvents tested,
chloroform was the most effective reaction medium for the three-
component coupling reaction with a yield of 79% (Table 1, entry
12). When we employed dichloromethane, acetonitrile, DMF,
DMSO or 1,2-dichloroethane (DCE) as the solvents, product 1a was
Environmentally benign, efficient, economical and green synthesis
in organic chemistry has become more and more important in
chemical research.1 Over the past decade, one-pot three-compo-
nent coupling reactions of aldehydes, amines and alkynes (A3-
coupling) for the synthesis of propargylamines have obtained
tremendous development.2 Since Li’s group reported gold
catalyzed three-component coupling reaction for the first time in
2003,3 numerous efficient three-component coupling reactions in
different solvents catalyzed by various metal catalysts such as Ag(I)
salt,4 Cu(I) salt,5 Au(III) salen complexes,6 In(III) salt,7 Fe(III) salt8
were developed, respectively.
In recent years, with the progress of nanoscience, the catalytic
properties of nanoparticles have attracted particular attention.9
For instance, Mozumdar et al. have reported gold10 and copper11
nanoparticle catalyzed three-component coupling of aldehydes,
amines and alkynes for the synthesis of propargylamines. Wang
et al. have represented an efficient three-component coupling
reaction catalyzed by silver oxide nanoparticles immobilized on
different templates.12 Very recently, Reddy13 and Li1b developed
reusable Fe3O4 nanoparticles to catalyze three-component cou-
pling reactions effectively several times without significant loss of
catalytic activity.
However, high reaction temperature and long reaction time are
the major obstructions in the three-component coupling reactions
catalyzed by these reported metal nanoparticles. Herein, we report
an efficient recyclable silver oxide nanoparticle catalyzed A3-
Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry,
School of Chemistry and Chemical Engineering, Nanjing National Laboratory of
Microstructures, Nanjing University, Nanjing 210093, China.
E-mail: sunwy@nju.edu.cn; Fax: +86 25 8331 450
Electronic Supplementary Information (ESI) available: Experimental details. See
3
Fig. 1 The SEM image of the silver oxide nanoparticles.
This journal is ß The Royal Society of Chemistry 2013
DOI: 10.1039/c2ra22390b
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Table 1 Optimization of the reaction conditionsa
Table 2 Silver oxide nanoparticles catalyzed three-component coupling of
aldehyde, amine and phenylacetylenea
Entry
1
Aldehyde
Amine
Yield (%)b
94
Entry
Solvent
Yield (%)b
1
2
3
4
5
6
7
8
CH2Cl2
CH3CN
DMF
DMSO
DCE
65
60
65
70
67
50
27
32
31
44
44
79
43
80
2
67
3
80
THF
CH3OH
CH2CH2OH
n-Hexane
Toluene
H2O
CHCl3
CHCl3
CHCl3
4
CH3(CH2)5CHO
CH3(CH2)5CHO
paraformaldehyde
99
9
10
11
12
13c
14d
5
92
6
48
a
All reactions were carried out with cyclohexanecarboxaldehyde (1.0
mmol), pyrrolidine (1.1 mmol), phenylacetylene (1.2 mmol) and
silver oxide nanoparticles (0.05 mmol) in different solvents (2 mL) at
7
77
b
room temperature for 10 h. Isolated yield based on
cyclohexanecarboxaldehyde. 0.02 mmol silver oxide nanoparticles
were used as catalyst. 0.10 mmol silver oxide nanoparticles were
c
8
Ph2NH
NRc
NRc
NRc
48
d
used as catalyst.
9
CH3(CH2)4NH2
generated in slightly low yields (Table 1, entries 1–5). Meanwhile,
THF, methanol, ethanol, n-hexane, toluene and water only
afforded 1a in moderate or low yields (Table 1, entries 6–11).
Compared to using 5 mol% catalyst, a much lower yield was
observed by using 2 mol% (Table 1, entry 13), however, no
significant increase was found when increasing the catalyst
amount to 10 mol% (Table 1, entry 14). In addition, we found
10
11
12
13
trace
9.4
that 10 h was most suitable for the reaction (Table S1 ).
3
Finally, the optimized reaction condition was obtained: 1.0
equivalent of aldehyde, 1.1 equivalents of amine, 1.2 equivalents of
alkyne and 5 mol% of silver oxide nanoparticles in chloroform at
room temperature in the air for 10 h. Only 8% product was
obtained when silver oxide powder (5 mol%) was applied as
catalyst under the same reaction conditions. The low yield
indicated that Ag2O nanoparticles, owing to the larger surface
area than their powder form, presented far superior catalytic
activities in the A3-coupling reaction.
With the optimized reaction conditions in hand, various
aldehydes and secondary amines were chosen as substrates to
expand the scope of this coupling reaction to prepare a variety of
propargylamines (Table 2). In general, aliphatic aldehydes and
secondary amines underwent the A3-coupling reaction smoothly to
provide good yields (Table 2, entries 1–7). Then, we chose
diphenylamine, as well as primary amines, such as n-pentylamine
and 4-toluenesulfonamide, as substrates, and no desirable
products were obtained even when we prolonged the reaction
time to 24 h (Table 2, entries 8–10). It is possible that primary
amines are not suitable for this reaction. It was found that
14
15
16
17
79
80
75
55
18
42
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In summary, we have developed an efficient, economic and
environmentally benign silver oxide nanoparticle catalyzed three-
component coupling of aldehyde, amine and alkyne (A3-coupling).
The method allows us to prepare a variety of progargylamines in
moderate to high yield with water as the only theoretical by-
product under mild conditions in air, and no additional co-
catalyst or ligand is required. Furthermore, the catalyst can be
recovered readily and reused directly without significant loss of
activity. The simple preparation and reusability of the catalyst
which shows significant advantages make this reaction more
economical and environmentally acceptable.
Table 2 (Continued)
Entry
19
Aldehyde
Amine
Yield (%)b
64
20
25
a
All reactions were carried out with aldehyde (1.0 mmol), amine (1.1
mmol), phenylacetylene (1.2 mmol) and silver oxide nanoparticles
(0.05 mmol) in chloroform (2 mL) at room temperature for 10 h.
b
c
Isolated yield based on aldehyde. The reaction was carried out for
24 h.
Acknowledgements
This work was financially supported by the National Natural
Science Foundation of China (Grant nos. 91122001 and
21021062) and the National Basic Research Program of
China (Grant no. 2010CB923303).
aromatic amines, such as indoline, 2-methylindoline, and 1,2,3,4-
tetrahydroquinoline, gave low yields (Table 2, entries 11–13). Next,
we examined the effect of aromatic aldehydes (Table 2, entries 14–
19). Both electron-donating and electron-withdrawing substituted
aromatic aldehydes gave moderate to good yields. The para- and
ortho-methoxyl-substituted aromatic aldehydes displayed higher
reactivity than the meta-substituted one due to the electronic
effect. Furthermore, heterocyclic aldehydes such as 4-pyridinecar-
boxyaldehyde showed low yield (Table 2, entry 20). In addition,
1-pentyne was tested, however no product was obtained.
To check the activity of the residual catalyst, the nanoparticles
were isolated and washed with ethanol, air-dried and reused
directly for the next cycle of the reaction without further
purification. As can be seen in Table 3, the silver oxide
nanoparticles could be cycled at least 6 times without significant
decrease of yields.
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1734 | RSC Adv., 2013, 3, 1732–1734
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