Y. Liu et al.
gel (200–300 mesh) column. 1H and 13CNMR data are provided as
supporting information.
Table 4. Efficiency of catalyst reusea
General Procedure for Synthesis of Product 3
Compound 1a 0.5 mmol, 2a 0.6 mmol and 5% mol Ag/CNTs were
stirred at 80ꢀC in MeCN for 10 h. When all starting material was con-
sumed (thin-layer chromatographic analysis) the mixture was cooled
to room temperature and the Ag/CNTs were deposited on the but-
ton. The catalyst was recovered by filtration and washed three times
with water (2 Â 4 ml).The aqueous solution was extracted with
diethyl ether (3 Â 10 ml) and the combined extract was dried with
anhydrous MgSO4. The solution was removed by evaporating to dry-
ness under reduced pressure and the crude product was purified by
column chromatography to give a sample of 3aa.
Entry
Run
t (h)
Yield (%)
1
2
3
4
1
10
10
10
10
81
81
80
79
1st reuse
2nd reuse
3rd reuse
Acknowledgments
aIsolated yields.
The work was financially supported by the Natural science Foun-
dation of Guangdong Province (10151022501000033).
tested 1c and the result indicated that the product 3 cc was
obtained in 80% yield (entry 10). Unfortunately, the
corresponding products were not observed by GC-MS when
1,2-diphenylethyne was used as substrate, as shown in Scheme 1.
These results have shown that this process is stereoselective
and provides cis product due to formation of a hydrogen
bond between N–H and oxygen in the carbonyl group. These
compounds were characterized by previous reports.[27,28]
We investigated the efficiency of catalyst reuse and recycling in
the following steps. As shown in Table 4, the results clearly
indicated that the Ag/CNTs catalyst could be efficiently recycled
and separated by filtration. The catalytic activity of heterogeneous
catalyst remained unchanged after reusing three times in the
reaction.
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Conclusions
In summary, we have reported a convenient heterogeneous
catalytic hydroamination process by Ag/CNT catalysts. It repre-
sents an efficient method for synthesis of enamines that have a
high reaction activity to rapidly construct complex and novel
heterocycles. This heterogeneous catalytic system is reusable
and applicable, and can be used efficiently for intermolecular
hydroamination. Our study has indicated the ability of Ag/CNT
catalysts to promote a regioselective hydroamination of activated
alkynes with aromatic amine.
Experimental
General Information
The reactions were performed at 80ꢀC under air atmosphere. NMR
spectra and 13H NMR spectra were recorded with a Bruker 300 or
400 spectrometer in a CDCl3 solution with tetramethylsilane as in-
ternal standard. 1a–1c were purchased from Aldrich Chemicals.
All products were isolated by short chromatography on a silica
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wileyonlinelibrary.com/journal/aoc
Copyright © 2012 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2013, 27, 206–208