Energy-efficient green catalysis: Supported gold nanoparticle-catalyzed aminolysis of esters with inert tertiary amines by C-O and C-N bond activations

Article abstract of DOI:10.1021/jo500877m

Catalyzed by supported gold nanoparticles, an aminolysis reaction between various aryl esters and inert tertiary amines by C-O and C-N bond activations has been developed for the selective synthesis of tertiary amides. Comparison studies indicated that the gold nanoparticles could perform energy-efficient green catalysis at room temperature, whereas Pd(OAc)₂ could not.

Full text of DOI:10.1021/jo500877m

Note
pubs.acs.org/joc
Energy-Efficient Green Catalysis: Supported Gold Nanoparticle-
Catalyzed Aminolysis of Esters with Inert Tertiary Amines by C−O
and C−N Bond Activations
Yong-Sheng Bao,* Menghe Baiyin, Bao Agula, Meilin Jia, and Bao Zhaorigetu*
College of Chemistry and Environmental Science, Inner Mongolia Key Laboratory of Green Catalysis, Inner Mongolia Normal
University, Hohhot 010022, China
S
* Supporting Information
ABSTRACT: Catalyzed by supported gold nanoparticles, an
aminolysis reaction between various aryl esters and inert tertiary
amines by C−O and C−N bond activations has been developed
for the selective synthesis of tertiary amides. Comparison studies
indicated that the gold nanoparticles could perform energy-
efficient green catalysis at room temperature, whereas Pd(OAc)2
could not.
to the reaction of perfluorophenyl indole-2-carboxylate (1a)
with triethylamine (TEA, 2a). After 24 h of refluxing in PhCl in
the presence of 3% Pd/Al2O3, 3% Pd/ZrO2, and 3% Pd/CeO2,
the desired product, N,N-diethylindole-2-carboxamide (3aa)
was isolated in yields of 71%, 72%, and 68%, respectively
(Table 1, entries 1−3). These results further confirmed the
hypothesis that the Pd(OAc)2-catalyzed aminolysis reaction
was performed via a Pd0/PdII catalytic cycle that began with
Pd0. However, comparison of the yields of 3aa showed that the
catalytic activity of PdNPs was apparently lower than that of
Pd(OAc)2 (entry 4). Alternatively, a series of supported AuNPs
he synthesis of amides under smooth, atom-economical
Tconditions starting from carboxylic acids or esters was
recognized as one of the pending challenges for the synthetic
chemical and pharmaceutical industries by the American
Chemical Society Green Chemistry Institute in 2007. The
conventional aminolysis of esters is performed mainly by the
reaction between esters and amines under the catalysis of acids
or bases. In recent years, main efforts have been devoted to the
development of Lewis bases,1 imidazolylidene carbenes,2 and
anionic nucleophiles3 as efficient catalysts to improve the
aminolysis of esters with primary or secondary amines.
However, to the best of our knowledge, there has been no
report on the selective aminolysis of esters with inert tertiary
amines to form tertiary amides via C−N bond activation,
although many C−N bond activation reactions of tertiary
amines have been reported.4
Table 1. Screening of Heterogeneous Catalysts for the
a
Aminolysis Reaction
We recently developed the Pd(OAc)2-catalyzed aminolysis
reaction of aryl esters using inert tertiary amines as amino
donors via C−O and C−N bond activations.5 In that study we
found that when PdCl2 was used as the catalyst, a palladium
mirror appeared on the tube wall at the end of the reaction,
which indicated that this reaction may be performed via a Pd0/
PdII catalytic cycle. Therefore, we postulated that Pd(OAc)2
could be replaced by heterogeneous catalysis with metallic
palladium or other metals. In recent years, metal nanoparticles
(NPs), especially PdNPs and AuNPs, have been proven to be
efficient and selective heterogeneous catalysts for many
reactions, such as oxidation of alcohols and aldehydes,
epoxidation of propylene, hydrochlorination of ethyne, and
carbon−carbon coupling.6,7
b
entry
catalyst
solvent
yield (%)
1
2
3% Pd/Al2O3
3% Pd/ZrO2
3% Pd/CeO2
3% Pd(OAc)2
3% Au/CeO2
3% Au/ZrO2
3% Au/Al2O3
2% Au/Al2O3
1% Au/Al2O3
γ-Al2O3
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
PhCl
71
72
68
87
86
83
91
83
77
0
3
4
5
6
7
8
9
10
a
Reaction conditions: 1a (0.2 mmol), 2a (2 equiv), and catalyst (10
mol %) in solvent (1.5 mL) for 24 h at 115 °C. Isolated yields.
Therefore, to test the possibility of heterogeneous catalytic
aminolysis of tertiary amines with esters, PdNPs and AuNPs
supported on three various oxide powders, including Al2O3,
ZrO2, and CeO2, were prepared by the impregnation−
reduction method7d (see the Experimental Section) and applied
b
Received: April 24, 2014
Published: June 17, 2014
© 2014 American Chemical Society
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Note
were investigated to study their catalytic performance in the
model reaction. We were pleased to find that AuNPs not only
smoothly catalyzed the aminolysis reaction but also gave 3aa in
significantly higher yields than the PdNP-catalyzed reaction
(entries 5−7). Moreover, the catalytic performance of 3% Au/
Al2O3 was superior to that of Pd(OAc)2 in the model reaction.
Since a gold loading higher than 3 wt % will led to aggregation
of the NPs,7d we tested lower loadings of gold (2 and 1 wt %
Au/Al2O3). The results showed that the catalytic efficiency was
significantly reduced when the gold loading was decreased
(entries 8 and 9). It was noteworthy that no reaction was
observed in a blank experiment conducted with γ-Al2O3 powder
instead of AuNPs under otherwise identical conditions (entry
10).
catalytic reaction, when the AuNP catalyst was used, 1-
methylpyrrolidine (2c) reacted with 1a exclusively at the
exocyclic C−N bond to give (indol-2-yl)(pyrrolidin-1-yl)-
methanone (3ac) in 93% yield; the Pd(OAc)2-catalyzed
reaction afforded 3ac in 92% yield (entry 6). In order to
study the difference of the two kinds of catalysts in more detail,
less active substrates such as phenyl esters5 were tested.
Surprisingly, we found that when the AuNP catalyst was used,
phenyl indole-2-carboxylate (1e) could react with 2c at room
temperature (25 °C) to afford desired product 3ac in 85%
yield, whereas no product formation was observed with the
Pd(OAc)2 catalyst at the same temperature (entry 7). When
the temperature was raised to 115 °C, the yield of the AuNP-
catalyzed reaction did not increase, and not only that, the
difference between the homogeneous- and heterogeneous-
catalyzed systems disappeared. Likewise, when phenyl benzoate
(1f) was used as the ester source to compare the two kinds of
catalysts, the same result was obtained (entry 8). In summary,
although the catalytic performance of AuNPs was inferior to
Pd(OAc)2 at high temperature, AuNPs could perform the
catalytic aminolysis reaction at room temperature, whereas
Pd(OAc)2 could not. We postulated that this is attributed to
abundant low-coordinated atoms and the high d10 energy of
small gold nanoparticles, which results in the formation of
active sites.8
To compare homogeneous- and heterogeneous-catalyzed
systems, a variety of esters and amines were subjected to the
conditions from Table 1, entry 7, and representative results are
summarized in Table 2. Other esters including perfluorophenyl
Table 2. Comparative Study of the Catalytic Activities of Au/
a
Al2O3 and Pd(OAc)2 in Aminolysis Reactions
To demonstrate the synthetic utility of the energy-efficient
green catalysis, the scope of the present transformation was
examined using 2c as a model substrate to react with various
esters 1 at 25 °C. As shown in Table 3, except for ethyl indole-
2-carboxylate (1n), all of the carboxylic esters tested, including
benzoate, picolinate, pyrazine-2-carboxylate, and pyridin-2-yl 4-
cyanobenzoate, reacted with 2c to give the corresponding
amides in 61−94% yield. The results further proved that the
catalyzed aminolysis reaction applies only to aryl and heteroaryl
esters and not to alkyl esters whether homogeneous or
heterogeneous catalysis is used. It is clear that having
electron-withdrawing groups on the benzene ring of the aryl
ester is more beneficial to this reaction, as the yields with 1b−i
were higher than 90% (entries 1−6). Furthermore, comparison
of phenyl 4-cyanobenzoate (1j) (entry 7) with phenyl benzoate
(1f) (Table 2, entry 8) shows that the cyano group (a typical
electron-withdrawing group) on the benzoyl of the aryl ester
increased the yield of the amide as well. Further experiments
showed that naphthalen-2-yl 4-cyanobenzoate (1k) underwent
the aminolysis reaction expediently to give the same product as
1j, namely, 4-(pyrrolidine-1-carbonyl)benzonitrile (3hc), in
74% yield (entry 8). However, when pyridin-2-yl 4-
cyanobenzoate (1l) (a heteroaryl ester) was used as the ester
source, the yield of 3hc increased significantly to 84% (entry 9).
This result indicates that the 2-pyridyloxy group is a very good
leaving group and that the coordination of the nitrogen to the
catalyst promotes cleavage of the acyl C−O bond of the ester.9
Similarly, naphthalen-2-yl pyrazine-2-carboxylate (1m), which
includes nitrogen atoms in the acyl part of the ester, underwent
the aminolysis reaction to give 3mc in higher yield than
obtained with 1k (entry 10). This was also the case in our
earlier studies.10 These results clearly show that the pyridine or
benzene ring serves as a directing group for cleavage of the acyl
C−O bond of the ester and that coordination of the nitrogen
atom to the catalyst is favorable for the catalyzed reaction
(Scheme 1).
a
Reaction conditions: 1 (0.2 mmol), 2 (2 equiv), and catalyst (10 mol
b
%) in PhCl (1.5 mL) for 24 h. Isolated yields.
benzoate (1b), 2,4,5-trichlorophenyl picolinate (1c), and 2,3-
dichlorophenyl picolinate (1d) were used instead of 1a to react
with TEA (2a) (entries 1−3). Under the catalysis of AuNPs or
Pd(OAc)2, all three esters underwent this aminolysis reaction
to give the corresponding tertiary amides in similar yields.
However, when N,N-diethylaniline (2b), which contains a
C(sp2)−N bond, was chosen as the amine source, the yields
with the AuNP-catalyzed reaction system were much less than
with Pd(OAc)2 (entries 4 and 5). As in the homogeneous
We also examined the possibility of recycling the AuNP
catalyst in the reaction of perfluorophenyl indole-2-carboxylate
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(1a) with 1-methylpyrrolidine (2c). The results showed that
the catalytic performance of the AuNPs did not apparently
decline even after recycling five times (see the Experimental
Section). Therefore, this AuNP-catalyzed aminolysis reaction is
more aligned with green catalysis than the homogeneous
catalysis is.
Table 3. Reactions of Various Esters 1 with 2c at Room
Temperature
a
In order to get information on the eventual state of Au on
the surface of the catalyst, AuNPs with three gold loadings (1.0,
2.0, and 3.0 wt %) on γ-Al2O3 were studied by transmission
electron microscopy (TEM), UV−vis spectroscopy, and X-ray
photoelectron spectroscopy (XPS). TEM images of Au/Al2O3
showed that the gold existed on Al2O3 as nanoparticles of about
2.4 nm in size (Figure 1). The UV−vis spectra of AuNPs on the
Al2O3 support as well as the support alone are shown in Figure
2a. An absorption band at about 520 nm is observed in the
Figure 2. (a) UV−vis diffuse reflectance spectra of the Al2O3 support
and 1−3 wt % Au/Al2O3. (b) The XPS spectrum of the supported
AuNPs.
UV−vis spectra of the catalysts, which is the characteristic
surface plasmon resonance absorption by AuNPs. The XPS
spectra of the supported AuNPs with different gold contents all
showed the same pattern. The binding energies of Au 4f7/2 and
Au 4f5/2 electrons were found to be 83.7 and 87.5 eV,
respectively (Figure 2b). These values are identical to those for
metallic gold, which suggests that catalysts exist in the metallic
state.
a
Reaction conditions: 1 (0.2 mmol), 2 (2 equiv), and catalyst (10 mol
b
%) in PhCl (1.5 mL) for 24 h. Isolated yields.
Scheme 1. Directing Effect of Pyridine and Benzene Rings
On the basis of GC−MS analysis results (see the
Experimental Section) and the commonly accepted mechanism
from the literature, the proposed reaction pathway is shown in
Scheme 2. Initially, AuNPs undergo an oxidative addition with
the acyl C−O bond in aryl ester 1, generating the acylgold
alkoxide. Then the highly Lewis acidic gold species coordinates
Figure 1. (left, center) TEM images of AuNPs on a γ-Al2O3 support. The lengths of the scale bars in the images are 50 and 20 nm, respectively.
(right) Histogram showing the AuNP size distribution.
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3. Preparation of Esters (1a−n). A mixture of the carboxylic acid
(10 mmol), phenol or pyridine-2-ol (10 mmol), DMAP (1 mmol), and
1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide hydrochloride
(EDC·HCl, 10 mmol) in THF (50 mL) was stirred overnight at 25
°C. The resulting mixture was filtered, and the filtrate was evaporated
in vacuo. The residue was purified by flash column chromatography
(silica gel, ethyl ether/petroleum ether = 1:2−1:5 as the eluent),
affording the corresponding aryl ester 1a−n.
Scheme 2. Proposed Mechanism for the AuNP-Catalyzed
Aminolysis Reaction
4. Aminolysis Reaction for Synthesis of Versatile Amides.
The general procedure for the aminolysis reaction was as follows: A
mixture of ester 1 (0.20 mmol), tertiary amine 2 (0.30 mmol), and 3%
Au/Al2O3 (15 mg, 0.02 mmol, 10 mol %) in PhCl (1.5 mL) was sealed
in a 30 mL vial. The reaction mixture was stirred at 115 or 25 °C for
24 h. After cooling to room temperature, the mixture was filtered, and
the filtrate was evaporated in vacuo. The residue was purified by flash
column chromatography (silica gel, ethyl acetate/petroleum ether =
1:2−1:5 as the eluent) to afford the desired amide 3.
N,N-Diethylindole-2-carboxamide (3aa). Liquid. Yield: 91% (39.3
1
mg). H NMR (500 MHz, CDCl3): δ 10.10 (s, 1H), 7.66 (d, J = 7.7
Hz, 1H), 7.46 (d, J = 8.0 Hz, 1H), 7.32−7.19 (m, 1H), 7.19−7.04 (m,
J = 7.1 Hz, 1H), 6.81 (s, 1H), 3.97−3.45 (m, 4H), 1.47−1.24 (m, 6H).
13C NMR (126 MHz, CDCl3): δ 162.3, 135.5, 129.8, 127.9, 124.2,
121.9, 120.3, 111.8, 104.3, 43.4, 39.4, 14.1, 12.8. MS (ESI): m/z
433.02 [2M + H]+. Anal. Calcd for C13H16N2O: C, 72.19; H, 7.46; N,
12.95%. Found: C, 72.15; H, 7.51; N, 13.04%.
to the nitrogen of tertiary amine 2 and reacts with it to give the
iminium-type intermediate by elimination of phenol via the
generally accepted mechanism.11 The complex is then hydro-
lyzed to be converted into the acylgold amino salt by
elimination of aldehyde.4c Reductive elimination from this salt
results in the desired tertiary amide 3 and regenerates Au0 to
complete the catalytic cycle.
In conclusion, it was found for the first time that supported
gold nanoparticles can catalyze the aminolysis reaction between
various aryl esters and inert tertiary amines to form tertiary
amides via C−O and C−N bond activations. Compared with
the homogeneous catalyst Pd(OAc)2, the most outstanding
feature of the AuNP catalyst is its superior ability to catalyze the
aminolysis reaction at room temperature. The experimental
results indicated that the activity order of esters in the
aminolysis reaction is pyridin-2-yl carboxylates > phenyl
carboxylates. Also, electron-withdrawing groups in either the
alkyl part or the acyl part of the ester are more beneficial for
this reaction. This study opens the door to heterogeneous
catalysis of esters by C−O activation and inspires the
application of the catalyzed aminolysis reaction.
N,N-Diethylbenzamide (3ba).12 Yield: 85% (30.1 mg). H NMR
1
(300 MHz, CDCl3): δ 7.46−7.30 (m, 5H), 3.55 (s, 2H), 3.26 (s, 2H),
1.34−1.02 (m, 6H). 13C NMR (75 MHz, CDCl3): δ 171.7, 136.8,
129.2, 128.4, 126.2, 43.4, 39.4, 14.1, 12.8. MS (ESI): m/z 178.10 [M +
H]+.
5
1
N,N-Diethylpicolinamide (3ca). Yield: 79% (28.1 mg). H NMR
(300 MHz, CDCl3): δ 8.58 (d, J = 4.7 Hz, 1H), 7.89−7.68 (m, 1H),
7.55 (d, J = 7.8 Hz, 1H), 7.40−7.30 (m, 1H), 3.57 (q, J = 7.1 Hz, 2H),
3.36 (q, J = 7.1 Hz, 2H), 1.27 (t, J = 7.0 Hz, 3H), 1.14 (t, J = 7.1 Hz,
3H). MS (ESI): m/z 379.15 [2M + Na]+.
N-Ethyl-N-phenylindole-2-carboxamide (3ab).5 Yield: 48% (25.3
1
mg). H NMR (300 MHz, CDCl3): δ 9.40 (s, 1H), 7.55−7.46 (m,
3H), 7.40−7.28 (m, 4H), 7.25−7.16 (m, 1H), 7.05−6.94 (m, 1H),
5.18 (d, J = 1.1 Hz, 1H), 3.97 (q, J = 7.1 Hz, 2H), 1.27 (t, J = 7.1 Hz,
3H). MS (ESI): m/z 265.05 [M + H]+.
5
1
N-Ethyl-N-phenylpicolinamide (3bb). Yield: 36% (16.3 mg). H
NMR (300 MHz, CDCl3): δ 8.37 (s, 1H), 7.69−7.53 (m, 1H), 7.37
(d, J = 5.7 Hz, 1H), 7.23−6.92 (m, 6H), 4.01 (q, J = 6.5 Hz, 2H), 1.25
(t, J = 8.4 Hz, 3H). MS (ESI): m/z 227.05 [M + H]+.
(1H-Indol-2-yl)(pyrrolidin-1-yl)methanone (3ac).13 Yield: 93%
1
(39.8 mg). H NMR (500 MHz, CDCl3): δ 10.07 (s, 1H), 7.68 (d,
EXPERIMENTAL SECTION
J = 8.0 Hz, 1H), 7.49 (d, J = 8.3 Hz, 1H), 7.29 (t, J = 7.6 Hz, 1H), 7.13
(t, J = 7.5 Hz, 1H), 6.90 (s, 1H), 3.90 (t, J = 6.7 Hz, 2H), 3.78 (t, J =
6.8 Hz, 2H), 2.14−2.02 (m, 2H), 2.02−1.92 (m, 2H). 13C NMR (125
MHz, CDCl3): δ 161.0, 135.6, 130.8, 128.1, 124.4, 122.0, 120.3, 111.9,
105.3, 48.3, 47.5, 26.7, 24.0.
■
1. Catalyst Preparation. AuNPs on γ-Al2O3 and other supports
were prepared by the impregnation−reduction method. For example,
3 wt % Au/γ-Al2O3 was prepared by the following procedure: γ-Al2O3
powder (1.0 g) was dispersed into 50 mL of 3.3 × 10−3 HAuCl4
aqueous solution with magnetic stirring, and 0.1 M NaOH aqueous
solution was added to the mixture to adjust the pH to 6. Next, 4 mL of
0.03 M lysine was added with vigorous stirring. To this suspension, 4
mL of 0.35 M NaBH4 solution was added dropwise over 10 min. The
mixture was left to stand for 24 h and then filtered, and the residue was
washed with water and ethanol and dried at 80 °C. The residue was
used directly as the catalyst. Catalysts on other supports were prepared
in a similar manner.
Phenyl(pyrrolidin-1-yl)methanone (3fc).14 Yield: 90% (31.5 mg).
1H NMR (500 MHz, CDCl3): δ 7.56−7.44 (m, 2H), 7.44−7.31 (m,
3H), 3.64 (t, J = 7.0 Hz, 2H), 3.41 (t, J = 6.6 Hz, 2H), 2.07−1.90 (m,
2H), 1.90−1.77 (m, 2H). 13C NMR (125 MHz, CDCl3): δ 169.8,
137.2, 129.8, 128.3, 127.1, 49.6, 46.2, 26.4, 24.5.
Pyridin-2-yl(pyrrolidin-1-yl)methanone (3cc). Liquid. Yield: 92%
1
(32.4 mg). H NMR (400 MHz, CDCl3): δ 8.59 (d, J = 4.6 Hz, 1H),
7.87−7.73 (m, 2H), 7.42−7.31 (m, 1H), 3.74 (t, J = 6.5 Hz, 2H), 3.69
(t, J = 6.6 Hz, 2H), 2.02−1.83 (m, 4H). 13C NMR (100 MHz,
CDCl3): δ 166.6, 154.5, 148.0, 136.9, 124.7, 123.9, 49.1, 46.9, 26.6,
24.1. HRMS (ESI): m/z [M + H]+ calcd for C10H12N2O 177.1028,
found 177.1028.
2. Catalyst Characterization. TEM images were recorded with a
JEOL JEM-1210 transmission electron microscope employing an
accelerating voltage of 200 kV. The samples were suspended in ethanol
and dried on holey carbon-coated Cu grids. The compositions of
samples were determined using the energy-dispersive X-ray spectros-
copy attachment of the transmission electron microscope. The XPS
spectra were measured with an ESCALAB210 spectrometer (British
VG Co.). All of the binding energies were referenced to the C 1s
hydrocarbon peak at 285.00 eV. The UV−vis spectra were obtained
using a Shimadzu UV-2550 spectrophotometer in the range of 200−
800 nm at room temperature with BaSO4 as the reference.
4-(Pyrrolidine-1-carbonyl)benzonitrile (3hc). Liquid. Yield: 94%
1
(37.6 mg). H NMR (500 MHz, CDCl3): δ 7.71 (d, J = 8.2 Hz, 2H),
7.61 (d, J = 8.1 Hz, 2H), 3.65 (t, J = 6.9 Hz, 2H), 3.37 (t, J = 6.6 Hz,
2H), 2.03−1.94 (m, 2H), 1.94−1.87 (m, 2H). 13C NMR (126 MHz,
CDCl3): δ 167.6, 141.4, 132.3, 127.8, 118.2, 113.5, 49.5, 46.4, 26.4,
24.4. HRMS (ESI): m/z [M + H]+ calcd for C12H12N2O 201.1028,
found 201.1030.
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Pyrrolidin-1-yl(4-(trifluoromethyl)phenyl)methanone (3ic).
Liquid. Yield: 92% (44.7 mg). H NMR (500 MHz, CDCl3): δ 7.63
(2) (a) Movassaghi, M.; Schmidt, M. A. Org. Lett. 2005, 7, 2453.
(b) Vora, H. U.; Rovis, T. J. Am. Chem. Soc. 2007, 129, 13796.
(c) Bode, J. W.; Sohn, S. S. J. Am. Chem. Soc. 2007, 129, 13798.
(3) Yang, X.; Birman, V. B. Org. Lett. 2009, 11, 1499.
(4) For C−N bond activation of tertiary amines, see: (a) Murahashi,
S. I.; Hirano, T.; Yano, T. J. Am. Chem. Soc. 1978, 100, 348. (b) Lei, Y.;
Wrobleski, A. D.; Golden, J. E.; Powell, D. R.; Aube, J. J. Am. Chem.
́
Soc. 2005, 127, 4552. (c) Guo, S. M.; Qian, B.; Xie, Y. J.; Xia, C. G.;
Huang, H. M. Org. Lett. 2011, 13, 522.
(5) Bao, Y. S.; Bao, Z.; Bao, A.; Baiyin, M. H.; Jia, M. L. J. Org. Chem.
2014, 79, 803.
(6) For some reviews of palladium nanoparticle catalysis, see:
(a) Phan, N. T. S.; Van Der Sluys, M.; Jones, C. W. Adv. Synth. Catal.
2006, 348, 609. (b) Yin, L. X.; Liebscher, J. Chem. Rev. 2007, 107, 133.
(c) Roucoux, A.; Schulz, J.; Patin, H. Chem. Rev. 2002, 102, 3757.
1
(dd, J = 21.8, 8.2 Hz, 4H), 3.64 (t, J = 6.7 Hz, 2H), 3.37 (t, J = 6.4 Hz,
2H), 2.01−1.92 (m, 2H), 1.92−1.83 (m, 2H). 13C NMR (125 MHz,
CDCl3): δ 168.2, 140.7, 131.6 (q, JC−F = 32.6 Hz), 127.5, 125.4 (q,
JC−F = 3.8 Hz), 123.8 (q, JC−F = 272.3 Hz), 49.5, 46.3, 26.4, 24.4.
HRMS (ESI): m/z [M + H]+ calcd for C12H12F3NO 244.0949, found
244.0948.
Pyrazin-2-yl(pyrrolidin-1-yl)methanone (3mc). Liquid. Yield: 81%
(28.7 mg). 1H NMR (500 MHz, CDCl3): δ 9.12 (s, 1H), 8.63 (s, 1H),
8.54 (s, 1H), 3.83−3.73 (m, 2H), 3.73−3.65 (m, 2H), 1.95 (dt, J = 6.8,
3.5 Hz, 4H). 13C NMR (126 MHz, CDCl3): δ 164.2, 149.5, 145.9,
145.4, 142.3, 49.0, 47.1, 26.7, 23.9. HRMS (ESI): m/z [M + H]+ calcd
for C9H11N3O 178.0980, found 178.0983.
5. Study of Recycling of the AuNP Catalyst. We examined
recycling of the AuNPs catalyst in the reaction of perfluorophenyl
indole-2-carboxylate (1a) with 1-methylpyrrolidine (2c) (Table 4).
(d) Jansat, S.; Gom
C.; Castillon, S.; Chaudret, B. J. Am. Chem. Soc. 2004, 126, 1592.
(e) Scheuermann, G. M.; Rumi, L.; Steurer, P.; Bannwarth, W.;
́
ez, M.; Philippot, K.; Muller, G.; Guiu, E.; Claver,
́
Mulhaupt, R. J. Am. Chem. Soc. 2009, 131, 8262.
(7) For some reviews of gold nanoparticle catalysis, see: (a) Pina, C.
D.; Falletta, E.; Rossi, M. Chem. Soc. Rev. 2012, 41, 350. (b) Corma, A.;
́
Leyva-Perez, A.; Sabater, M. J. Chem. Rev. 2011, 111, 1657. (c) Chen,
̈
Table 4. Catalyst Recycling Study
recycle no.
yield (%)
1
2
3
4
5
93
92
90
90
87
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The catalyst was recycled five times after being used in a catalytic
reaction. The catalyst was separated by centrifugation, washed twice
with ethanol, and dried in an oven at 80 °C.
6. GC−MS Analysis of the Reaction Solution. To identify a
byproduct formed by the cleavage of the C−N bond and the C−O
bond, the reaction solution of 1d with N-benzyl-N-ethylaniline 2d (a
higher-molecular-weight amine) was detected with GC−MS after the
end of reaction (see the Supporting Information). Two kinds of
aminated products, N-benzyl-N-phenylpicolinamide (3dd) and N-
ethyl-N-phenylpicolinamide (3dd′ = 3cb), were detected in an almost
14:1 ratio, which indicated that cleavage of the sterically less hindered
ethyl group is much more facile. The GC area % data showed that
along with 3dd′, a similar amount of benzaldehyde was obtained.
Therefore, this aminolysis reaction proceeds via the formation of an
iminium intermediate, which would cause the formation of an
aldehyde.15 In addition, 2,3-dichlorophenol, derived from the alkoxy
group of the ester, was detected.
(12) Beak, P.; Brown, R. A. J. Org. Chem. 1982, 47, 34.
(13) CAS Number: 123500-70-9.
(14) Sezen, B.; Sames, D. J. Am. Chem. Soc. 2005, 127, 5284.
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4700.
ASSOCIATED CONTENT
■
S
* Supporting Information
1H NMR, 13C NMR, and HRMS spectra and analysis by GC−
MS. This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Authors
*Fax: (+86)471-4392442. E-mail: sbbys197812@163.com.
*Fax: (+86)471-4393099. E-mail: zrgt@imnu.edu.cn.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Financial support from the High-Level Personnel Fund Project
of Inner Mongolia Normal University (2013YJRC039) and the
Opening Project of the Natural Science Foundation of Inner
Mongolia (2010KF02) is gratefully acknowledged.
REFERENCES
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(1) (a) Denmark, S. E.; Beutner, G. L. Angew. Chem., Int. Ed. 2008,
47, 1560. (b) Sabot, C.; Kumar, K. A.; Meunier, S.; Mioskowski, C.
Tetrahedron Lett. 2007, 48, 3863.
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dx.doi.org/10.1021/jo500877m | J. Org. Chem. 2014, 79, 6715−6719