Cesium carbonate-catalyzed reduction of amides with hydrosilanes

Article abstract of DOI:10.1021/om400951n

Cesium carbonate has been found to be an effective catalyst for the reduction of tertiary carboxamides with the simple, commercially available PhSiH₃ under solvent-free conditions. The catalytic system can effectively reduce a range of amides under relatively mild conditions (from room temperature to 80 C) to yield the corresponding amines in good to excellent yields (71-100%) and thus has the potential for practical applications.

Full text of DOI:10.1021/om400951n

Article
pubs.acs.org/Organometallics
Cesium Carbonate-Catalyzed Reduction of Amides with Hydrosilanes
Weilong Xie, Mengdi Zhao, and Chunming Cui*
State Key Laboratory and Institute of Elemento-Organic Chemistry, Nankai University, Tianjin, 300071, People’s Republic of China,
and Collaborative Innovation Center of Chemical Science and Technology, Tianjin, People’s Republic of China
S
* Supporting Information
ABSTRACT: Cesium carbonate has been found to be an effective catalyst for the reduction of
tertiary carboxamides with the simple, commercially available PhSiH3 under solvent-free
conditions. The catalytic system can effectively reduce a range of amides under relatively mild
conditions (from room temperature to 80 °C) to yield the corresponding amines in good to excellent yields (71−100%) and
thus has the potential for practical applications.
Scheme 1. Selected Metal-Catalyzed Reduction of Amides
with Silanes
INTRODUCTION
■
Amines constitute an important class of compounds in organic
chemistry and chemical biology.1 The reduction of carbox-
amides represents an indispensable synthetic route to amino
groups in organic synthesis. The most common approach for
this transformation is based on the reduction of amides with
stoichiometric amounts of aluminum and boron hydrides.2
However, the drawbacks of these hydrides lie in their air and
moisture sensitivity as well as the poor selectivity. Hydrosilanes
and hydrogen are relatively mild reducing reagents, but
reduction with these reagents requires suitable catalysts.
Thus, the development of highly effective and selective catalytic
systems using these reducing reagents has attracted much
attention. In the past several decades, many transition metal-
based catalytic systems for the reduction of carboxamides with
hydrogen and hydrosilanes have been reported.3,4 However,
most of these catalytic systems still suffer from poor
chemoselectivity and a limited substrate scope. Recently,
several efficient and selective catalysts based on ruthenium
clusters and iridium complexes have been developed by
Nagashima et al.3d−i and Brookhart et al.5 The direct use of
cheap and commercially available metal compounds as the
catalysts is also of great interest in view of practicability. In
1962, Calas and co-workers reported the ZnCl2-catalyzed
reduction of tertiary amides to tertiary amines with various
trialkylsilanes at high temperatures (Scheme 1).6 Recently,
Beller et al. reported on Zn(OAc)2 and Fe3(CO)12-catalyzed
reduction of various amides at high temperature.7 These cheap
catalysts are tolerant to several types of functional groups but
generally require an excess of hydrosilanes and relatively high
catalyst loadings (10−20 mol %).
the reduction of tertiary amides with only 1 equiv of PhSiH3
under relatively mild conditions.
RESULTS AND DISCUSSION
■
Initially, the reduction of DMF with Ph2SiH2 was investigated
in the presence of 1.0 mol % Cs2CO3 under solvent-free
conditions. The 1H NMR spectrum of the crude reaction
mixture disclosed the reaction was complete in about 6 h. DMF
can also be reduced by the secondary silane Ph2SiH2; the
reaction yielded the cyclosiloxane (Ph2SiO)4 in nearly
quantitative yield. Since reduction of DMF yielded the volatile
Me3N as the product, the reduction of phenyl(piperidin-1-
yl)methanone (C6H5CONC5H10) with PhSiH3 was inves-
tigated as a model system to optimize reaction conditions.
The reaction catalyzed by the other alkali carbonates Na2CO3
and K2CO3 has also been investigated under the same
conditions. It was found that the reaction catalyzed by
Na2CO3 and K2CO3 cannot take place probably due to their
low solubility.8 However, the reaction catalyzed by Cs2CO3
proceeded smoothly at elevated temperature (Table 1, entries
Cesium carbonate has been widely used as a strong base in
organic synthesis due to its ease of handling, low hygro-
scopicity, and high solubility in organic solvents compared to
alkali metal hydroxides. In the course of our investigation on
Si−O coupling reaction, we found that cesium carbonate can
catalyze the reduction of DMF in the presence of PhSiH3 to
yield siloxanes at room temperature with only 1% molar loading
of the catalyst. Since cesium carbonate is commercially available
and cost-effective, we have investigated the cesium carbonate-
catalyzed reduction chemistry in detail. Herein, we report on
Received: September 25, 2013
© XXXX American Chemical Society
A
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presence of 18-crown-6 ether at room temperature yielded a
small amount of formic anion (HCOO−) as indicated by the 1H
NMR analysis (see Figure S1 in the Supporting Information).
On the basis of this observation, we proposed the possible
activation mechanism shown in Scheme 2. The hypervalent
Table 1. Condition Selection for Cs2CO3-Catalyzed Tertiary
Amide Formation
a
temp
(°C)
time
(h)
conv
(%)
Scheme 2. Possible Activation Mechanism
entry
R
cat
silane
1
H
80
80
80
25
40
40
60
60
80
25
60
80
80
80
24
24
24
24
12
24
12
24
24
24
5
PhSiH3
PhSiH3
PhSiH3
PhSiH3
PhSiH3
PhSiH3
PhSiH3
PhSiH3
PhSiH3
PhSiH3
PhSiH3
Ph2SiH2
PhMe2SiH
(EtO)3SiH
0
0
2
H
Na2CO3
K2CO3
3
H
0
4
H
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
0
5
H
0
6
H
83
100
80
95
100
0
7
H
8
Cl
Cl
OMe
H
9
silicon species A formed by the attack of carbonate to PhSiH3
underwent hydride transfer to the carbon atom to form B
followed by cleavage of the SiO−C bond to yield formic anion
and the silicate C. This assumption is in agreement with our
experimental observation that the reduction of phenyl-
(piperidin-1-yl)methanone (C6H5CONC5H10) with PhSiH3
can also be complete with 5.0 mol % loadings of SiMe3OK
as the catalyst under the same conditions.
After surveying the reaction conditions, various amides have
been reduced with the Cs2CO3/PhSiH3 catalytic system. The
results are given in Table 2. All of the amides listed in Table 2
can be completely reduced with only 1 equiv of PhSiH3.
However, the amides with some functional groups such as
carbonyl, ester, and nitro groups did not yield clean products,
and the reduction of primary and secondary amides proved to
be sluggish. As shown in Table 2, the steric hindrance of the
substituents on the nitrogen atom and carbonyl group affects
the reactivity: the reaction can take place at room temperature
using only 1.0 mol % of catalyst for the small substituents
(entries 4, 5, and 14 in Table 2); for sterically hindered
substrates, the high catalyst loading (5.0 mol %) and the
elevated temperature (80 °C) are required for a complete
reduction. Cyclic tertiary amides can be easily reduced to the
corresponding amines under room temperature (entries 5−7).
The catalyst is selective in the presence of thiophene, furan,
halogenm and ether groups (Table 2, entries 10−13). For the
substrate with two amide bonds, the reaction can also give the
desired product in high yield (Table 2, entry 16).
10
11
b
12
H
24
24
24
0
c
13
H
0
c
14
H
0
a
Reaction conditions: amide (3.0 mmol), Cs2CO3 (5.0 mol %),
1
PhSiH3 (0.32 g, 3.0 mmol). Conversion was determined by H NMR
spectroscopy of the crude reaction mixture. Ph2SiH2 (0.83 g, 4.5
mmol). 9 mmol of the silanes.
b
c
1−7) and achieved 100% conversion at 60 °C in 12 h (Table 1,
entry 7). The substituents on the phenyl ring of the amide have
pronounced effects on the reaction; the electron-donating
group on the phenyl ring obviously facilitates the reaction,
while the substrates with electron-withdrawing groups are less
reactive (Table 1, entries 7−10). Hydrosilanes also have
significant effects on the reaction; the primary silane PhSiH3 is
the most reactive reagent for the reaction. Compared to the
facile reduction of DMF with a low catalyst loading at room
temperature, it can be concluded that steric factors of amides
have pronounced effects on the catalytic activity. The
experiment results demonstrated that the activation process is
rather slow (Table 1, entry 11) since almost no conversions
have been observed in 5 h.
In order to investigate solvent effects, the reaction was also
carried out in THF and toluene. It was found that reaction in
THF is much faster than in toluene (see the Supporting
Information, Table S1). The reaction under solvent-free
conditions is the most efficient one. This might be related to
the solubility of the catalyst. Under neat conditions, the highly
polarized amides also acted as solvents and thus promote the
catalytic reaction. The mechanism for the reduction chemistry
is not clear at this stage. The solvent effects for the reduction
chemistry indicate that the reaction may proceed via an ionic
mechanism. It is quite possible that the “naked” carbonate acts
as a strong base to initiate the catalytic process. In line with this
assumption, the complete reduction of phenyl(piperidin-1-
yl)methanone with PhSiH3 catalyzed by 5% molar loadings of
K2CO3 in the presence of 18-crown-6 ether was observed at 80
°C in 24 h. We reasoned that the most plausible initial step may
involve the reduction of carbonate anion by PhSiH3. In order to
have experimental support for this assumption, the reaction of
Cs2CO3 with PhSiH3 was conducted. However, this reaction
does not proceed under solvent-free conditions because
Cs2CO3 cannot be dissolved in PhSiH3 in the absence of
amides. Instead, the reaction of K2CO3 with PhSiH3 in the
CONCLUSION
■
In summary, we have developed the Cs2CO3-catalyzed
reduction of carboxamides with 1 equiv of PhSiH3. Both the
catalyst and reducing reagent are commercially available in large
quantity; thus the reduction process can be easily performed in
the laboratory and potentially on a large scale for practical
applications. However, the limited substrate scope and unique
chemistry involved in the catalytic cycle have yet to be
investigated. Further studies dealing with applications of the
catalytic system to reduction of other substrates and the
mechanism of the activation mode are ongoing in our
laboratory.
EXPERIMENTAL SECTION
■
General Considerations. All solvents were freshly distilled from
sodium/benzophenone. CDCl3 was purchased from Cambridge
Isototope Laboratories. Amides (a, b, d−g, n), Cs2CO3 (99.9%),
and silanes were purchased from Alfa-Aesar or J&K Scientific Ltd.
B
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a
Table 2. Cs2CO3-Catalyzed Reduction of Tertiary Amides
a
b
c
d
Reaction conditions: amide (3.0 mmol), PhSiH3 (0.33 g, 3.0 mmol). Isolated yield. The values in parentheses refer to the NMR yield. As the
1
product is volatile, the conversion was determined by the H NMR spectroscopy of the crude reaction mixture.
Other amides have been previously reported, and only 1H NMR
spectroscopic data are presented.
(4-Methoxyphenyl)(piperidin-1-yl)methanone7a (k). Using 4-
methoxybenzoyl chloride (8.53 g, 50 mmol) and piperidine (4.36 g,
50 mmol) in the presence of triethylamine (6.07 g, 60 mmol) in
dichloromethane (50 mL) at room temperature yielded a colorless
General Procedure for the Preparation of Amides.7a The acyl
chloride (50.0 mmol) was slowly added to a solution of the amine
(50.0 mmol) in the presence of triethylamine (60.0 mmol) in
dichloromethane (50 mL) at room temperature, resulting rapidly in a
boiling solution. The reaction mixture was stirred for 30−60 min at
room temperature and then was diluted with dichloromethane (50
mL). The solution was transferred to a separation funnel and was
washed with 1 N HCl (250 mL). The organic layer was filtered on a
short silica gel column and washed with ethyl acetate/hexane (1:1).
The combined fractions were concentrated under reduced pressure.
Characterization of the Amides. N,N-Dibenzylbenzamide7b (c).
Using benzoyl chloride (7.03 g, 50 mmol) and dibenzylamine (9.87 g,
50 mmol) in the presence of triethylamine (6.07 g, 60 mmol) in
dichloromethane (50 mL) at room temperature yielded a white solid
1
liquid (10.40 g, 47.5 mmol, 95%). H NMR (400 MHz, CDCl3): δ
7.35−7.37 (m, 2H), 6.88−6.90 (m, 2H), 3.82 (s, 3H), 3.53 (br s, 4H),
1.67 (br s, 2H), 1.58 (br s, 4H).
Furan-2-yl(piperidin-1-yl)methanone7a (l). Using furan-2-carbonyl
chloride (6.53 g, 50 mmol) and piperidine (4.36 g, 50 mmol) in the
presence of triethylamine (6.07 g, 60 mmol) in dichloromethane (50
mL) at room temperature yielded a white solid (8.06 g, 45.0 mmol,
90%). 1H NMR (400 MHz, CDCl3): δ 7.47 (dd, J = 1.6, 0.7 Hz, 1H),
6.93 (dd, J = 3.4, 0.6 Hz, 1H), 6.46 (dd, J = 3.4, 1.8 Hz, 1H), 3.67 (br
s, 4H), 1.66 (br s, 2H), 1.60 (br s, 4H).
Piperidin-1-yl(thiophen-2-yl)methanone7a (m). Using thiophene-
2-carbonyl chloride (7.33 g, 50 mmol) and piperidine (4.36 g, 50
mmol) in the presence of triethylamine (6.07 g, 60 mmol) in
dichloromethane (50 mL) at room temperature yielded a white solid
(8.30 g, 42.5 mmol, 85%). 1H NMR (400 MHz, CDCl3): δ 7.35 (dd, J
= 5.0, 1.0 Hz, 1H), 7.19 (dd, J = 3.6, 1.0 Hz, 1H), 6.96 (dd, J = 5.0, 3.7
Hz, 1H), 3.60 (br s, 4H), 1.62 (br s, 2H), 1.57 (br s, 4H).
2,2-Dimethyl-1-(piperidin-1-yl)propan-1-one (o). Using pivaloyl
chloride (6.03 g, 50 mmol) and piperidine (4.36 g, 50 mmol) in the
presence of triethylamine (6.07 g, 60 mmol) in dichloromethane (50
mL) at room temperature yielded a colorless liquid (7.36 g, 43.5
mmol, 87%). 1H NMR (400 MHz, CDCl3): δ 3.56 (br s, 4H), 1.62 (br
s, 2H), 1.52 (br s, 4H), 1.25 (s, 9H). 13C NMR (101 MHz, CDCl3): δ
175.9, 46.1, 38.1, 28.3, 26.0, 24.6. HRMS (ESI): calcd for [C10H19NO,
M + H]+ 170.1545, found 170.1539.
1
(13.6 g, 45 mmol, 90%). H NMR (400 MHz, CDCl3): δ 7.40−7.43
(m, 2H), 7.17−7.32 (m, 11H), 7.07 (s, 2H), 4.63 (br s, 2H), 4.32 (br
s, 2H).
Phenyl(piperidin-1-yl)methanone7a (h). Using benzoyl chloride
(7.03 g, 50 mmol) and piperidine (4.26 g, 50 mmol) in the presence of
triethylamine (6.07 g, 60 mmol) in dichloromethane (50 mL) at room
1
temperature yielded a colorless liquid (8.52 g, 45 mmol, 90%). H
NMR (400 MHz, CDCl3): δ 7.40 (s, 5H), 3.70 (br s, 2H), 3.33 (br s,
2H), 1.67 (br s, 4H), 1.52 (br s, 2H).
Morpholino(phenyl)methanone7a (i). Using benzoyl chloride
(7.03 g, 50 mmol) and piperidine (4.36 g, 50 mmol) in the presence
of triethylamine (6.07 g, 60 mmol) in dichloromethane (50 mL) at
room temperature yielded a colorless liquid (8.12 g, 42.5 mmol, 85%).
1H NMR (400 MHz, CDCl3): δ 7.40−7.42 (m, 5H), 3.77 (br s, 4H),
3.63 (br s, 2H), 3.44 (br s, 2H).
1,4-Phenylenebis(piperidin-1-ylmethanone) (p). Using terephtha-
loyl dichloride (10.15 g, 50 mmol) and piperidine (8.72 g, 100 mmol)
in the presence of triethylamine (12.14 g, 120 mmol) in dichloro-
methane (50 mL) at room temperature yielded a white solid (10.96 g,
(4-Chlorophenyl)(piperidin-1-yl)methanone9 (j). Using 4-chloro-
benzoyl chloride (8.75 g, 50 mmol) and piperidine (4.36 g, 50 mmol)
in the presence of triethylamine (6.07 g, 60 mmol) in dichloromethane
(50 mL) at room temperature yielded a white solid (10.62 g, 47.5
1
36.5 mmol, 73%). Mp: 220 °C. H NMR (400 MHz, CDCl3): δ 7.32
1
(s, 4H), 3.61 (br s, 4H), 3.23 (br s, 4H), 1.58 (br s, 8H), 1.40 (br s,
mmol, 95%). H NMR (400 MHz, CDCl3): δ 7.32−7.38 (m, 4H),
3.69 (br s, 2H), 3.33 (br s, 2H), 1.67 (br s, 4H), 1.52 (br s, 2H).
4H). 13C NMR (101 MHz, CDCl3): δ 169.4, 137.4, 126.8, 48.6, 43.0,
C
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26.4, 25.5, 24.4. HRMS (ESI): calcd for [C18H24N2O2, M + H]+
301.1916, found 301.1914.
4-Benzylmorpholine.7a Using morpholino(phenyl)methanone
(574 mg, 3 mmol), Cs2CO3 (49 mg, 0.15 mmol), and PhSiH3 (325
mg, 3 mmol) yielded a colorless liquid (404 mg, 2.28 mmol, 76%). 1H
NMR (400 MHz, CDCl3): δ 7.26−7.33 (m, 5H), 3.70−3.72 (m, 4H),
3.50 (s, 2H), 2.43−2.45 (m, 4H). 13C NMR (101 MHz, CDCl3): δ
137.7, 129.2, 128.2, 127.1, 67.0, 63.4, 53.6. HRMS (ESI): calcd for
[C11H15NO, M + H]+ 178.1232, found 178.1229.
Typical Procedure for the Catalytic Reduction of Amides.
N,N-Dimethyl-1-phenylmethanamine.3i A 25 mL Schlenk tube
containing a stir bar was charged with 5.0 mol % Cs2CO3 (49 mg,
0.15 mmol). Subsequently, N,N-dimethylbenzamide (450 mg, 3.0
mmol) and PhSiH3 (325 mg, 3.0 mmol) were added. The mixture was
stirred at room temperature for 24 h. Dichloromethane (0.5 mL) was
added to the mixture. The mixture was purified on a short silica gel
column and washed with ethyl acetate/hexane/Et3N (100:10:1). The
solvents were removed to give the product as a colorless liquid (353
mg, 2.61 mmol, 87%). 1H NMR (400 MHz, CDCl3): δ 7.15−7.25 (m,
5H), 3.35 (s, 2H), 2.17 (s, 6H). 13C NMR (101 MHz, CDCl3): δ
138.6, 129.1, 128.2, 127.0, 64.3, 45.3. HRMS (ESI): calcd for
[C9H13N, M + H]+ 136.1126, found 136.1118.
1-(4-Chlorobenzyl)piperidine. Using (4-chlorophenyl)(piperidin-1-
yl)methanone (671 mg, 3 mmol), Cs2CO3 (49 mg, 0.15 mmol), and
PhSiH3 (325 mg, 3 mmol) yielded a colorless liquid (528 mg, 2.52
1
mmol, 84%). H NMR (400 MHz, CDCl3): δ 7.16−7.21 (m, 4H),
3.36 (s, 2H), 2.28 (br s, 4H), 1.47−1.52 (m, 4H), 1.35−1.37 (m, 2H).
13C NMR (101 MHz, CDCl3): δ 137.0, 132.5, 130.5, 128.2, 63.0, 54.4,
25.9, 24.3. HRMS (ESI): calcd for [C12H16ClN, M + H]+ 210.1050,
found 210.1044.
1-(4-Methoxybenzyl)piperidine.7a Using (4-methoxyphenyl)-
(piperidin-1-yl)methanone (658 mg, 3 mmol), Cs2CO3 (49 mg, 0.15
mmol), and PhSiH3 (325 mg, 3 mmol) yielded a colorless liquid (585
mg, 2.85 mmol, 95%). 1H NMR (400 MHz, CDCl3): δ 7.20−7.23 (m,
2H), 6.83−6.86 (m, 2H), 3.80 (s, 3H), 3.41 (s, 2H), 2.35 (br s, 4H),
1.53−1.59 (m, 4H), 1.42−1.43 (m, 2H). 13C NMR (101 MHz,
CDCl3): δ 158.5, 130.5, 130.4, 113.4, 63.2, 55.2, 54.3, 25.9, 24.4.
HRMS (ESI): calcd for [C13H19NO, M + H]+ 206.1545, found
206.1540.
Reduction of the Other Amides. The other reactions were
performed similarly to that described for the amide a. For amides
d−g, k, and n, the reactions were conducted at 80 °C; the others were
performed at room temperature. The mixtures were stirred for 24 h
(for amide d, 30 h; e, 12 h; f and g, 48 h).
N-Benzyl-N-isopropylpropan-2-amine.7b Using N,N-diisopropyl-
benzamide (616 mg, 3 mmol), Cs2CO3 (49 mg, 0.15 mmol), and
PhSiH3 (325 mg, 3 mmol) yielded a colorless liquid (528 mg, 2.76
1
mmol, 92%). H NMR (400 MHz, CDCl3): δ 7.39−7.41 (m, 2H),
7.28−7.31 (m, 2H), 7.19−7.22 (m, 1H), 3.66 (s, 2H), 3.03 (sept, 3J =
6.6 Hz, 2H), 1.04 (d, 3J = 6.6 Hz, 12H). 13C NMR (101 MHz,
CDCl3): δ 143.3, 128.0, 127.9, 126.1, 48.9, 47.8, 20.8. HRMS (ESI):
calcd for [C13H21N, M + H]+ 192.1752, found 192.1743.
1-(Furan-2-ylmethyl)piperidine.7a Using furan-2-yl(piperidin-1-yl)-
methanone (538 mg, 3 mmol), Cs2CO3 (49 mg, 0.15 mmol), and
PhSiH3 (325 mg, 3 mmol) yielded a colorless liquid (451 mg, 2.73
mmol, 91%). 1H NMR (400 MHz, CDCl3): δ 7.36 (dd, J = 1.8, 0.8 Hz,
1H), 6.30 (dd, J = 3.1, 1.9 Hz, 1H), 6.17 (dd, J = 3.1, 0.5 Hz, 1H), 3.49
(s, 2H), 2.39 (br s, 4H), 1.56−1.60 (m, 4H), 1.40−1.42 (m, 2H). 13C
NMR (101 MHz, CDCl3): δ 152.1, 141.9, 109.9, 108.5, 55.6, 54.1,
25.8, 24.1. HRMS (ESI): calcd for [C10H15NO, M + H]+ 166.1232,
found 166.1229.
Tribenzylamine.7b Using N,N-dibenzylbenzamide (904 mg, 3
mmol), Cs2CO3 (49 mg, 0.15 mmol), and PhSiH3 (325 mg, 3
1
mmol) yielded a white solid (672 mg, 2.34 mmol, 78%). H NMR
(400 MHz, CDCl3): δ 7.31−7.33 (m, 5H), 7.20−7.23 (m, 7H), 7.12−
7.14 (m, 3H), 3.46 (s, 6H). 13C NMR (101 MHz, CDCl3): δ 139.6,
128.7, 128.2, 126.8, 57.9. HRMS (ESI): calcd for [C21H21N, M + H]+
288.1752, found 288.1743.
1-Methylpiperidine. Using piperidine-1-carbaldehyde (340 mg, 3
mmol), Cs2CO3 (10 mg, 0.03 mmol), and PhSiH3 (325 mg, 3 mmol)
and distillation yielded a colorless liquid (152 mg, 1.53 mmol, 51%).
1H NMR (400 MHz, CDCl3): δ 2.30−2.31(br s, 4H), 2.22 (s, 3H),
1.54−1.60 (m, 4H), 1.40 (br s, 2H). 13C NMR (101 MHz, CDCl3): δ
56.5, 46.9, 26.0, 23.7. HRMS (ESI): calcd for [C6H13N, M + H]+
100.1126, found 100.1121.
1-(tThiophen-2-ylmethyl)piperidine.7a Using piperidin-1-yl-
(thiophen-2-yl)methanone (586 mg, 3 mmol), Cs2CO3 (49 mg, 0.15
mmol), and PhSiH3 (325 mg, 3 mmol) yielded a colorless liquid (457
1
mg, 2.52 mmol, 84%). H NMR (400 MHz, CDCl3): δ 7.14 (dd, J =
5.1, 1.2 Hz, 1H), 6.87 (dd, J = 5.1, 3.4 Hz, 1H), 6.82 (dd, J = 3.4, 0.9
Hz, 1H), 3.62 (s, 2H), 2.34 (br s, 4H), 1.48−1.54 (m, 4H), 1.34−1.36
(m, 2H). 13C NMR (101 MHz, CDCl3): δ 141.8, 126.3, 125.9, 124.7,
57.7, 54.0, 25.9, 24.2. HRMS (ESI): calcd for [C10H15NS, M + H]+
182.1004, found 182.0996.
1-Methylpyrrolidine. Using 1-methylpyrrolidin-2-one (594 mg, 6
mmol), Cs2CO3 (20 mg, 0.06 mmol), and PhSiH3 (650 mg, 6 mmol)
and distillation yielded a colorless liquid (178 mg, 2.10 mmol, 35%).
1H NMR (400 MHz, CDCl3): δ 2.43−2.46 (m, 4H), 2.34 (s, 3H),
1.76−1.79 (m, 4H). 13C NMR (101 MHz, CDCl3): δ 56.3, 42.1, 24.0.
HRMS (ESI): calcd for [C5H11N, M + H]+ 86.0970, found 86.0961.
1-Methylazepane.10 Using 1-methylazepan-2-one (382 mg, 3
mmol), Cs2CO3 (49 mg, 0.15 mmol), and PhSiH3 (325 mg, 3
mmol) and distillation yielded a colorless liquid (241 mg, 2.13 mmol,
N,N-Dimethylethanamine. Using N,N-dimethylacetamide (522
mg, 6 mmol), Cs2CO3 (20 mg, 0.06 mmol), and PhSiH3 (650 mg,
6 mmol). NMR yield: 100%.
1-Neopentylpiperidine. Using 2,2-dimethyl-1-(piperidin-1-yl)-
propan-1-one (508 mg, 3 mmol), Cs2CO3 (49 mg, 0.15 mmol), and
PhSiH3 (325 mg, 3 mmol) yielded a colorless liquid (359 mg, 2.31
mmol, 77%). 1H NMR (400 MHz, CDCl3): δ 2.43 (br s, 4H), 1.99 (s,
2H), 1.51−1.54 (m, 4H), 1.36−1.47 (m, 2H), 0.85 (s, 9H). 13C NMR
(101 MHz, CDCl3): δ 70.8, 57.3, 33.1, 27.8, 26.5, 24.1. HRMS (ESI):
calcd for [C10H21N, M + H]+ 156.1752, found 156.1748.
1,4-Bis(piperidin-1-ylmethyl)benzene. Using 1,4-phenylenebis-
(piperidin-1-ylmethanone) (901 mg, 3 mmol), Cs2CO3 (49 mg, 0.15
mmol), and PhSiH3 (650 mg, 6 mmol) yielded a white solid (711 mg,
2.61 mmol, 87%). Mp: 93 °C. 1H NMR (400 MHz, CDCl3): δ 7.24−
7.26 (m, 4H), 3.45 (s, 4H), 2.36 (br s, 8H), 1.54−1.59 (m, 8H), 1.42−
1.43 (m, 4H). 13C NMR (101 MHz, CDCl3): δ 137.1, 129.0, 63.7,
54.5, 26.0, 24.4. HRMS (ESI): calcd for [C18H28N2, M + H]+
273.2331, found 273.2328.
1
71%). H NMR (400 MHz, CDCl3): δ 2.54−2.57 (m, 4H), 2.35 (s,
3H), 1.66−1.68 (m, 4H), 1.60−1.62 (m, 4H). 13C NMR (101 MHz,
CDCl3): δ 58.4, 47.3, 27.8, 26.6. HRMS (ESI): calcd for [C7H15N, M
+ H]+ 114.1283, found 114.1276.
1-Benzylpyrrolidine.3i Using 1-benzylpyrrolidin-2-one (526 mg, 3
mmol), Cs2CO3 (49 mg, 0.15 mmol), and PhSiH3 (325 mg, 3 mmol)
1
yielded a colorless liquid (363 mg, 2.25 mmol, 75%). H NMR (400
MHz, CDCl3): δ 7.29−7.33 (m, 3H), 7.24−7.26 (m, 2H), 3.62 (s,
2H), 2.50−2.52 (m, 4H), 1.77−1.80 (m, 4H). 13C NMR (101 MHz,
CDCl3): δ 139.2, 128.9, 128.2, 126.9, 60.7, 54.1, 23.4. HRMS (ESI):
calcd for [C11H15N, M + H]+ 162.1283, found 162.1274.
1-Benzylpiperidine.7a Using phenyl(piperidin-1-yl)methanone (568
mg, 3 mmol), Cs2CO3 (49 mg, 0.15 mmol), and PhSiH3 (325 mg, 3
mmol) yielded a colorless liquid (473 mg, 2.70 mmol, 90%). 1H NMR
(400 MHz, CDCl3): δ 7.16−7.24 (m, 5H), 3.41 (s, 2H), 2.31 (br s,
4H), 1.48−1.53 (m, 4H), 1.35−1.37 (m, 2H). 13C NMR (101 MHz,
CDCl3): δ 138.3, 129.3, 128.1, 126.9, 63.8, 54.4, 25.9, 24.3. HRMS
(ESI): calcd for [C12H17N, M + H]+ 176.1439, found 176.1434.
ASSOCIATED CONTENT
■
S
* Supporting Information
Text and figures giving general procedures and characterization
data as well as 1H, 13C NMR spectra and HRMS for amides and
amines. This material is available free of charge via the Internet
at http://pubs.acs.org.
D
dx.doi.org/10.1021/om400951n | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
AUTHOR INFORMATION
Corresponding Author
*E-mail: cmcui@nankai.edu.cn.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the National Natural Science
Foundation of China and 973 Program (grant no.
2012CB821600).
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dx.doi.org/10.1021/om400951n | Organometallics XXXX, XXX, XXX−XXX