Easily-controlled chemoselective hydrogenation by using palladium on boron nitride

Article abstract of DOI:10.1002/cctc.201300035

The hydrogenation catalyzed heterogeneously by palladium on boron nitride (Pd/BN) in methanol realized the chemoselective hydrogenation of only azides, alkenes, and alkynes in the presence of other reducible functionalities such as benzyl ethers, aryl halides, aryl ketones, and nitro groups. Furthermore, the totally chemoselective semihydrogenation of alkynes could also be achieved without the reduction of other coexisting reducible functionalities, which include azides and alkenes, by using Pd/BN in pyridine as a solvent. Be unique, be selective: The chemoselective hydrogenation of azides, alkenes, and alkynes was achieved without the reduction of other reducible functionalities by the use of a heterogeneous palladium on boron nitride (Pd/BN) catalyst. Furthermore, Pd/BN was applicable to the unique and chemoselective semihydrogenation of alkynes without the reduction of azido functionalities in the presence of pyridine or diethylenetriamine.

Full text of DOI:10.1002/cctc.201300035

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Be unique, be selective: The chemo-
selective hydrogenation of azides, al-
kenes, and alkynes was achieved with-
out the reduction of other reducible
functionalities by the use of a heteroge-
neous palladium on boron nitride (Pd/
BN) catalyst. Furthermore, Pd/BN was
applicable to the unique and chemose-
lective semihydrogenation of alkynes
without the reduction of azido function-
alities in the presence of pyridine or
diethylenetriamine.
Y. Yabe, Y. Sawama, T. Yamada,
S. Nagata, Y. Monguchi, H. Sajiki*
&& – &&
Easily-Controlled Chemoselective
Hydrogenation by using Palladium on
Boron Nitride
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DOI: 10.1002/cctc.201300035
Easily-Controlled Chemoselective Hydrogenation by using
Palladium on Boron Nitride
Yuki Yabe, Yoshinari Sawama, Tsuyoshi Yamada, Saori Nagata, Yasunari Monguchi, and
[a]
Hironao Sajiki*
The hydrogenation catalyzed heterogeneously by palladium
on boron nitride (Pd/BN) in methanol realized the chemoselec-
tive hydrogenation of only azides, alkenes, and alkynes in the
presence of other reducible functionalities such as benzyl
ethers, aryl halides, aryl ketones, and nitro groups. Further-
more, the totally chemoselective semihydrogenation of alkynes
could also be achieved without the reduction of other coexist-
ing reducible functionalities, which include azides and alkenes,
by using Pd/BN in pyridine as a solvent.
Introduction
Catalytic hydrogenation using heterogeneous Pd catalysts (Pd/
C) is widely used to reduce reducible functionalities, such as
alkyne, alkene, azide, nitro, benzyl ether, benzyl ester, aromatic
halide, aromatic ketone, N-benzyloxycarbonyl (N-Cbz), and ep-
ties has been little investigated. Indeed, only one example of
the semihydrogenation of an alkyne in the presence of
[13g–h]
a benzyl ether group has been reported.
Recently, we reported the development of a new heteroge-
[
1]
[16]
oxide groups, in organic syntheses. Although the Pd/C-cata-
lyzed chemoselective hydrogenation of these functionalities
can be imperfectly achieved by careful control of the catalyst
loading, additives, solvents, and/or the reaction time and tem-
perature, recent advanced studies on new heterogeneous Pd
neous Pd on boron nitride (BN) catalyst (Scheme 1). BN pos-
[
2]
[3,4]
catalysts (e.g., Pd-SH-SILC, Pd nanoparticles,
Pd/CeO2-
[
5]
ZrO2 ) enabled the respective chemoselective hydrogenation
[
2–6]
under mild reaction conditions.
In addition, we have also
developed many chemoselective hydrogenation catalysts
based on dual categorized concepts. Our methodologies to
suppress the Pd catalytic activity are 1) the use of a catalyst-
poisoning effect as a result of the coordination of lone pairs of
[
7]
amines or sulfides, such as Pd/C(en) (en=ethylenediamine),
[
8]
[9]
Pd/PEI (PEI=polyethyleneimine), and Pd/C(Ph S), and 2) the
2
suppression effect that uses the characteristic properties of
[
10]
new materials as the catalyst support, such as Pd/Fib (Fib=
[
11]
fibroin) and Pd/MS3A or MS5A.
Regardless of the many
recent developments, the chemoselective hydrogenation of
nitro groups, azides, alkenes, and alkynes still require the care-
ful control of the reaction conditions owing to their extremely
[12]
reducible properties under the conditions of Pd catalysis. In
particular, the semihydrogenation of monosubstituted (termi-
nal) alkynes to the corresponding alkenes is regarded as a chal-
Scheme 1. Pd/BN-catalyzed semihydrogenation.
[
13–15]
lenging issue.
Therefore, semihydrogenation accompanied
sesses numerous lone pairs on the N atoms, which can sub-
stantially coordinate with Pd to play a dual role as an efficient
catalyst suppressor for hydrogenations and as a catalyst sup-
port. We have revealed that Pd/BN is a suitable catalyst for the
by the chemoselective reduction of other reducible functionali-
[
a] Dr. Y. Yabe, Dr. Y. Sawama, T. Yamada, S. Nagata, Dr. Y. Monguchi,
Prof. Dr. H. Sajiki
Laboratory of Organic Chemistry, Gifu Pharmaceutical University
-25- Daigaku-nishi, Gifu 501-1196 (Japan)
Fax: (+81)58-230-8109
E-mail: sajiki@gifu-pu.ac.jp
[16a]
semihydrogenation
kynes to alkenes with the addition of diethylenetriamine
DETA) to further suppress the catalytic activity of Pd/BN (Pd/
BN-DETA-MeOH) and we have also established regioselective
of both mono- and disubstituted al-
1
(
[16b]
synthetic methods for deuterated alkenes
by the use of Pd/
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201300035.
BN with pyridine as a solvent. During our ongoing research,
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we have developed a new Pd/BN-catalyzed, easily controlled
chemoselective hydrogenation method for azides, alkenes, and
alkynes without the reduction of mainstream reducible func-
tionalities, such as nitro, benzyl ether, aryl ketone, and aryl
halide groups, in MeOH (Pd/BN-MeOH; Figure 1, route a).
Table 1. Chemoselective hydrogenation of azides.
[
a]
Azide
Amine
t [h]
Yield [%]
[
b]
(
TON)
9
960)
6
24
(
9
990)
9
1
1
1
0
5
2
(
(
(
90
900)
99
990)
Figure 1. New chemoselective hydrogenation using Pd/BN.
9
950)
5
4
(
Moreover, the improved method for the semihydrogenation of
alkynes into alkenes by using pyridine as the catalyst suppres-
sor and solvent instead of MeOH can be realized without the
hydrogenation of azides in a simple and easy manner (Pd/BN-
pyridine; Figure 1, route b).
[a] Isolated yield. [b] TON=turnover number.
functionalities with perfect chemoselectivity (Table 1). Benzoic
acid (2a), benzyl ether (2b), benzyl ester (2c), and aryl ketone
(2d) functionalities tolerated the hydrogenation conditions to
form the corresponding amine products (3a–3d) in high
yields. Although the azides and nitro groups have similar reac-
tivities under typical Pd-catalyzed hydrogenation conditions,
only the azide group of 2-azide-5-nitrotoluene (2e) was che-
moselectively hydrogenated to give the corresponding nitroa-
niline derivative 3e in excellent yield.
We now report the details of these new studies, which pro-
vide perfect chemoselective hydrogenation by using Pd/BN.
Results and Discussion
Chemoselective hydrogenation of azides
The screening of the Pd/BN catalytic activity for hydrogenation
in MeOH at room temperature revealed that the benzyl ether,
aldehyde, aryl halide, nitrile, aryl ketone, epoxide, and even
nitro groups of various substrates (1a–1 f) were not hydrogen-
ated (Scheme 2). Meanwhile, Pd/BN chemoselectively and effi-
ciently catalyzed the hydrogenation of azides, alkenes, and al-
kynes (Tables 1 and 2).
Chemoselective hydrogenation of alkynes and alkenes
The Pd/BN-catalyzed hydrogenation could be adapted for the
chemoselective reduction of alkynes and alkenes into alkanes
(Table 2). Various alkynes that bear a benzyl ether (4a), tertiary-
alcohol (4b), N-Cbz (4c), and even a nitro group (4d) within
the molecule were chemoselectively transformed into alkanes
Notably, the Pd/BN-catalyzed hydrogenation of azides in
MeOH proceeded without the reduction of other reducible
(
6a–6d) without further hydrogenation. The alkene derivatives
were also chemoselectively hydrogenated to form alkanes in
the same manner as alkynes. Benzyl ester (5 f), nitrile (5g), aryl
halide (5h), and nitro groups (5i) tolerated the Pd/BN-cata-
lyzed hydrogenation conditions in MeOH. The unreacted func-
tionalities shown in Scheme 2 and Tables 1 and 2 were not hy-
drogenated even with prolonged reaction times.
Test for Pd leaching
Pd/BN was recovered easily by simple filtration and washing
with water and MeOH. As expected, the strong interaction be-
tween BN and Pd because of the numerous N lone pairs ena-
bles efficient hydrogenation without any metal leaching into
Scheme 2. Screening of the catalytic activity of Pd/BN.
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Table 2. Chemoselective hydrogenation of alkynes and alkenes.
Scheme 4. Application of the Pd/BN-catalyzed semihydrogenation of alkynes
[
a]
using amine additives.
Substrate
Alkane
t [h] Yield [%]
À1 [b]
(
TOF [h ])
7
87)
8
of alkynes by the additional use of DETA and we have adapted
the Pd/BN-DETA-MeOH combination to the chemoselective
semihydrogenation of alkynes in the presence of nitro, benzyl
9
(
[16a]
ether, tert-butyldimethylsilyl ether, and other groups.
In our previous work on the semihydrogenation of alkynes
99
2
4
(
41)
[16a]
to alkenes by using Pd/BN-DETA-MeOH,
the use of DETA
was adjusted depending on the substrate (Table 3). Although
9
165)
9
6
4
(
(
Table 3. Screening of substrates.
95
238)
9
990)
9
1
6
(
(
94
157)
9
41)
9
2
4
(
9
157)
4
6
6
(
(
Entry
4
Catalyst
X
Solvent
4/5/6
81
[a]
1
2
3
4
5
6
7
8
9
4e
4e
4e
4c
4c
4c
4e
4e
4e
4d
4d
4j
0.3% Pd/BN
0.3% Pd/BN
0.3% Pd/BN
0.3% Pd/BN
0.3% Pd/BN
0.3% Pd/BN
10% Pd/C
1
0.5
2
1.3
1
1.5
1
1
–
1
–
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
pyridine
MeOH
pyridine
MeOH
pyridine
MeOH
pyridine
0/100/0 (99)
0/100/0
0/100/0
0/100/0 (96)
0/65/35
14/86/0
135)
[a] Isolated yield. [b] TOF=turnover frequency.
[a]
0/0/100
100/0/0
BN
[
a]
a]
0.3% Pd/BN
0.3% Pd/BN
0.3% Pd/BN
0.3% Pd/BN
0.3% Pd/BN
0.3% Pd/BN
0.3% Pd/BN
0/100/0 (96)
0/95/5
0/100/0 (97)
18/82/0
0/100/0 (99)
0/95/5
0/100/0 (96)
1
0
[
1
1
1
1
1
1
2
3
4
5
1
–
1.5
–
[
b]
[a]
4j
4k
4k
Scheme 3. Test for Pd leaching.
[
a]
[
a] Isolated yield. [b] 0.10 mol% of 0.3% Pd/BN was used.
the reaction media under the Pd/BN-H -MeOH conditions
2
[
17,18]
(below the detection limit of 1 ppm) (Scheme 3).
the semihydrogenation of 4-ethynylanisole (4e) was not influ-
enced by DETA (Table 3, entries 1–3), the product ratio was sig-
nificantly affected in the case of benzyl 4-ethynylphenylcarba-
mete (4c; entries 4–6). As the hydrogenation could not be
controlled by the use of Pd/C or BN as a catalyst instead of Pd/
BN even in the presence of one equivalent of DETA, the use of
Pd/BN as a catalyst is essential to achieve the semihydrogena-
tion (entries 7 and 8). However, the semihydrogenation of al-
kynes to the corresponding alkenes with perfect selectivity
could be achieved in pyridine as a solvent instead of the DETA-
MeOH combination without any adjustment of the reaction
conditions (entries 9, 11, 13, and 15). In particular, alkynes 4d,
Application of improved Pd/BN-catalyzed semi-
hydrogenation
As mentioned above, the semihydrogenation of alkynes is still
a challenging issue as the alkenes generated by the initial re-
duction of alkynes can easily and rapidly undergo over hydro-
genation to form alkanes. Therefore, the combined use of the
Pd/BN catalyst and amines that bear lone pairs coordinating
with Pd, which act as an appropriate catalyst poison, enabled
the reproducible semihydrogenation of alkynes to alkenes
(Scheme 4). We have already achieved the semihydrogenation
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4
5
j, and 4k were efficiently semihydrogenated to alkenes 5d,
ciently semihydrogenated without any reduction of the aro-
matic and aliphatic azide functionalities with perfect chemose-
j, and 5k under Pd/BN-H -pyridine conditions with perfect
2
chemoselectivities and high yields (entries 11, 13, and 15), al-
though the slight over hydrogenation to alkanes or incomplete
reaction indicated by the presence of starting materials was
lectivities. The Pd/BN-H -DETA-MeOH combination was also
2
adapted to the chemoselective semihydrogenation of 4l in the
presence of azide 2g. In every case, the reduction of the azide
groups to amines was not observed. Moreover, alkyne 4e was
also chemoselectively transformed to alkene 5e without the
hydrogenation of the alkene moiety on the styrene derivative
(5m). Furthermore, substrate 7, which bears an azide and
alkyne within the molecule, was smoothly semihydrogenated
to the allyl ether 8 without the reduction of the azide.
observed with Pd/BN-H -DETA-MeOH (entries 10, 12, and 14).
2
In all cases, the N-Cbz (4c) and nitro functionalities (4d) were
not hydrogenated.
We next investigated the unprecedented chemoselective hy-
drogenation of alkynes and azides/alkenes by using Pd/BN-H2-
pyridine (Table 4). Notably, alkynes 4e, 4l, and 4j were effi-
Conclusions
Table 4. Chemoselective semihydrogenation of alkynes in the presence
of azides.
We have developed a new chemoselective hydrogenation of
azides, alkynes, and alkene functionalities by using Pd/BN as
a heterogeneous catalyst in MeOH that distinguishes other re-
ducible functionalities such as nitro, N-Cbz, aromatic ketone,
and benzyl ester groups. Furthermore, the Pd/BN-catalyzed
semihydrogenation of monosubstituted alkynes in pyridine
provided only the corresponding alkenes with perfect chemo-
selectivities and excellent yields. The Pd/BN catalyst was reusa-
ble and could be separated by simple filtration, and the subse-
quent extraction produced the nearly pure desired products.
These environmentally friendly catalyst systems are expected
to provide various new organic synthetic routes and contribute
to the development of organic chemistry.
[
a]
Substrates
t [h]
Product
1
1
1
1
Experimental Section
General Information
All reagents were purchased from commercial sources and used
1
13
without further purification. The H and C NMR spectra were re-
corded by using a JEOL ECA 500 spectrometer (500 MHz for
1
13
H NMR and 125 MHz for C NMR). The chemical shifts (d) are ex-
pressed in ppm and were referenced internally (7.26 ppm for CDCl
3
1
13
for H NMR and 77.0 ppm for CDCl3 for C NMR, 3.30 ppm for
CD OD for H NMR and 49.0 ppm for CD OD for C NMR). Induc-
1
13
3
3
[
b]
1
tively coupled plasma atomic emission spectroscopy (ICP-AES) was
performed by using an ISPS-8100 instrument (Shimadzu Co., Ltd.,
Japan).
4
2
Typical chemoselective hydrogenation procedure
A mixture of a substrate (0.25 mmol) and 0.3% Pd/BN (9.0 mg,
.5
0
.10 mol% of the substrate) in MeOH (1 mL) was stirred under at-
mospheric (balloon) H pressure at 258C. The resulting mixture was
2
diluted with Et O (10 mL) and filtered through a membrane filter
2
(
Millipore, Millex-LH, 0.45 mm). The filtrate was concentrated under
1
4
reduced pressure to give the product.
Typical procedure for the semihydrogenation of alkynes
Pd/BN-DETA-MeOH combination:
A
mixture of substrate
(
0.25 mmol), 0.3% Pd/BN (2.7 mg, 0.03 mol% of the substrate) and
1
[
a] Yield was determined by H NMR spectroscopy. [b] 1 equivalent of
DETA (27 mL, 0.25 mmol) in MeOH (1 mL) was stirred under atmos-
pheric (balloon) H pressure at 258C for 6 h. The resulting mixture
was diluted with Et O or hexanes (10 mL) and H O (10 mL) and fil-
DETA in MeOH was used instead of pyridine. [c] 0.5 mol% of Pd/BN was
used.
2
2
2
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tered through a membrane filter (Millipore, Millex-LH, 0.45 mm).
The filtrate was separated into two layers, and the aqueous layer
(ATR): n˜ =3418, 3330, 3260, 3210, 2957, 1864, 1610, 1854, 1511,
1469, 1451, 1430, 1409, 1344, 1298, 1176, 1115, 1056, 1029 cm .
À1
was extracted into Et O or hexanes (10 mLꢁ2). The combined or-
2
[10c] 1
Benzyl 4-aminomethylbenzoate (3c):
H NMR (CDCl ): d=8.04
3
ganic layers were dried over Na SO and concentrated in vacuo to
2
4
(
d, J=8.3 Hz, 2H), 7.46–7.26 (m, 7H), 5.36 (s, 2H), 3.94 ppm (s, 2H);
C NMR (CDCl ): d=166.3, 136.1, 130.1, 128.7, 128.6, 128.2, 128.1,
give the product.
1
3
3
Pd/BN-pyridine combination:
A
mixture of substrates (4:
127.0, 66.6, 46.0 ppm.
0
.25 mmol) and 0.3% Pd/BN (2.7 mg, 0.03 mol% of the substrate)
[
19] 1
4
-Aminobenzophenone (3d):
H NMR (CDCl ): d=7.73–7.70 (m,
3
in pyridine (1 mL) was stirred under atmospheric (balloon) H pres-
sure at 258C. The resulting mixture was diluted with Et O or hex-
anes (5 mL) and filtered through a Celite pad. The filtrate was sepa-
rated into two layers with aqueous HCl (20 mL, 1m), and the or-
2
4
H), 7.55–7.43 (m, 3H), 6.66 (d, J=8.2 Hz, 2H), 4.19 ppm (brs, 2H);
C NMR (CDCl ): d=195.3, 151.0, 138.8, 132.9, 131.4, 129.5, 128.0,
2
13
3
1
27.3, 113.6 ppm.
[11] 1
ganic layer was washed with H O (10 mL). The combined organic
4-Amino-3-methyl-nitrobenzene (3e):
H NMR (CDCl ): d=7.99–
3
2
layers were dried over Na SO and concentrated in vacuo to give
the analytically pure product.
7.95 (m, 2H), 6.62 (d, J=8.8 Hz, 1H), 4.33 (brs, 2H), 2.21 ppm (s,
2
4
13
3H);
C NMR (CDCl3): d=150.9, 126.6, 124.1, 121.1, 113.1,
1
7.2 ppm.
[20] 1
Benzyl propionate (6a):
H NMR (CDCl ): d=7.38–7.31 (m, 5H),
3
Typical procedure for the chemoselective semi-
hydrogenation of alkynes
5
.13 (s, 2H), 2.40 (q, J=7.5 Hz, 2H), 1.17 ppm (t, J=7.5 Hz, 3H);
1
3
C NMR (CDCl ): d=174.3, 136.1, 128.5, 128.1, 66.1, 27.6, 9.1 ppm.
3
A mixture of substrates (4: 0.25 mmol and 2 or 5: 0.25 mmol) and
[
21]
1
1
(
6
2
9-Nor-17a-pregna-1,3,5(10)-triene-3,17-diol (6b):
H NMR
0
(
2
.3% Pd/BN (9.0 mg, 0.10 mol% of the substrate) in pyridine
1 mL) was stirred under atmospheric (balloon) H2 pressure at
58C. The resulting mixture was diluted with Et O or hexanes
CD OD): d=7.06 (d, J=9.0 Hz, 1H), 6.52 (dd, J=9.0, 3.0 Hz, 1H),
3
.46 (d, J=9.0 Hz, 1H), 2.78–2.74 (m, 2H), 2.31–2.27 (m, 1H), 2.12–
.07 (m, 1H), 1.96–1.91 (m, 1H), 1.88–1.85 (m, 1H), 1.65–1.25 (m,
1H), 0.98 (t, J=7.0 Hz, 3H), 0.90 ppm (s, 3H); C NMR (CD OD):
d=155.9, 138.8, 132.7, 127.2, 116.0, 113.7, 84.4, 51.0, 48.1, 45.2,
1.4, 33.4, 32.8, 30.8, 29.7, 28.8, 27.7, 24.4, 15.3, 8.2 ppm.
2
(
5 mL) and filtered through a Celite pad. The filtrate was separated
13
1
3
into two layers with aqueous HCl (20 mL, 1m), and the organic
layer was washed with H O (10 mL). The combined organic layers
2
4
were dried over Na SO and concentrated in vacuo to give the ana-
2
4
[11] 1
lytically pure product.
Benzyl N-(4-ethylphenyl)carbamate (6c):
H NMR (CDCl ): d=
3
7
2
.30–7.26 (m, 7H), 7.14 (d, J=8.0 Hz, 2H), 6.78 (brs, 1H), 5.20 (s,
H), 2.62 (q, J=7.5 Hz, 2H), 1.23 ppm (t, J=7.5 Hz, 3H); C NMR
1
3
Reuse of Pd/BN catalyst
(CDCl ): d=153.4, 139.5, 136.0, 135.3, 128.5, 128.3, 128.2, 128.2,
3
118.9, 66.9, 28.1, 15.6 ppm.
A mixture of 4c (0.25 mmol, 62.8 mg) and 0.3% Pd/BN (2.7 mg,
[22] 1
0
.03 mol% of the substrate) in MeOH (1 mL) in a 15 mL test tube
4
-Nitro-1-ethylbenzene (6d):
H NMR (CDCl ): d=8.14 (d, J=
3
was stirred under atmospheric (balloon) H pressure at 258C for
2
8.4 Hz, 2H), 7.34 (d, J=8.4 Hz, 2H), 2.76 (q, J=7.2 Hz, 2H),
13
6
h. The resulting mixture was diluted with Et O or hexanes
2
1.29 ppm (t, J=7.2 Hz, 3H); C NMR (CDCl ): d=152.0, 146.1,
3
(
10 mL) and H O (10 mL) and filtered through a Kiriyama funnel.
2
128.5, 123.5, 28.7, 14.9 ppm.
The catalyst collected on the filter paper was washed with MeOH/
[
23] 1
1
-Methoxy-4-ethylbenzene (6e):
H NMR (CDCl ): d=7.11 (d, J=
3
H O and dried under reduced pressure for 2 d to recover the cata-
2
8
2
1
.5 Hz, 2H), 6.83 (d, J=8.5 Hz, 2H), 3.78 (s, 3H), 2.59 (q, J=7.6 Hz,
H), 1.21 ppm (t, J=7.6 Hz, 3H); C NMR (CDCl ): d=157.6, 136.4,
lyst. The filtrate was separated into two layers, and the aqueous
13
3
layer was further extracted with Et O or hexanes (2ꢁ10 mL). The
2
28.7, 113.7, 55.2, 28.0, 15.9 ppm.
combined organic layers were dried over MgSO and concentrated
4
in vacuo to give 5c.
[24] 1
Phenylmethyl 3-phenylpropionate (6 f):
H NMR (CDCl ): d=
3
7
.37–7.17 (m, 10H), 5.11 (s, 2H), 2.97 (t, J=7.8 Hz, 2H), 2.68 ppm (t,
13
J=7.8 Hz, 2H); C NMR (CDCl ): d=172.7, 140.4, 135.9, 128.5,
3
Pd metal leaching test
1
28.5, 128.3, 128.2, 126.2, 66.2, 35.9, 30.9 ppm.
A mixture of 4e (2.5 mmol, 330 mg) and 0.3% Pd/BN (90 mg,
[25] 1
3
5
-Phenylpropionitrile (6g):
H NMR (CDCl ): d=7.46–7.22 (m,
3
0
.10 mol% of the substrate) in MeOH (10 mL) in a 100 mL egg-
13
H), 2.95 (t, J=7.3 Hz, 2H), 2.61 ppm (t, J=7.3 Hz, 2H); C NMR
(CDCl ): d=138.0, 128.8, 128.2, 127.2, 119.1, 31.5, 19.3 ppm.
3
plant-shaped flask was stirred under atmospheric (balloon) H pres-
2
sure at 258C for 2 h. The reaction mixture was filtered through two
membrane filters (Millipore Corporation, Billerica, USA; Millex-LH,
[26] 1
1
-Bromo-4-ethylbenzene (6h):
H NMR (CDCl ): d=7.39 (d, J=
3
8
1
1
.4 Hz, 2H), 7.06 (d, J=8.4 Hz, 2H), 2.60 (q, J=7.6 Hz, 2H),
0
.45 mm and 0.20 mm). The filtrate was diluted with Et O (20 mL),
2
13
.21 ppm (t, J=7.6 Hz, 3H); C NMR (CDCl ): d=143.1, 131.3,
and no Pd leaching was observed by ICP-AES analysis.
3
29.6, 119.2, 28.3, 15.4 ppm.
[11] 1
1
-Nitrohexane (6i):
H NMR (CDCl ): d=4.38 (t, J=7.1 Hz, 2H),
3
Spectroscopic data of products
2
.01 (m, 2H), 1.43–1.28 (m, 6H), 0.90 ppm (t, J=7.0 Hz, 3H);
1
13
13
4
-Aminobenzoic acid (3a): H and C NMR spectra of the product
C NMR (CDCl ): d=75.7, 30.9, 27.3, 25.8, 22.3, 13.8 ppm.
3
were identical to those of the commercial authentic sample.
[27] 1
4
2
-Methoxystyrene (5e):
H NMR (CDCl ): d=7.35 (d, J=8.6 Hz,
3
1
H NMR (CD OD): d=7.74 (d, J=8.6 Hz, 2H), 6.62 ppm (d, J=
3
H), 6.86 (d, J=8.6 Hz, 2H), 6.67 (dd, J=17.6, 10.8 Hz, 1H), 5.62 (d,
J=17.6 Hz, 1H), 5.13 (d, J=10.8 Hz, 1H), 3.82 ppm (s, 3H); C NMR
1
3
8
.6 Hz); C NMR (CDCl ): d=170.7, 154.6, 132.8, 119.0, 114.3 ppm.
13
3
1
4
-Methoxybenzyl carbamate (3b): H NMR (CDCl ): d=7.30 (d, J=
(CDCl
3
): d=159.3, 136.2, 130.4, 127.4, 113.9, 111.5, 55.3 ppm.
3
8
.6 Hz, 2H), 6.89 (d, J=8.6 Hz), 5.03 (s, 2H), 3.81 ppm (s, 3H);
1
3
C NMR (CDCl ): d=159.4, 130.0, 128.2, 113.9, 66.7, 55.3 ppm; IR
3
ꢀ
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CHEMCATCHEM
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[
28] 1
N-Benzyloxycarbonyl-4-vinylaniline (5c):
7
5
H NMR (CDCl ): d=
H. Qian, B. A. Drake, R. Jin, Angew. Chem. 2010, 122, 1317–1320; Angew.
Chem. Int. Ed. 2010, 49, 1295–1298; b) Y. Hong, K.-Q. Sun, G.-R. Zhang,
R.-Y. Zhong, B.-Q. Xu, Chem. Commun. 2011, 47, 1300–1302; c) M. Taka-
saki, Y. Motoyama, K. Higashi, S.-H. Yoon, I. Mochida, H. Nagashima, Org.
Lett. 2008, 10, 1601–1604; d) S. Ichikawa, M. Tada, Y. Iwasawa, T. Ikariya,
Chem. Commun. 2005, 924–926; e) F. Wang, J. Liu, X. Xu, Chem.
Commun. 2008, 2040–2042; f) M. Boronat, P. Concepciꢂn, A. Corma, S.
Gonzꢃlez, J. Am. Chem. Soc. 2007, 129, 16230–16237; g) L. Liu, B. Qiao,
Z. Chen, J. Zhang, Y. Deng, Chem. Commun. 2009, 653–655.
3
.42–7.36 (m, 9H), 6.80 (brs, 1H), 6.67 (dd, J=17.8, 10.9 Hz, 2H),
.68 (d, J=17.8 Hz, 1H), 5.21–5.18 ppm (m, 3H); C NMR (CDCl3):
d=153.2, 137.3, 136.0, 145.9, 132.9, 128.6, 128.3, 128.2, 126.8,
18.6, 112.7, 67.0 ppm.
13
1
[29] 1
1
-Nitro-4-vinylbenzene (5d):
H NMR (CDCl ): d=8.18 (d, J=
3
.8 Hz, 2H), 7.53 (d, J=8.8 Hz, 2H), 6.77 (dd, J=17.8, 10.9 Hz, 1H),
.92 (d, J=17.8 Hz, 1H), 5.49 ppm (d, J=10.9 Hz, 1H); C NMR
CDCl ): d=147.1, 143.8, 134.9, 126.7, 123.9, 118.6 ppm.
3
8
5
(
13
[
[
7] a) H. Sajiki, K. Hattori, K. Hirota, J. Org. Chem. 1998, 63, 7990–7992; b) K.
Hattori, H. Sajiki, H. K. Hirota, Tetrahedron 2000, 56, 8433–8441; c) H.
Sajiki, K. Hattori, K. Hirota, J. Chem. Soc. Perkin Trans. 1 1998, 4043–
[
30] 1
Dimethyl-2-propen-1-ylsilylbenzene (5j):
H NMR (CDCl ): d=
3
4044; d) H. Sajiki, K. Hattori, K. Hirota, Chem. Eur. J. 2000, 6, 2200–2204;
7
2
1
.55–7.53 (m, 2H), 7.39–7.36 (m, 3H), 5.80 (m, 1H), 4.90–4.86 (m,
H), 1.78 (d, J=8.0 Hz, 2H), 0.30 ppm (s, 6H); C NMR (CDCl ): d=
38.6, 134.6, 133.6, 130.0, 127.7, 113.4, 23.7, À3.5 ppm.
H NMR (CDCl ): d=7.39–7.34
3
m, 4H), 6.06 (ddd, J=16.7, 10.4, 5.8 Hz, 1H), 5.36 (d, J=16.7 Hz,
H), 5.22–5.19 (m, 2H), 1.98 ppm (brs, 1H); C NMR (CDCl ): d=
42.5, 140.2, 128.6, 127.8, 126.3, 115.1, 76.7 ppm.
1
3
e) K. Hattori, H. Sajiki, H. K. Hirota, Tetrahedron 2001, 57, 2109–2114.
8] a) H. Sajiki, S. Mori, T. Ohkubo, T. Ikawa, A. Kume, T. Maegawa, Y. Mongu-
chi, Chem. Eur. J. 2008, 14, 5109–5111; b) S. Mori, T. Ohkubo, T. Ikawa,
A. Kume, T. Maegawa, Y. Monguchi, H. Sajiki, J. Mol. Catal. A 2009, 307,
77–87.
3
[16a]
1
1
-Phenyl-2-propene-1-ol (5k):
(
1
1
1
3
[9] A. Mori, T. Mizusaki, M. Kawase, T. Maegawa, Y. Monguchi, S. Takao, Y.
Takagi, H. Sajiki, Adv. Synth. Catal. 2008, 350, 406–410.
3
[
[
10] a) H. Sajiki, T. Ikawa, K. Hirota, Tetrahedron Lett. 2003, 44, 171–174; b) H.
Sajiki, T. Ikawa, K. Hirota, Tetrahedron Lett. 2003, 44, 8437–8439; c) T.
Ikawa, H. Sajiki, K. Hirota, Tetrahedron 2005, 61, 2217–2231; d) Y. Kita-
mura, A. Tanaka, M. Sato, K. Oono, T. Ikawa, T. Maegawa, Y. Monguchi,
H. Sajiki, Synth. Commun. 2007, 37, 4381–4388.
11] a) T. Maegawa, T. Takahashi, M. Yoshimura, H. Suzuka, Y. Monguchi, H.
Sajiki, Adv. Synth. Catal. 2009, 351, 2091–2095; b) T. Takahashi, M. Yoshi-
mura, H. Suzuka, T. Maegawa, Y. Sawama, Y. Monguchi, H. Sajiki, Tetrahe-
dron 2012, 68, 8293–8299.
[27] 1
2
-Methoxy-6-vinylnaphthalene (5l):
H NMR (CDCl ): d=7.73–
3
.70 (m, 3H), 7.63 (dd, J=8.6, 1.2 Hz, 1H), 7.15 (m, 2H), 6.87 (dd,
J=17.5, 10.9 Hz, 1H), 5.84 (d, J=17.5 Hz, 1H), 5.30 (d, J=10.9 Hz,
H), 3.93 ppm (s, 3H); C NMR (CDCl ): d=157.7, 136.9, 134.3,
7
13
1
1
3
32.9, 128.9, 127.0, 126.2, 123.7, 118.9, 113.1, 105.8, 55.3 ppm.
[31] 1
[
1-Azido-2-(prop-2-ynyloxy)ethyl]benzene (7):
d=7.43–7.33 (m, 5H), 4.75 (dd, J=8.5, 4.3 Hz, 1H), 4.27 (dd, J=
6.3, 2.2 Hz, 1H), 4.21 (dd, J=16.3, 2.2 Hz, 1H) 3.78 (dd, J=10.1,
.3 Hz, 1H), 3.71 (dd, J=10.3, 8.5 Hz, 1H), 2.47 ppm (t, J=2.2 Hz,
H); C NMR (CDCl ): d=136.3, 128.8, 128.5, 127.0, 79.0, 75.1, 73.4,
H NMR (CDCl3):
[
12] We have reported the Pd/MS3A-catalyzed chemoselective hydrogena-
tion of azide, alkyne, and alkene functionalities in the presence of other
reducible groups. See Ref. [11].
1
4
1
6
1
3
3
[
13] For semihydrogenations, see: a) H. Lindlar, R. Dubuis, Org. Synth. Coll.
5.0, 58.5 ppm.
1
973, 5, 880–883; b) C. A. Brown, V. K. Ahuja, J. Chem. Soc. Chem.
Commun. 1973, 553–554; c) C. A. Brown, V. K. Ahuja, J. Org. Chem.
1973, 38, 2226–2228; d) ꢄ. Mastalir, Z. Kirꢃly, G. Szçllçsi, M. Bartꢂk, J.
Catal. 2000, 194, 146–152; e) M. Gruttadauria, L. F. Liotta, R. Noto, G.
Deganello, Tetrahedron Lett. 2001, 42, 2015–2017; f) ꢄ. Mastalir, Z.
Kirꢃly, J. Catal. 2003, 220, 372–381; g) F. Alonso, I. Osante, M. Yus, Adv.
Synth. Catal. 2006, 348, 305–308; h) F. Alonso, I. Osante, M. Yus, Tetrahe-
dron 2007, 63, 93–102; i) J. Panpranot, K. Phandinthong, T. Sirikajorn,
[
1-Azido-2-(prop-2-enyloxy)ethyl]benzene (8): Pale yellow oil;
1
H NMR (CDCl ): d=7.39–7.31 (m, 5H), 5.92 (ddd, J=17.0, 10.5,
3
5
1
.5 Hz, 1H), 5.30 (dd, J=17.0, 1.3 Hz, 1H), 5.22 (dd, J=10.5, 1.3 Hz,
H) 4.73 (dd, J=8.0, 5.0 Hz, 1H), 4.09–4.02 (m, 2H), 3.67–3.61 ppm
1
3
(
m, 2H); C NMR (CDCl ): d=136.6, 134.1, 128.7, 128.4, 127.0,
3
À1
1
1
2
17.5, 74.0, 72.2, 65.2; IR (ATR) cm : 2857, 2092, 1495, 1453, 1344,
310, 1257, 1107 ppm; HRMS (ESI): m/z: calcd for C H N ONa:
11 13 3
M. Arai, P. Praserthdam, J. Mol. Catal. A 2007, 261, 29–35;
+
26.0951 [M+Na ]; found: 226.0944.
j) S. D. Dominguez-Dominguez, ꢄ. B. Murcia, B. K. Pradhan, ꢄ. L. Solano,
D. C. Amorꢂs, J. Phys. Chem. C 2008, 112, 3827–3834; k) P. Weerachawa-
nasak, O. Mekasuwandumrong, M. Arai, S. Fujita, P. Praserthdam, J. Pan-
pranot, J. Catal. 2009, 262, 199–205; l) J. Hori, K. Murata, T. Sugai, H.
Shinohara, R. Noyori, K. Arai, N. Kurono, T. Ohkuma, Adv. Synth. Catal.
Acknowledgements
2
2
009, 351, 3143–3149; m) Y. Zhao, Q. Liu, J. Li, Z. Liu, B. Zhou, Synlett
010, 12, 1870–1872; n) M. Armbrꢅster, K. Kovnir, M. Behrens, D. Tesch-
We thank the N.E. Chemcat Corporation for the gift of Pd(OAc)2,
STEM measurements, and ICP analysis of Pd/BN.
ner, Y. Grin, R. Schlçgl, J. Am. Chem. Soc. 2010, 132, 14745–14747; o) Z.
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555–1558; p) A. Ota, M. Armbrꢅster, M. Behrens, D. Rosenthal, M. Frie-
Keywords: boron
heterogeneous catalysis · palladium
·
chemoselectivity
·
hydrogenation
·
drich, I. Kasatkin, F. Girgsdies, W. Zhang, R. Wagner, R. Schlçgl, J. Phys.
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hoven, J. Phys. Chem. C 2011, 115, 8457–8465.
nd
[14] Although Lindlar’s catalyst is frequently used as a heterogeneous semi-
hydrogenation catalyst for disubstituted alkynes, it possesses some dis-
[
1] a) R. C. Larock, Comprehensive Organic Transformations, 2 ed., Wiley-
VCH, New York, 1999; b) S. Nishimura, Handbook of Heterogeneous Cata-
2
advantages, such as the use of toxic Pb(OAc) for the deactivation of
lytic Hydrogenation for Organic Synthesis, Wiley-Interscience, New York,
nd
the catalyst and the difficulty of the semihydrogenation for monosub-
stituted alkynes. See Ref. [8].
[15] Although Pd/PEI enabled the semihydrogenation of both mono- and
disubstituted alkynes, the careful adjustment of the reaction conditions,
such as the solvent, was required for each substrate. Furthermore, the
reuse of the catalyst was not possible. See Ref. [8].
[16] a) Y. Yabe, T. Yamada, S. Nagata, Y. Sawama, Y. Monguchi, H. Sajiki, Adv.
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2
8
[
[
5] S. Bhogeswararao, D. Srinivas, Catal. Lett. 2010, 140, 55–64.
6] For selected papers on chemoselective hydrogenation using transition
metals other than supported Pd heterogeneous catalysts, see: a) Y. Zhu,
[17] A small amount of Pd metal (2.2%) was leached during the semihydro-
genation catalyzed by Pd/BN-DETA in MeOH. Therefore, the leaching of
Pd might be slightly promoted by the addition of DETA. See Ref. [17a].
ꢀ
2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 0000, 00, 1 – 8
&
7
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ÞÞ
These are not the final page numbers!

CHEMCATCHEM
FULL PAPERS
www.chemcatchem.org
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Received: January 16, 2013
Revised: February 22, 2013
Published online on && &&, 0000
944.
ꢀ
2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 0000, 00, 1 – 8
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8
&
ÞÞ
These are not the final page numbers!