Nickel-catalyzed (E)-selective semihydrogenation of internal alkynes with hypophosphorous acid

Article abstract of DOI:10.1016/j.jorganchem.2013.09.023

A facile Ni-catalyzed semihydrogenation of internal alkynes to (E)-alkenes using the cheap and easily handled hypophosphorous acid as a hydrogen donor was described. This reaction is featured by high reaction efficiency to produce the corresponding (E)-al

Full text of DOI:10.1016/j.jorganchem.2013.09.023

Journal of Organometallic Chemistry 749 (2014) 51e54
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Note
Nickel-catalyzed (E)-selective semihydrogenation of internal alkynes
with hypophosphorous acid
a
,
b
a
a
a
b,
*
Tieqiao Chen , Jing Xiao , Yongbo Zhou , Shuangfeng Yin , Li-Biao Han
a
College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, China
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8565, Japan
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 19 July 2013
Received in revised form
A facile Ni-catalyzed semihydrogenation of internal alkynes to (E)-alkenes using the cheap and easily
handled hypophosphorous acid as a hydrogen donor was described. This reaction is featured by high
reaction efficiency to produce the corresponding (E)-alkenes selectively.
16 September 2013
Ó 2013 Elsevier B.V. All rights reserved.
Accepted 17 September 2013
Keywords:
Semihydrogenation
Hypophosphorous acid
Alkyne
Nickel catalyst
(
E)-Selectivity
1. Introduction
Therefore, the development of a more economical and greener
method for the preparation of (E)-alkene is desirable.
The transition metal catalyzed semihydrogenation of alkynes to
alkenes with defined (E) or (Z)-configuration is an important
transformation which is widely used in the preparation of synthetic
intermediates, pharmaceuticals and natural products [1]. As
exemplified by the famous Lindlar protocol, direct reductions of
alkynes to (Z)-alkenes with good functional group tolerance are
well known [2,3aec]. However, in contrast, only few methods are
known for the selective semihydrogenation of alkynes to (E)-al-
Following our report on palladium-catalyzed selective hydro-
genation of alkynes using formic acid as a reducing reagent [3a],
herein, we described an effective selective Ni-catalyzed semi-
hydrogenation of alkynes to (E)-alkenes using the easily handled
hypophosphorous acid as hydrogen donor (Eq. (1)) [5]. This
method reported herein features a high tolerance to a variety of
functional groups and is a good complementary to the classic Birch
reduction.
3
kenes [3]. Thus, the Birch-type reduction using NH or amine as
hydrogen donors can selectively produce (E)-alkenes. However,
these reactions have to use a stoichiometric amount of alkali metals
dissolving in amines which can damage the functional groups. Very
recently, a selective (E)-alkene formation via semihydrogenation of
alkynes mediated by ruthenium and silver heterogeneous catalysts
was reported [3b,g]. Another example for selective generation of
(1)
2
. Result and discussion
Table 1 summarized the results for the reduction of diphenyla-
cetylene using hypophosphorous acid catalyzed by metals.
Although RhCl(PPh and palladium on carbon were ineffective at
all (runs 1 and 2), under similar conditions at room temperature,
palladium complexes (runs 3e5) could catalyze the semi-
hydrogenation of diphenylacetylene to afford the (Z)-stilbene
selectively. Nickel complexes were also effective for selective
semihydrogenation of diphenylacetylene. Notably, however, being
different from palladium and rhodium, nickel produced (E)-stil-
(E)-alkene was developed by Trost using a two-step process in
which alkynes first underwent Ru-catalyzed trans hydrosilylation
followed by the desilylation of the resulting alkenylsilanes with a
fluoride. [4] Although this two-step protocol showed good func-
tional group tolerance compared to the Birch reduction, the sacri-
fice of the expensive hydrosilane limits its general application.
3 3
)
bene. Thus, under similar conditions, NiCl
yield of stilbene with a ratio of E/Z ¼ 60/40. Complex NiCl
2
(PPh
3
)
2
produced 5%
dppp was
*
Corresponding author.
E-mail address: libiao-han@aist.go.jp (L.-B. Han).
2
0
022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.09.023

52
T. Chen et al. / Journal of Organometallic Chemistry 749 (2014) 51e54
Table 1
a
Selective reduction of diphenylacetylene using hypophosphorous acid.
Table 2
Ni-catalyzed selective semihydrogenation of alkynes affording (E)-alkenes.a
ꢀ
Run
Catalyst
Tem. ( C)
H
3
PO
2
Time (h)
GC Yield (E/Z)
(equivs)
Run Substrate
Time GC yield Isolated
1
2
3
4
5
6
7
8
9
1
1
1
1
RhCl(PPh
Pd/C
3
)
3
25
25
25
25
25
25
25
50
80
100
80
80
80
5
5
5
5
5
5
5
5
5
5
1
3
3
24
24
24
24
24
24
24
1
1
1
1
1
0%
0%
(h)
(E:Z)
yield
Pd
PdCl
Pd(PPh
2
(dba)
3
33% (1:99)
46% (1:99)
48% (1:99)
5% (60:40)
91% (90:10)
16% (56:44)
91% (98:2)
93% (97:3)
67% (86:14)
94% (97:3)
98% (98:2)
2
(PPh
3
)
2
3
)
4
1
2
3
4
5
4
2a, 98%
85%
NiCl
NiCl
NiCl
NiCl
NiCl
NiCl
NiCl
NiCl
2
2
2
2
2
2
2
2
(PPh
3
)
2
(98:2)
dppp
dppp
dppp
dppp
dppp
dppp
dppp
6
4
6
4
2b, 99%
86%
70%
80%
73%
0
1
2
3
(98:2)
b
b
c
4
2c, 95%
>99:1)
a
3 2
Condition: a mixture of diphenylacetylene (0.2 mmol), H PO 50% aqueous
(
solution and a catalyst in 0.5 mL of acetic acid was allowed to react at the tem-
P(CH PPh
perature shown in the table. dppp ¼ Ph
2
2
)
3
2
.
b
5
3
mol% NiCl
mol% NiCl
2
dppp.
dppp.
c
2d, 96%
99:1)
2
(
a more effective catalyst which could give better selectivity and
higher yield of (E)-stilbene. Thus, in the presence of 10 mol%
NiCl dppp, the semireduction with 5 equivs H PO at room tem-
2 3 2
2e, 91%
>99:1)
(
perature for 24 h gave the desired product (E)-stilbene in 91% yield
with 90% selectivity (run 6). After optimizing the reaction condi-
tions by changing temperature and catalyst loading, it was found
that 98% yield of stilbene could be obtained with a ratio of E/Z ¼ 98/
6b
48
6
2f, 90%
99:1)
82%
83%
e
(
2
5
by simply heating the reaction mixture of diphenylacetylene with
ꢀ
0% H
NiCl
3
PO
2
aqueous solution at 80 C for 4 h in the presence of 3 mol
%
2
dppp (run 13). It is noted that acetic acid seems to be the
7
8
9
2g, 92%
99:1)
(
solvent of choice because other solvents such as DMSO, DMF,
dioxane, THF, toluene and hexane only gave low yields of the
products.
By using the optimized conditions described in Table 1, other
internal alkynes could also be smoothly converted to the corre-
sponding (E)-alkenes. As shown in Table 2, this Ni-catalyzed re-
action was effective for various aromatic internal alkynes bearing
both electron-donating and electron-withdrawing groups. Worth
noting was that this reaction had a wide functional group toler-
ance. Thus, functional groups such as chloro (run 2), fluoro (run
4
2h, 70%
>99:1)c
(
28
2i, 80%
55%
(99:1)d
10
4
2j, 82%
(98:2)
23%e
3
), carboxyl (run 4), and methoxy (run 7) all were compatible.
Especially, trimethylsilyl group which was easily hydrolyzed [3a]
also survived and the corresponding product (E)-alkenes 2f was
produced in 82% yield with 99:1 selectivity under the catalytic
conditions (run 6). Boronic ester group was also tolerant with
this nickel-catalyzed semihydrogenation and the corresponding
11
6.5 2k, 44%
e
e
f
(98:2)
(
(
E)-alkene was produced in good yield with high selectivity
>99:1) (run 5). In the presence of 3 mol% NiCl dppp, 1,4-bis(2-
2
12
4
2l, Trace
g
phenylethynyl)benzene can be readily converted to the corre-
sponding (E,E)-product 2h in moderate yield (run 8). In addition,
(ꢁ)
a
Condition: a mixture of 0.2 mmol of an alkyne, 0.6 mmol of 50% aqueous H
3
PO
2
2
i could also be obtained highly selectively from the corre-
solution and 3 mol% NiCl
2
dppp was dissolved in 0.5 mL of acetic acid and heated at
ꢀ
8
0
C until the alkyne was consumed.
sponding 2-(2-phenylethynyl)thiophene (run 9). It was noted
that 20% over reduced alkane was also generated although
similar over reduction products were hardly detected in other
cases. An alkylearyl internal alkyne 1-(pent-1-ynyl)benzene also
produced the corresponding product efficiently (run 10). Only a
moderate yield of the product was obtained from an alkylealkyl
internal alkyne dodec-6-yne (run 11) in which the hydration side
product was generated in a large amount. Finally, terminal
b
ꢀ
4
2
2
0
C.
3% yield of the partial reduction product remained.
0% yield of the over reduction alkane was produced. The product was isolated
c
d
by a preparative GPC.
e
A low isolated yield due to the low boiling point of the product.
Yield determined by NMR. ca 48% yield of 6-dodecanone was formed.
The hydration product acetophenone was produced predominantly.
f
g

T. Chen et al. / Journal of Organometallic Chemistry 749 (2014) 51e54
53
alkynes such as phenylacetylene could not be used in the reac-
3. Conclusion
tion because significant hydration, rather than hydrogenation,
took place (run 12).
In summary, a simple one-pot highly stereoselective Ni-
catalyzed reduction of internal alkynes to (E)-alkenes using the
cheap and environmental-friendly hypophosphorous acid was
developed. This method featured high tolerance to a variety of
functional groups and is a convenient method for the synthesis of
(E)-alkenes.
MeO
MeO
MeO
2 2
PO ,
3
3
equivs NaH
mol% NiCl dppp
2
OMe
HOAc,80 oC,overnight
MeO
m, 71% yield, E/ Z = 96/ 4
OMe
2
4. Experimental section
(
2)
4
.1. A typical procedure for the Ni-catalyzed semihydrogenation of
As shown in Eq. (2), the synthetic value of the present Ni-
alkynes
catalyzed semihydrogenation was further demonstrated by the
efficient synthesis of precursors of resveratrol, the well-known
bioactive natural products which have antitumor [6a,b],
antibacterial [6c,d], antioxidation [6e], antiaging [6f,g], vascular
protective, [6h] and metabolic regulation effects [6i,j]. Thus, by
Under N
lene, 3 equivs 50% H
NiCl
until diphenylacetylene was consumed as followed by GC. The
volatiles were pumped off and the crude products were subject
to purification by column chromatography on silica gel (silica gel
2
atmosphere, a mixture 0.2 mmol of diphenylacety-
3
PO
2
aqueous solution (65
m
L), and 3 mol%
ꢀ
2
dppp (3.3 mg) in 0.5 mL of AcOH was stirred at 80 C for 4 h
0
employing the Ni-catalyzed selective semihydrogenation, 3,5,4 -
trimethoxydiphenylacetylene was smoothly converted to the cor-
responding (E)-alkene 2m in 71% isolated yield selectively (Eq. (2)).
Following the established procedures, [7] 2m can be efficiently
converted to the natural product resveratrol.
size: 38e63
m
m, 40 g; column size: 2 cm ꢂ 30 cm) using hexane
as an eluent to obtain the pure 2a in 85% yield (30.6 mg, E/
Z ¼ 98/2).
4
.1.1. (E)-Stilbene (2a) [3a]
1
6
H NMR (400 MHz, DMSO-d ) d 7.60e7.62 (m, 4H), 7.38 (t, 4H,
13
J ¼ 7.2 Hz), 7.25e7.29 (m, 4H); C NMR (100 MHz, DMSO-d
6
)
d
137.50, 129.17, 128.90, 128.11, 126.95.
(
3)
4
.1.2. (E)-1-(4-Chlorophenyl)-2-phenyl-ethylene (2b) [3a]
1
3
H NMR (400 MHz, CDCl ) d 7.50e7.52 (m, 2H), 7.43e7.47 (m,
13
2
H), 7.27e7.39 (m, 5H), 7.07 (d, 2H, J ¼ 2.8 Hz); C NMR (100 MHz,
3
CDCl ) d
136.95, 135.81, 133.16, 129.27, 128.87, 128.78, 127.91, 127.68,
127.35, 126.57.
As to the mechanism for the generation of (E)-alkenes, it was
assumed that (Z)-alkenes were initially generated which iso-
merized to the more stable (E)-alkenes by nickel catalysts. Indeed,
as shown in Eq. (3), (Z)-stilbene was quantitatively converted to (E)-
4
.1.3. (E)-1-(4-Fluorophenyl)-2-phenyl-ethylene (2c) [3c]
1
H NMR (400 MHz, CDCl
J ¼ 7.0 Hz), 7.27 (t, 1H, J ¼ 6.0 Hz), 7.00e7.10 (m, 4H); C NMR
100 MHz, CDCl
162.28 (d, J ¼ 247.8 Hz), 137.11, 133.46 (d,
J ¼ 2.9 Hz), 128.67, 128.44 (d, J ¼ 1.9 Hz), 127.93 (d, J ¼ 7.6 Hz),
27.63, 127.43, 126.40, 115.58 (d, J ¼ 21.0 Hz).
3
) d 7.47e7.51 (m, 4H), 7.37 (t, 2H,
13
(
3
) d
stilbene under the reaction conditions. It was noted that H
essential for this isomerization and the isomerization hardly pro-
ceeded in the absence of H PO
3 2
PO was
1
3
2
.
A proposed catalytic cycle was shown in Scheme 1. The Ni-
catalyzed selective reduction of an alkyne to alkene took place via
a catalytic cycle involving hydrometalation of the tripe bond with
the combination of Ni(0) complex [8] and HOAc affording the
alkenylnickel species 4 [3a], which was reduced by H PO gener-
3 2
ating intermediate 5. Subsequent reductive elimination of 5 and
isomerization of (Z)-2 produced (E)-2 (Scheme 1).
4
.1.4. 1-[4-((1E)-2-Phenylethenyl)phenyl]ethanone (2d) [3a]
1
H NMR (400 MHz, CDCl
3
)
d
7.98 (d, 2H, J ¼ 8.4 Hz), 7.61 (d, 2H,
J ¼ 8.4 Hz), 7.57 (d, 2H, J ¼ 7.2 Hz), 7.41 (t, 2H, J ¼ 7.6 Hz), 7.31e7.35
13
(m, 1H), 7.14e7.24 (m, 2H), 2.63 (s, 3H); C NMR (100 MHz, CDCl
3
)
d
197.42, 142.03, 136.73, 136.01, 131.50, 128.87, 128.79, 128.31,
127.48, 126.82, 126.50, 26.55.
4.1.5. (E)-4,4,5,5-Tetramethyl-2-(4-styrylphenyl)-1,3,2-
dioxaborolane (2e) [3a]
1
H NMR (400 MHz, CDCl
3
)
d
7.81 (d, 2H, J ¼ 8.0 Hz), 7.53 (d, 4H,
Ni(0)
R
R
J ¼ 8.0 Hz), 7.37 (t, 2H, J ¼ 8.0 Hz), 2.28 (d, 1H, J ¼ 8.0 Hz), 7.10e7.21
13
(
3
m, 2H), 1.37 (s, 12H); C NMR (100 MHz, CDCl ) d 140.02, 137.19,
R
R
H
R
H
R
135.17, 129.65, 128.72, 128.63, 127.81, 126.63, 125.81, 83.82, 24.93.
(
Z)-2
Ni
Ni
3
4.1.6. (E)-1-(4-Trimethylsilylphenyl)-2-phenyl-ethylene (2f)
H
1
5
H
3
H NMR (400 MHz, CDCl ) d 7.49e7.53 (m, 6H), 7.36 (t, 2H,
H
R
R
J ¼ 7.2 Hz), 7.26 (t, 1H, J ¼ 7.6 Hz), 7.13 (d, 2H, J ¼ 3.6 Hz), 0.28 (s,
R
H
R
HOAc
13
9
H); C NMR (100 MHz, CDCl
3
) d 141.14, 140.04, 138.84, 138.45,
H
134.84, 130.03, 129.80, 128.77, 127.67, 126.92, 1.12.
H PO
3
Ni
OAc
2
(
E)-2
4
4
.1.7. (E)-1-(4-Fluorophenyl)-2-(4-propylphenyl)-ethylene (2g)
1
H NMR (400 MHz, CDCl
3
) d 7.40e7.46 (m, 4H), 7.16 (d, 2H,
Scheme 1. A proposed mechanism for Ni-catalyzed selective semihydrogenation of
alkynes. Ligands were omitted for clarity.
J ¼ 8.0 Hz), 6.88e7.05 (m, 4H), 3.83 (s, 3H), 2.58 (t, 2H, J ¼ 7.2 Hz),

54
T. Chen et al. / Journal of Organometallic Chemistry 749 (2014) 51e54
1
.56e1.69 (m, 2H), 0.95 (t, 3H, J ¼ 7.2 Hz); 13C NMR (100 MHz,
(c) C. Oger, L. Balas, T. Durand, J.-M. Galano, Chem. Rev. 113 (2013) 1313e1350;
d) P. Hauwert, G. Maestri, J.W. Sprengers, M. Catellani, C.J. Elsevier, Angew.
Chem. Int. Ed. 47 (2008) 3223e3226;
e) P. Hauwert, R. Boerleider, S. Warsink, J.J. Weigand, C.J. Elsevier, J. Am. Chem.
Soc. 132 (2010) 16900e16910;
(
3
CDCl ) d 159.13, 141.97, 135.11, 130.36, 128.80, 127.60, 127.26, 126.60,
126.16, 114.10, 55.35, 37.82, 24.57, 13.88.
(
(
(
(
f) C. Belger, N.M. Neisius, B. Plietker, Chem. Eur. J. 16 (2010) 12214e12220;
g) J. Li, R. Hua, T. Liu, J. Org. Chem. 75 (2010) 2966e2970;
h) T. Mitsudome, Y. Takahashi, S. Ichikawa, T. Mizugaki, K. Jitsukawa, K. Kaneda,
4
.1.8. 1,4-Di-(E)-styrylbenzene (2h) [3a]
1
3
H NMR (400 MHz, CDCl ) d 7.52e7.54 (m, 8H), 7.35e7.39 (m,
1
3
4
d
H), 7.25e7.29 (m, 2H), 7.13 (s, 4H); C NMR (100 MHz, CDCl
3
)
Angew. Chem. Int. Ed. 52 (2013) 1481e1485;
(
(
(
i) T.L. Gianetti, N.C. Tomson, J. Arnold, R.G. Bergman, J. Am. Chem. Soc. 133
2011) 14904e14907;
j) A.M. Kluwer, T.S. Koblenz, T. Jonischkeit, K. Woelk, C.J. Elsevier, J. Am. Chem.
137.33, 136.71, 128.71, 128.60, 128.28, 127.66, 126.85, 126.52.
4
.1.9. 2-(E)-Styrylthiophene (2i) [3b]
Soc. 127 (2005) 15470e15480.
[3] (a) R. Shen, T. Chen, Y. Zhao, R. Qiu, Y. Zhou, S. Yin, X. Wang, M. Goto, L.-B. Han,
J. Am. Chem. Soc. 133 (2011) 17037e17044;
1
H NMR (400 MHz, CDCl
3
)
d
7.47 (d, 2H, J ¼ 7.6 Hz), 7.35 (t, 2H,
J ¼ 7.6 Hz), 7.19e7.27 (m, 3H), 7.08 (s, 1H), 7.01 (t, 1H, J ¼ 4.0 Hz),
(b) J. Li, R. Hua, Chem. Eur. J. 17 (2011) 8462e8465;
13
6
.94 (d,1H, J ¼ 16.4 Hz); C NMR (100 MHz, CDCl
3
) d 142.90,136.98,
(c) F. Luo, C. Pan, W. Wang, Z. Ye, J. Cheng, Tetrahedron 66 (2010) 1399e1403;
(d) K. Tani, A. Iseki, T. Yamagata, Chem. Commun. (1999) 1821e1822;
(e) E. Shirakawa, H. Otsuka, T. Hayashi, Chem. Commun. (2005) 5885e5886;
(f) A. Reyes-Sánchez, F. Cañavera-Buelvas, R. Barrios-Francisco, O.L. Cifuentes-
128.72, 128.35, 127.62, 126.31, 126.12, 124.36, 121.80.
4.1.10. (E)-1-Phenylbut-1-en (2j) [9]
Vaca, M. Flores-Alamo, J. García, Organometallics 30 (2011) 3340e3345;
(g) K. Radkowski, B. Sundararaju, A. Fürstner, Angew. Chem. Int. Ed. 52 (2013)
1
H NMR (400 MHz, CDCl
3
)
d
7.24e7.33 (m, 4H), 7.14e7.18 (m,
355e360;
1
H), 6.21e6.38 (m, 2H), 2.18e2.25 (m, 2H), 1.08 (t, 3H, J ¼ 7.2 Hz);
(
(
h) I.N. Michaelides, D.J. Dixon, Angew. Chem. Int. Ed. 52 (2013) 806e808;
i) C. Wang, Y. Pan, D. Yang, J. Organomet. Chem. 690 (2005) 1705e1709.
1
3
C NMR (100 MHz, CDCl
25.96, 26.10, 13.68.
3
) d 138.02, 132.66, 128.89, 128.50, 126.79,
1
[4] (a) B.M. Trost, Z.T. Ball, T. Jöge, J. Am. Chem. Soc. 124 (2002) 7922e7923;
(b) B.M. Trost, Z.T. Ball, J. Am. Chem. Soc. 127 (2005) 17644e17655;
(c) B.M. Trost, M.R. Machacek, Z.T. Ball, Org. Lett. 5 (2003) 1895e1898;
(d) B.M. Trost, Z.T. Ball, Synthesis (2005) 853e887.
0
.1.11. (E)-1-(4 -Methoxyphenyl)-2-(3,5-dimethoxyphenyl)ethene
4
(
2m) [7]
[5] For selected examples for the application of hypophosphorous acid as hydrogen
donor, see (a) G.G. Wu, F.X. Chen, D. LaFrance, Z. Liu, S.G. Greene, Y.-S. Wong,
J. Xie, Org. Lett. 13 (2011) 5220e5223;
1H NMR (400 MHz, CDCl
3
)
d
7.45 (d, 2H, J ¼ 8.8 Hz), 6.89e7.07
(
m, 4H), 6.66 (d, 2H, J ¼ 2.4 Hz), 6.39 (t, 1H, J ¼ 1.6 Hz), 3.83 (b, 9H);
(
b) J.E. Milne, T. Storz, J.T. Colyer, O.R. Thiel, M.D. Seran, R.D. Larsen, J.A. Murry,
J. Org. Chem. 76 (2011) 9519e9524;
c) C. McMaster, R.N. Bream, R.S. Grainger, Org. Biomol. Chem. 10 (2012) 4752e
758;
d) S.R. Graham, J.A. Murphy, D. Coates, Tetrahedron Lett. 40 (1999) 2415e2416;
(e) P.E. Gordon, A.J. Fry, Tetrahedron Lett. 42 (2001) 831e833;
1
3
C NMR (100 MHz, CDCl
3
) d 160.10, 159.42, 139.73, 129.96, 128.76,
(
4
(
1
27.82, 126.60, 114.17, 104.37, 99.65, 55.37, 55.33.
Acknowledgments
(
(
(
f) L.D. Hicks, J.K. Han, A.J. Fry, Tetrahedron Lett. 41 (2000) 7817e7820;
g) A.J. Fry, M. Allukian, A.D. Williams, Tetrahedron 58 (2002) 4411e4415;
h) M.M. Abu-Omar, E.H. Appelman, J.H. Espenson, Inorg. Chem. 35 (1996)
Authors are grateful for the financial support from Fundamental
Research Funds for the Central Universities (Hunan University), the
Canon Foundation and National Nature Science Foundation of
China (Grant No. 21172062).
7751e7757;
(i) M.M. Robison, B.L. Robison, Org. Synth. 36 (1956) 94e97.
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J.M. Pezzuto, Science 275 (1997) 218e220;
[
Appendix A. Supplementary data
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