Z-Stereoselective semi-reduction of alkynes: Modification of the Boland protocol

Article abstract of DOI:10.1016/j.tet.2013.03.038

Highly Z-selective semi-reduction of alkynes has been achieved by adding TMSCl to a mixture of Zn(Cu/Ag), water, and methanol. The conjugated Z-alkenes have been prepared in high yields at ambient temperature. The formation of isomeric E-alkenes and over-reduction to alkanes were suppressed in our modified Boland reduction protocol. The methodology was extended to the preparation of Z-substituted stilbenes.

Full text of DOI:10.1016/j.tet.2013.03.038

Tetrahedron 69 (2013) 3872e3877
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Z-Stereoselective semi-reduction of alkynes: modification of the
Boland protocol
*
Yasser M.A. Mohamed, Trond Vidar Hansen
School of Pharmacy, Department of Pharmaceutical Chemistry, University of Oslo, PO Box 1068, Blindern, N-0316 Oslo, Norway
a r t i c l e i n f o
a b s t r a c t
Article history:
Highly Z-selective semi-reduction of alkynes has been achieved by adding TMSCl to a mixture of
Zn(Cu/Ag), water, and methanol. The conjugated Z-alkenes have been prepared in high yields at ambient
temperature. The formation of isomeric E-alkenes and over-reduction to alkanes were suppressed in our
modified Boland reduction protocol. The methodology was extended to the preparation of Z-substituted
stilbenes.
Received 29 November 2012
Received in revised form 19 February 2013
Accepted 11 March 2013
Available online 15 March 2013
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Reduction
Z-Stereoselectivity
Zn(Cu/Ag)
Alkynes
Z-alkenes
1. Introduction
Many of the methods available for the stereoselective synthesis
of Z-alkenes are often hampered by low selectivity, isomerization to
Alkynes are important for the preparation of many bioactive
compounds.1 In particular, stereoselective reductions of internal
alkynes have been employed in the synthesis of many conjugated
polyunsaturated natural products (Fig. 1).2,3
the undesired E-isomer, and over-reductions to alkanes. These
problems are even more severe for the synthesis of conjugated
Z-alkenes.4 The protocol reported by Boland and co-workers has
emerged as the method of choice for the preparation of conjugated
Z-alkenes.5 The original protocol employs a combination of zinc,
copper, and silver in aqueous methanol. However, prolonged re-
action times and/or elevated temperatures are often necessary.6
These conditions often lower the Z-stereoselectivity by isomeriza-
tion to the thermodynamically more stable E-alkene(s).
During our synthetic studies toward the total synthesis of the
highly conjugated polyunsaturated fatty acid bosseopentaenoic
acid (1), the reduction of the E,E-conjugated dialkyne 5 was
investigated.2a Unfortunately, low Z-selectivity was observed in the
initial preparation of compound 2 (Scheme 1).
Fig. 1. Examples of conjugated polyunsaturated natural products prepared from
alkynes.
Scheme 1. Reduction of dialkyne 5.
When the Boland protocol was employed for the semi-reduction
of 5 a sluggish reaction was observed; after 24 h reaction time at
* Corresponding author. Tel.: þ47 22857450; fax: þ47 22856067; e-mail address:
t.v.hansen@farmasi.uio.no (T.V. Hansen).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.03.038

Y.M.A. Mohamed, T.V. Hansen / Tetrahedron 69 (2013) 3872e3877
3873
ambient temperature only a 5% isolated yield of alkene 2 was
obtained, together with recovered starting material. Changing the
amount of zinc, copper, or silver did not result in an improved
Z-selectivity. Activation or the use of additives has been reported
to improve the reaction rates and the Z-stereoselectivity in
zinc-mediated reductions of alkynes.7,8 Moreover, Knochel and
co-workers have reported the activation of zinc by the addition of
TMSCl in Negishi-type reactions.9 Hence, the effect of adding TMSCl
to the Boland reduction protocol was investigated. Herein, we
the modified Boland protocol was applied to other conjugated al-
kynes and the results are compiled in Table 1. When the modified
protocol was employed on alkyne 6 the Z,E,Z-substituted triene 7
was obtained in 90% yield with a 19:1 stereoisomeric ratio. Once
again, the reaction was performed at ambient temperature and
only 30 min of reaction time was required for full conversion. A
slightly higher stereoisomeric ratio (25:1) was observed when the
dialkyne alcohol 8 was reduced to the Z,E,Z-substituted alkene 9,
which was obtained in an excellent 92% yield.
Table 1
Reduction of E-conjugated alkynes
Entry
Alkyne
Product
Time (min)
Diastereomeric ratioa
Yieldb (%)
1
60
50:1
88
2
3
30
30
19:1
25:1
90
92
4
5
90
90
50:1
19:1
82
87
6
7
90
90
19:1
16:1
86
89
8
60
50:1
86
a
The stereoisomeric ratios of the alkenes were determined by HPLC analysis. Two experiments were performed. The ratio is given of the stereoisomer depicted compared to
the sum of all other isomers formed. The structures of the minor isomers were not determined.
b
The yields are of the stereoisomer depicted determined after purification by chromatography and are the average of two experiments.
report these results for the preparation of several Z,E-substituted
alkenes and Z-stilbenes.
Furthermore, short reaction time and full conversion of the
aliphatic compound 10 to the Z,E,Z-substituted alkene 11 were ob-
served; alkene 11 was obtained in 82% yield with
a 50:1
stereoisomeric ratio. Reducing the triple bond present in alcohol 12
to the Z,E,E-substituted triene alcohol 13 (87% yield, 19:1 stereoiso-
meric ratio) once again demonstrated the advantage of the addition
of TMSCl. Since the E,E-substituted allylic alcohol 12 was well toler-
ated, the reductions of bis-homopropargylic and propargylic alco-
hols 14 and 16 were attempted. These alcohols underwent smooth
reduction to their corresponding Z,E-alkenes 15 and 17 in 86 and 89%
yields, respectively. As in the previous experiments, a high degree of
stereoselectivity was observed (Table 1, entries 6 and 7). The re-
duction of the phenyl-conjugated alkyne 18 was also examined. This
reduction yielded the Z,E-substituted product 19 with an excellent
50:1 stereoisomeric ratio in 86% yield after 60 min of reaction time.
Based on the outcome of the final transformation in Table 1, several
substituted 1,2-diaryl alkynes were then employed as substrates,
given that the Z-stilbene is present in many natural products.10 These
compounds are often prepared by the stereoselective reduction of
2. Results and discussion
When 1 equiv of TMSCl was added to the zinc/copper/silver
mixture in a water/methanol solution of 5, a disappointing 30%
yield of the desired alkene 2 was obtained after 8 h reaction time at
room temperature. The desired Z,E,E,Z-isomer of 2 was formed in
a 12:1 ratio compared to all other isomers. However, adding 5 equiv
of TMSCl afforded the desired isomer of 2 in 82% isolated yield after
chromatographic purification. Full conversion of the starting ma-
terial 5 was observed after 4 h reaction time at ambient tempera-
ture. Gratifyingly, addition of 10 equiv of TMSCl resulted in full
conversion of 5 after only 1 h of reaction time at room temperature.
The isolated yield of 2 was 88% after chromatographic purification.
HPLC and 1H NMR spectroscopic analyses of the reaction mixture
showed that the formation of the Z,E,E,Z-isomer of 2 had taken
place with a stereoisomeric ratio of 50:1. Pleased with these results,

3874
Y.M.A. Mohamed, T.V. Hansen / Tetrahedron 69 (2013) 3872e3877
1,2-disubstitued alkynes.11 When our protocol was applied to the
reduction of 1,2-diphenylacetylene (20), Z-stilbene 21 was isolated in
a disappointingly low 28% yield. The corresponding E-isomer was not
detected by GLC analysis. Interestingly, when a combination of trie-
thylsilane8b and TMSCl was employed the alkyne 20 was reduced to
Z-stilbene 21 in 70% chemical yield (Scheme 2).
over-reduced product. The dialkyne 31 was also reduced to the Z,Z-
diol 32 in 60% yield. Only one of the four possible isomers of the
product was observed by GLC analysis of the reaction mixture. The
results from the semi-reductions of 1,2-diaryl alkynes have been
compiled in Table 2.
At this stage, the effect of adding either TMSCl or triethylsi-
lane is not established. Many methods have been reported for
the purification15 or activation of zinc,4c including the addition
of TMSCl.9 The very high selectivities observed after short re-
action times render support for the activation of zinc. The Boland
method has been reported to work best at 50 ꢀC in mixtures of
water and methanol with prolonged reaction times.4c,5 The
trans-reduction of alkynes by hydrosilylationeprotodesilylation
has been reported.16 In our protocol HCl and trimethylsilane are
Scheme 2. Reduction of 1,2-diphenylacetylene (20).
Table 2
Reduction of 1,2-diaryl alkynes and alkyne substituted thiophenes
Entry
Alkyne
Product
Time (h)
24
Diastereomeric ratioa
Yieldb (%)
1
>98
70
2
3
24
18
>98
>98
70
72
+
4
15
>98
54
30
5
6
15
15
>98
>98
70
60
a
The stereoisomeric ratios of the stilbenes were determined by GLC analysis. Two experiments were performed. The ratio is given for the Z-isomer.
The yields are of the Z-isomer determined after purification by chromatography and are the average of two experiments.
b
Other 1,2-disubstituted alkynes were then used as substrates.
produced of which the latter is a known reducing agent. Silanes
have been employed in the reduction of alkynes for the prepa-
ration of Z-silylalkenes; after protodesilylation the correspond-
ing alkenes as stereoisomeric mixtures are often formed.17 The
less active 1,2-diaryl alkynes required the addition of a large
excess of both TMSCl and triethylsilane for the preparation of
Z-stilbenes. These alkynes have been reported to react sluggishly
in the Boland reduction method5 and also in the presence of
activated zinc.18 Moreover, adding triethylsilane alone yielded
no conversion of 1,2-diphenylacetylene (20). Hence, the effect
of adding TMSCl is most likely due to the activation of zinc.
We will investigate the content of the zinc-mixture, the origin
of the selectivity as well as the mechanistic details of our
modified Boland protocol. These results will be reported in due
time.
The carbonechlorine bond in compound 22 was not affected and
the product 23 was obtained as one single isomer in 70% yield. The
carbonyl group in alkyne 24 was not reduced and the Z-stilbene 25
was obtained in 72% yield. On the other hand, the nitro-group was
affected under our conditions and a mixture of compounds 27 and
28 was obtained from alkyne 26. Thiophenes conjugated with al-
kenes are also present in some natural products.12 de Souse and
Taylor have investigated the Boland reduction method for the re-
duction of thiophene-substituted alkynes.13 Alkynes substituted in
the 2-position of thiophenes are not easily reduced to Z-alkenes
since isomeric mixtures of alkenes are often obtained together with
over-reduced products.13,14 Gratifyingly, the reduction of the thio-
phenyl substituted alkyne 29 afforded the Z-substituted alkene 30
in 70% isolated yield without any detection of the E-isomer or the

Y.M.A. Mohamed, T.V. Hansen / Tetrahedron 69 (2013) 3872e3877
3875
3. Conclusions
1260 cmꢁ1
.
1H NMR (300 MHz, CDCl3):
d
¼6.55e6.29 (m, 2H),
6.17e5.91 (m, 2H), 5.41 (ddt, J¼18.7, 10.7, 7.7 Hz, 2H), 3.64 (s, 3H),
2.31 (t, J¼7.5 Hz, 2H), 2.19 (dqd, J¼16.6, 7.5, 1.5 Hz, 4H), 1.71 (pent,
J¼7.5 Hz, 2H), 1.44e1.17 (m, 6H), 0.85 (t, J¼6.8 Hz, 3H). 13C NMR
The results of our modifications to the Boland protocol for
Z-selective reductions of alkynes have been demonstrated for the
preparation of conjugated Z-alkenes and Z-stilbenes. Short reaction
times at ambient temperature, good yields, and high Z-selectivity
are attractive features of the reported protocol.
(75 MHz, CDCl3):
d
¼174.4, 133.5, 131.1, 130.3, 128.9, 128.9, 127.8,
51.9, 33.8, 31.9, 29.8, 28.3, 27.5, 25.2, 22.9, 14.5. HRMS (EI): Mþ,
found 250.1929. C16H26O2 requires 250.1933. Purity (HPLC) 95%.
The spectral data were in accord with literature.19
4. Experimental section
4.1. General
4.3.3. (4Z,6E,8Z)-Tetradeca-4,6,8-trien-1-ol (9). The product was
obtained as colorless oil (77 mg, 92%). Rf (hexane/EtOAc 8:2) 0.52. IR
(film):
n
¼3413, 2932, 2871, 1719, 1457, 1260 cmꢁ1
.
1H NMR
All reagents and solvents were used as purchased without fur-
ther purification. Melting points were determined in open capillary
tubes and are uncorrected. Analytical TLC was performed on silica
gel 60 F254 Aluminum sheets (Merck). Flash column chromatogra-
(300 MHz, CDCl3):
d
¼6.45 (ddp, J¼15.5, 10.9, 1.6 Hz, 2H), 6.06
(dq, J¼13.7, 6.7 Hz, 2H), 5.43 (dt, J¼10.7, 7.7 Hz, 2H), 3.65
(t, J¼6.4 Hz, 2H), 2.24 (qd, J¼7.5, 1.6 Hz, 2H), 1.75 (dd, J¼6.7, 1.6 Hz,
3H),1.64 (dt, J¼13.7, 6.7 Hz, 2H). 13C NMR (75 MHz, CDCl3):
¼133.5,
d
phy was performed on silica gel 60 (40e60
m
m, Fluka). IR spectra
131.6, 129.8, 129.0, 128.8, 127.8, 62.7, 32.8, 31.8, 29.7, 28.2, 24.5, 22.9,
14.4. HRMS (EI): Mþ, found 208.1824. C14H24O requires 208.1827.
Purity (HPLC) 99%.
(4000e600 cmꢁ1) were obtained on a PerkineElmer Spectrum BX
series FTIR spectrophotometer. NMR spectra were recorded on
a Bruker Avance DPX spectrometer at 300 or at 400 MHz for 1H
NMR, and 75 or 101 MHz for 13C NMR, respectively. Coupling
constants (J) are reported in hertz, and chemical shifts are reported
4.3.4. (6Z,8E,10Z)-Hexadeca-6,8,10-triene (11).20 The product was
obtained as colorless oil (72 mg, 82%). Rf (hexane/EtOAc, 8:2) 0.62.
in parts per million (ppm) (
d
) relative to CDCl3 (7.24 ppm for 1H and
IR (film):
(300 MHz, CDCl3):
n
¼3413, 2932, 2871, 1719, 1457, 1260 cmꢁ1
.
1H NMR
77.40 ppm for 13C) and DMSO-d6 (2.49 ppm for 1H and 39.5 ppm for
13C). High resolution mass spectra were performed with VG Prospec
mass spectrometer. The GLC analyses were performed on a Shi-
madzu GC system with an LC-6A column, coupled with refractive
index detector (RID-10A). The HPLC analyses were performed on
d
¼6.52e6.34 (m, 2H), 6.14e5.88 (m, 2H), 5.42
(dt, J¼10.7, 7.6 Hz, 2H), 2.17 (qd, J¼7.6, 1.6 Hz, 4H), 1.48e1.16 (m,
12H), 0.86 (t, J¼6.8 Hz, 6H). 13C NMR (75 MHz, CDCl3):
¼133.1,
d
129.1, 128.3, 31.9, 29.8, 28.3, 22.9, 14.4. HRMS (EI): Mþ, found
220.2190. C16H28 requires 220.2191. Purity (HPLC) 99%. The spectral
data were in accord with literature.20
a Agilent Technologies 1200 Series with an Eclipse XD 8-C18 5 mm,
4.6ꢂ150 mm column.
4.3.5. (2E,4E,6Z)-Dodeca-2,4,6-trien-1-ol (13). The product was
obtained as colorless oil (62 mg, 87% yield). Rf (hexane/EtOAc, 4:1)
4.2. General procedures
0.39. IR (film):
n
¼3447, 3060, 2993, 2963, 2930, 2859, 1653, 1458,
4.2.1. Preparation of Zn(Cu/Ag). The Zn(Cu/Ag) mixture was pre-
1265 cmꢁ1. 1H NMR (300 MHz, CDCl3):
d
¼6.48 (dd, J¼14.7, 11.3 Hz,
pared as described by Boland et al.5
1H), 6.36e6.24 (m, 1H), 6.17 (dd, J¼14.7, 10.7 Hz, 1H), 5.99
(t, J¼10.7 Hz, 1H), 5.81 (dt, J¼14.9, 6.0 Hz, 1H), 5.46 (dt, J¼10.8,
7.7 Hz, 1H), 4.18 (d, J¼5.9 Hz, 2H), 2.16 (qd, J¼7.3, 1.5 Hz, 2H),
1.43e1.22 (m, 6H), 0.86 (t, J¼6.8 Hz, 3H). 13C NMR (75 MHz, CDCl3):
4.3. General procedure for the reduction of conjugated
alkynes
d
¼133.9, 132.3, 132.0, 131.8, 129.2, 128.7, 63.9, 31.9, 29.7, 28.3, 22.9,
To a suspension of the Zn(Cu/Ag) mixture (2.0 g) in MeOH/water
(1:1, 6 mL), the substrate (0.4 mmol, 1 equiv) was added followed
by the addition of TMSCl (0.5 mL, 4.0 mmol, 10 equiv). The reaction
was stirred at ambient temperature for the specified time for each
reaction. Et2O (10 mL) was added, the reaction mixture was filtered
through a short plug of silica gel, and eluted with Et2O (30 mL). The
combined organic phases were washed with water (10 mL), the
organic layer was separated, dried (MgSO4), and then removal of
the solvent afforded a residue that was purified by column chro-
matography (SiO2).
14.4. HRMS (EI): Mþ, found 180.1509. C12H20O requires 180.1514.
Purity (HPLC) 98%.
4.3.6. (4Z,6E)-Octa-4,6-dien-1-ol (15).21 The product was obtained
as colorless oil (43 mg, 86% yield). Rf (hexane/EtOAc, 4:1) 0.30. IR
(film):
n
¼3420, 2982, 2926, 1653, 1276 cmꢁ1
.
1H NMR (300 MHz,
CDCl3):
d
¼6.32 (ddt, J¼15.1, 11.0, 1.5 Hz, 1H), 5.96 (t, J¼10.9 Hz, 1H),
5.67 (dq, J¼13.7, 6.7 Hz, 1H), 5.35e5.18 (m, 1H), 3.65 (t, J¼6.4 Hz,
2H), 2.24 (qd, J¼7.5, 1.5 Hz, 2H), 1.75 (dd, J¼6.4, 1.5 Hz, 3H), 1.64
(pent, J¼6.7 Hz, 2H). 13C NMR (75 MHz, CDCl3):
¼130.1, 129.7,
d
128.9, 127.1, 62.9, 32.9, 24.4, 18.7. HRMS (EI): Mþ, found 126.1041.
C8H14O requires 126.1045. Purity (HPLC) 98%. The spectral data
were in accord with literature.21
4.3.1. Methyl
(5Z,8Z,10E,12E,14Z)-eicosapentaenoate
(2).2a The
product was obtained as colorless oil (110 mg, 88% yield). Rf (hex-
ane/EtOAc 9:1) 0.46. IR (film):
n
¼2983, 2871, 1735, 1458, 1265 cmꢁ1
.
1H NMR (300 MHz, CDCl3):
d
¼6.47 (dd, J¼13.4, 10.8 Hz, 2H),
4.3.7. (2Z,4E)-Hexa-2,4-dien-1-ol (17).22 The product was ob-
tained as colorless oil (35 mg, 89% yield). Rf (hexane/EtOAc, 4:1)
6.32e6.22 (m, 2H), 6.10e5.95 (m, 2H), 5.52e5.26 (m, 4H), 3.65
(s, 3H), 2.91 (t, J¼6.2 Hz, 2H), 2.31 (t, J¼7.5 Hz, 2H), 2.23e2.03
(m, 4H), 1.69 (pent, J¼7.5 Hz, 2H), 1.45e1.17 (m, 6H), 0.87
0.25. IR (film):
DMSO-d6):
n
¼3368, 2859, 1653 cmꢁ1
.
1H NMR (400 MHz,
d
¼6.32 (ddt, J¼14.6, 11.0, 1.6 Hz, 1H), 5.92 (t, J¼11.0 Hz,
(t, J¼6.8 Hz, 3H). 13C NMR (75 MHz, CDCl3):
d¼174.4, 133.8, 133.7,
1H), 5.69 (dq, J¼13.8, 6.7 Hz, 1H), 5.36 (dt, J¼11.9, 6.6 Hz, 1H), 4.62
132.9, 130.5, 129.7, 129.3, 129.0, 128.9, 128.8, 128.0, 51.9, 33.8, 31.9,
29.7, 28.3, 26.9, 26.6, 25.1, 22.9, 14.4. HRMS (EI): found 316.2402,
C21H32O2 requires 316.2412. Purity (HPLC) 99%. The spectral data
were in accord with literature.2a
(t, J¼5.4 Hz, 1H), 4.09 (t, J¼5.4 Hz, 2H), 1.74 (dd, J¼6.7, 1.6 Hz, 3H).
13C NMR (101 MHz, DMSO-d6):
d
¼130.0, 129.5, 128.4, 126.9, 57.1,
17.9. HRMS (EI): Mþ, found 98.0728. C6H10O requires 98.0732.
Purity (HPLC) 97%. The spectral data were in accord with
literature.22
4.3.2. (5Z,7E,9Z)-Methyl pentadeca-5,7,9-trienoate (7).19 The prod-
uct was obtained as colorless oil (88 mg, 92% yield). Rf (hexane/
4.3.8. (1Z,3E)-Penta-1,3-dien-1-ylbenzene (19).23 The product was
obtained as colorless oil (49 mg, 86% yield). Rf (hexane/EtOAc, 4:1)
EtOAc 9:1) 0.53. IR (film):
n
¼2955, 2933, 2870, 1734, 1653, 1457,

3876
Y.M.A. Mohamed, T.V. Hansen / Tetrahedron 69 (2013) 3872e3877
0.56. IR (film):
n
¼3034, 2982, 2926, 1685, 1450, 1275, 1260 cmꢁ1
.
193.0891. Purity (GLC) >98%. The spectral data were in accord with
1H NMR (300 MHz, CDCl3):
d
¼7.38e7.25 (m, 5H), 6.66 (ddd, J¼15.1,
literature.26
10.6, 1.8 Hz, 1H), 6.32 (t, J¼11.4 Hz, 1H), 6.23 (d, J¼11.3 Hz, 1H), 5.92
(dq, J¼13.9, 6.8 Hz, 1H), 1.84 (dd, J¼6.7, 1.6 Hz, 3H). 13C NMR
4.3.15. (Z)-2-(Hept-1-en-1-yl)thiophene (30).13 The product was
obtained as colorless oil (50 mg, 70% yield). Rf (hexane/EtOAc, 98:2)
(75 MHz, CDCl3):
d
¼138.2, 132.9, 130.9, 129.3, 128.6, 128.3, 127.7,
127.0, 18.8. HRMS (EI): Mþ, found 1044.0931. C11H12 requires
144.0939. Purity (HPLC) 99%. The spectral data were in accord with
literature.23
0.58. IR (film):
n
¼3105, 2956, 2929, 2859, 1714, 1676, 1464, 1416,
1233 cmꢁ1 1H NMR (300 MHz, CDCl3):
.
d
¼7.27 (d, J¼6.2 Hz, 1H),
7.07e6.95 (m, 2H), 6.56 (d, J¼11.5 Hz, 1H), 5.61 (dt, J¼11.5, 7.2 Hz,
1H), 2.43 (qd, J¼7.3, 1.8 Hz, 2H), 1.62e1.47 (m, 2H), 1.39 (dq, J¼7.3,
3.4 Hz, 4H), 0.95 (t, J¼8.6 Hz, 3H). 13C NMR (75 MHz, CDCl3):
4.3.9. Reduction of diaryl substituted alkynes. To a suspension of
the Zn(Cu/Ag)-mixture (2.0 g) in MeOH/water (1:1, 6 mL), the al-
kyne (0.4 mmol, 1 equiv) in THF (0.3 mL) was added followed by
the addition of Et3SiH (0.8 mmol, 2 equiv) and TMSCl (0.5 mL,
4.0 mmol, 10 equiv). The reaction mixture was stirred for the
specified time for each reaction. Et2O (10 mL) was added, and the
reaction mixture was filtered through a short plug of silica gel and
eluted with Et2O (30 mL). The combined organic phases were
washed with water (10 mL). The organic layer was separated and
dried (MgSO4). The solvent was evaporated under reduced pres-
sure and the residue was purified by column chromatography
(SiO2).
d
¼141.3, 131.8, 127.4, 127.1, 125.3, 122.0, 32.1, 29.7, 29.6, 22.9, 14.5.
HRMS (EI): Mþ, found 180.0968. C11H16S requires 180.0973. Purity
(GLC) >98%. The spectral data were in accord with literature.13
4.3.16. (Z)-3-(5-((Z)-Hept-1-en-1-yl)thiophen-2-yl)prop-2-en-1-ol
(32). The product was obtained as colorless oil (57 mg, 60% yield).
Rf (hexane/EtOAc, 4:1) 0.54. IR (film):
n
¼3342, 3008, 2926, 2852,
1653, 1275, 1261 cmꢁ1. 1H NMR (300 MHz, CDCl3):
d
¼6.84 (s, 2H),
6.53 (dt, J¼11.7, 1.9 Hz, 1H), 6.45 (dt, J¼11.5, 1.9 Hz, 1H), 5.73 (dt,
J¼11.7, 6.2 Hz, 1H), 5.58 (dt, J¼11.5, 7.3 Hz, 1H), 4.56 (td, J¼5.9,
1.8 Hz, 2H), 2.39 (qd, J¼7.3, 1.9 Hz, 2H), 1.54e1.52 (m, 2H), 1.36e1.32
(m, 4H), 0.89 (t, J¼6.8 Hz, 3H). 13C NMR (75 MHz, CDCl3):
¼142.3,
d
4.3.10. (Z)-1,2-Diphenylethene(21).24 The product was obtained as
139.4, 132.4, 129.6, 128.3, 127.7, 123.2, 122.0, 60.8, 32.0, 29.9, 29.6,
22.9, 14.5. HRMS (EI): Mþ, found 236.1230. C14H20OS requires
236.1235. Purity (GLC) >98%.
colorless oil (50 mg, 70% yield). Rf (hexane) 0.76. IR (film):
n
¼3080,
1601, 1497, 1178 cmꢁ1. 1H NMR (300 MHz, CDCl3):
d
¼7.32e7.15 (m,
10H), 6.63 (s, 2H). 13C NMR (75 MHz, CDCl3):
d
¼137.6, 130.6, 129.3,
128.6, 127.5. HRMS (EI): Mþ, found 180.0933. C14H12 requires
180.0939. Purity (GLC) >98%. The spectral data were in accord with
literature.24
Acknowledgements
Financial support to Y.M.A.M. from the University of Oslo (The
Quota Scheme) is gratefully acknowledged.
4.3.11. (Z)-1-Chloro-4-styrylbenzene (23).8b The product was ob-
tained as colorless oil (60 mg, 70% yield). Rf (hexane) 0.60. IR (film):
Supplementary data
n
¼3082, 3015, 3060, 1651, 1590, 1487, 1443, 1395 cmꢁ1
.
1H NMR
(300 MHz, CDCl3):
d
¼7.26e7.17 (m, 9H), 6.66 (d, J¼12.2 Hz, 1H),
Supplementary data associated with this article can be found in
the online version, at http://dx.doi.org/10.1016/j.tet.2013.03.038.
6.56 (d, J¼12.2 Hz, 1H). 13C NMR (75 MHz, CDCl3):
¼137.3, 136.0,
d
133.1, 131.4, 130.6, 129.3, 129.2, 128.8, 128.8, 127.7. HRMS (EI): Mþ,
found 214.0544. C14H11Cl requires 214.0549. Purity (GLC) >98%. The
spectral data were in accord with literature.8b
References and notes
1. (a) Brandsma, L. In Preparative Acetylenic Chemistry, 2nd ed.; Elsevier: Am-
sterdam, The Netherlands, 1988; (b) Stang, P. J.; Diederich, F.; Tykwinski, R. R. In
Acetylene Chemistry: Chemistry, Biology, and Material Science; Wiley-VCH:
Weinheim, Germany, 2005.
2. (a) Mohamed, Y. M. A.; Hansen, T. V. Tetrahedron Lett. 2011, 52, 1057e1059; (b)
Petasis, N. A.; Yang, R.; Winkler, J. W.; Zhu, M.; Uddin, J.; Bazan, N. G.; Serhan, C.
N. Tetrahedron Lett. 2012, 53, 1695e1698; (c) Francais, A.; Leyva, A.; Etxebarria-
Jardi, G.; Ley, S. V. Org. Lett. 2009, 12, 340e343; (d) Oger, C.; Balas, L.; Durand, T.;
Galano, J.-M. Chem. Rev. 2013, 113, 1313e1350.
4.3.12. (Z)-1-(4-Styrylphenyl)ethanone (25).25 The product was
obtained as colorless oil (64 mg, 72% yield). Rf (hexane/EtOAc, 9:1)
0.44. IR (film):
n
.
¼3049, 2919, 1683, 1601, 1266 cmꢁ1 1H NMR
(300 MHz, CDCl3):
d
¼7.83 (d, J¼8.4 Hz, 2H), 7.35e7.33 (m, 2H), 7.27
(d, J¼8.9 Hz, 5H), 6.75 (d, J¼12.3 Hz, 1H), 6.63 (d, J¼12.3 Hz, 1H),
2.59 (s, 3H). 13C NMR (75 MHz, CDCl3):
d
¼198.1, 142.7, 137.1, 135.9,
132.8, 129.5, 129.5, 129.2, 128.8, 128.7, 127.9, 27.0. HRMS (EI): Mþ,
found 222.1040. C16H14O requires 222.1045. Purity (GLC) >98%. The
spectral data were in accord with literature.25
3. Selected examples of Z-selective semi-reduction of alkynes: (a) Lindlar, H. Helv.
Chim. Acta 1952, 35, 446e450; (b) Brown, C. A.; Ahuja, V. K. J. Chem. Soc., Chem.
Commun. 1973, 553e554; (c) Molander, G. A.; Ellis, N. M. J. Org. Chem. 2008, 73,
6841e6844; (d) Chou, W.-N.; Clark, D. L.; White, J. B. Tetrahedron Lett. 1991, 32,
299e302; (e) Rieke, R. D.; Uhm, S. J. Synthesis 1975, 452e453; (f) van Laren, M.
W.; Elsevier, C. J. Angew. Chem., Int. Ed. 1999, 38, 3715e3717; (g) Rajaram, J.;
Narula, A. P. S.; Chawla, H. P. S.; Dev, S. Tetrahedron 1983, 39, 2315e2322; (h)
Choi, J.; Yoon, N. M. Tetrahedron Lett. 1996, 37, 1057e1060; (i) Trost, B. M.;
Braslau, R. Tetrahedron Lett. 1989, 30, 4657e4660; (j) Avignon-Tropis, M.;
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Y.; Minato, T.; Fujita, T.; Chen, L.-C.; Bao, M.; Asao, N.; Chen, M.-W.; Yamamoto,
Y. J. Am. Chem. Soc. 2012, 134, 17536e17542; (l) Hauwert, P.; Maestri, G.;
Sprengers, J. W.; Catellani, M.; Elsevier, C. J. Angew. Chem., Int. Ed. 2008, 47,
3223e3226; (m) La Pierre, H. S.; Arnold, J.; Toste, F. D. Angew. Chem., Int. Ed.
2011, 50, 3900e3903; (n) Gianetti, T. L.; Tomson, N. C.; Arnold, J.; Bergman, R. G.
J. Am. Chem. Soc. 2011, 133, 14904e14907; (o) Shen, R.; Chen, T.; Zhao, Y.; Qiu, Y.;
Zhou, Y.; Yin, S.; Wang, X.; Goto, M.; Han, L.-B. J. Am. Chem. Soc. 2011, 133,
17037e17044; (p) Savoia, D.; Tagliavini, E.; Trombini, C.; Umani-Ronchi, A. J.
Org. Chem. 1981, 46, 5340e5343; (q) Brunet, J. J.; Caubere, P. J. Org. Chem. 1984,
49, 4058e4060; (r) Gruttadauria, M.; Noto, R.; Deganello, G.; Liotta, L. F. Tet-
rahedron Lett. 1999, 40, 2857e2858; (s) Gruttadauria, M.; Liotta, L. F.; Noto, R.;
Deganello, G. Tetrahedron Lett. 2001, 42, 2015e2017; (t) Alonso, F.; Osante, I.;
Yus, M. Adv. Synth. Catal. 2006, 348, 305e308; (u) Hori, J.; Murata, K.; Sugai, T.;
Shinohara, H.; Noyori, R.; Arai, N.; Kurono, N.; Ohkuma, T. Adv. Synth. Catal.
2009, 351, 3143e3149; (v) Venkatesan, R.; Prechtl, M. H. G.; Scholten, J. D.;
Pezzi, R. P.; Machado, G.; Dupont, J. J. Mater. Chem. 2011, 21, 3030e3036; (w)
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4.3.13. (Z)-4-Styrylaniline (27).26 The product was obtained as
colorless oil (42 mg, 54% yield). Rf (hexane/EtOAc, 4:1) 0.32. IR
(film):
(300 MHz, CDCl3):
n
¼3384, 3004, 1617, 1516, 1275, 1260 cmꢁ1
.
1H NMR
d
¼7.34e7.23 (m, 5H), 7.09 (d, J¼3.0 Hz, 2H), 6.56
(d, J¼3.0 Hz, 2H), 6.49 (d, J¼5.3 Hz, 2H), 3.68 (s, br, 2H). 13C NMR
(75 MHz, CDCl3):
d
¼145.9, 138.4, 130.6, 130.5, 129.2, 128.6, 128.0,
127.9, 127.1, 115.1. HRMS (EI): Mþ, found 195.1044. C14H13N requires
195.1048. Purity (GLC) >98%. The spectral data were in accord with
literature.26
4.3.14. 4-(Phenylethynyl)aniline (28).26 The product was obtained
as yellow solid (23 mg, 30% yield) mp 122e124 ꢀC. Rf (hexane/
EtOAc, 4:1) 0.44. IR (film):
n
¼3380, 3201, 3030, 2212, 1617, 1592,
1292 cmꢁ1
.
1H NMR (300 MHz, CDCl3):
d
¼7.50e7.56 (m, 2H),
7.42e7.36 (m, 5H), 6.56 (d, J¼8.6 Hz, 2H), 3.81 (s, br, 2H). 13C NMR
(75 MHz, CDCl3):
d
¼147.2, 133.4, 131.8, 128.8, 128.2, 124.4, 115.2,
112.9, 90.7, 87.9. HRMS (EI): Mþ, found 193.0887. C14H11N requires

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