A facile regio- and stereocontrolled synthesis of (Z)-1,3-enylnylselenides via cross coupling of (E)-α-iodovinylselenides with terminal alkynes

Article abstract of DOI:10.1081/SCC-120001521

(Z)-1,3-Enylnylselenides were conveniently obtained under mild condition via the cross coupling of the corresponding (E)-α-iodovinylselenides with terminal alkynes in the presence of Pd(PPh₃)₄ and CuBr.

Full text of DOI:10.1081/SCC-120001521

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A FACILE REGIO- AND STEREOCONTROLLED
SYNTHESIS OF (Z)-1,3-ENYLNYLSELENIDES VIA CROSS
COUPLING OF (E)-α-IODOVINYLSELENIDES WITH
TERMINAL ALKYNES
Ping Zhong & Nanping Huang a
a Department of Chemistry, Wenzhou Teachers College , Wenzhou, 325027, P. R. China
Published online: 21 Aug 2006.
To cite this article: Ping Zhong & Nanping Huang (2002) A FACILE REGIO- AND STEREOCONTROLLED SYNTHESIS OF
(Z)-1,3-ENYLNYLSELENIDES VIA CROSS COUPLING OF (E)-α-IODOVINYLSELENIDES WITH TERMINAL ALKYNES, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 32:1, 139-145, DOI:
10.1081/SCC-120001521
To link to this article: http://dx.doi.org/10.1081/SCC-120001521
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SYNTHETIC COMMUNICATIONS, 32(1), 139–145 (2002)
A FACILE REGIO- AND
STEREOCONTROLLED SYNTHESIS
OF (Z )-1,3-ENYLNYLSELENIDES
VIA CROSS COUPLING OF
(E )-a-IODOVINYLSELENIDES WITH
TERMINAL ALKYNES
Ping Zhong* and Nanping Huang
Department of Chemistry, Wenzhou Teachers College,
Wenzhou 325027, P. R. China
ABSTRACT
(Z )-1,3-Enylnylselenides were conveniently obtained under
mild condition via the cross coupling of the corresponding
(E )-a-iodovinylselenides with terminal alkynes in the presence
of Pd(PPh3)4 and CuBr.
The conjugated enynes are of great in organic synthesis,1,2 because
they are incorporated in a number of natural products and can be readily
converted in a stereospecific manner into the corresponding diene system.3,4
A number of methods for the preparation of conjugated enynes have been
previously reported. The synthesis of enynes has been performed using
coupling of halloalkynes with vinyl metals like as vinylboron,5 vinylcopper,6
vinylzinc,7 vinylaluminum,8 vinylaluminum reagents9 or vinylzirconium.10
*Corresponding author.
139
Copyright & 2002 by Marcel Dekker, Inc.
www.dekker.com

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ZHONG AND HUANG
The synthesis of enynes has also been performed using coupling of vinylic
iodides with terminal alkynes.11
Recently, it has become popular that syn-addition of Schwarte’s
reagent onto a alkyne followed by treatment with electrophiles provides a
functionalized alkene with a high level of stereochemical purity.12 We had
tried to synthesize (Z )-1,3-enylnylselenides via coupling of (E )-selanyl-
vinylzirconium with alkynyl halides like phenylethynyl iodide, but failed
to do it. It was reported that the cross-couple of (E )-a-selanylvinyl-
zirconium with alkynyliodonium tosylates afforded (Z )-1,3-enylnylsele-
nides,13 but the alkynyliodonium tosylates were not easily available.
Herein we report the stereoselective formation of selanyl-substituted
1,3-enynes via a new carbon–carbon bond-forming reaction, involving the
coupling of (E )-a-iodovinylselenides with terminal alkynes in the presence
of Pd(PPh3)4 and CuBr.
Treatment of terminal alkynes 1 with butyllithium in THF at 0ꢀC gave
lithium alkynylselenolate anions 2. Treatment of 2 with Cp2Zr(H)Cl14
in THF at room temperature afforded the a-zirconated vinylselenolate
intermediates 3,15 which by treatment with an alkyl halide afforded the
a-zirconated vinyl alkylselenide intermediates 4, 4 reacted with iodine at
room temperature to afford (E )-a-iodovinylselenides 5. In one pot reaction,
the crude iodides 5 were treated directly with terminal alkynes under Pd–Cu
catalysis to accomplish coupling reactions, work up and chromatography of
the concentrated reaction mixtures on silica gel afforded the pure
(Z )-1,3-enynylselenides 6 in good overall yields (see Table and Scheme 1).
Scheme 1.

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141
Table 1. Synthesis of (Z )-1,3-Enylylselenides 6a–ia
1
Product
RR
R2
Yield (%)b
6a
6b
6c
6d
6e
6f
Ph
Ph
Ph
Ph
n-C4H9
Me
Et
n-C4H9
n-C4H9
Et
Ph
CH3OCH2
CH3OCH2
n-C4H9
Ph
54
50
45
48
45
46
51
CH3OCH2
CH3OCH2
n-C4H9
Ph
Ph
6g
Et
1
aThe products were identified by MS, H NMRand IRspectroscopy.
bIsolated yield.
All the compounds 6a, 6b,13 6c,13 6d, 6e, 6f13 and 6g13 were fully
characterized by NMRspectroscopy. The configuration of selenoenyne 6a
could be confirmed from compound 7 which was obtained by treatment of
6a with n-butyllithium in THF followed by hydrolysis; the reaction occurs
stereoselectively (Scheme 2).16,17 Particularly diagnostic for the stereo-
chemistry of 6 was the coupling constant between the vicinal protons Ha
and Hb which show a typical value of JHH of 16 Hz which is consistent with
an E configuration. Therefore, we could confirm that the 1,3-enynylselenides
6 have Z configuration.
Scheme 2.
(Z )-1,3-enynylselenides 6 are important useful synthetic intermediates
and are effective precursors for preparation of conjugated enynes. For ex-
ample, the coupling of (Z )-1,3-enynylselenide 6a with PhZrBr at room
temperature in the presence of NiCl2(PPh3)2 for 3 h to give 1,3-enyne 8 in
61% yield (Scheme 3).
It was reported16 that hydrozirconation of 1-(butylseleno)-2-alkynes
resulted in a mixture of the a-zirconated vinyl selenide and b-zirconated

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ZHONG AND HUANG
Scheme 3.
vinyl selenide. Hydrozirconation of Lithium alkynylselenolate anions, how-
ever, resulted in the a-zirconated vinylselenolate intermediates 3. In this way
a plausible mechanism to explain the exclusive formation of the a-zirco-
zirconated vinylselenolate intermediates 3, and the necessity of only 1.0
equiv. of Schwartz’s reagent, is based on the postulated formation of a
cyclic five-membered intermediate 9 (Scheme 4).
Scheme 4.
In conclusion, the hydrozirconation/coupling strategy provides a
direct route to (Z )-1,3-enynylselenides from terminal alkynes. The method
has some attractive advantages such as readily available starting materials,
mild reaction conditions, simple procedure (one pot reaction), lower reac-
tion time and high regio- and stereoselectivity.
EXPERIMENTAL
1H NMRspectra were recorded on a Bruker AC-300 spectrometer
with TMS as internal standard. Mass spectra were obtained on a
Finnigan 4021 mass spectrometer. IRspectra were taken on a Shimadzu
IR400 spectra meter. All reactions were carried out in pre-dried glassware
(140ꢀC, 4h) and cooled under a stream of dry nitrogen. All solvents were
dried, deoxygenated and redistilled before use.

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143
General Procedure for the Synthesis of 6a–g
To a solution of the terminal alkyne 1 (2.0 mmol) in THF (8 ml) under
a nitrogen atmosphere was added butyllithium (2.0 mmol, 2 ml, 1.0 M in
hexane) at 0ꢀC, and the solution was stirred for 15 min. The mixture was
allowed to reach room temperature, and elemental selenium (0.158 g,
2.0 mmol) was added. After total disappearance of selenium, the solid
Cp2Zr(H)Cl (2 mmol) was added rapidly. The resulting mixture was stirred
for 30 min. The alkyl halide (2.0 mmol) was added, and the reaction mixture
was stirred at room temperature for an additional 1 h. The resulting solution
was cooled to 0ꢀC and I2 (2 mmol) was added, than the mixture was stirred
at room temperature for 1 h. The solvent was removed under reduced
pressure. To a mixture of this crude material in pyrrolidine (5 ml) were
added successively Pd(PPh3)4 (0.1 mmol), 1-alkyne (4 mmol) and CuBr
(0.2 mmol). The reaction was stirred at room temperature and monitored
by TLC analysis until complete consumption of the unsaturated vinyl iodide
5 before to be treated with a saturated aqueous solution of ammonium
chloride and extracted with Et2O. The organic extract was dried over
MgSO4 and the solvent was removed in vacuum. The residue was purified
by preparative TLC on silica gel and eluted with light petroleum.
(Z )-1,4-diphenyl-2-(butylselanyl)but-1-en-3-yne 6a, a pale yellow oil.
(Found: C, 70.52; H, 5.90. Calc. for C20H20Se: C, 70.79; H, 5.94); nmax
(film)/cmꢁ1: 3080, 2200, 1610, 1480, 1015, 750; dH (300 MHz; CDCl3):
7.42–7.02 (m, 11H, Ph, HC¼), 1.50–0.65 (m, 9H, Bu); m/z 340 (Mþ).
(Z )-5-methoxy-1-phenyl-2-(methylselanyl)pent-1-en-3-yen 6b, a pale
yellow oil. (Found: C, 58.68; H, 5.39. Calc. for C13H14OSe: C, 58.87; H,
5.32.); nmax (film)/cmꢁ1: 3085, 2205, 1590, 1482, 1020, 810; dH (300 MHz;
CDCl3): 7.50–7.10 (m, 6H, Ph, HC¼), 4.10 (s, 2H, CH2O), 3.28 (s, 3H,
OCH3), 2.15 (s, 3H, CH3); m/z 266 (Mþ).
(Z )-5-methoxy-1-phenyl-2-(ethylselanyl)pent-1-en-3-yne 6c,
a
pale
yellow oil (Found: C, 60.43; H, 5.71. Calc. for C14H16OSe: C, 60.22; H,
5.78); nmax (film)/cmꢁ1: 3080, 3020, 2340, 1490, 1440, 1075; dH (300 MHz;
CDCl3): 7.45–7.00 (m, 6H, Ph, HC¼), 4.10 (s, 2H, CH2O), 3.25 (s, 3H,
OCH3), 2.65 (q. 2H, SeCH2), 1.50 (t, 3H, CH3); m/z 280 (Mþ).
(Z )-1-phenyl-2-(butylselanyl)oct-1-en-3-yne 6d, apale yellow oil(Found:
C, 67.52; H, 7.52. Calc. for C18H24Se: C, 67.70; H, 7.57); nmax (film)/cmꢁ1
:
3080, 3010, 2360, 1590, 1490, 1140, 1075, 1030; dH (300 MHz; CDCl3):
7.50–7.05 (m, 6H, Ph, HC¼), 2.20–0.70 (m, 18H, C4H9); m/z 320 (Mþ).
(Z )-5-methoxy-1-phenyl-3-(butylselanyl)-pent-3-en-1-yne 6e,
a pale
yellow oil. (Found: C, 62.68; H, 6.50. Calc. for C16H20OSe: C, 62.54; H,
6.56); nmax (film)/cmꢁ1: 3085, 2210, 1610, 1580, 1015, 810; dH (300 MHz;
CDCl3): 7.45–7.25 (m, 5H, Ph), 5.95 (t, J ¼ 6 Hz, 1H, HC¼), 3.85

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ZHONG AND HUANG
(d, J ¼ 6.5 Hz, 2H, OCH2), 3.26 (s, 3H, CH3O), 2.55 (q. 2H, SeCH2), 1.55 (t,
3H, CH3); m/z 308 (Mþ).
(Z )-5-methoxy-1-phenyl-3-(ethylselanyl)-pent-3-en-1-yne 6f,
a pale
yellow oil. (Found: C, 60.48; H, 5.74. Calc. for C14H16OSn: C, 60.22; H,
5.78); nmax (film)/cmꢁ1: 3085, 2210, 1610, 1580, 1015, 810; dH (300 MHz;
CDCl3): 7.45–7.25 (m, 5H, Ph), 6.10 (t, J ¼ 6.5 Hz, 1H, HC¼), 3.85 (d,
J ¼ 6.5 Hz, 2H, OCH2), 3.26 (s, 3H, CH3O), 2.55 (q. 2H, SeCH2), 1.55 (t,
3H, CH3); m/z 280 (Mþ).
(Z )-1-phenyl-3-(ethylselanyl)oct-3-en-1-yne 6g, a pale yellow oil.
(Found: C, 65.62; H, 6.98. Calc. for C16H20Se: C, 65.97; H, 6.92); nmax
(film)/cmꢁ1: 3080, 3010, 2360, 1590, 1490, 1440, 1075, 1030; dH (300 MHz;
CDCl3): 7.65–7.15 (m, 5H, Ph), 6.10 (t, J ¼ 6.5 Hz, 1H, HC¼), 2.52 (q, 2H,
SeCH2), 1.98–2.25 (m, 2H), 1.48 (t, 3H, CH3), 1.15–1.50 (m, 4H), 0.80 (t,
3H, CH3); m/z 292 (Mþ).
The Synthesis of (E )-1,4-Diphenylbut-1-en-3-yne 7
1 ml BuLi (1.1 M hexane solution) was added to a THF (5.0 ml)
solution of 6a (1.0 mmol) at ꢁ 78ꢀC. After stirring for 30 min, the mixture
was hydrolyzed with saturated aq. NH4Cl and extracted with CH2Cl2
(2 ꢂ 10 ml). The organic extract was dried with MgSO4, filtered and con-
centrated in vacuum. The residue was purified by column chromatography
over silica gel, eluting with petroleum to give (E )-enyne 7. (yield: 86%)
as a pale yellow oil;18 nmax (film)/cmꢁ1: 3010, 2190, 1590, 1480, 1240, 950,
800; dH (300 MHz; CDCl3) 7.50–7.00 (m, 11H, Ph, HC ¼), 6.43 (d, 1H,
J ¼ 16, ¼CH ).
The Synthesis of (E )-1,2,4-Triphenylbut-1-en-3-yen 8
(Z )-1,3-enynylselenide 6a (0.5 mmol) and PhZnBr (0.5 mmol) were
dissolved in THF (5 ml) under nitrogen at room temperature.
NiCl2(PPh3)2 (0.05 mol) (0.4 mmol) was then added. The mixture was stirred
at room temperature and monitored by TLC for the disappearance of 6a.
The reaction mixture was diluted with CH2Cl2 (15 ml) and washed with
saturated aq. NH4Cl. The product was extracted with hexane and dried
over MgSO4, filtered and concentrated in vacuo. The residue was purified
by column chromatography on silica gel, eluting with light petroleum
to give enyne 8 (yield: 61%) as a solid, mp 49–50ꢀC (lit.19 49–50ꢀC); nmax
(film)/cmꢁ1: 3090, 2210, 1590, 1460, 740; dH (300 MHz; CDCl3): 7.75–7.05
(m, 15H, Ph), 6.95 (s, 1H, HC¼).

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(Z )-1,3-ENYLNYLSELENIDES
145
ACKNOWLEDGMENT
This work was supported by The National Nature Science Foundation
of Zhejiang Province.
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Received in the Netherlands February 28, 2001

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