First Example of Alkynyliodonium Tosylates coupling with 1,1-Bimetalloalkenes of Selenium and Zirconium

Article abstract of DOI:10.1039/a801589i

Hydrozirconation of internal acetylenic selenides afforded 1,1-bimetalloalkenes, (E)-α-selanylvinylzirconium, which can cross-couple with alkynyliodonium tosylates directly in the presence of Pd(PPh₃)₄ as the catalyst.

Full text of DOI:10.1039/a801589i

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616 J. CHEM. RESEARCH (S), 1998
J. Chem. Research (S),
1998, 616±617$
First Example of Alkynyliodonium Tosylates coupling
with 1,1-Bimetalloalkenes of Selenium and Zirconium$
Ai-Ming Sun and Xian Huang*
Department of Chemistry, Hangzhou University, Hangzhou, 310028, P.R. China
Hydrozirconation of internal acetylenic selenides afforded 1,1-bimetalloalkenes, (E)-ꢀ-selanylvinylzirconium, which can
cross-couple with alkynyliodonium tosylates directly in the presence of Pd(PPh3)4 as the catalyst.
The stereoselective synthesis of conjugated enynes is of great
importance in organic chemistry because of many natural
compounds containing their structural skeletons.1 A number
of methods for the preparation of conjugated enynes
have been previously reported, particularly transition-metal-
catalyzed processes.1 Coupling of stereode®ned alkenyl
Scheme 2
metallic compounds include vinylboron,2 vinylcopper,3,4
vinylzinc,5,6 vinylaluminium7 or vinylmagnesium reagents8
with haloalkynes. Recently, the synthesis of conjugated
at room temperature in about 2 h. The con®guration of
yields, and more importantly, the reaction can be performed
functionalized enynes have received more attention.
Although various methods for the synthesis of vinylic
selenoenyne 5a could be con®rmed from compound 6 which
was obtained by treatment of 5a with n-butyllithium in
selenides have been studied intensively,9 the synthesis of
THF followed by hydrolysis; the reaction occurs stereo-
1,3-enynylselenides has been little explored.10 In a previous
paper, we reported the coupling of diaryliodonium salts and
vinylzirconium compounds in the presence of Pd(PPh3)4,11
compared with the cross-coupling of vinylzirconium com-
pounds with arylhalides, which has the advantages of lower
reaction time and mild reaction conditions. As an extension
of our studies, herein we report the stereoselective formation
of selanyl-substituted 1,3-enynes via a new carbon±carbon
bond-forming reaction, involving the coupling of alkynyl-
iodonium tosylates 1 and (E)-a-selanylvinylic zirconium
compounds 4 in the presence of Pd(PPh3)4.
selectively (Scheme 3).13 Particularly diagnostic for the
stereochemistry 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 con®guration.
Scheme 3
Alkynyliodonium tosylates
1
are readily available
Conjugated enynylselenides are important synthetic inter-
mediates and are e€ective precursors for synthesizing conju-
gated enynes, for example, 5a at room temperature in THF
can be coupled with PhZnBr in the presence of 5 mmol%
NiCl2(PPh3)2 for 3 h to give 7 in an isolated yield of 60%
(Scheme 4).
in reasonable yields by interaction of Koser's reagent,
PhI(OH)OTs, with terminal alkynes.12 (E)-a-Selanylvinylic
zirconium compounds 4 are readily made by hydrozircona-
tion of internal acetylenic selenides 2, 3; hydrozirconation
of phenylacetylenic selenides
3
can not be directly
performed even over extended times or at a raised tempera-
ture, however, in the presence of 5% mmol Pd(PPh3)4, 3
can react with Cp2Zr(H)Cl rapidly in about 1 h at room
temperature (Scheme 1). Alkynyliodonium tosylate 1 was
added to a mixture of (E)-a-selanylvinylic zirconium com-
pound 4 and 5% mmol Pd(PPh3)4 in THF and stirred for
about 3 h, which resulted in the stereoselective synthesis of
conjugated enynylselenides 5 (Scheme 2).
Scheme 4
In summary, we have combined vinylzirconium com-
pounds and hypervalent iodine salts to synthesize conju-
gated enynes. Compared to other methods that have been
reported, this method has the advantages of mild conditions,
simple procedure and lower reaction time.
As the data in Table 1 show, this method a€ords
a variety of 1,3-enynylselenides stereoselectively in good
Experimental
1H NMR spectra were recorded on an AZ-300 MHz with TMS
as internal standard. Mass spectra were determined using a Finigan
8230 mass spectrometer. IR spectra were obtained in neat capillary
cells on a Shimadzu IR-408 instrument. The reactions were carried
out in pre-dried glassware (150 8C, 4 h) and cooled under a stream
of dry nitrogen. All solvents were dried, deoxygenated and re-
distilled before use.
General Procedure for the Synthesis of 1,3-Enynylselenides 5a±f.Ð
To a freshly prepared suspension of Cp2Zr(H)Cl (2 mmol) in THF
(15 ml) at r.t. was injected acetylenic selenides 2 (2 mmol) in
Scheme 1
THF (2 ml) [for added phenylacetylenic selenides 3, Pd(PPh3)4
(2Â 5% mmol) must be added simultaneously]. The reaction mix-
ture was stirred for ca. 30 min and turned green, then Pd(PPh3)4
(2Â 5% mmol) and alkynyliodonium tosylates 1 (2 mmol) in THF
(2 ml) were added to the solution at r.t. and stirred for 2 h. The
*To receive any correspondence.
$This is a Short Paper as de®ned in the Instructions for Authors,
Section 5.0 [see J. Chem. Research (S), 1998, Issue 1]; there is there-
fore no corresponding material in J. Chem. Research (M).

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J. CHEM. RESEARCH (S), 1998 617
Table 1 Alkynyliodonium/(E)-a-selanylvinylzirconium compound couplings
Entry
Alkynyliodonium salt
(E)-a-Selanylvinylzirconium
Enzyne
Yielda (%)
80
5a
5b
5c
5d
5e
5f
75
85
83
75
70
aIsolated yield. bIn the presence of Pd(PPh3)4.
product was washed with saturated aq. NH4Cl (10 ml) then
extracted into diethyl ether, dried with MgSO4, ®ltered and concen-
trated in vacuo. The residue was puri®ed by ¯ash chromatography
on a 3 ft 1 in column with light petroleum (bp 30±60 8C) eluent to
give 5a±f.
also supported by the Laboratory of Organometallic
Chemistry, Shanghai Institute of Organic Chemistry,
Academia Sinica.
5a: 1H NMR d 7.70±7.20 (m, 5H), 6.10 (t, J 6.6 Hz, 1H), 2.18
(s, 3H), 1.96±2.34 (m, 2H), 1.14±1.49 (m, 4H), 0.81 (t, 3H). MS:
Received, 25th February 1998; Accepted, 11th June 1998
Paper E/8/01589I
‡
m/z 278 (M ‡1) (Found: C, 64.93; H, 6.44. C15H18Se requires
C, 64.98; H, 6.54%).
5b: 1H NMR d 7.69±7.18 (m, 5H), 6.08 (t, J 6.6 Hz, 1H), 2.53
(q, 2H), 1.94±2.30 (m, 2H), 1.47 (t, 3H), 1.12±1.50 (m, 4H), 0.79
‡
(t, 3H). MS: m/z 292 (M ‡1) (Found: C, 65.65; H, 6.46. C16H20Se
References
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‡
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‡
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(1.6 M hexane solution, 1.1 mmol) was added to a THF (5.0 ml)
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with CH2Cl2 (2Â10 ml). The organic extract was dried with
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THF (3.0 ml) was added to a THF (5.0 ml) solution of selenoenyne
5a (1.0 mmol) and NiCl2(PPh3)2 (1.0Â5% mmol) at r.t. After
stirring for 3 h, the mixture was washed with saturated aq. NH4Cl.
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chromatography on a 3 ft Â1 in column with hexane as eluent
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Projects 29493800, 29772007 supported by the National
Natural Science Foundation of China. This work was
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