The cross-coupling reaction of vinylindiums generated via hydroindation of terminal alkynes with diaryliodoniums salts

Article abstract of DOI:10.1016/j.jorganchem.2005.09.031

In InCl₃-NaBH₄-MeCN system, vinylindiums generated by hydroindation of aryl terminal alkynes can undergo cross-coupling reaction with diaryliodonium salts high regio- and stereoselectively. But under the same conditions, the aliphatic terminal alkynes do not react very well.

Full text of DOI:10.1016/j.jorganchem.2005.09.031

Journal of Organometallic Chemistry 691 (2006) 247–250
www.elsevier.com/locate/jorganchem
Communication
The cross-coupling reaction of vinylindiums generated via
hydroindation of terminal alkynes with diaryliodoniums salts
*
Zhao Xue, DeYu Yang , ChunYan Wang
Department of Chemistry, Zhejiang University (Xi-xi Campus), Tianmushan Road, Hangzhou, Zhejiang 310028, PR China
Received 22 July 2005; received in revised form 10 September 2005; accepted 21 September 2005
Available online 26 October 2005
Abstract
In InCl3–NaBH4–MeCN system, vinylindiums generated by hydroindation of aryl terminal alkynes can undergo cross-coupling reac-
tion with diaryliodonium salts high regio- and stereoselectively. But under the same conditions, the aliphatic terminal alkynes do not
react very well.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Terminal alkynes; Diaryliodonium salts; (E)-disubstituted alkenes; Cross-coupling; Vinylindiums
1. Introduction
organic synthesis widely, such as dehalogenation of alkyl
halides and other radical cyclizations [11], cross-coupling
reaction of terminal alkynes with iodides [12], dimerization
of terminal alkynes [13] and reduction of alkynylphospho-
nates [14]. Our previous work showed that vinylindiums
could be easily generated in situ by hydroindation of termi-
nal alkynes in InCl3–NaBH4–MeCN system [13]. Now, this
paper wants to report a regio- and stereoselective synthesis
of (E)-disubstituted alkenes by vinylindiums coupling with
diaryliodonium salts.
The cross-coupling reaction of organometallic reagents
with organic halides has been proven to be an extremely
powerful tool in organic synthesis for the selective forma-
tion of C–C bond [1,2]. Compared to aryl halides, aryliod-
onium salts showed high electrophilicity in the reaction
with nucleophiles [3], in which the highly electron with-
drawing nature of the ArI+ moiety activated the carbon–
iodine bond towards various reactions [4]. So lots of efforts
have been devoted in the cross-coupling reaction of hyper-
valent iodine with alkenylmetallic reagents, such as alke-
nylcopper(I) [5], alkenylboron [6,8], alkenystannane [7,8]
and alkenylzirconium [9]. However, up to now, the cross-
coupling reaction of alkenylindium with diaryliodonium
salts has not been reported.
2. Results and discussion
To determine the optimum reaction conditions, we trea-
ted the di(p-methylphenyl)iodonium bromide with 4-bromo-
phenylacetylene under different conditions. After a series
of experiments, it was found that the preferable mole ratio
of InCl3, NaBH4 and alkyne was 3:10:2. With this ratio,
reaction occurred at ꢀ15 ꢁC to give a quantitative yield
of (E)-disubstituted alkene (a). The products were purified
by silica gel column chromatography. The conversion and
ratio of (E)-4-bromo-40-methylstilbene (E-Ia), (Z)-4-bro-
mo-40-methylstilbene (Z-IIa) and 1-bromo-4-[1-(4-methyl-
Since dichloroindium hydride (Cl2InH) was first gener-
ated using the transmetalation between indium trichloride
and tributylstannane at ꢀ78 ꢁC [10], it has received more
and more attentions. Recently, it has been applied in
*
Corresponding author. Tel.: +86 571 88739652; fax: +86 571
88212853.
1
E-mail address: deyu18@hotmail.com (D. Yang).
phenyl)ethenyl]benzene (IIIa) were detected by H NMR
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.09.031

248
Z. Xue et al. / Journal of Organometallic Chemistry 691 (2006) 247–250
Scheme 1.
Scheme 2.
(400 MHz) and MS. The stereochemistry in the double
ture reported in the references cited [9]. E-Ia was the major
product. The ratio of E-Ia, Z-IIa and IIIa was 96:3:1, show-
ing high regio- and stereoselectivity (Scheme 1). Further-
more, the yield of the reaction was satisfactory.
bond C@C of the isomer (E or Z) was assigned on the basis
1
of the value of the H NMR coupling constants between
the olefinic protons, which was consistent with the litera-
Table 1
The coupling reactions in InCl3-NaBH4-MeCN system
Entry
Terminal alkynes
p-BrC6H4C CH
Diaryliodonium salts
Yield (%)b
83
-
-
-
-
-
a
+
+
+
+
+
96:3:1
95:3:2
88:9:3
89:9:2
91:9:0
H
3C
I
Br
Br
Br
Br
Br
2
PhC
CH
81
86
81
78
b
c
H3
H3
C
I
2
p-CH3C6H4C
CH
CH
C
I
2
p-CH3OC6H4C
d
e
H3C
I
2
H3
C
I
2
p-BrC6H4C
CH
Ph2I+Br-
Ph 2I+Br-
Ph 2I+Br-
Ph 2I+Br-
Ph 2I+Br-
96:3:1
100:0:0
94:5:2
92:8:0
100:0:0
81
84
83
80
81
f
PhC
CH
g
h
i
p-CH3C6H4C
p-CH3OC6H C
CH
CH
4
j
p-BrC6H4C
CH
87:10:3
99:1:0
99:1:0
81:17:2
91:9:0
70
70
73
69
61
k
l
-
-
-
-
-
+
+
+
+
+
I
Br
Br
Br
Br
Br
S
S
S
S
S
2
PhC
CH
I
2
p-CH3C6H4C
CH
CH
m
n
o
I
2
p-CH3OC6H4C
I
2
I
2
p
q
r
Diaryliodoniumc
Diaryliodoniumc
Diaryliodoniumc
–
–
–
–
–
–
n-C8H17OCH2C
CH
i-BuC
CH
Determined by 1H NMR (400 MHz).
Isolated yield by terminal alkynes.
a
b
c
The diaryliodonium was Ar2I+Brꢀ (Ar: Ph, p-CH3C6H4, 2-thienyl).

Z. Xue et al. / Journal of Organometallic Chemistry 691 (2006) 247–250
249
Scheme 3.
Under the same conditions, a wide array of terminal
alkynes were tested (Scheme 2). It was found that when
R was the aryl group, such as Ph, p-CH3C6H4, p-BrC6H4
or p-CH3OC6H4, the reaction could take place smoothly
(a–d, f–i, k–n). Both the selectivity and the yield were satis-
factory. But when R was the aliphatic group, such as i-Bu,
n-C8H17OCH2 or cyclopropyl, no expected product was
obtained (p, q, r). Interestingly, when (1-cyclohexen-1-
yl)ethynyl was used as the aliphatic terminal alkyne, the
desired cross-coupling product was obtained (e, j, o). In
addition, compared with the reactions in which the 2,
20-dithienyliodonium salts participated, the yields of these
reactions in which the diphenyliodonium salts participated
(E)-disubstituted alkenes without using the expensive palla-
dium as catalyst.
3. Experimental
1H NMR spectra were obtained with a Brucker AC-P-
400 NMR spectrometer with TMS as an internal standard
and CDCl3 as solvent. Mass spectra were determined using
a Finnigan Trace DSQ mass spectrometer. The reactions
were carried out in pre-dried (150 ꢁC, 4 h) glassware and
cooled under a stream of dry nitrogen. Acetonitrile was
freshly distilled from phosphorus pentoxide before use.
Terminal alkynes [17] and diaryliodonium salts [18] were
prepared according to the literature.
1
were higher. The products were determined by H NMR
and MS, which were consistent with the previous papers
[15]. The results were listed in Table 1.
A general procedure was as follows: a mixture of InCl3
(3 mmol) and NaBH4 (10 mmol) in dry CH3CN (10 ml)
was stirred for 30 min at ꢀ15 ꢁC under nitrogen, and termi-
nal alkyne (2 mmol) was subsequently added. The mixture
was stirred another an hour, and then diaryliodonium salts
(2 mmol) was added. Followed by warming to room tem-
perature automatically and the mixture was stirred for an-
other 15 h. The reaction was quenched with 5 ml deionized
water, filtered and the filtrate was extracted with ether
(3 · 10 ml). The combined organic layer was dried over
anhydrous Na2SO4 and concentrated in vacuum. Purifica-
tion by silica gel column (100–200 mesh), using petroleum
ether (b.p. 60–90 ꢁC) as eluent could afford the correspond-
ing products.
According to all these results, a plausible mechanism
was proposed (Scheme 3) [13,14]. There is an equilibration
between two configurations of the alkenyl radical (A and
B). Furthermore, the intermediate A is more stable than
B. A precedent for such an equilibration has been reported
in the literature [16]. The radical intermediate in which aryl
ring bears an electron-withdrawing group is more stable
than the intermediate bearing an electron-releasing group.
In this paper, the conjugation of the terminal alkynes could
also make the radical intermediate (A and B) stable, but the
radical intermediate generated from the aliphatic terminal
alkynes is not stable enough to react with the diaryliodo-
nium salts in our experiments.
(E)-4-bromo-40-methylstilbene (Ia) [15a], (E)-4-methyl-
stilbene (Ib, Ih) [15b], (E)-4,40-dimethylstilbene (Ic) [15a],
(E)-4-methoxy-40-methylstilbene (Id) [15c,15d,15e], (E)-
4-bromostilbene (If) [15c,15f], (E)-stilbene (Ig) [15b], (E)-4-
methoxystilbene (Ii) [15b], (E)-1-(2-phenylethenyl)cyclohexene
In summary, InCl3–NaBH4–MeCN system was first em-
ployed in the cross-coupling reaction of vinylindiums with
diaryliodonium salts successfully. The results showed that
the presented method was efficient and simple to synthesize

250
Z. Xue et al. / Journal of Organometallic Chemistry 691 (2006) 247–250
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2 H), dH = 5.87 (t, 1 H, J = 4 Hz), dH = 6.56 (d, 1 H,
J = 16 Hz), dH = 6.61 (d, 1 H, J = 16 Hz), dH = 6.93 (m,
2H), dH = 7.10 (d, 1 H, J = 5.2 Hz); MS (EI): 190 [M+].
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