Stereospecific synthesis of (E)-alkenyl(phenyl)iodonium tetrafluoroborates via zirconium-iodane exchange

Article abstract of DOI:10.1039/a807118g

Reaction of vinylzirconium with hypervalent phenyl-iodanes leads to zirconium-iodane exchange in THF at room temperature yielding alkenyl(phenyl)iodonium salts stereoselectively with retention of configuration. Vinyl-iodonium salts are highly effective as the activated species of vinyl iodides. They reacted with RMgBr in the presence of CuI to afford (E)-1,2-disubstituted alkenes.

Full text of DOI:10.1039/a807118g

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Stereospecific synthesis of (E)-alkenyl(phenyl)iodonium
tetrafluoroborates via zirconium–iodane exchange
Xian Huang* and Xin-Hua Xu
Department of Chemistry, Hangzhou University, Hangzhou 310028, P. R. China
Received (in Cambridge) 11th September 1998, Accepted 11th September 1998
Table
1
Synthesis of (E)-alkenyl(phenyl)iodonium tetrafluoro-
borates 4a–c and (E)-1,2-disubstituted alkenes 4d–f
Reaction of vinylzirconium with hypervalent phenyl-
iodanes leads to zirconium–iodane exchange in THF at
room temperature yielding alkenyl(phenyl)iodonium salts
stereoselectively with retention of configuration. Vinyl-
iodonium salts are highly effective as the activated species
of vinyl iodides. They reacted with RMgBr in the presence
of CuI to afford (E)-1,2-disubstituted alkenes.
Product
R
RЈ
Yield (%)a
4a
4b
4c
4d
4e
4f
CH3OCH2
C4H9
Ph
CH3OCH2
C4H9
Ph
85
80
80
78
80
76
Ph
Ph
Alkenyl(phenyl)iodonium salts are a novel electrophilic vinyl-
ating agent. They can undergo nucleophilic vinylic substitution
under mild conditions. Thus they provide a useful route for the
synthesis of various kinds of substituted alkenes.1–4 The general
methods for the preparation of alkenyl(phenyl)iodinoum salts
are the reaction of vinylmetal–iodane exchange. For example,
vinylsilane reacted with iodosylbenzene in the presence of tri-
ethyloxonium tetrafluoroborate at room temperature in CH2-
Cl2.5 Vinylstannanes reacted with cyano(phenyl)iodonium tri-
flate at Ϫ40 ЊC in CH2Cl2.6 Vinylboronic acids or esters reacted
with (diacetoxyiodo)benzene in the presence of BF3ؒOEt2 at
0 ЊC in CH2Cl2.7 But the reaction of vinylzirconium–iodane
exchange has not been reported. We now report stereoselective
synthesis of (E)-alkenyl(phenyl)iodonium salts via the reaction
of vinylzirconium–iodane exchange and their application in the
synthesis of (E)-1,2-disubstituted alkenes.
m-CH3C6H4
a Isolated yield.
To our knowledge, the reaction of vinyliodonium salts with
RMgBr has not been reported. Thus we investigated the reac-
tion and found it affords the (E)-1,2-disubstituted olefins
in good yield (Scheme 2) in the presence of CuI at 0 ЊC in
THF.
R
H
H
R
H
H
CuI
+
R′MgBr
THF, 0 °C
I(Ph)OAc
R′
3
4d–f
Hydrozirconation of alk-1-ynes in THF at room temperature
yields the (E)-alkenylzirconium compounds stereoselectively.
We investigated the reactivity of (E)-alkenylzirconium com-
pounds with (diacetoxyiodo)benzene and found that in the
absence of catalyst the reaction occurs in THF at room tem-
perature. This is due to the vinylzirconium compounds being
more active than vinylsilanes and vinylboronic compounds.
After ligand exchange with aqueous NaBF4 solution, the (E)-
alkenyl(phenyl)iodonium tetrafluoroborates 4 were obtained in
high yields (Scheme 1).
Scheme 2
The stereochemistry of 1,2-disubstituted alkenes 4d–e
was easily established, since they give rise to a doublet at
δ 6.20–6.38 with a coupling constant of 16 Hz typical of E
configuration.
Since the preparation of the (E)-vinylzirconium compounds
is very convenient by hydrozirconation of alk-1-ynes and
vinylzirconium–iodane exchange can occur under mild condi-
tions, the above method provides a practical route for the
stereoselective synthesis of alkenyl(phenyl)iodonium salts.
R
H
H
R
H
H
Cp2Zr(H)Cl
THF, r.t.
PhI(OAc)2
THF, r.t.
RC CH
ZrCp2Cl
I(Ph)OAc
Experimental
2
3
1H NMR spectra were recorded on Bruker AM-300 and
PMX-60 spectrometers, using CDCl3 as the solvent with TMS
as an internal standard. IR spectra were determined on a
PE-683 spectrophotometer. MS spectra were obtained on
an HP5989A spectrometer. Elemental analyses were con-
ducted using a Yanaco MT-3CHN elemental analyser. Melting
points were uncorrected. THF was distilled from sodium
benzophenone.
aq.NaBF4
CH2Cl2
R
H
H
+
–
I(Ph)BF4
4a-c
Scheme 1
General procedure for the synthesis of (E)-alkenyl(phenyl)-
iodonium acetate
Particularly diagnostic for the stereochemistry of E-alkenyl-
(phenyl)iodonium tetrafluoroborates 4a–c was the coupling
constant between the proton HA geminal to iodine and the
vicinal proton HB; typical values of 3JHH are in the range 13.6–
14 Hz which is consistent with an E configuration, and the
melting point of 4c is similar to the melting point of E type
1-phenylhex-1-ene reported.8
A mixture of Cp2Zr(H)Cl (1.0 mmol) and alk-1-yne (1.0 mmol)
in THF (5.0 cm3) was stirred under nitrogen at room temper-
ature for 20 min. A solution of (diacetoxyiodo)benzene (1.2
mmol) in THF (5.0 cm3) was added at room temperature and
the mixture was stirred for 4.0 h.
J. Chem. Soc., Perkin Trans. 1, 1998, 3321–3322
3321

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Preparation of the (E)-alkenyl(phenyl)iodonium tetrafluoro-
borates
J = 16, 6 Hz, 1H), 6.37 (d, J = 16 Hz, 1H), 7.20–7.45 (m, 5H).
MS(EI) m/z 148 (100%), 115(87), 117(87), 71(23), 105(32),
91(26), 77(25).
THF was removed from the above mixture under vacuum,
CH2Cl2 (10 cm3) and a saturated aqueous solution of NaBF4
(15 cm3) were then added. The mixture was stirred for 15 min
at room temperature. Extraction with CH2Cl2, filtration and
then concentration gave the crude product which was washed
several times with hexane by decantation. Further purification
by decantation using hexane–diethyl ether gave the (E)-vinyl-
iodonium salts.
Compound 4e. Oil (lit.,10 bp 108.5–109 ЊC/10 mmHg);
νmax(film)/cmϪ1 3050, 1640, 1595, 1450, 960. 1H NMR (60 MHz)
0.8–1.6 (m, 7H), 1.9–2.3 (m, 2H), 6.22 (dt, J = 16, 7 Hz, 1H),
6.38 (d, J = 16 Hz, 1H), 7.15–7.35 (m, 5H).
Compound 4f. Mp 47–48 ЊC (lit.,11 48.6–49.2 ЊC); νmax(CHCl3
1
film)/cmϪ1 3030, 1590, 950, 705, 670. H NMR (60 MHz) 2.33
Compound 4a. Oil, νmax(film)/cmϪ1 3040, 1590, 1490, 1070,
826. 1H NMR (300 MHz) 3.20 (s, 3H), 3.80 (dd, J = 5.6, 1.2 Hz,
2H), 6.60 (dt, J = 13.6, 1.2 Hz, 1H), 6.76 (dt, J = 13.6, 5.6 Hz,
1H), 7.40–7.55 (m, 2H), 7.60–7.65 (m, 1H), 7.98–8.03 (m, 2H).
MS(EI) m/z 275 (M Ϫ BF4)ϩ (3.6%), 204 (100), 71 (43), 45 (50),
77 (57). (Found: C, 33.43; H, 3.08. C10H12BF4IO requires C,
33.18; H, 3.34%).
(s, 3H), 7.03–7.70 (m, 11H).
Acknowledgements
Project 29772007, 29672008 was supported by the National
Nature Science Foundation of China and the Laboratory of
Organometallic Chemistry, Shanghai Institute of Organic
Chemistry, Chinese Academy of Science.
Compound 4b. Oil (lit.,7 oil), νmax(film)/cmϪ1 3075, 1560, 1465,
1440, 1050. 1H NMR (300 MHz) 0.88 (t, J = 7.4 Hz, 3H), 1.05–
1.5 (m, 4H), 2.30 (m, 2H), 6.70 (dt, J = 13.6, 1.2 Hz, 1H), 6.86
(dt, J = 13.6, 6.8 Hz, 1H), 7.46–7.55 (m, 2H), 7.63–7.70 (m,
1H), 7.98–8.03 (m, 2H).
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Compound 4c. Mp 99–100 ЊC (lit.,8 98–99 ЊC); νmax(CHCl3
1
film)/cmϪ1 3050, 1560, 1465, 1440, 1050. H NMR (300 MHz)
7.30–7.40 (m, 3H), 7.41–7.46 (m, 4H), 7.48 (d, J = 14 Hz, 1H),
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2H).
Synthesis of (E)-1,2-disubstituted alkenes
To the above mixture was added the solution of RMgBr (1.0
mmol) in THF (2.0 cm3) at 0 ЊC, then stirred under nitrogen for
1.0 h. The solvent THF was removed under vacuum and diluted
with light petroleum, then stirred for 5 min. The supernatant
was filtered. After evaporation of the filtrate, the residue was
purified by preparative TLC on silica gel, using light petroleum
as eluent.
Compound 4d. Oil (lit.,9 bp 107–108 ЊC/5 mmHg); νmax(film)/
1
cmϪ1 3040, 2940, 1610, 1500, 1460, 1260, 1100, 960, 780. H
NMR (60 MHz) 3.20 (s, 3H), 3.80 (d, J = 6 Hz, 2H), 6.20 (dt,
Communication 8/07118G
3322
J. Chem. Soc., Perkin Trans. 1, 1998, 3321–3322