9
082
J . Org. Chem. 1996, 61, 9082-9083
Cop p er -Ca ta lyzed Cr oss-Cou p lin g a n d
Ca r bon yla tive Cr oss-Cou p lin g of
Sch em e 1
Or ga n osta n n a n es a n d Or ga n obor a n es w ith
Hyp er va len t Iod in e Com p ou n d s
Suk-Ku Kang,* Tokutaro Yamaguchi,
Tae-Hyun Kim, and Pil-Su Ho
Department of Chemistry, Sung Kyun Kwan University,
Natural Science Campus, Suwon 440-746, Korea
Sch em e 2
Received October 31, 1996
The palladium-catalyzed cross-coupling of organostan-
nanes and organoboranes with an organic electrophile
(
i.e., halides and triflates) are known as the Stille and
1
,2
Suzuki reactions, respectively, and have become ex-
tremely powerful tools for the construction of carbon-
carbon bonds. Although these coupling reactions tolerate
many functional groups, they usually require a longer
reaction time and higher temperatures, which reduce the
yields due to the thermal instability of the substrates,
products, or the catalyst itself. To seek alternatives to
the palladium-catalyst and organic electrophiles, we have
investigated copper-catalyzed cross-coupling and carbo-
nylative cross-coupling of hypervalent iodonium salts
with organostannanes and organoboranes. The recent
synthetic applications of hypervalent iodine compounds
are due to their ready availability and nontoxic proper-
ties.3 In palladium-catalyzed carbon-carbon bond-form-
ing reactions, the utility of Cu(I)X as a cocatalyst known
(phenyl)iodonium bromide (2b),13 p-iodostyrene (4a ) was
produced as the sole product. Treatment of 2-furyltribu-
tylstannane (1b) with the tetrafluoroborate 2a afforded
2-phenylfuran (3b). It is notable that allyltributylstan-
nane (1c) with the bromide 2b afforded 4-iodophenyl-
substituted product 4b as the sole product. In consid-
ering the mechanism, it is presumed that facile oxidative
addition of Cu(I) salt to iodonium salts results in the
4
as the “copper effect” was well recognized in the Stille
5
cross-coupling. Transmetallation of RSnBu
3
with CuI
6
is now known, and cross-coupling of organostannanes
with organic halides mediated by stoichiometric amounts
1
4
formation of an organo PhCuIX or IC
which is ready for transmetallation with RSnBu
PhRCuI or IC RCuI. The intermediate PhRCuI or
IC RCuI then undergoes reductive elimination to
afford PhR or IC R. As supporting evidence for the
formation of PhCuIX or IC CuIX from CuI in the first
6
H
4
CuIX species,
7
8
of copper alone was performed by Piers and Liebeskind.
3
to form
Falck et al.9 reported the copper(I)-catalyzed cross-
coupling of R-heteroatom-substituted alkyltributylstan-
nanes with organic halides. Recently, the palladium-
catalyzed carbon-carbon bond formation utilizing
hypervalent iodinanes as organic electrophiles has been
reported.10
6
H
4
6
H
4
6
H
4
6
H
4
step, when hypervalent iodonium salts were replaced by
15
PhI, the reaction did not proceed.
In our attempt to find alternatives for efficient cross-
coupling and mild conditions in this Stille-type coupling,
we have found that the coupled products could be easily
obtained under mild conditions when organostannanes
were reacted with hypervalent iodonium salts using CuI
The palladium-catalyzed carbonylative coupling reac-
tion of aryl halides with organostannanes is a valuable
synthetic procedure for the preparation of aryl ketones.
1
6
Sometimes, the utility of this route is limited by the
requirement of a high pressure of carbon monoxide and
high temperature. The copper-catalyzed coupling of
iodonium salts with organostannanes in the presence of
atmospheric pressure of carbon monoxide under mild
conditions was accomplished (Scheme 2). The reaction
of vinyltributylstannane (1a ) with diphenyliodonium
tetrafluoroborate (2a ) for 10 min afforded phenyl vinyl
ketone 5a in 85% yield. When (p-iodophenyl)(phenyl)-
iodonium bromide (2b) was treated with vinyltributyl-
stannane (1a ) for 10 min, p-iodophenyl vinyl ketone 6a
was formed as the sole product in 83% yield. 2-Furyl-
tributylstannane (1b) was reacted with 2a under the
similar conditions for 2 h to provide 2-benzoylfuran (5b).
This method was applied to alkynyl-substituted orga-
(
2.5 mol %) as a catalyst in DMF at room temperature
1
1
for 10 min (Scheme 1).
Vinyltributylstannane 1a was first coupled with tet-
rafluoroborate 2a 12 to afford styrene (3a ) in 87% yield.
When the reaction was conducted with (p-iodophenyl)-
(
1) (a) Stille, J . K. Angew. Chem., Int. Ed. Engl. 1986, 25, 508-
5
5
24. (b) Mitchell, T. N. Synthesis 1992, 803-815.
(
(
(
2) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457-2483.
3) Stang, P. J .; Zhdankin, V. V. Chem. Rev. 1996, 96, 1123-1178.
4) Liebeskind, L. S.; Fengl, R. W. J . Org. Chem. 1990, 55, 5359-
364.
(
5) Farina, V. Pure Appl. Chem. 1996, 68, 73-78.
(6) Behling, J .; Babiak, K.; Ng, J .; Campbell, A.; Moretti, R.; Koerner,
M.; Lipshutz, B. J . Am. Chem. Soc. 1988, 110, 2641-2643.
7) Piers, E.; Romero, M. A. J . Am. Chem. Soc. 1996, 118, 1215-
216.
(
1
2
5
4
(
8) Allred, G. D.; Liebeskind, L. S. J . Am. Chem. Soc. 1996, 118,
(12) Ochiai, M.; Sumi, K.; Takaoka, Y.; Nagao, Y.; Shiro, M.; Fugita,
E. Tetrahedron 1988, 44, 4095-4112.
(13) Kazmierczak, P.; Skulski, L. Synthesis 1995, 1027-1032.
(14) Oxidative addition of organic halides to Cu(I) salts has been
known. See: Cohen, T.; Cristea, I. J . Am. Chem. Soc. 1976, 98, 748-
753.
(15) When CuBF or CuBr were used instead of CuI, the reaction
4
produced only a low yield of the products.
(16) (a) Goure, W. F.; Wright, M. E.; Davis, P. D.; Labadie, S. S.;
Stille, J . K. J . Am. Chem. Soc. 1984, 106, 6417-6422. (b) Crisp, G.
T.; Scott, W. J .; Stille, J . K. J . Am. Chem. Soc. 1984, 106, 7500-7506.
748-2749.
(
973-5982.
(
9) Falck, J . R.; Bhatt, R. K.; Ye, J . J . Am. Chem. Soc. 1996, 117,
10) (a) Moriarty, R. M.; Epa, W. R. Tetrahedron Lett. 1992, 33,
095-4098. (b) Hinkle, R. J .; Poulter, G. T.; Stang, P. J . J . Am. Chem.
Soc. 1993, 115, 11626-11627. (c) Kang, S.-K.; Lee, H.-W.; Kim, J .-S.;
Choi, S.-C. Tetrahedron Lett. 1996, 37, 3723-3726. (d) Kang, S.-K.;
Lee, H.-W.; J ang, S.-B.; Ho, P.-S. J . Org. Chem. 1996, 61, 4720-4724.
(
11) Among the catalysts CuI, CuBr, CuCl, CuBF
4
tested, CuI was
the best choice.
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