ORGANIC
LETTERS
2004
Vol. 6, No. 24
4555-4558
Radical Alkenylation of
Compounds with Alkenylindiums
r-Halo Carbonyl
Kazuaki Takami, Hideki Yorimitsu, and Koichiro Oshima*
Department of Material Chemistry, Graduate School of Engineering,
Kyoto UniVersity, Kyoto 615-8510, Japan
Received September 22, 2004
ABSTRACT
Alkenylation reaction of
r
-halo carbonyl compounds with alkenylindiums proceeded via a radical process in the presence of triethylborane.
carbon double bonds
Unactivated alkene moieties as well as a styryl group could be introduced by this method. The geometry of the carbon
−
of the alkenylindiums was retained. Preparation of an alkenylindium via a hydroindation of 1-alkyne followed by radical alkenylation established
an efficient one-pot strategy.
Alkenylation reactions of organic halides are among the most
important transformations in organic synthesis. Aside from
Scheme 1
comprehensive studies on transition-metal-mediated alkeny-
lation reactions, alkenylation reactions of organic halides by
1-alkenystannanes1 or 1-alkenyl sulfones2 via a free-radical
process3 often offer a unique method for installation of a
1-alkenyl moiety. However, activation of the carbon-carbon
double bond with the aid of an electron-withdrawing group
or an aryl group at the alkenyl â-carbon is indispensable to
carry out these reactions (Scheme 1). In addition, vigorous
conditions are necessary to perform these reactions success-
fully. Radical vinylation thus deserves further exploitation.
In recent years, we have focused on the chemistry of divalent
indium compounds and disclosed their ability as radical
mediators in radical chain reactions.4,5 Now we wish to report
a radical alkenylation of R-halo carbonyl compounds under
mild conditions by utilizing alkenylindium reagents. The
present alkenylation allows us to incorporate unactivated
alkene moieties with retention of configuration.
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As the starting point of our investigation, we attempted
radical alkenylation of ethyl iodoacetate (3) with â-styrylin-
(4) (a) Takami, K.; Yorimitsu, H.; Oshima, K. Org. Lett. 2002, 4, 2993-
2995. (b) Takami, K.; Mikami, S.; Yorimitsu, H.; Shinokubo, H.; Oshima,
K. Tetrahedron 2003, 59, 6627-6635. (c) Takami, K.; Mikami, S.;
Yorimitsu, H.; Shinokubo, H.; Oshima, K. J. Org. Chem. 2003, 68, 6627-
6631.
(5) Baba also reported radical reactions mediated by dichloroindium
radical. (a) Inoue, K.; Sawada, A.; Shibata, I.; Baba, A. J. Am. Chem. Soc.
2002, 124, 906-907. (b) Inoue, K.; Sawada, A.; Shibata, I.; Baba, A.
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M.; Shibata, I.; Baba, A. Tetrahedron Lett. 1998, 39, 1929-1932.
10.1021/ol048070o CCC: $27.50
© 2004 American Chemical Society
Published on Web 10/27/2004