Stereoselective Hydroxycarbonylation of Vinyl
Bromides to r,â-Unsaturated Carboxylic Acids in
the Ionic Liquid [BMIM]PF6
on. Transition-metal-catalyzed carbonylation is of significant
importance to form the carbonyl group in a wide range of
molecules. Specifically, vinyl bromides were employed as
starting materials, affording the corresponding R,â-unsaturated
acids by transition-metal-catalyzed carbonylation, usually in the
presence of water. For instance, Miura and co-workers realized
the transformation of (E)- or (Z)-R,â-vinyl halides to (E)- or
Xiaodan Zhao,†,‡ Howard Alper,* and Zhengkun Yu*,‡
,†
Centre for Catalysis Research and InnoVation, Department of
Chemistry, UniVersity of Ottawa, 10 Marie Curie, Ottawa,
Ontario K1N 6N5, Canada, and Dalian Institute of Chemical
Physics, Chinese Academy of Sciences, 457 Zhongshan Road,
Dalian, Liaoning 116023, People’s Republic of China
(
Z)-R,â-unsaturated acids using nickel and cobalt complexes as
7
the catalysts. In 1989, our group successfully used phase-
transfer catalysis to effect stereospecific carbonylation of (E)-
R,â-vinyl bromides and some unsaturated chlorides to make (E)-
8
R,â-unsaturated acids. To our knowledge, until recently only
a few stereospecific R,â-vinyl bromides had been used, and the
reported catalysts could not be recycled in the reactions.
One of the increasing areas of green chemistry is focused on
room-temperature ionic liquids to protect human health and the
environment as a result of their features of low vapor pressure
and ease of handling. Recently, many reactions have been
ReceiVed December 25, 2005
9
c,d
9e
9i
carried out in ionic liquids, such as Heck,
Suzuki,
9f
9g
9h
Sonogashira, Stille, Ullmann, Diels-Alder, Trost-Tsuji,
9
j
9k
9l
9m-o
aldol, hydrogenation, oxidation, carbonylation,
and
9
oligomerization reactions. Although some satisfactory results
were obtained, ionic liquids as attractive clean reaction media
have not achieved their full potential. Transition-metal-catalyzed
cross-coupling reactions in ionic liquids have been reported from
1
0
our laboratories. In this note, we describe the hydroxycarbo-
nylation of vinyl bromides to the corresponding R,â-unsaturated
carboxylic acids in the ionic liquid [BMIM]PF6.
(
E/Z)-Isomers containing vinyl bromides were stereoselec-
â-Bromostyrene (1a) containing (E)- and (Z)-isomers (E/Z
) 88:12) was chosen as the model substrate to examine the
hydroxycarbonylation reaction with 10 bar of CO using 3 mol
% Pd(PPh3)4 as the catalyst in the ionic liquid [BMIM]PF6 at
100 °C for 5 h. The product cinnamic acid (2a) was obtained
in good yield (82%) with an E/Z ) 96:4 molar ratio, as
tively carbonylated to the corresponding (E)-R,â-ethylenic
carboxylic acids in the ionic liquid [BMIM]PF . Vinyl
6
dibromides also underwent hydroxycarbonylation to give
monoacids. The products are pure by proton NMR spectro-
scopic determination without purification by silica gel
column chromatograghy or recrystallization.
1
determined by H NMR spectroscopy. Unfortunately, the
catalyst cannot be recycled. Increasing the loading of the catalyst
(
E)-R,â-Ethylenic carboxylic acids are not only versatile
(7) (a) Miura, M.; Okuro, K.; Hattori, A.; Nomura, M. J. Chem. Soc.,
Perkin Trans. 1 1989, 73. (b) Miura, M.; Shimoura, N.; Nomura, M. J.
Chem. Soc., Perkin Trans. 1 1988, 1993. (c) Miura, M.; Akase, F.;
Shinohara, M.; Nomura, M. J. Chem. Soc., Perkin Trans. 1 1987, 1021.
synthons, but also exist widely in natural products, for example,
honeybee and caffeir acid, and in biologically active molecules
such as (E)-2-methyl-3-(4-(myristyloxy)-phenyl)-prop-2-enoic
acid. Some methods have been developed to produce ste-
reospecific R,â-unsaturated carboxylic acids from different
substrates such as aldehydes, alkynes, aryl iodides, and so
1
2
(8) Alper, H.; Amer, I.; Vasapollo, G. Terahedron Lett. 1989, 30, 2615.
3
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4
5
6
*
To whom correspondence should be addressed.
University of Ottawa.
Dalian Institute of Chemical Physics.
†
‡
(
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(
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10.1021/jo052651p CCC: $33.50 © 2006 American Chemical Society
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J. Org. Chem. 2006, 71, 3988-3990
Published on Web 04/14/2006