DOI: 10.1002/chem.201001387
Room-Temperature Deoxygenation of Epoxides with CO Catalyzed by
Hydrotalcite-Supported Gold ACTHUNTGRNEUNGNanoparticles in Water
Takato Mitsudome,[a] Akifumi Noujima,[a] Yusuke Mikami,[a] Tomoo Mizugaki,[a]
Koichiro Jitsukawa,[a] and Kiyotomi Kaneda*[a, b]
Deoxygenation of epoxides to alkenes is useful in organic
synthesis because it allows the use of the oxirane ring as a
protective group for carbon–carbon double bonds.[1] The
transformation is also of great importance in biological
chemistry for the reproduction of vitamin K in the vita-
min K cycle,[2] and has been recently applied to quantifica-
tion methods to find the epoxide content in graphite epox-
ide or oxygenated carbon nanotubes.[3] Although many stoi-
chiometric deoxygenations of epoxides have been developed
by using a variety of reagents,[4] catalytic systems are rare[5]
and they have suffered from problems such as low catalytic
activity and the need for harsh and/or air-sensitive reaction
conditions.
Recently, we have discovered that gold nanoparticles
(NPs) efficiently catalyze the liquid-phase deoxygenation of
epoxides into the corresponding alkenes by using alcohols
as reducing reagents in organic solvents.[6] This process can
overcome the above problems that have plagued previously
reported catalytic systems. However, our reported deoxyge-
nation system required high temperatures (1108C), which
could cause an incompatibility with functionalized epoxides.
From the environmental and practical synthetic point of
view, our next target is the design of a high-performance
catalyst system for the deoxygenation of epoxides under
much milder reaction conditions. Herein, we report an alter-
native green methodology for the catalytic deoxygenation of
epoxides with supported gold NPs by using CO/H2O as a re-
ducing reagent under mild reaction conditions. Namely, an
inorganic material of hydrotalcite supporting gold NPs (Au/
HT) catalyzes the highly efficient deoxygenation of many
epoxides into the corresponding alkenes in water without or-
ganic solvents under an atmospheric pressure of CO at
room temperature. The use of water in organic reactions in-
stead of organic solvents is attractive[7] because of the low
cost, safety (nonexplosive, nonflammable, and nontoxic),
and ease of phase-separation of water-insoluble products in
the work-up procedure. A further advantage of this deoxy-
genation method is that only CO2 is formed as a byproduct,
which can be easily released from the reaction system and
hence facilitating purification of the alkene products. The
solid Au/HT catalyst is also easily separable from the prod-
ucts, and can be reused while maintaining its activity and se-
lectivity. To the best of our knowledge, this is the first report
of the catalytic deoxygenation of epoxides in water under
organic-solvent-free conditions.
Au/HT was synthesized according to our reported proce-
dure.[8] Au/HT and styrene oxide (1a) were added to water
and the heterogeneous mixture was stirred under an atmos-
pheric pressure of CO at room temperature. The reduction
reaction of 1a smoothly occurred to give styrene (2a) in
over 99% yield accompanied by the formation of an equi-
molar amount of CO2 (Table 1, entry 1).[9] No other byprod-
ucts, such as a further reduction product of ethylbenzene, a
hydration product of styrene glycol, and a CO2 cycloaddition
product of styrene carbonate were formed. Notably, water
was found to be the best solvent to promote the deoxygena-
tion efficiently, and lower yields were obtained in organic
solvents (Table 1, entry 1 vs. entries 4–6). Among the inor-
ganic materials tested as supports for gold NPs, the HT sup-
port afforded the highest yield of 2a. Other base supports of
Al2O3 and MgO also gave good yields of 2a (Table 1, en-
tries 10 and 11). On the other hand, TiO2 resulted in a low
conversion of 1a (Table 1, entry 9), and SiO2 and boron ni-
tride were inactive (Table 1, entries 14 and 15). Interestingly,
[a] Dr. T. Mitsudome, A. Noujima, Y. Mikami, Dr. T. Mizugaki,
Prof. Dr. K. Jitsukawa, Prof. Dr. K. Kaneda
Department of Materials Engineering Science
Graduate School of Engineering Science
Osaka University, 1–3 Machikaneyama, Toyonaka
Osaka 560-8531 (Japan)
[b] Prof. Dr. K. Kaneda
Research Center for Solar Energy Chemistry
Osaka University, 1-3, Machikaneyama, Toyonaka
Osaka 560-8531 (Japan)
Fax : (+81)6-6850-6260
Supporting information for this article is available on the WWW
11818
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Chem. Eur. J. 2010, 16, 11818 – 11821