Dehalogenation of α-halocarbonyls using decaborane as a transfer hydrogen agent in methanol

Article abstract of DOI:10.1081/SCC-100104823

Decaborane reduces α-halocarbonyl compounds to the corresponding dehalogenated products in the presence of Pd/C in methanol at room temperature efficiently and chemoselectively.

Full text of DOI:10.1081/SCC-100104823

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
Chemistry
ISSN: 0039-7911 (Print) 1532-2432 (Online) Journal homepage: http://www.tandfonline.com/loi/lsyc20
DEHALOGENATION OF α-HALOCARBONYLS USING
DECABORANE AS A TRANSFER HYDROGEN AGENT
IN METHANOL
Seung Hwan Lee , Yeon Joo Jung , Young Jin Cho , Choon-Ock Maing Yoon ,
Han-Joon Hwang & Cheol Min Yoon
To cite this article: Seung Hwan Lee , Yeon Joo Jung , Young Jin Cho , Choon-Ock Maing Yoon ,
Han-Joon Hwang & Cheol Min Yoon (2001) DEHALOGENATION OF α-HALOCARBONYLS USING
DECABORANE AS A TRANSFER HYDROGEN AGENT IN METHANOL, Synthetic Communications,
31:15, 2251-2254, DOI: 10.1081/SCC-100104823
To link to this article: http://dx.doi.org/10.1081/SCC-100104823
Published online: 09 Nov 2006.
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SYNTHETIC COMMUNICATIONS, 31(15), 2251–2254 (2001)
DEHALOGENATION OF
a-HALOCARBONYLS USING
DECABORANE AS A TRANSFER
HYDROGEN AGENT IN METHANOL
Seung Hwan Lee, Yeon Joo Jung, Young Jin Cho,
Choon-OckMaing Yoon, Han-Joon Hwang, and
Cheol Min Yoon*
Graduate School of Biotechnology, Korea University, 1, 5-Ka,
Anam-Dong, Sungbuk-Ku, Seoul, 136-701, S. Korea
ABSTRACT
Decaborane reduces a-halocarbonyl compounds to the corre-
sponding dehalogenated products in the presence of Pd/C in
methanol at
chemoselectively.
room
temperature
efficiently
and
The reductive dehalogenation reaction has been received considerable
attention in organic chemistry and could be accomplished with many redu-
cing agents.1 The choice of a reducing agent usually depends on what other
functional groups are present. There are several reagents that reduce only
the halogen of a-haloketones, leaving the carbonyl group intact. Several
reagents have recently been reported for the reductive dehalogenation of
a-halo ketones without affecting the carbonyl group.2
*Corresponding author. Fax: þ82-2-3290-8178.
2251
Copyright & 2001 by Marcel Dekker, Inc.
www.dekker.com

ORDER
REPRINTS
2252
LEE ET AL.
Decaborane (B10H14) is a boron cluster, which is nontoxic and stable
white solid. It is a well-known reagent for the synthesis of ortho-carboranes.3
It is more electron-deficient than borane(BH3), and therefore less reactive
as a reducing agent. However, it was found out to have a reducing power
and generated hydrogen gas slowly in protic solvent, which was identified
to be synthetically useful.4 In connection with our works of decaborane
as a hydrogen transfer agent, dehalogenation of a-haloacetophenones
using decaborane in methanol was studied and a-haloacetophenones were
found to be smoothly converted into the corresponding dehalogenated
ketones in the presence of 10% Pd/C under nitrogen atmosphere at room
temperature.
Here we wish to report the efficient reducing systems based on the
combination of decaborane with palladium-on-carbon in methanol under
mild condition (Scheme 1).
Scheme 1.
In a typical experimental procedure, to a solution of a-halocarbonyls
in methanol were added decaborane and 10% palladium-on-carbon under
a nitrogen atmosphere. The solution was stirred at room temperature until
the reaction is complete (monitored by TLC). The decomposed decaborane
was easily removed by filtration through a short silica gel pad. The reaction
mixture was chromatographed to give acetophenones in excellent yield,
which shows identical spectroscopic properties with authentic materials.
As shown in Table 1, the carbonyl groups of all substrates (entries 1–7)
were remained unaffected under our reduction condition. The other bromo
substituent (of bromoalkyl or bromoaryl) was leaved intact under the reac-
tion condition (entries 4 and 8). The nitro group of the substrate (entry 5) was
survived under the condition. The reactions are reasonably fast and high-
yielding. The reduction of a-halosubstituted carbonyls into dehalogenated
ketones using hydrogen gas and transition metal had been reported by
Denton, et al.5 The catalytic hydrogenations were generally required base,
because the reaction was inhibited by the halogen acid released.6 However,
under our condition, the reaction was proceeded smoothly in high yield
without any base.

ORDER
REPRINTS
DEHALOGENATION OF a-HALOCARBONYLS
2253
Table 1. Reduction of a-Halo Ketones by Using Decaborane
aAll yields refer to isolated products fully characterized by spectral data.
In conclusion, the reaction of a-halo ketones with decaborane under
our mild condition chemoselectively gave the corresponding carbonyl
compounds in excellent yields.
EXPERIMENTAL
All starting materials were purchased from Aldrich Chemical
1
Company and were used without any further purification. The H NMR
spectra were recorded on a Varian 300. Silica gel 60 (230–400 mesh, Merk)
was used for column chromatography, and silica gel 60F254 plates (0.25 mm,
Merk) were used for TLC.
Typical Procedure for Reduction of a-Halo Ketones
To a solution of 2-bromo-40-methylacetophenone (100 mg, 0.469 mmol)
in methanol (15 ml) under a nitrogen atmosphere was added decaborane

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2254
LEE ET AL.
(5.7 mg, 0.047 mmol) and 10% Pd/C (10 mg). The solution was stirred at
room temperature. The reaction monitored by TLC, was complete within
1 h, as indicated by the complete disappearance of starting material. The
solution was removed under reduced pressure and then traces of decom-
posed decaborane was removed by chromatography on silica gel (ethyl
acetate:hexane ¼ 1:4) to afford 40-methylacetophenone (62 mg, 98%) as a
colorless syrup, identical in every respect with authentic sample.
ACKNOWLEDGMENTS
This workwas supported by Korea Research Foundation
(KRF-99-2000).
REFERENCES
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Hayakawa, Y. Org. React. (N.Y.) 1983, 29, 163.
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Received in Japan July 10, 2000

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