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Published on the web April 16, 2011
Silica Sulfuric Acid-promoted Deacylation of ¡-Bromo-¢-diketones
Tadashi Aoyama,*1,2 Sho Kubota,1 Toshio Takido,1 and Mitsuo Kodomari3
1Department of Materials and Applied Chemistry, College of Science and Technology, Nihon University,
Kanda Surugadai, Chiyoda-ku, Tokyo 101-8308
2The Center for Creative Materials Research, Research Institute of Science and Technology, College of Science and Technology,
Nihon University, Kanda Surugadai, Chiyoda-ku, Tokyo 101-8308
3Department of Bioscience and Engineering, Shibaura Institute of Technology, Fukasaku, Minuma-ku, Saitama 337-8570
(Received February 9, 2011; CL-110113; E-mail: aoyama@chem.cst.nihon-u.ac.jp)
Table 1. Deacetylation of 1a using various acidsa
Novel deacylation of ¡-bromo-¢-diketones using silica
sulfuric acid (SSA) has been developed. Deacylation of 3-
bromopentane-2,4-diones and 2-bromobutane-1,3-diones were
carried out in the presence of SSA in dichloroethane under mild
conditions to obtain the corresponding ¡-bromo ketones in good
to excellent yields. SSA also promoted the Friedel-Crafts type
alkylation of benzene with 3-(sec-alkyl)-2,4-pentanediones to
give the corresponding triarylmethanes in high yields in
benzene.
O
O
O
Acid (x mol %)
Bn
Benzene
60 °C, 1 h
Br
Bn
Br
2a
Yield/%
1a 2a
1a
Entry
Acid
x/mol %
1
2
3
4
5
6
7
8
9
SSA
NaHSO4/SiO2
Amberlyst-15μ
HClO4/SiO2
PPA/SiO2
H2SO4
HCl
PTS
ZnCl2/SiO2
185
210
480
10
0
83
98
100
100
0
100
100
100
100
17
2
0
0
85
0
0
Deacylation is one of the most important transformations in
organic synthesis because it has been widely used for the
synthesis of natural products, biological active compounds, etc.
Many methods for deacylation have been developed. The
reactions are usually catalyzed by acids and bases. Base
catalysts have been employed to catalyze deacylation of ¢-
dicarbonyl compounds.1-5 In contrast, acid catalysts are scarcely
used for deacylations of ¢-dicarbonyl compounds. Adkins and
co-workers6 first reported acid-catalyzed deacylation using
hydrogen chloride and alcohol, and Zinnes’s group7 reported
deacylation of 3-acyl-2H-1,2-benzothiazin-4(3H)-one 1,1-diox-
ide using PTS and ethylene glycol in benzene.
®
900
600
100
150
0
aRecovery and yield were determined by GLC area ratio.
Table 2. Deacetylation of 1a in various solvents
SSA
Solvent
1a
2a
In the course of our study of synthetic reactions using
inorganic solid-supported reagents, we found out that silica
sulfuric acid (SSA)8 promotes deacylation of ¡-halo-¢-dicar-
bonyl compounds to afford ¡-bromo ketones. To the best of our
knowledge there are no reports of deacylation of ¡-halo-¢-
dicarbonyl compounds using an acid.
Deacylation of ¡-halo-¢-dicarbonyl compounds is usually
catalyzed by bases.9-11 This transformation has been used in
the synthesis of pharmaceuticals such as triamcinolone12 and
juvenile hormone.13 ¡-Halo ketones are important compounds in
organic synthesis, which are useful in the synthesis of a variety
of heterocycles such as thiazoles,14 imidazoles,15 and pyran-2,5-
diones,16 as well as in other synthetic applications. In this paper
we describe deacylation of ¡-halo-¢-dicarbonyl compounds
using SSA.
First, conversion of 3-benzyl-3-bromopentane-2,4-dione
(1a) into 3-bromo-4-phenylbutane-2-one (2a) was carried out
in the presence of various acids (Table 1). Among the acids
tested, SSA showed the highest activity. The other acids without
sulfuric acid were inactive. NaHSO4/SiO2 and Amberlyst-15μ
had slight effects for the reaction of 1a into 2a, but the yield was
very low at 17% and 2% respectively. The activity of H2SO4
was the same as SSA, but the yield of 2a was lower than that
using SSA because some undesirable side reactions occurred.
When HCl and p-toluenesulfonic acid (PTS) were used as an
60 °C, 1 h
Entry Solvent
Conversion (Isolated yield)/%
1
2
3
4
5
Benzene
Toluene
100 (79)
4 (®)
100 (85)
100 (92)
100 (69)
Chlorobenzene
1,2-Dichloroethane
Hexane
acid, 1a was recovered quantitatively. Lewis acid, ZnCl2/SiO2,
did not work for this reaction.
Various solvents can be used for this reaction except for
toluene. 1,2-Dichloroethane was the most suitable solvent,
whereas using toluene as a solvent, the conversion was only 4%
and large amount of unchanged 1a was observed in the reaction
mixture (Table 2). In order to make clear this reaction profile, a
suspension of SSA in toluene was stirred at 80 °C for 5 h. PTS
was formed in good yield. Thus, in the reaction of 1a with SSA
in toluene, PTS did not work as an acid catalyst for deacylation.
Hajipour and co-workers17 have reported that active aromatics
are sulfonated by SSA.
We tried to synthesize various ¡-bromo ketones 2 from 3-
bromo-3-substituted pentane-2,4-diones 1 using SSA (Table 3).
A mixture of 1a (1 mmol) and SSA (1 g) in 1,2-dichloroethane
Chem. Lett. 2011, 40, 484-485
© 2011 The Chemical Society of Japan