A novel synthesis of 1,3-diketones by reaction of an α-bromoketone with acyl chlorides promoted by gallium triiodide

Article abstract of DOI:10.1039/a904972j

Promoted by gallium triiodide, an α-bromoketone, bromomethyl phenyl ketone, is treated with acyl chlorides to synthesize 1,3-diketones in good yields under mild and neutral conditions.

Full text of DOI:10.1039/a904972j

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666 J. CHEM. RESEARCH (S), 1999
J. Chem. Research (S),
1999, 666^667y
A Novel Synthesis of 1,3-Diketones by Reaction
of an -Bromoketone with Acyl Chlorides
Promoted by Gallium Triiodidey
Rener Chen, Huayue Wuz and Yongmin Zhang*
Department of Chemistry, Zhejiang University at Xixi Campus, Hangzhou, 310028, P. R. China
Promoted by gallium triiodide, an a-bromoketone, bromomethyl phenyl ketone, is treated with acyl chlorides to
synthesize 1,3-diketones in good yields under mild and neutral conditions.
Recently gallium and its compounds are gradually
attracting attention as useful reagents in organic
As far as we know, this was the ¢rst example of
1,3-diketone synthesis using GaI3. The mechanism of the
reaction may be through the gallium enolate intermediate
(Scheme 2). In the classical procedures, 1,3-diketones
may be synthesized by condensation of ketones, having
an a-hydrogen atom, with acyl chlorides, but the reaction
is usually e¡ected by means of a strong basic reagent such
as sodium amide,10 with anhydrides a Lewis acid such as
boron tri£uoride is generally used.11 O-Acyl derivatives
are also formed in these reaction.12 In our methodology
synthesizing 1,3-diketones with acyl chlorides, the ratio
of O-acyl derivatives is negligably small.
7
synthesis.1 Gallium enolate-mediated intermolecular aldol
reaction and addition of a-bromoketone with imine, a
straightforward and versatile preparation of prop-2-ynylic
alcohols from alklynes and aldehydes via GaI3 and amine
have been documented.3 Kobayashi reported that gallium
reagents could e¤ciently promote the glycosidation of
glycopyranosyl £uoride.4 The reaction of alkynes with
aldehydes produce conjugated enones in the presence of
GaI3-NBu3 in CH2Cl2,5 Ga/PbCl2 bimetal redox
system-mediated carbon^carbon bond formation reactions
between carbonyl compounds and ethyl trichloroacetate
and iodoacetonitrile,6 gallium-mediated highly regioselective
reactions of trimethylsilyprop-2-ynyl bromide and
trimethylsilylallyl bromide with carbonyl compounds7 are
known. We have also reported gallium mediated allylation
and prop-2-ynylation of 1-(a-aminoalkyl)benzotriazole.8
All those reactions above indicated that the scope of utility
of gallium reagents in organic chemistry can be broadened.
Our previous work of 1,3-diketone synthesis by reaction
of a-haloketones with acyl chlorides or anhydrides pro-
moted by samarium diiodide has been reported.9 Here
we report that an a-bromoketone, bromomethyl phenyl
ketone can reductively couple with acyl chlorides mediated
by GaI3 to give 1,3-diketones (Scheme 1).
I2Ga I–
O
OGaIII
O
O
O
O
Br
CH2
GaI3
–IBr
RC Cl
Ph
Ph
CH2
PhCCH2Br
PhCCH2CR
I2Ga I–
O
O
–I2
GaI3
GaI3
I
I
Ph
CH2
Ph
CH2
Scheme 2
From the result of the experiment, we found that this
reaction proceeded quickly and smoothly at room tempera-
ture in neutral, mild condition and gives good yields (Table
1). The solvent (MeCN) and acyl chlorides must be dried
thoroughly and freshly redistilled, otherwise the amounts
of byproducts due to reduction of the a-bromoketone will
be increased. This also suggests that the reaction
intermediates may be gallium(III) enolates formed in situ
from the a-bromoketone. THF can not be used as solvent
as in the presence of GaI3 acyl chlorides lead to THF ring
opening.13
O
O
O
O
GaI3
+
PhCCH2Br
RC Cl
PhCCH2CR
MeCN, r.t.
Scheme 1
Table 1 Reaction of bromomethyl phenyl ketone with acyl chlorides
Entry
Acyl chloride
Product
Reaction time/h
Yield(%)a
1
2
3
4
5
6
7
8
9
MeCOCl
EtCOCl
PrCOCl
Me[CH2]3COCl
Me2CHCH2COCl
Me[CH2]4COCl
Me[CH2]7COCl
Me[CH2]10COCl
PhCOCl
PhCOCH2COMe
PhCOCH2COEt
PhCOCH2COPr
0.5
0.5
0.5
1
1
1
1
1
0.5
0.5
1
77
82
75
83
79
75
78
72
75
68
69
78
PhCOCH2CO[CH2]3Me
PhCOCH2COCH2CHMe2
PhCOCH2CO[CH2]4Me
PhCOCH2CO[CH2]7Me
PhCOCH2CO[CH2]10Me
PhCOCH2COPh
p-O2NC6H4COCH2COPh
PhCOCH2COCMe3
PhCOCH2COCH2Ph
10
11
12
p-O2NC6H4COCl
Me3CCOCl
PhCH2COCl
1
aIsolated yields.
Experimental
1H NMR spectra were recorded on a JEOL PMX 60 SI instrument
in CCl4 using TMS as internal standard. IR spectra were determined
on a Perkin-Elmer 683 spectrometer. Metallic gallium and other
chemicals were purchased from commercial sources and used without
puri¢cation. MeCN was freshly distilled prior to use.
* To receive any correspondence.
y This is a Short Paper as de¢ned in the Instructions for Authors,
Section 5.0 [see J. Chem. Research (S), 1999, Issue 1]; there is
therefore no corresponding material in J. Chem. Research (M).
z Visiting scholar from Wenzhou Normal College.

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J. CHEM. RESEARCH (S), 1999 667
General Procedure.öUnder a nitrogen atmosphere, a metallic
gallium bar (1 mmol) and iodine (1.5 mmol) were placed in a
three-necked reaction £ask, then MeCN (10 ml) was added in one
portion. The mixture was stirred at room temperature until the colour
of iodine disappeared completely. Then the a-bromoketone (1 mmol)
and acyl chloride (1 mmol) were added sequentially to the mixture.
After stirring at room temperature for the time indicated in Table
1, a dilute solution of HCl was added and the resulting mixture
was stirred for a few minutes. The mixture was extracted with diethyl
ether (20 ml  2 and the organic layer was washed with water
(20 ml  2† and dried over anhydrous Na2SO4. The solvent was
removed in vacuo. The residue was then puri¢ed by preparative
TLC on silica gel with cyclohexane and ethyl acetate as eluent to give
pure product.
We are grateful to the National Natural Science Foun-
dation of China (Project No. 29872010), the NSF of
Zhejiang Province, China, and the Laboratory of
Organometallic Chemistry, Shanghai Institute of Organic
Chemistry, Chinese Academy of Sciences for ¢nancial
support.
Received, 22nd June; Accepted, 28th July 1999
Paper E/9/04972J
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1
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PhCOCH2COCH2[CH2]3Me9; Oil; dH 0.85^1.76 (m, 9 H),
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1
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p-O2NC6H4COCH2COPh16; mp 160^161 8C; dH 6.68 (s, 1 H),
1
7.35±8.00 (m, 9 H), 16.85 (s, 1 H), n/cm 1610, 1350.
15
PhCOCH2COCMe3 Oil; dH 1.15 (s, 9 H), 6.20 (s, 1 H), 7.34^7.38
1
(m, 3 H), 7.79^7.83 (m, 2 H), 16.50 (s, 1 H); n/cm 1619.
PhCOCH2COCH2Ph15; mp 50^51 8C; dH 3.70 (s, 2 H), 6.08 (s,
1
1 H), 7.29±7.48 (m, 8 H), 7.75±7.79 (m, 2 H), OH unfound; n/cm
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