Beilstein Journal of Organic Chemistry 2010, 6, No. 35.
During optimization of reaction conditions, the model reaction
was carried out in different solvents. It was found that DMSO
used as shown in Table 2. This is not surprising in view of the
fact that the reaction intermediate is a carbanion and therefore
will have a greater stability in a polar solvent.
Table 2: CuO-nanoparticles catalyzed coupling reaction of acet-
ylacetone and iodobenzene in various solventsa.
Scheme 2: Synthesis of 3-phenylpentane-2,4-dione using CuO-nano-
particles.
Entry
Solvent
Time (h)
Yieldb (%)
1
2
3
4
DMSO
Toluene
THF
8
80
8
15
15
15
12
32
Acetonitrile
The above results encouraged us to investigate further reactions.
Under similar reaction conditions, diethyl malonate was treated
aryl halides. The results are summarized in Table 4.
aReaction conditions: acetylacetone (3 mmol), iodobenzene (1 mmol),
0 mol % CuO-nanoparticles, Cs2CO3 (0.5 mmol), solvent; temperature
0 °C; N2; 1 atm.
1
8
bIsolated and optimized yield.
Moreover, the advantage of the nanoparticles is that, unlike
other catalysts, their use is not restricted by their solubility, as
the nanoparticles can be dispersed in the desired solvent by agit-
ation or slight sonication.
When an equimolar mixture of chlorobenzene and iodobenzene
was treated with acetylacetone under similar reaction condi-
tions, the chlorobenzene was largely unreactive. This shows that
Scheme 3: Synthesis of diethyl 2-aryl-malonate using CuO-nano-
particles.
The observed decrease in reactivity in the order p-nitroiodoben-
To study the scope of this procedure, acetylacetone was reacted zene > iodobenzene > p-methyliodobenzene > 1-iodo-4-meth-
with various aryl halides and gave the corresponding products oxybenzene suggests that the reaction proceeds by oxidative
in 78–83% yield. It was observed that aryl halides having elec- addition followed by reductive elimination. In addition to this,
tron withdrawing groups showed greater reactivity and gave the order of reactivity suggests that aryl halides having electron
good yield of products compared to aryl halides having elec- withdrawing groups stabilize the transition state which corres-
Table 3: C-arylation of acetylacetone using different aryl halidesa
Entry Aryl halide
Product
Time (h)
Yieldb (%)
1
2
3
4
5
6
7
iodobenzene
3-phenylpentane-2,4-dione
8
10
6
80
79
83
78
81
76
75
bromobenzene
3-phenylpentane-2,4-dione
p-nitroiodobenzene
3-(4-nitrophenyl)-pentane-2,4-dione
3-p-tolylpentane-2,4-dione
p-methyliodobenzene
m-trifluoromethyliodobenzene
1-iodo-2-methylbenzene
1-iodo-4-methoxybenzene
10
7
3-(3-trifluromethyl-phenyl)-pentane-2,4-dione
3-o-tolyl-pentane-2,4-dione
11
12
3-(4-methoxy-phenyl)-pentane-2,4-dione
aReaction conditions: acetylacetone (3 mmol), aryl halide (1 mmol), 10 mol % CuO-nanoparticles, Cs2CO3 (0.5 mmol), DMSO; temperature 80 °C; N2; 1
atm.
bIsolated and optimized yields.
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