Electrooxidative formation of 1,2-diaroylcyclopropanes from 1,3-diaroylpropanes in the presence of KI

Article abstract of DOI:10.1246/bcsj.76.207

Various 1,2-diaroylcyclopropanes were obtained in good yields by the indirect electrochemical oxidation of 1,3-diaroylpropanes in the presence of catalytic amounts of KI under very mild conditions.

Full text of DOI:10.1246/bcsj.76.207

c. Jpn.
Bull. Chem. Soc. Jpn., 76, 207–208 (2003)
207
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Table 1. Influence of Halide Ions and Electrolytes for the
Electrooxidative Formation of
1,2-Diaroylcyclopropanes from
1,3-Diaroylpropanes in the Presence
of KI
Formation of 1,2-Dibenzoylcyclopropane 2aa)
03
7
8
SJA8
09-2673
2742
Halide ion source
Electrolyte (5 mmol) Yieldb) of 2a/%
M. Okimito et al.
(2 mmol)
Mitsuhiro Okimoto,* Yukio Takahashi, and
Toyoji Kakuchi†
KI
KI
KI
KI
NaI
KBr
KCl
None
NaOMe
NaOAc
(Et)4NTs
None
NaOMe
NaOMe
NaOMe
NaOMe
87
41
46
69
85
7
Department of Applied Chemistry and Circumstance
Engineering, Kitami Institute of Technology, Koen-cho 165,
Kitami 090-8507
02
02
8
0
†Division of Molecular Chemistry, Graduate School of
Engineering, Hokkaido University, W8N13 Kita-ku, Sapporo
060-8628
a) 1a (6 mmol) was oxidized by passing 2.6 F/mol of elec-
tricity. b) The yields were determined by GLC analysis.
(Received August 7, 2002)
less, based on the amount of 1a.
Table 2 gives indirect electrochemical oxidation reactions
using substituted 1 under conditions that are based on the re-
sults from Table 1. The oxidations of methyl, halo, and unsub-
stituted 1(a–c, i, j) proceeded smoothly, using 2.4 F/mol of
electricity at 15 °C, to afford the corresponding 2 in good
yields. In those cases where the substitutions on the aromatic
ring of 1(d–h) involved electron-donating groups, such as
alkoxy or aryloxy groups, relatively lower reactivities were ob-
served for indirect oxidation; for example, 85% of 1d re-
mained unreacted after passing 2.6 F/mol of electricity at 15
°C, and 70% of 1f was unreacted, even with an excess passing
of 8.5 F/mol of electricity at 15 °C. However, raising the reac-
tion temperature from 15 °C to 45 °C significantly increased
both the current efficiency and the yield of the corresponding
1,2-diaroylcyclopropanes 2(d–h). These results appear to be
based not only on the reactivity of the cationic iodide species
formed on the anode, but also on the solubility of the sub-
strates in MeOH.
In fact, most of the substrates dissolved in MeOH at a temper-
ature of 45 °C to give a homogeneous solution in the initial
stage of the oxidation. In conclusion, several 1,3-diaroylpro-
panes were cyclized in the presence of catalytic amounts of KI
with the formation of a new carbon–carbon bond at the two α
positions of the carbonyl groups to afford the corresponding
1,2-diaroylcyclopropanes in good to excellent yields under
very mild conditions.
Various 1,2-diaroylcyclopropanes were obtained in
good yields by the indirect electrochemical oxidation of 1,3-
diaroylpropanes in the presence of catalytic amounts of KI
under very mild conditions.
Oxidations using molecular halogen as the oxidant have
been extensively utilized in the syntheses of various organic
compounds.1–8 Among these oxidation reactions, it is known
that 1,2-dibenzoylcyclopropane can be formed by reacting
equivalent amounts of iodine and 1,3-dibenzoylpropane.9
However, an alternative oxidation of the compound, without
the use of molecular halogen, can be advantageous as a conve-
nient synthetic method. Previously, Shono and co-workers re-
ported on various indirect electrooxidations of organic com-
pounds in a successive manner.10–13 We have also reported on
the indirect electrooxidation of aromatic aldehydes,14 ke-
tones,15 and benzil hydrazones16 to afford the corresponding
methyl carboxylate, oxiranecarbonitrile, and diazomethanes,
respectively, using halide ions as the mediator in MeOH. As a
continuation in this series of studies, we carried out the indi-
rect electrochemical oxidation of 1,3-diaroylpropanes (1) in
the presence of catalytic amounts of KI to afford 1,2-diaroyl-
cyclopropanes (2) in good yields.
Table 1 lists the reactions of 1,3-dibenzoylpropane (1a) in-
volving various halide ion sources and electrolytes, and the re-
sulting yields of 1,2-dibenzoylcyclopropanes (2a). According
to the Table, the use of iodide ion sources in the presence of
NaOMe was the most favorable reaction condition for obtain-
ing high yields of 2a. In the absence of a halide ion source, the
formation of 2a was not observed. In cases involving KBr or
KCl instead of KI, the yields of 2a were less than 10%, and
most of the unreacted 1a was recovered. In the case involving
KI without a base, a lower yield was observed for 2a (69%),
along with the recovery of unreacted 1a (22%). The addition
of neutral or weakly basic electrolytes, such as (Et)4NTs or
NaOAc, respectively, resulted in decreasing the yield of 2a.
The required amount of KI was approximately one third or
Experimental
The substrates were prepared via Friedel–Crafts acylation un-
der typical conditions17 using 2 equivalences of the aromatic com-
pounds, with glutaryl dichloride in CH2Cl2, and AlCl3 as the cata-
lyst. Other reagents were obtained from commercial suppliers,
and were used without further purification. Preparative-scale elec-
trooxidations were carried out in a tall beaker (50 mL) equipped
with a fine frit cup as the cathode compartment, a cylindrical plat-
inum net anode (diameter, 33 mm; height, 40 mm), and a nickel
coil cathode. Compounds 1 were oxidized under the following
conditions: a heterogeneous solution of 1 (6 mmol), KI (2 mmol),

208 Bull. Chem. Soc. Jpn., 76, No. 1 (2003)
© 2003 The Chemical Society of Japan
Table 2. Indirect Electrochemical Oxidation of 1,3-Diaroylpropanes in the Presence of KI
Current passed
Reaction
tempa)/°C
Yieldb) of 2
mp/°C
Compound
R
F mol−1
2.4
2.4
2.4
2.8
2.8
2.8
2.8
2.8
%
85
83
87
84
86
87
82
89
88
76
1
2
1a
1b
1c
1d
1e
1f
1g
1h
1i
Ph-
15
15
15
45
45
45
45
45
15
15
70–71
105–107
4-Me-C6H4-
112–114 108–110
88–90 84–86
99–101 100–102
3,4-diMe-C6H3-
4-MeO-C6H4-
4-n-BuO-C6H4-
4-PhO-C6H4-
4-MeO-3-Me-C6H3-
2-MeO-5-Me-C6H3-
4-Cl-C6H4-
95–97
99–101
77–79
89–91
135–137 106–107
68–70 124–126
120–122 117–119
149–151 151–153
2.4
2.4
1j
4-Br-C6H4-
a) The temperature was maintained within 2 °C. b) Isolated yield.
and NaOMe (5 mmol) in MeOH (40 mL) was electrooxidized un-
der a constant current (0.3 A). During electrooxidaton, the anolyte
was stirred using a magnetic stirring bar, and the temperature of
the cell was maintained at approximately 15 °C or 45 °C (as indi-
cated in Table 2). After completion of the electrolysis, a treatment
of the reaction mixture was carried out as follows: the anolyte was
cooled using an ice water bath; the resulting solids that precipitat-
ed were collected by filtration, washed with small portions of cold
MeOH, and dried. In the case of 1a and 1b, the filtrate was con-
centrated in vacuo, followed by the addition of water to the resi-
due. The organic substrates were extracted twice using ether, and
dried over anhydrous sodium sulfate. The residue obtained after
removal of the ether was recrystallized from small volumes of
EtOH and added to the original precipitated solids.
trans-1,2-Di(4-bromobenzoyl)cyclopropane (2j): mp 151–
153 °C. IR (CCl4) 1670, 1587, 1398, 1337, 1215, 1072, 1008
cm−1. 1H NMR (CDCl3) δ 1.86 (t, 2H, J = 7 Hz), 3.35 (t, 2H, J =
7 Hz), 7.60, 7.89 (d, d, 8H, J = 9 Hz). 13C NMR (CDCl3) δ 20.44
(CH2), 28.30 (CH), 128.76 (C), 129.82 (CH), 132.02 (CH), 135.68
(C),196.15 (CO). MS m/z (rel intensity %) 408 (M+, 15), 327 (13),
223 (18), 183 (100), 144 (60). Found: C, 49.80; H, 2.94; Br,
39.13%. Calcd for C17H12Br2O2: C, 50.03; H, 2.96; Br, 39.16%.
References
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1128 cm−1. H NMR (CDCl3) δ 1.74 (t, 2H, J = 7 Hz), 2.24 (s,
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1
1031 cm−1. H NMR (CDCl3) δ 1.79 (t, 2H, J = 7 Hz), 2.27 (s,
6H), 3.37 (t, 2H, J = 7 Hz), 3.77 (s, 6H), 6.7–7.1 (m, 2H), 7.2–7.6
(m, 4H). 13C NMR (CDCl3) δ 19.55 (CH2), 20.24 (CH3), 34.08
(CH), 55.71 (CH3), 111.86 (CH), 128.51 (C), 129.81 (C), 130.39
(CH), 134.05 (CH), 156.98 (C), 200.02 (CO). MS m/z (rel intensi-
ty %) 338 (M+, 10), 189 (14), 149 (100), 106 (12), 91 (26). Found:
C, 74.45; H, 6.65%. Calcd for C21H22O4: C, 74.54; H, 6.55%.
trans-1,2-Di(4-chlorobenzoyl)cyclopropane (2i): mp 117–
118 °C. IR (CCl4) 1670, 1591, 1404, 1336, 1215, 1093, 1010
cm−1. 1H NMR (CDCl3) δ 1.81 (t, 2H, J = 7 Hz), 3.37 (t, 2H, J =
7 Hz), 7.44, 7.98 (d, d, 8H, J = 9 Hz). 13C NMR (CDCl3) δ 20.44
(CH2), 28.34 (CH), 129.04 (CH), 129.74 (CH), 135.32 (C), 140.04
(C), 195.90 (CO). MS m/z (rel intensity %) 318 (M+, 11), 283 (9),
179 (25), 139 (100), 111 (52). Found: C, 63.73; H, 3.85; Cl,
22.17%. Calcd for C17H12Cl2O2: C, 63.97; H, 3.79; Cl, 22.21%.
17 R. C. Fuson and J. T. Walker, Org. Synth., Coll. Vol. 2, 169
(1943).