Copper-mediated aerobic oxidative cleavage of α,β-unsaturated ketones to 1,2-diketones

Article abstract of DOI:10.1039/c4ra05307a

The copper-mediated aerobic oxidative cleavage of α,β- unsaturated ketones to synthesize 1,2-diketones by using potassium acetate as a catalyst and sodium iodide as a promoter in acetic acid is described. The protocol has the advantages of using inexpensive and non-toxic raw materials, high yield and simple work-up procedure. the Partner Organisations 2014.

Full text of DOI:10.1039/c4ra05307a

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Copper-mediated aerobic oxidative cleavage of
a,b-unsaturated ketones to 1,2-diketones†
Cite this: RSC Adv., 2014, 4, 32298
*
Zheng Li, Junjun Yin, Gong Wen, Tianpeng Li and Xiaoli Shen
Received 4th June 2014
Accepted 14th July 2014
The copper-mediated aerobic oxidative cleavage of a,b-unsaturated ketones to synthesize 1,2-diketones
by using potassium acetate as a catalyst and sodium iodide as a promoter in acetic acid is described. The
protocol has the advantages of using inexpensive and non-toxic raw materials, high yield and simple
work-up procedure.
DOI: 10.1039/c4ra05307a
www.rsc.org/advances
Results and discussion
Introduction
Initially, the investigation was selected chalcone (1a) as
substrate. The reactions were ever conducted under the condi-
tion of sodium iodide as a promoter and potassium acetate as a
catalyst under reuxing condition in acetic acid. However, the
It is known that 1,2-diketones are important synthetic building
blocks1 and have attracted the attention of many organic
chemists, especially for use as precursors to some compounds
such as a-hydroxy ketones2 and heterocyclic compounds.3 They
have also shown interesting applications as photoinitiators4
and corrosion inhibitors.5
The reported synthetic methods for 1,2-diketones (Scheme
1), for example 1,2-diaryl-1,2-diones, included: (1) the C–H
oxidation of 1,2-diarylethanes using graphite oxide (GO);6 (2)
the oxidation of stilbenes using GO;6 (3) the oxidation of 1,2-
diarylethynes using DMSO catalyzed by Pd–Cu;7 (4) the
oxidation of deoxybenzoins using iodine and DMSO cata-
lyzed by CuO;8 (5) the aerobic oxidation of benzoins catalyzed
by zinc;9 (6) the aerobic oxidation of 2-bromo-1,2-diarylethan-
1-ones catalyzed by ruthenium complexes;10 (7) the oxidation
of 1,2-diaryl-1,2-dibromoethanes using DMSO;11 and (8) the
oxidation of hydrobenzoins using t-BuOOH (TBHP) catalyzed
by vanadium complexes, etc.12
The recent research showed that 1,2-diketones could also be
synthesized by oxidative cleavage of 1,3-diketones using
different oxidants (Scheme 2).13
It is worthy to mention that McKillop reported a method to
1,2-diketones from chalcones using thallium(III) nitrate as a
oxidant in perchloric acid medium (Scheme 3).14 However,
this method required highly toxic thallium salt as a strong
oxidizing agent in strong acid medium, meanwhile only
middle yield was afforded in reuxing condition. Therefore,
it is necessary to nd new methods for 1,2-diketones. Herein,
we report the copper-mediated aerobic oxidative cleavage of
a,b-unsaturated ketones to synthesize 1,2-diketones under
mild conditions.
Scheme 1 The general synthetic methods for 1,2-diketones.
Scheme 2 Synthesis of 1,2-diketones by oxidative cleavage.
College of Chemistry and Chemical Engineering, Northwest Normal University,
Lanzhou, Gansu, 730070, P. R. China. E-mail: lizheng@nwnu.edu.cn
† Electronic supplementary information (ESI) available: Copies of IR, 1H and 13
C
NMR spectra of all compounds. See DOI: 10.1039/c4ra05307a
Scheme 3 Synthesis of 1,2-diketones from chalcones.
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Table 1 The effect of mediators on the yield of 1a to 2aa
Table 2). It was found that a,b-unsaturated ketones bearing
both electron-donating (CH3, CH3O) and electron-withdrawing
(Cl, F, NO2) groups on aromatic rings could participate in
reactions. However, the former afforded the desired 1,2-dike-
tones in slightly higher yield than the latter.
A plausible mechanism for the aerobic oxidative cleavage of
a,b-unsaturated ketones is presented in Scheme 5. The initial
step of the reaction involves the formation of epoxide A from
Entry
Mediator
Promoter
Catalyst
Yieldb (%)
1
2
3
4
5
6
7
None
CuCl2
CuSO4
Cu(OAc)2
Cu(NO3)2$5H2O
Cu(NO3)2$5H2O
Cu(NO3)2$5H2O
NaI
NaI
NaI
NaI
NaI
None
NaI
KOAc
KOAc
KOAc
KOAc
KOAc
KOAc
None
0
5
21
34
83
51
47
Table 2 The copper-mediated aerobic oxidative cleavage of a,b-
unsaturated ketones to 1,2-diketonesa
a
Reaction condition: 1a (1 mmol), mediator (1.1 mmol), NaI (1.1
mmol), KOAc (0.2 mmol) in 10 mL of HOAc at 100 ꢀC for 9 h.
b
Isolated yields.
Entry
R1
R2
Yieldb (%)
Mp (ꢀC) (lit.)
corresponding product benzil (2a) was not observed (Table 1,
entry 1). In the later research, it was found that the reaction
could efficiently give 2a using some copper salts as mediators.
The use of copper chloride, copper sulfate and copper acetate
gave relatively low efficiency, while copper chloride was almost
inactive (Table 1, entries 2–4). However, the reaction was
effective under the condition of copper nitrate pentahydrate as a
mediator to afford 2a in high yield (Table 1, entry 5). The
possible reason is that copper nitrate pentahydrate may have
dual functions in the reaction, in addition to copper as a
mediator, nitrate as a oxidant as well as air. It was also note-
worthy to mention that the absence of either of sodium iodide
or potassium acetate in the reaction system could cause the
obvious decrease of the reaction yield (Table 1, entries 6 and 7).
The solvents also played an important role in the reaction of
1a to 2a. The reaction in many solvents such as water, 1,4-
dioxane, toluene and methylene chloride was not occurred,
while the reaction in ethanol or acetonitrile only gave uniden-
tied by-products in low yield by comparison with corre-
sponding product using TLC. However, acetic acid was an
efficient solvent for the reaction to afford the corresponding
product in 83% yield. In fact, the role of acetic acid in the
reaction is both as solvent and as acidic medium.
1
2
3
4
C6H5
4-CH3C6H4
C6H5
C6H5
83
78
86
71
83–84 (94–95)7
82–83
4-CH3C6H4
4-CH3OC6H4
4-CH3C6H4
49–50
C6H5
82–83 (96)7
5
C6H5
88
96–98
6
4-CH3C6H4
82
102–103
7
8
9
10
11
12
13
14
15
16
4-FC6H4
4-FC6H4
4-ClC6H4
2-ClC6H4
2-ClC6H4
4-ClC6H4
2-ClC6H4
2,4-Cl2C6H3
C6H5
4-CH3OC6H4
C6H5
75
72
68
75
73
82
70
66
73
61
62–64
50–51
118–120
90–92
66–67
116–117
80–82
82–83
4-CH3OC6H4
4-CH3OC6H4
4-CH3C6H4
4-CH3C6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
C6H5
66–67
4-NO2C6H4
131–132 (141)7
a
Reaction condition: a,b-unsaturated ketone (1 mmol), Cu(NO3)2$5H2O
(1.1 mmol), NaI (1.1 mmol), KOAc (0.2 mmol) in 10 mL of HOAc for 9 h.
b
Isolated yields.
Based on the above promising ndings, a series of a,b-
unsaturated ketones were attempted for aerobic oxidative
cleavage to synthesize 1,2-diketones using copper nitrate pen-
tahydrate as a mediator, sodium iodide as a promoter and
potassium acetate as a catalyst in acetic acid (Scheme 4 and
Scheme 4 The aerobic oxidative cleavage of a,b-unsaturated ketones
to 1,2-diketones.
Scheme 5 Proposed mechanism for the formation of 1,2-diketones.
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a,b-unsaturated ketone 1 under air. Then A is attacked by Iꢁ in
acetic acid to get B and C. C is further oxidized to D under air.
Then Iꢁ of D is replaced by hydroxy from water to a-hydroxy
dicarbonyl compound E, followed by a further oxidation to tri-
carbonyl compound F under air. The carbonyl of F is coordi-
nated with Cu(II) to form a Cu(II) complex G, which undergoes a
1,2-Wagner-Meerwein-type rearrangement of a carbonyl group
with an electron pair to the electrophilic carbon resulting in the
formation of intermediate H.13,15 The subsequent (or simulta-
neous) liberation of carbon monoxide and Cu(II) from inter-
mediate H results in the nal product 1,2-diketone 2.
1,2-Di(p-tolyl)ethane-1,2-dione
Yellow solid (185.6 mg, 78% yield); Mp: 89–92 ꢀC; IR (KBr,
cmꢁ1): n 3053, 2917, 2849, 1664, 1601; 1H NMR (400 MHz,
CDCl3): d 7.78 (d, J ¼ 8.0 Hz, 4H, ArH), 7.22 (d, J ¼ 8.0 Hz, 4H,
ArH), 2.35 (s, 6H, CH3); 13C NMR (100 MHz, CDCl3) d 194.5,
146.0, 130.7, 130.0, 129.7, 21.9. Anal. calcd for C16H14O2: C,
80.65; H, 5.92. Found: C, 80.78; H, 5.94%.
1-(4-Methoxyphenyl)-2-phenylethane-1,2-dione
Yellow solid (206.4 mg, 86% yield); Mp: 49–50 ꢀC; IR (KBr,
cmꢁ1): n 2918, 2848, 1668, 1599, 1508, 1454; 1H NMR (400 MHz,
CDCl3) d 7.94–7.96 (m, 4H, ArH), 7.63–7.65 (m, 1H, ArH), 7.50 (d,
J ¼ 7.6 Hz, 2H, ArH), 6.97–6.99 (m, 2H, ArH), 3.89 (s, 3H, CH3);
13C NMR (100 MHz, CDCl3) d 194.8, 193.1, 165.0, 134.7, 133.2,
132.3, 129.9, 128.9, 126.1, 114.4, 55.6. Anal. calcd for C15H12O3:
C, 74.99; H, 5.03. Found: C, 75.11; H, 5.01%.
Conclusions
In summary, an efficient method has developed for the aerobic
oxidative cleavage of a,b-unsaturated ketones to synthesize 1,2-
diketones using copper nitrate pentahydrate as a mediator,
sodium iodide as a promoter and potassium acetate as a catalyst
in acetic acid. The protocol has advantages of using inexpensive
and non-toxic raw materials, high yield and simple work-up
procedure.
1-Phenyl-2-p-tolylethane-1,2-dione
Yellow solid (159.1 mg, 71% yield); Mp: 82–83 ꢀC; IR (KBr,
cmꢁ1): n 3054, 2926, 2854, 1674, 1603, 1449; 1H NMR (400 MHz,
CDCl3) d 7.88 (d, J ¼ 8.0 Hz, 2H, ArH), 7.78 (d, J ¼ 8.4 Hz, 2H,
ArH), 7.54–7.58 (m, 1H, ArH), 7.40–7.44 (m, 2H, ArH), 7.22 (d, J
¼ 8.0 Hz, 2H, ArH), 2.35 (s, 3H, CH3); 13C NMR (100 MHz,
CDCl3): d 194.7, 194.2, 146.1, 134.7, 133.1, 130.6, 130.0, 129.8,
129.7, 128.9, 21.9. Anal. calcd for C15H12O2: C, 80.34; H, 5.39.
Found: C, 80.25; H, 5.41%.
Experimental
IR spectra were recorded using KBr pellets on an Alpha Centauri
1
FTIR spectrophotometer. H NMR and 13C NMR spectra were
recorded on a Mercury-400BB instrument using CDCl3 as
solvent and Me4Si as internal standard. Elemental analyses
were performed on a Vario El Elemental Analysis instrument.
Melting points were observed in an electrothermal melting
point apparatus. a,b-Unsaturated ketones were prepared
according to literature procedure.16
1-(Benzo[d][1,3]dioxol-5-yl)-2-phenylethane-1,2-dione
Yellow solid (223.5 mg, 88% yield); Mp: 96–98 ꢀC; IR (KBr,
cmꢁ1): n 3082, 2918, 2849, 1659, 1595, 1488, 1444; 1H NMR (400
MHz, CDCl3) d 7.96 (d, J ¼ 8.4 Hz, 2H, ArH), 7.63–7.67 (m, 1H,
ArH), 7.48–7.52 (m, 4H, ArH), 6.87 (d, J ¼ 8.8 Hz, 1H, ArH), 6.09
(s, 2H, CH2); 13C NMR (100 MHz, CDCl3) d 194.5, 192.7, 153.4,
148.6, 134.7, 133.1, 129.8, 128.9, 127.8, 108.3, 108.2, 106.8,
102.2. Anal. calcd for C15H10O4: C, 70.86; H, 3.96. Found: C,
70.94; H, 3.97%.
The general procedure for the preparation of 1,2-diketones
To a stirred mixture of copper nitrate pentahydrate (1.1 mmol),
sodium iodide (1.1 mmol), potassium acetate (0.2 mmol) in
10 mL of acetic acid, a,b-unsaturated ketone (1 mmol) was
added. Then the reaction system was stirred under air at 100 ꢀC
for 9 h. Aer the completion of the reaction, the mixture was
cooled to room temperature, diluted with ethyl acetate and
washed with saturated sodium carbonate solution. The result-
ing organic phase was dried over anhydrous magnesium
sulfate, and concentrated under reduced pressure. The residue
was isolated by column chromatography using petroleum ether
and ethyl acetate (100 : 1) as eluent to give pure product. The
nal product can also be further recrystallized from petroleum
ether to give purer product. The analytical data for products are
given below.
1-(Benzo[d][1,3]dioxol-5-yl)-2-p-tolylethane-1,2-dione
Yellow solid (219.8 mg, 82% yield); Mp: 102–103 ꢀC; IR (KBr,
cmꢁ1): n 3082, 1664, 1658, 1599, 1488, 1447; 1H NMR (400 MHz,
CDCl3) d 7.85 (d, J ¼ 8.0 Hz, 2H, ArH), 7.46–7.49 (m, 2H, ArH),
7.30 (d, J ¼ 8.0 Hz, 2H, ArH), 6.86 (d, J ¼ 8.8 Hz, 1H, ArH), 6.08
(s, 2H, CH2), 2.43 (s, 3H, CH3); 13C NMR (100 MHz, CDCl3) d
194.2, 192.9, 153.3, 148.6, 146.0, 130.2, 129.9, 129.6, 129.1,
127.8, 108.3, 108.2, 102.2, 21.9. Anal. calcd for C16H12O4: C,
71.64; H, 4.51. Found: C, 71.51; H, 4.49%.
Benzil
1-(4-Fluorophenyl)-2-(4-methoxyphenyl)ethane-1,2-dione
Yellow solid (174.3 mg, 83% yield); Mp: 83–84 ꢀC; IR (KBr, cmꢁ1
)
Yellow solid (193.5 mg, 75% yield); Mp: 62–64 ꢀC; IR (KBr,
n 3064, 1662, 1589, 1449; 1H NMR (400 MHz, CDCl3): d 7.98 (d, J cmꢁ1): n 3074, 2917, 2847, 1660, 1599, 1506; 1H NMR (400 MHz,
¼ 7.6 Hz, 4H, ArH), 7.64–7.68 (m, 2H, ArH), 7.49–7.53 (m, 4H, CDCl3) d 8.00–8.03 (m, 2H, ArH), 7.95 (d, J ¼ 9.0 Hz, 2H, ArH),
ArH); 13C NMR (100 MHz, CDCl3): d 194.5, 134.8, 133.0, 129.9, 7.16–7.20 (m, 2H, ArH), 6.98 (d, J ¼ 9.0 Hz, 2H, ArH), 3.89 (s, 3H,
129.0. Anal. calcd for C14H10O2: C, 79.98; H, 4.79. Found: C, CH3); 13C NMR (100 MHz, CDCl3) d 192.9, 192.5, 167.8, 165.3,
79.76; H, 4.77%.
165.0, 132.6, 132.5, 132.3, 129.6, 125.8, 116.3, 116.1, 114.3, 55.6.
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Anal. calcd for C15H11FO3: C, 69.76; H, 4.29. Found: C, 69.83; CDCl3) d 193.0, 190.3, 140.9, 134.4, 133.6, 133.5, 131.7, 131.2,
H, 4.30%.
130.5, 130.1, 129.0, 127.1. Anal. calcd for C14H8Cl2O2: C, 60.25;
H, 2.89. Found: C, 60.31; H, 2.88%.
1-(4-Fluorophenyl)-2-phenylethane-1,2-dione
1-(4-Chlorophenyl)-2-(2,4-dichlorophenyl)ethane-1,2-dione
Yellow solid (164.2 mg, 72% yield); Mp: 50–51 ꢀC; IR (KBr,
cmꢁ1): n 3071, 1665, 1593, 1503, 1448; 1H NMR (400 MHz,
CDCl3) d 8.01–8.04 (m, 2H, ArH), 7.97–7.98 (m, 2H, ArH), 7.66–
7.69 (m, 1H, ArH), 7.50–7.54 (m, 2H, ArH), 7.17–7.22 (m, 2H,
ArH). 13C NMR (100 MHz, CDCl3) d 194.0, 192.7, 168.0, 165.5,
134.9, 132.8, 132.7, 132.6, 129.9, 129.5, 129.0, 116.5, 116.2. Anal.
calcd for C14H9FO2: C, 73.68; H, 3.98. Found: C, 73.77; H, 3.99%.
Yellow solid (206.9 mg, 66% yield); Mp: 82–83 ꢀC; IR (KBr,
1
cmꢁ1): n 3074, 1661, 1581, 1469; H NMR (400 MHz, CDCl3) d
7.97 (d, J ¼ 8.4 Hz, 2H, ArH), 7.85 (d, J ¼ 8.0 Hz, 1H, ArH), 7.52
(d, J ¼ 8.4 Hz, 2H,ArH), 7.43–7.46 (m, 2H, ArH); 13C NMR
(100 MHz, CDCl3) d 192.1, 190.2, 141.4, 140.7, 134.7, 132.9,
132.2, 131.5, 130.6, 130.4, 129.4, 128.0. Anal. calcd for
C
14H7Cl3O2: C, 53.63; H, 2.25. Found: C, 53.50; H, 2.26%.
1-(4-Chlorophenyl)-2-(4-methoxyphenyl)ethane-1,2-dione
Yellow solid (186.7 mg, 68% yield); Mp: 119–120 ꢀC; IR (KBr,
cmꢁ1): n 3082, 1658, 1599, 1488, 1447; 1H NMR (400 MHz,
CDCl3) d 7.91–7.95 (m, 4H, ArH), 7.48 (d, J ¼ 8.8 Hz, 2H, ArH),
6.98 (d, J ¼ 8.8 Hz, 2H, ArH), 3.89 (s, 3H, CH3); 13C NMR (100
MHz, CDCl3) d 193.3, 192.4, 165.1, 141.3, 132.4, 131.6, 131.2,
129.3, 125.9, 114.4, 55.6. Anal. calcd for C15H11ClO3: C, 65.59; H,
4.04. Found: C, 65.69; H, 4.03%.
1-(4-Chlorophenyl)-2-phenylethane-1,2-dione
Yellow solid (178.5 mg, 73% yield); Mp: 66–67 ꢀC; IR (KBr,
1
cmꢁ1): n 1668, 1585, 1485, 1449; H NMR (400 MHz, CDCl3) d
7.84–7.90 (m, 4H, ArH), 7.58–7.62 (m, 1H, ArH), 7.41–7.47 (m,
4H, ArH); 13C NMR (100 MHz, CDCl3) d 194.7, 194.2, 146.1,
134.7, 133.1, 130.6, 130.0, 129.8, 129.7, 128.9. Anal. calcd for
C
14H9ClO2: C, 68.73; H, 3.71. Found: C, 68.68; H, 3.70%.
1-(2-Chlorophenyl)-2-(4-methoxyphenyl)ethane-1,2-dione
1-(4-Nitrophenyl)-2-phenylethane-1,2-dione
Yellow solid (205.9 mg, 75% yield); Mp: 90–92 ꢀC; IR (KBr,
cmꢁ1): n 3068, 3007, 2935, 2843, 1666, 1595, 1570, 1508; 1H NMR
(400 MHz, CDCl3) d 8.02 (d, J ¼ 8.8 Hz, 2H, ArH), 7.87–7.90
(m, 1H, ArH), 7.50–7.54 (m, 1H, ArH), 7.41–7.44 (m, 2H, ArH),
7.01 (d, J ¼ 8.8 Hz, 2H, ArH), 3.90 (s, 3H, CH3); 13C NMR
(100 MHz, CDCl3) d 193.8, 190.7, 164.7, 134.3, 134.1, 133.8,
132.6, 132.1, 130.5, 127.2, 125.5, 114.2, 55.6. Anal. calcd for
Yellow solid (155.6 mg, 61% yield); Mp: 131–132 ꢀC; IR (KBr): n
3108, 1663, 1597, 1527, 1448; 1H NMR (400 MHz, CDCl3) d 8.36
(d, J ¼ 8.8 Hz, 2H, ArH), 8.18 (d, J ¼ 8.8 Hz, 2H, ArH), 7.99 (d, J ¼
7.2 Hz, 2H, ArH), 7.70–7.74 (m, 1H, ArH), 7.54–7.58 (m, 2H,
ArH); 13C NMR (100 MHz, CDCl3) d 192.8, 192.0, 151.2, 137.3,
135.4, 132.4, 130.9, 130.0, 129.2, 124.1. Anal. calcd for
C
14H9NO4: C, 65.88; H, 3.55, N, 5.49. Found: C, 65.94; H, 3.56,
C
15H11ClO3: C, 65.59; H, 4.04. Found: C, 65.48; H, 4.05%.
N, 5.51%.
1-(2-Chlorophenyl)-2-p-tolylethane-1,2-dione
Acknowledgements
Yellow solid (188.7 mg, 73% yield); Mp: 66–67 ꢀC; IR (KBr,
1
cmꢁ1): n 3066, 1665, 1598, 1439; H NMR (400 MHz, CDCl3) d
The authors thank the National Natural Science Foundation of
China (21162024) and Key Laboratory of Eco-Environment-
Related Polymer Materials for Ministry of Education for the
nancial support of this work.
7.89–7.95 (m, 3H, ArH), 7.51–7.56 (m, 1H, ArH), 7.41–7.45
(m, 2H, ArH), 7.34 (d, J ¼ 8.0 Hz, 2H, ArH), 2.45 (s, 3H, CH3); 13
C
NMR (100 MHz, CDCl3) d 193.7, 191.8, 145.7, 134.4, 133.9, 132.1,
130.5, 130.3, 130.0, 129.6, 127.3, 21.9. Anal. calcd for
C
15H11ClO2: C, 69.64; H, 4.29. Found: C, 69.53; H, 4.30%.
Notes and references
´
1 (a) J. Mendez-Andino and L. A. Paquette, Org. Lett., 2000, 2,
1-(4-Chlorophenyl)-2-p-tolylethane-1,2-dione
1263–1265; (b) E. P. Balskus, J. Mendez-Andino, R. M. Arbit
and L. A. Paquette, J. Org. Chem., 2001, 66, 6695–6704; (c)
O. Bortolini, G. Fantin, M. Fogagnolo, P. P. Giovannini,
V. Venturi, S. Pacico and A. Massi, Tetrahedron, 2011, 67,
8110–8115; (d) A. Hense, S. V. Ley, H. M. I. Osborn,
D. R. Owen, J. F. Poisson, S. L. Warriner and K. E. Wesson,
J. Chem. Soc., Perkin Trans. 1, 1997, 2023–2031; (e)
B. M. Trost and G. M. Schroeder, J. Am. Chem. Soc., 2000,
122, 3785–3786; (f) S. Samanta and C. G. Zhao, Tetrahedron
Lett., 2006, 47, 3383–3386.
Yellow solid (212.0 mg, 82% yield); Mp: 116–117 ꢀC; IR (KBr,
cmꢁ1): n 3092, 3064, 1662, 1600, 1483; 1H NMR (400 MHz,
CDCl3) d 7.91 (d, J ¼ 8.4 Hz, 2H, ArH), 7.86 (d, J ¼ 8.0 Hz, 2H,
ArH), 7.48 (d, J ¼ 8.0 Hz, 2H, ArH), 7.31 (d, J ¼ 8.0 Hz, 2H, ArH),
2.44 (s, 3H, CH3); 13C NMR (100 MHz, CDCl3) d 193.5, 193.2,
146.4, 141.4, 131.5, 131.2, 130.4, 130.0, 129.8, 129.3, 21.9. Anal.
calcd for C15H11ClO2: C, 69.64; H, 4.29. Found: C, 69.70;
H, 4.28%.
1-(2-Chlorophenyl)-2-(4-chlorophenyl)ethane-1,2-dione
2 (a) R. Hayakawa, T. Sahara and M. Shimizu, Tetrahedron
Lett., 2000, 41, 7939–7942; (b) J. V. Sinisterra, F. Molinary,
Yellow solid (195.3 mg, 70% yield); Mp: 80–82 ꢀC; IR (KBr,
1
cmꢁ1): n 3083, 1672, 1585, 1439; H NMR (400 MHz, CDCl3) d
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