An improved synthesis of bis(cyclopentadienone)

Article abstract of DOI:10.1016/j.cclet.2010.04.005

An improved strategy for the synthesis of 3,3′-(oxy-p-phenylene)bis(2,4,5-triphenylcyclopentadienone) was developed, which includes three steps: Friedel-Crafts reaction, oxidation and condensation. Importantly, the use of KMnO₄ made the second step simple and efficient, which has potential application to synthesis of bis(cyclopentadienone)s. The course of oxidation has been confirmed by isolated intermediates.

Full text of DOI:10.1016/j.cclet.2010.04.005

Available online at www.sciencedirect.com
Chinese Chemical Letters 21 (2010) 1157–1161
www.elsevier.com/locate/cclet
An improved synthesis of bis(cyclopentadienone)
Ming Ming Yu a,1, Xia Li a,b,1, Miao Luan a, Jun Na Gao a,
a
a,
Qiu Zhi Shi a, , Ming Sheng Tang , Liu He Wei
*
*
a Department of Chemistry, Zhengzhou University, Zhengzhou 450001, China
b College of Polymer Science and Engineering, Sichuan University, Chengdu 610065, China
Received 11 January 2010
Abstract
An improved strategy for the synthesis of 3,30-(oxy-p-phenylene)bis(2,4,5-triphenylcyclopentadienone) was developed, which
includes three steps: Friedel–Crafts reaction, oxidation and condensation. Importantly, the use of KMnO4 made the second step
simple and efficient, which has potential application to synthesis of bis(cyclopentadienone)s. The course of oxidation has been
confirmed by isolated intermediates.
# 2010 Liu He Wei. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Bis(cyclopentadienone); Friedel–Crafts reaction; Oxidation; Condensation
Cyclopentadienone could react with ethynylbenzenes [1] and acetylenes [2–4] through Diels–Alder reaction.
Bis(cyclopentadienone)s are promising versatile intermediates for preparing aromatic polymers with high glass
transition temperature, thermal stability and solubility, since Diels–Alder polymerization between diacetylenes and
bis(cyclopentadienone) firstly developed by Stille and Noren [5]. Cyclopentadienones could be synthesized by several
methods such as t-BuOK-catalyzed oxygenation of cyclopentadienones [6], coupling of propargylic alcohols with
cyclopropylcarbene–chromium complexes [7], penta-carbonylation promoted silicon tethered [2 + 2 + 1] cyclo-
carbonylation reaction of two alkynes [8], transition metal mediated carbonylative coupling reactions and insertion of
CO into zirconacyclopentadienes [9]. However, for aromatic bis(cyclopentadienone)s, one of the important raw
materials for the preparation of highly aromatic polymers, there is no new synthetic method reported recently.
Normally the three-step synthesis of bis(cyclopentadienones) comprises Friedel–Crafts reaction, oxidation and
condensation, which suffer from serious drawbacks such as the use of hazardous reagents, complicated purification
and different by-products. To solve these problems, here we describe research directed towards improving the
synthesis of 3,30-(oxy-p-phenylene)bis(2,4,5-triphenylcyclopentadienone) (3) from diphenyl ether (Scheme 1) by
using appropriate solvents and reagents. In the conversion of deoxybenzoins to benzils, KMnO4 was firstly used as an
alternative oxidant and the intermediate was successfully isolated, which helps to monitor the course of the oxidation
reaction.
* Corresponding authors.
E-mail addresses: qzshi@zzu.edu.cn (Q.Z. Shi), weiliuhe@zzu.edu.cn (L.H. Wei).
1
These two authors contributed equally to this work.
1001-8417/$ – see front matter # 2010 Liu He Wei. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2010.04.005

[(Scheme_1)TD$FIG]
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M.M. Yu et al. / Chinese Chemical Letters 21 (2010) 1157–1161
Scheme 1. The present synthetic route to compound 3: (a) C6H5CH2COCl, AlCl3, CH2Cl2; HCl; NaHCO3; (b) KMnO4, TEBA, CH2Cl2, NaHCO3,
H2O; HCl, NaSO3; NaHCO3; (c) 1,3-diphenylacetone, KOH, CH3CH2OH, reflux.
[(Fig._1)TD$FIG]
Fig. 1. Structure of the Friedel–Crafts reaction products according to literature method.
We have tried to obtain phenylacetylphenyl ether (1) according to literature method [10]. The molar ratio of
biphenyl ether to phenyl acetyl chloride was 1:2.4, hazardous CS2 was used as solvent and AlCl3 as catalyst.
Unfortunately, the product could not be separated efficiently via repeated recrystallization in benzene, and different
by-products formed. Besides, the reaction mixture became sticky and hard to stir upon the addition of HCl to stop the
reaction. With the combination of repeated recrystallization and column chromatography, we isolated most of the
compounds. Results indicated that the mixture included di-substituted, tri-substituted and multi-substituted products
as shown in Fig. 1. In the improved method, CH2Cl2 was used as solvent in place of CS2. We screened the molar ratio
of diphenyl ether to phenylacetyl chloride in the reaction and the results showed that the 1.0:2.0 molar ratio gave the
best yield by recrystallization from acetone or simple washing the product with ethanol (Table 1). Under the improved
conditions, only a small amount mono-substituted by-product (4) (Fig. 2) was detected.
In the oxidation step, the most commonly used oxidants are toxic selenium dioxide and expensive N,N-diethyl-4-
nitrosoaniline [10]. In case of selenium dioxide, the reduced red powder of Se with unpleasant odor is very difficult to
remove from the product. In case of N,N-diethyl-4-nitrosoaniline, the crude product is a intractable black sticky
material. Herein, in the synthesis of 4-phenylglyoxalylphenyl ether (2), KMnO4 was employed as oxidant. The
reaction preceded smoothly and efficiently at 39 8C (Table 2). The reaction monitored by TLC shows that an
intermediate (5) exists (Fig. 3), and the intermediate has been successfully separated. The conversion of 1 to the
intermediate could be achieved in a few minutes, while the conversion from the intermediate to 2 was relatively slow,
implying that oxidation of the first methylene group raised activation energy of oxidation of the second methylene
group. Under proper conditions, 1 completely converts into 2 through the process of intermediate.
Catalyzed by KOH in ethanol, condensation between bisbenzils and 1,3-diphenylacetone depends on the
temperature critically. When the temperature of adding KOH was controlled precisely at 75 8C, target product 3 could
be prepared in a good yield.
Table 1
Data for the modified Friedel–Crafts reaction.
Entry
1
Molar ratioa
1:1.94
Refluxing time (h)
1.5
Yield (crude product) (%)
84.7
Yield (pure product)
72.4
Purification
Washed with ethanol/recrystallized
from acetone
2
3
1:2.06
1:2.0
2.5
3
94.3
88.7
>84.6
86.9
Washed with ethanol
Washed with ethanol
The concentration of biphenyl ether in CH2Cl2 (500 mL) was 0.32 M.
a
Molar ratio of biphenyl ether to phenylacetyl chloride.

[(Fig._2)TD$FIG]
M.M. Yu et al. / Chinese Chemical Letters 21 (2010) 1157–1161
1159
Fig. 2. Structure of the mono-substituted by-product (4) in improved Friedel–Crafts reaction.
Table 2
Effect of reaction conditions on the results in the oxidation reaction.
Entry Concentration of 1 (mol/L) [1]:[KMnO4]:[NaHCO3]:[TEA] Temperature (8C)
Time (h)
Yield (%)
TLC results
Oa
Rb
Ic
Pd
1
2
0.138
0.132
0.069
0.062
0.062
0.109
0.059
0.109
0.059
0.059
0.063
0.083
0.106
0.059
0.059
1:3.17:1.21:0.46
1:3.26:1.25:0.48
1:4.6:1.21:1.38
1:9.19:1.23:1.41
1:4.67:1.27:1.40
1:2.58:2.32:1.93
1:4.61:2.31:2.77
1:4.59:2.31:1.93
1:4.64:2.31:1.94
1:4.6:2.3:1.93
r.t.
r.t.
r.t.
r.t.
39
39
39
39
39
39
39
39
39
39
39
60
48
36
35
15
12
5
51
54
_
+
+
+
_
_
&
_
_
_
_
_
_
_
_
_
+
+
_
+
+
3
>56
>62.4
>58
52
_
+
+
4
_
&
&
+
*
*
+
5
_
6
_
7
92.3
>93.4
>87
88.3
90.1
90.1
>93.8
93.4
92.3
&
&
&
&
&
&
&
&
&
&
&
&
&
_
*
*
*
*
*
*
*
*
*
8
4
9
6
10
11
12
13
14
15
6.5
6
1:4.58:2.32:1.93
1:4.6:2.3:1.93
6
_
1:4.6:2.3:1.93
4
&
&
&
1:4.59:2.29:2.75
1:4.61:2.31:2.77
5.5
5
+, visible; ꢀ, invisible; &, an extremely light spot; *, a thick and round spot.
a
A spot which does not move.
b
The spot corresponding to 1.
The spot corresponding to 5.
The spot corresponding to 2.
c
d
[(Fig._3)TD$FIG]
Fig. 3. Structure of the intermediate (5) in the improved oxidation reaction.
In conclusion, we report an efficient and mild synthesis method to prepare 3,30-(oxy-p-phenylene)bis(2,4,5-
triphenylcyclopentadienone).
1. Experimental
1H NMR and 13C NMR spectra were recorded on Bruker DRX400MHz spectrometer. FT-IR was recorded on IR
spectrometer 4000. Elemental analyses were obtained from Flash EA1112 Elemental Analyzer. Melting points were
determined using an X-4 micro-melting point apparatus. Differential scanning calorimetry (DSC) was done on a
Mettler-Toledo DSC822e at a heating rate of 10 8C/min under N2 atmosphere. The peak of the exotherm determined
by DSC was also taken as the melting point. UV–vis spectra were recorded on a TU-1901 UV–vis spectrometer.
Analytical thin-layer chromatography (TLC) was performed on silica gel plates precoated with a fluorescent indicator.
Visualization was effected with ultraviolet light. Mass spectra were recorded on APEXII FT-ICR and BIFLEX III
MALDI-TOF spectrometer.
Preparation of 4-phenylacetylphenyl ether (1). In a typical protocol, anhydrous aluminum chloride (42.67 g,
0.32 mol) was dissolved in 400 mL of dry CH2Cl2 under stirring and cooled in an ice bath. A solution of diphenyl ether
(27.23 g, 0.16 mol) and phenylacetyl chloride (49.47 g, 0.32 mol) in dichloromethane (100 mL) was then slowly

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M.M. Yu et al. / Chinese Chemical Letters 21 (2010) 1157–1161
added over a 1 h period at 0.5–1.5 8C. The resulting suspension was stirred for 2 h at room temperature, then refluxed
for 3 h. 50 mL of concentrated hydrochloric acid in 50 mL of distilled water was added dropwise to the above mixture
under vigorous stirring in an ice bath. The mixture was allowed to stand at room temperature. The resulting precipitate
was collected by filtration. The organic layer was neutralized with aqueous solution of NaHCO3 and washed with
distilled water. The solvent was removed by rotary evaporation. The yellowish solid was combined with the precipitate
and washed with hot ethanol and dried in a vacuum oven to give 4-phenylacetylphenyl ether (1) as a white solid
(56.6 g, 87%). Mp: 175.2 8C. 1H NMR (CDCl3, TMS): d 4.25(s, 4H, –CH2–), 7.05(d, 4H, aromatics), 7.34(m, 10H,
aromatics), 8.03(d, 4H, aromatics). 13C NMR (CDCl3, TMS): d 45.53, 118.88, 127.00, 128.78, 129.43, 131.11, 132.51,
132.54, 134.58, 160.20, 196.15, 196.17. MS(ESI): Calcd. for C28H22O3 m/z: 315, Found 315. Elem. anal. calcd. for
C28H22O3: C, 82.74; H, 5.46. Found: C, 82.66; H, 5.46.
Preparation of mono-substituted product (4). Evaporation of ethanol afforded the mono-substituted product (4). 1H
NMR (DMSO–d6): d 4.27(s, 2H), 7.02(d, 2H, aromatics), 7.10(d, 2H, aromatics), 7.44–7.22(m, 8H, aromatics),
8.04(d, 2H, aromatics). 13C NMR (DMSO–d6): d 45.42, 117.30, 120.31, 126.90, 128.73, 128.86, 129.44, 130.09,
130.12, 131.00, 131.19, 134.80, 162.10, 196.21. MS: Calcd. for C20H16O2 m/z: 288.1, Found: 289.1. Elem. anal. calcd.
for C20H16O2: C, 83.31; H, 5.59. Found: C, 83.67; H, 5.66.
Preparation of 4-phenylglyoxalylphenyl ether (2). In a typical protocol, to a 1000 mL three-necked flask
equipped with a condenser and a stirrer, 1 (15.12 g) and CH2Cl2 (350 mL) was added, followed by the addition of a
solution of NaHCO3 (7.4 g) and tetraethylammonium bromide (TEBA) (15.12 g) in 220 mL of water, then KMnO4
(27.63 g) was added to the above mixture accompanied by vigorous stirring. After stirring at 39 8C for 4 h, the
reaction mixture was allowed to cool to room temperature. The resulting dark brown suspension was poured into a
2000 mL beaker containing 100 mL of ice water, 200 mL of concentrated hydrochloric acid and 52.0 g of
anhydrous Na2SO3. The color faded rapidly and disappeared finally. The mixture was allowed to stand at room
temperature. The yellow organic layer was neutralized with aqueous solution of NaHCO3 and washed with water
for several times. Removal of the solvent by rotary evaporation afforded a bright yellow powder (more than 15.16 g,
1
yield: higher than 94%). Mp: 106 8C. H NMR: d 7.14(d, 4H, aromatics), 7.53(t, 4H, aromatics), 7.67(t, 2H,
aromatics), 7.98(d, 4H, aromatics), 8.01(d, 4H, aromatics). Elem. anal. calcd. for C28H18O5: C, 77.41; H, 4.18.
Found: C, 77.47; H, 4.47.
Preparation of the intermediate (5). In order to determine the structure of the intermediate, we conduct the reaction
at room temperature and stop the reaction at initial stage (before the formation of 2). By column chromatography, with
CH2Cl2 as the eluent, we successfully separated the intermediate from 1. The results of 1H NMR, 13C NMR, dept and
1
MS clearly confirmed the structure of the intermediate. H NMR (DMSO–d6): d 4.38(s, 2H), 7.33–7.20(m, 9H,
aromatics), 7.62(t, 2H, aromatics), 7.79(t, 1H, aromatic), 7.92(d, 2H, aromatics), 7.99(d, 2H, aromatics), 8.14(d, 2H,
aromatics). 13C NMR (DMSO–d6): d 45.06, 119.39, 120.02, 126.97, 128.23, 128.78, 129.95, 130.09, 130.16, 131.61,
132.70, 132.97, 133.25, 135.52, 135.99, 159.23, 162.15, 193.72, 195.13, 196.78. dept (DMSO–d6): d 45.05(CH2),
119.39, 120.02, 126.97, 128.78, 129.95, 130.09, 130.16, 131.62, 132.98, 136.00 (18CH, aromatics). MS(ESI): Calcd.
for C28H20O4 m/z: 420, Found 443.5(420 plus 23 of Na).
Preparation of 3,30-(oxy-p-phenylene)bis(2,4,5-triphenylcyclopentadienone) (3). In a typical protocol, to a
1000 mL three-necked flask equipped with a condenser and a stirrer, were added 2 (9.57 g, 0.022 mol), 1,3-
diphenylacetone (9.50 g, 0.045 mol) and absolute ethanol (633 mL). The mixture was heated to 75 8C, then a solution
of KOH (4.2 g, 0.063 mol) in water (22.3 mL) was added. The mixture immediately turned to red then to black. The
temperature was raised to 78 8C within 3 min. The mixture was heated at reflux for 45 min, then allowed to cool to
room temperature. The precipitate was collected by filtration and washed with water and ethanol to give crude product
1
of 3. Further purification by washing with toluene and ethanol gave pure 3. Mp: 273 8C. H NMR: d 6.78(d, 4H,
aromatics), 6.88(d, 4H, aromatics), 6.94(d, 4H, aromatics), 7.18–7.28(26H, aromatics). 13C NMR: d 118.31, 125.11,
125.49, 127.52, 128.06, 128.13, 128.22, 128.57, 129.38, 130.14, 130.64, 130.81, 131.20, 133.10, 153.75, 154.08,
156.74, 200.15. Elem. anal. calcd. for C58H38O3: C, 88.98; H, 4.89. Found: C, 88.87; H, 4.92. MS(MALDI-TOF):
Calcd for C58H38O3 782, Found 782.8.
Acknowledgments
We thank the National Natural Science Foundation of China for financial support (Nos. 50873093; 50903075); we
also thank Professor Tong Zhao, Professor Fengqi Guo and Caimei Ren for assistance.

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