Quinones synthesis via hydrogen peroxide oxidation of dihydroxy arenes catalyzed by homogeneous and macroporous-polymer-supported ruthenium catalysts

Article abstract of DOI:10.1016/j.tet.2013.07.069

Ruthenium(II)/dimethyl phenyloxazoline (Ru(II)/dm-Pheox) complex 2a and its macroporous-polymeric-catalyst 4 were found to be very rapid and efficient catalysts in the hydrogen peroxide oxidation of 1,2- and 1,4-dihydroxy arenes. Most of the quinone products were delivered in 99% yield. The polymeric-catalyst 4 could be reused at least five times.

Full text of DOI:10.1016/j.tet.2013.07.069

Tetrahedron 69 (2013) 8612e8617
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Quinones synthesis via hydrogen peroxide oxidation of dihydroxy
arenes catalyzed by homogeneous and macroporous-polymer-
supported ruthenium catalysts
Abdel-Moneim Abu-Elfotoh, Kazuyuki Tsuzuki, Tram Bao Nguyen, Soda Chanthamath,
*
Kazutaka Shibatomi, Seiji Iwasa
Department of Environmental and Life Sciences, Toyohashi University of Technology, 1-1 Tempaku-cho, Toyohashi, Aichi 441-8580, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 June 2013
Received in revised form 18 July 2013
Accepted 21 July 2013
Available online 5 August 2013
Ruthenium(II)/dimethyl phenyloxazoline (Ru(II)/dm-Pheox) complex 2a and its macroporous-polymeric-
catalyst 4 were found to be very rapid and efficient catalysts in the hydrogen peroxide oxidation of
1,2- and 1,4-dihydroxy arenes. Most of the quinone products were delivered in 99% yield. The polymeric-
catalyst 4 could be reused at least five times.
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Quinone
Dihydroxy arene
Oxidation
Hydrogen peroxide
Ruthenium catalyst
1. Introduction
complexes/O
isopoly compounds/H
2
, copper sulfateealumina/O
2
,12 and heteropoly and
The main drawback with the
13
14
2
O
2
2
or O .
Quinones are useful compounds not only as synthetic in-
previous catalytic systems is the use of homogeneous catalysts that
leads to two major problems, one is the catalyst separation and the
second is the contamination of the quinone products by the tran-
sition metal traces. From this regard, using polymer-supported
catalysts for quinone synthesis in the presence of hydrogen per-
oxide is an interesting research subject owing to the well-known
advantages of the heterogeneous catalysts over the homogeneous
catalysts such as the efficient recovery of the often-expensive cat-
alysts, and potentially reuse of these catalysts. In addition, when
using heterogeneous catalyst, there is no contamination of the re-
action product by the metal traces. Especially, polymer-supported
ruthenium complex was found to be effective as catalyst for the
1
termediates such as dienophiles in the chemical transformations,
2
but also as biological active compounds. For example, they have
3
a potential value in cancer chemotherapy as well as their antitu-
4
mor, antibacterial, and antiprotozoan activities. 2-Methyl-1,4-
3
naphthoquinone (vitamin K ) and its derivatives are also used as
5
6
blood coagulating agents and as a supplement in animal feed and
currently attracting much attention because of its interesting
7
pharmacological activities. In addition, trimethyl-p-benzoquinone
is a key compound in the vitamin E synthesis. Quinones are usually
prepared by direct oxidations of hydroquinone, catechol, naph-
8
thols, and their derivatives. Although a wide variety of oxidants
9
were used for oxidation of dihydroxy arenes, molecular oxygen
2 2
decomposition of H O along with good ability for recycling several
15
and hydrogen peroxide are the best oxidants from the environ-
mental and economical point of view as clean and cheap oxidants.
There are several reported catalytic systems that have been de-
veloped for quinones synthesis using molecular oxygen and hy-
drogen peroxide as an oxidant. Among these catalytic systems
times without loss of activity. Notably, the insoluble cross-linked
polymers are used widely as they are inert, non-toxic, thermally
16
stable, and easy to be recycled. Despite the tremendous efforts
devoted to quinones synthesis using polymer-supported catalysts,
17
4a,18
kinetic studies or limited substrate scope
have so far been
1
0
11
are copper salts/O
2
,
ruthenium salts/H
2
O
2
,
Schiff base cobalt
achieved. Recently, polymer-incarcerated platinum catalyst was
found to be very efficient catalyst for aerobic oxidation of hydro-
19
quinone derivatives. In this case, treatment of the recovered
catalyst with base is essential for preventing the gradual decline in
reusability. Although one catechol derivative was presented, Park
*
Corresponding author. Tel./fax: þ81 532 44 6817; e-mail address: iwasa@en-
s.tut.ac.jp (S. Iwasa).
0
040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.07.069

A.-M. Abu-Elfotoh et al. / Tetrahedron 69 (2013) 8612e8617
8613
et al.20 developed a highly efficient and recyclable copper catalyst
Cu/AlO(OH)) for the aerobic oxidation of a wide range of hydro-
quinones. Our recent study on quinones synthesis showed that
a)
+
(
O
N
O
N
(i)
II
I
Ru and Ir are efficient homogeneous catalysts for hydrogen per-
Ru
(
21
oxide oxidation of phenols and methoxyarenes. As a comple-
mentary study for this interesting research area, we focused on
the hydrogen peroxide oxidation of dihydroxy arenes by using
macroporous-polymer-supported catalysts. To the best of our
knowledge, there is no report with a wide substrate scope for ox-
NCCH3)4
−
PF
6
1a
2a
b)
II
Cl
HO
O
N
O
N
idation of dihydroxy arenes using polymer-supported Ru -catalyst
(ii) - (iii)
and hydrogen peroxide as an oxidant.
1b
1c
2
. Results and discussion
+
HO
O
Very recently, we explored a novel strategy for the synthesis of
II
22a
(i)
O
(iv)
macroporous-polymer-supported Ru -catalyst.
We found that
N
Ru
(NCCH3)4
the catalyst on cross-linked support with pores of molecular di-
mension has shown significant increase in its selectivity and re-
activity due to high concentration of the active sites within the
small pores. Inspired by our previous work, we successfully
−
6
PF
2b
2
2b
immobilized the catalyst 2a
onto a macroporous cross-linked
+
polymeric-support to afford 4. The catalysts 2a and 4 promoted
the hydrogen peroxide oxidation of a broad class of dihydroxy
arenes to furnish the quinone products in excellent yields (99% in
most of the cases). The polymeric-catalyst 4 could be reused at least
five times without loss in reactivity. The Ru(II)/dm-Pheox catalyst
O
N
O
(
v)
Ru
(
NCCH3)4
−
PF6
3
2
a could be easily synthesized in high yield as described on the
2
2b
previous report (Scheme 1a).
Initially, we evaluated the catalytic
activity of 2a in hydrogen peroxide oxidation of 1,4-dihydroxy
naphthalene using various solvents as shown in Table 1. Pleas-
ingly, naphthoquinone products were obtained in quantitative
yields with most of the used solvents. And THF was found to be the
best solvent (Table 1, entry 4). It is noteworthy that the quinone
products resulted in a pure form after extraction with diethyl ether
or dichloromethane and there is no necessity for further column
purification compared with the previous studies.
z
y
x
O
+
O
N
O
Ru
x,y,z 1,90,9
=
(NCCH3)4
−
PF
6
4
Next, by using THF as a solvent, we optimized the reaction
conditions as shown in Table 2. We found that different loadings of
catalyst 2a quantitatively oxidized 1,4-dihydroxy naphthalene
Scheme 1. Synthesis of catalysts 2a and 4. Reagents and conditions: (i) [RuCl
2
(ben-
ꢀ
zene)]
2
(0.5 equiv), KPF
6
(4.0 equiv), 1 N NaOH (1.0 equiv), CH
3
CN, 80 C, 24 h; (ii)
AcONa$3H
2
O (5.0 equiv), NaI (5.0 equiv), CH
3
CN, reflux, 24 h; (iii) MeOH/H
2
O (5:1 v/v),
ꢀ
2.5 N NaOH (6.0 equiv), 3 h, 0 C/rt; (iv) acrylic acid (3.0 equiv), DCC (3.0 equiv),
(Table 2, entries 1e5). A high TON was achieved with 0.01 mol % of
ꢀ
DMAP (2.0 equiv), CH
3
CN, 0 C/rt, 3 h; (v) styrene, DVB, AIBN (2.0 equiv), CH
2
Cl
2
,
2
a (Table 2, entry 5) while a high TOF was obtained with 0.25 mol %
ꢀ
H
2
O, 60 C, 24 h.
of 2a (Table 2, entry 3). When we replaced hydrogen peroxide by
molecular oxygen as an oxidant, the naphthoquinone product was
isolated in 25% yield in 1 day (Table 2, entry 7). The blank test
showed that only 6% of the naphthoquinone product was obtained
in 5 days (Table 2, entry 8). Since catalyst 2a was found to be very
efficient in quinone synthesis, we decided to immobilize it onto
polymeric-support and evaluate its catalytic activity in hydrogen
peroxide oxidation of various dihydroxy arenes. The steps to
functionalize the homogeneous Ru-catalyst 2a to be ready for the
polymerization step started by the reaction between 4-(chlor-
omethyl)benzoyl chloride and 2-amino-2-methyl-1-propanaol to
furnish the ligand 1b in 86% yield. The Ru-catalyst 2b was syn-
thesized from 1b in two steps in excellent yield (92%) as shown in
Scheme 1b.
conditions with the polymeric-heterogeneous-catalyst 4.23 Under
the optimized reaction conditions, we studied the hydrogen per-
oxide oxidation of various hydroquinone and catechol derivatives
along with dihydroxy naphthalene by using 2a or 4 as the catalyst
(Table 3).
Table 1
Solvent screening
a
The monomeric Ru(II)/dm-Pheox complex
3
was readily
Yieldb (%)
Entry
Solvent
Time
prepared from 2b in 70% yield as a new monomeric complex
1
2
3
4
5
6
7
8
Toluene
Acetone
21.5 h
8 min
12.5 h
5 min
7 min
10 min
8 min
10 min
37
99
36
99
99
99
99
97
that was easily cross-link polymerized with styrene and 1,4-
0
divinylbenzene (DVB) in the presence of 2,2 -azobisizobutyroni-
CH
Cl
2 2
THF
1,4-Dioxane
DMF
trile (AIBN) as an initiator. The reaction was carried out in the
presence of water to afford the macroporous-polymer-supported
Ru(II)/dm-Pheox (4) in quantitative yield, as shown in Scheme
CH
3
OH
1
b and Fig. 1. The exact amount of the Ru(II)/dm-Pheox complex
2
Et O
loaded onto the polymeric network was determined by elemental
analysis of the nitrogen content. Encouraged by the excellent re-
sults from the homogeneous catalyst 2a, we optimized the reaction
a
Reactions were performed by using 0.34 mmol of 1,4-dihydroxy naphthalene in
1.0 mL of solvent with 0.0034 mmol of 2a and 0.44 mmol of H O .
2 2
b
Isolated yield.

8614
A.-M. Abu-Elfotoh et al. / Tetrahedron 69 (2013) 8612e8617
Table 2
Effect of catalyst loading
Table 3
a
Hydrogen peroxide oxidation of various dihydroxy arenes catalyzed by 2a or 4a
Entry
Catalyst
Product
Yieldb (%)
Time
c
1
2
2a
4
75
5 min
2.5 h
c
70
3
4
2a
4
99
99
5 min
2 h
Entry
2a (mol %)
Time
Yieldb (%)
TONc
TOFd
1
2
3
4
5
6
1.0
0.5
5 min
5 min
5 min
2 h
6 h
6 h
99
99
99
99
99
13
25
6
100
200
400
1000
10,000
2600
25
1200
2400
4800
500
500
433
1
0.25
0.1
0.01
0.005
1.0
5
6
2a
4
99
99
5 min
2 h
e
7
8
24 h
5 days
7
8
2a
4
99
99
5 min
24 h
d
d
d
a
Reactions were performed on 0.34 mmol of 1,4-dihydroxy naphthalene in
1
.0 mL THF with 0.44 mmol H
2
O
2
.
b
Isolated yields.
9
2a
4
99
99
5 min
48 h
c
Turnover number (moles of product/moles of catalyst).
Turnover frequency (TON/h).
Using O as oxidant instead of H O .
2 2 2
d
e
10
1
1
1
2
2a
4
99
70
5 min
24 h
d
1
3
4
2a
4
99
99
5 min
3 h
1
1
1
5d
6
2a
4
98
99
4 h
48 h
1
1
7d
2a
4
86
85
2 h
d
8
24 h
1
2
9e
2a
4
71
65
30 min
24 h
e
0
2
1
2
2a
4
99
99
5 min
3 h
2
a
Reaction conditions: in case of catalyst 2a, reaction was performed on
0
.34 mmol of dihydroxy arenes in 1.0 mL of THF with 0.0034 mmol of 2a (1.0 mol %)
ꢀ
and 0.44 mmol of 30% aq H
2
O
2
at 0 C to rt. In case of catalyst 4, reaction was
performed on 1.0 mmol of dihydroxy arenes in 3.0 mL of THF with 0.022 mmol of 4
ꢀ
(
2.2 mol %) and 1.3 mmol of 30% aq H
2
O
2
at 0 C to rt.
b
Isolated yield.
c
1
H NMR and TLC showed that all starting material had completely oxidized and
after vacuum we got only this yield.
d
The crude product was purified by column chromatography (n-hexane/
EtOAc¼5:1).
e
2
The mixture was concentrated under reduced pressure and washed by Et O.
Fig. 1. Images of the macroporous polymer-supported Ru(II)/dm-Pheox complex 4.
oxidation reaction (Table 3, even entries 2e14). We expect that the
high catalytic efficiency of catalyst 4 owing to its macroporous
structure, as revealed by the SEM (Fig. 1). In addition, it was ob-
served that by using 4 as the catalyst, catechol derivatives were
slowly oxidized to 1,2-benzoquinone derivatives in very good yields
(68e99%; Table 3, even entries 16e20). On the other hand, 2a has
catalytic power to oxidize catechol derivatives in the presence of
Notably, the hydroquinone derivatives were quantitatively oxi-
dized in 5 min under the catalytic influence of 2a (Table 3, odd
1
entries 1e13). From H NMR and TLC we found that unsubstituted
hydroquinone was completely oxidized but after extraction and
dryness we obtained only 75% isolated yield of the quinone product
H
2
O
2
in a short time (10 min to 4 h; Table 3, odd entries 15e19).
(Table 3, entry 1). We attributed this decrease in yield to the low
It is well-known that 1,4-naphthoquinone derivatives possess
molecular weight of the quinone product, which leads to decrease
in the amount of the product during the dryness step. In the case of
polymeric-catalyst 4, 2 h to 2 days is necessary to complete the
antibacterial and antitumor properties because of their aromatic
stability. Interestingly, we found that both of 2a and 4 are very
efficient in the oxidation of 1,4-dihydroxy naphthalene to the

A.-M. Abu-Elfotoh et al. / Tetrahedron 69 (2013) 8612e8617
8615
corresponding naphthoquinone (Table 3, entries 21 and 22). Finally,
we tested whether the polymeric-catalyst 4 has ability to be recy-
cled or not. In the hydrogen peroxide oxidation of 1,4-dihydroxy
naphthalene, we found that the macroporous-catalyst 4 was eas-
ily recovered from the reaction mixture by addition of diethyl ether,
centrifugation, decantation of the quinone product, washing the
catalyst with diethyl ether, and carefully dried under vacuum be-
fore the next cycle. The polymeric-catalyst showed ability to be
reused at least five times without any decrease in catalytic
activity. In all cycles, the quinone products resulted in a pure form
and there is no necessity to do further purification by column
chromatography.
Saturated NaHCO
3
(aqua, 50 mL) was added to the residue with
stirring for 5 min. The organic product was extracted with
dichloromethane (3ꢂ50 mL), dried over anhydrous Na SO or
MgSO , filtered, and concentrated under reduced pressure. Sub-
2
4
4
sequently, to a solution of the previous reaction residue in 1,4-
dioxane (20.0 mL) was added 2.5 N NaOH(aq) (16.0 mL, 40 mmol,
ꢀ
ca. 2.5 M) at 0 C. After stirring for 12 h at room temperature, the
solvent was removed under vacuum, followed by addition of water
(30.0 mL) and dichloromethane (3ꢂ25 mL) for extraction. The or-
2 4
ganic layer was dried over anhydrous Na SO , filtered, and evapo-
rated under vacuum. The crude product was purified by column
chromatography on silica gel (EtOAc/n-hexane¼1:10 v/v) to afford
ligand 1b in 86% yield for three steps as a pale yellow solid. Mp
ꢀ
1
3
. Conclusion
78 C. H NMR (400 MHz, CDCl
H), 7.42 (d, J¼8.4 Hz, 2H), 7.92 (d, J¼8.4 Hz, 2H). C NMR
(100 MHz, CDCl 28.6, 45.8, 67.9, 79.4, 128.3, 128.7, 128.8, 140.6,
161.8. Anal. Calcd for C12 14ClNO: C, 64.43; H, 6.31; N, 6.26%. Found:
C, 64.27; H, 6.34; N, 6.22%. IR (neat) 3384.5, 2972.7, 2931.3, 2896.6,
3
) d 1.37 (s, 6H), 4.10 (s, 2H), 4.59 (s,
13
2
In conclusion, quinones were easily and quantitatively synthe-
3
) d
sized via hydrogen peroxide oxidation of dihydroxy arenes cata-
lyzed by ruthenium(II)/dimethyl phenyloxazoline (Ru(II)/dm-
Pheox) (2a) and its environmentally benign macroporous-
polymeric-support (4). The homogeneous 2a and the polymeric 4
catalysts delivered the quinones in excellent yields (99%). The
polymeric-catalyst 4 could be readily recovered and recycled at
least five times without loss of its catalytic activity. Notably, qui-
none products resulted in a pure form without necessity for further
purification in most of the cases. Further investigation is currently
underway to improve the ability of our catalysts for aerobic oxi-
dation of dihydroxy arenes.
H
n
ꢁ
1
1660.4 cm
.
4.3. (4-(4,5-Dihydro-4,4-dimethyloxazol-2-yl)phenyl)metha-
nol {dm-Pheox ligand (1c)}
A mixture of 1b (2237.0 mg, 10.0 mmol), CH
(6804.0 mg, 50.0 mmol), and NaI (7494.5 mg, 50.0 mmol) was
3 2 2
CO Na$3H O
suspended in CH
80 C. The solvent was removed by evaporation under reduced
3
CN (60.0 mL) and refluxed under N
2
for 24 h at
ꢀ
3 2
pressure and the resulted crude ester was dissolved in CH OH/H O
4
4
. Experimental section
(54.0 mL, 5:1 v/v) using a sonicator and followed by the slow ad-
dition of 2.5 N NaOH (24.0 mL, 60.0 mmol) at 0 C. The reaction
mixture was stirred for 3 h at room temperature and the product
ꢀ
.1. General
was extracted by CH
was dried over anhydrous Na
2
Cl
2
(3ꢂ50 mL). The combined organic layer
All reactions were performed under the normal air atmosphere.
2
SO , and concentrated under reduced
4
CH
Co., Inc. THF, MeOH, and Et
Wako Pure Chemical Industries Co., Ltd. Reactions were monitored
by TLC, glass plates pre-coated with silica gel Merck KGaA 60 F254
2
Cl
2
and DMF dehydrated were purchased from Kanto Chemical
pressure. The residue was purified by column chromatography on
silica gel (EtOAc/n-hexane¼1:10 v/v) to afford (4-(4,5-dihydro-4,4-
dimethyloxazol-2-yl)-phenyl)methanol 1c (1744.6 mg, 8.50 mmol,
2
O dehydrated were purchased from
ꢀ
1
,
85.0% yield) as a white solid. Mp 115 C. H NMR (400 MHz, CDCl
3
)
layer thickness 0.2 mm. All the starting materials are commercially
available and were used as received. Flash column chromatography
d
1.4 (s, 6H), 1.87 (t, J¼6.0 Hz, 1H), 4.12 (s, 2H), 4.76 (d, J¼6.4 Hz, 2H),
13
7.41 (d, J¼8.3 Hz, 2H), 7.93 (d, J¼8.5 Hz, 2H). C NMR (100 MHz,
CDCl 28.6, 64.4, 67.6, 79.4, 126.7, 128.56, 128.57, 145.1, 162.6.
Anal. Calcd for C12 : C, 70.22; H, 7.37; N, 6.82%; Found: C,
69.98; H, 7.50; N, 6.84%. IR (neat) 3257.2, 2966.0, 2931.3, 2896.6,
1
was performed over Merck (Art. No. 7734). H NMR (400 MHz or
3
) d
3
00 MHz) and 13C NMR (100 MHz or 75 MHz) spectra were
H15NO
2
recorded on Varian Inova-400 or Mercury-300 spectrometer.
Chemical shifts are reported as values (ppm) relative to internal
tetramethylsilane (0.00 ppm) in CDCl . IR spectra were recorded by
using JASCO FT/IR-230 spectrometer and are reported in reciprocal
n
ꢁ
1
d
1648.8 cm .
3
4.4. [2-(4-Hydroxymethyl)phenyl-4,4-dimethyloxazole)
Ru(CH CN) ]PF {Ru(II)/dm-Pheox complex (2b)}
ꢁ1
centimeter (cm ). Melting points were measured on a Yanaco MP-
J3 and not corrected. Elemental analyses were measured on
a Yanaco CHN CORDER MT-6. Field emission scanning electron
microscope (FESEM) studies were performed using a Hitachi S-
3
4
6
Complex 2b was synthesized from 1c (1026.3 mg, 5.0 mmol) in
92% yield by the same procedure as that for 2a and was obtained as
a yellow solid. Mp (dec) 85e87 C. H NMR (400 MHz, CDCl ) d 1.37
ꢀ
1
4
800 (FESEM) with accelerating voltage of 10.0 kV and the fracture
3
surfaces were sputter-coated with PtePd under an electric current
of 15 mA at 6 Pa for 60 s. Ru(II)/dm-Pheox complex was prepared by
our own method.
(s, 6H), 1.73 (t, J¼6.1 Hz, 1H), 2.16 (s, 6H), 2.52 (s, 3H), 2.57 (s, 3H),
4.39 (s, 2H), 4.75 (d, J¼6.0 Hz, 2H), 6.94 (dd, J¼1.6, 7.7 Hz, 1H), 7.41
13
(d, J¼7.7 Hz, 1H), 7.84 (d, J¼1.4 Hz, 1H). C NMR (100 MHz, CD
3
CN)
d
3.1, 3.7, 26.7, 64.7, 66.1, 81.6, 119.4, 121.9, 122.5, 125.3, 134.7, 136.6,
142.4, 172.2, 185.8. Anal. Calcd for C20 PRu: C, 39.09; H,
4.26; N 11.40%. Found: C, 39.12; H, 4.23; N,11.29%. IR (neat) 3587.9,
4
.2. 2-(4-(Chloromethyl)phenyl)-4,5-dihydro-4,4-
26 6 5 2
H F N O
dimethyloxazole {dm-Pheox ligand (1b)}
n
ꢁ
1
2984.3, 2937.1, 2281.4, 1624.7, 847.6, 567.9 cm .
To a mixture of 2-amino-2-methyl-1-propanol (784.4 mg,
8
.8 mmol) and triethylamine (4.5 ml, 32 mmol) in dichloromethane
4.5. Synthesis of the monomeric Ru(II)/dm-Pheox complex (3)
(
20.0 mL) was added a solution of 4-(chloromethyl)benzoyl chlo-
ꢀ
0
ride (1512.0 mg, 8.0 mmol) in dichloromethane (15.0 mL) at 0 C.
After stirring for 10 h at room temperature, the reaction mixture
was concentrated under reduced pressure. The residue was dis-
A mixture of 2b (200.0 mg, 0.32 mmol), N,N -dicyclohex-
ylcarbodiimide (DCC) (201.2 mg, 0.96 mmol), and 4-dimethyl
aminopyridine (DMAP) (7.4 mg, 0.06 mmol) was placed in a two-
necked flask equipped with a magnetic stirring bar. The system was
3
CN (6.0 mL) was injected
and the flask was immersed in ice followed by the slow injection of
solved in CHCl
3
(20.0 mL) and was treated with SOCl
2
(3.0 mL,
0 mmol) at 0 C. After stirring for 24 h at room temperature,
the solvent and SOCl were removed under reduced pressure.
ꢀ
4
evacuated and backfilled with argon. CH
2

8616
A.-M. Abu-Elfotoh et al. / Tetrahedron 69 (2013) 8612e8617
acrylic acid (66.6 mL, 0.96 mmol). The starting material had com-
pletely reacted after 3 h at room temperature. The solvent was
evaporated under reduced pressure and the crude product was
Na
2 4
SO and condensed under vacuum to afford the corresponding
quinone in a pure form.
1
9
purified by column chromatography on silica gel with CH
CH CN (20:1 (v/v)) to afford a yellow solid product 3 in 70% yield
150.5 mg, 0.225 mmol). R Cl /CH CN¼5:2 v/v). Mp
¼0.78 (CH
dec) 100e102 C. H NMR (400 MHz, CDCl 1.37 (s, 6H), 2.16 (s,
H), 2.52 (s, 3H), 2.55 (s, 3H), 4.39 (s, 2H), 5.27 (s, 2H), 5.87 (dd,
J¼1.7, 10.5 Hz, 1H), 6.22 (dd, J¼10.5, 17.3 Hz, 1H), 6.48 (dd, J¼1.6,
7.6 Hz,1H), 6.94 (dd, J¼1.6, 7.7 Hz,1H), 7.40 (d, J¼7.7 Hz, 1H), 7.8 (d,
2
Cl
2
/
4.8.1. 2,3-Dimethyl-1,4-benzoquinone. Green solid. R
f
¼0.37 (n-
1.99 (s, 6H),
12.4, 136.4, 141.2, 187.6. IR
1
3
hexane/EtOAc¼10:1). H NMR (300 MHz, (CD
3 2
) CO) d
13
(
(
f
2
2
3
6.76 (s, 2H). C NMR (100 MHz, CDCl
3
)
d
ꢀ
1
ꢁ1
3
)
d
(neat)
n
1659.5 cm
.
6
4.8.2. Trimethyl-1,4-benzoquinone. Green oil. R
f
¼0.67 (n-hexane/
1.96 (m, 3H), 1.99 (m,
3
) d 12.3, 12.6, 16.1, 133.3,
1
1
EtOAc¼6:1). H NMR (300 MHz, (CD CO)
6H), 6.60 (m, 1H). C NMR (100 MHz, CDCl
ꢁ
140.9, 141.1, 145.5, 187.7, 188.1. IR (neat) 1648.8 cm .
3
)
2
d
13
13
J¼1.4 Hz, 1H). C NMR (100 MHz, CDCl
6.2, 81.7, 120.0, 121.2, 121.4, 121.9, 125.5, 134.8, 136.8, 141.5, 172.2,
85.6. Anal. Calcd for C23 PRu: C, 41.32; H, 4.22; N, 10.48%.
Found: C, 41.30; H, 4.16; N, 10.50%. IR (neat) 2998.1, 2951.3, 2198.4,
3
)
d
3.5, 4.1, 4.5, 27.6, 66.0,
1
6
n
1
28 6 5 3
H F N O
19
n
4.8.3. 2-tert-Butyl-1,4-benzoquinone. Green solid.
R
f
¼0.47 (n-
1.29 (s, 9H), 6.59
29.3,
ꢁ
1
1
1769.8, 1634.7, 1199.9, 1094.8, 874.9 cm
.
hexane/EtOAc¼10:1). H NMR (300 MHz, CDCl
3
) d
13
(
3
s, 1H), 6.68 (d, J¼1.0 Hz, 2H). C NMR (100 MHz, CDCl
3
) d
ꢁ1
5.5, 131.7, 135.1, 138.9, 156.3, 187.7, 188.6. IR (neat) n 1654.6 cm .
4
.6. Synthesis of macroporous-polymer-supported Ru(II)/dm-
Pheox complex (4)
1
9,20
4
.8.4. 2-Phenyl-1,4-benzoquinone.
Brown solid. ¼0.25 (n-
R
f
1
hexane/EtOAc¼10:1). H NMR (300 MHz, (CD
3
)
2
CO) d 6.85e6.97
Cross-link polymerization of the monomeric Ru(II)/dm-Pheox
complex (3) to afford (4) as a macroporous polymer. The mono-
meric complex 3 (100.0 mg, 0.149 mmol) was placed in a 100 mL
round two-necked flask fitted with a magnetic stirring bar and
a reflux condenser. After evacuation and refilling with argon,
13
(
m, 3H), 7.44e7.50 (m, 3H), 7.53e7.58 (m, 2H). C NMR (100 MHz,
CDCl 128.7, 129.4, 130.4, 132.9, 136.5, 137.3, 146.1, 186.9, 187.9. IR
3
) d
ꢁ
1
(neat) n 1649.8 cm .
13
4
(
1
.8.5. 2,5-Di-tert-Butyl-1,4-benzoquinone. Brown solid. R
f
¼0.67
1.26 (s,
29.3, 34.8, 133.8,
CH
lution of the monomer was supplied with styrene (1.5 mL,
3.41 mmol), 1,4-divinylbenzene (DVB) (0.19 mL, 1.34 mmol), and
2 2
Cl (4.5 mL) was injected from the side arm. The resulting so-
1
n-hexane/EtOAc¼5:1). H NMR (300 MHz, (CD
3 2
) CO) d
13
8H), 6.47 (s, 2H). C NMR (100 MHz, CDCl
3
)
d
1
ꢁ
1
0
154.5, 188.7. IR (neat) n 1647.9 cm .
distilled H O (1.5 mL) via syringe. Finally, 2,2 -azobisizobutyroni-
2
trile (AIBN) (48.9 mg, 0.29 mmol) was added and the reaction
mixture was heated under reflux for 24 h. The content of the flask
completely polymerized. The polymerized product was washed
with n-hexane, diethyl ether. and acetonitrile, respectively, until
nothing detected in the washing filtrate under UV then, dried under
vacuum and grinded in a mortar to afford a yellow solid product 4
in a quantitative yield (1600.0 mg). Anal. Found: C, 85.48%; H,
1
9,20
4
.8.6. 2-Methoxy-1,4-benzoquinone.
Brown solid. R
f
¼0.42 (n-
1
hexane/EtOAc¼5:1). H NMR (300 MHz, CDCl
3
)
d
3.82 (s, 3H), 5.94
56.5, 107.9, 134.7,
13
(
3
s, 1H), 6.71 (s, 2H). C NMR (100 MHz, CDCl )
d
ꢁ
1
137.5, 158.8, 181.9, 187.7. IR (neat)
n
2856.1, 1648.8 cm
.
.8.7. 3,5-Di-tert-Butyl-1,2-benzoquinone19,20. Green solid. H NMR
1
4
3
(300 MHz, CDCl ) d
1.22 (s, 9H), 1.26 (s, 9H), 6.21 (d, J¼2.4 Hz, 1H),
7
.36%; N, 0.98% (loading 0.14 mmol/g). IR (neat) n 3482.8, 2990.1,
13
ꢁ
1
6.92 (d, J¼2.4 Hz, 1H). C NMR (100 MHz, CDCl
3
) d 28.1, 29.4, 35.7,
2
931.3, 2118.4, 1729.8, 1624.7, 1189.9, 1084.8, 864.9, 573.7 cm
.
ꢁ
1
3
6.2, 122.3, 133.7, 150.1, 163.6, 180.2, 181.3. IR (neat) n 1655.6 cm .
4
.7. General procedure for 2a catalyzed H oxidation of
2
O
2
19
4
.8.8. 4-tert-Butyl-1,2-benzoquinone. Brown solid. R
f
¼0.26 (n-
1.26 (s, 9H),
.19 (d, J¼2.5 Hz, 1H), 6.35 (d, J¼10.4 Hz, 1H), 7.46 (dd, J¼2.4,
dihydroxy arenes
1
hexane/EtOAc¼5:1). H NMR (300 MHz, (CD
3 2
) CO) d
6
1
To a solution of dihydroxy arene (0.34 mmol) and 2a (1.98 mg,
13
3
0.4 Hz, 1H). C NMR (100 MHz, CDCl ) d 28.0, 35.8, 124.0, 129.6,
0
0
.0034 mmol) in THF (1.0 mL) was added H
.44 mmol) at 0 C. After 5 min the starting material had com-
2
O
2
(30% aq, 50.0
mL,
ꢁ1
140.2, 162.3, 180.5. IR (neat)
n
1659.5 cm
.
ꢀ
pletely oxidized to the quinone product. The quinone product was
then extracted by ether or dichloromethane, dried over anhydrous
Na SO , and concentrated under reduced pressure to afford the
2 4
desired product. Pleasingly, the resulted quinone products were
pure enough and there is no necessity for column chromatography
in most of the cases.
24
4
.8.9. 3-Methoxy-1,2-benzoquinone. Black solid. R
f
¼0.20 (n-hex-
1
ane/EtOAc¼3:2). H NMR (400 MHz, (CD
3 2
) CO) d 3.73 (s, 3H), 5.97
(
d, J¼10.2 Hz, 1H), 6.13 (d, J¼7.2 Hz, 1H), 7.15 (dd, J¼7.3, 8.8 Hz, 1H).
13
C NMR (100 MHz, (CD
3
)
2
CO)
d
55.4,107.5,122.5,141.9,154.3,176.0.
ꢁ1
IR (neat)
n
1657.5 cm
.
1
9
4
.8.10. 1,4-Naphthoquinone. Brown solid.
R
f
¼0.61 (n-hexane/
7.05 (s, 2H), 7.86e7.91
(m, 2H), 8.03e8.08 (m, 2H). C NMR (100 MHz, CDCl 126.6,
1
4
.8. General procedure for 4 catalyzed H
2
O
2
oxidation of di-
EtOAc¼3:1). H NMR (400 MHz, (CD
3 2
) CO) d
13
hydroxy arenes
3
) d
ꢁ
1
1
32.0, 134.1, 138.8, 185.2. IR (neat)
n 1662.3 cm .
The polymer-supported Ru(II)/dm-Pheox complex 4 (160.0 mg,
2
.2 mol %) was suspended in THF (3.0 mL). Dihydroxy arene of
Acknowledgements
ꢀ
1.0 mmol was added with constant stirring at 0 C followed by the
addition of H
2
O
2
(30% aq, 0.15 mL, 1.3 mmol). The reaction mixture
This work was supported by a Grant-in-Aid for Scientific Re-
search (C) (No. 20550137) from Japan Society for the Promotion of
Science.
was then stirred at room temperature. After the starting material
had completely oxidized, diethyl ether (3.0 mL) was added, fol-
lowed by centrifugation of the mixture. The quinone product was
collected by decantation and the polymeric-catalyst was quantita-
tively recovered by washing the residue with diethyl ether
Supplementary data
(
3ꢂ3.0 mL). The polymeric-catalyst was dried under vacuum before
Supplementary data associated with this article can be found in
the online version, at http://dx.doi.org/10.1016/j.tet.2013.07.069.
the next cycle. The collected product was dried over anhydrous

A.-M. Abu-Elfotoh et al. / Tetrahedron 69 (2013) 8612e8617
8617
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