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

Tetrahedron 69 (2013) 8612e8617

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Quinones synthesis via hydrogen peroxide oxidation of dihydroxy arenes catalyzed by homogeneous and macroporous-polymersupported 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-polymericcatalyst 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 polymericcatalyst 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 Quinones are useful compounds not only as synthetic intermediates1 such as dienophiles in the chemical transformations, but also as biological active compounds.2 For example, they have a potential value in cancer chemotherapy3 as well as their antitumor, antibacterial, and antiprotozoan activities.4 2-Methyl-1,4naphthoquinone (vitamin K3) and its derivatives are also used as blood coagulating agents5 and as a supplement in animal feed6 and currently attracting much attention because of its interesting pharmacological activities.7 In addition, trimethyl-p-benzoquinone is a key compound in the vitamin E synthesis. Quinones are usually prepared by direct oxidations of hydroquinone, catechol, naphthols, and their derivatives.8 Although a wide variety of oxidants were used for oxidation of dihydroxy arenes,9 molecular oxygen and hydrogen peroxide are the best oxidants from the environmental and economical point of view as clean and cheap oxidants. There are several reported catalytic systems that have been developed for quinones synthesis using molecular oxygen and hydrogen peroxide as an oxidant. Among these catalytic systems are copper salts/O2,10 ruthenium salts/H2O2,11 Schiff base cobalt

* Corresponding author. Tel./fax: þ81 532 44 6817; e-mail address: [email protected] (S. Iwasa). 0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.tet.2013.07.069

complexes/O2, copper sulfateealumina/O2,12 and heteropoly and isopoly compounds/H2O213 or O2.14 The main drawback with the 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 transition metal traces. From this regard, using polymer-supported catalysts for quinone synthesis in the presence of hydrogen peroxide 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 catalysts, and potentially reuse of these catalysts. In addition, when using heterogeneous catalyst, there is no contamination of the reaction product by the metal traces. Especially, polymer-supported ruthenium complex was found to be effective as catalyst for the decomposition of H2O2 along with good ability for recycling several times without loss of activity.15 Notably, the insoluble cross-linked polymers are used widely as they are inert, non-toxic, thermally stable, and easy to be recycled.16 Despite the tremendous efforts devoted to quinones synthesis using polymer-supported catalysts, kinetic studies17 or limited substrate scope4a,18 have so far been achieved. Recently, polymer-incarcerated platinum catalyst was found to be very efficient catalyst for aerobic oxidation of hydroquinone derivatives.19 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

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

et al.20 developed a highly efficient and recyclable copper catalyst (Cu/AlO(OH)) for the aerobic oxidation of a wide range of hydroquinones. Our recent study on quinones synthesis showed that RuII and IrI are efficient homogeneous catalysts for hydrogen peroxide oxidation of phenols and methoxyarenes.21 As a complementary 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 oxidation of dihydroxy arenes using polymer-supported RuII-catalyst and hydrogen peroxide as an oxidant.

a)

+

O

O

(i)

N Ru (NCCH 3)4

N 1a

PF 6−

2a

b) Cl

O

HO

(ii) - (iii)

O

N

N

1b

2. Results and discussion Very recently, we explored a novel strategy for the synthesis of macroporous-polymer-supported RuII-catalyst.22a We found that the catalyst on cross-linked support with pores of molecular dimension has shown significant increase in its selectivity and reactivity due to high concentration of the active sites within the small pores. Inspired by our previous work, we successfully immobilized the catalyst 2a22b 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 2a could be easily synthesized in high yield as described on the previous report (Scheme 1a).22b 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. Pleasingly, 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. 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 (Table 2, entries 1e5). A high TON was achieved with 0.01 mol % of 2a (Table 2, entry 5) while a high TOF was obtained with 0.25 mol % 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-(chloromethyl)benzoyl chloride and 2-amino-2-methyl-1-propanaol to furnish the ligand 1b in 86% yield. The Ru-catalyst 2b was synthesized from 1b in two steps in excellent yield (92%) as shown in Scheme 1b. The monomeric Ru(II)/dm-Pheox complex 3 was readily prepared from 2b in 70% yield as a new monomeric complex that was easily cross-link polymerized with styrene and 1,4divinylbenzene (DVB) in the presence of 2,20 -azobisizobutyronitrile (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 1b and Fig. 1. The exact amount of the Ru(II)/dm-Pheox complex loaded onto the polymeric network was determined by elemental analysis of the nitrogen content. Encouraged by the excellent results from the homogeneous catalyst 2a, we optimized the reaction

8613

1c HO

+

O

(i)

N Ru (NCCH 3)4

(iv)

−

PF 6

2b

O

O

+

O N Ru (NCCH 3)4

(v)

−

PF 6

3

z

y O

x O

O N Ru (NCCH 3)4

x,y,z = 1,90,9

+

PF 6−

4 Scheme 1. Synthesis of catalysts 2a and 4. Reagents and conditions: (i) [RuCl2(benzene)]2 (0.5 equiv), KPF6 (4.0 equiv), 1 N NaOH (1.0 equiv), CH3CN, 80  C, 24 h; (ii) AcONa$3H2O (5.0 equiv), NaI (5.0 equiv), CH3CN, reflux, 24 h; (iii) MeOH/H2O (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), DMAP (2.0 equiv), CH3CN, 0  C/rt, 3 h; (v) styrene, DVB, AIBN (2.0 equiv), CH2Cl2, H2O, 60  C, 24 h.

conditions with the polymeric-heterogeneous-catalyst 4.23 Under the optimized reaction conditions, we studied the hydrogen peroxide oxidation of various hydroquinone and catechol derivatives along with dihydroxy naphthalene by using 2a or 4 as the catalyst (Table 3). Table 1 Solvent screeninga

Entry

Solvent

Time

Yieldb (%)

1 2 3 4 5 6 7 8

Toluene Acetone CH2Cl2 THF 1,4-Dioxane DMF CH3OH Et2O

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

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 H2O2. b Isolated yield.

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Table 2 Effect of catalyst loadinga

Table 3 Hydrogen peroxide oxidation of various dihydroxy arenes catalyzed by 2a or 4a Entry

Entry

2a (mol %)

Time

Yieldb (%)

TONc

TOFd

1 2 3 4 5 6 7e 8

1.0 0.5 0.25 0.1 0.01 0.005 1.0 d

5 min 5 min 5 min 2h 6h 6h 24 h 5 days

99 99 99 99 99 13 25 6

100 200 400 1000 10,000 2600 25 d

1200 2400 4800 500 500 433 1 d

a

Reactions were performed on 0.34 mmol of 1,4-dihydroxy naphthalene in 1.0 mL THF with 0.44 mmol H2O2. b Isolated yields. c Turnover number (moles of product/moles of catalyst). d Turnover frequency (TON/h). e Using O2 as oxidant instead of H2O2.

Catalyst

Product

Yieldb (%)

Time

1

2a

75c

5 min

2

4

70c

2.5 h

3

2a

99

5 min

4

4

99

2h

5 6

2a 4

99 99

5 min 2h

7

2a

99

5 min

8

4

99

24 h

9

2a

99

5 min

10

4

99

48 h

11

2a

99

5 min

12d

4

70

24 h

13 14

2a 4

99 99

5 min 3h

15d

2a

98

4h

16

4

99

48 h

17d

2a

86

2h

18d

4

85

24 h

19e 20e

2a 4

71 65

30 min 24 h

21

2a

99

5 min

22

4

99

3h

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 H2O2 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 H2O2 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 The mixture was concentrated under reduced pressure and washed by Et2O.

Fig. 1. Images of the macroporous polymer-supported Ru(II)/dm-Pheox complex 4.

Notably, the hydroquinone derivatives were quantitatively oxidized in 5 min under the catalytic influence of 2a (Table 3, odd entries 1e13). From 1H 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 (Table 3, entry 1). We attributed this decrease in yield to the low 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

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 observed 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 H2O2 in a short time (10 min to 4 h; Table 3, odd entries 15e19). It is well-known that 1,4-naphthoquinone derivatives possess 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

corresponding naphthoquinone (Table 3, entries 21 and 22). Finally, we tested whether the polymeric-catalyst 4 has ability to be recycled or not. In the hydrogen peroxide oxidation of 1,4-dihydroxy naphthalene, we found that the macroporous-catalyst 4 was easily 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 before 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. 3. Conclusion In conclusion, quinones were easily and quantitatively synthesized via hydrogen peroxide oxidation of dihydroxy arenes catalyzed by ruthenium(II)/dimethyl phenyloxazoline (Ru(II)/dmPheox) (2a) and its environmentally benign macroporouspolymeric-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, quinone 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 oxidation of dihydroxy arenes. 4. Experimental section 4.1. General All reactions were performed under the normal air atmosphere. CH2Cl2 and DMF dehydrated were purchased from Kanto Chemical Co., Inc. THF, MeOH, and Et2O dehydrated were purchased from Wako Pure Chemical Industries Co., Ltd. Reactions were monitored by TLC, glass plates pre-coated with silica gel Merck KGaA 60 F254, layer thickness 0.2 mm. All the starting materials are commercially available and were used as received. Flash column chromatography was performed over Merck (Art. No. 7734). 1H NMR (400 MHz or 300 MHz) and 13C NMR (100 MHz or 75 MHz) spectra were recorded on Varian Inova-400 or Mercury-300 spectrometer. Chemical shifts are reported as d values (ppm) relative to internal tetramethylsilane (0.00 ppm) in CDCl3. IR spectra were recorded by using JASCO FT/IR-230 spectrometer and are reported in reciprocal centimeter (cm1). Melting points were measured on a Yanaco MPJ3 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 S4800 (FESEM) with accelerating voltage of 10.0 kV and the fracture 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. 4.2. 2-(4-(Chloromethyl)phenyl)-4,5-dihydro-4,4dimethyloxazole {dm-Pheox ligand (1b)} 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 (20.0 mL) was added a solution of 4-(chloromethyl)benzoyl chloride (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 dissolved in CHCl3 (20.0 mL) and was treated with SOCl2 (3.0 mL, 40 mmol) at 0  C. After stirring for 24 h at room temperature, the solvent and SOCl2 were removed under reduced pressure.

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Saturated NaHCO3 (aqua, 50 mL) was added to the residue with stirring for 5 min. The organic product was extracted with dichloromethane (350 mL), dried over anhydrous Na2SO4 or MgSO4, filtered, and concentrated under reduced pressure. Subsequently, to a solution of the previous reaction residue in 1,4dioxane (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 (325 mL) for extraction. The organic layer was dried over anhydrous Na2SO4, filtered, and evaporated 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 78  C. 1H NMR (400 MHz, CDCl3) d 1.37 (s, 6H), 4.10 (s, 2H), 4.59 (s, 2H), 7.42 (d, J¼8.4 Hz, 2H), 7.92 (d, J¼8.4 Hz, 2H). 13C NMR (100 MHz, CDCl3) d 28.6, 45.8, 67.9, 79.4, 128.3, 128.7, 128.8, 140.6, 161.8. Anal. Calcd for C12H14ClNO: C, 64.43; H, 6.31; N, 6.26%. Found: C, 64.27; H, 6.34; N, 6.22%. IR (neat) n 3384.5, 2972.7, 2931.3, 2896.6, 1660.4 cm1. 4.3. (4-(4,5-Dihydro-4,4-dimethyloxazol-2-yl)phenyl)methanol {dm-Pheox ligand (1c)} A mixture of 1b (2237.0 mg, 10.0 mmol), CH3CO2Na$3H2O (6804.0 mg, 50.0 mmol), and NaI (7494.5 mg, 50.0 mmol) was suspended in CH3CN (60.0 mL) and refluxed under N2 for 24 h at 80  C. The solvent was removed by evaporation under reduced pressure and the resulted crude ester was dissolved in CH3OH/H2O (54.0 mL, 5:1 v/v) using a sonicator and followed by the slow addition 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 was extracted by CH2Cl2 (350 mL). The combined organic layer was dried over anhydrous Na2SO4, and concentrated under reduced pressure. The residue was purified by column chromatography on silica gel (EtOAc/n-hexane¼1:10 v/v) to afford (4-(4,5-dihydro-4,4dimethyloxazol-2-yl)-phenyl)methanol 1c (1744.6 mg, 8.50 mmol, 85.0% yield) as a white solid. Mp 115  C. 1H NMR (400 MHz, CDCl3) d 1.4 (s, 6H), 1.87 (t, J¼6.0 Hz, 1H), 4.12 (s, 2H), 4.76 (d, J¼6.4 Hz, 2H), 7.41 (d, J¼8.3 Hz, 2H), 7.93 (d, J¼8.5 Hz, 2H). 13C NMR (100 MHz, CDCl3) d 28.6, 64.4, 67.6, 79.4, 126.7, 128.56, 128.57, 145.1, 162.6. Anal. Calcd for C12H15NO2: C, 70.22; H, 7.37; N, 6.82%; Found: C, 69.98; H, 7.50; N, 6.84%. IR (neat) n 3257.2, 2966.0, 2931.3, 2896.6, 1648.8 cm1. 4.4. [2-(4-Hydroxymethyl)phenyl-4,4-dimethyloxazole) Ru(CH3CN)4]PF6 {Ru(II)/dm-Pheox complex (2b)} 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. 1H NMR (400 MHz, CDCl3) d 1.37 (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 (d, J¼7.7 Hz, 1H), 7.84 (d, J¼1.4 Hz, 1H). 13C NMR (100 MHz, CD3CN) 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 C20H26F6N5O2PRu: C, 39.09; H, 4.26; N 11.40%. Found: C, 39.12; H, 4.23; N, 11.29%. IR (neat) n 3587.9, 2984.3, 2937.1, 2281.4, 1624.7, 847.6, 567.9 cm1. 4.5. Synthesis of the monomeric Ru(II)/dm-Pheox complex (3) A mixture of 2b (200.0 mg, 0.32 mmol), N,N0 -dicyclohexylcarbodiimide (DCC) (201.2 mg, 0.96 mmol), and 4-dimethyl aminopyridine (DMAP) (7.4 mg, 0.06 mmol) was placed in a twonecked flask equipped with a magnetic stirring bar. The system was evacuated and backfilled with argon. CH3CN (6.0 mL) was injected and the flask was immersed in ice followed by the slow injection of

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acrylic acid (66.6 mL, 0.96 mmol). The starting material had completely reacted after 3 h at room temperature. The solvent was evaporated under reduced pressure and the crude product was purified by column chromatography on silica gel with CH2Cl2/ CH3CN (20:1 (v/v)) to afford a yellow solid product 3 in 70% yield (150.5 mg, 0.225 mmol). Rf¼0.78 (CH2Cl2/CH3CN¼5:2 v/v). Mp (dec) 100e102  C. 1H NMR (400 MHz, CDCl3) d 1.37 (s, 6H), 2.16 (s, 6H), 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, 17.6 Hz, 1H), 6.94 (dd, J¼1.6, 7.7 Hz, 1H), 7.40 (d, J¼7.7 Hz, 1H), 7.8 (d, J¼1.4 Hz, 1H). 13C NMR (100 MHz, CDCl3) d 3.5, 4.1, 4.5, 27.6, 66.0, 66.2, 81.7, 120.0, 121.2, 121.4, 121.9, 125.5, 134.8, 136.8, 141.5, 172.2, 185.6. Anal. Calcd for C23H28F6N5O3PRu: C, 41.32; H, 4.22; N, 10.48%. Found: C, 41.30; H, 4.16; N, 10.50%. IR (neat) n 2998.1, 2951.3, 2198.4, 1769.8, 1634.7, 1199.9, 1094.8, 874.9 cm1. 4.6. Synthesis of macroporous-polymer-supported Ru(II)/dmPheox complex (4) Cross-link polymerization of the monomeric Ru(II)/dm-Pheox complex (3) to afford (4) as a macroporous polymer. The monomeric 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, CH2Cl2 (4.5 mL) was injected from the side arm. The resulting solution of the monomer was supplied with styrene (1.5 mL, 13.41 mmol), 1,4-divinylbenzene (DVB) (0.19 mL, 1.34 mmol), and distilled H2O (1.5 mL) via syringe. Finally, 2,20 -azobisizobutyronitrile (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, 7.36%; N, 0.98% (loading 0.14 mmol/g). IR (neat) n 3482.8, 2990.1, 2931.3, 2118.4, 1729.8, 1624.7, 1189.9, 1084.8, 864.9, 573.7 cm1. 4.7. General procedure for 2a catalyzed H2O2 oxidation of dihydroxy arenes To a solution of dihydroxy arene (0.34 mmol) and 2a (1.98 mg, 0.0034 mmol) in THF (1.0 mL) was added H2O2 (30% aq, 50.0 mL, 0.44 mmol) at 0  C. After 5 min the starting material had completely oxidized to the quinone product. The quinone product was then extracted by ether or dichloromethane, dried over anhydrous Na2SO4, and concentrated under reduced pressure to afford the desired product. Pleasingly, the resulted quinone products were pure enough and there is no necessity for column chromatography in most of the cases. 4.8. General procedure for 4 catalyzed H2O2 oxidation of dihydroxy arenes 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 1.0 mmol was added with constant stirring at 0  C followed by the addition of H2O2 (30% aq, 0.15 mL, 1.3 mmol). The reaction mixture was then stirred at room temperature. After the starting material had completely oxidized, diethyl ether (3.0 mL) was added, followed by centrifugation of the mixture. The quinone product was collected by decantation and the polymeric-catalyst was quantitatively recovered by washing the residue with diethyl ether (33.0 mL). The polymeric-catalyst was dried under vacuum before the next cycle. The collected product was dried over anhydrous

Na2SO4 and condensed under vacuum to afford the corresponding quinone in a pure form. 4.8.1. 2,3-Dimethyl-1,4-benzoquinone.19 Green solid. Rf¼0.37 (nhexane/EtOAc¼10:1). 1H NMR (300 MHz, (CD3)2CO) d 1.99 (s, 6H), 6.76 (s, 2H). 13C NMR (100 MHz, CDCl3) d 12.4, 136.4, 141.2, 187.6. IR (neat) n 1659.5 cm1. 4.8.2. Trimethyl-1,4-benzoquinone. Green oil. Rf¼0.67 (n-hexane/ EtOAc¼6:1). 1H NMR (300 MHz, (CD3)2CO) d 1.96 (m, 3H), 1.99 (m, 6H), 6.60 (m, 1H). 13C NMR (100 MHz, CDCl3) d 12.3, 12.6, 16.1, 133.3, 140.9, 141.1, 145.5, 187.7, 188.1. IR (neat) n 1648.8 cm1. 4.8.3. 2-tert-Butyl-1,4-benzoquinone.19 Green solid. Rf¼0.47 (nhexane/EtOAc¼10:1). 1H NMR (300 MHz, CDCl3) d 1.29 (s, 9H), 6.59 (s, 1H), 6.68 (d, J¼1.0 Hz, 2H). 13C NMR (100 MHz, CDCl3) d 29.3, 35.5, 131.7, 135.1, 138.9, 156.3, 187.7, 188.6. IR (neat) n 1654.6 cm1. 4.8.4. 2-Phenyl-1,4-benzoquinone.19,20 Brown solid. Rf¼0.25 (nhexane/EtOAc¼10:1). 1H NMR (300 MHz, (CD3)2CO) d 6.85e6.97 (m, 3H), 7.44e7.50 (m, 3H), 7.53e7.58 (m, 2H). 13C NMR (100 MHz, CDCl3) d 128.7, 129.4, 130.4, 132.9, 136.5, 137.3, 146.1, 186.9, 187.9. IR (neat) n 1649.8 cm1. 4.8.5. 2,5-Di-tert-Butyl-1,4-benzoquinone.13 Brown solid. Rf¼0.67 (n-hexane/EtOAc¼5:1). 1H NMR (300 MHz, (CD3)2CO) d 1.26 (s, 18H), 6.47 (s, 2H). 13C NMR (100 MHz, CDCl3) d 29.3, 34.8, 133.8, 154.5, 188.7. IR (neat) n 1647.9 cm1. 4.8.6. 2-Methoxy-1,4-benzoquinone.19,20 Brown solid. Rf¼0.42 (nhexane/EtOAc¼5:1). 1H NMR (300 MHz, CDCl3) d 3.82 (s, 3H), 5.94 (s, 1H), 6.71 (s, 2H). 13C NMR (100 MHz, CDCl3) d 56.5, 107.9, 134.7, 137.5, 158.8, 181.9, 187.7. IR (neat) n 2856.1, 1648.8 cm1. 4.8.7. 3,5-Di-tert-Butyl-1,2-benzoquinone19,20. Green solid. 1H NMR (300 MHz, CDCl3) d 1.22 (s, 9H), 1.26 (s, 9H), 6.21 (d, J¼2.4 Hz, 1H), 6.92 (d, J¼2.4 Hz, 1H). 13C NMR (100 MHz, CDCl3) d 28.1, 29.4, 35.7, 36.2, 122.3, 133.7, 150.1, 163.6, 180.2, 181.3. IR (neat) n 1655.6 cm1. 4.8.8. 4-tert-Butyl-1,2-benzoquinone.19 Brown solid. Rf¼0.26 (nhexane/EtOAc¼5:1). 1H NMR (300 MHz, (CD3)2CO) d 1.26 (s, 9H), 6.19 (d, J¼2.5 Hz, 1H), 6.35 (d, J¼10.4 Hz, 1H), 7.46 (dd, J¼2.4, 10.4 Hz, 1H). 13C NMR (100 MHz, CDCl3) d 28.0, 35.8, 124.0, 129.6, 140.2, 162.3, 180.5. IR (neat) n 1659.5 cm1. 4.8.9. 3-Methoxy-1,2-benzoquinone.24 Black solid. Rf¼0.20 (n-hexane/EtOAc¼3:2). 1H NMR (400 MHz, (CD3)2CO) 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, (CD3)2CO) d 55.4, 107.5, 122.5, 141.9, 154.3, 176.0. IR (neat) n 1657.5 cm1. 4.8.10. 1,4-Naphthoquinone.19 Brown solid. Rf¼0.61 (n-hexane/ EtOAc¼3:1). 1H NMR (400 MHz, (CD3)2CO) d 7.05 (s, 2H), 7.86e7.91 (m, 2H), 8.03e8.08 (m, 2H). 13C NMR (100 MHz, CDCl3) d 126.6, 132.0, 134.1, 138.8, 185.2. IR (neat) n 1662.3 cm1. Acknowledgements This work was supported by a Grant-in-Aid for Scientific Research (C) (No. 20550137) from Japan Society for the Promotion of Science. Supplementary data 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.

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