Journal of the Korean Chemical Society (대한화학회지)

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DABCO-Catalyzed Green Synthesis of 2-Hydroxy-1,4-diones via Direct Aldol Reaction of Arylglyoxals in Water

  • Received : 2012.11.27
  • Accepted : 2013.03.13
  • Published : 2013.04.20
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Abstract

A green and simple method to synthesize of 1,4-diketones via aldol reaction of arylglyoxals and ketones such as 1-(4-methoxyphenyl)-2-propanone, deoxybenzoin and substituted acetophenones in the presence of a catalytic amount of DABCO in water at room temperature has been reported. Corresponding 2-hydroxy-1,4-diones were obtained in moderate to high yields with simple separation of obtained solid from reaction mixture and recrystallization.

Keywords

INTRODUCTION

Because of water is one of the most abundant and cheap solvents, and also makes the reactions environmentally amenable, much safer and easier to handle,1 the organic reactions in aqueous media have attracted much attention in synthetic organic chemistry.2 Also, reactions in water exhibit interesting reactivity and selectivity, which are different from conventional organic solvents.

The routes for formation of C−C bonds are the most important topics in synthetic organic chemistry. The aldol reaction is one of the most powerful C−C bond-forming reactions in organic synthesis,3 leading to the β-hydroxycarbonyl structural units, which are found in several biologically active compounds, such as macrolide antibiotics and anti-cancer drugs,4 and also are important building blocks in the synthesis of polyfunctional compounds and natural products.3d,5

Additionally, 1,4-dicarbonyl compounds are versatile precursors for the synthesis of substituted cyclopentenones, 6 such as jasmones,6g−i cuparenones,6c and prostaglandins, 6j−l and also various heterocyclic compounds, for example, furan, thiophene, pyrrole, and pyridazine derivatives. 7 Thus the development of the synthetic methods of the 1,4-diketones have a significant impact on organic chemistry. A number of methods have already been reported for the preparation of 1,4-diketone derivatives,8 and among them, most widely used approach is the Michael addition to α,β-unsaturated ketones of either unmasked acyl anions such as acyllithium,9 and acyl-transition metal complexes,10 or masked acyl anions and their equivalents.11 Also, the preparation of 1,4-dicarbonyl compounds were carried out by the classic utilization of α-halo ketones,12 by application of the Stetter reagent,13 thiazolium salts in the presence of a tertiary amine,14 or 1,3-dithiane derivatives.15

Recently, we have reviewed the application of arylglyoxals (aromatic α-ketoaldehyds) in synthesis of heterocyclic compounds,16 that encouraged us to work on aldol reaction of arylglyoxals to prepare 1,4-dicarbonyl compounds.

However, aldol reaction with some α-dicarbonyl compounds such as benzil, isatin and ethyl phenylglyoxalate17 to synthesize of 1,4-dicarbonyl compounds were previously reported,18 as the best of our knowledge, there is one report on aldol reaction of arylglyoxals in the literature using expensive chiral ligand with limited scope of products, in which trimethylsilyl enols of ketones were used in CH2Cl2.19

Herein, we wish to report the direct aldol reaction of different ketones such as 1-(4-methoxyphenyl)-2-propanone, deoxybenzoin and substituted acetophenones with arylglyoxals in water to produce 2-hydroxy-1,4-diketones in the presence of a catalytic amount of DABCO.

 

RESULTS AND DISCUSSION

We first studied the aldol reaction of 1-(4-methoxyphenyl) propan-2-one 1a with phenylglyoxal hydrate 2a, which were prepared by oxidation of acetophenone using SeO2,20 in water in the presence of different tertiary amines such as Et3N, DMAP and DABCO, and also NaOH at room temperature to give 2-hydroxy-3-(4-methoxyphenyl)-1- phenylpentane-1,4-dione 3a (Scheme 1). When DABCO was used, 2-hydroxy-1,4-dione 3a was obtained in 95% yield as only syn isomer, determined using 1H NMR spectroscopy. The crystal structure of the compound 3a (Fig. 1),21 which was synthesized by the similar procedure,22 was reported by K. Harms,23 which is consistent with syn isomer.

Scheme 1.Reaction of 1a with phenylglyoxal hydrate 2a in water.

Fig. 1.ORTEP representation of 3a with 45% ellipsoid probability. 21

Aldol reactions of 1a with different substituted phenylglyoxal hydrates 2b−f were also investigated. The reactions were carried out by addition of DABCO to a mixture of 1a (0.5 mmol) and 2 (0.05 mmol) in water and stirred at room temperature for appropriate time. The corresponding 2-hydroxy-1,4-diones 3b−f were obtained in good to high yields. Also the aldol reaction of deoxybenzoin 1b was conducted with different arylglyoxals 2 under the same conditions, and the corresponding 2-hydroxy- 1,4-diones 3g−i were obtained in good to high yields (Scheme 2). The results are summarized in Table 1. The products were characterized using FT-IR, 1H NMR and 13C NMR spectroscopy.

Scheme 2.Reaction of 1b with arylglyoxal hydrates in water in the presence of DABCO.

Table 1.aReaction time was 24 h, except in the case of 3i which was 48 h. bYields refer to isolated products by simple filtration of the reaction mixture. cAnti/syn ratio was determined using 1H NMR spectroscopic analysis of the crude reaction mixture.

As shown in Table 1, electron-withdrawing substituted phenylglyoxals such as 4-Cl and 4-Br worked as well as electron-donating substituted phenylglyoxals such as 3- MeO, 4-MeO and 3,4-(MeO)2 in DABCO-catalyzed aldol reaction in water. Phenyl-, 4-Clphenyl- and 4-Br-phenylglyoxals underwent aldol reaction with excellent diastereoselectivity (3a−c and 3g,h), while electron-donating substituted phenylglyoxals afforded corresponding 2-hydroxy-1,4- diketones 3d−f and 3i as a mixture of two stereoisomers.

As shown in Fig. 2, the syn/anti ratio was determined by 1H NMR, using the intensity of the Ha for two isomers. The coupling constant (3JHa,Hb) for signal of the anti-isomer is higher than that of the syn-isomer. According to the 1H NMR spectrum, the Ha signal for the syn-isomer has a higher δ value than that for the anti-isomer. For instance, in the 1H NMR spectra of 2-hydroxy-1,3-bis(4-methoxyphenyl) pentane-1,4-dione (3d), the signal at δ = 5.78 ppm (3JHa,Hb = 4.4 Hz) is contributed by the syn-isomer, while the one at 5.28 ppm (3JHa,Hb = 5.6 Hz) is contributed by the anti-isomer.

Fig. 2.Identification of anti and syn isomer by 1H NMR.

Scheme 3.Chemoselectivity of the aldol reaction of 1a toward phenylglyoxal, in preference to benzaldehyde.

Another characteristic feature of the present protocol is the high chemoselectivity of the aldol reaction toward phenylglyoxal, in preference to benzaldehyde as shown in Scheme 3. When aldol reaction of phenylglyoxal with 1a in the presence of 1 equiv. of benzaldehyde was carried out under same conditions, only 3a was isolated and benzaldehyde was recovered without changes.

The results encouraged us to work on the aldol reaction of acetophenone derivatives 4 with arylglyoxal hydrates 2 (Scheme 4). The reactions were conducted by stirring of a mixture of acetophenones and arylglyoxal hydrates in water at room temperature in the presence of catalytic amount of DABCO. The reaction mixture was solidified after appropriate time. The obtained solid was filtered off and washed with hot water to remove arylglyoxal and acetophenone residue. The results are summarized in Table 2.

Scheme 4.DABCO-catalyzed aldol reaction of acetophenones 4 with 2 in water at room temperature.

Table 2.aYields refer to isolated products by simple filtration of the reaction mixture and washing with warm water and cold EtOH to remove unreacted arylglyoxals and acetophenones, respectively.

As shown in Table 2, different 4 were subjected to DABCOcatalyzed aldol reaction with 2 to give corresponding 2- hydroxy-1,4-diones 5 in 25−88% yields. Also, heterocyclic methyl ketones such as 2-furyl and 2-thienyl methyl ketones underwent aldol reaction in water at room temperature to afford corresponding 1,4-diones 5g,l in good yields. The structure of products were established using FT-IR, 1H NMR and 13C NMR.

Attempts to aldol reaction of arylglyoxals with aliphatic ketones such as acetone and cyclohexanone under the same conditions were failed and a mixture of products was obtained.

 

CONCLUSION

In conclusion, a new green and simple methodology for construction of 1,4-diketone along with 2- and 3-hydroxy structural motifs was developed. Reactions were carried out in water at room temperature using DABCO as catalyst. Ketones such as 1a,b worked well in aldol reaction in water and afforded corresponding 2-hydroxy-1,4-diones in good to high yields. Electron-withdrawing substituted phenylgyloxals afforded the 1,4-diones with excellent syn selectivity, while arylglyoxals with electron-donating substituents gave corresponding 1,4-diones as a two diastereoisomers with ratio of about 2/1 of syn/anti. Also, acetophenone deivatives worked well in aldol reaction with arylglyoxals in water.

 

EXPERIMENTAL

All chemicals were purchased and used without any further purification. NMR spectra were recorded at 400 MHz for proton and at 100 MHz for carbon nuclei in CDCl3 or DMSO-d6. Most of compounds were new and characterized by their spectroscopic data (FT-IR, NMR and elemental analysis).

General Procedure of the Aldol Reaction

To a mixture of arylglyoxal 2 (0.55 mmol) and ketone 1 or 4 (0.5 mmol) in 3−5 mL water, was added 0.02 g DABCO and stirred at room temperature. The progress of the reaction was monitored by TLC (n-hexane/ethyl acetate; 7/3). After completion of the reaction, the products were isolated as solid from reaction mixture, which was filtered off and washed with hot water and cold EtOH to remove unreacted arylglyoxals and ketones, respectively. All obtained products are almost pure, but further purification for elemental analysis were carried out by recrystallization from EtOH.

2-Hydroxy-3-(4-methoxyphenyl)-1-phenylpentane-1,4- dione (3a)

White solid, m.p. 95−95.3 ℃. FT-IR (KBr) ν = 3316 (O−H), 3068, 2891 (C−H), 1712, 1674 (C=O), 1645 (C=C), 1245 (C−O) cm˗1. 1H NMR (500 MHz, CDCl3): δ = 7.90 (dd, 3JH,H = 7.9 Hz, 4JH,H = 0.8 Hz, 2H, CHAr), 7.66 (m, 1H, CHAr), 7.53 (t, 3JH,H = 7.9 Hz, 2H, CHAr), 7.01 (d, 3JH,H = 9.5 Hz, 2H, CHAr), 6.86 (d, 3JH,H = 9.6 Hz, 2H, CHAr), 5.85 (d, 3JH,H = 4.0 Hz, 1H, CH−O), 4.03 (d, 3JH,H = 4.1 Hz, 1H, CH), 3.82 (s, 3H, OCH3), 3.26 (s, br., 1H, OH, Exchange with D2O), 2.14 (s, 3H, CH3) ppm. 13C NMR (125 MHz, CDCl3): δ = 206.8 (C=O), 200.4 (C=O), 159.9, 134.8, 134.2, 131.5, 129.3, 129.0, 125.4, 114.6, 73.3, 62.1, 55.6, 29.5 ppm. Anal. Calcd for C18H18O4 (298.33): C 72.47, H 6.08; Found: C 72.51, H 6.10%.

1-(4-Chlorophenyl)-2-hydroxy-3-(4-methoxyphenyl) pentane-1,4-dione (3b)

White solid, m.p. 119−123 ℃. FT-IR (KBr) ν = 3355 (br., O−H), 3071, 2943 (C−H), 1716, 1685 (C=O), 1583 (C=C), 1244 (C−O), 601 (C−Cl) cm˗1. 1H NMR (400 MHz, CDCl3) δ = 7.82 (d, 3JH,H = 8.8 Hz, 2H, CHAr), 7.37 (d, 3JH,H = 8.4 Hz, 2H, CHAr), 7.20 (d, 3JH,H = 8.8 Hz, 2H, CHAr), 6.84 (d, 3JH,H = 8.8 Hz, 2H, CHAr), 5.23 (d, 3JH,H = 5.2 Hz, 1H, CH−O), 4.20 (d, 3JH,H = 5.2 Hz, 1H, CH), 3.80 (s, 3H, OCH3), 2.20 (s, 3H, CH3) ppm. 13C NMR (100 MHz, CDCl3) δ = 209.6, 199.0 (C=O), 159.5, 139.9, 133.4, 130.5, 130.3, 128.7, 126.1, 114.5, 76.1, 59.8, 55.3, 30.2 ppm. Anal. Calcd for C18H17ClO4 (332.78): C 64.97, H 5.15; Found: C 64.90, H 5.30%.

1-(4-Bromophenyl)-2-hydroxy-3-(4-methoxyphenyl) pentane-1,4-dione (3c)

White solid, m.p. 118.5−120.1 ℃. FT-IR (KBr) ν = 3335 (br., O−H), 3069, 2941 (C−H), 1695 (C=O), 1578 (C=C), 1244 (C−O), 579 (C−Br) cm˗1. 1H NMR (400 MHz, CDCl3) δ = 7.72−7.75 (m, 2H, CHAr), 7.53−7.56 (m, 2H, CHAr), 7.19− 7.22 (m, 2H, CHAr), 6.83−6.86 (m, 2H, CHAr), 5.22−5.28 (m, 1H, CH−O) 4.33 (m, br., 1H, OH), 4.20 (d, 3JH,H = 5.6 Hz, 1H, CH), 3.80 (s, 3H, OCH3), 2.20 (s, 3H, CH3) ppm. 13C NMR (100 MHz, CDCl3) δ = 209.6, 199.3 (C=O), 159.5, 133.8, 131.7, 130.6, 130.3, 128.6, 126.1, 114.5, 76.1, 59.8, 55.3, 30.1 ppm. Anal. Calcd for C18H17BrO4 (377.23): C 57.31, H 4.54; Found: C 56.76, H 4.27%.

2-Hydroxy-1,3-bis(4-methoxyphenyl)pentane-1,4- dione (3d)

syn/anti = 67/33. Yellow oil, FT-IR (KBr) ν = 3442 (br., O−H), 3040, 2943 (C−H), 1706, 1670 (C=O), 1602 (C=C), 1255 (C−O) cm˗1. 1H NMR (400 MHz, CDCl3) δ = 7.82− 7.92 (2×m, 2H, CHAr), 6.79−7.21 (3×m, 6H, CHAr), 5.78 (d, 3JH,H = 4.4 Hz, 0.67H, CH−O, anti), 5.28 (d, 3JH,H = 5.6 Hz, 0.33H, CH−O, syn), 4.16 (d, 3JH,H = 5.6 Hz, 0.33H, CH, syn), 4.02 (d, 3JH,H = 4.4 Hz, 0.67H, CH, anti), 3.84- 3.90 [2×S: (3.90, ~2H, anti; 3.84, ~1H, syn), 3H, OCH3], 3.76-3.79 [2×S: (3.79, ~2H, anti; 3.76, ~1H, syn), 3H, OCH3], 2.12−2.17 [2×S: (2.17, ~1H, syn; 2.12, ~2H, anti), 3H, CH3] ppm. 13C NMR (100 MHz, CDCl3) δ = 209.3, 206.6, 198.4, 198.2 (C=O), 164.1, 163.8, 159.4, 159.3, 132.2, 131.4, 131.1, 130.3, 127.8, 127.0, 126.5, 125.2, 114.4, 114.17, 114.16, 113.7, 75.5, 72.5, 61.9, 60.3, 55.6, 55.5, 55.3, 55.2, 30.4, 29.2 ppm. Anal. Calcd for C19H20O5 (328.36): C 69.50, H 6.14; Found: C 69.83, H 6.21%.

2-Hydroxy-1-(3-methoxyphenyl)-3-(4-methoxyphenyl) pentane-1,4-dione (3e)

syn/anti = 67/33. Yellow oil, FT-IR (KBr) ν = 3504 (br., O−H), 3098, 2947 (C−H), 1693 (br., C=O), 1596 (C=C), 1253 (C−O) cm˗1. 1H NMR (400 MHz, CDCl3) δ = 6.78− 7.50 (9×m, 8H, CHAr), 5.82 (d, 3JH,H = 4.0 Hz, 0.67H, CH−O, anti), 5.30 (d, 3JH,H = 5.6 Hz, 0.33H, CH−O, syn), 4.19 (d, 3JH,H = 5.6 Hz, 0.33H, CH, syn), 4.04 (d, 3JH,H = 4.0 Hz, 0.67H, CH, anti), 3.83−3.87 [2×S: (3.87, ~2H, anti; 3.83, ~1H, syn), 3H, OCH3], 3.78−3.81 [2×S: (3.81, ~2H, anti; 3.78, ~1H, syn), 3H, OCH3], 2.13−2.17 [2×S: (2.17, ~1H, syn; 2.13, ~2H, anti), 3H, CH3] ppm. 13C NMR (100 MHz, CDCl3) δ = 209.3, 206.4, 200.0, 199.8 (C=O), 160.0, 159.6, 159.5, 159.4, 136.3, 135.6, 131.1, 130.3, 256 Mahnaz Saraei, Bagher Eftekhari-Sis, and Sakineh Mozaffarnia Journal of the Korean Chemical Society 130.0, 129.4, 126.4, 125.0, 121.6, 121.1, 120.3, 120.2, 114.4, 114.2, 113.0, 112.9, 75.9, 72.9, 61.7, 60.3, 55.5, 55.4, 55.3, 55.2, 30.2, 29.1 ppm. Anal. Calcd for C19H20O5 (328.36): C 69.50, H 6.14; Found: C 68.89, H 5.78%.

1-(3,4-Dimetoxyphenyl)-2-hydroxy-3-(4-metoxyphenyl) pentane-1,4-dione (3f)

syn/anti = 64/36. Yellow oil, FT-IR (KBr) ν = 3511 (br., O−H), 3093, 2941 (C−H), 1712, 1672 (C=O), 1598 (C=C), 1265 (C−O) cm˗1. 1H NMR (400 MHz, CDCl3) δ = 7.51- 7.61 [2×dd: 7.59 (dd, 3JH,H = 8.4 Hz, 4JH,H = 2.0 Hz), 7.50 (dd, 3JH,H = 8.4 Hz, 4JH,H = 2.0 Hz) 1H, CHAr], 7.39-7.41 (m, 1H, CHAr), 7.12−7.20 [2×d: 7.20 (d, 3JH,H = 8.8 Hz), 7.12 (d, 3JH,H = 8.8 Hz), 1H, CHAr], 6.93−7.02 [2×d: 7.02 (d, 3JH,H = 8.8 Hz), 6.93 (d, 3JH,H = 8.4 Hz), 2H, CHAr], 6.79−6.85 (m, 2H, CHAr), 5.78 (d, 3JH,H = 4.4 Hz, 0.64H, CH−O, anti), 5.29 (d, 3JH,H = 5.6 Hz, 0.36H, CH−O, syn), 4.18 (d, 3JH,H = 5.6 Hz, 0.36H, CH, syn), 4.04 (d, 3JH,H = 4.4 Hz, 0.64H, CH, anti), 3.88−3.97 (3×s, 6H, OCH3), 3.73−3.79 [2×S: (3.79, ~1.9H, anti; 3.73, ~1.1H, syn), 3H, OCH3], 2.12−2.17 [2×S: (2.17, ~1.1H, syn; 2.12, ~1.9H, anti), 3H, CH3] ppm. 13C NMR (100 MHz, CDCl3) δ = 209.5, 206.7, 198.4, 198.2 (C=O), 159.4, 159.36, 153.9, 153.6, 149.3, 148.8, 131.1, 130.4, 127.9, 127.2, 126.4, 125.3, 124.1, 123.4, 114.4, 114.2, 110.9, 110.7, 110.3, 109.9, 75.5, 72.5, 62.1, 60.3, 56.2, 56.1, 55.9, 55.3, 55.2, 50.1, 30.3, 29.2 ppm. Anal. Calcd for C20H22O6 (358.39): C 67.03, H 6.19; Found: C 66.51, H 6.28%.

1-(4-Chlorophenyl)-2-hydroxy-3,4-diphenylbutane- 1,4-dione (3g)

White solid, m.p. 176.8−179.6 ℃. FT-IR (KBr) ν = 3367 (br., O−H), 3060, 2893 (C−H), 1670 (C=O), 1583 (C=C), 1199 (C−O), 694 (C−Cl) cm˗1. 1H NMR (400 MHz, CDCl3) δ = 7.97 (d, 3JH,H = 8.0 Hz, 2H, CHAr), 7.85 (d, 3JH,H = 8.8 Hz, 2H, CHAr), 7.52−7.56 (m, 1H, CHAr), 7.41−7.44 (m, 2H, CHAr), 7.19−7.36 (m, 7H, CHAr), 5.44−5.48 (dd, 3JH,H = 5.6, 9.2 Hz, 1H, CH−O), 5.13 (d, 3JH,H = 5.6 Hz, 1H, CH), 4.53 (d, 3JH,H = 9.2 Hz, 1H, OH) ppm. 13C NMR (100 MHz, CDCl3) δ = 200.4, 199.3 (C=O), 139.9, 136.2, 134.5, 133.6, 133.5, 130.7, 129.2, 129.0, 128.9, 128.7, 128.0, 59.5, 55.7, 31.3 ppm. Anal. Calcd for C22H17ClO3 (364.82): C 72.43, H 4.70; Found: C 72.50, H 4.80%.

1-(4-Bromophenyl)-2-hydroxy-3,4-diphenylbutane- 1,4-dione (3h)

White solid, m.p. 180−184.5 ℃. FT-IR (KBr) ν = 3361 (br., O−H), 3059, 2914 (C−H), 1666 (C=O), 1577 (C=C), 1199 (C−O), 702 (C−Br) cm˗1. 1H NMR (400 MHz, CDCl3) δ = 7.97 (d, 3JH,H = 7.6 Hz, 2H, CHAr), 7.77 (d, 3JH,H = 7.6 Hz, 2H, CHAr), 7.51−7.56 (m, 3H, CHAr), 7.41−7.44 (m, 2H, CHAr), 7.19−7.33 (m, 5H, CHAr), 5.45 (m, 1H, CH−O), 5.13 (d, 3JH,H = 6.0 Hz, 1H, CH), 4.53 (d, 3JH,H = 7.6 Hz, 1H, OH) ppm. 1H NMR (400 MHz, CDCl3+drops of D2O) δ = 7.97 (d, 3JH,H = 8.8 Hz, 2H, CHAr), 7.77 (d, 3JH,H = 8.8 Hz, 2H, CHAr), 7.51−7.56 (m, 3H, CHAr), 7.41−7.44 (m, 2H, CHAr), 7.19−7.33 (m, 5H, CHAr), 5.43 (d, 3JH,H = 5.6 Hz, 1H, CHO), 5.13 (d, 3JH,H = 5.6 Hz, 1H, CH) ppm. 13C NMR (100 MHz, CDCl3) δ = 200.5, 199.5 (C=O), 136.2, 134.5, 133.9, 133.6, 131.7, 130.7, 129.2, 129.0, 128.9, 128.7, 128.6, 128.0, 58.4, 55.6, 31.0 ppm. Anal. Calcd for C22H17BrO3 (409.27): C 64.56, H 4.19; Found: C 64.01, H 4.72%.

2-Hydroxy-1-(4-methoxyphenyl)-3,4-diphenylbutane- 1,4-dione (3i)

Syn/anti = 65/35. White solid. FT-IR (KBr) ν = 3471 (O− H), 3064, 2952 (C−H), 1670 (C=O), 1591 (C=C), 1267 (C−O) cm˗1. 1H NMR (400 MHz, CDCl3) δ = 7.96−7.99 (m, 2H, CHAr), 7.86−7.90 (m, 2H, CHAr), 7.16−7.55 (7×m, 8H, CHAr), 6.83−6.98 [2×d: (6.98, 3JH,H = 9.2 Hz; 6.83, 3JH,H = 8.8 Hz), 2H, CHAr), 5.84 (m, br., 0.65H, CH− O, anti), 5.53 (m, br., 0.35H, CH−O, syn), 5.09 (d, 3JH,H = 6.4 Hz, 0.35H, CH, syn), 5.05 (d, 3JH,H = 5.2 Hz, 0.65H, CH, anti), 4.45 (m, br., 0.35H, OH, syn), 3.86−3.92 [2×S: (3.92, ~2H, anti; 3.86, ~1H, syn), 3H, OCH3], 3.03 (s, br., 0.65H, OH, anti) ppm. 13C NMR (100 MHz, CDCl3) δ = 200.0, 198.7, 198.0, 197.9 (C=O), 164.1, 163.8, 136.5, 136.0, 134.1, 133.4, 133.1, 131.6, 131.4, 129.7, 129.1, 129.0, 128.97, 128.9, 128.6, 128.5, 127.9, 127.8, 127.5, 114.1, 113.6, 76.3, 73.6, 57.5, 56.2, 55.6, 55.5 ppm. Anal. Calcd for C23H20O4 (360.40): C 76.65, H 5.59; Found: C 76.09, H 5.72%.

4-(4-Chlorophenyl)-2-hydroxy-1-phenylbutane-1,4- dione (5a)

White solid, m.p. 132.5−136 ℃. FT-IR (KBr) ν = 3743 (O−H), 3061 (C−H), 1681 (C=O), 1552 (C=C), 1195 (C−O), 651 (CCl) cm˗1. 1H NMR (400 MHz, CDCl3) δ = 8.01 (d, 3JH,H = 8.4 Hz, 2H, CHAr), 7.91 (d, 3JH,H = 8.4 Hz, 2H, CHAr), 7.66 (t, 3JH,H = 7.2 Hz, 1H, CHAr), 7.54 (t, 3JH,H = 7.6 Hz, 2H, CHAr), 7.46 (d, 3JH,H = 8.8 Hz, 2H, CHAr), 5.69 (s, br., 1H, OH), 4.05 (m, 1H, CH−O), 3.33−3.45 (m, 2H, CH2) ppm. 1H NMR (400 MHz, DMSO-d6) δ = 8.03 (d, 3JH,H = 7.2 Hz, 2H, CHAr), 8.00 (d, 3JH,H = 8.4 Hz, 2H, CHAr), 7.67 (t, 3JH,H = 7.2 Hz, 1H, CHAr), 7.62 (d, 3JH,H = 8.4 Hz, 2H, CHAr), 7.56 (t, 3JH,H = 7.6 Hz, 2H, CHAr), 5.85 (d, 3JH,H = 7.6 Hz, 1H, OH), 5.43−5.48 (m, 1H, CH−O), 3.35−3.59 [2×dd: 3.54−3.59 (dd, 3JH,H = 6.8, 17.2 Hz, 1H, CH2), 3.35−3.41 (dd, 3JH,H = 6.4, 17.2 Hz, 1H, CH2)] ppm. 13C NMR (100 MHz, DMSO-d6) δ = 199.5, 197.5 (C=O), 138.8, 135.7, 135.5, 133.7, 130.5, 129.3, 129.2, 129.17, 69.1, 42.6 ppm. Anal. Calcd for C16H13ClO3 (288.73): C 66.56, H 4.54; Found: C 66.49, H 4.51%.

4-(4-Bromophenyl)-2-hydroxy-1-phenylbutane-1,4- dione (5b)

White solid, m.p. 145.8−149.6 ℃. FT-IR (KBr) ν = 3448 (br., O−H), 3058, 2964 (C−H), 1676 (C=O), 1583 (C=C), 1191 (C−O), 696 (C−Br) cm˗1. 1H NMR (400 MHz, CDCl3) δ = 8.01 (d, 3JH,H = 7.6 Hz, 2H, CHAr), 7.83 (d, 3JH,H = 8.4 Hz, 2H, CHAr), 7.61−7.67 (m, 3H, CHAr), 7.54 (t, 3JH,H = 7.6 Hz, 2H, CHAr), 5.68 (m, 1H, CH−O), 4.04 (d, 3JH,H = 6.0 Hz, 1H, OH), 3.33−3.44 (m, 2H, CH2) ppm. 13C NMR (100 MHz, CDCl3) δ = 200.6, 196.3 (C=O), 135.4, 134.1, 133.5, 132.0, 129.9, 129.0, 128.9, 128.7, 70.1, 43.5 ppm. Anal. Calcd for C16H13BrO3 (333.18): C 57.68, H 3.93; Found: C 57.50, H 4.00%.

2-Hydroxy-4-(4-nitrophenyl)-1-phenylbutane-1,4- dione (5c)

Yellow solid, m.p. 128−132 ℃. FT-IR (KBr) ν = 3450 (O−H), 3076 (C−H), 1670 (C=O), 1593 (C=C), 1521, 1315 (NO2), 1195 (C−O) cm˗1. 1H NMR (400MHz, CDCl3) δ = 8.34 (d, 3JH,H = 8.8 Hz, 2H, CHAr), 8.13 (d, 3JH,H = 8.8 Hz, 2H, CHAr), 8.02 (d, 3JH,H = 7.6 Hz, 2H, CHAr), 7.67 (t, 3JH,H = 7.6 Hz, 1H, CHAr), 7.54−7.58 (m, 2H, CHAr), 5.68− 5.72 (m, 1H, CH−O), 4.05 (d, 3JH,H = 6.0 Hz, 1H, OH), 3.41− 3.47 (m, 2H, CH2) ppm. 13C NMR (100 MHz, CDCl3) δ = 200.2, 195.9 (C=O), 150.6, 141.1, 134.3, 133.3, 129.4, 129.1, 128.7, 123.9, 70.0, 44.1 ppm. Anal. Calcd for C16H13NO5 (299.28): C 64.21, H 4.38, N 4.68; Found: C 64.18, H 4.31, N 4.55%.

1-(4-Chlorophenyl)-2-hydroxy-4-phenylbutane-1,4- dione (5d)

White solid, m.p. 151−155 ℃. FT-IR (KBr) ν = 3440 (O− H), 3080 (C−H), 1679 (C=O), 1554 (C=C), 1190 (C−O), 750 (C−Cl) cm˗1. 1H NMR (400 MHz, CDCl3) δ = 7.96− 8.00 (m, 4H, CHAr), 7.62 (t, 3JH,H = 7.6 Hz, 1H, CHAr), 7.48−7.52 (m, 4H, CHAr), 5.59−5.63 (m, 1H, CH−O), 4.02 (d, 3JH,H = 6.4 Hz, 1H, OH), 3.38−3.52 [2×dd: 3.46−3.52 (dd, 3JH,H = 6.8, 17.2 Hz, 1H, CH2), 3.38−3.44 (dd, 3JH,H = 3.6, 17.2 Hz, 1H, CH2)] ppm. 13C NMR (100 MHz, CDCl3) δ = 199.5, 197.5 (C=O), 140.4, 136.5, 133.8, 132.1, 130.3, 129.3, 128.8, 128.3, 70.4, 43.2 ppm. Anal. Calcd for C16H13ClO3 (288.73): C 66.56, H 4.54; Found: C 66.50, H 4.50%.

1,4-Bis(4-chlorophenyl)-2-hydroxybutane-1,4-dione (5e)

White solid, m.p. 159−162 ℃. FT-IR (KBr) ν = 3427 (O−H), 3071 (C−H), 1673 (C=O), 1588 (C=C), 1200 (C− O), 745 (C−Cl) cm˗1. 1H NMR (400 MHz, CDCl3) δ = 7.98 (d, 3JH,H = 8.8 Hz, 2H, CHAr), 7.91 (d, 3JH,H = 8.8 Hz, 2H, CHAr), 7.51 (d, 3JH,H = 8.8 Hz, 2H, CHAr), 7.47 (d, 3JH,H = 8.4 Hz, 2H, CHAr), 5.57−5.61 (m, 1H, CH−O), 4.01 (d, 3JH,H = 6.4 Hz, 1H, OH), 3.34−3.47 [2×dd: 3.41− 3.47 (dd, 3JH,H = 7.2, 17.2 Hz, 1H, CH2), 3.34−3.39 (dd, 3JH,H = 3.6, 17.2 Hz, 1H, CH2)] ppm. 13C NMR (100 MHz, CDCl3) δ = 199.3, 196.3 (C=O), 140.6, 140.3, 134.8, 132.0, 130.2, 129.8, 129.3, 129.1, 70.3, 43.1 ppm. Anal. Calcd for C16H12Cl2O3 (323.17): C 59.46, H 3.74; Found: C 59.40, H 3.74%.

4-(4-Bromophenyl)-1-(4-chlorophenyl)-2-hydroxybutane- 1,4-dione (5f)

White solid, m.p. 172−177 ℃. FT-IR (KBr) ν = 3450 (O−H), 3080 (C−H), 1674 (C=O), 1581 (C=C), 1197 (C− O), 771 (C−Cl), 574 (C−Br) cm˗1. 1H NMR (400 MHz, CDCl3) δ = 7.98 (d, 3JH,H = 8.4 Hz, 2H, CHAr), 7.83 (d, 3JH,H = 8.4 Hz, 2H, CHAr), 7.64 (d, 3JH,H = 8.4 Hz, 2H, CHAr), 7.51 (d, 3JH,H = 8.4 Hz, 2H, CHAr), 5.59-5.61 (m, 1H, CH−O), 4.01 (d, 3JH,H = 6.4 Hz, 1H, OH), 3.33−3.47 [2×dd: 3.41−3.47 (dd, 3JH,H = 6.8, 17.2 Hz, 1H, CH2), 3.33−3.39 (dd, 3JH,H = 3.2, 17.2 Hz, 1H, CH2)] ppm. 13C NMR (100 MHz, CDCl3) δ = 199.3, 196.6 (C=O), 140.6, 135.2, 132.1, 131.9, 130.2, 129.8, 129.3, 129.1, 70.3, 43.1 ppm. Anal. Calcd for C16H12BrClO3 (367.62): C 52.27, H 3.29; Found: C 52.30, H 3.22%.

1-(4-Chlorophenyl)-2-hydroxy-4-(thiophen-2-yl)butane- 1,4-dione (5g)

Cream solid, m.p. 131.6−135.1 ℃. FT-IR (KBr) ν = 3450 (O−H), 3085, 2943 (C−H), 1695 (C=O), 1649 (C=C), 1203 (C−O), 721 (C−Cl) cm˗1. 1H NMR (400 MHz, DMSO-d6) δ = 8.02−8.11 (m, 4H, CHAr), 7.63 (d, 3JH,H = 8.4 Hz, 2H, CHAr), 7.26−7.28 (m, 1H, CHAr), 5.92 (d, 3JH,H = 7.6 Hz, 1H, OH), 5.38−5.43 (m, 1H, CH−O), 3.35−3.51 (m, 2H, CH2) ppm. 13C NMR (100 MHz, CDCl3) δ = 199.2, 190.1, 143.7, 140.5, 134.9, 133.0, 131.9, 130.3, 129.3, 128.3, 70.4, 43.9 ppm. Anal. Calcd for C14H11ClO3S (294.75): C 57.05, H 3.76; Found: C 56.60, H 3.49%.

1-(4-Bromophenyl)-2-hydroxy-4-phenylbutane-1,4- dione (5h)

White solid, m.p. 154.5−157.0 ℃. FT-IR (KBr) ν = 3438 (O−H), 3086 (C−H), 1676 (C=O), 1573 (C=C), 1190 (C− O), 654 (C−Br) cm˗1. 1H NMR (400 MHz, DMSO-d6) δ = 7.95−8.04 (m, 4H, CHAr), 7.78 (d, 3JH,H = 8.4 Hz, 2H, CHAr), 7.67 (t, 3JH,H = 7.6 Hz, 1H, CHAr), 7.53−7.57 (m, 2H, CHAr), 5.89 (d, 3JH,H = 7.6 Hz, 1H, OH), 5.38−5.44 (m, 1H, CH−O), 3.31−3.62 (m, 2H, CH2) ppm. 13C NMR (100 MHz, DMSO-d6) δ = 198.9, 198.3 (C=O), 136.9, 134.6, 133.9, 132.2, 131.3, 129.2, 128.5, 127.7, 69.2, 42.5 ppm. Anal. Calcd for C16H13BrO3 (333.18): C 57.68, H 3.93; Found: C 57.66, H 3.93%.

1-(4-Bromophenyl)-4-(4-chlorophenyl)-2-hydroxybutane- 1,4-dione (5i)

Cream solid, m.p. 168−173 ℃. FT-IR (KBr) ν = 3440 (O− H), 3074 (C−H), 1676 (C=O), 1558 (C=C), 1197 (C−O), 771 (C−Cl), 690 (C−Br) cm˗1. 1H NMR (400 MHz, CDCl3) δ = 7.89−7.92 (m, 4H, CHAr), 7.68 (d, 3JH,H = 7.6 Hz, 2H, CHAr), 7.47 (d, 3JH,H = 8.4 Hz, 2H, CHAr), 5.57−5.59 (m, 1H, CH−O), 4.01 (s, br., 1H, OH), 3.34−3.47 [2×dd: 3.41− 3.47 (dd, 3JH,H = 7.2, 17.2 Hz, 1H, CH2), 3.34−3.39 (dd, 3JH,H = 3.6, 17.2 Hz, 1H, CH2)] ppm. 13C NMR (100 MHz, CDCl3) δ = 199.6, 196.3 (C=O), 140.3, 134.8, 132.4, 132.3, 130.3, 129.8, 129.3, 129.1, 70.3, 43.1 ppm. Anal. Calcd for C16H12BrClO3 (367.62): C 52.27, H 3.29; Found: C 52.60, H 3.41%.

1,4-Bis(4-bromophenyl)-2-hydroxybutane-1,4-dione (5j)

White solid, m.p. 185−189 ℃. FT-IR (KBr) ν = 3441 (O−H), 3081 (C−H), 1674 (C=O), 1575 (C=C), 1199 (C− O), 675 (C−Br) cm˗1. 1H NMR (400 MHz, CDCl3) δ = 7.90 (d, 3JH,H = 8.4 Hz, 2H, CHAr), 7.83 (d, 3JH,H = 8.0 Hz, 2H, CHAr), 7.68 (d, 3JH,H = 8.4 Hz, 2H, CHAr), 7.64 (d, 3JH,H = 8.4 Hz, 2H, CHAr), 5.57−5.59 (m, 1H, CH−O), 4.00 (d, 3JH,H = 6.0 Hz, 1H, OH), 3.39−3.47 [2×dd: 3.41− 3.47 (dd, 3JH,H = 6.8, 17.2 Hz, 1H, CH2), 3.39−3.42 (dd, 3JH,H = 3.6, 17.2 Hz, 1H, CH2)] ppm. 13C NMR (100 MHz, CDCl3) δ = 199.5, 196.5 (C=O), 135.2, 134.4, 132.3, 132.1, 130.3, 129.8, 129.3, 129.1, 70.3, 43.1 ppm. Anal. Calcd for C16H12Br2O3 (412.07): C 46.64, H 2.94; Found: C 46.54, H 2.89%.

1-(4-Bromophenyl)-2-hydroxy-4-(4-nitrophenyl)butane- 1,4-dione (5k)

Yellow solid, m.p. 146−150 ℃. FT-IR (KBr) ν = 3429 (br., O−H), 3097 (C−H), 1677 (C=O), 1581 (C=C), 1519, 1328 (NO2), 1195 (C−O), 688 (C−Br) cm˗1. 1H NMR (400 MHz, DMSO-d6) δ = 8.36 (d, 3JH,H = 8.8 Hz, 2H, CHAr), 8.22 (d, 3JH,H = 8.8 Hz, 2H, CHAr), 7.98 (d, 3JH,H = 8.4 Hz, 2H, CHAr), 7.78 (d, 3JH,H = 8.4 Hz, 2H, CHAr), 6.00 (d, 3JH,H = 7.6 Hz, 1H, OH), 5.41−5.46 (m, 1H, CH−O), 3.44−3.69 [2×dd: 3.62−3.69 (dd, 3JH,H = 6.4, 17.2 Hz, 1H, CH2), 3.44−3.49 (dd, 3JH,H = 6.0, 17.2 Hz, 1H, CH2)] ppm. 13C NMR (100 MHz, DMSO-d6) δ = 199.2, 196.2 (C=O), 151.1, 140.9, 139.6, 132.4, 130.3, 129.5, 129.4, 124.0, 70.3, 43.6 ppm. Anal. Calcd for C16H12BrNO5 (378.17): C 50.82, H 3.20, N 3.70; Found: C 50.80, H 3.21, N 3.89%.

1-(4-Bromophenyl)-4-(furan-2-yl)-2-hydroxybutane- 1,4-dione (5l)

Cream solid, m.p. 168.0−173.0 ℃. FT-IR (KBr) ν = 3620 (O−H), 1679 (C−O), 1550 (C=C), 1198 (C=O), 675 (C−Br) cm˗1. 1H NMR (400 MHz, DMSO-d6) δ = 7.96 (d, 3JH,H = 8.4 Hz, 2H, CHAr), 7.92 (d, 3JH,H = 8.4 Hz, 2H, CHAr), 7.75−7.79 (m, 3H, CHAr), 5.91 (d, 3JH,H = 7.6 Hz, 1H, OH), 5.37−5.42 (m, 1H, CH−O), 3.33−3.59 (m, 2H, CH2) ppm. 13C NMR (100 MHz, DMSO-d6) δ = 198.8, 197.6 (C=O), 135.9, 134.6, 132.3, 132.2, 131.3, 130.6, 127.9, 127.8, 69.4, 42.5 ppm. Anal. Calcd for C14H11BrO4 (323.14): C 52.04, H 3.43; Found: C 52.20, H 3.40%

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