3.2. General Procedure for the Synthesis of Compounds 4a–4g
The mixture of 2,4-dihydroxybenzaldehyde (1, 1 mmol), various substituted acetophenone (2a–2g, 1 mmol), and boric acid (0.5 mmol) were dissolved in PEG-400 and then were stirred to react for 6 h at 130 °C. After the completion of the reaction, the reaction mixture was extracted with ethyl acetate three times. The collected organic layers were combined and concentrated in vacuum, and the residue was subjected to column chromatography on silica gel using CH2Cl2 (4a, 4e–4g) and CH2Cl2-MeOH (30:1, 4b–4d) as eluent to generate the pure product.
2-(7-Hydroxy-2-phenyl-chromen-4-ylidene)-1-phenyl-ethanone (4a): Yellow power; m.p. 260 °C; Yield 4.79%; ESI-MS m/z 339.1 [M − H]−; 1H-NMR (400 MHz, DMSO-d6) δ ppm: 10.58 (1H, s, OH-4′′), 8.88 (1H, s, H-10), 8.24 (1H, d, J = 9.6 Hz, H-6′′), 8.10 (2H, d, J = 7.6 Hz, H-2, 6), 7.95 (2H, d, J = 7.2 Hz, H-2′, 6′), 7.58 (2H, d, J = Hz, H-3′, 5′), 7.58 (1H, s, H-8), 7.56 (1H, m, H-4), 7.53 (2H, d, J = 7.6 Hz, H-3, 5), 7.19 (1H, s, H-4′), 6.90 (2H, overlapped, H-3′′, 5′′); 13C-NMR (100 MHz, DMSO-d6) δ ppm: 188.5 (C=O, C-7), 161.3 (C, C-4′′), 155.1 (C, C-11), 153.9 (C, C-2′′), 142.1 (C, C-1′′), 140.7 (C, C-1′), 132.0 (C, C-1), 131.5 (CH, C-4), 130.7 (CH, C-4′), 129.1 (CH, C-2, 6), 128.37 (CH, C-2′, 6′), 127.6 (CH, C-3, 5), 125.6 (CH, C-6′′), 125.4 (CH, C-3′, 5′), 114.8 (CH, C-10), 111.5 (C, C-9), 103.0 (CH, C-5′′), 101.8 (CH, C-3′′), 101.0 (CH, C-8).
2-[7-Hydroxy-2-(2-hydroxy-phenyl)-chromen-4-ylidene]-1-(2-hydroxy-phenyl)-ethanone (4b): Red power; m.p. 249 °C; Yield 6.46%; ESI-MS m/z 371.1 [M − H]−; 1H-NMR (400 MHz, DMSO-d6) δ ppm: 13.82 (1H, s, OH-2), 10.65 (2H, s, OH-2′, 4′′), 9.20 (1H, s, H-10), 8.32 (1H, d, J = 9.2 Hz, H-6′′), 8.26 (1H, d, J = 8.0 Hz, H-6), 7.84 (1H, d, J = 7.6 Hz, H-6′), 7.46 (1H, t, J = 7.6 Hz, H-4), 7.35 (1H, t, J = 8.0 Hz, H-4′), 7.21 (1H, s, H-8), 7.02 (1H, d, J = 8.8 Hz, H-3′), 6.98 (1H, d, J = 7.6 Hz, H-3), 6.93 (1H, overlapped, H-5′), 6.92 (1H, overlapped, H-5), 6.90 (1H, overlapped, H-3′′), 6.88 (1H, overlapped, H-5′′); 13C-NMR (100 MHz, DMSO-d6) δ ppm: 192.3 (C=O, C-7), 162.3 (C, C-2), 161.6 (C, C-4′′), 156.2 (C, C-2′), 154.4 (C, C-11), 154.3 (C, C-2′′), 145.0 (C, C-1′′), 134.6 (CH, C-4), 131.7 (CH, C-4′), 129.4 (CH, C-6), 128.3 (CH, C-6′), 126.0 (CH, C-6′′), 121.8 (C, C-1), 119.3 (CH, C-3), 118.6 (C, C-1′), 118.4 (CH, C-5′), 117.7 (CH, C-5), 116.8 (CH, C-3′), 115.0 (CH, C-5′′), 111.6 (C, C-9), 106.6 (CH, C-10), 102.8 (CH, C-3′′), 98.6 (CH, C-8).
2-[7-Hydroxy-2-(3-hydroxy-phenyl)-chromen-4-ylidene]-1-(3-hydroxy-phenyl)-ethanone (4c): Red power; m.p. 310 °C; Yield 19.27%; ESI-MS m/z 371.1 [M − H]−; 1H-NMR (400 MHz, DMSO-d6) δ ppm: 10.56 (1H, s, OH-4′′), 9.82 (1H, s, OH-3), 9.62 (1H, s, OH-3′), 8.79 (1H, s, H-10), 8.18 (1H, d, J = 9.2 Hz, H-6′′), 7.55 (1H, d, J = 8.0 Hz, H-6), 7.41 (1H, H-4), 7.38 (2H, overlapped, H-5′, 6′), 7.35 (1H, H-4′), 7.31 (1H, t, J = 8.0 Hz, H-5), 7.10 (1H, s, H-8), 6.97 (1H, H-2), 6.95 (1H, H-2′), 6.88 (1H, dd, J = 8.8, 2.4 Hz, H-5′′), 6.85 (1H, d, J = 2.4 Hz, H-3′′); 13C-NMR (100 MHz, DMSO-d6) δ ppm: 188.5 (C=O, C-7), 161.2 (C, C-4′′), 157.8 (C, C-3′), 157.4 (C, C-3), 155.0 (C, C-11), 153.8 (C, C-2′′), 142.2 (C, C-1), 141.9 (C, C-1′′), 133.2 (C, C-1′), 130.2 (CH, C-5′), 129.3 (CH, C-5), 125.5 (CH, C-6′′), 118.6 (CH, C-6), 118.4 (CH, C-2), 117.9 (CH, C-2′), 116.2 (CH, C-6′), 114.8 (CH, C-5′′), 114.0 (CH, C-4), 111.9 (CH, C-4′), 111.5 (C, C-9), 102.9 (CH, C-3′′), 101.7 (CH, C-10), 101.0 (CH, C-8).
2-[7-Hydroxy-2-(4-hydroxy-phenyl)-chromen-4-ylidene]-1-(4-hydroxy-phenyl)-ethanone (4d): Red power; m.p. 197 °C; Yield 3.06%; ESI-MS m/z 371.2 [M − H]−; 1H-NMR (400 MHz, DMSO-d6) δ ppm: 10.15 (3H,br s, OH-4, 4′, 4′′), 8.74 (1H, s, H-10), 8.17 (1H, d, J = 8.8 Hz, H-6′′), 8.00 (2H, d, J = 8.8 Hz, H-2, 6), 7.79 (2H, d, J = 8.4 Hz, H-2′, 6′), 7.09 (1H, s, H-8), 6.96 (2H, d, J = 8.8 Hz, H-3′, 5′), 6.86 (2H, d, J = 8.8 Hz, H-3, 5), 6.85 (2H, overlapped, H-3′′, 5′′); 13C-NMR (100 MHz, DMSO-d6) δ ppm: 187.2 (C=O, C-7), 160.9 (C, C-4′′), 160.7 (C, C-4), 159.9 (C, C-4′), 155.0 (C, C-11), 153.7 (C, C-2′′), 141.4 (C, C-1′′), 132.2 (C, C-1), 129.9 (CH, C-2, 6), 127.2, 127.1 (CH, C-2′, 6′), 125.4 (CH, C-6′′), 122.7 (C, C-1′), 116.0, 115.8 (CH, C-3′, 5′), 115.0, 114.8 (CH, C-3, 5), 111.7 (C, C-9), 103.1, 102.8 (CH, C-3′′, 5′′), 99.8 (CH, C-8, 10).
2-(7-Hydroxy-2-p-tolyl-chromen-4-ylidene)-1-p-tolyl-ethanone (4e): Yellow power; m.p. 258 °C; Yield 25.28%; ESI-MS m/z 367.2 [M − H]−; 1H-NMR (400 MHz, DMSO-d6) δ ppm: 10.52 (1H, s, OH-4′′), 8.84 (1H, s, H-10), 8.20 (1H, d, J = 8.8 Hz, H-6′′), 8.00 (2H, d, J = 8.0 Hz, H-2, 6), 7.82 (2H, d, J = 8.4 Hz, H-2′, 6′), 7.37 (2H, d, J = 8.4 Hz, H-3′, 5′), 7.31 (2H, d, J = 8.0 Hz, H-3, 5), 7.15 (1H, s, H-8), 6.88 (1H, dd, J = 8.0, 2.4 Hz, H-5′′), 6.87 (1H, d, J = 2.4 Hz, H-3′′); 13C-NMR (100 MHz, DMSO-d6) δ ppm: 188.7 (C=O, C-7), 161.2 (C, C-4′′), 155.0 (C, C-11), 153.8 (C, C-2′′), 141.9 (C, C-1′′), 141.6 (C, C-4), 140.7 (C, C-4′), 138.1 (C, C-1), 129.7 (CH, C-2, 6), 129.2 (C, C-1′), 129.0 (CH, C-2′, 6′), 127.7 (CH, C-3, 5), 125.6 (CH, C-6′′), 125.3 (CH, C-3′, 5′), 114.7 (CH, C-10), 111.6 (C, C-9), 103.0 (CH, CH-5′′), 101.2 (CH, C-3′′), 100.6 (CH, C-8), 21.0 (CH3-4, 4′).
2-[7-Hydroxy-2-(4-methoxy-phenyl)-chromen-4-ylidene]-1-(4-methoxy-phenyl)-ethanone (4f): Yellow power; m.p. 260 °C; Yield 19.37%; ESI-MS m/z 399.2 [M − H]−; 1H-NMR (400 MHz, DMSO-d6) δ ppm: 8.78 (1H, s, H-10), 8.20 (1H, d, J = 9.6 Hz, H-6′′), 8.09 (2H, d, J = 8.8 Hz, H-2, 6), 7.88 (2H, d, J = 8.4 Hz, H-2′, 6′), 7.13 (2H, d, J = 8.8 Hz, H-3′, 5′), 7.121 (1H, s, H-8), 7.03 (2H, d, J = 8.8 Hz, H-3, 5), 6.87 (1H, overlapped, H-3′′), 6.86 (1H, overlapped, H-5′′); 13C-NMR (100 MHz, DMSO-d6) δ ppm: 187.3 (C=O, C-7), 162.0 (C, C-4′′), 161.3 (C, C-4), 161.1 (C, C-4′), 154.9 (C, C-11), 153.8 (C, C-2′′), 141.7 (C, C-1′′), 133.6 (C, C-1), 129.8 (CH, C-2, 6), 127.2 (CH, C-2′, 6′), 125.5 (CH, C-6′′), 124.3 (C, C-1′), 114.6 (CH, C-3′, 5′), 114.6 (CH, C-10), 113.6 (CH, C-3, 5), 111.7 (C, C-9), 103.0 (CH, CH-5′′), 100.4 (CH, C-3′′), 100.2 (CH, C-8), 55.5 (CH3O-4), 55.4 (CH3O-4′).
1-(4-Chloro-phenyl)-2-[2-(4-chloro-phenyl)-7-hydroxy-chromen-4-ylidene]-ethanone (4g): Yellow power; m.p. 298 °C; Yield 20.45%; ESI-MS m/z 407.1 [M − H]−; 1H-NMR (400 MHz, DMSO-d6) δ ppm: 8.79 (1H, s, H-10), 8.16 (1H, d, J = 8.8 Hz, H-6′′), 8.08 (2H, d, J = 8.4 Hz, H-2, 6), 7.92 (2H, d, J = 8.4 Hz, H-2′, 6′), 7.60 (2H, d, J = 8.4 Hz, H-3′, 5′), 7.53 (2H, d, J = 8.4 Hz, H-3, 5), 7.12 (1H, s, H-8), 6.89 (1H, dd, J = 8.8, 2.0 Hz, H-5′′), 6.86 (1H, d, J = 2.4 Hz, H-3′′); 13C-NMR (100 MHz, DMSO-d6) δ ppm: 187.0 (C=O, C-7), 161.3 (C, C-4′′), 153.6 (C, C-11), 153.7 (C, C-2′′), 142.2 (C, C-1′′), 139.2 (C, C-1), 136.3 (C, C-4), 135.3 (C, C-4′), 130.7 (C, C-1′), 129.2 (CH, C-2, 6), 128.2 (CH, C-2′, 6′), 127.0 (CH, C-3, 5), 125.3 (CH, C-6′′), 114.8 (CH, C-10), 111.3 (C, C-9), 102.9 (CH, CH-5′′), 102.1 (CH, C-3′′), 100.8 (CH, C-8).