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Synlett 2006(11): 1657-1662  
DOI: 10.1055/s-2006-944204
LETTER
© Georg Thieme Verlag Stuttgart · New York

An Efficient Method to Synthesize Benzofurans and Naphthofurans

Chongfeng Pana, Jie Yua, Yuqing Zhoua, Zhiyong Wang*a, Ming-Ming Zhoub
a Hefei National Laboratory for Physical Science at Microscale and Department of Chemistry, University of Science and Technology of China, Hefei, Anhui, 230026, P. R. of China
Fax: +86(551)3603185; e-Mail: zwang3@ustc.edu.cn;
b Department of Physiology and Biophysics, Mount Sinai School of Medicine, New York University, One Gustave L. Levy Place, New York, NY 10029-6574, USA
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Publikationsverlauf

Received 16 February 2006
Publikationsdatum:
04. Juli 2006 (online)

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Abstract

A new method for synthesis of benzofurans and naphthofurans from 2-hydroxystilbene derivatives via an intermolecular ­cyclization is reported in this study with up to 94% isolated yield.

Key words

benzofuran - naphthofuran - iodine - cyclization - syn­thesis

5

Optimized Procedure for the Synthesis of the PBF.
Hydroxystilbene (1 mmol) was dissolved in 7 mL of anhyd THF, and then K2CO3 (8 mmol) was added with stirring at r.t. After 5 min, I2 (8 mmol) was added in one portion. The mixture was stirred at r.t. for 2 h, and then sat. aq NaHCO3 solution (20 mL) was added. NaHSO3 was slowly added to the system until the excess I2 was completely reduced. The system was subsequently extracted with Et2O, 3 × 20 mL. The organic layer was dried over anhyd MgSO4, evaporated, and purified by chromatography on silica gel to give the product. 2-(4-Chlorophenyl)benzofuran: 1H NMR (300 MHz, CDCl3): δ = 7.78 (dd, J = 6.5, 1.8 Hz, 2 H), 7.59-7.49 (m, 2 H), 7.41 (d, J = 6.5 Hz, 2 H), 7.32-7.20 (m, 2 H), 7.00 (s, 1 H). 13C NMR (75 MHz, CDCl3): δ = 155.07, 154.94, 124.48, 129.28, 129.19, 126.44, 126.29, 124.71, 123.25, 121.15, 111.34, 101.90. IR (film): 1580, 1487, 1451, 1404, 1256, 1093 cm-1. HRMS: m/z calcd for C14H9 35ClO: 228.0342; found: 228.0351.
2-Phenylbenzofuran: 1H NMR (400 MHz, CDCl3): δ = 7.87 (dd, J = 8.5, 1.4 Hz, 2 H), 7.52-7.23 (m, 7 H), 7.03 (d, J = 0.9 Hz, 1 H). 13C NMR (100 MHz, CDCl3): δ = 155.94, 154.91, 130.52, 129.25, 128.80, 128.56, 124.96, 124.27, 122.95, 120.91, 111.19, 101.31. IR (film): 2926, 2856, 1562, 1470, 1455, 1121 cm-1. HRMS: m/z calcd for C14H10O: 194.0732; found: 194.0728.
2-(4-Methylphenyl)benzofuran: 1H NMR (300 MHz, CDCl3): δ = 7.75 (d, J = 8.1 Hz, 2 H), 7.57-7.49 (m, 2 H), 7.26-7.21 (m, 4 H), 6.95 (s, 1 H), 2.39 (s, 3 H). 13C NMR (75 MHz, CDCl3): δ = 156.36, 154.94, 138.72, 129.62, 129.51, 127.92, 125.05, 124.13, 123.00, 120.88, 111.23, 100.70, 21.51. IR (film): 2919, 1617, 1502, 1450, 1258, 1167, 1111, 1034 cm-1. HRMS: m/z calcd for C15H12O: 208.0888; found: 208.0885.
4-(Benzofuran-2-yl)phenyl Acetate: 1H NMR (300 MHz, CDCl3): δ = 7.87 (d, J = 8.9 Hz, 2 H), 7.59-7.56 (m, 1 H), 7.53-7.50 (m, 1 H), 7.31-7.16 (m, 4 H), 6.98 (d, J = 0.9 Hz, 1 H), 2.32 (s, 3 H). 13C NMR (75 MHz, CDCl3): δ = 169.35, 155.25, 155.02, 150.92, 129.30, 128.35, 126.15, 124.45, 123.11, 122.12, 121.05, 111.27, 101.50, 21.20. IR (film): 2927, 1750, 1498, 1451, 1374, 1218, 1194 cm-1. HRMS: m/z calcd for C16H12O3: 252.0786; found: 252.0790.
2-(2-Methoxyphenyl)benzofuran: 1H NMR (300 MHz, CDCl3): δ = 8.07 (dd, J = 7.7, 1.7 Hz, 1 H), 7.60-7.58 (m, 1 H), 7.5 (d, J = 7.9 Hz, 1 H), 7.35 (d, J = 0.5 Hz, 1 H), 7.32-7.18 (m, 3 H), 7.10-6.99 (m, 2 H), 4.00 (s, 3 H). 13C NMR (75 MHz, CDCl3): δ = 156.63, 154.03, 152.31, 129.93, 129.35, 127.18, 124.22, 122.76, 121.15, 120.89, 119.52, 111.17, 110.94, 106.45, 55.54. IR (film): 3063, 2936, 2837, 1603, 1585, 1493, 1448, 1282, 1249, 1018 cm-1. HRMS: m/z calcd for C15H12O2: 224.0837; found: 224.0831.
5-Bromo-2-phenylbenzofuran: 1H NMR (300 MHz, CDCl3): δ = 7.84 (dd, J = 8.5, 1.5 Hz, 2 H), 7.72-7.68 (m, 1 H), 7.47-7.36 (m, 5 H), 6.95 (s, 1 H). 13C NMR (75 MHz, CDCl3): δ = 157.35, 153.72, 131.33, 130.02, 129.11, 128.96, 127.19, 125.18, 123.59, 116.13, 112.70, 100.74. IR (film): 3091, 2923, 2853, 1605, 1578, 1491, 1450, 1440 cm-1. HRMS: m/z calcd for C14H9 79BrO: 271.9837; found: 271.9833.
2-(4-Methoxyphenyl)naphtho[2,1- b ]furan: 1H NMR (300 MHz, CDCl3): δ = 8.14 (d, J = 8.0 Hz, 1 H), 7.93 (d, J = 8.0 Hz, 1 H), 7.87-7.83 (m, 2 H), 7.70-7.64 (m, 2 H), 7.60-7.54 (m, 1 H), 7.50-7.44 (m, 1 H), 7.37 (s, 1 H), 7.02-6.98 (m, 2 H), 3.86 (s, 3 H). 13C NMR (75 MHz, CDCl3): δ = 159.97, 155.73, 152.21, 130.59, 128.90, 127.68, 126.30, 126.23, 124.91, 124.71, 124.58, 123.73, 123.62, 114.47, 112.33, 99.01, 55.49. IR (film): 1606, 1498, 1251, 1024 cm-1. HRMS: m/z calcd for C19H14O2: 274.0994; found: 274.0987.
2-(4-Methylphenyl)naphtho[2,1- b ]furan: 1H NMR (300 MHz, CDCl3): δ = 8.15 (d, J = 8.2 Hz, 1 H), 7.93 (d, J = 8.2 Hz, 1 H), 7.81 (d, J = 8.1 Hz, 2 H), 7.72-7.65 (m, 2 H), 7.60-7.55 (m, 1 H), 7.50-7.45 (m, 2 H), 7.27 (d, J = 8.1 Hz, 2 H), 2.40 (s, 3 H). 13C NMR (75 MHz, CDCl3): δ = 155.80, 152.30, 138.34, 130.56, 129.63, 128.89, 128.06, 127.72, 126.25, 124.97, 124.74, 124.58, 123.59, 112.35, 99.83, 21.46. IR (film): 2916, 2857, 1501, 1384 cm-1. HRMS:
m/z calcd for C19H14O: 258.1045; found: 258.1053.
2-Phenylnaphtho[2,1- b ]furan: 1H NMR (300 MHz, CDCl3): δ = 8.17 (dd, J = 0.6, 7.8 Hz, 1 H), 7.96-7.91 (m, 3 H), 7.74-7.67 (m, 2 H), 7.62-7.57 (m, 1 H), 7.52-7.45 (m, 4 H), 7.38-7.33 (m, 1 H). 13C NMR (75 MHz, CDCl3): δ = 155.53, 152.51, 130.80, 130.59, 128.96, 128.94, 128.38, 127.77, 126.38, 125.31, 124.80, 124.69, 123.59, 112.41, 100.58. IR (film): 3053, 2924, 2854, 1628, 1603, 1488 cm-1. HRMS: m/z calcd for C18H12O: 244.0888; found: 244.0890.
2-(4-Chlorophenyl)naphtho[2,1- b ]furan: 1H NMR (300 MHz, CDCl3): δ = 8.15 (d, J = 8.1 Hz, 1 H), 7.94 (d, J = 8.1 Hz, 1 H), 7.84 (d, J = 8.6 Hz, 2 H), 7.73 (d, J = 9.0 Hz, 1 H), 7.67 (d, J = 9.0 Hz, 1 H), 7.62-7.57 (m, 1 H), 7.52-7.47 (m, 2 H), 7.43 (d, J = 8.6 Hz, 2 H). 13C NMR (75 MHz, CDCl3): δ = 154.33, 152.55, 134.08, 130.58, 129.23, 129.17, 128.96, 127.69, 126.50, 125.93, 125.65, 124.81, 124.56, 123.52, 112.32, 100.98. IR (film): 1585, 1481, 1383, 1277, 1266, 1167 cm-1. HRMS: m/z calcd for C18H11 35ClO: 278.0498; found: 278.0511.
Methyl 4-(Naphtho[2,1- b ]furan-2-yl)benzoate: 1H NMR (300 MHz, CDCl3): δ = 8.17-8.11 (m, 3 H), 7.97-7.93 (m, 3 H), 7.75 (d, J = 8.9 Hz, 1 H), 7.71 (d, J = 8.9 Hz, 1 H), 7.62-7.58 (m, 2 H), 7.53-7.47 (m, 1 H), 3.94 (s, 3 H). 13C NMR (75 MHz, CDCl3): δ = 166.85, 154.28, 153.05, 134.77, 130.65, 130.35, 129.54, 129.04, 127.80, 126.71, 126.30, 124.98, 124.54, 124.45, 123.56, 112.41, 102.72, 52.31.
IR (film): 1715, 1607, 1435, 1411, 1340, 1278, 1179, 1107 cm-1. HRMS: m/z calcd for C20H14O3: 302.0943; found: 302.0951.
2-(2-Chlorophenyl)naphtho[2,1- b ]furan: 1H NMR (300 MHz, CDCl3): δ = 8.20 (dd, J = 8.1, 0.5 Hz, 1 H), 8.10 (dd, J = 7.9, 1.7 Hz, 1 H), 8.00 (d, J = 0.5 Hz, 1 H), 7.94 (d, J = 7.9 Hz, 1 H), 7.75 (d, J = 9.0 Hz, 1 H), 7.67 (d, J = 9.0 Hz, 1 H), 7.62-7.57 (m, 1 H), 7.52-7.46 (m, 2 H), 7.41-7.35 (m, 1 H), 7.29-7.23 (m, 1 H). 13C NMR (75 MHz, CDCl3): δ = 151.87, 151.47, 130.99, 130.52, 129.15, 128.89, 128.80, 128.74, 127.95, 127.06, 126.52, 126.03, 124.73, 124.44, 123.60, 112.16, 106.50. IR (film): 3060, 2924, 1629, 1590, 1521, 1469, 1385, 1172 cm-1. HRMS: m/z calcd for C18H11 35ClO: 278.0498; found: 278.0505.
2-(2-Bromophenyl)naphtho[2,1- b ]furan: 1H NMR (300 MHz, CDCl3): δ = 8.21 (d, J = 8.1 Hz, 1 H), 8.03-8.01 (m, 2 H), 7.95 (d, J = 8.1 Hz, 1 H), 7.77-7.66 (m, 3 H), 7.63-7.58 (m, 1 H), 7.52-7.40 (m, 2 H), 7.24-7.17 (m, 1 H). 13C NMR (75 MHz, CDCl3): δ = 152.60, 152.00, 134.40, 131.15, 130.49, 129.62, 129.16, 128.89, 127.92, 127.59, 126.52, 125.99, 124.73, 124.20, 123.60, 120.48, 112.23, 106.18. IR (film): 2925, 1626, 1585, 1465, 1416, 1384, 1168 cm-1. HRMS: m/z calcd for C18H11 79BrO: 321.9993; found: 321.9985.
2-(2-Methoxyphenyl)naphtho[2,1- b ]furan: 1H NMR (300 MHz, CDCl3): δ = 8.22 (d, J = 8.0 Hz, 1 H), 8.12 (dd, J = 7.7, 1.7 Hz, 1 H), 7.94 (d, J = 8.0 Hz, 1 H), 7.83 (s, 1 H), 7.73-7.66 (m, 2 H), 7.61-7.55 (m, 1 H), 7.49-7.44 (m, 1 H), 7.35-7.29 (m, 1 H), 7.13-7.07 (m, 1 H), 7.03 (d, J = 8.3 Hz, 1 H), 4.05 (s, 3 H). 13C NMR (75 MHz, CDCl3): δ = 156.35, 151.87, 151.49, 130.51, 129.07, 128.86, 128.00, 126.90, 126.20, 125.12, 125.07, 124.47, 123.72, 120.97, 119.70, 112.24, 111.22, 105.53, 55.62. IR (film): 3058, 3000, 1626, 1597, 1584, 1491, 1462, 1445, 1380, 1250 cm-1. HRMS: m/z calcd for C19H14O2: 274.0994; found: 274.0991.
2-(3,5-Dimethoxyphenyl)naphtho[2,1- b ]furan: 1H NMR (300 MHz, CDCl3): δ = 8.16 (d, J = 8.1 Hz, 1 H), 7.94 (d, J = 8.1 Hz, 1 H), 7.74-7.67 (m, 2 H), 7.62-7.57 (m, 1 H), 7.50-7.46 (m, 2 H), 7.09 (d, J = 1.3 Hz, 2 H), 6.48 (s, 1 H), 3.90 (s, 6 H). 13C NMR (75 MHz, CDCl3): δ = 161.33, 155.34, 152.45, 132.51, 130.58, 128.95, 127.76, 126.43, 125.47, 124.73, 124.60, 123.59, 112.39, 102.91, 101.10, 100.99, 55.63. IR (film): 3002, 2936, 2837, 1597, 1561, 1460, 1424, 1385, 1266, 1204, 1157 cm-1. HRMS: m/z calcd for C20H16O3: 304.1099; found: 304.1099.
2-(Naphthalen-1-yl)naphtho[2,1- b ]furan: 1H NMR (300 MHz, CDCl3): δ = 8.56 (d, J = 8.1 Hz, 1 H), 8.21 (d, J = 8.1 Hz, 1 H), 7.98-7.88 (m, 4 H), 7.75 (s, 2 H), 7.63-7.50 (m, 6 H). 13C NMR (75 MHz, CDCl3): δ = 155.17, 152.67, 134.15, 130.78, 130.58, 129.44, 128.95, 128.78, 128.50, 127.83, 127.28, 127.01, 126.45, 126.23, 125.68, 125.45, 125.39, 124.71, 124.45, 123.62, 112.49, 105.08. IR (film): 3053, 2924, 1629, 1524, 1509, 1385 cm-1. HRMS: m/z calcd for C22H14O: 294.1045; found: 294.1032.
4-(Naphtho[2,1- b ]furan-2-yl)pyridine: 1H NMR (300 MHz, CDCl3): δ = 8.70-8.67 (m, 2 H), 8.16 (dd, J = 8.0, 2.2 Hz, 1 H), 7.95 (d, J = 8.1 Hz, 1 H), 7.80-7.59 (m, 6 H), 7.54-7.51 (m, 1 H). 13C NMR (75 MHz, CDCl3): δ = 152.96, 152.18, 150.28, 137.26, 130.43, 128.88, 127.55, 126.80, 126.70, 124.97, 123.96, 123.29, 118.29, 112.14, 103.82.
IR (film): 1602, 1538, 1519, 1414, 1384 cm-1. HRMS: m/z calcd for C17H11NO: 245.0841; found: 245.0839.
Methyl Naphtho[2,1- b ]furan-2-carboxylate: 1H NMR (300 MHz, CDCl3): δ = 8.14 (d, J = 7.9 Hz, 1 H), 8.00 (s, 1 H), 7.95 (d, J = 7.9 Hz, 1 H), 7.86 (d, J = 9.0 Hz, 1 H), 7.70-7.61 (m, 2 H), 7.56-7.51 (m, 1 H), 4.01 (s, 3 H). 13C NMR (75 MHz, CDCl3): δ = 159.98, 154.17, 144.90, 130.65, 129.33, 129.13, 128.13, 127.43, 125.56, 123.44, 122.86, 113.10, 112.84, 52.44. IR (film): 2952, 1731, 1586, 1551, 1439, 1331, 1282, 1227, 1206, 1171, 1117 cm-1. HRMS: m/z calcd for C14H10O3: 226.0630; found: 226.0644.
3-Methyl-2-phenylbenzofuran: 1H NMR (300 MHz, CDCl3): δ = 7.81 (dd, J = 8.5, 1.3 Hz, 2 H), 7.52-7.45 (m, 4 H), 7.38-7.24 (m, 3 H), 2.48 (s, 3 H). 13C NMR (75 MHz, CDCl3): δ = 153.93, 150.80, 131.56, 131.30, 128.72, 127.96, 126.82, 124.43, 122.45, 119.39, 111.37, 111.04, 9.55.
IR (film): 3059, 2924, 1600, 1450, 1259, 1211, 1109, 1068 cm-1. HRMS: m/z calcd for C15H12O: 208.0888; found: 208.0895.
2,3-Diphenylnaphtho[2,1- b ]furan: 1H NMR (300 MHz, CDCl3): δ = 7.90 (d, J = 8.0 Hz, 1 H), 7.76-7.70 (m, 2 H), 7.57-7.52 (m, 8 H), 7.40-7.35 (m, 1 H), 7.29-7.19 (m, 4 H). 13C NMR (75 MHz, CDCl3): δ = 151.52, 150.17, 134.84, 131.05, 130.98, 130.67, 129.46, 129.06, 128.49, 128.27, 127.86, 126.32, 126.08, 124.34, 123.72, 123.16, 119.65, 112.27. IR (film): 3056, 2925, 2854, 1602, 1524, 1502, 1483, 1443, 1393, 1344, 1393 cm-1. HRMS: m/z calcd for C24H16O: 320.1201; found: 320.1193.
3-Methyl-2-phenylnaphtho[1,2- b ]furan: 1H NMR (300 MHz, CDCl3): δ = 8.37 (d, J = 8.3 Hz, 1 H), 7.94-7.87 (m, 3 H), 7.68-7.44 (m, 6 H), 7.39-7.33 (m, 1 H), 2.55 (s, 3 H). 13C NMR (75 MHz, CDCl3): δ = 150.26, 149.27, 131.79, 131.71, 128.71, 128.49, 127.58, 126.55, 126.49, 126.26, 125.00, 123.10, 121.33, 120.25, 118.05, 112.60, 9.71.
IR (film): 2923, 1604, 1491, 1446, 1384 cm-1. HRMS:
m/z calcd for C19H14O: 258.1045; found: 258.1051.
2-(2-Phenylprop-1-enyl)cyclohexa-2,5-diene-1,4-dione: 1H NMR (300 MHz, CDCl3): δ = 7.68-7.63 (m, 2 H), 7.59-7.55 (m, 2 H), 7.38-7.21 (m, 4 H), 7.09 (t, J = 7.5 Hz, 1 H), 1.83 (d, J = 0.5 Hz, 3 H). 13C NMR (75 MHz, CDCl3): δ = 201.74, 171.39, 138.38, 138.33, 128.71, 128.26, 125.36, 124.89, 124.76, 122.28, 119.63, 113.52, 24.46. IR (film): 2926, 2855, 1721, 1612, 1476, 1462 cm-1. HRMS: m/z calcd for C15H12O2: 204.0837; found: 224.0829.
4b,9b-Dihydrobenzo[ b ]benzofuro[2,3- d ]furan: 1H NMR (300 MHz, CDCl3): δ = 7.53 (dd, J = 0.8, 7.5 Hz, 2 H), 7.30-7.25 (m, 2 H), 6.99-6.94 (m, 2 H), 6.86 (d, J = 8.2 Hz, 2 H), 6.28 (s, 2 H). 13C NMR (75 MHz, CDCl3): δ = 160.18, 131.46, 126.68, 124.56, 121.27, 110.95, 86.59. IR (film): 3051, 2923, 2852, 1602, 1483, 1464, 1326, 1314, 1241, 1225, 1173 cm-1. HRMS: m/z calcd for C14H10O2: 210.0681; found: 210.0678.
5,7-Di- tert -butyl-2-phenylbenzofuran: 1H NMR (300 MHz, CDCl3): δ = 7.86 (dd, J = 7.5, 1.4 Hz, 2 H), 7.47-7.24 (m, 5 H), 6.97 (s, 1 H), 1.58 (s, 9 H), 1.39 (s, 9 H). 13C NMR (75 MHz, CDCl3): δ = 155.27, 151.47, 145.87, 133.90, 131.10, 129.51, 128.91, 128.34, 124.91, 119.25, 115.17, 101.60, 35.04, 34.71, 32.09, 30.24. IR (film): 3108, 2958, 2867, 1607, 1466, 1406, 1391, 1362, 1280, 1244, 1163
cm-1. HRMS: m/z calcd for C22H26O: 306.1984; found: 306.1973.