Synlett 2006(2): 207-210  
DOI: 10.1055/s-2006-926226
LETTER
© Georg Thieme Verlag Stuttgart · New York

A Facile Synthesis of Benzofuroisocoumarins from C-2 Arylated 1,3-Indanediones

Suven Dasa, Roland Fröhlichb, Animesh Pramanik*a
a Department of Chemistry, University of Calcutta, 92, A. P. C. Road, Kolkata 700 009, India
b Organisch-Chemisches Institut, Universität Münster, Corrensstraße 40, 48149 Münster, Germany
Fax: +91(33)23519755; e-Mail: animesh_in2001@yahoo.co.in;
Further Information

Publication History

Received 5 October 2005
Publication Date:
24 January 2006 (online)

Abstract

Refluxing 2-hydroxy-2-(2′-hydroxy-aryl/naphthyl)-1,3-indanediones in ethyleneglycol with a catalytic amount of tri­ethylamine produces benzofuroisocoumarins after a short reaction time (15 min) in very good yields.

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Adducts 2j-p; General Procedure A mixture of ninhydrin (0.25 g, 1.4 mmol) and the appropriate phenol, 1j-p (4.2 mmol) was refluxed in AcOH for the time indicated in Table [1] . Then the cold reaction mixture was poured into ice cold H2O and was left to sit undisturbed overnight. The crystalline solid product was filtered and washed with H2O. Recrystallization(acetone) gave pure products 2. 2j (as hemiketal 3j) IR (KBr): 3497, 3415, 1703, 1602, 1457, 1288, 1182, 955, 771 cm-1. 1H NMR (500 MHz, CDCl3): δ = 8.08 (1 H, d, J = 7.8 Hz), 7.84 (1 H, t, J = 7.5 Hz), 7.81 (1 H, d, J = 7.7 Hz), 7.60 (1 H, t, J = 7.5 Hz), 7.39 (1 H, d, J = 7.6 Hz), 7.29 (1 H, d, J = 7.9 Hz), 6.92 (1 H, t, J = 7.8 Hz). 13C NMR (75 MHz, CDCl3): δ = 198.0, 153.5, 148.0, 137.4, 134.1, 132.3, 131.5, 125.6, 125.3, 124.0, 123.5, 123.0, 116.5, 109.5, 82.9. Anal. Calcd for C15H9ClO4: C, 62.40; H, 3.14. Found: C, 62.53; H, 3.22. 2o (as hemiketal 3o) IR (KBr): 3304, 1725, 1692, 1607, 1296, 1235, 1098, 1012, 871 cm-1. 1H NMR (300 MHz, acetone-d 6): δ = 8.18 (1 H, s), 8.10-7.89 (3 H, m), 7.82-7.79 (1 H, m), 7.71-7.69 (1 H, m), 7.09 (1 H, s), 6.92 (1 H, d, J = 8.5 Hz), 6.11 (1 H, s), 4.34 (2 H, q, J = 7.0 Hz), 1.36 (3 H, t, J = 7.1 Hz). 13C NMR (75 MHz, acetone-d 6): δ = 198.1, 165.1, 160.7, 148.7, 136.8, 134.5, 133.6, 131.3, 127.4, 126.0, 125.1, 124.1, 123.2, 111.7, 110.4, 82.1, 60.4, 13.8. Anal. Calcd for C18H14O6: C, 66.25; H, 4.32. Found: C, 66.34; H, 4.25.

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Benzofuroisocoumarins 4a-p; General Procedure Et3N (cat., 0.5 mL) was added to substrates 2a-p (1.4 mmol) in ethyleneglycol (5 mL) and refluxed for 15 min until the solution turned a red color. Then the cold reaction mixture was acidified with HCl (6 N) to pH 6 and the solid product separated. After extraction with CHCl3, work-up was carried out as usual. The residue from the CHCl3 layer was purified by column chromatography over silica gel (EtOAc-petroleum ether). 4b IR (KBr): 1728 (CO) cm-1. 1H NMR (300 MHz, CDCl3): δ = 8.40 (1 H, d, J = 8.2 Hz), 7.95 (1 H, d, J = 7.1 Hz), 7.88-7.83 (1 H, m), 7.63-7.52 (2 H, m), 7.29-7.23 (2 H, m), 2.61 (3 H, s). 13C NMR (125 MHz, CDCl3): δ = 162.1 (CO), 153.3, 138.2, 135.63, 135.59, 132.0, 130.0, 128.4, 128.2, 124.3, 123.0, 119.9, 119.8, 119.1, 116.6, 15.1. Anal. Calcd for C16H10O3: C, 76.79; H, 4.03. Found: C, 76.88; H, 4.15. 4e IR (KBr): 1730 (CO) cm-1. 1H NMR (300 MHz, CDCl3): δ = 8.39 (1 H, d, J = 8.0 Hz), 7.93 (1 H, d, J = 7.6 Hz), 7.87-7.82 (1 H, m), 7.56-7.51 (1 H, m), 7.18 (1 H, d, J = 7.6 Hz), 7.05 (1 H, d, J = 7.6 Hz), 3.57-3.48 (1 H, m), 2.74 (3 H, s), 1.42 (6 H, d, J = 7.0 Hz). 13C NMR (125 MHz, CDCl3): δ = 162.2 (CO), 152.4, 139.3, 135.5, 135.0, 132.0, 130.9, 130.1, 129.2, 128.2, 125.2, 124.2, 119.8, 119.3, 118.6, 28.4, 23.1 (2 C), 18.6. Anal. Calcd for C19H16O3: C, 78.06; H, 5.52. Found: C, 78.21; H, 5.63. 4f IR (KBr): 1746 (CO) cm-1. 1H NMR (300 MHz, CDCl3): δ = 8.39 (1 H, d, J = 7.9 Hz), 7.98 (1 H, d, J = 7.8 Hz), 7.87-7.81 (1 H, m), 7.58-7.52 (1 H, m), 7.37 (1 H, d, J = 7.8 Hz), 7.30-7.25 (1 H, m), 6.95 (1 H, d, J = 7.9 Hz), 4.07 (3 H, s). 13C NMR (125 MHz, CDCl3): δ = 162.0 (CO), 146.1, 143.7, 138.0, 137.0, 135.7, 132.0, 129.9, 128.5, 125.1, 121.2, 120.1, 119.8, 111.2, 109.2, 56.6. Anal. Calcd for C16H10O4: C, 72.18; H, 3.78. Found: C, 72.31; H, 3.65. 4h IR (KBr): 1734 (CO) cm-1. 1H NMR (300 MHz, CDCl3): δ = 8.67 (1 H, d, J = 8.1 Hz), 8.42 (1 H, d, J = 8.0 Hz), 8.00-7.83 (4 H, m), 7.72-7.67 (2 H, m), 7.60-7.52 (2 H, m). 13C NMR (75 MHz, CDCl3): δ = 161.7 (CO), 152.0, 139.4, 135.3, 134.9, 131.7, 130.5, 129.6, 128.5, 128.0, 127.7, 127.4, 126.4, 125.7, 124.6, 119.2, 118.6, 113.6, 112.6. Anal. Calcd for C19H10O3: C, 79.71; H, 3.52. Found: C, 79.62; H, 3.63. 4j IR (KBr): 1747 (CO) cm-1. 1H NMR (300 MHz, CDCl3): δ = 8.41 (1 H, d, J = 8.0 Hz), 8.02 (1 H, d, J = 7.7 Hz), 7.92-7.86 (1 H, m), 7.70 (1 H, dd, J = 7.6, 1.1 Hz), 7.63-7.58 (1 H, m), 7.45 (1 H, dd, J = 7.6, 1.1 Hz), 7.31 (1 H, m). 13C NMR (75 MHz, CDCl3): δ = 161.1 (CO), 149.5, 137.1, 136.2, 135.4, 131.6, 128.9, 128.6, 126.8, 124.8, 120.8, 119.8, 119.5, 117.9, 117.2. Anal. Calcd for C15H7ClO3: C, 66.55; H, 2.61. Found: C, 66.69; H, 2.78. 4o IR (KBr): 1745 (CO) cm-1. 1H NMR (300 MHz, CDCl3): δ = 8.52 (1 H, d, J = 1.6 Hz), 8.40 (1 H, d, J = 7.9 Hz), 8.16 (1 H, dd, J = 8.8, 1.6 Hz), 7.92-7.85 (2 H, m), 7.63-7.56 (2 H, m), 4.43 (2 H, q, J = 7.1 Hz), 1.44 (3 H, t, J = 7.1 Hz). 13C NMR (125 MHz, CDCl3): δ = 166.3 (CO2Et), 161.5 (CO), 156.5, 137.7, 137.1, 135.8, 132.1, 129.5, 129.1, 128.6, 127.2, 121.4, 120.0, 119.6, 112.7, 112.6, 61.7, 14.7. Anal. Calcd for C18H12O5: C, 70.13; H, 3.92. Found: C, 70.27; H, 4.04.