2H-Naphtho[1,2-b]pyran-2-one, 4-hydroxy-

Synthesis

4-Hydroxy-2H-benzo[h]chromen-2-one is obtained by reacting 2-Acetyl-1-naphthol with sodium hydride in diethyl carbonate. 2-Acetyl-1-naphthol (2.00 g, 10.7 mmol) in diethyl carbonate (10.3 ml) was added dropwise into a suspension of sodium hydride (60% dispersion in mineral oil, 2.14 g, 53.5 mmol) in diethyl carbonate (10.3 ml) and heated under reflux at 100 ℃ for 3 hours. The resultant mixture was left to cool to 0 ℃ in an ice bath and quenched by dropwise addition of water until effervescence ceased. The aqueous layer was washed with diethyl ether (3 × 20 ml) and acidified using concentrated hydrochloric acid to pH 1. The precipitate was filtered and washed with water, followed by petroleum ether and left to dry overnight at 90 ℃ to give the title compound as a colourless solid (1.06 g, 47%): mp: 273 – 277 ℃ (Lit.: 272 – 273 ℃);
vmax/cm-1 3410bw (O-H), 1646s (C=O), 1600s (C=C), 1560s (aro. C=C); δH (300 MHz; DMSO-d6) 12.68 (1H, br. s, OH), 8.40-8.33 (1H, m, C(7)H or C(10)H), 8.10-8.02 (1H, m, C(7)H or C(10)H), 7.86-7.82 (2H, m, C(5)H and C(6)H), 7.78-7.68 (2H, m, C(8)H and C(9)H), 5.71 (1H, s, C(3)H); δC (75 MHz; DMSO-d6) 166.6 (Ar-C), 161.7 (Ar-C), 150.7 (Ar-C), 134.8 (Ar-C), 128.7 (Ar-CH), 128.1 (Ar-CH), 127.3 (Ar-CH), 123.5 (Ar-CH), 122.2 (Ar-C), 121.7 (Ar-CH), 118.9 (Ar-CH), 111.1 (Ar- C), 90.6 (C(3)H); m/z (-ES) 211 (100%, [M-H]-).