Molecules 2015, 20
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intense blue fluorescence under short wave UV light. After the heating period, the volatiles were
removed under reduced pressure and the residue adsorbed into silica gel which was directly applied to
the chromatographic column packed with silica gel. Elution with hexane/EtOAc in a gradient (7/3, 6/4,
5/5) afforded pure benzofuran 14 as a dark brown powder (1.98 g, 64%). 1H-NMR (CDCl3): δ 10.03 (s,
1H); 7.63 (s, 1H); 7.61 (d, J = 8.2 Hz, 1H); 7.40 (dd, J = 8.1, 1.7 Hz, 1H); 7.25 (d, J = 1.8 Hz, 1H); 6.91
(d, J = 8.1 Hz, 1H); 6.79 (d, J = 8.1 Hz, 1H); 1.71 (s, 6H). 13C-NMR (CD3SOCD3) δ: 190.91, 159.52,
148.77, 148.10, 145.85, 139.22, 131.99, 130.57, 123.11, 122.56, 119.45, 118.84, 110.31, 108.62, 105.60,
101.02, 25.87. HRMS Calculated for C18H14O5: 310.0841, found: 310.0840.
2-(3,4-Dihydroxyphenyl)-7-hydroxybenzofuran-4-carbaldehyde (Tournefolal) 3. Benzofuran aldehyde
14 (100 mg, 0.322 mmol) was added to a cooled solution of neat trifluoroacetic acid (2 mL). The mixture
was stirred at room temperature during 16 h. The trifluoroacetic acid was removed in vacuo and the
residue was purified by column chromatography on Sephadex LH20 eluting with methanol. Compound
3 was obtained as a greenish powder (61 mg, 70%). The spectral data agreed with the reported
values [19,34]. 1H-NMR (CD3SOCD3): δ 9.98 (s, 1H); 7.67 (d, J = 8.2 Hz, 1H), 7.55 (s, 1H); 7.34 (d,
J = 2.1 Hz, 1H); 7.30 (dd, J = 8.2, 2.1 Hz, 1H); 6.88 (d, J = 9 Hz, 1H); 6.86 (d, J = 8.2 Hz, 1H).
13C (CD3SOCH3): δ 190.42, 158.83, 147.91, 147.26, 145.72, 142.49, 131.58, 130.37, 120.77, 120.58,
117.27, 116.21, 112.38, 110.20, 99.16.
(E)-3-(2-(2,2-dimethylbenzo[d][1,3]dioxol-5-yl)-7-hydroxybenzofuran-4-yl)acrylic acid (16). Benzofuran
aldehyde 14 (310 mg, 1 mmol) was dissolved in pyridine (5 mL) and then malonic acid (1 g, 9.56 mmol)
and a drop of piperidine was added. The mixture was stirred at room temperature during 5 days and then
heated in an oil bath at 85–90 °C for 1 h. The volatiles were removed under reduced pressure and the
dark brown residue was purified by column chromatography eluting with a gradient of hexane/acetone
(7/3, 6/4, 5:5) to afford acid 16 as a golden solid strongly fluorescent under short wave UV light
(150 mg, 88%). 1H-NMR (CDCl3): δ 7.92 (d, J = 16.1 Hz, 1H); 7.63 (s, 1H); 7.57 (dd, J = 8.1, 1.8 Hz,
1H); 7.50 (d, J = 1.7 Hz, 1H); 7.47 (dd, J = 8.3, 0.6 Hz, 1H); 6.91 (dd, J = 8.2, 0.4 Hz, 1H); 6.86 (d,
J = 8.3 Hz, 1H); 6.52 (d, J = 16.0 Hz, 1H); 1.71 (s, 6H).13C CD3COCD3) 168.30, 158.11, 149.34, 149.03,
145.01, 143.48, 131.79, 126.21, 124.59, 119.90, 119.81, 119.63, 116.41, 111.87, 109.37, 106.15, 100.33,
25.89 HRMS: Calculated for C20H16O6: 352.0947, found: 352.0934.
2-(2,2-Dimethylbenzo[d][1,3]dioxol-5-yl)-7-methoxybenzofuran-4-carbaldehyde (23). To a solution of
aldehyde 14 (750 mg, 2.41 mmol) in DMF (5 mL) finely powdered K2CO3 (750 mg, 5.42 mmol) was
added. The mixture was stirred and to this, iodomethane (0.5 mL, 8.03 mmol) was added in one portion.
The mixture was heated in an oil bath at 70–80 °C for 24 h. The reaction mixture was cooled and diluted
with chloroform (50 mL). The mixture was diluted with water and the phases separated. The organic
phase was washed with water (6 × 25 mL) and dried over Na2SO4. Solvent removal at reduced pressure
and column chromatography (SiO2) of the residue eluting with hexane/ethyl acetate 4/1 afforded pure
23 as a dark yellow solid (610 mg, 78%). 1H-NMR (CDCl3): δ 10.04 (s, 1H); 7.64 (d, J = 8.3 Hz, 1H);
7.62 (s, 1H); 7.44 (dd, J = 8.1, 1.8 Hz, 1H); 7.29 (d, J = 1.7 Hz, 1H); 6.86 (d, J = 8.3 Hz, 1H); 6.80 (d,
J = 8.1 Hz, 1H); 4.13 (s, 3H); 1.71 (s, 6H).13C-NMR (CDCl3): δ 190.74, 159.28, 149.59, 148.62, 148.04,