86
Lovricꢀ et al.
portionwise over 2 h. The reaction mixture was stirred at 10ꢀC and allowed to reach room
temperature overnight. The precipitate (potassium tetrafluoroborate) was filtered off and
washed with dichloromethane (3 £ 200 mL) and the filtrate was evaporated to dryness.
The resulting oily dark brown residue was distilled under high vacuum to afford pure 3a
as a pale yellow oil (162.13 g, 74%, bp. 230–233ꢀC/23 mmHg), Rf (dichloromethane) D
0.57. MS (ESI) m/z 219.3 [MCH]C. IR (film): 3069, 2950, 1726 (CDO, ester group),
1598, 1571, 1482 cm¡1. 1H NMR (300 MHz, CDCl3): d 3.71 (s, 3 H, OCH3), 7.02–7.04
(m, 2 H, Ar), 7.45–7.48 (m, 2 H, Ar), 7.31–7.33 (m, 2 H, Ar), 7.69–7.72 (m, 1 H, Ar).
13C NMR (300 MHz, CDCl3): d 51.92 (OCH3), 125.66, 126.08, 126.99, 127.48, 129.21,
130.76, 130.94, 131.55, 133.93, 141.82, 168.85 (COOCH3).
o-(2-Furyl)benzoic Acid (4a)30
To a solution of o-(2-furyl)benzoic acid methyl ester (3a, 32.22 g, 0.17 mol) in ethanol
(275 mL) was added potassium hydroxide (28.49 g, 0.51 mol). The reaction mixture was
heated at reflux temperature for 4 h and concentrated in vacuo. The residue was dissolved
in water (200 mL) and dichloromethane (200 mL) was added. The resulting biphasic
solution was cooled to 10ꢀC and hydrochloric acid (37%, 50 mL, 59.25 g solution,
21.93 g HCl, 0.6 mol) was added dropwise during 30 min. The phases were separated
and the aqueous phase was additionally extracted with dichloromethane (2 £ 50 mL).
Organic layers were collected, dried over Na2SO4, filtered and evaporated to afford pure
4a as pale brown oily crystals (30.08 g, 95%), mp 84–86ꢀC, (lit.30 87ꢀC), Rf (dichlorome-
thane/methanol 9/1) D 0.44. MS (ESI) m/z 211.8 [MCNa]C. IR (KBr): 3855, 3840, 3819,
3691, 3673, 3650, 3121, 2817, 2659, 2550, 1688 (CDO, carboxyl group), 1605 cm¡1. 1H
NMR (300 MHz, CDCl3): d 6.45–6.47 (m, 1 H, Ar), 6.63–6.64 (m, 1 H, Ar), 7.34–7.39
(m, 1 H, Ar), 7.48–7.55 (m, 2 H, Ar), 7.58–7.61 (m, 1 H, Ar), 7.83–7.86 (m, 1 H, Ar),
12.16 (s, 1 H, COOH). 13C NMR (300 MHz, CDCl3): d 108.33, 111.37, 127.56, 128.58,
128.71, 129.99, 130.58, 131.73, 142.75, 152.02, 174.45 (COOH).
o-(2-Thienyl)benzoic Acid (4b)
To a solution of o-(2-thienyl)benzoic acid methyl ester (3b, 160.00 g, 0.7 mol) in ethanol
(1300 mL) was added sodium hydroxide (44.00 g, 1.1 mol). The reaction mixture was
heated at reflux temperature for 1 h and concentrated in vacuo. The residue was dissolved
in distilled water (800 mL) and cooled to 10ꢀC. Hydrochloric acid (37%, 100 mL,
118.50 g solution, 43.85 g HCl, 1.2 mol) was added dropwise over 30 min. The mixture
was extracted with chloroform (1 £ 600 mL, 2 £ 200 mL). Organic layers were col-
lected, dried over Na2SO4, filtered and evaporated to afford pure 4b as a pale yellow crys-
tals (147.30 g, 98%), mp 83–86ꢀC, (lit.6 80ꢀC, lit.13 93–94ꢀC), Rf (dichloromethane/
methanol 9/1) D 0.36. MS (ESI) m/z 227.9 [MCNa]C. IR (KBr): 3818, 3734, 3648, 2922,
1
2353, 1687 (CDO, carboxyl group), 1594 cm¡1. H NMR (300 MHz, CDCl3): d 7.09–
7.15 (m, 2 H, Ar), 7.37–7.52 (m, 2 H, Ar), 7.53–7.60 (m, 2 H, Ar), 7.94–8.01 (m, 1 H,
Ar), 11.82 (s, 1 H, COOH). 13C NMR (300 MHz, CDCl3): d 125.91, 126.61, 127.09,
127.60, 129.96, 130.62, 131.63, 131.76, 134.95, 141.38, 173.86 (COOH).
o-(2-Furyl)benzamide (5a)
To a solution of o-(2-furyl)benzoic acid (4a, 30.00 g, 0.16 mol) in toluene (225 mL) and
dimethylformamide (DMF, 1 mL) previously cooled to ¡5ꢀC oxalyl chloride (15 mL,