Potassium Carbonate → 3-Bromo-2-methyl-1-benzofuran

Participants

Reaction Steps

Methyl benzofuran-5-carboxylate (1.74 g, 9.9 mmol) is dissolved in CH2Cl2 (50 mL), layered with saturated NaHCO3 (75 mL) using very slow magnetic stirring so that the two layers are not mixed and treated with Br2 (3.1 mL, 59.1 mmol). The bi-phasic mixture is stirred slowly for 2 h, then vigorously for 1 h. The layers are separated and the aqueous layer is extracted with CH2Cl2 (2×50 mL). The organics are dried (Na2SO4) and concentrated under reduced pressure without heat. The residue is dissolved in MeOH (100 mL), treated with K2CO3 (8.17 g, 59.1 mmol) and stirred at RT for 18 h. The mixture is concentrated to dryness, partitioned between 50% saturated NaHCO3 (75 mL) and EtOAc (2×75 mL) and the organics are dried (Na2SO4) and concentrated in vacuo. The crude material (2.21 g) is adsorbed onto silica gel (4.5 g) chromatographed over 90 g slurry-packed silica gel, eluting with 8% EtOAc/hexane then 15% EtOAc/hexane. The appropriate fractions are combined and concentrated to afford 1.88 g (75%) of methyl 3-bromo-1-benzofuran as a white solid. 1H NMR (300 MHz, CDCl3): δ 3.99, 7.55, 7.74, 8.11, 8.31 ppm.

Provenance & Evidence