Ethylene Glycol → 2-(3-Bromofuran-2-yl)-1,3-dioxolane

Beteiligte Stoffe

Reaktionsschritte

3-Bromofuran (8.99 mL, 100.0 mmol) is dissolved in DMF (8.5 mL), cooled to 0° C., treated dropwise with POCl3 (9.79 mL, 105.0 mmol), stirred for 1 h at RT and then heated to 80° C. for 2 h. The mixture is cooled to RT, poured over ice (1 kg) and neutralized to pH 9 with solid K2CO3. The mixture is stirred for 1 h, extracted with Et2O (3×500 mL), dried over K2CO3 and concentrated to a dark brown oil. The crude material is chromatographed over 600 g slurry-packed silica gel, eluting with 6% EtOAc/hexane (4 L), 8% EtOAc/hexane (2 L), 10% EtOAc/hexane (1 L), and finally 20% EtOAc/hexane. The appropriate fractions are combined and concentrated in vacuo to afford 14.22 g (81%) of 3-bromo-2-furaldehyde as a yellow oil. MS (EI) m/z: 174 (M+). 3-Bromo-2-furaldehyde (14.22 g, 81.3 mmol) is combined with ethylene glycol (6.55 mL, 117.4 mmol) and para-toluene sulfonic acid monohydrate (772 mg, 4.06 mmol) in benzene (200 mL) and heated to reflux with a Dean-Stark trap for 5 h. Additional ethylene glycol (1.64 mL, 29.41 mmol) and benzene (150 mL) are added and the solution is heated for an additional 2 h. The mixture is cooled to RT, treated with saturated NaHCO3 and stirred for 0.5 h. The layers are separated and the organics are dried over Na2SO4 and concentrated to a brown oil (18.8 g). The crude material is chromatographed over 700 g slurry-packed silica gel, eluting with 15% EtOAc/hexane. The appropriate fractions are combined and concentrated in vacuo to afford 16.45 g (92%) of 2-(3-bromo-2-furyl)-1,3-dioxolane as a yellow-orange oil. MS (EI) m/z: 218 (M+).

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