反应详情

To a solution of commercially available 5,6,7,8-tetrahydroquinoxaline (3.08 g, 23.0 mmol) in CCl4 (200 mL) was added N-bromosuccinamide (4.09 g, 23.0 mmol) and a catalytic amount (56 mg) of benzoyl peroxide. The reaction mixture was heated at reflux for 17 hours. Saturated sodium bicarbonate solution was added (100 mL), the layers were separated and the aqueous phase was extracted with CH2Cl2 (2×200 mL). The organic extracts were dried and concentrated. The crude material contained 1:3:1 ratio (GC) of starting material, mono- and dibromo products which were separated by column chromatography on silica gel using a mixture of 1:1 EtOAc:hexanes to give 5-bromo-5,6,7,8-tetrahydroquinoxaline (3.03 g, 54%) as a brown liquid: 1H NMR (CDCl3): δ 1.99-2.03 (m, 1H), 2.20-2.49 (m, 3H), 2.97-3.10 (m, 1H), 3.11-3.20 (m, 1H), 5.48 (t, 1H, J=1.5 Hz), 8.40 (s, 2H). It should be noted that this material is unstable when exposed to air over 2-3 days and was used immediately in the next reaction.

1. temperatureThe reaction mixture was heated
2. temperatureat reflux for 17 hours
3. customthe layers were separated
4. extractionthe aqueous phase was extracted with CH2Cl2 (2×200 mL)
5. customThe organic extracts were dried
6. concentrationconcentrated
7. customwere separated by column chromatography on silica gel using
8. additiona mixture of 1:1 EtOAc