Hydrochloric Acid → 8-bromo-3-methylquinoxalin-2(1H)-one

Participants

Reaction Conditions

Reaction Steps

A solution of (S)-8-bromo-3-methyl-3,4-dihydroquinoxalin-2(1H)-one (17 g, 70.5 mmol), MeOH (141 mL), and 1.0 N aq. NaOH (141 mL, 141 mmol) was stirred at 85° C. in a three-necked round-bottom flask fitted with a septum, reflux condenser, and addition funnel. A mixture of H2O2 (30% in water; 25.2 mL, 247 mmol) and deionized water (10 mL) was then added, dropwise via the addition funnel, over 45 min, and the resulting mixture was heated at 85° C. for 17 h. The mixture was cooled to RT, 5 N aq. HCl (36 mL) was added, and the resulting slurry was extracted with 10% MeOH/DCM (3×150 mL). The combined extracts were dried over Na2SO4, filtered, and concentrated in vacuo to give 8-bromo-3-methylquinoxalin-2(1H)-one (126d; 13.16 g, 55.1 mmol, 78% yield) as a tan solid, which was used without further purification in the subsequent step: 1H NMR (400 MHz, CDCl3) δ ppm 9.03 (1H, s), 7.77 (1H, d, J=8.2 Hz), 7.67 (1H, d, J=7.6 Hz), 7.22 (1H, t, J=7.8 Hz), 2.61 (3H, s). m/z (ESI, +ve) 239.0 (M+H)+.

Provenance & Evidence