Sulfuric Acid → (S)-1-(6-bromo-2-methyl-3,4-dihydroquinoxalin-1(2H)-yl)ethanone

Participants

Reaction Steps

A 1-L round bottomed flask was charged with (S)-1-(6-bromo-2-methyl-4-tosyl-3,4-dihydroquinoxaline-1(2H)-yl)ethanone (13.32 g, 31.5 mmol) and sulfuric acid (67.1 mL, 1259 mmol). The reaction mixture was stirred until all the viscous oil had dissolved (ca. 1 h). The reaction mixture was then quenched over crushed ice (ca. 50 g). The mixture was carefully neutralized with 10 N sodium hydroxide (157 mL, 1573 mmol) while not allowing internal temperature to exceed 10° C. The mixture was diluted with dichloromethane (200 mL) and the layers separated. The aqueous layer was extracted with dichloromethane (100 mL). The organic layers were combined and concentrated under reduced pressure. The crude product was purified by column chromatography (eluting with 4:1 dichloromethane-ethyl acetate) to afford (S)-1-(6-bromo-2-methyl-3,4-dihydroquinoxaline-1(2H)-yl)ethanone (7.18 g, 85%) as an off-white solid. MS (ESI, pos. ion) m/z 269 [M+1]+.

Provenance & Evidence