N-bromobutanimide → (6-Bromo-7-methyl-3-oxo-2,3-dihydro-benzo[1,4]oxazin-4-yl)-propionic acid ethyl ester

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Reaction Steps

To a solution of 2-(7-methyl-3-oxo-2,3-dihydro-benzo[1,4]oxazin-4-yl)-propionic acid ethyl ester (21.0 g, 80 mmol) in DCM (250 mL) was added 1-bromopyrrolidine-2,5-dione (15.6 g, 88 mmol) and the reaction mixture was stirred at ambient temperature for 3 h. The reaction mixture was quenched by addition of a saturated solution of thiosulfate in water (50 mL). The organic phase was separated and the aqueous portion was extracted with DCM (3×20 mL). The combined organic phase was washed with brine (100 mL), dried over anhydrous Na2SO4, filtered and concentrated in vacuo. The residue was purified by column chromatography on silica gel (eluting with 20% EtOAc in petroleum ether) to give -(6-bromo-7-methyl-3-oxo-2,3-dihydro-benzo[1,4]oxazin-4-yl)-propionic acid ethyl ester as solid (23.1 g, 85%). LC/MS (Table 1, Method 3) Rt=1.259 min.; MS m/z: 342/344 [M+H]+.

Provenance & Evidence