To a solution of 2-chloro-3-methoxypropanoyl chloride (500 mg, 3.18 mmol) and 4-amino-3-hydroxy-N-(4-methoxybenzyl)-N-(thiazol-2-yl)benzenesulfonamide (Intermediate AD; 1.04 g, 2.65 mmol) in DMF (20 mL) was added Cs2CO3 (2.59 g, 7.95 mmol). The reaction mixture was stirred at ambient temperature for 16 h. The reaction mixture was diluted with water (200 mL) and extracted with ethyl acetate (2×100 mL). The combined organic layers were dried over sodium sulfate, filtered and concentrated under reduced pressure to obtain the crude material which was further purified by column chromatography (silica gel 100-200 mesh and 0-30% ethyl acetate in hexane) to obtain N-(4-methoxybenzyl)-2-(methoxymethyl)-3-oxo-N-(thiazol-2-yl)-3,4-dihydro-2H-benzo[b][1,4]oxazine-7-sulfonamide (500 mg, 33.1%) as an off white solid. m/z (ESI) 476.1 (M+H)+.
