To a solution of N-(4-methoxybenzyl)-2-methyl-3-oxo-N-(thiazol-2-yl)-3,4-dihydro-2H-benzo[b][1,4]oxazine-7-sulfonamide (1.45 g, 3.14 mmol) in THF (25 ml.) was added borane dimethyl sulfide (1M in THF) (0.343 g, 4.71 mmol, Aldrich) at 0° C. and reaction mixture was stirred at 25° C. for 5 h. The reaction mixture was quenched with MeOH (15 mL) and the solvent was removed under vacuum. The residue obtained was diluted with MeOH and stirred at 25° C. for 1 h, then concentrated in vacuo. The resulting residue was purified by silica gel column chromatography using a gradient of 0-50% EtOAc in hexanes as the eluent to afford 1.3 g of N-(4-methoxybenzyl)-2-methyl-N-(thiazol-2-yl)-3,4-dihydro-2H-benzo[b][1,4]oxazine-7-sulfonamide (INTERMEDIATE AE) as off white solid in 92% yield.
