[C:1]1([S:7]([C:10]2[CH:20]=[CH:19][C:13]3[NH:14][C:15](=O)[CH2:16][O:17][C:12]=3[CH:11]=2)(=[O:9])=[O:8])[CH:6]=[CH:5][CH:4]=[CH:3][CH:2]=1.Cl.O.C(=O)([O-])[O-].[K+].[K+]>C1COCC1>[C:1]1([S:7]([C:10]2[CH:20]=[CH:19][C:13]3[NH:14][CH2:15][CH2:16][O:17][C:12]=3[CH:11]=2)(=[O:9])=[O:8])[CH:6]=[CH:5][CH:4]=[CH:3][CH:2]=1
A suspension of 7-benzenesulfonyl-4H-benzo[1,4]oxazin-3-one (2.314 g., 8.00 mmol) in 30 ml anhydrous THF was brought to reflux, and borane-dimethyl sulfide complex (2.4 mL, 10 M solution) was added dropwise via syringe. The solution was refluxed for two hours, at which time the solution was cooled to room temperature and ethanolic HCl (10 mL., 2 N solution) was added dropwise. The resulting solution was refluxed for 3 hours and allowed to cool to room temperature. The reaction mixture was poured into 100 mL water, the resulting solution made basic with potassium carbonate and extracted three times with 50 mL Et2O. The organic fractions were washed with 100 mL brine, dried over Na2SO4 and concentrated in vacuo. The resulting residue was purified by flash chromatography (20 to 50% EtOAc in hexanes) to give 1.75 g of 7-benzenesulfonyl-3,4-dihydro-2H-benzo[1,4]oxazine (79.5%) as a yellow solid. MS: 276 (M+H)+.
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