[S:1]1[C:6]2[CH:7]=[CH:8][CH:9]=[CH:10][C:5]=2[NH:4][C:3](=O)[CH2:2]1.C[C:13]([CH3:16])([O-:15])C.[K+].[C:18]([OH:21])(=O)[CH3:19].[CH3:22][N:23](C=O)C>O>[CH:22]1[N:4]2[C:3]([CH2:2][S:1][C:6]3[CH:7]=[CH:8][CH:9]=[CH:10][C:5]=32)=[C:19]([C:18]([O:15][CH2:13][CH3:16])=[O:21])[N:23]=1To a solution of 2H-1,4-benzothiazin-3(4H)-one (0.7 g, 4.24 mmol, 1 eq) in DMF (20 mL) is added potassium tert- butoxide (0.50 g, 4.49 mmol, 1.06 eq) and the reaction mixture is stirred at RT for 10 min. The reaction mixture is cooled with ice and diethyl chloro phosphonate (1.1 mL, 7.63 mmol, 1.8 eq) is added and the reaction mixture is stirred at RT for 5 minutes. The reaction mixture is then cooled with ice and a solution of ethyl isocyano acetate (0.65 mL, 5.94 mmol, 1.4 eq) in DMF and potassium tert-butoxide (0.66 g, 5.93 mmol, 1.4 eq) are sequentially added and the reaction mixture is stirred at RT overnight. The reaction mixture is acidified with 10 mL of acetic acid, diluted with water and poured into ice and extracted with ethylacetate. The organic layer is dried over Na2SO4 and concentrated. The crude is purified by column chromatography to afford the title compound. 1H NMR (DMSO-d6, 400 MHz): δ 8.50 (s, 1H), 7.90-7.88 (d, J=7.3 Hz, 1H), 7.56-7.54 (m, 1H), 7.39-7.36 (m, 1H), 7.32-7.30 (m, 1H), 4.42 (s, 2H), 4.27 (q, J=7.7 Hz, 2H), 1.29 (t, J=6.6 Hz, 3H). MS (ESI+): 261.2. HPLC (max plot) 95.13%; Rt 3.62 min.
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