[C:1](=O)([S:3][CH2:4][C:5]1[O:6][C:7]([C:10]2[CH:11]=[N:12][CH:13]=[CH:14][CH:15]=2)=[CH:8][CH:9]=1)C.C[O-].[Na+].CI.C(=O)(O)[O-].[Na+]>CO>[CH3:1][S:3][CH2:4][C:5]1[O:6][C:7]([C:10]2[CH:11]=[N:12][CH:13]=[CH:14][CH:15]=2)=[CH:8][CH:9]=1
(See FIG. 7.) To a solution of 13 (27 mg, 0.12 mmol) in anhydrous CH3OH (3 mL) at 0° C. under argon was added a solution of sodium methoxide (15 mg, 0.28 mmol) in anhydrous CH3OH (1 mL) dropwise, over 10 min and the resultant solution was stirred for 30 min. To the solution was added methyl iodide (17 μL, 0.28 mmol) in anhydrous CH3OH (1 mL) dropwise over 1 min and the resultant solution was stirred for 30 min. The reaction was stopped by the addition of aqueous sodium bicarbonate (satd. soln., 10 mL). The CH3OH was removed in vacuo and the aqueous fraction was extracted with EtOAc (3×10 mL). The combined organic fractions were dried (Na2SO4), filtered and the solvent was removed in vacuo. The crude material was chromatographed on silica gel (EtOAc/Hex, 25/75, Rf=0.2) to afford the title compound 15 (13 mg, 54% yield) as an off white solid: mp=67-68° C.; 1H NMR (CDCl3) δ 8.90 (br s, 1H), 8.46 (m, 1H), 7.90 (m, 1H), 7.29 (m, 1H), 6.66 (d, J=3.3 Hz, 1H), 6.29 (d, J=3.3 Hz, 1H), 3.74 (s, 2H), 2.14 (s, 3H); LRMS (ESI) m/z calcd for C11H12NOS [M+H]+ 206. found 206.
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