[SH:1][C:2]1[O:3][C:4]2[CH:10]=[C:9]([C:11]([O:13][CH3:14])=[O:12])[CH:8]=[CH:7][C:5]=2[N:6]=1.[C:15]([O-])([O-])=O.[K+].[K+].CI>CN(C=O)C.O>[CH3:15][S:1][C:2]1[O:3][C:4]2[CH:10]=[C:9]([C:11]([O:13][CH3:14])=[O:12])[CH:8]=[CH:7][C:5]=2[N:6]=1To a stirred mixture of methyl 2-mercaptobenzo[d]oxazole-6-carboxylate (5 g, 23.92 mmol) and solid K2CO3 (9.9 g, 71.76 mmol) in anhydrous DMF (50 mL) at rt was added methyl iodide (10.2 g, 71.76 mmol). The mixture was stirred at rt for 15 h. The reaction mixture was diluted with water then extracted with DCM (×3). The combined organic layers were washed with water and 2 M aq HCl. The organic layer was separated and dried over MgSO4, filtered, and concentrated under reduced pressure to afford methyl 2-(methylthio)benzo[d]oxazole-6-carboxylate (4.24 g, 80%) as a light pink solid that did not require further purification. 1H NMR (300 MHz, CDCl3) δ 8.12 (d, J=1.1 Hz, 1H), 8.04 (dd, J=1.1, 8.3 Hz, 1H), 7.61 (d, J=8.3 Hz, 1H), 3.95 (s, 3H), 2.79 (s, 3H). LCMS (ESI) m/z 224 (M+H)+.
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