[Cl:1][C:2]1[N:7]=[C:6]2[S:8][C:9](SC)=[N:10][C:5]2=[CH:4][CH:3]=1.[CH3:13][O-:14].[Na+].C(Cl)Cl.CO>C(OCC)(=O)C.C(O)(=O)C>[Cl:1][C:2]1[N:7]=[C:6]2[S:8][C:9]([O:14][CH3:13])=[N:10][C:5]2=[CH:4][CH:3]=1
To a round bottom flask was added 5-chloro-2-(methylthio)[1,3]thiazolo[5,4-b]pyridine (1-2) (11.5 g, 53.3 mmol), sodium methoxide (10.8 g, 200 mmol), anhydrous DCM (200 mL) and anhydrous MeOH (200 mL). The reaction mixture was then permitted to stir at room temperature under an atmosphere of nitrogen for 18 hours. The reaction mixture was then acidified to pH 5 with glacial acetic acid, then suspended in ethyl acetate and washed with water, then brine, dried over sodium sulfate, filtered, and concentrated. The resulting residue was purified by silica gel chromatography (0-6% IPA/DCM) to give 5-chloro-2-methoxy[1,3]thiazolo[5,4-b]pyridine (1-3) as an off-white solid. HRMS (M+H)+: observed=198.9998, calculated=198.9994.
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