C(OC([NH:8][C:9]1[S:13][C:12]([C:14]([O:16][CH3:17])=[O:15])=[CH:11][C:10]=1[NH:18][CH2:19][C:20]([O:22]C)=O)=O)(C)(C)C.C([O-])(O)=O.[Na+]>O1CCOCC1.Cl>[O:22]=[C:20]1[NH:8][C:9]2[S:13][C:12]([C:14]([O:16][CH3:17])=[O:15])=[CH:11][C:10]=2[N:18]=[CH:19]1To a solution of 90 (0.035 mmol, 12 mg) in dioxane (0.5 mL), HCl 4N in dioxane (1.742 mmol, 436 μl) was added and the solution was heated overnight at 80° C. The reaction was neutralized with a saturated solution of NaHCO3 and extracted with CH2Cl2 (2×). The organic layer was dried with phase separator and concentrated to give methyl 3-oxo-3,4-dihydrothieno[2,3-b]pyrazine-6-carboxylate 91 (7.3 mg, 100%). NMR (400 MHz, CDCl3) 3.96 (s, 3H), 8.05 (s, 1H), 8.29 (s, 1H). (m/z)=211 (M+H)+.
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