[C:1]([S:5](/[N:7]=[CH:8]/[C:9]1[N:17]2[C:12]([CH2:13][CH2:14][CH2:15][CH2:16]2)=[CH:11][C:10]=1[C:18]([O:20][CH3:21])=[O:19])=[O:6])([CH3:4])([CH3:3])[CH3:2].[BH4-].[Na+].CO>O>[CH3:3][C:1]([CH3:4])([S:5]([NH:7][CH2:8][C:9]1[N:17]2[C:12]([CH2:13][CH2:14][CH2:15][CH2:16]2)=[CH:11][C:10]=1[C:18]([O:20][CH3:21])=[O:19])=[O:6])[CH3:2]A 250-mL single-neck round-bottomed flask equipped with a magnetic stirrer was charged with 238a (4.0 g, 12.8 mmol, 1.0 eq.), NaBH4 (2.9 g, 76.9 mmol, 6.0 eq.), and methanol (100 mL). The reaction mixture was stirred at room temperature for 1 h. After this time water (50 mL) was added to the reaction and the resulting mixture was concentrated under reduced pressure. The residue was extracted with dichloromethane (3×50 mL). The combined organic layer was evaporated under reduced pressure to afford 238b (3.9 g, 96%), which was directly used in next step without further purification. MS: [M-C4H10NOS]+ 192.3.
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