[Br:1][C:2]1[CH:3]=[C:4]([NH:10][C:11]2[CH:16]=[CH:15][C:14]([N:17]3[CH2:22][CH2:21][NH:20][CH2:19][C@@H:18]3[CH2:23][CH3:24])=[CH:13][N:12]=2)[C:5](=[O:9])[N:6]([CH3:8])[CH:7]=1.[O:25]1[CH2:28][C:27](=O)[CH2:26]1.[BH3-]C#N.[Na+].O>CO.[Cl-].[Zn+2].[Cl-]>[Br:1][C:2]1[CH:3]=[C:4]([NH:10][C:11]2[CH:16]=[CH:15][C:14]([N:17]3[CH2:22][CH2:21][N:20]([CH:27]4[CH2:28][O:25][CH2:26]4)[CH2:19][C@@H:18]3[CH2:23][CH3:24])=[CH:13][N:12]=2)[C:5](=[O:9])[N:6]([CH3:8])[CH:7]=1A mixture of 111d (263 mg, 0.67 mmol), oxetan-3-one (96 mg, 1.34 mmol), NaBH3CN 104 mg, 1.68 mmol), and zinc chloride (227 mg, 1.68 mmol) in methanol (10 mL) was stirred at 50° C. for 5 hours. water (10 mL) was then added to the reaction. The resulting mixture was concentrated under reduced pressure. The residue was extracted with dichloromethane three times. The combined organic layer was concentrated under reduced pressure and the residue was purified by silica-gel column chromatography eluting with 50:1 dichloromethane/methanol to afford 111e (203 mg, 68%). MS: [M+H]+ 448.
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