N[C@@H:2]1[C:17](=[O:18])[N:4]2[C:5]([C:10]([O:12][C:13]([CH3:16])([CH3:15])[CH3:14])=[O:11])=[C:6]([CH3:9])[CH2:7][S:8][C@H:3]12.[BrH:19].N([O-])=O.[Na+].[Cl-].[Na+]>O.C(O)C>[Br:19][C@H:2]1[C:17](=[O:18])[N:4]2[C:5]([C:10]([O:12][C:13]([CH3:16])([CH3:15])[CH3:14])=[O:11])=[C:6]([CH3:9])[CH2:7][S:8][C@H:3]12
To an ice-cooled mixture of t-butyl 7β-amino-3-methyl-3-cephem-4-carboxylate (1.3 g, 0.0048 mol), ethanol (30 ml), water (8.5 ml), hydrobromic acid (48%, 5.83 ml), sodium nitrite (0.48 g, 0.00696 mol) was added portionwise over 15 minutes and the mixture was stirred at ice-temperature (-5° C.) for 3 hours, saturated with sodium chloride, extracted with ethyl acetate (3 times). The combined ethyl acetate extract was washed with water, brine, dried and concentrated to give 800 mg (50%) of pure t-butyl 7α-bromo-3-methyl-3-cephem-4-carboxylate.
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