[CH:1]1[CH:6]=[C:5]2[C:7]3[C:12]4[C:13]([C:18](=[O:19])[C:4]2=[CH:3][CH:2]=1)=[N:14][CH:15]=[C:16](Br)[C:11]=4[CH:10]=[CH:9][N:8]=3.[N-:20]=[N+]=[N-].[Na+]>CC(C)=O.O>[CH:1]1[CH:6]=[C:5]2[C:7]3[C:12]4[C:13]([C:18](=[O:19])[C:4]2=[CH:3][CH:2]=1)=[N:14][CH:15]=[C:16]([NH2:20])[C:11]=4[CH:10]=[CH:9][N:8]=3A mixture of 4-bromosampangine (622 mg, 2.0 mmol) in acetone (40 mL) and sodium azide (1.30 g, 20.0 mmol) in H2O (10 mL) was heated at reflux for 1 h. The acetone was then removed by evaporation, MeOH (40 mL) added, and the mixture transferred to a three necked flask and cooled to 10° C. Piperidine (2 drops) was added and a stream of hydrogen sulfide bubbled through the reaction. After 30 min, the temperature was allowed to rise to 23° C. and the reaction continued for an additional 30 min. The solvent was then removed evaporated and the residue chromatographed as above to give 4-aminosampangine (23) (450 mg, 91%).
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