O.O.[Sn](Cl)Cl.[C:6]([C:8]1[CH:13]=[CH:12][C:11]([NH:14][C:15]2[CH:20]=[CH:19][N:18]=[CH:17][C:16]=2[N+:21]([O-])=O)=[CH:10][CH:9]=1)#[N:7]>Cl.O.C(O)C>[NH2:21][C:16]1[CH:17]=[N:18][CH:19]=[CH:20][C:15]=1[NH:14][C:11]1[CH:12]=[CH:13][C:8]([C:6]#[N:7])=[CH:9][CH:10]=1According to a modification of the method of Pharm. Helv. Acta, 1975, 50, 188 , tin (II) dichloride dihydrate (56.4 g, 250 mmol) was added to a suspension of 4-[N-(4-cyanophenyl)amino]-3-nitropyridine (see part (a)) (12.0 g, 50 mmol) in 2N aqueous hydrochloric acid (35 ml), water (150 ml) and ethanol (75 ml) and the resulting mixture was heated to reflux for 10 minutes under nitrogen. The mixture was cooled in ice, poured into ice-cold 2N aqueous sodium hydroxide (400 ml) and filtered. The creamy-coloured solid was washed with 2N aqueous sodium hydroxide and water, and then dried in a vacuum desiccator to provide the title compound, (9.31 g), which gradually turns reddish brown on exposure to light and air.
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