A mixture of 4-acetyl-N-[3-(1-methyl-1,2,3,6-tetrahydropyrid-5-yl)phenyl]-2-nitroaniline (5) (1 g, 3 mmol), sodium sulfide nonahydrate (4.32 g, 18 mmol) and ammonium chloride (0.96 g, 18 mmol) in methanol (50 ml) was heated to reflux over night. The solvent was removed under reduced pressure and the residue was partitioned between ethyl acetate and water. The organic phase was dried over sodium sulfate and concentrated to leave an oil (m/e: 321) which was stirred in formic acid (10 ml) at 80° C. for 4 hours. The resulting mixture was concentrated under reduced pressure. The residue was dissolved in water and filtered. The filtrate was rendered alkaline by addition of solid sodium carbonate and extracted with ethyl acetate. This extract was dried over sodium sulfate. Evaporation of the solvent left 5-acetyl-1-[3-(1-methyl-1,2,3,6-tetrahydropyrid-5-yl)phenyl]benzimidazole (7) as an oil. Yield: 0.5 g (50%), m/e: 331. A minor sample of this oil was dissolved in ethanol and precipitated as the hydrochloride by addition of hydrogen chloride in diethyl ether. Mp 227-233° C.
