Fusion of 2-(furan-2-yl)thiazole to 1-methyl-1H-benzimidazole

Methylation of 5(6)-nitro-1 H -benzimidazole with methyl iodide in the presence of potassium hydroxide and N -methylpyrrolidin-2-one gave a mixture of isomeric 1-methyl-5-nitro- and 1-methyl-6-nitro-1 H -benzimidazoles which were reduced with tin in concentrated aqueous HCl on heating. The resulting amines reacted with furan-2-carbonyl chloride in N -methylpyrrolidin-2-one to give furan-2-carboxamides which were treated with excess P 2 S 5 in pyridine. Oxidation of isomeric furan-2-carbothioamides with K 3 [Fe(CN) 6 ] in alkaline medium afforded a mixture of intramolecular cyclization products, 2-(furan-2-yl)-6-methyl-6 H -imidazo[4,5- g ][1,3]benzothiazole and 2-(furan-2-yl)-8-methyl-8 H -imidazo[4,5- g ][1,3]benzothiazole which were separated by column chromatography and identified.