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

Abstract

Methylation of 5(6)-nitro-1H-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-1H-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 P₂S₅ in pyridine. Oxidation of isomeric furan-2-carbothioamides with K₃[Fe(CN)₆] in alkaline medium afforded a mixture of intramolecular cyclization products, 2-(furan-2-yl)-6-methyl-6H-imidazo[4,5-g][1,3]benzothiazole and 2-(furan-2-yl)-8-methyl-8H-imidazo[4,5-g][1,3]benzothiazole which were separated by column chromatography and identified.