Interaction of benzimidazole-2-thione with propargyl bromide and 1,3-dibromopropyne

Interaction of benzimidazole-2-thione with propargyl bromide under found conditions permitted the direct synthesis of 2-(2-propynylsulfanyl)-3H-1,3-benzimidazolium bromide, the base 2-(2-propynylsulfanyl)-1H-1,3-benzimidazole, stable crystalline 2-(1,2-propadienylsulfanyl)-1H-1,3-benzimidazole, and 3-methyl[1,3]thiazolo[3,2-a][1,3]benzimidazole. The reaction of benzimidazole-2-thione with 1,3-dibromopropyne in chloroform or absolute methanol gave 2-(3-bromo-2-propynylsulfanyl)-3H-1,3-benzimidazolium bromide, and in absolute methanole in the presence of a twofold excess of sodium methoxide the reaction proceeded stereo-and regioselectively to give 3-[(Z)-bromomethylidene][1,3]thiazolo[3,2-a][1,3]benzimidazole.