The condensation of 3-chloro-6-nitroacetanilide (I) with propylmercaptane (A) by means of aqueous refluxing NaOH gives 2-nitro-5-propylthioaniline (II), which was reduced with H2 over Pd/C in ethanol HCl to yield 4-propylthio-o-phenylenediamine (III). The cyclization of (III) with cyanogen bromide affords 2-amino-5-propylthiobenzimidazole (IV), which is finally condensed with methyl chloroformate. It can be condensed directly with a mixture of cyanamide and methyl chloroformate or with carbomethoxycyanamide (B). All these condensations are performed in basic medium.