2H-BENZIMIDAZOLES (ISOBENZIMIDAZOLES) .7. A NEW ROUTE TO TRICLABENDAZOLE [5-CHLORO-6-(2,3-DICHLOROPHENOXY)-2-METHYLTHIO-1H-BENZIMIDAZOLE] AND CONGENERIC BENZIMIDAZOLES

A new synthesis of the selective anthelmintic agent triclabendazole 7 from the readily available 5,6-dichloro-2H-benzimidazole-2-spirocyclohexane 2 by simple steps is described. Analogous benzimidazoles difficult to prepare by conventional methods are similarly obtained. Triclabendazole can exist as a low-melting metastable solid (m.p. 85-90-degrees-C) convertible by heating or recrystallisation from ethanol into its stable form (m.p. 1 76-1 78-degrees-C).