2H-benzimidazoles (isobenzimidazoles). Part 7. A new route to triclabendazole [5-chloro-6-(2,3-dichlorophenoxy)-2-methylthio-1H-benzimidazole] and congeneric benzimidazoles
Abstract
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 benzi-midazoles difficult to prepare by conventional methods are similarly obtained. Triclabendazole can exist as a low-melting metastable solid (m.p. 85–90 °C) convertible by heating or recrystallisation from ethanol into its stable form (m.p. 176–178 °C).