Reaction of 2-(4'-Thiazolyl)benzimidazole (thiabendazole) with alkyl halides

2-(4?-Thiazolyl)benzimidazole (thiabendazole) is alkylated at a benzimidazole nitrogen by reaction with sodium hydride and an alkyl halide. With 1,3-dibromo-propane and 1,2-dibromoethane, the thiazole nitrogen is also alkylated to give quaternary salts containing the 6,7- dihydro-5H-thiazolo[3?,4?:1.2][1,4]diazepino-[8,9-a]benzimidazole and 5,6-dihydrothiazolo[3?,4?:1,2]pyrazino[7,8-a]benzimidazole ring systems respectively. The structures proposed for these tetracyclic products are supported by spectroscopic examination of the products formed by alkali fission of their thiazole rings.