Formation of a benzimidazole ring accompanied by the cleavage of a nitrogen-carbon bond

The reaction of thionyl chloride with arylamides of aromatic acids, which usually gives rise to stable imidoyl chlorides, leads in the case of N-(o-dimethylaminophenyl)benzimide and N-(o-piperidinophenyl)-benzimide to the formation of a benzimidazole ring, which is accompanied by the cleavage of the nitrogen-carbon bond. This reaction and the reaction of chloral oxime with o-dialkylaminoanilines studied previously, which also leads to the formation of a benzimidazole ring, are compared with the Braun reaction. It has been shown that when thionyl chloride reacts with N-(o-dimethylaminophenyl)isonitrosoacetamide, no formation of a benzimidazole ring takes place and only N-(o-dimethylaminophenyl)carbamoyl cyanide is formed.