Study on halogen promoted cyclization of 2-alkynylthiobenzimidazoles

Electrophile promoted nucleophilic cyclization of 2-alkynylthiobenzimidazoles was investigated. N-halosuccinimides were chosen as electrophile source in formation of substituted benzimidazo[2,1-b]thiazoles and benzimidazo[2,1-b][1,3]thiazines. Reaction pathway via 6-endo-dig or 5-exo-dig cyclization of substrates depended on substituents to the alkyne moiety, though with bromine electrophile in some cases benzimidazole moiety predominated alkyne and aromatic substitution reaction was observed. Compounds with prolonged linkage in 2-(propynylthio)methylbenzimidazoles formed only 7-endo-dig products.

Automated summary

This study investigated the electrophile promoted nucleophilic cyclization of 2-alkynylthiobenzimidazoles. N-halosuccinimides were chosen as the electrophile source for the formation of substituted benzimidazo[2,1-b]thiazoles and benzimidazo[2,1-b][1,3]thiazines. The reaction pathway via 6-endo-dig or 5-exo-dig cyclization of substrates depended on the substituents to the alkyne moiety. However, in some cases, bromine electrophile caused the benzimidazole moiety to predominate over the alkyne moiety, and aromatic substitution reactions were observed. Compounds with prolonged linkage in 2-(propynylthio)methylbenzimidazoles formed only 7-endo-dig products.