Study on halogen promoted cyclization of 2‐alkynylthiobenzimidazoles

Abstract 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.