Compounds containing an imidazo[2,1-b][1,3]thiazine fragment exhibit a wide range of biological properties, including anti-tuberculosis [1], anti-inflammatory [2], antifungal [3], and amyloid aggregation inhibitory [4] activities. These compounds demonstrate excellent chemical stability and the ability to selectively bind to various biomolecules, making them highly attractive for synthetic and medicinal applications.
Typically, the imidazo[2,1-b][1,3]thiazine fragment formation involves nucleophilic substitution or condensation reactions, which often require multiple synthetic steps. A growing approach to synthesizing heterocyclic systems from alkynes is using nucleophilic cyclization reactions promoted by electrophiles [5]. This method allows for the efficient formation of imidazo[2,1-b][1,3]thiazine rings and ensures good selectivity and high yields. However, the electrophile-initiated cyclization of 2-alkenylthioimidazoles has been scarcely explored. The heterocycles produced by this reaction are expected to possess novel chemical properties and enhanced biological activity. In this study, 2-cinnamylthiobenzimidazole was chosen as a model compound to investigate the cyclization reaction outcome and optimize its conditions. After applying the best conditions, other 5-arylimidazo[2,1-b][1,3]thiazines were synthesized. Formed compounds obtain a readily cleavable group, which can be replaced by other nucleophiles or eliminated by treatment with a base yielding 5-aryl-5H-benzimidazo[2,1-b][1,3]thiazine.
