Synthesis of 2-Aryl-3-(organoselanyl)-4<i>H</i>-benzo[4,5]imidazo[2,1-<i>b</i>][1,3]thiazines Promoted by <i>N</i>-Fluorobenzenesulfonimide (NFSI)

An approach has been developed for the direct synthesis of various selenium-functionalized benzo[4,5]imidazo[2,1-<i>b</i>][1,3]thiazine derivatives via the electrophilic cyclization reaction between 2-(methylthio)-1-(3-arylprop-2-yn-1-yl)-1<i>H</i>-benzo[<i>d</i>]imidazoles and diorganyl diselenides promoted by <i>N</i>-fluorobenzenesulfonimide (NFSI). This strategy is used to construct fused heterocyclic scaffolds based on selenium-functionalized 4<i>H</i>-benzo[4,5]imidazo[2,1-<i>b</i>][1,3]thiazines using NFSI as a stable and nonhazardous oxidizing agent in the presence of CH₃CN at 80 °C. The protocol allowed a broad substrate scope leading to the synthesis of 16 novel selenium-functionalized benzo[4,5]imidazo[2,1-<i>b</i>][1,3]thiazines in yields of up to 95%. Furthermore, control studies, including ¹H, ¹⁹F, and ⁷⁷Se NMR experiments, were conducted to identify intermediates, which contributed to the elucidation of the reaction mechanism.