Seleno/Thio-functionalized <i>ipso</i>-Annulation of <i>N</i>‑Propiolyl-2-arylbenzimidazole to Construct Azaspiro[5,5]undecatrienones

Till date, the ipso-cyclization of propiolamides is limited to provide azaspiro­[4,5]­decatrienones. Herein, we present the first example of ipso-carbocyclization, leading to azaspiro­[5,5]-undecatrienones from N-propiolyl-2-arylbenzimidazoles, involving both the radical-based and electrophilic reactions. This report establishes an access to a wide range of chalcogenated (SCN/SCF3/SePh) benzimidazo-fused azaspiro­[5,5]­undecatrienones in good yields