ABSTRACT A base‐promoted 4+2 annulation reaction between indole‐2‐carboxamides and vinylsulfonium salts has been developed, affording the pyrazinoindolones in 39%–96% yields with high chemoselectivity. The synthesis strategy of vinylsulfonium salts can also approach to benzimidazole‐fused azabicyclo3.1.0hexanes via a 3+2/2+1 annulation process with benzimidazole‐derived acrylonitriles as the reaction partners.
Wang et al. (Thu,) studied this question.