Silver(I) triflate-catalyzed protocol for the post-ugi synthesis of spiroindolines

A silver(I) triflate-catalyzed protocol for the post-Ugi synthesis of tetracyclic spiroindolines has been developed. The protocol worked best for indole-3-carbaldehyde-derived Ugi adducts obtained using anilines and 3-aryl propiolic acids. Thus, it is complementary to the previous cationic gold-catalyzed procedure that was developed for analogues Ugi substrates derived from aliphatic amines and 3-alkyl propiolic acids. Furthermore, we have demonstrated that under our new settings this domino Friedel-Crafts ipso cyclization / imine trapping process could be efficiently combined with the preceding four-component Ugi reaction into a two-step one-pot transformation