Regiodivergent Trifluoromethanesulfonic Acid‐Promoted Cycloisomerizations of Ynenamines to Fused Indoles

Abstract

Abstract Trifluoromethanesulfonic acid (TfOH)‐mediated cycloisomerizations were controlled through the choice of the electron‐withdrawing functional group at C3 of indoles to provide pyrrolo[3,2,1‐ ij ]quinolines and benzo[3,4]azepino[1,2‐ a ]indoles via 6‐endo‐dig and 7‐endo‐dig cyclizations, respectively. The natures of the different cyclizations could be controlled by tuning the electronic influences; indole substrates with carbonyl groups (such as −CO 2 Et and −COMe) gave products with six‐membered rings, while substrates with sulfonyl groups (such as −Ts and −Ms) gave products with seven‐membered rings in moderate to good yields. By comparison, electronically‐neutral substituents (such as −Ph and −H) turned out to give seven‐membered products through different mechanism. magnified image