Acid-Modulated Construction of Cyclopenta[ b ]indole and Cyclohepta[ b ]indole via Unprecedented C3/C2 Carbocation Rearrangement.

p -TsOH-catalyzed cycloaddition of various 3-vinylindoles and (indol-2-yl)diphenylmethanols in acetonitrile gave the functionalized cyclopenta[ b ]indoles in good yields and with high diastereoselectivity via [3 + 2] cycloaddition reaction. More importantly, FeCl 3 -catalyzed annulation reaction afforded unexpected functionalized cyclohepta[1,2- b :4,5- b ']diindoles in satisfactory yields, in which a formal [4 + 3] cycloaddition and an unprecedented C3/C2 carbocation rearrangement were first confirmed by the determination of single-crystal structure.