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, FeCl3-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.