Selective construction of polycyclic cyclohepta[b]indoles and cyclopenta[b]indoles via cycloaddition reaction of 3-(indol-3-yl)maleimides and (indol-2-yl)methanols

Abstract

p-TsOH promoted annulation reaction of 3-(indol-3-yl)maleimides and (indol-2-yl)diphenylmethanols in chloroform afforded functionalized pyrrolo[3′,4′:6,7]cyclohepta[1,2-b:4,5-b′]diindoles in satisfactory yields, in which a formal [4+3] cycloaddition and an unprecedented rearrangement of the maleimide motif from the C3- to C2-position of the indole ring was firstly observed. Alternatively, the similar reaction of 3-(indol-3-yl)maleimides and 3-hydroxy-3-(indol-3-yl)-indolin-2-ones in acetonitrile gave functionalized spiro[indoline-3,9′-pyrrolo[3′,4′:4,5]cyclopenta[1,2-b]indole] in good yields and with high diastereoselectivity. On the other hand, p-TsOH promoted reaction of 3-(indol-3-yl)maleimides and 2-hydroxy-2-(indol-3-yl)-indene-1,3-diones gave functionalized spiro[indene-2,9′-pyrrolo[3′,4′:4,5]cyclopenta[1,2-b]indoles] as major products and spiro[indene-2,9′-pyrrolo[3′,4′:6,7]cyclohepta[1,2-b:4,5-b′]diindoles] as minor products.