Access to Tetrasubstituted Tri(indolyl)methanes through Copper-Catalyzed Addition/Substitution Sequence

Chemistry of 3-cyanoacetyl indoles: synthesis, reactions and applications: a recent update

“…Electrophilic substitution occurs readily on indole due to excessive π-electron delocalization. 8 Indole is reactive at four different positions including carbon atom 3, 9–13 nitrogen atom 1, the C2–C3 π-bond 14–17 and the C2–N sigma bond 18,19 (Fig. 2).…”