Electrophilic carbonyl activation: competing condensative cyclizations of tryptamine derivatives

Abstract

A series of tryptamine derived bisindole substrates were subjected to electrophilic activation of the func-tional grouping at their [alpha]-nitrogen in the form of iminium ions to enable cyclization onto the sterically hindered indole substructure. Our observations regarding divergent cyclization outcomes using electronically distinct bisindole substrates are described. Surprising preference for the Friedel–Crafts alkylation reaction and evidence for an intriguing reversible spirocyclization are discussed.