We report a one-pot procedure for forming a dimeric pyrroloindoline framework with a thionium reagent. The cyclization of tryptamine with DMSO and Tf2O, followed by substitution with indole derivatives, produced racemic 3a-indolylpyrroloindolines. The method enables rapid access to heterodimeric pyrroloindolines as well as to homodimeric pyrroloindolines.