Synthesis of diverse indole-containing scaffolds by gold(I)-catalyzed tandem reactions of 3-propargylindoles initiated by 1,2-indole migrations: scope and computational studies.

Similar to propargylic carboxylates and sulphides, 3-propargylindoles undergo 1,2-indole migrations under cationic gold(I) catalysis. The intermediate Au-carbenoid complex may evolve through different pathways depending on the substituents at the propargylic and terminal positions of the alkyne moiety. Thus, 3-indenylindole derivatives were easily obtained through formal iso-Nazarov or Nazarov cyclizations. DFT computations support the formation of an alkylidenecyclopropane intermediate that undergoes gold-iso-Nazarov or gold-Nazarov cyclizations upon torquoselective ring opening. In addition, 3-dienylindoles could be accessed when none of the referred pathways were accessible and so the intermediate Au-carbenoid complex evolved via a 1,2-C-H insertion reaction. We have also demonstrated that the final products can be obtained in a one-pot protocol from easily available propargylic alcohols and indoles.