Gold(I)-Catalyzed and Ligand-Controlled Regioselective Cascade Cycloisomerizations of Bis(indolyl)-1,3-diynes and a Mechanistic Explanation.

A regioselective synthetic method for the preparation of indole-fused seven-membered rings and bis(indole) connected to five-membered heterocyclic units from gold(I)-catalyzed cascade cycloisomerization of bis(indolyl)-1,3-diynes is described. This divergence in product selectivity was induced by introducing another alkynyl moiety to change the electron density at the internal alkyne and fine-tuning the steric nature of the phosphine ligand in the Au(I) catalyst. Mechanistic studies including DFT calculations uncovered the ligand-controlled manner.