Direct Synthesis of Fused Indoles by Gold-Catalyzed Cascade Cyclization of Diynes

A direct, concise, and atom-economical synthetic method for the generation of fused indoles, using a gold-catalyzed cascade cyclization of diynes, has been developed. The reaction gave various fused indoles, such as aryl-annulated[a]carbazoles, dihydrobenzo[g]indoles, and azepino- or oxepinoindole derivatives in good to excellent yields, through an intramolecular cascade 5-endo-dig hydroamination followed by a 6- or 7-endo-dig cycloisomerization, without producing theoretical byproduct. Three of the resulting indoles exhibited potent antifungal activities against T. mentagrophytes and T. rubrum, demonstrating the practical application of the described cascade reaction for drug discovery.