Gold(I)-Catalyzed Cascade Cyclization of Anilines with Diynes: Controllable Formation of Eight-Membered Ring-Fused Indoles and Propellane-Type Indolines

Heterocycle-fused indoles or indolines are distributed widely in a variety of natural products, bioactive agents, and pharmaceuticals. Herein, we describe the development of gold-catalyzed cascade reactions of anilines with diynes to form eight-membered ring-fused indoles and propellane-type indolines, both of which proceed through an intramolecular 5-endo-dig hydroamination followed by an 8-endo-dig cycloisomerization. Controllable formation of eight-membered ring-fused indoles and propellane-type indolines was achieved through selection of the ligands and/or solvents. Protic solvents such as alcohols or IPr ligand favored the formation of eight-membered ring-fused indoles, whereas the use of Buchwald’s type ligands and/or nonpolar solvents gave propellane-type indoline predominantly. This reaction provides rapid access to two types of fused nitrogen heterocycles from simple aniline derivatives

Gold(I)-Catalyzed Oxidative Cascade Cyclization of 1,4-Diyn-3-ones for the Construction of Tropone-Fused Furan Scaffolds

Gold(I)-catalyzed cascade cyclization of 1, 4-diyn-3-ones with a pyridine N-oxide enabled direct construction of a benzo[6, 7]cyclohepta[1, 2-b]furan scaffold with the formation of four bonds. This reaction would proceed through oxidative cyclization, alkynyl migration, and 5-endo-dig type cyclization. Synthesis of benzotropone-fused naphtho[1, 2-b]furans through a two-step sequence, including epoxidation and In(OTf)₃-catalyzed intramolecular carbon–carbon bond formation, is also presented

Gold(I)-Catalyzed Oxidative Cascade Cyclization of 1,4-Diyn-3-ones for the Construction of Tropone-Fused Furan Scaffolds

Gold­(I)-catalyzed cascade cyclization of 1,4-diyn-3-ones with a pyridine <i>N</i>-oxide enabled direct construction of a benzo­[6,7]­cyclohepta­[1,2-<i>b</i>]­furan scaffold with the formation of four bonds. This reaction would proceed through oxidative cyclization, alkynyl migration, and 5-<i>endo-dig</i> type cyclization. Synthesis of benzotropone-fused naphtho­[1,2-<i>b</i>]­furans through a two-step sequence, including epoxidation and In­(OTf)₃-catalyzed intramolecular carbon–carbon bond formation, is also presented