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.