Selective Gold(I)-Catalyzed Formation of Tetracyclic Indolines: A Single Transition Structure and Bifurcations Lead to Multiple Products

Several alkynylindoles undergo gold(I)-catalyzed cyclization reactions to form a single isomer in each case. Density functional theory shows why this reaction is favored over the many possible regio- and stereoisomeric reaction pathways. This transformation involves a two-step no-intermediate mechanism with surface bifurcations leading to two or three products. Such bifurcations could explain reactivity in many gold(I)-catalyzed enyne cyclization reactions.