Access to Tetrahydrothiopyrano[2,3-b]Indole Derivatives via Zinc-Catalyzed Asymmetric [3+3] Annulation of Indoline-2-Thiones with Yne-Enones

We report herein an enantioselective [3+3] annulation of indoline-2-thiones with yne-enones by chiral dinuclear zinc catalysts via a Bronsted base and Lewis acid cooperative activation model. This transformation proceeded through sequential conjugate addition, allenyl ketone formation and intramolecular sulfa-Michael 6-endo-trig cyclization. A range of enantioenriched tetrahydrothiopyrano[2,3-b]indole derivatives bearing an exocyclic double bond were obtained in moderate yields with excellent stereoselectivities (up to 20 : 1 dr, 20:1 Z/E ratio and 95% ee). Late-stage functionalization, large-scale experiment and further derivatizations were also explored.