Defluorinative Annulation of Indoline-2-thiones with Trifluoromethyl Enones for the Divergent Synthesis of 4,9- and 2,9-Dihydrothiopyrano[2,3- <i>b</i> ]indoles

An efficient base- and solvent-controlled [3 + 3] defluorinative annulation of indoline-2-thiones with β,β-ditrifluoromethylated enones has been developed. The current protocol proceeds through a sequential intermolecular nucleophilic addition, β-fluorine elimination, and defluoroannulation, enabling the divergent synthesis of 4,9- and 2,9-dihydrothiopyrano[2,3- b ]indoles in moderate to good yields with a broad substrate scope and good functional group compatibility.