Asymmetric Construction of Spiro[thiopyranoindole-benzoisothiazole] Scaffold via a Formal [3 + 3] Spiroannulation.

An enantioselective formal thio[3 + 3] spiroannulation reaction of indoline-2-thiones to 1-azadienes has been developed by the use of a quinine-derived bifunctional tertiary amine-thiourea catalyst, which furnished a series of optically active spiro[thiopyranoindole-benzoisothiazole] heterocycles with a spiro quaternary C-N/C-S stereogenic centers in high yields with good to excellent diastereo- and enantioselectivities.