Organocatalytic Enantioselective Assembly of Spirooxindole-naphthopyrans through Tandem Friedel-Crafts Type/Hemiketalization

A new synthetic strategy to construct spirooxindole-naphthopyran scaffold has been demonstrated via Friedel-Crafts type/hemiketalization of oxindole α-ketoester with 2-naphthol. Under the established reaction condition, quaternary chiral center at C3-position of oxindole has been created with very good asymmetric induction up to 98 % for a broad range of substrates. DFT calculations, which account for the stereochemical outcome, were performed.