Enantioselective [2 + 2] cycloaddition of 1,2-dihydroquinolines with 3-olefinic oxindoles via Brønsted acid catalysis

Mutually complementary regiodivergent Brønsted acid-catalyzed atom-economical [2 + 2] cycloaddition and ene reactions of 1,2-dihydroquinolines with 3-olefinic oxindoles are reported. In the presence of a chiral phosphoramide catalyst, the [2 + 2] cycloaddition affords products with four contiguous stereocenters in good to excellent yields (up to 95%) and with high stereoselectivities (up to >99% ee, >20 : 1 dr). Conversely, with a stronger Brønsted acid, the trifluoromethanesulfonic acid catalyst leads to ene reaction products in high yields (up to 77%). Furthermore, the mechanisms of the reactions are discussed based on control experiments and DFT calculations.