Asymmetric Povarov Reactions Cobalt-Catalyzed by Chiral Ureas/Achiral Acids

Significance

Jacobsen and co-workers report an asymmetric [4+2] cycloaddition of imines 2 with electron-rich alkenes (Povarov reaction) catalyzed by chiral urea-sulfinamide catalyst 1 and ortho-nitrobenzenesulfonic acid ­(NBSA) as an achiral co-catalyst. Detailed kinetic and computational studies strongly supported a cationic reaction intermediate. Cooperative catalysis of a chiral urea and an achiral Brønsted acid rendered a broad substrate scope with reasonable yield, dia­stereoselectivity, and high enantioselectivity. In particular, glyoxylate ester derived imines generated tetrahydroquinolines which are useful in the synthesis of a variety of natural products, such as martinelline.