Cascade Dearomative Hydride Transfer/Enantioselective Semipinacol Rearrangement of Quinolines by a Chiral Brønsted Acid

Herein, we report a chiral Brønsted-acid-catalyzed dearomatization of quinolines. The reaction proceeds via dearomative hydride transfer and subsequent enantioselective semipinacol rearrangement. The key to this reaction sequence is to guide the imine intermediate to a rearrangement pathway other than over-reduction. Utilizing a bulky chiral imidodiphosphorimidate catalyst guarantees the desired reactivity. A series of chiral spiro tetrahydroquinoline products is afforded in good yields (up to 93%) and enantioselectivity (up to 93% ee). Detailed mechanistic insights are obtained based on DFT calculations.