Enantioselective Iridium-Catalyzed Intramolecular Hydroarylation of (Hetero)Arene-Tethered Prochiral Diketones.

The enantioselective iridium(I)-catalyzed hydroarylation of C-C unsaturated bonds ranks among the most atom-efficient technologies in organic synthesis. We now report an enantioselective desymmetrizing cyclization that entails carbonyls instead of C═C partners, providing direct access to architecturally complex (hetero)polycyclic frameworks bearing a tertiary alcohol and an adjacent all-carbon quaternary stereocenter at their ring junctions. The in situ dehydration of the initially formed alcohol was occasionally observed to yield products bearing an allylic quaternary stereocenter, which offers excellent opportunities for downstream functionalization. Mechanistically intriguing, we demonstrated that this dehydration can be suppressed by adding Et3SiH, an additive that also accelerates the overall transformation. Computational studies support a carbometalation/O-H reductive elimination pathway and shed light on the stereochemical origin of the enantioselectivity.