CuH-Catalyzed Atropoenantioselective Reduction of Bringmann's Lactones via Dynamic Kinetic Resolution.

A CuH-catalyzed atropoenantioselective reduction of Bringmann's lactones via dynamic kinetic resolution has been disclosed. This protocol features a broad substrate scope and good functional group tolerance and allows the rapid assembly of various valuable axially chiral biaryls in good to high yields (up to 92% yield) with high to excellent enantioselectivities (up to 96% ee). Moreover, this report represents a rare example that a carbonyl group of esters is reduced under homogeneous asymmetric CuH catalysis.

Design and Synthesis of Chiral oxa-Spirocyclic Ligands for Ir-Catalyzed Direct Asymmetric Reduction of Bringmann's Lactones with Molecular H2.

We herein present a facile and column-free synthetic route toward a structurally unique oxa-spirocyclic diphenol, termed as O-SPINOL. Features of the synthesis include the construction of the all-carbon quaternary center at an early stage, a key double intramolecular SNAr step to introduce the spirocycles and the feasibility of operating on >100 g scale. Both enantiomers of O-SPINOL can be easily accessed through optical resolution with l-proline by control of the solvent. The chiral tridentate ligand O-SpiroPAP derived from O-SPINOL has been successfully synthesized and applied in the iridium-catalyzed asymmetric hydrogenation of bridged biaryl lactones under mild reaction conditions, providing valuable and enantioenriched axially chiral molecules in excellent yields and enantioselectivities (up to 99% yield and >99% ee). This method represents a rare example of constructing axially chiral molecules by direct reduction of esters with H2.